Severe Thunderstorms Strike The Front Range Again

Severe thunderstorms impacted much of the Front Range on Tuesday June 19th, less than 24 hours after Monday’s severe weather outbreak over Colorado. Tuesday’s storms brought heavy rainfall, tornadoes, and hail up to 3.00″ in diameter to several portions of eastern Colorado. Severe hail was reported as far north as the Fort Collins area, while additional storms further south pounded portions of Littleton, Parker, Centennial, and Aurora. Sadly, some areas in E Boulder County and SW Weld County experienced severe hail for the 2nd consecutive day. 

Here are a few maps of preliminary hail reports across the Front Range. The Fort Collins and Greeley area experienced severe hail between 1.25-1.75″ in diameter (click image to enlarge)
Further south, severe hail struck the Niwot, Longmont, Firestone, and Hudson areas with hail diameter between 1.25-2.00″ reported. The largest hail on Tuesday was reported over southern and eastern portions of the Denver Metro area, which saw hail diameter size between 1.25-3.00″. Here are a few pictures of hailstones just shy of tennis ball sized (2.5″), sent to us from a Skyview Weather friend in S Aurora. 

While consecutive days of severe hail are generally rare over the Front Range Urban Corridor, hail of this magnitude is certainly not unheard of. Regardless, these communities are certainly still reeling from damages incurred over the past 48-hours. The best news we received was there were no reports of serious injury or loss of life associated with Monday or Tuesday’s severe thunderstorms. Though, the financial burden of damages and impact on local communities will certainly be felt for months to come. 

Severe Storms Slam Northern Colorado with Heavy Rainfall and Large Hail

A round of severe storms developed over northern Colorado during the evening and overnight on Monday 6/18 into the early am hours on Tuesday.  Storms initiated over northern Jefferson County and Boulder County spreading out to the NE over the plains.  Hail and accumulating hail up to 3″ in Diameter pounded the NE plains with the worst hit areas being Weld and Morgan Counties.  Heavy rainfall also spawned Flash Flood Warnings from the NWS at 2-5″ or more of rain was reported.  There was heavy damage from flooding and the hail under the stronger storms some of which impacted the northern Denver Metro area and Boulder County but to a lesser degree than Weld and Morgan Counties.  Above is a hail map of some of the reports and below is is the text version of the storm reports.  This information and more can be found on the NWS Boulder page at:  https://www.weather.gov/bou/HailJune18th    

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE DENVER CO
534 AM MDT TUE JUN 19 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1135 PM     FLASH FLOOD      2 W KEENESBURG          40.11N 104.57W
06/18/2018                   WELD               CO   EMERGENCY MNGR

            FRONTAGE ROAD AT I-76 AND WELD COUNTY RD 53
            HAS WATER FLOWING OVER ROAD AND PART OF ROAD
            IS COMPLETELY WASHED OUT. IMPASSABLE
            ROADWAYS AT WELD COUNTY RD 8 AND 45, WELD
            COUNTY RD 16 AND 63, AND HIGHWAY 52 AND WELD
            COUNTY RD 49. PARTIAL FLOODING AT I-76 AND
            WELD COUNTY RD 55.

1100 PM     HEAVY RAIN       1 ENE KEENESBURG        40.11N 104.50W
06/18/2018  M2.47 INCH       WELD               CO   COCORAHS

            2.47 INCHES OF RAIN IN PAST 40 MINUTES.

1054 PM     HAIL             4 NW BURDETT            40.40N 103.03W
06/18/2018  M1.75 INCH       WASHINGTON         CO   TRAINED SPOTTER



1033 PM     HAIL             12 S ATWOOD             40.38N 103.27W
06/18/2018  M1.75 INCH       WASHINGTON         CO   TRAINED SPOTTER

            HAIL DEPTH OF 2 INCHES ON THE HIGHWAY.

1033 PM     TSTM WND GST     12 S ATWOOD             40.38N 103.27W
06/18/2018  E60 MPH          WASHINGTON         CO   TRAINED SPOTTER



1013 PM     HAIL             WELDONA                 40.35N 103.97W
06/18/2018  M1.00 INCH       MORGAN             CO   TRAINED SPOTTER

            1.5 INCHES OF RAIN.

0957 PM     HAIL             3 ENE HILLROSE          40.34N 103.47W
06/18/2018  M1.75 INCH       WASHINGTON         CO   TRAINED SPOTTER



0939 PM     HAIL             3 NW SNYDER             40.35N 103.62W
06/18/2018  M1.50 INCH       MORGAN             CO   TRAINED SPOTTER

            HOUSE WINDOWS BROKEN.

