The Weather Wire

March 2017 Volume 24 Number 3

Contents: A Drought-Busting Winter for California

Current Colorado and West-Wide Snowpack

Drought Monitor

February Summary/Statistics

March Preview

Snowfall Totals

A Drought-Busting Winter for California

For several years, most of California has been under severe to exceptional drought conditions, but that is finally coming to an end this year as an exceptionally wet weather pattern has slammed the Golden State over the past few months. The last time California experienced an above-average water year was in 2010-2011, then the next four years were much drier than normal, resulting in devastating drought conditions. Last winter finally saw close to average precipitation across most of the state, before the pattern shifted this winter, resulting in well-above average precipitation.

While heavy rains and rain falling on top of snow during warmer events at higher elevations have both resulted in areas of flooding at times this winter, the longer-term impact is positive for water resources and agricultural purposes especially. Below is a look at some of the precipitation amounts from December through February (the period defined as meteorological winter) for select locations in California, with the long-term average precipitation over this period in parenthesis. South Lake Tahoe’s precipitation total compared to average is particularly impressive, and a testament to the heavy snowfall that has occurred in the Sierra Nevada Mountains!

December-February Precipitation Totals compared to average

South Lake Tahoe – 31.56” (average 8.22”)

Eureka – 29.48” (average 20.25”)

Redding – 25.06” (average 17.74”)

Sacramento – 21.78” (average 11.42”)

San Francisco – 21.39” (average 9.11”)

Los Angeles – 17.10” (average 7.85”)

Monterey – 16.42” (average 7.84”)

Modesto – 11.04 (average 4.01”)

San Diego – 10.94” (average 5.16”)

Here is a look at the percent of average precipitation during the 3-month meteorological winter period from December through February across California. Well above average for most of the state, and near-record precipitation for some areas!

Next, let’s take a look at the current drought conditions in California compared to this time one year ago (yellow = abnormally dry, darkest red = exceptional drought). Last year at this time, nearly the entire state was still under drought, with a large portion in severe to exceptional drought. Currently, most of California is now drought-free!

U.S. Drought Monitor

March 1, 2016 March 1, 2017

The main meteorological reason for the wet and snowy winter in California has been a persistent deep trough of low pressure off the coast of the Pacific Northwest that has directed the jet stream southward into California, which has driven storm systems packed with deep Pacific moisture into the state. The mean jet stream has been located south of the Pacific Northwest (Washington and Oregon), where precipitation amounts have been closer to average in this typically wet and snowy region.

The active winter has also been a boon to skiers in California, where exceptional snowfall has occurred across ski areas in the Sierra Nevada Mountains. Some areas are experiencing their heaviest winter in decades so far, with another month or two of good skiing left to go. Some ski areas will likely remain open through late spring or even early summer, including Squaw Valley, which has already announced that it will remain open through July 4th!

Here are some of the seasonal snowfall amounts through March 2nd at California ski areas, with the current base snow depths in parenthesis. Some areas are already approaching 600” for the season! According to local snow telemetry data, current snowpack in the Sierra Nevada Mountains is over 200% of average in many areas. Also, note that Mammoth Mountain’s current snowfall and base depth are reported at the bottom of the mountain – at the summit of Mammoth Mountain, seasonal snowfall is not available, but the current base depth is an incredible 350”, so one can only imagine how much snow has fallen over the course of the season at the summit!

California Ski Area 2016-2017 Snowfall Totals through March 2 (current snow depths in parenthesis)

Boreal – 598” (base 265”)

Kirkwood – 578” (base 210”)

Squaw Valley – 575” (base 229”)

Northstar – 561” (base 108”)

Heavenly – 556” (base 131”)

Mammoth Mtn – 512” (base 200”)

Current Colorado and West-Wide Snowpack

Although it’s been a drier than average winter across the I-25 corridor in Colorado, snowpack remains above average across the mountains of Colorado. February snowfall was a bit less than December and January for most of the high country, but snowpack remains very healthy across all of Colorado’s mountain ranges, with the deepest snowpack relative to average across the San Juan and Elk Mountains of southwest Colorado.

Overall, this has been a very strong snow year for the mountain areas of the Western U.S., with most areas experiencing currently experiencing an above average snowpack heading into March. The deepest snowpacks relative to average are currently found in California, Utah, northeast Nevada, western Wyoming, southwest Colorado, and central and eastern Idaho. Across Washington, northern Idaho, and Montana, snowpack is closer to average in most areas.

Drought Update

Drought conditions have not changed much in Colorado over the past month, with areas of moderate drought remaining east of the Continental Divide and across the eastern plains, while the high country and western Colorado remains drought-free. Significant drought improvement has occurred over California and much of the western U.S., with pockets of drought existing across portions of the central and eastern U.S.

