UWFPS 2017 daily cold-air pool forecast valid Sunday 01/15/2017  1400 MST (2 pm local time; updated 6 pm local time)

Key summary:  Moderate cold-air pool episode in Salt Lake and Utah Valleys is underway (strong in Cache Valley). At this time it appears the episode will continue until early Thursday morning January 19th, followed by several storms through Monday January 23rd. 

Drier air is expected to reduce low clouds overall Monday afternoon through Tuesday. However, potential fog formation a concern for aircraft operations, particularly in night and morning hours.   

Current weather synopsis:

PM2.5 Pollution levels have remained steady in the 15-20 micrograms/m3 this evening in the Salt Lake Valley at UDAQ and University of Utah, and other monitors. Much higher PM2.5 has been observed in Cache Valley (over 40 micrograms/m3).

http://meso2.chpc.utah.edu/gslso3s/cgi-bin/current_map.cgi?tz=local&region=GSL&var=PM25

A thin stratus deck located at mid-elevation mountain slopes about 1,900 feet above the Great Salt Lake Basin persisted over the Wasatch Front today, although clearing was noted in the Cache Valley:

MODIS image late morning 15 January. White areas are cloudy while red areas are snow-covered.

Short-term forecast (12-36 h forecast Monday 16 January):

Cold-air pool conditions expected to continue as a ridge of high pressure builds over the region. Model forecast soundings indicate that drier northwest flow may erode much of the low clouds Monday afternoon. 

The concern, thereafter, will be the formation of dense surface fog in low-lying areas during nocturnal cooling of the moist boundary-layer Monday night. Stay tuned as these clouds are notoriously hard to predict.

Visibility/ceiling/clouds:  Stratus deck located between 1000 and 2000 ft above ground level expected to lift Sunday night in Salt Lake Valley. 30% chance of local dense fog (visibility < 1/2 mile) at KSLC and in Cache late Sunday night. 

Winds: light and variable.

Mid-term forecast (Tues-Thurs 17-19 January):
 

Moderate cold-air pool conditions continue until end of episode Thursday morning. A axis of ridge of high pressure will be centered over Utah on Tuesday.  Warm air advection during at mountaintop will warm 700 mb temperatures from -5.0 C on Sunday to around 0 C on Monday and +1 C on Tuesday. This will resulting in a moderate-intensity capping temperature inversion or cold-air pool over the Salt Lake Valley beginning Saturday night and continuing through Tuesday or Wednesday. A stronger cold-air pool is in place in the Cache Valley (where snow cover remains on the ground) and surface temperatures will run 10 F colder than in the Salt Lake Valley. 

Visibility/ceiling/clouds: 30% chance of low clouds and fog (most widespread in the morning) below 775 hPa level. 

Winds: generally light and variable on Tuesday. Southerly winds increasing with a channeled jet located between 300-1000 m AGL in Salt Lake and Utah Valley ahead of storm system on Wednesday.

Long-term forecast (Fri-Mon Jan 20-23):

A significant and prolonged series of storms (with no inversion or cold-air pool conditions) is expected beginning Thursday 19th January. At this time significant rainfall followed by significant snowfall is forecast. Models also hint at colder air approaching from the west toward the 22nd January. Stay tuned.