0921 PM     HAIL             LOCHBUIE                40.01N 104.72W
06/18/2018  M1.75 INCH       WELD               CO   PUBLIC

            REPORT VIA TWITTER.

0915 PM     TSTM WND GST     FORT MORGAN AIRPORT     40.33N 103.80W
06/18/2018  M71 MPH          MORGAN             CO   AWOS



0905 PM     HAIL             1 W BRIGHTON            39.99N 104.82W
06/18/2018  M2.75 INCH       ADAMS              CO   PUBLIC

            REPORT VIA TWITTER.

0849 PM     HAIL             3 NW HENDERSON          39.95N 104.92W
06/18/2018  M2.50 INCH       ADAMS              CO   NWS EMPLOYEE



0848 PM     HAIL             3 NE NORTHGLENN         39.94N 104.93W
06/18/2018  M1.75 INCH       ADAMS              CO   TRAINED SPOTTER



0847 PM     HAIL             3 NNE NORTHGLENN        39.94N 104.95W
06/18/2018  M2.00 INCH       ADAMS              CO   NWS EMPLOYEE



0846 PM     HAIL             1 SSW NORTHGLENN        39.89N 104.99W
06/18/2018  M1.00 INCH       ADAMS              CO   TRAINED SPOTTER



0835 PM     HAIL             1 ENE WESTMINSTER       39.89N 105.03W
06/18/2018  M1.00 INCH       ADAMS              CO   NWS EMPLOYEE



0834 PM     HAIL             1 NW BROOMFIELD         39.93N 105.08W
06/18/2018  M1.50 INCH       BROOMFIELD         CO   NWS EMPLOYEE



0831 PM     HAIL             1 W BROOMFIELD          39.92N 105.09W
06/18/2018  M1.00 INCH       BROOMFIELD         CO   NWS EMPLOYEE



0827 PM     HAIL             2 W WESTMINSTER         39.88N 105.10W
06/18/2018  M1.00 INCH       JEFFERSON          CO   NWS EMPLOYEE



0823 PM     HAIL             2 S ROCKY FLATS         39.87N 105.20W
06/18/2018  M1.75 INCH       JEFFERSON          CO   TRAINED SPOTTER

            REPORT VIA TWITTER.

0800 PM     HAIL             1 N ERIE                40.04N 105.04W
06/18/2018  M1.00 INCH       WELD               CO   PUBLIC

            REPORT VIA TWITTER.

0757 PM     HAIL             1 S LAFAYETTE           39.99N 105.10W
06/18/2018  M1.50 INCH       BOULDER            CO   TRAINED SPOTTER

            REPORT VIA TWITTER.

0752 PM     HAIL             1 N LAFAYETTE           40.01N 105.10W
06/18/2018  M2.50 INCH       BOULDER            CO   TRAINED SPOTTER

            SHATTERED VEHICLE WINDSHIELDS.

0746 PM     HAIL             1 NNW LOUISVILLE        39.99N 105.15W
06/18/2018  M2.00 INCH       BOULDER            CO   TRAINED SPOTTER

            REPORT VIA TWITTER.

0746 PM     HAIL             1 NW LAFAYETTE          40.00N 105.11W
06/18/2018  E2.00 INCH       BOULDER            CO   TRAINED SPOTTER



0745 PM     HAIL             2 WNW LAFAYETTE         40.00N 105.13W
06/18/2018  M1.00 INCH       BOULDER            CO   NWS EMPLOYEE



0743 PM     HAIL             1 NNW LOUISVILLE        39.99N 105.15W
06/18/2018  M1.75 INCH       BOULDER            CO   TRAINED SPOTTER



0740 PM     HAIL             1 NNW LOUISVILLE        39.99N 105.15W
06/18/2018  E1.25 INCH       BOULDER            CO   TRAINED SPOTTER



