484
FXUS65 KPIH 210911
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
311 AM MDT Tue May 21 2024

.SHORT TERM...Today through Wednesday night.
Expect a dry day for the most part with the exception of some
showers mainly in the extreme east along the Wyoming border. It
will remain very cool but a couple of degrees warmer than Monday
as a weak short wave ridge moving east ahead of the next system
which will spread showers and thunderstorms back into southeast
Idaho Wednesday morning into the central mountains and into the
remainder of southeast Idaho Wednesday afternoon. Highs today will
be in the 50s and 60s with milder lows tonight ahead of the next
system with lows in the 30s mountains and 40s valleys tonight.
This next system system will drive through another cold front
with widespread precipitation across the region above 0.10 in the
Snake River Plain and higher amounts of 0.20 to 0.50 in the
eastern highlands and central mountains. Snow levels will drop
from 7 to 8 thousand feet to 5 to 6 thousand feet overnight. Snow
amounts of 1 to 3 inches may fall in the Island Park area and
Stanley. highs amounts of 3 to 6 inches are possible above 8
thousand feet.  Winds will increase Wednesday as well especially
in the Snake River Plain but will be mainly below advisory level
with the highest in the Arco Desert where will see 30 to 40 mph
gusts with 20 to 30 mph gusts in the interstate corridor expected.
Gusts potentially higher near thunderstorms Wednesday afternoon.
Low temperatures Wednesday night will be much cooler in the 20s
mountains and 30s valleys and expect will likely see more frost
advisories in the Magic Valley and Snake River Plain.
GK

.LONG TERM...Thursday through next Tuesday.
Behind a cold front on Thursday, temperatures will be well below
normal with highs only reaching the 40s/50s as a mix of rain/snow
showers and isolated thunderstorms continue associated with a H5 low
situated directly overhead. This system will continue to track east
into Wyoming and Montana throughout the day Thursday into early
Friday which will bring a return to dry conditions as we begin to
see a warming trend return through the weekend. Before we get
carried away with this warming trend however, another system will
begin to move into SRN Idaho for Saturday into early Sunday as a
cold front helps to bring another round of rain/snow showers and
isolated thunderstorms to kick off Memorial Day Weekend.

High confidence amongst ECMWF/GFS ensembles and deterministic models
will make this weekend system a quick moving one in nature as a H5
ridge of high pressure builds into our area throughout the day
Sunday into Monday. For those heading outdoors this Memorial Day
Weekend, outside of some isolated showers/storms on Saturday and
Sunday, it will be a great weekend out there with highs in the
50s/60s for Saturday and Sunday before warming up to the 60s/70s on
Memorial Day as dry conditions return regionwide to kick off next
week. That warming trend will continue into Tuesday and Wednesday as
a H5 ridge axis shifts overhead, supporting highs rebounding back
into the 70s/80s as soon as Tuesday which would mark the warmest air
mass moving into our region so far this year. Taking a look at
climatology in Pocatello, our first average 80 degree day falls on
May 10th making this year in the top 10 latest years since 1939 of
reaching that 80 degree mark. Similarly elsewhere, all of our
climate sites have not reached 80 degrees yet this year but with
high confidence on all sites except Stanley reaching 80 degrees on
either Tuesday or Wednesday next week, warmer weather is on the way!

The EPS/GEFS ensemble models show little in ways of preventing this
ridge feature from being overhead through much of next week with the
only caveat to that being a deep H5 trough in the NE Pacific up into
the Gulf of Alaska. Long range models keep that trough at bay
through the work week with the potential for a weakened form of this
system moving onshore later in the week as our blocking H5 ridge
begins to shift east onto the Great Plains. Stay tuned. MacKay

&&

.AVIATION...For the 12Z TAFS through 12Z Wednesday.
Predominant VFR and dry conditions will continue for Tuesday under
partly to mostly clear skies. Outside of very isolated showers early
this morning, another round of rain/high elevation snow showers and
isolated thunderstorms will develop this afternoon and evening
(mostly across ERN Idaho) with the HREF model showing a 10-20%
chance of thunder at KDIJ and less than a 10% chance at all other
terminals. Dry conditions will return regionwide for sunset tonight
with our next system arriving tonight and throughout the day on
Wednesday NW to SE with a mix of rain/snow showers, thunderstorms,
and elevated W/SW winds of which will continue into Thursday. MacKay

&&

.FIRE WEATHER...
Unsettled and seasonably cool weather will continue through Thursday
as isolated showers/thunderstorms today transition to more scattered
to numerous for Wednesday/Thursday as a H5 low works directly
overhead SRN/CNTRL Idaho. The most widespread precipitation will
accompany a cold front as it passes through on Wednesday with those
chances building in NW to SE throughout the day. A mix of rain/snow
showers and thunderstorms will accompany this front with well below
normal temperatures settling in for Thursday with highs only in the
40s/50s. QPF/rainfall and snow amounts for this midweek system
remain similar to previous forecasts showing around 0.10-0.40" with
locally higher totals in FWZ 411 and especially in Lemhi County
where around 0.50-1" is expected. Even higher totals in excess of 1"
will be possible across northern portions of FWZ 475 and 476. Best
chances for any accumulating snow will remain above 5500-6000` with
light snow possible across our northern and eastern mountain valleys
as more moderate to heavy snow accumulations are expected in the
high country of FWZ 411, 422, 475, and 476. We may also see light
snow accumulations down to around 4500-5000` dependent on where
bands of precipitation set up with this system.

As this H5 trough departs east into Wyoming and Montana Thursday
night into Friday, drier conditions will return regionwide ahead of
a secondary H5 low building in for Saturday into early Sunday. This
2nd system will support another round of rain/snow showers and
thunderstorms but with lesser QPF than the midweek system.
Conditions will ultimately dry out for Sunday and Monday associated
with a H5 ridge of high pressure building in from the Pacific. This
will bring a return to seasonably warm temperatures with highs in
the valleys back in the 70s/80s as soon as Tuesday, marking the
warmest airmass so far this year moving into our area. MacKay

&&

.HYDROLOGY...
Elevated river levels continue on the Portneuf River at Pocatello
and Topaz. River levels are expected to gradually recede over the
upcoming week but will likely remain high enough to warrant
continued flood products for much of the week. McKaughan

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Frost Advisory until 9 AM MDT this morning for IDZ051>055.

&&

$$