Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Boise Idaho
241 am MST Monday Feb 8 2016
Short term...upper ridge still building...and strengthening the
inversion. Several weather differences from last night at 09z. An area
of fog/stratus has formed in the Magic Valley and slowly expanding
West. Fairfield/Idaho is much colder than last night...near zero this
morning vs middle 20s last night when winds were near 15 miles per hour. Winds
have become NE at Jerome/Idaho draining from the cold Camas Prairie.
With MOS guidance continuing to forecast NE wind we can also expect
a continuation of cold temperatures in the Camas Prairie through Tuesday.
As for the fog/stratus...we see that NAM and nambc are the only
models that keep maximum temperatures down throughout the snake basin today and
Tuesday. That suggests cold foggy air will spread over nearly all of
the lower snake basin. But those two models also show Idaho City
colder than the upper Treasure valley today which is probably
incorrect. No other models do this. Yesterday Idaho City had a
high of 52 vs only upper 40s in the Treasure valley...and similar
temperatures are expected today. No precipitation through Tuesday. Light east winds
today and Tuesday...except moderate NE near Jerome/ID.
Long term...Tuesday night through Monday...inversion will remain in
place through Friday under a high amplitude upper level ridge. Did
adjust temperatures a bit higher especially on Wednesday as model
sounding are showing the stratus deck breaking up. Increasing east-
southeasterly flow across the region on Thursday/Friday ahead of the
next upper level trough off the coast will also limit fog/stratus
coverage. Temperatures will reach the lower 40s Wednesday through
Friday except in the lower Treasure Valley. High temperatures above
the inversion will be in the 40s and lower 50s. The upper trough
moves inland Friday night/Saturday but weakens significantly by the
time it reaches the intermountain west. 00z GFS doesn/T even have the
trough making it that far inland. 00z European model (ecmwf) does bring in the though
though but with very little precipitation. The upper ridge rebuilds
over the western Continental U.S. Beginning Sunday which looks to last through
the middle of next week. Temperatures will continue to be above
normal Friday through Monday.
Aviation...mainly VFR. Expect areas of IFR/LIFR fog and low stratus
throughout the Snake River Valley through early this afternoon...with
patchy valley fog in the kbno..kbke..and kmyl areas. Fog and stratus
should dissipate around 21z...but it will redevelop this evening.
Surface winds...variable 10 kts or less. Winds aloft...northwest 10-
20 kts through 10k feet mean sea level.
Air stagnation...inversion will strengthen through Tuesday then
continue through at least next weekend. Lower valleys will see
mixing heights drop to around 1500 feet above ground level by Tuesday afternoon.
East winds in the mixed layer will increase slightly Tuesday...
especially in the upper Treasure and western Magic Valleys.
With dry air aloft and east winds the extent of fog/stratus later
this week is still uncertain.