The map below shows forecasted temperature deviances for March 2017. There is a moderate bias toward above normal temperatures across much of Colorado, with a strong bias toward above normal temperatures across southeast Colorado.

The map below shows forecasted precipitation deviances for March 2017. There is a moderate bias toward below normal precipitation across much of Colorado, with a strong bias toward below normal precipitation across the southern third of Colorado.

Drought conditions are expected to persist east of the Continental Divide in Colorado, with additional drought development likely across portions of the Colorado plains not already under drought. Little change is expected in drought conditions across the remainder of the Western U.S. where most areas west of the Continental Divide are now drought-free.

February Summary

February 2017 was an overall quiet month with temperatures much warmer than average and snowfall well below average. The first couple of days of the month started off chilly with periods of very light snow and freezing drizzle, but the next few weeks were dry and unseasonably warm, and snow did not fall again until the 23-24th, when 1.6” was recorded at DIA. This was the only measurable snow at this location for the entire month, and well below the monthly average of 5.7”. DIA’s snowfall deficit for the season is now 15.9”. Precipitation was also below average with a monthly total of 0.23”, compared to an average of 0.37”. Measurable precipitation was only recorded on 3 days during the month. Temperature-wise, February 2017 is tied for the 6th warmest February on record, and featured four days with record high temperatures. Amazingly, the highest temperature of the month was 80 degrees, which occurred on February 10th. This was the all-time warmest February temperature on record, and also by far the earliest 80-degree temperature in Denver’s history, beating the old record by more than a month! Daily record high temperatures also occurred on the 15th, 16th, and 21st. Colder weather finally arrived over the last week of the month, with a low for the month of 11 occurring on the 26th. Overall, February’s average temperatures were 7.7 degrees above normal, with an average high of 53.9 and an average low 26.6. Gusty downslope winds often contributed to the warmth, with a peak wind gust of 58mph occurring on the 10th, the same day the high temperature of 80 occurred.

February Stats

TEMPERATURE (IN DEGREES F)

AVERAGE MAX 53.9 NORMAL 46.2 DEPARTURE 7.7

AVERAGE MIN 26.6 NORMAL 18.9 DEPARTURE 7.7

MONTHLY MEAN 40.2 NORMAL 32.5 DEPARTURE 7.7

HIGHEST 80 on 2/10

LOWEST 11 on 2/26

DAYS WITH MAX 90 OR ABOVE 0 NORMAL 0.0

DAYS WITH MAX 32 OR BELOW 3 NORMAL 3.9

DAYS WITH MIN 32 OR BELOW 21 NORMAL 26.9

DAYS WITH MIN ZERO OR BELOW 0 NORMAL 1.3

TEMPERATURE RECORDS 2/10 – monthly record high of 80 set

2/15 – daily record high of 67 set

2/16 – daily record high of 75 set

2/21 – daily record high of 73 set

HEATING DEGREE DAYS

MONTHLY TOTAL 685 NORMAL 908 DEPARTURE -223

SEASONAL TOTAL 3802 NORMAL 4439 DEPARTURE -637

COOLING DEGREE DAYS

MONTHLY TOTAL 0 NORMAL 0 DEPARTURE 0

YEARLY TOTAL 0 NORMAL 0 DEPARTURE 0

PRECIPITATION (IN INCHES)

MONTHLY TOTAL 0.23 NORMAL 0.37 DEPARTURE -0.14

YEARLY TOTAL 0.77 NORMAL 0.78 DEPARTURE -0.01

GREATEST IN 24 HOURS 0.18 on 2/23-24

DAYS WITH MEASURABLE PRECIP. 3

SNOWFALL (IN INCHES)

MONTHLY TOTAL 1.6 NORMAL 5.7 DEPARTURE -4.1

SEASONAL TOTAL 19.3 NORMAL 35.2 DEPARTURE -15.9

GREATEST IN 24 HOURS 1.6” on n 2/23-24

GREATEST DEPTH TR on multiple dates

WIND (IN MILES PER HOUR)