0739 PM     HAIL             1 NNW LOUISVILLE        39.99N 105.15W
06/18/2018  M1.00 INCH       BOULDER            CO   TRAINED SPOTTER



0731 PM     HAIL             SUPERIOR                39.93N 105.15W
06/18/2018  M3.00 INCH       BOULDER            CO   TRAINED SPOTTER



0730 PM     HAIL             1 ESE FREDERICK         40.10N 104.93W
06/18/2018  M1.50 INCH       WELD               CO   TRAINED SPOTTER



0728 PM     HAIL             2 N MARSHALL            39.98N 105.24W
06/18/2018  M1.00 INCH       BOULDER            CO   TRAINED SPOTTER



0720 PM     HAIL             3 NW MARSHALL           39.98N 105.26W
06/18/2018  M1.00 INCH       BOULDER            CO   NWS EMPLOYEE



0718 PM     HAIL             3 NNW FIRESTONE         40.16N 104.96W
06/18/2018  E1.75 INCH       WELD               CO   TRAINED SPOTTER



0711 PM     HAIL             5 NE MILTON RESERVOIR   40.29N 104.56W
06/18/2018  E1.00 INCH       WELD               CO   TRAINED SPOTTER



0700 PM     HAIL             1 NE DACONO             40.09N 104.92W
06/18/2018  M2.50 INCH       WELD               CO   NWS EMPLOYEE



0655 PM     HAIL             1 NE DACONO             40.09N 104.92W
06/18/2018  M1.75 INCH       WELD               CO   NWS EMPLOYEE



0651 PM     HAIL             FREDERICK               40.10N 104.94W
06/18/2018  M1.75 INCH       WELD               CO   TRAINED SPOTTER



0648 PM     HAIL             1 NW DACONO             40.09N 104.96W
06/18/2018  M1.00 INCH       WELD               CO   TRAINED SPOTTER



0643 PM     HAIL             1 W MEAD                40.24N 105.00W
06/18/2018  M1.75 INCH       WELD               CO   TRAINED SPOTTER

            REPORT VIA TWITTER.

0635 PM     HAIL             4 N ERIE                40.09N 105.06W
06/18/2018  M1.00 INCH       BOULDER            CO   TRAINED SPOTTER

            REPORT VIA TWITTER.

0632 PM     HAIL             1 NNW PLATTEVILLE       40.23N 104.83W
06/18/2018  M1.00 INCH       WELD               CO   TRAINED SPOTTER



0625 PM     HAIL             2 N LONGMONT            40.20N 105.11W
06/18/2018  M1.75 INCH       BOULDER            CO   TRAINED SPOTTER



0619 PM     HAIL             3 SSW MEAD              40.20N 105.01W
06/18/2018  M1.25 INCH       WELD               CO   TRAINED SPOTTER

            REPORT VIA TWITTER.

0610 PM     HAIL             1 NE BOULDER            40.04N 105.24W
06/18/2018  E1.75 INCH       BOULDER            CO   PUBLIC

            REPORTED AT 3450 MITCHELL LANE, BOULDER, CO.

0610 PM     HAIL             1 NE BOULDER            40.04N 105.24W
06/18/2018  E1.75 INCH       BOULDER            CO   PUBLIC

            REPORTED AT NCAR FOOTHILLS LAB, BOULDER, CO.

0610 PM     HAIL             1 ENE BOULDER           40.00N 105.26W
06/18/2018  E1.25 INCH       BOULDER            CO   TRAINED SPOTTER



0608 PM     HAIL             2 SSW BOULDER           40.00N 105.27W
06/18/2018  M1.50 INCH       BOULDER            CO   TRAINED SPOTTER



0600 PM     HAIL             2 SSW BOULDER           40.00N 105.26W
06/18/2018  M1.00 INCH       BOULDER            CO   EMERGENCY MNGR



0558 PM     HAIL             4 WNW BOULDER           40.04N 105.32W
06/18/2018  M1.00 INCH       BOULDER            CO   PUBLIC

Hot and dry start to June for Colorado

Following a relatively active May for Northeast Colorado, the pattern has become very warm and dry across the entire state over the first 12 days of June.  The drought and fire situation has turned dire for many areas, which suffered from a below average winter snowpack.  The San Juan Mountains in Southwest Colorado experienced one of their worst winters for snowfall on record, and not surprisingly this has been a focal point for wildfire activity so far.  The 416 Fire near Durango started on June 1st, and so far has burned over 22,000 acres and is only 10% contained.  The situation in the San Juans has resulted in a closure of the entire San Juan National Forest to humans due to the wildfire threat.

