Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 220440

Area Forecast Discussion
National Weather Service Pocatello ID
940 PM MST Tue Nov 21 2017

.UPDATE...Have made a couple of minor updates this evening to
precipitation chances and related fields. Earlier update was to
spread slight chance shower wording further south through the
Snake Plain. QPF amounts remained very light, and likely Trace
amounts in most locations, but radar and observations showed
rainfall spread was a little farther than previously anticipated.
Second update was to increase the spread of fog across the
region. Kept mention in lower elevations where temp/dew point
spreads are small. Do not believe that dense fog will be an issue,
but a few locations will likely see visibilities around 1/2 mile
at times overnight. DMH


.PREV DISCUSSION... /issued 118 PM MST Tue Nov 21 2017/

SHORT TERM...Tonight through Friday afternoon. A ridge of high
pressure will continue to build over Idaho through Wednesday. This
has raised snow levels close to 9000 feet elevation. Horton Peak at
8800 feet just north of Galena Summit was reporting a temperature of
38F at noon today. Some rain has fallen in the mountains, probably
absorbed by the high elevation snow pack. Certainly no snow
accumulation concerns. Precipitation shifts a little further north
with the building ridge on Wednesday, roughly a Challis to Island
Park line by afternoon. Thanks Giving Day starts off with some
partly cloudy skies, then increasing clouds in the afternoon ahead
of a cold front that will make the Snake Plain close to Friday
morning. Snow levels drop to about 6000 feet elevation Friday
afternoon with this passing disturbance. Some breezy winds expected,
but well below advisory levels. The precipitation is short lived,
late Thursday night and Friday morning and not enough for
significant travel concerns. RS

LONG TERM...Friday night through next Tuesday. Mean upper ridge
will be situated over the Intermountain West on Saturday, then shift
to the east. Moisture feeding into the ridge will support some
slight chance-chance PoPs over the Central Mountains and the Island
Park area. Precipitation chances increase and spread through the
rest of east Idaho on Sunday night/Monday with the approach of a
strong cold front. This will also impact winds across the area as
the front passes. Current guidance is keeping winds just shy of
advisory levels. Synoptically, the GFS is slightly more progressive
than the ECMWF with regard to the upper trough, but models overall
are in general agreement through early next week. GFS and ECMWF show
an improving trend throughout the day Tuesday. Hinsberger

AVIATION...Low-level moisture represented by forecast BUFKIT
soundings this afternoon for KPIH, KIDA, and KDIJ. Teton Valley
webcams and KDIJ observations indicate the presence of patchy dense
fog, which I`ve left in a TEMPO group for the first hour of the TAF.
Gradual improvement is anticipated through the afternoon and into
this evening. Models suggest a period of rain tonight, keying in on
upslope-favored areas in a westerly flow. Best chances will be at
KSUN and KDIJ tonight into tomorrow morning. Perhaps a bit more
prolonged at KDIJ, which would support the lower ceilings.



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