151
FXUS65 KPIH 021934
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
134 PM MDT Thu May 2 2024

.SHORT TERM...Tonight through Friday night.
Another upper level trof will move through southern Idaho tonight
with another batch of rain and snow showers late this afternoon
through tonight. Snow levels will range between 4500 and 5500 feet
through Friday morning. Generally 1 to 3 inches in the central
mountains and eastern highlands with localized amounts up to 6
inches above 8 thousand feet. Very little snow forecast in the
Snake River Plain although there is a low chance of an inch or two
as a Snake Plain Convergence zone may develop late tonight and
Friday morning, but at this point extremely low confidence in that
possibility so for now very minimal low level snow accumulations
are expected. A variety of freeze warnings and frost advisories
are in effect once again. Will not be as cold as this morning with
significant cloud cover expected to elevate overnight lows in the
Magic Valley and Snake Plain although Idaho Falls and north are
still likely to go below freezing. Lows tonight in the 20s and 30s
with highs Friday in the 40s and 50s and it will be dry late
Friday morning through Friday night everywhere. With clearing
skies Friday will likely need more freeze warnings and frost
advisories Friday night into Saturday morning with lows again in
the 20s to lower 30s.
GK

.LONG TERM...Saturday through next Thursday.
Confidence continues to increase on a return to widespread, moderate
precipitation starting Saturday night and continuing into Sunday and
Monday as a well organized H5 low moves onshore from the NE Pacific.
Saturday is still shaping up to be the warmest day in over a week
with highs in the 60s/70s courtesy of a warm front and strong
southerly flow ahead of the arrival of this next system. Winds aloft
at 700 mb will steadily increase throughout the day Saturday into
Sunday as a 40-50 kt jet streak is established over ERN Idaho. This
will support strong winds out of the south for Saturday before
shifting to being out of the west for Sunday as this low tracks
directly over SRN Idaho and the NRN Great Basin. Winds will continue
to remain elevated out of the west/southwest through Monday and
Tuesday before lighter winds return for Wednesday aided by a ridge
of high pressure in the ERN Pacific attempting to move inland.

The position and track of this weekend low remains supportive for
widespread moderate precipitation with some locations forecast to
see more precipitation in a 2-day period (Sunday/Monday) than during
the entire month of April. This wet solution is reflected well
amongst ensemble and deterministic solutions with the NBM showing a
40-80% chance of 0.50" of rain or more  and a 10-20% chance of 1.00"
of rain or more across the entire region. The latest forecast calls
for 0.50-1.25" of rain with locally higher totals in the mountains
around that 1.25-2.00" range. Snow levels will initially start off
above 8000-9000` on Saturday before steadily decreasing into early
next week as colder air settles in behind a cold front on Sunday.
This will support a mix of rain and snow in the valleys with
predominant snow favored in the mountains. WINTER WEATHER ADVISORIES
may also be needed along the Idaho/Wyoming border region where
places such as Pine Creek and Teton Passes are currently seeing the
potential for up to around 12-18" of snow. Expect these numbers to
change over the coming days as there is increased uncertainty of
snow amounts but with a moist, cool airmass in place, be mindful of
the potential for a return to winter travel conditions.

As this low ultimately departs east onto the Great Plains for
Tuesday, what will be left in its wake will be a broad troughing
pattern over the PacNW and NRN Rockies. This will lead to continued
below normal temperatures and precipitation chances through the work
week but not to the extent of what we saw on Sunday/Monday given the
lesser organized nature of several weaker troughs. Highs starting
Sunday will be in the 40s/50s or about 10-25 degrees colder than
Saturday and will continue to be there through the work week. Models
remain in reasonable agreement heading into later in the week as an
aforementioned ridge of high pressure remains on track to build in
later in the week with over 75% of ensemble cluster solutions
favoring this solution. The other 25% show a continued trough over
the NRN Rockies which would delay any warmup however this remains
the less likely solution at this time. MacKay

&&

.AVIATION...For the 18Z TAFS through 18Z Friday.
Predominant VFR conditions continue as early afternoon radar imagery
shows scattered showers across WRN and CNTRL Idaho of which will
continue to track east through this evening. Given dew point
depressions around 20-30 degrees however, much of this precipitation
is not reaching the ground and we are seeing more virga as a result.
Have continued with VCSH on the leading edge of this moisture before
ultimately transitioning to a mix of rain/snow showers later today
through the overnight hours as surface dew points increase. In
addition to showers this afternoon, the HREF model probability of
thunder shows a 10-30% chance at KPIH, KBYI, and KSUN with best
chances at KBYI where VCTS has been included. As precipitation
shifts east overnight tonight into Friday morning, we are tracking
the potential for an organized band of snow to work north to south
across ERN Idaho with an emphasis on the Snake Plain corridor. This
will support possible MVFR/IFR CIGS/VIS at KPIH, KIDA, and KDIJ with
best chances at KPIH. MacKay

&&

.HYDROLOGY...
Moderate flooding remains ongoing at the Portneuf River at
Pocatello with the level remaining above moderate stage and
forecast to do so through today and drop below Friday and continue
before rising again late next week. Minor flooding continues for
the Portneuf River at Topaz where the gauge remains above flood
stage and will remain so for several days. Flood warnings also
remain in effect for the Blackfoot River near Shelley at
Wolverine Canyon where the river has gone above flood stage and
also near Blackfoot where the river has also now gone above flood
stage in the last 24 hours.
GK

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Frost Advisory from 2 AM to 9 AM MDT Friday for IDZ051-054-055.

Freeze Warning from 2 AM to 9 AM MDT Friday for IDZ052-053.

&&

$$