647 
FXUS65 KPIH 030939
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
239 AM MST Sun Feb 3 2019

.SHORT TERM...Today through Tuesday. Long-wave trough is oriented 
over the West Coast with three notable shortwaves/closed upper 
lows seen in this morning's satellite imagery. The first shortwave
is lifting out of the Great Basin, and is reflected at the surface
as a cold front. Some uncertainty still in how low snow levels 
will drop this morning behind the cold front, but expect the snow 
levels to remain just above valley floors along the I-86 corridor.
Pocatello to Idaho Falls could get 0.1 to 0.2 inches of snow, but
may possibly be mixed with rain. Heaviest snow will be around 
Monida Pass to the Island Park area, which will see around 4 to 7 
inches through the rest of today. Overall no changes to headlines 
this morning.

The next upper wave will lift across the region on Monday, though
models are not consistent with the timing of the wave of precip.
So some timing uncertainty remains as well as uncertainty in the 
snow levels, which appear to be a bit lower than today's levels. 
The Central Mountains will once again get hit with about 5 to 8 
inches of new snowfall with this system, as will parts of the 
Caribou Highlands and again the Island Park area. 

Finally, a deep upper low will drop into California via the OR/WA
coastline late Monday. This will bring another 4 to 7 inches of
snow to the higher terrain, and possibly 1 to 2 inches in the
Snake Plain. Hinsberger

.LONG TERM...Tuesday night through next Sunday. There continue to be 
some substantial continuity issues with the forecast later Tuesday 
and Wednesday. All indications are that the main low is going to dig 
south out to our west, amplifying the storm as it moves the state on 
Wednesday. The issue comes down to how split the flow becomes and 
where the closed low tracks across the West. A track of the low 
farther south could spell drier conditions until the back edge of 
the trough moves across our area, which is shown in some instances. 
The opposite happens with a track more to the north. The Blend of 
Models seems to have a good handle on it since it takes into account 
many scenarios. That gives up a decent of chance of precipitation 
across the board into Wednesday afternoon. We should see MOSTLY snow 
by the time we get to this point, but we couldn't rule out a mix 
ahead of the colder surge of air. Thursday looks to be dry, although 
we will likely see some fog or stratus around thanks to recent 
moisture. We run into similar issues by the end of next week, as the 
next major storm digs south across the West. The ECMWF is farther 
west toward the coast, carving out a colder and deeper trough over 
the region. The GFS doesn't take the low that far southwest, and 
consequently had a faster storm track across Idaho. A blend of 
models seems to be the best way to go here. We know it will be 
colder, but again how cold depends on how deep the trough ends up 
becoming. We do increase the chance of snow across all of eastern 
Idaho heading toward next weekend, with a bit higher probability for 
the high country.  Keyes

&&

.AVIATION...The aviation forecasts for today are going to be all 
over the place today, as we transition from one or more bands of 
steady rain or snow to a more spotty/showery situation for our TAF 
sites. In more general terms, we should see our valley airports 
(BYI, PIH and IDA) stay mostly VFR to MVFR with rain. There could be 
a short window early on this morning with the main push of 
precipitation going to IFR from lower ceilings. We are also 
expecting gusty south to southwest winds at these sites as well, 
around 15-30kts including gusts. For our mountain airports (DIJ and 
SUN) things will be a bit tricky as snow levels lower today. SUN is 
already going to a wet snow as of 230am with the main batch of 
precipitation. They should stay mostly snow, although another degree 
or two upward and they could go back to a mix or plain ol' rain. 
They are sitting IFR and should stay there most of the morning, 
before improving this afternoon. The caveat would be if any heavier 
showers redevelop in the mountains and pass over the airport. That 
isn't likely but definitely a non-zero possibility. DIJ is VFR with 
rain thanks to downslope limiting snow and lower FR weather. The 
question is later this morning when the main band and front sweep 
across the Teton Valley. We will likely fluctuate from VFR to IFR. 
The longer we see downslope winning out, even if it cools off and 
starts snowing as expected, better conditions prevail. If rain or 
snow is heavy enough to overcome this, it will quickly drop to IFR 
and potentially stay there.  Conditions should readily improve 
later today either way. Keyes 

&&

.AIR STAGNATION...Improving air quality is expected across 
Franklin County today as a storm system pushes into the region. 
Huston/Hinsberger

&&
.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 PM MST Monday for IDZ066-067-069-
071>074.

Winter Weather Advisory until noon MST today for IDZ052-060>064-
068-070-075.

&&

$$