Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 200956

Area Forecast Discussion
National Weather Service Pocatello ID
356 AM MDT Fri May 20 2022

.SHORT TERM...Today and Saturday. Looking at the current water
vapor imagery, our area remains under a broad upper level trough
behind an exiting cold front. Cold breezy flow at the surface
continues to move into area over the Montana divide behind
yesterday`s cold front. Look very light rain and snow showers to
move down the Snake plain today. With heating look for isolated to
scattered showers and isolated thunderstorms, especially in the
mountains, this afternoon into early evening. The Central
mountains and Eastern Highlands will see 1 to 2 inches of high
mountain snow. Expect winds from the north today, 10 to 15
sustained with gusts of 20 to 30 mph. As a result, have issued a
Lake Wind Advisory for the American Falls reservoir, as North
Northeast winds of 10 to 15 mph sustained with gusts of around 25
mph are expected today. Also, freezing to near freezing
temperatures are already occurring this morning. Thus, have
continued the freeze warning across the Snake Plain and Eastern
Magic valley.

Another freeze warning will be needed across the Snake
Plain/Eastern Magic valley on Saturday morning as cold air
continues Saturday. Saturday look for a weak upper level low,
currently located over the central British Columbia and central
Alberta, to drop into our area. More high mountain snow is
possible, look for 1 to 3 inches, for the Central mountains late
Saturday into Sunday morning. Around 1 inch of snow is expected
for the Montana divide and the Big Hole mountains.

Temperatures will be around 10 to 15 degrees below normal both
today and Saturday.

.LONG TERM...Sunday through Friday. The trends still show a low
moving across eastern Idaho on Sunday. Expect showers and even a few
storms as the storm will be directly overhead in the afternoon.
There is some uncertainty now with the depth of this low, which is
shown in the differences between the GFS, NAM, ECMWF, and 80% of the
cluster forecasts. (There are 20% that actually still show hardly
anything impacting us.) The bulk of the rain and snow, which is a
lot when you look at amounts, will fall across the central mountains
and eastern highlands. At the moment, the western sides of the Magic
Valley may end up with nothing based on the current forecast.
Temperatures will remain cool and just a few degrees BELOW AVERAGE.
The forecast gets more convoluted for Monday and Tuesday. The GFS
and ECMWF both show a developing trough/low east of the Divide. As
it deepens/develops just to our east, enough moisture spills over
for some showers and storms (especially Tuesday) across the
area...especially the central mountains and eastern highlands.
Looking at the clusters, 80-90% agree with the initial stages of
this system clipping the Divide Monday.  By Tuesday, the clusters
admittedly don`t offer a ton of help. They are struggling with the
depth and position of the storm, which also impacts where the ridge
begins developing along the West Coast. About 20% of the forecasts
are spot on in matching the GFS and ECMWF, while about 15-20% are
farther west with the developing pattern, and finally around 60%
show a shallower trough and the ridge already impacting us Tuesday.
The Blend of Models forecast gives up something closer to the
GFS/ECMWF idea although maybe a bit more westward. High pressure and
warmer weather returns for midweek. Thursday looks to be warmest day
as the ridge is actually far enough east to allow southwest flow to
warm up well into the 80s. That is supported by 60+% probability of
exceeding 80 degrees in the Blend of Models. There is also plenty of
support looking meteograms from the GFS, ECMWF and Canadian models.
Getting an early glimpse at Memorial Day may not be the
most pleasant weatherwise across the region.


.AVIATION...The main issues for today will be increasing showers
across eastern Idaho today, and the eventual shift to gusty winds
out of the north. While nowhere near as strong as yesterday, we will
see pockets of 15-20kts sustained and gusts 25-30kts. The current
TAFs will show VFR, even with showers or VCSH. There isn`t much
evidence that we would see a much lower drop in ceilings and
visibility, but certainly something to keep an eye once those
showers develop later today. We should see precipitation quickly
ending after sunset.


.FIRE WEATHER...Heading through the weekend, we are still looking at
BELOW AVERAGE temperatures with several rounds of rain and snow
showers...along with a few thunderstorms each day. It looks like the
best days for showers are today and Sunday, as a low drops south
today and another swings through Sunday. It does look like a decent
shot each day for wetting precipitation across the central
mountains. We may also see over 0.10 inches around Bear Lake today,
and on Sunday around Island Park and Zone 411. The potential for
seeing over 0.25 inches in those locations is less than 10%. Winds
today eventually turn northerly and gusty (pockets of 20-30mph).
They will be lighter over the weekend and eventually turn more
westerly by Sunday. Drier conditions return for midweek along with
ABOVE AVERAGE temperatures. By Wednesday and Thursday, lowest
elevations look to exceed 80 degrees. This is backed by 60+%
probabilities of exceeding 80 across the Snake Plain/Magic Valley,
the valleys across Zones 413 and 427, and also from Challis north
into Lemhi County. In fact, there is a 15-25% chance of exceeding 90
across the Snake Plain, Magic Valley and lower elevations of 427 on
Thursday. This will NOT be a prolonged period of dry and warm
conditions as it appears we return to wet and cooler conditions for
the Memorial Day weekend.


Lake Wind Advisory from 10 AM this morning to 9 PM MDT this
evening for IDZ054.

Freeze Warning until 9 AM MDT this morning for IDZ051>055.


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