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000
FXUS65 KPIH 252102
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
302 PM MDT Thu Apr 25 2024

.SHORT TERM...Today and Friday.
There continues to be a couple of weak lows near our area, one
over eastern Wyoming and one over southern Utah. Plus, there are
a couple of low pressure systems just off the Pacific coast, one
just off the Washington coast and one off the Oregon coast.

Wrap around moisture and instability from the two lows near our
border will bring isolated to scattered convection across our
Eastern areas this afternoon, mainly east of I-15. Cape looks to
be around 200 to 400 J/kg with only 20 to 30 kts of shear. Best
chances of thunderstorms this afternoon continue to be east of
I-15, particularly along the Wyoming border where there is a 70
percent chance of thunderstorms. There is only a a 10 to 20
percent chance of thunderstorms along our western areas.
Thunderstorms are again capable of small to moderate hail, brief
moderate to heavy rainfall, and wind gusts up to around 30 to 35
mph. Hail could be up to around nickel size. Cannot rule out a few
storms with slightly bigger hail. Winds will pick up in our
southwest areas today with gusts of 30 to 35 mph from winds ahead
of the next system coming in tonight into tomorrow.

Temperatures will be slightly above normal today before dropping
off Friday to slightly below normal.

With the next system (currently on the Pacific coast) coming in
tonight into tomorrow look for widespread precipitation across the
area Friday with 0.05 to 0.15 for valley locations and 0.25 to
0.75 inches for mountains. Snow levels will start high around 8500
and drop to around 7000 feet (especially to our north) by Friday
night, though there is some uncertainty on how quickly and low
these snow levels will drop. Westerly winds look to still be
gusting near 35 mph across our southwest areas Friday. On Friday
northerly winds will start coming over the Montana Divide. Snow
amounts look to be around 4 inches to 8 inches for the Big Lost
mtns, Lemhi mtns, Beaverhead mtns and, to a lesser degree, the
western Central mountains. Again these amounts look to be above
8000 to 8500 feet. However, snow levels could drop to 7000 feet
earlier Friday apposed to late Friday, which is what is expected
now.
Wyatt

.LONG TERM...Saturday through next Thursday.
Valley rain and mountain snow will continue on Saturday with
wraparound moisture filtering into Idaho. Precipitation will favor
the eastern half of the CWA as the closed low shifts south and then
lifts northeastward. National Blend probabilities suggest a 25% to
45% probability of 0.35 inch liquid precipitation in the central
mountains and a 50% to 60% chance of 0.45 inch along the MT Divide,
Big Holes, and Bear River Range. It also indicates a 20% to 40%
probability of 0.30 inch QPF from Pocatello to Idaho Falls with a
20% or less chance of the same amount elsewhere outside of the
central mountains and E/SE Highlands. Precipitation chances will
decrease to below 15% across much of the area on Sunday, with the
greatest potential across the E and SE Highlands. Amounts look very
light, generally around one tenth of an inch or less. Thunderstorm
chances will favor the E and SE Highlands both Saturday and Sunday
afternoon, as well. 500 mb ensemble clusters continue to depict
model uncertainty regarding the timing and track of a Pacific
Northwest low and a ridge building in from the west/southwest early
next week. While both the deterministic GFS and ECMWF feature a
shortwave moving through on Monday, the ECMWF brings the main low
directly over Idaho on Wednesday whereas the GFS keeps the low much
further north and tracks it east along the US-Canadian border.
Models continue to show westerly 700 mb winds increasing to around
30 to 40 mph which will support breezy conditions at the surface.
Considering the uncertainty regarding the synoptic setup throughout
much of next week, confidence remains low in forecast temperatures
and precipitation chances and amounts. At this time, the NBM favors
the much drier GFS solution, as it features minimal PoPs Tuesday
through the end of the extended, as well as a warming trend with
highs around 15 degrees above normal by next Thursday.
Cropp

&&

.AVIATION...VFR to MVFR conditions forecast throughout the
period,although any moderate rain to directly impact a terminal
could intermittently degrade conditions. Hi-resolution models show
isolated to scattered rain showers and storms favoring the E & SE
Highlands. HREF thunder probabilities increase throughout the
afternoon, peaking early this evening to around 40% over KDIJ with
15% chance or lower near the other terminals. Southwest/west
winds will be breezy today with gusts to 20 to 25 kts at all
terminals aside from KDIJ. Thunderstorm outflow winds will be
stronger, around 35 to 40 kts.
Cropp

&&

.HYDROLOGY...
Water levels remain elevated on the Portneuf River in Pocatello
and Topaz where River Flood Warnings and River Flood Advisories
remain in place respectively until further notice. Minor to
moderate flooding is expected or ongoing in these areas with both
locations forecast to crest this weekend before dropping slightly
heading into early next week. Further north and west along the
Snake River, water managers have increased releases from upstream
reservoirs leading to high flows in excess of 10,000 cfs
downstream from Palisades to Milner. The Snake River near Heise
gauge has also reached action stage and is forecast to be at that
stage until further notice due to releases from Palisades. Willow
Creek below Tex Creek above Ririe Reservoir and the Blackfoot
River above Blackfoot Reservoir both also continue to be in action
stage since Monday with no major impacts seen elsewhere in our
CWA as of Thursday morning.
MacKay

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$