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.

Two Rounds of Snow Showers Impact Colorado Front Range on April 24

A spring low pressure system moved across the Central Rockies and into the high plains on Tuesday April 24, resulting in two rounds of snow showers across the Front Range of Colorado.  This activity followed the first appreciable round of thunderstorm activity of the season across the Denver Metro area on Monday evening.  The first round of snow arrived early Thursday morning, as a band of snow moved across the I-25 corridor between about 4:30am-6:30am Thursday.  Snowfall amounts with this system were generally under an inch for most of the Denver-Boulder metro area, though up to 2″ fell around Golden and in the Boulder and Jefferson foothills.

On Tuesday afternoon, a more widespread round of snow shower activity developed across the region, favoring the southern and western Denver suburbs.  These snow showers were fueled by a combination of favorable upslope flow and an upper level jet streak (i.e. a local wind maximum in the jet stream).  While much of the Denver metro area received non-accumulating (or minimally accumulating) snow Tuesday afternoon, higher elevation suburbs and foothills areas saw respectable amounts.  Up to 3″ of snow fell in Douglas County around Castle Rock, as well as in the Golden area near the foothills.  For the Front Range foothills, heavier snowfall of 5-8″ fell around Nederland while the Jefferson foothills picked up a general 2-4″ of snow.  

For the rest of this week, the pattern will be less active across Colorado.  By this weekend, temperatures will be getting well into the 70s across the lower elevations, but the pattern will also begin to turn more unsettled over the weekend and through much of next week.  A slow-moving trough of low pressure will move into the Great Basin on Saturday, and despite the warm temperatures enough moisture will stream into Colorado to result in convective activity, i.e. isolated thunderstorms across the mountains and possibly out on the plains as well from Saturday through Monday. 

For the middle of next week, the trough of low pressure should move across the Central Rockies and into the plains, and although the impacts are highly uncertain and storm-track dependent this far out, the pattern will likely be active during this time with the potential for respectable moisture across Colorado.  It may continue to be more of the convective shower/thunderstorm variety, but we may see a more widespread precipitation with colder temperatures fill in at some point, which would include high elevation snow for portions of Colorado.  It will be interesting to see how this plays out, but for now expect unsettled conditions next week.  Below is an image of NOAA’s Climate Prediction Center which gives an outlook for above average precipitation in the 6-10 day timeframe.

 

Some Colorado Snowfall totals for SE Colorado

The latest spring storm system produced much needed precipitation over SE Colorado with Colorado Setting a daily precipitation record on the 20th of 0.80″.  Higher elevations saw some snow but totals were generally limited to grass/natural surfaces as roadways have been warm with the mild weather ahead of the system.  Above is a map generated by the NWS in Pueblo that shows some of the snow totals through this morning. 

High Winds Blast Eastern Colorado – Wind Gust Reports April 17, 2018

A major downslope wind event occurred across Eastern Colorado on Tuesday April 17 as a fast-moving trough of low pressure and Pacific cold front moved across the state.  Wind gusts exceeded hurricane force in many areas of Eastern Colorado, and the extremely dry conditions also resulted in numerous wildfires breaking out across Eastern Colorado, including in Douglas and El Paso Counties.  Most of the wildfires are under control now, but the high winds did cause power outages and damage to structures across many areas.  Below are some of the reported wind gusts across the region per NWS storm reports.  Several areas in Boulder and Northern Jefferson County recorded gusts in excess of 80mph.  And even Denver International Airport recorded a gust of 70mph!  This was not a localized wind event either, as high winds were widespread across the Front Range and eastern plains of Colorado.

Maximum Wind Gusts – April 17, 2018:

  • Louisville – 89 mph
  • Broomfield/Jeffco Airport – 86 mph
  • Wolf Creek Pass – 85 mph
  • Superior – 84 mph
  • Rocky Flats – 83 mph
  • Holyoke – 81 mph
  • Loveland – 80 mph
  • La Veta Pass – 79 mph
  • Akron – 78 mph
  • La Junta – 77 mph
  • Cheesman Reservoir – 74 mph
  • Colorado City – 73 mph
  • Longmont – 72 mph
  • Pikes Peak Summit – 72 mph
  • Denver – 71 mph
  • DIA – 70 mph
  • Colorado Springs – 69 mph
  • Pueblo – 69 mph
  • Limon – 69 mph
  • Boulder – 68 mph
  • Alamosa – 68 mph
  • Canon City – 67 mph
  • Berthoud Pass – 62 mph

High Winds and Extreme Fire Danger for Eastern Colorado Today

A fast-moving trough of low pressure and dry cold front moving across Colorado today are resulting in fire strong downslope winds, and also extreme fire danger on the plains and I-25 corridor given the dry fuels and low relative humidity.  A couple of fires have already started in Douglas County this morning, which unfortunately includes a multi-structure fire in the Castle Rock area per South Metro Fire on a recent twitter post.  Firefighters are having to battle high winds as they fight this fire.  Below is today’s forecast from the National Interagency Fire Center, which outlines very high to extreme fire danger across much of Eastern Colorado.  Winds today will be gusting to 60mph or higher across much of eastern (and especially southeastern) Colorado, before decreasing tonight.  A wind shift from southwest to northwest this afternoon could result in challenging fire behavior with any ongoing fires.  Fortunately winds are expected to be much lighter on Wednesday, with the potential for significant moisture across portions of Eastern Colorado on Friday and Saturday.