The maps below show the departure from average precipitation and departure from average temperature over Colorado through the first half of the month.  Certainly not a situation that helps the fire and drought concerns.  Interestingly enough, portions of Southern Colorado and the San Luis Valley are showing an above average precipitation anomaly so far for June, but keep in mind that this area receives very little precipitation on average in June, so it doesn’t take much to be “above average” there at this time of year.

 

June 1-10, 2018 Departure from Average Precipitation (Source: Western Regional Climate Center)

 

June 1-10, 2018 Departure from Average Temperatures (Source: Western Regional Climate Center)

 

In addition to the 416 Fire near Durango, additional fires have recently started in or near Colorado.  On Sunday, the Badger Creek Fire started in the Snowy Range of Southern Wyoming, near the Colorado border.  Closer to home, the Buffalo Mountain Fire started just outside of Silverthorne in Summit County this morning, and is burning beetle kill forest and threatening numerous structures.  

Colorado and the Southwest U.S. is in dire need of moisture right now.  The image below shows the current drought situation in Colorado.  Southern Colorado in particular is experiencing an exceptional drought, but drought conditions are projected to expand to include much of Northern Colorado over the next month as well.

 

There is both good and bad news with regards to the weather outlook for moisture over the next couple of weeks.  In the short-term, the pattern looks to remain mostly dry across much of the state with hot temperatures and only some isolated thunderstorm chances.  Fortunately, there are no widespread strong winds expected during this time.

As we head into the weekend, we will finally start to see some better moisture potentially arrive as a trough of low pressure deepens across the Western U.S. and moisture from Hurricane Bud in the Pacific Ocean becomes entrained into the flow and likely reaches Colorado.  This should start to bring better chances for rainfall across Western Colorado on Saturday, before spreading into the Front Range and Eastern Colorado on Sunday.  Good chances for rain and thunderstorms could persist well into next week, although it’s too early to say which parts of Colorado will be favored more than others.  This pattern will be watched by many with great interest given the current dry spell.

Monsoon Preview?

With the hot and dry conditions we’ve seen over the past several days in Colorado, the wetting rains of the North American Monsoon pattern may seem like a long-lost, distant memory. July and August are our most active months for monsoon-enhanced precipitation, but it’s not unusual to see the first glimpses of pattern emergence during the month of June. This summer is no exception, as it looks like we’ll get our first taste of subtropical moisture this weekend. But first, here is a little background information to put things into perspective. 

North American Monsoon Pattern (NAM)

Most simply, the NAM is a prolonged, intra-seasonal shift in the wind pattern over the southwestern United States during the mid and late-summer months. This wind shift allows moisture-rich subtropical air to stream north out of the Gulfs of Mexico and California, and move over the Desert Southwest and eventually Colorado. The influx of moisture can contribute to showers and thunderstorms producing heavy rainfall over areas with typically-arid climates. 

The key to diagnosing the NAM lies in the presence and strength of large-scale weather features over the southwestern United States. Here’s a nice schematic of the pattern, courtesy of Mike Baker (NWS Boulder). 

During the summer months in the northern hemisphere, subtropical high pressure positions over the middle part of the United States. Clockwise flow around the high efficiently transports moisture northward over a good portion of the country. The second key feature typically seen with the NAM is an area of low pressure known as a “heat low” or “thermal low.” This feature arises as temperatures hit their seasonal peak over the Desert Southwest. Counterclockwise flow around the low also ushers moisture-rich subtropical air northward. The result is (2) persistent large-scale weather features working in concert to pump deep moisture into our region. 

One of the keys to understanding the NAM is recognizing that it is an intra-seasonal process, and its spatial scope is regional. The NAM is not a storm, nor is it an exceptionally-rainy afternoon. In this sense, the NAM is more similar to a process like ENSO (El Nino Southern Oscillation). Nothing occurs very quickly with the NAM. It takes weeks for large-scale features to strengthen and position correctly. Similarly, the process does not arrive overnight. Typically, the influx of monsoonal moisture slowly ramps up during late June/early July, peaks for a few weeks, then slowly relaxes as we move into September. 

