Flood in Idaho, April 10 to 18, 2023

Area Forecast Discussion
National Weather Service Pocatello ID
338 AM MDT Mon Apr 10 2023

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT...
A ridge of high pressure will continue to support warm high temps 5-
10 degrees above normal for early April through Tue. Ripening of the
snowpack, runoff, and localized flooding will continue, aided by AM
low temps not dropping below freezing in most valley population
areas. The ridge will very slowly surrender to an advancing trough
of low pressure starting Tue, but initial impacts should be confined
to a few light rain/snow showers brushing across the Central Mntns
and Upper Snake Highlands/Teton Valley region through Tue night,
along with increasing SSW winds. The strongest winds are expected
between 9 AM and 9 PM Tue across portions of the Central Mntns,
where a WIND ADVISORY has been issued. 01

.LONG TERM...WEDNESDAY THROUGH NEXT MONDAY...
In the extended forecast, we will see on and off precipitation
chances and fluctuating temperatures. On Wednesday, a cold front
passes through ahead of a low that will be arriving in our area on
Thursday. This cold front will drop our temperatures and our snow
levels once again with highest precip chances on Wednesday up in
the Central Mountains and in the Eastern Highlands as the front
sweeps through, and these will be the areas that have the best
chance to see snow Wednesday PM through Thursday. As the low
continues moving eastward, we see a brief break in precipitation
early Friday before a trough drops through Friday afternoon and
brings more moisture along with it. Both of these systems will
keep breezy winds around Wednesday through Friday with gusts 20 to
30 mph. At this time, snow totals don't look to be particularly
impressive with the first system. In the 24 hour period from
Wednesday morning to Thursday morning, the NBM 4.1 shows a 10 to
30 percent chance of at least 2 inches of snow up in the Central
Mountains, Centennial Mountains, Big Hole Mountains, and Bear
River Range. This system will bring quite the drop in
temperatures, too, as we fall from the 50s and 60s for most on
Tuesday to 40s and 50s on Wednesday. Thursday will be cooler yet,
with highs generally in the 30s and 40s. Ridging begins to build
in again next weekend which will allow our highs to warm back into
the 50s and 60s on Saturday and Sunday. AMM

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.AVIATION...12Z TODAY THROUGH 12Z TUESDAY...
High pressure is set up over the southwestern US as we start the
week, resulting in ridging over most of Idaho and VFR conditions
at all sites for this forecast period. Winds will pick up as the
day goes on with gusts up to 20 kts at all sites except KSUN. Look
for more changes as Tuesday goes on with increasing cloud cover
and increasing wind gusts. AMM

&&

.HYDROLOGY...
Existing snowpack, combined with warm high temps 5-10 degrees above
normal and AM low temps increasingly not falling below freezing
(especially across valley population centers), will continue to
support ripening of the snowpack regionwide along with melting,
runoff, and localized flooding. A FLOOD WARNING remains in effect
for south-central Jefferson County due to reported sheet flooding
impacting homes and roads. An advancing trough of low pressure will
initiate a cooling trend starting Wed which will help stabilize the
snowpack and slow melting, with precip amounts generally remaining
light this week. Mainstem river responses will lag the warmest temps
and will remain quite modest for most areas...the Portneuf River at
Topaz and Pocatello, and the Bear River at the ID/UT border, are
forecast to approach bankful Wed and Thu. Continue to refer to our
Hydrologic Outlook (ESF) for additional details and suggested
preparedness actions. 01

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 9 AM to 9 PM MDT Tuesday for IDZ069>071-074.

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