Extremely Dry through Midweek

Posted Sunday, November 18th, 2018 by Lucas Bohne

After the clouds and showers yesterday, today was a different story with blue skies and sun dominating due to upper-level ridging (high pressure) in place over the western United States. For those who made it to the mountains today, the extremely dry air was probably noticeable. Observations from about 11,000 feet at Mt. Baldy (AMB) today show just how effective this high pressure is at at producing extremely dry conditions through subsidence, or sinking, of air which causes it to warm in temperature while the total moisture in the air remains constant. As you can see, dew point temperatures were extremely low today aloft, in the area of -25 to -65 degrees Fahrenheit, with relative humidity in the single digits. This means that the air today has only contained about 1-8% of the water vapor that it has the potential to hold at these temperatures. Images below show the Mesowest observations from AMB. as well as a vertical profile of the atmosphere from 6PM local time this evening at Salt Lake International Airport. The red line shows the temperature through the atmosphere while the green line shows the dew point temperature (in Celsius on the sounding). Mount Baldy is at 11,000 feet, which is near the 700 millibar pressure level of the atmosphere (numbers on far left of the image). You can see the difference in air masses between the valleys and the higher elevations with the sharp changes in temperature and moisture around 800 millibars.

 

Observations from Mt. Baldy over the last ~24 hours, showing extremely dry conditions aloft. (https://mesowest.utah.edu/cgi-bin/droman/meso_base.cgi?stn=amb)
Observations from Mt. Baldy over the last ~24 hours, showing extremely dry conditions aloft. (https://mesowest.utah.edu/cgi-bin/droman/meso_base.cgi?stn=amb). I’m guessing the quality check warning is due to the values of RH and dew point being so very low.
Atmospheric sounding from 6PM local time this eving from SLC Intl Airport. ( https://www.spc.noaa.gov/exper/soundings/18111900_OBS/)
Atmospheric sounding from 6PM local time this eving from SLC Intl Airport. ( https://www.spc.noaa.gov/exper/soundings/18111900_OBS/)

Short Term Forecast (Monday – Wednesday):

These dry, sunny, calm conditions will last through Tuesday. On Wednesday, prefrontal southwesterly winds will pick up and begin to bring in some air that is slightly more moist. Take a look at the time-height section viewer from weather.utah.edu from the North American Mesoscale Forecast System (NAM) output, which is one of the  weather models run by the National Centers for Environmental Prediction (NCEP). You can see the dry conditions persist over the next few days with relative humidity values generally below 10% in the mid to lower atmosphere. (Hint: time increases to the left on these types of plots).

Time-height section from weather.utah.edu (University of Utah Dept. of Atmospheric Sciences).
Time-height section from weather.utah.edu (University of Utah Dept. of Atmospheric Sciences) showing dry conditions through Wednesday, with increasing winds from the SW beginning during the day Wednesday.

Mid-Range Forecast (Wednesday night – Sunday):

It’s looking like several snow-producing storms will begin to impact the area beginning sometime late Wednesday or early Thursday. The first one (Thursday) has the potential to bring several inches or more of snow to the higher elevations of Northern Utah. At this time, the Thursday system does not look like it is cold enough to bring snow down to valley floors but the mountains should fare well.

Another significant wave of moisture moving in is anticipated for sometime around Friday evening, with what seems to be higher snow totals than the Wednesday/Thursday event. These storms should be beneficial for the resorts that have just opened or are scheduled to open in the next week.

Since we are several days out from both of these events, we will keep you updated as the week goes on about what you can expect for Thanksgiving Day and the upcoming weekend regarding timing and intensity. Depending on your holiday plans, these storms could either impact your holiday travel or put down some nice fresh snow for you to ski.

Lucas

 

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