And just because the NAM pattern is in place, it doesn’t mean you’re going to get rain. Thunderstorm coverage is highly-sensitive to the position of the subtropical moisture plume. This plume can position as far west as California/Oregon/Washington, or as far east as the southern plains. Typically, the moisture plume slowly oscillates from east-to-west as the large-scale feature’s shape and strength evolve. 

So, how do we know know when the NAM officially arrives? 

Monsoon daily dewpoint tracker for Tucson

The NAM pattern is declared once the daily-average dewpoint in Tuscon, Arizona reaches 54°F or higher for three-consecutive days. The 54°F threshold is relatively arbitrary, but it does typically signal a large-scale influx of subtropical moisture into the mid latitudes associated with the NAM. As we would expect this time of year, surface moisture is slowly increasing over Arizona, but we still have a lot of work to do to reach the NAM threshold. As the red curve indicates, NAM conditions typically arrive during early-to-mid July and persist for about two months. 

We’ll need to wait a few more days to iron out the finer details, but it looks like we’ll see a preview of NAM conditions over Colorado by this weekend. 

This is GFS model imagery, courtesy of TropicalTidbits. The map shows precipitable water normalized anomaly. Basically, a map of integrated moisture in the atmosphere, and how unusual the values are for this date in June. Anomalous moisture streaming north is clearly evident, and the plume appears to position over much of Colorado this weekend. We’ll get an extra boost from Hurricane Bud in the E Pacific (not pictured), which will move north and phase with the large-scale circulation. 

This is not the North American Monsoon per se, but it is a very monsoon-esque pattern concerning moisture trajectory and magnitude. 

So, is the weekend ahead a wash for outdoor activities in Colorado? Not necessarily. We still need the same daily ingredients at the local scale for thunderstorms to form and eventually capitalize on the increased moisture. 

For now, we’ll keep our eye on the weekend ahead, recognizing that a return to wetter conditions appears likely. We’ll also watch the dewpoints and storm activity over Arizona during the coming weeks as evidence the NAM has arrived and is here to stay. 

Severe Thunderstorms Possible for Denver and Eastern Colorado on Memorial Day

Memorial Day weekend has been hot and dry so far for Denver, as we outlined in Friday’s post.  While the lack of thunderstorm activity has been a bonus for holiday weekend outdoor activities, temperatures have been a little too hot outside of the mountains.  The high temperature on Saturday peaked at 93 in Downtown Denver and 94 at DIA, falling just shy of the record high for the date of 95.  Following another very warm (but not quite as hot) day on Sunday, the pattern will turn cooler and more active on Memorial Day.

A trough of low pressure has been spinning over the Great Basin since yesterday, resulting in active weather for areas west and north of Colorado.  A very similar setup to what we have seen all month long!  Late tonight and into Monday, this trough will be pushing into Colorado, as can be seen in the image below, setting the stage for more active weather to close out the holiday weekend.

 

NAM Model 500mb Heights – Graphics Courtesy of the College of DuPage

 

As the trough approaches, a surface cold front will also arrive late tonight, ushering in more clouds and cooler temperatures on Monday.  Temperatures on Monday will be much more comfortable after the past few days of hot weather, with highs in Denver about 20 degrees cooler compared to Saturday and Sunday!  However, behind this cold front winds will turn northeasterly, ushering in low level moisture from the Gulf of Mexico.  The upslope winds, increase in low level moisture, and cooling temperatures aloft will allow for the airmass to destabilize Monday afternoon.  Below is a look at the projected surface dewpoints Monday afternoon.  Dewpoints in the 50s across Northeast Colorado, and even into the low 60s across the far northeast corner of the state. 

 

NAM Model Projected Surface Dewpoints for Monday afternoon – Graphics Courtesy of the College of DuPage

 

The key ingredients for severe thunderstorms are all coming together across Northeast Colorado for Monday afternoon.  Colder temperatures aloft associated with the approaching trough will result in greater instability (as will terrain lift due to upslope winds), and increasing low level moisture will also provide the fuel necessary for strong to severe thunderstorms.  In addition, the presence of wind shear will be another primary factor into severe thunderstorm development.  Low level winds will be northeasterly, whereas winds will shift with increasing altitude to southwesterly, and also increase in speed with height.  This type of wind profile with height will support rotating supercell thunderstorms.  The Storm Prediction Center has already highlighted Northeast Colorado under a risk for severe thunderstorms on Monday.

