Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 210302

Area Forecast Discussion
National Weather Service Pocatello ID
902 PM MDT Sat May 20 2017

.UPDATE...Brief update to going forecast for tonight. Generally
weak convection continues across the region this evening, with
focus shifting to the Eastern Magic/Lower Snake Plain region and
south toward the UT/NV borders. Expect storms to remain weak
overnight. Grid forecast adjustments were to tweak precip
potential toward southwest portions of the region overnight. DMH


.PREV DISCUSSION... /issued 159 PM MDT Sat May 20 2017/

SHORT TERM...A low pressure disturbance over northern Idaho will
slide southeastward over this area this afternoon and evening.
Expect some scattered light showers with isolated thunderstorms
possible. Lightning has been detected around Lewiston. By sunday
morning, there will be a chance of rain showers over the Caribou
and Southern Highlands with the disturbance slowly move south of
the state by sunset. Monday and Tuesday, northerly winds aloft
will prevail with a ridge of high pressure moving inland. Both
days are expected to be dry with temperatures warming into the 60s
in the mountains and lower to middle 70s in the lower valleys by
Tuesday. RS

LONG TERM...Tuesday night through Saturday. Good deal of
uncertainty as we head into the long-term periods. GFS ensembles
having problems resolving upper trough digging in from British
Columbia Wednesday morning. The deterministic 12Z ECMWF/GFS guidance
seems to have a fair amount of agreement with respect to the
evolution of the upper pattern, though GFS is slightly deeper with
the trough over the Pac NW. Still, enough confidence to go with
cooler and wetter conditions Thursday and Friday. Models seem to be
settling in on this pattern over the last couple of runs. Afternoon
thunder is possible as base of upper trough lowers into the region
with the focus being over the mountains. Hinsberger

AVIATION...Energy from a shortwave will drop into southeast Idaho
through the next 24 hours, keeping thunder chances alive, mainly
over the mountains. Showers are possible over the terminals today,
but keeping vcsh mention at KPIH and KBYI. Terminals should remain
VFR, though a brief period of MVFR is indicated in some NAM
statistical guidance tomorrow morning. Hinsberger

HYDROLOGY...A transitory high pressure ridge expected Monday
through Tuesday night will help warm temperatures into the 65-75F
range in the mountains and 70 to 80F range in the lower valleys
by Wednesday. By Wednesday afternoon through Friday there will be
a chance of afternoon showers and possible thunderstorms. Snow
melt in the mountains is expected to increase pace again the later
part of the week. RS



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