Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 232008

Area Forecast Discussion
National Weather Service Pocatello ID
208 PM MDT Sun Apr 23 2017

.SHORT TERM...Sunday night through Wednesday. A wet pattern in
store for the next few days, satellite imagery shows nice fetch of
moisture across the Eastern Pacific. An embedded disturbance in
the flow is crossing Southeast Idaho this afternoon. Isolated
lightning strike detected just west of Sun Valley a few minutes
ago. Best instability this afternoon and evening will be in the
Central Mountains, kept isolated thunderstorms in the forecast for
that area. There will also be some showers sliding through the
South Central and Caribou Highlands this afternoon, but cloud
cover has been pretty substantial in that area, confidence in
thunderstorms is not so high. Snow levels drop to around 6000 to
6500 feet Monday morning and more so on Tuesday morning. Mountain
passes around Galena Summit, Banner Summit, Willow Creek, and the
passes along the Idaho and Wyoming border should see some 2 to 4
inch snow amounts the next two days. Afternoon temperatures near
40 and warm road temperatures will mean some melting or slushy
snow on the passes during the day, with a better chance of snow
sticking at night. Precipitation appears to focus Monday afternoon
into Tuesday, then another surge of moisture on Wednesday. Models
have not been the most consistent with start and stop times. Two
day total precipitation amounts in the Northern Wasatch and
Caribou Highlands could see a half inch or more, and bring more
threat of standing water in fields as well as increased flows on
streams. RS

.LONG TERM...Wednesday night through Sunday. Wet conditions continue
through the end of next week. Westerly flow from the Pacific is
keeping the door open for waves of rain and snow showers. Cooler
temperatures remain which means lower snow levels, especially Friday
when we could see light snow possible in the Snake Plain. By the
weekend, the pattern dries out somewhat and the flow becomes
northwest vs the low begins to deepen and drop toward the
Four Corners and Rockies. Lingering showers along the Divide remain
a possibility as a storm clips those areas. Keyes


.AVIATION...Shortwave noted on Satellite products late this morning
over central Nevada racing NE towards Idaho. Ahead of this wave
extensive VFR mid-level cloud cover has limited potential to
generate instability necessary for widespread thunderstorms.
However, think there will be just enough instability generated for
an isolated TS, therefore have maintained mention of VCTS at
terminals, and have delayed the initiation time to around 21Z at all
sites, although in reality KSUN has the best potential to see
activity around this time, with impacts from TS not realized at PIH
and IDA until the 00-03Z timeframe, when the potential exists for
gusty westerly outflow winds of up to 35KT -- as hinted at in hi-res
model depictions. W-SW gradient flow of 10-20KT should develop by
around 21Z at BYI, IDA and PIH and gradually diminish after 03Z.
Next wave will bring showers into the region Monday morning. Model
guidance is well-clustered in its depiction of keeping heaviest
showers south of the terminals until the tail-end of the forecast
period, so have brought MVFR CIGS and a hint of BR into all
terminals by mid-late morning Monday. Exception is at BYI where
precip and resultant reduced CIGs should occur closer to 12Z.




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