 

Graphic Courtesy of the NWS Storm Prediction Center

 

As is typical, the best chance of severe thunderstorms will be across the plains of Northeast Colorado on Monday afternoon.  However, the I-25 corridor from Denver to Ft. Collins, extending west to the lower foothills, will all be very much in play for severe thunderstorms, so be prepared tomorrow afternoon if you have outdoor plans in the metro area.  The primary threat with thunderstorms tomorrow will be large hail and strong straight-line winds.  In addition, there will likely be a tornado threat Monday afternoon, especially east of the metro area. 

The one limiting factor Monday afternoon will be the cooler surface temperatures, with a “capping” inversion that could inhibit thunderstorm development – especially if cloud cover lingers.  However, as an upper level disturbance tracks across the region during the afternoon, it could be enough to allow the cap to break and for thunderstorms to quickly develop.  Bottom line, be sure to keep your guard up on Monday afternoon for the possibility of a strong or severe thunderstorm!

 

 

Memorial Day Weekend Forecast

Overview 

It’s looking like a bit of mixed bag along the Front Range this Memorial Day Weekend, but we could do far worse during the month of May. The weekend will start with warm and dry conditions Saturday, featuring the warmest temperatures of the season to date. Sunday will be pleasant as well, with continued above-average temperatures along with a very slight chance for afternoon showers and thunderstorms. However, changes arrive by Monday, including some much-welcomed cooler temperatures and a better chance for afternoon and evening storms. 

Details

Two large-scale weather features will shape this weekend’s weather, the first being a strong ridge of high pressure anchored over the Rocky Mountains. The second feature is a Pacific trough currently impacting California, which will contribute to our next chances for precipitation Sunday and Monday. 

500mb Heights – Graphic Courtesy of Tropical Tidbits 

Saturday & Sunday

High pressure will slide east on Saturday and Sunday, as the mentioned Pacific trough settles into the Great Basin to our west. Southwest flow will transport warm and dry desert air into Colorado, boosting daytime temperatures into the low to mid 90s over the plains. Both Saturday and Sunday are great days for outdoor activities, but be sure and pack the sunscreen and extra H2O. Denver’s record high temperature for May 26th and 27th is 95°F and 93°F, respectively. Both of these records are in reach this weekend, but we may fall just shy of a new record(s). 

Surface moisture increases slightly Sunday afternoon, which could combine with a weak disturbance out ahead of the Pacific trough. Isolated showers and thunderstorms remain in the forecast, so keep an eye on the sky during the afternoon and evening hours. 

Fire weather will also be a concern Saturday and Sunday, as we expect relative humidity in the single digits, along with gusty southwest winds. You may want to reschedule any burning this weekend, while also keeping a watchful eye on barbecue grills and camp fires. 

Memorial Day

By Monday, the Pacific trough lifts into the Northern Rockies, ushering in a cooler and more unstable airmass. The result will be afternoon temperatures falling back into the low 80s, along with a better chance for afternoon showers and thunderstorms. With the main storm system positioned to our north over Wyoming, storm coverage may be greatest along and north of Interstate 70, with drier conditions expected further south. 

Modeled Precipitation Monday Evening – Graphic Courtesy of Tropical Tidbits

Rockies Gameday

The Rockies continue their home stand vs. the Cincinnati Reds this weekend , with a 7:10pm first pitch scheduled for Saturday, and a 1:10pm start on Sunday. Expect warm and generally-dry conditions for these games at Coors Field. Again, pack the sunscreen, and maybe a rain jacket for Sunday afternoon if you want to be prepared. 

Temperatures will be more comfortable for Monday night’s showdown with the NL West rival San Francisco Giants, but you’ll certainly want to pack the rain jacket if headed to the ballpark. 

A wet May so far for Denver, Boulder, and Fort Collins

While Northeast Colorado experienced a lackluster winter in terms of moisture, May of 2018 has been a much different story so far.  However, there has been a noticeable difference in precipitation with areas from Denver north to the Wyoming border experiencing above average precipitation this month, while areas south of the Palmer Divide, including Colorado Springs and Pueblo, have been much drier.  Here is a look at departure from average precipitation across Colorado so far this month.

