Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 262021

Area Forecast Discussion
National Weather Service Pocatello ID
221 PM MDT Sun Mar 26 2017

.SHORT TERM...Tonight through Tuesday night. The next upstream storm
system was approaching the NW coast early this afternoon while
associated precipitation was noted spreading inland across
Washington, Oregon, and NW Nevada. Numerical models drive this first
band of light precipitation into the CNTRL mountains and ERN Magic
Valley late this afternoon/early this evening and then further east
into the Wyoming border area by around midnight. The main upper
trough begins to work inland late tonight with a fairly enhanced
band of precipitation sweeping through the Boise area into our WRN
border region before the developing split begins to take full
effect. During the morning hours Monday, an enhanced band of
precipitation is expected to lift NE into the Panhandle/Lost River
Region with the NRN branch of the split while a second area of
enhanced precipitation spreads ESE into NRN Utah with the SRN
branch. SE Idaho may yet see some precipitation out of this passing
system as instability showers develop during the afternoon hours.
Both the GFS and NAM have been trying to develop some sort of Snake
Plain convergence event Monday evening which weakens overnight as
the upper trough begins to push east into Wyoming. As a result,
drier conditions are expected Tuesday and Tuesday night as SE Idaho
falls between the system exiting to our east and the next system
developing off the NW coast. Daytime temps remain near
climatological norms throughout the period. Huston

.LONG TERM...Wed through next Sun night. A strong spring storm
expected to bring clouds on Wed, a chance of precipitation for Wed
night in the western half, and moderate to heavy rain and high
elevation snow for Thu/Thu night, with a tapering off on Fri. Not
expecting snow to reach the Snake River plain, but the snow level on
Thu night likely as low as 5000 feet elevation. This will also come
with 20 to 30 mph wind. Right now, snow accumulation for the Thu/Thu
night time period above 5000 ft is mainly 0.5 to 3 inches in the
central Idaho mountains, and 3 to 6 in the eastern highlands
bordering Wyoming. It is lower in the central mountains because the
front passes through during the warmest part of the day there, and
dwells over the eastern highlands during the overnight hours.

What happens after a clear and mild Sat/Sat night, is still up to
much difference of opinion. The GFS remains very dry, while the
ECMWF brings a low in from the south. Have split the difference
during this portion of the forecast. One thing they do agree on is
below freezing temperatures for the Snake River plain Fri night and
Sat night due to northerly dry air flow. Messick

.AVIATION...Showers appear to be holding off from previous thinking,
until later this evening with the line of showers having only
reached the KMUO area at this time. Once the line starts passing
through, the 3 northern airports have the only threat of marginal
VFR conditions: KSUN, KIDA, and KDIJ. KSUN and KDIJ are high enough
in elevation where they should see some snow. At KDIJ this could
bring conditions very close to IFR, depending on how heavy it snows
there. That airdrome has the least confident forecast. Not expecting
much in the wind department, mainly southerly wind ahead of this
line of showers and mainly west behind it. Precipitation ends from
west to east, anywhere from 27/08Z to 27/14Z, with another secondary
line of precipitation beginning to move into western airports around
27/14Z. Messick

.HYDROLOGY...There are no changes to the advisories or watch areas
this update. The Portneuf at Pocatello remains at Minor flood
stage with forecasts now back at putting the river at Moderate
flood stage later in the week. The line between Minor and Moderate
is less than 1/2 a foot of difference. The Snake at Blackfoot is
in action stage, nearing Minor floor stage throughout the week but
forecast to remain below it. The Bear River at Border is in Minor
flood stage with forecasts to decrease today. Not much precip is
expected to fall today, which will assist in mitigating any
flooding situation but temperatures will be climbing back above
freezing tonight for most. The exception will be most of the Bear
Lake region and along the Continental Divide. An incoming weather
system will provide a decent chance of lower valley rain tonight and
Monday with upwards of 1/4 inch or more of liquid which would
exacerbate or extend any current flood issues. Huston/NP

Flood Watch continues until 1 PM MDT Monday for IDZ017>019-022>025-


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