Western U.S. Snowpack Update – March 8, 2018

The current snowpack across the Western U.S. is much different across northern areas than across central and southern areas.  Overall, February was a more active month across the entire Western U.S. with most areas experiencing gains in the snowpack.  However, March has turned more “divisive” again so far with some areas experiencing above average snowfall, and others (such as Colorado) experiencing much drier conditions.




As of March 8th, snowpack in Colorado is 75-90% of average across the northern half of the state, and 50-60% of average across the southern half of the state.  The state is projected to experience below average precipitation in March, which unfortunately means it will be very difficult for areas to come anywhere close to experiencing average snowpack, even if April and May turn out to be wetter. 

A good portion of the state, excluding the northern/central Continental Divide region, is now experiencing drought conditions, with severe to extreme drought now occurring across southern parts of the state.  If these areas do not experience above average precipitation this spring, then drought conditions would likely worsen heading into the summer, and the wildfire risk would also increase for many areas, such as the San Juan Mountains.



Elsewhere across the Western U.S., Utah and California are also experiencing well below average snowpack.  The late winter pattern is now turning more favorable for California with March expected to have above average precipitation, but it will likely be too little too late for building up the snowpack.  If above average precipitation were to continue into the spring for California, then that would certainly help from a drought and wildfire perspective, but that remains to be seen as the long range pattern does not offer any clear signals for the Golden State.  Utah is more likely to struggle making up ground in the snowpack and moisture department in this spring, and could end up with worsening drought conditions heading into the summer.

The best snowpack relative to average is across the Northern Rockies, including Wyoming, Montana, and Northern Idaho.  Snowpack in Western Montana is 125-165% of average, and local skiers at places like Big Sky are reporting their best skiing conditions in years.  More importantly, the increase in snowpack and moisture with a favorable moisture outlook for the spring should result in lower wildfire potential this summer compared to last summer, which was a bad fire year for Montana.  

For the Pacific Northwest, the Washington Cascades are near average in snowpack, while the far northern Cascades near the Canadian border are above average.  Farther south, the snowpack in Oregon is in much worse shape compared to Washington.  In general, the Pacific Northwest looks to be more favored for precipitation this spring, and at this point Oregon could use the moisture more than Washington.

It will be interesting to see how things play out this spring, but there is a significant difference in snowpack health between the northern states and the southern states across the Western U.S., and this could have a major impact on water supply, drought, and fire danger this summer.

Denver Thunderstorm Climatology

While the weather is generally quiet this week across Colorado and the Western and Central U.S., it’s never too early to start thinking about thunderstorm season now that meteorological spring is upon us.  We did some data digging today to compile monthly thunderstorm frequencies in Denver over the past 20 years during the primary thunderstorm season, which lasts from April through October.  Thunderstorms occur very frequently during the warm season in Colorado, and lightning poses a significant danger to the many people who spend their time outdoors in Colorado.

The chart below shows the average number of thunderstorm days per month over the past 20 years in Denver.  The data was taken from airport thunderstorm observations at the Centennial Airport on the south side of Denver.  This location was chosen both as a more representative location for Denver compared to DIA, and due to the fact that official records were moved from Stapleton to DIA in the mid 2000’s which could result in some data inconsistencies.  The average number of total thunderstorm days during the period April-October over the past 20 years is 51.8 days.  There is a noticeable peak in thunderstorm activity during June, July, and August, as noted in the chart below.



In future blog posts, we will take a look at thunderstorm climatology for other cities across Colorado and the western and central U.S. for comparison.

If your company’s operations and the safety of your personnel and clients are impacted by lightning, then you may be interested in Skyview Weather’s Lightning Notification Service.  Our meteorologists provide personalized lightning notifications via phone or text to clients that are more accurate and more timely than automated lightning alert systems.  This service is ideal for golf courses, outdoor concerts, and sports events.  



Western U.S. Weekly Weather Outlook – March 6, 2018

A powerful storm system toward the end of last week brought heavy snow to many areas of the west, including California, Idaho, Utah, and Western Wyoming, while areas east of the Continental Divide remained in a much drier and warmer pattern.  For the upcoming week, most of the West is experiencing a relatively less active pattern aside from a weak storm system toward the end of the week.  