 

colorado precipitation may 2018

 

The precipitation distribution shows a much more favorable trend to areas north of the Palmer Divide and areas east of the Continental Divide.  A low pressure system at the beginning of the month tracked favorably across Northern Colorado, bringing significant moisture to the Northern Front Range (and even heavy snow to the foothills).  Since then, persistent low pressure over the Great Basin has kept the weather unsettled across Northeast Colorado, but the best moisture has consistently remained over Northeast Colorado.  This is great news for areas such as Denver, Boulder, and Fort Collins who received below average snowfall this winter. 

However, the pattern has been unfortunate for drought-stricken areas of southern and western Colorado.  May is one of the wettest months on average for much of the state, and these areas have largely missed out on the beneficial moisture that Northeast Colorado has experienced.  Take a look at the latest drought monitor.  Most of Northern Colorado is in good shape, while drought conditions across Southern Colorado are rated as exceptional to extreme.

 

colorado drought conditions

 

Below is a list of some of the rainfall totals across the I-25 corridor and Eastern Colorado through May 20th, with the departure from average rainfall for the period May 1 – May 20 listed in parenthesis.  Notice how the precipitation departure noticeably decreases from north to south.  The most impressive amounts have been over the northeast plains, such as in Akron where 4.82″ of rain has fallen so far this month! 

 

Colorado Rainfall Totals – May 1 through May 20, 2018 (Departure from Average in parenthesis):

  • Akron:  4.82″ (+ 2.80″)
  • Boulder:  4.40″ (+ 2.48″)
  • Greeley:  3.82″ (+ 2.27″)
  • Ft. Collins:  2.98″ (+ 1.21″)
  • Denver (downtown):  2.11″ (+ 0.56″)
  • Castle Rock:  1.99″ (+ 0.51″)
  • Monument:  1.46″  (- 0.17″)
  • Pueblo:  0.37″  (- 0.69″)
  • Colorado Springs:  0.35″  (- 0.99″)
  • Walsenburg:  0.32″  (- 0.93″)

 

The outlook for the next 7-10 days looks relatively unsettled, but generally drier compared to the first 3 weeks of the month with less rainfall potential.  The past few weeks have helped Northeast Colorado out a lot after a dry winter, but there is no drought relief in sight for Southern Colorado unfortunately.

Warm and dry weather for Colorado this week, but the weekend is looking wet

Following last week’s significant precipitation event across the Front Range of Colorado, we have entered a stretch of dry weather and warm temperatures over the past several days as high pressure has taken control across the Western U.S.  Temperatures across Eastern Colorado will be pushing into the 80s over the next couple of days, and may even approach 90 in some areas on Thursday!  The warm temperatures have accelerated snowmelt in the mountains as well, even after last week’s significant dump of snow across the Northern Colorado mountains.  Farther north in Wyoming and Montana where snowpack is above average, the warm temperatures are causing rapid snowmelt and rising stream levels.

Although much of Colorado and the Western U.S. is enjoying nice spring weather right now, the pattern will begin to shift late this week as a slow-moving trough of low pressure takes hold across the Intermountain West, before stalling just west of Colorado this weekend.  Just exactly where the area of low pressure sets up will determine the impacts across Colorado, but for now this nearly stationary feature will likely result in several days of active weather from Friday of this week through early next week.

On Friday, Eastern Colorado will see an elevated threat of thunderstorms on the leading edge of this system, before colder temperatures and more widespread rain showers are projected to arrive Saturday.  This system looks warm enough that snow levels should remain above 8,000′ for the most part.  As a result, the outlook for areas below 8,000′ in Colorado is a wet one across most of the state, while higher elevation mountain areas could pick up good snowfall amounts.  

There is still a lot of uncertainty with this system as some recent model runs are actually shifting the track too far west for Colorado to receive significant precipitation amounts.  If these trends were to continue, then the expectations for moisture may have to be reduced, at least for some portions of Colorado.  Areas of southern/central Wyoming such as the Wind River Mountains, as well as the Uinta Mountains of Northeast Utah currently stand a better chance of seeing significant precipitation, while Colorado is more of a wild card – unsettled/showery weather is expected for Colorado at the very least, but just how wet depends on how far east or west this area of low pressure sets up.  For now, here is NOAA’s precipitation projection from Friday morning through Sunday morning, which still keeps Colorado on the wetter side.

