Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 252012
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
212 PM MDT Thu May 25 2017

.Discussion...A disturbance moving south from Canada this
afternoon will develop into a closed circulation over the Central
Mountains and the west side of the state. Instability is marginal
for thunderstorms this evening, but can`t rule out that
possibility on the west side of the forecast area near Stanley.
This disturbance then makes slow eastward progression through
Friday night, leaving a few showers near Bear lake by Saturday
morning. Model consensus favors up to a half inch liquid
equivalent on the higher mountain tops tonight through Friday,
.LONG TERM...less amounts at lower elevations. Snow levels dip
to about 7300 feet elevation by Friday morning, only to begin
rising again Friday afternoon and night as the disturbance moves
east. Some 1 to 3 inch accumulation possible, mainly above about
8000 foot level. The instability is greater on Friday across the
entire area with cold air aloft and steeper temperature lapse
rates. Thus included the possibility of isolated thunderstorms
over the entire area. Temperatures begin to warm Saturday and
continue into the middle of next week, with the lower valleys
climbing into the lower 80s by Tuesday and Wednesday. Sunday
through Wednesday, there is just enough instability for a slight
chance of thunderstorms each afternoon with a high pressure ridge
moving slowly across this area. By next Wednesday night the flow
off the Pacific will bring a couple of disturbances inland. The
timing and amplitude of these disturbances is not real consistent
in the models. What looked like a single strong disturbance by
Thursday, now looks like it could be a couple of smaller
disturbances, but still more active for thunderstorms in the
afternoon. RS.

&&

.AVIATION...An approaching trough is forecast to evolve into a
closed low directly over SE Idaho by Friday afternoon. On the
northern flank of the closed low, models develop a swath of
precipitation. For areas under the precipitation shield, model
trends are increasingly coming on board with the development of MVFR
(with brief IFR CIGS) on Friday. This is currently forecast to
develop around 12Z and BYI, and expand eastward to PIH around 15Z
and to around IDA, SUN and DIJ towards 18Z. Have introduced MVFR
CIGS at BYI, IDA and DIJ, where confidence is highest in this
potential. Still some uncertainty as to the exact position of the
precipitation shield, so future adjustments in CIG forecasts are
possible. Models generate enough instability to warrant the
inclusion of VCTS, particularly at DIJ and SUN just beyond the TAF
period Friday afternoon. Winds are expected to remain generally
under 12KT through the period at TAF sites. AD/RS

&&

.HYDROLOGY...A chance of showers tonight and Friday over the
Central Mountains will be partly off set by colder temperatures.
A warming trend begins on Saturday and continues through about
Wednesday of next week. The lower valleys will warm into the lower
80s and the mountains the mid 60s to mid 70s. This should be a
warm enough few days to greatly accelerate snow melt in the
mountains. RS

&&

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

&&

$$



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