UWFPS 2017 daily cold-air pool forecast valid 01/13/2017  1830 MST

Key summary:  Moderate cold-air pool episode in Salt Lake and Utah Valleys (strong in Cache Valley) Sunday-Wednesday Jan 15-18th. Followed by potentially several major storms Wednesday-Sunday January 18th-22nd. Fog/low clouds are the primary concern for aircraft operations Sunday-Wednesday. 

Current weather synopsis and nowcast (0-12 h valid 1830 MST 13 January 2017 to 0630 MST 14 January).

Drier air will be ushered from the northwest overnight tonight (Friday) at mountaintop level. Local areas of dense log fog, favoring snow-covered areas in the Cache Valley and near the Great Salt Lake and Utah Lakes.  Low temperatures 20-25 F.

Visibility/ceiling/clouds: Dense fog possible in low lying areas, visibility 1/8-1/4 miles, IFR or lower in fog, clear conditions developing outside of foggy areas. Stratus deck clearing overnight between 800 and 700 hPa.

Winds: light and variable.

                           

Short-term forecast (12-36 h forecast Saturday 14 January):

Morning fog possible favoring Cache Valley and near the Great Salt Lake and Utah Lakes.  Otherwise, mostly sunny with highs near 38 F in Salt Lake and Utah Valley and 27 F in Cache Valley. 

Visibility/ceiling/clouds: Dense fog possible in low lying areas, visibility 1/8-1/4 miles, IFR or lower in fog, clear conditions developing outside of foggy areas. If fog develops, expected to erode in the Salt Lake Valley after noon. Fog could persist in the Cache Valley. National Weather Service 40% chance of fog and KSLC early morning Saturday.

Winds: light and variable less than 6 mph

Mid-term forecast (Sunday-Tues 15-17 January):

Recent model runs have strengthened the Sunday-Wednesday cold-air pool episode somewhat. A ridge of high pressure will be building over Utah starting on Sunday.  Warm air advection during at mountaintop will warm 700 mb temperatures from -5.0 C on Sunday to around 0 C on Monday and +2 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 likely 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.

Mostly clear skies and northerly winds are still expected during Sunday afternoon. Sounding profiles in some of the models continue to unfortunately produce fog and stratus formation in the Salt Lake Valley, particularly in the morning. Please stay tuned.  Persistence is a powerful forecast in these episodes, so Saturday will provide a decent sense of the potential fog issues for Sunday. These potential fog issues may continue into Monday and Tuesday.

Visibility/ceiling/clouds: Low clouds and fog possible (most widespread in the morning) below 775 hPa level, favoring Cache Valley.

Winds: generally light and variable. 

Sunday 1400 MST NAM model sounding. Note the fog in the near-surface layer.

GFS forecast 1100 MST Tuesday Jan 16th at forecast peak of the cold-air pool.

Long-term forecast (Wed-Sat Jan 18-21):

A significant and prolonged series of storms is expected beginning Wednesday/Thursday 18/19th January. At this time significant rainfall followed by significant snowfall is forecast. Stay tuned.