 

Colorado Rain and Snow Totals May 2-3, 2018

An impressive spring system tracked across Colorado on Wednesday May 2nd through Thursday May 3rd, bringing much needed moisture to the Northern Front Range and I-25 corridor of Colorado, including the City of Denver.  This was the best widespread moisture event (in terms of precipitation amounts) for the Front Range urban corridor in quite some time, with rainfall amounts between 1-2″ across much of the Denver metro area.  The track of this system was most favorable for the Northern Front Range, where the Ft. Collins area saw rainfall amounts well in excess of two inches!  

This system also had a snowy side to it for the higher terrain, as you might imagine with a spring storm system.  The Front Range mountains and foothills received impressive snowfall, with snowfall amounts ranging from 8-24″ for areas above 8,000′.  A few of the ski areas that remain open in the Northern Front Range were able to capitalize on the late season snow to freshen up the slopes as well.  On Thursday morning, some snowfall even made it down to about the 6,000′ elevation at times with areas from Castle Rock to Monument receiving minor accumulations on grassy surfaces.

Below is a compiled list of some of the rain and snow totals from this event.

 

Rain Totals May 2-3, 2018:

  • 2.45″ – Ft. Collins (West)
  • 2.21″ – Ft. Collins (Central)
  • 1.78″ – Lakewood
  • 1.71″ – Ken Caryl
  • 1.71″ – Greeley
  • 1.70″ – Boulder
  • 1.61″ – Littleton
  • 1.56″ – Longmont
  • 1.47″ – Loveland
  • 1.33″ – Parker
  • 1.32″ – Westminster
  • 1.32″ – SE Aurora
  • 1.31″ – Denver (Downtown)
  • 1.31″ – Broomfield
  • 1.17″ – Castle Rock
  • 0.94″ – DIA

 

Snow Totals May 2-3, 2018:

  • 23.2″ – Pinecliffe
  • 23.0″ – Loveland Ski Area
  • 20.5″ – Winter Park Ski Area
  • 20.3″ – Coal Creek Canyon
  • 16.0″ – Arapahoe Basin Ski Area
  • 14.3″ – Squaw Mountain
  • 13.3″ – Conifer
  • 11.5″ – Dillon
  • 10.5″ – Nederland
  • 8.0″ – Allenspark
  • 6.6″ – Evergreen
  • 4.4″ – Estes Park
  • 3.7″ – Woodland Park
  • 2.5″ – Monument
  • 1.0″ – Castle Rock

Storm system bringing beneficial moisture to Colorado this week

A slow-moving low pressure system is pushing into Colorado today, bringing a variety of weather from rain to thunderstorms to mountain snow.  Northeast Colorado, including Denver metro, is likely to experience some of its best moisture in quite some time.  Widespread rain showers and thunderstorms will fill in this afternoon and continue overnight into Thursday, with short-range models indicating anywhere from 0.75-2.00″ of rain across Northeast Colorado with the highest amounts along/west of I-25 from Denver north to the Wyoming border.  The image below shows the trough of low pressure tracking into Colorado.

 

Source: (National Center for Atmospheric Research)

 

In addition to the beneficial rains, there is also a threat for strong to possibly severe thunderstorms across the eastern plains of Colorado today.  East of Colorado, the threat for severe weather is further enhanced across Kansas and the plains states, where there will be a threat of tornadoes and large hail this afternoon.  Below is the Storm Prediction Center’s Outlook for today.

 

 

Of course, given the time of year with a system of this nature, we can also expect some good snow for the mountains of Colorado.  Snow levels are expected to dip to about 7,000′ tonight, so Denver will not see any snow out of this but the foothills west of Denver will likely pick up some wet snow accumulations.  The potential for snowfall will increase the higher up in elevation one goes.  Winter Storm Warnings and Winter Weather Advisories are out for much of the higher elevation mountain areas in Colorado, with some areas likely picking up double digit totals.  The highest snowfall amounts are expected in the Northern Front Range Mountains, including Rocky Mountain National Park.

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