AVERAGE SPEED 10.9 mph

PEAK WIND GUST 58 mph from the SW on 2/10

MISCELLANEOUS WEATHER

NUMBER OF DAYS WITH THUNDERSTORM

0 NORMAL 0

NUMBER OF DAYS WITH HEAVY FOG 4 NORMAL 2

NUMBER OF DAYS WITH HAIL 0

NUMBER OF SUNNY DAYS 9

NUMBER OF PARTLY CLOUDY DAYS 7

NUMBER OF CLOUDY DAYS 12

AVERAGE RELATIVE HUMIDITY 47%

March Preview

March is the first month of meteorological spring (which is the period March 1 through May 31), but is typically one of Denver’s most active months, including the highest average snowfall of any month with 10.7”. Denver’s average precipitation in March of 0.98” is more than double February’s average precipitation, which indicates how quickly moisture typically increases as we head into the spring season. Due to the rapidly increasing solar angle that occurs during March, as well as increasing average temperatures, snow that falls in March tends to melt more quickly after storms are over, relative to the mid-winter months, and snow usually does not accumulate as much on pavement. However, big snowstorms are more likely to occur in March than any other month, which can result in significant travel impacts. Denver’s largest snowstorm in March history, and second largest storm in its overall history, occurred on March 17-19, 2003 when 31.8” of snow fell at Stapleton Airport (formerly Denver’s “official” climate station before the move to DIA). This incredible storm was one of the most significant snow events in the history of Colorado. In the foothills, a few locations received more than 80” of snow during the storm! March can sometimes be hit-or-miss with snowfall, with only minor snowfall amounts occurring in 2014 and 2015, but last March (2016) was a big month for snowfall in Denver with 18.4” falling at DIA, mostly over the second half of the month. Much of this snow fell during a blizzard event on March 23, where some locations in northern Denver metro received over two feet of snow – the biggest storm in at least a few years. Temperatures during March can be quite pleasant and spring-like during drier patterns, with an average high of 54.4 for the month (more than 10 degrees above December and January) and a record high of 84, which occurred in 1971. Arctic blasts are much less common compared to mid-winter, but brief cold snaps happen on occasion, especially following powerful winter storm systems. The coldest temperature on record in March is -11, which occurred in 1886. For March 2017, we are expecting warmer and drier than average conditions overall, especially over the first half of the month. During the second half of March, there will be a better chance of receiving some meaningful snowfall events, and if a storm system were to track favorably into eastern Colorado and tap into some Gulf moisture from the southeast, then a more significant snowstorm would be possible as this is climatologically one of the most likely times of year to receive a big snowfall.

DENVER'S MARCH CLIMATOLOGICALLY NORMAL (NORMAL PERIOD 1981-2010 DIA Data)

TEMPERATURE

AVERAGE HIGH 54.4 AVERAGE LOW 26.4 MONTHLY MEAN 40.4 DAYS WITH HIGH 90 OR ABOVE 0 DAYS WITH HIGH 32 OR BELOW 2 DAYS WITH LOW 32 OR BELOW 24 DAYS WITH LOWS ZERO OR BELOW 0

PRECIPITATION

MONTHLY MEAN 0.92”

DAYS WITH MEASURABLE PRECIPITATION 6

AVERAGE SNOWFALL IN INCHES 10.7” DAYS WITH 1.0 INCH OF SNOW OR MORE N/A

MISCELLANEOUS AVERAGES

HEATING DEGREE DAYS 763 COOLING DEGREE DAYS 0 WIND SPEED (MPH) 9.7mph WIND DIRECTION South DAYS WITH THUNDERSTORMS 0 DAYS WITH DENSE FOG 1 PERCENT OF SUNSHINE POSSIBLE 69%

EXTREMES

RECORD HIGH 84 on 3/26/1971 RECORD LOW -11 on 3/28/1886 WARMEST 50.4 in 1910 COLDEST 26.4 in 1912 WETTEST 4.56” in 1983 DRIEST 0.11” in 1908 SNOWIEST 35.2” in 2003 LEAST SNOWIEST Trace in 2012

Snowfall

October 2016 to April 2017

City Oct Nov Dec Jan Feb Mar Apr Total

Aurora (Central) 0.0 3.0 9.5 8.9 1.3 22.7

Boulder 0.0 4.4 13.0 18.5 9.9 45.8

Brighton 0.0 2.8 9.4 8.4 1.2 21.3

Broomfield 0.0 3.5 9.9 14.6 3.6 31.6

Castle Rock 0.0 5.2 7.1 7.8 5.6 25.7

Colo Sprgs Airport 0.0 0.0 6.4 6.3 0.7 13.4

Denver DIA 0.0 1.7 9.7 6.3 1.6 19.3

Denver Downtown 0.0 3.0 10.4 11.9 1.1 26.4

Golden 0.0 4.5 16.0 11.9 5.5 37.9

Fort Collins 0.0 3.0 8.2 11.1 4.0 26.3

Highlands Ranch 0.0 3.7 7.3 8.4 3.8 23.2

Lakewood 0.0 2.5 12.5 8.8 2.6 26.4

Littleton 0.0 3.5 11.2 9.0 4.5 28.2

Parker 0.0 3.5 8.1 6.9 4.0 22.5

Sedalia - Hwy 67 0.0 4.0 11.8 10.5 5.8 32.1

Thornton 0.0 2.9 11.9 10.5 2.9 28.2

Westminster 0.0 4.0 12.0 13.6 3.0 32.6

Wheat Ridge 0.0 3.5 14.4 13.1 1.6 32.6

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