Week 1 Outlook – March 6-12:

The week will start out quiet for most of the West, while the plains of Eastern Colorado continue to experience elevated fire danger due to strong winds, dry fuels, and low relative humidity values.  Over the weekend, a wildfire in Elbert County, CO claimed several homes and structures, but is now 100% contained.  Over the second half of the week, a minor disturbance will move across the Pacific Northwest and Northern Rockies, bringing light to moderate precipitation and snowfall to these areas through Friday.  In general temperatures will be undergoing a warming trend across most of the West.

On Sunday and Monday of next week, a deep trough of low pressure will be taking hold just off the Pacific Coast in Southern California while high pressure strengthens over the Rockies.  This pattern will result in a warm and moist southerly flow into portions of the Interior Western U.S.  Northern and Central California looks to be in the best position for significant precipitation in this pattern, and to a lesser extent Coastal Oregon and Washington.  The Sierra Nevada Mountains including Lake Tahoe could pick up heavy snowfall amounts during this time, although snow levels will be a good bit higher compared to recently given the warm air with this system.

The San Juan Mountains of Colorado and the mountains of Northern Arizona and New Mexico, and Southern Utah, could also get in on some of the heavier precipitation during the Sunday-Monday timeframe, although confidence is lower in how much moisture makes it to these areas.  Snow levels would likely be higher than usual for these areas as well with rain at the lower elevations.



Week 2 Outlook – March 13-20:

The first half of next week will likely feature active weather near the Pacific Coast and quiet weather for the Rockies and plains.  A trough of low pressure will slowly begin to progress inland, likely bringing colder temperatures, heavy precipitation, and heavy snowfall to the Sierra Nevada Mountains in Northern California, and to a lesser extent the Cascades of Oregon and Washington. 

Eventually, this trough of low pressure is projected to move into the Rockies by the 15th or 16th, which could be the start of a colder and more active pattern across the mountains of Montana, Wyoming, Utah, and Colorado.  However, it remains to be seen whether or not the active pattern toward the end of this outlook would translate to areas east of the Continental Divide, including the Denver metro area, but at the very least Denver will have better opportunities of seeing some meaningful moisture after about March 16th compared to the first couple of weeks of March.

High Fire Danger Across Eastern Colorado Today

Warm, dry, and windy conditions will result in critical fire danger across Eastern Colorado today.  Fuels are dry across the plains and relative humidity values will be dropping to 10% or lower across the I-25 corridor and eastern plains.  In addition, winds are going to become strong out of the west/southwest this afternoon as a trough of low pressure moves across the Rocky Mountains.  A Pacific cold front will reach the I-25 corridor late this afternoon and evening, resulting in a wind shift to northwest with strong winds continuing through the evening.  If any fires develop this afternoon, then the wind shift could cause erratic fire behavior.  Colder air will arrive from the northwest overnight and into Monday, but a Bora type wind event is expected during the day Monday with even stronger winds expected to keep the fire danger elevated.

Increasing Fire Danger Across Eastern Colorado Through the Weekend

A warm and breezy pattern will be developing across Eastern Colorado over the next few days, which will result in elevated fire danger across the plains.  A powerful low pressure system will be located near the west coast, while an upper level ridge of high pressure will be located over the Great Plains.  Strong southwesterly upper level flow ahead of the trough of low pressure will result in dry downslope winds east of the Continental Divide.  In addition, below average moisture this winter is leading to dry fuels across the plains.  The dry fuels, combined with low relative humidity and gusty winds associated with the downslope flow will enhance the fire threat.

The image below was produced by NOAA’s Storm Prediction Center, and indicates areas of high fire danger expected for Friday March 2nd.  High fire danger is also expected for portions of Eastern Colorado on Saturday, and again on Sunday as a Pacific cold front arrives with a possible Bora wind event.  This pattern could be a sign of things to come across Colorado this spring and summer given the low snowpack and lack of moisture in many areas.  Of course, climatologically speaking, significant precipitation events become more common during the spring in Colorado, so it will be interesting to see if the drier than average pattern persists, or if we are “saved” by a wet spring.  Stay tuned for our monthly newsletter early next week, for a preview of the upcoming month’s weather.  


Tahoe weather will feature heavy snow from tonight through Saturday

The biggest storm of the season so far will impact California late this week, bringing a 72-hour period of heavy snowfall to Lake Tahoe and the Sierra Nevada Mountains.  The storm will gradually progress eastward through the end of the week and into the weekend, with snow also in the Salt Lake City weather forecast, as well as in the central and western mountains of Colorado.  The image below was produced by NOAA and displays the 50th percentile snowfall ranges over the next 72-hours through Saturday morning, to give a general idea of where the highest snowfall amounts can be expected.



