Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
317 PM MST Monday Nov 30 2015
Synopsis...high pressure will gradually build over the region
through middle week.
Short term (through 00z friday)...
water vapor loop shows the storm system progressing over the
central rockies with a weak ridge over the interior west. Amdar
400-250mb wind observations places a 125kt-160kt westerly jet from
Arizona into the Southern Plains. GOES/hrrr/GPS/12z slc radiosonde observation
indicate the precipitable water value ranges between 0.05"-0.10"
mountains...to 0.15"-0.25" most valleys.
As column continues to dry and warm behind the storm system...not
expecting anything other than an increase in middle and high clouds as
the last wave pivots over northeast Utah overnight from Wyoming.
The remainder of the short term period of the forecast entails
ridging surface and aloft. Forecast challenge revolves around
temperatures due to building inversions...along with areas of haze
Nighttime periods look to range from clear to partly cloudy through
Wednesday night...allowing nearly pristine radiational cooling
conditions. Made sure to show relatively colder conditions for the
Uinta Basin/Cache Valley/west desert/San Rafael Swell and Castle
For a first guess fog area looked at where minimum temperature
forecast was at least 3f colder than 21z observed dewpoint.
Biggest departures were seen across the Cache Valley...Bear River
Valley...western Uinta Basin...and the Southern Mountain valleys
where placed areas of fog instead of the patchy fog wording.
Inserted mention of haze across the Wasatch front starting Wednesday
with it being the third day in inverted conditions.
First opportunity to break inversions is Thursday ahead of the next
splitting trough. But given 3 nights to entrench the inversion
conditions along with a pressure gradient not yet favorable for
gusty south winds...am only thinking there is a 10-20% chance for
breaking the inversion Thursday.
Medium term (00z Friday through 00z sunday)...
weak ridging in place and warm air advection of 700mb
temperatures will help warm day time temperatures closer to
seasonal normal /low to middle 40f/ late in the week for Thursday and
After the ridge progresses eastward the next upper level trough
moves inland of the West Coast. The operational models have large
differences of how this system will split but the overall trend has
remained the same. With a pre-frontal surface gradient aligning from
northwest to southeast...expecting increasing southern valley winds
Friday along ridgetops and through some narrow valleys. While the
moisture content doesn/T look over zealous...have kept low end probability of precipitation
for Friday and Friday night...mainly across northern Utah.
The trough feature is forecast to exit rather quickly after bringing
cold air into the Great Basin. With the ridge setting up
again...valley inversions will likely re-build but should be short
lived due to the fast nature of progressing storms through the
Long term (after 00z sunday)...
the 500 mb cut-off low centered over New Mexico will move east
Sunday. Model guidance diverges after the exit of this cut-off
low...although consensus appears to be that the large-scale
pattern over the western U.S. Will stay fairly progressive into
early next week.
Aviation...no operational impacts at kslc terminal this evening. 20
percent chance for lower ceilings to develop between 12z and 14z
Tuesday which should keep mostly VFR conditions present.
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