Key
summary : Temperature inversion associated with the persistent cold-air pool has increased in strength and descended overnight. Low clouds cover is less than in previous days, thus no visibility problems are anticipated Tuesday for research flights. Mix-out
of this episode at this time expected on Thursday morning with rain and light snow.
Current weather synopsis and
short-term forecast (12-36 h forecast from Tues am 17 January-Wednesday am 18th
January):
The cold-air pool conditions expected to continue as a positively-tilted ridge of high pressure crosses the over the region through this period. The inversion strength has increased notably over the past 25 hours, and the elevation of the capping inversion has descended around 20 hPa and will continue to descend over next 36 hours.
The cold-air pool conditions expected to continue as a positively-tilted ridge of high pressure crosses the over the region through this period. The inversion strength has increased notably over the past 25 hours, and the elevation of the capping inversion has descended around 20 hPa and will continue to descend over next 36 hours.
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| Satellite fog product at 1400 UTC 17 January. Note that extensive low clouds (yellow) are reduced compared to previous mornings. |
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| Salt Lake International Airport Rawinsonde at 1200 UTC 17 January. Note the increase in temperature inversion strength and decrease in the height of inversion compared to 15-16 January. |
Visibility/ceiling/clouds: Patchy areas of low clouds with reduced coverage compared to previous days. At this time evening fog formation is not expected in the Salt Lake Valley, but cannot be completely ruled out. Evening fog formation in Cache potential (40%) will need to be monitored.
Winds: light and variable.
PM2.5 Pollution levels have remained
steady in the 20 micrograms/m3 overnight in the Salt Lake Valley Much higher
PM2.5 continues in Cache Valley (over 45 micrograms/m3).
Pesky low clouds continue across the
Salt Lake Basin (yellow color in the image below):
The temperature inversion remains in place across the region, as seen by the 5 am Jan 17th Salt Lake Airport sounding. Comparing this morning’s sounding to yesterday morning we can see that the mixed-layer is much shallower, allowing the pollution levels to climb overnight into this morning.
Mid-term forecast (Wed-Fri 18-20
January):
Moderate cold-air pool conditions continue
until end of episode Thursday morning. However, on Wednesday afternoon, a
thick mid-level cloud deck is expected, which will start to weaken the
inversion (see forecast sounding below):
By Wednesday night, the clouds will be thick and light
precipitation will be approaching from the west. Thus, we do not expect much
nighttime cooling on Wednesday night. On Thursday morning, rain or a rain and
snow mix will start by mid-day and continue through the day, potentially
changing over to snow Thursday night. A significant snow storm is currently possible for Friday night into Saturday in northern Utah.
Visibility/ceiling/clouds:Mid-level clouds will be on the increase. Fog is not expected to be an issue during this period, but is difficult to forecast and cannot be ruled out.
Winds: Mountaintop winds will be increasing rapidly to35 kts at
mountaintop level by 5 am MST Thursday. At the same time, a southerly
channeled jet between 300 and 1000 m AGL with speeds of 10-15 kts will
develop in the Salt Lake Valley Wednesday evening and continue into Thursday.
Long-term
forecast (Sat-Tues Jan 21-24):
While forecast models could
change, at this time several storm
systems are expected during this time, with several chances of
accumulating snow in the Utah and Salt Lake Valley and no persistent inversion
or cold-air pool conditions through the period. Long-range
GFS model hints at a ridge of high pressure forming over the Western US around
January 25th, but the European Model has the storm track continuing. Check back, as confidence is low on this pattern change
this far out in the forecast cycle.
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