California – Lake Tahoe

A prolonged heavy snowfall event has prompted the National Weather Service to issue a Winter Storm Warning for the Sierra Nevada Mountains from tonight through Saturday morning.  Snow reports for the mountains surrounding Lake Tahoe are forecast to range from 2 to 5 FEET, and at lake level could range from 1 to 3 feet.  This will easily be the biggest snowfall of the season so far, in what has been an otherwise poor winter up to this point.  The storm will be a boon to ski resorts that have suffered from low snowpack this winter.


Utah – Salt Lake City

The storm system will impact Utah on Friday and Saturday, with a Winter Storm Watch in effect for the Wasatch Mountains and the greater Salt Lake City metro area from Friday morning through Saturday night.  Snowfall amounts are forecasted to range from 8-16″ across the Wasatch Mountains, with locally higher amounts of up to 30″ possible.  For the Salt Lake City area, including Ogden and Logan, snowfall amounts could range from 3-8″ with locally higher amounts of a foot or more possible in some areas.  This storm will also be great for local ski resorts, but will also cause difficult road conditions.



The slow-moving storm system will eventually reach Western Colorado Saturday night, bringing snow to the central and western mountains of Colorado through the day on Sunday.  The storm will be speeding up and weaker by this point, so snowfall amounts for the Colorado ski areas will not be as high compared to California or Utah.  However, at this time it looks like a decent storm with moderate snowfall amounts for the Colorado high country.  Snow potential for the Front Range cities east of the Continental Divide, including Denver and Boulder, remains more uncertain and will depend on just how far north or south the storm tracks across the state, and whether or not winds turn to upslope for long enough to get any meaningful snowfall.

Snow falling in the Southern California Mountains

A strengthening trough of low pressure moving from north to south into Southern California has transported Pacific moisture and cold air into the mountain ranges outside of Los Angeles and San Diego, bringing beneficial moisture to the region, including snow for the higher elevations.  Snow reports have been limited so far as of this morning, but a few spotters have reported snowfall amounts of 3-6″ so far as of 7am local time Tuesday morning. 

NWS San Diego has continued a Winter Storm Warning for the Southern California Mountains through 10pm this evening with total snowfall amounts of 3-6″ forecasted for areas between 4,000-6,000′, and 6-12″ above 6,000″.  Total amounts in excess of a foot will be possible above 7,000′.  Impressively, snow levels could drop as low as 2,000′ this morning, which speaks to the cold air involved with this system!  Below is a map produced by NWS San Diego Monday afternoon, which projects total snowfall amounts across the region.  Palomar, Big Bear, Wrightwood, and Mt. Laguna are expected to receive the highest snowfall totals.



As dry as California has been this winter, the pattern is finally starting to turn more favorable for the Golden State.  The mean jet stream and subsequent storm track look to remain near the West Coast in a favorable position to bring above normal precipitation and below normal temperatures to California through the first 10 days of March.  This should help to bring some beneficial moisture to the state, as well as good snow to the Sierra Nevada Mountains, including the Lake Tahoe area.

Western U.S. Weekly Weather Outlook – February 26, 2018

The weather pattern over the previous 10 days has been colder and more active across the Rocky Mountains than we have seen all winter up to this point.  Areas that have experienced warmer than average temperatures and below average snowfall for most of the winter finally got an extended period of winter-like weather recently. 


Week 1 Outlook – February 26 – March 4

Over the next week, the pattern will be transitioning as the mean trough of low pressure that has been in place over the Rockies shifts farther west closer to the Pacific Coast.  This type of pattern will result in a shift to more precipitation and snowfall across California, an area that is in great need of moisture!  Washington and Oregon also will be favored for precipitation under this pattern.  The map below was produced by NOAA, and is a projection of total precipitation over the next 7 days.  The West Coast and portions of the Northern Rockies will be favored for above average precipitation over the next week, while the Central/Southern Rockies and High Plains, including Colorado, will experience drier conditions.


As for temperatures, most of the Western U.S. will continue to experience colder than average temperatures this week.  The pattern will be favorable for good snowfall later this week for places such as Lake Tahoe as well as the Cascades of Oregon and Washington.  Despite less moisture in the Rockies, the mountain regions from Colorado to Montana will continue to experience below average temperatures as well.  The exception will be Eastern Colorado, where more frequent downsloping will result in warmer temperatures compared to the past week.


Week 2 Outlook – March 5-12

As we head into the second week of March, the longer term climate signals indicate a fairly similar pattern compared to what we’re going to experience during this upcoming week.  The mean upper level trough of low pressure looks to remain just off the West Coast in California, which would result in a favorable pattern for moisture in California.  Outside of California, the pattern looks drier for the rest of the Western U.S. during this timeframe, including the Pacific Northwest and the Rockies.  Portions of Utah, Idaho, and perhaps Western Wyoming may be closer to the primary storm track, so precipitation trends could go either way for these areas. 

There will almost certainly be occasional systems that move through the Rockies, but overall the pattern does not look particularly active from March 5-12th.  However, temperatures are projected to remain colder than average for all areas along and west of the Continental Divide during this time period.  Eastern Colorado, including the Denver area, is projected to have temperatures near average during this time period, likely as a result of periodic downslope winds, although there will likely be some colder days at times as well.  


Much-needed snow for portions of the San Juan Mountains

A low pressure system over the Four Corners region has brought some good snow to the Southern San Juan Mountains of Colorado, where 27″ of snow has fallen at Wolf Creek Ski Area over the previous 24 hours as of this morning.  Snowpack in the San Juans was only about 50% of average prior to this storm, so this has been a much-needed heavy snow event.  Of course, this heavy snow was fairly localized, with much lighter snowfall amounts reported at other ski areas in Colorado, even in the northern/western San Juan Range.

More snow is expected for Wolf Creek today as they will be in a favorable S/SW flow.  Elsewhere, a cold storm system dropping down the west coast continues to bring snowfall to the lower elevations near the coast in Oregon and even Northern California.  The past several days have featured well below average temperatures along the west coast, including low elevation snowfall in Washington and Oregon, including the Seattle and Portland areas.  Seattle itself has received only light snowfall amounts due to downsloping winds, but some areas of the San Juan Islands picked up impressive snowfall amounts.

Here is an image of NOAA’s 24-hour probabilistic snowfall forecast, showing the 50th percentile snowfall projection across the Western U.S.  While this shouldn’t be taken verbatim, it does give a good idea of which areas will be favored for snow today.


Very cold temperatures across the Western U.S.

A very cold airmass has become entrenched across the Rockies this week, resulting in bitterly cold temperatures across the region, including some record lows.  This morning, DIA set a daily record low of -8, following a daily record low maximum temperature of 13 on Tuesday.  The cold airmass is impressive both in terms of its persistence and for the time of year, given that we’re in the third week of February which is getting late in the season for extended cold snaps.  Also, the depth of the arctic airmass is impressive, meaning that mountain inversions are not as strong as usual with cold temperatures experienced at all elevations.  The West Coast has not been immune to the cold either, with record low temperatures this week from Seattle to San Francisco. 

Below are some of the low temperature readings over the past 24 hours (time ending 7am this morning) for both Colorado and the rest of the Rocky Mountain states.  The coldest temperature in Colorado was -26 in Fraser.  Elsewhere, the northwest side of Glacier National Park recorded a low of -42, Peter Sink in northern Utah recorded a low of -40, and West Yellowstone in SW Montana recorded a low of -38!

Colorado (24 hour lows):

  • -26, Fraser
  • -23, Crested Butte
  • -21, Craig
  • -20, Silverton
  • -18, Leadville
  • -17, Vail Pass
  • -15, Greeley
  • -14, Pikes Peak
  • -12, Steamboat Springs
  • -8, Denver/DIA
  • -8, Air Force Academy
  • -4, Ft. Collins

Rocky Mountains (24 hour lows, 7am Feb 20 – 7am Wed Feb 21):

  • -42, Polebridge/Glacier NP (MT)
  • -40, Peter Sinks (UT)
  • -38, West Yellowstone (MT)
  • -31, Yellowstone Lake (WY)
  • -31, Seeley Lake (MT)
  • -30, Butte (MT)
  • -28, Big Sandy Opening (WY)
  • -23, Pinedale (WY)
  • -20, Bozeman (MT)
  • -19, Stanley (ID)
  • -19, Cody (WY)
  • -18, Island Park (ID)
  • -18, McCall (ID)
  • -15, Laramie (WY)
  • -15, Togwotee Pass (WY)
  • -15, Dillon (MT)
  • -13, Jackson Hole Ski Area (WY)
  • -13, Lander (WY)
  • -12, Alta-Mt. Baldy (UT)
  • -11, Helena (MT)
  • -11, Kalispell (MT)
  • -8, Jackson Hole (WY)
  • -8, Park City (UT)
  • -5, Sun Valley (ID)