Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 270754
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
154 AM MDT Tue Jul 27 2021

.SHORT TERM...Today through Thursday night. A sub-tropical
disturbance was noted rotating around the periphery of the high
through the SRN Sierra early this morning. Associated cloud cover
was already pushing north through the SRN Idaho border and spotty
showers were noted on regional radar across NRN Utah and Nevada.
Numerical models drive the monsoon moisture north into SRN Idaho
through the day with deepening moisture across the Snake River Plain
and SRN mountains...enough to support decent rainfall amounts with
any showers and thunderstorms that develop. At this point, the main
dynamical circulation appears to rotate up into SW Idaho very late
this afternoon which may help to initiate convective development
over the SRN mountains and ERN Magic Valley which will continue and
spread into the Snake River Plain through the evening with scattered
wetting rains likely. The disturbance shifts NE of the region by
Wednesday morning with diminishing shower activity overnight. A deep
layer of moisture will be in place Wednesday and beyond as the
southerly monsoon flow brings embedded disturbances through the
region which, coupled with afternoon heating should be enough to
generate scattered diurnal showers and thunderstorms with wetting
rainfall. Daytime highs should moderate some under the added cloud
cover but remain above normal. Muggy might be a more apt
phraseology! Huston

.LONG TERM...Friday through next Tuesday. Overall pattern will
continue to favor monsoonal shower and thunderstorm activity through
much of the extended with deeper moisture taking up residence
throughout the Great Basin. This means a trend towards cooler and
wetter than average conditions even into the period beyond early
next week. Daily details of convection coverage and placement in
this regime may be difficult to pin down, but models are generally
favoring shower and thunderstorm chances peaking over the weekend as
the broad upper-level ridge degrades and weak waves skirt into the
Pac NW.

Some differences showing up in the guidance as to where high
temperatures trend through the weekend. NBM guidance favoring cooler
temperatures by early next week siding closer to the deterministic
and ensemble EC. Ultimately there is very little variance evident in
the clusters through day 7, so will stick closely with the NBM. This
could mean high temperatures some 7-10 degrees below average,
something not seen in quite a while.
TAX

&&

.AVIATION...Early morning satellite showing the last of the clear
skies as we begin our transition to an overall wetter pattern.
Leftover clouds from convection in UT Monday are moving into
southern Idaho and moisture is beginning to increase throughout the
forecast area. We`re expecting showers and isolated thunderstorms to
develop this afternoon, which could impact any or all terminals.
Exact timing and placement of individual cells will be difficult to
determine with great accuracy, so Amendments and TEMPOs may be
necessary. Any stronger showers or thunderstorms could produce gusty
and erratic winds. Beyond today, expect daily showers and
thunderstorm chances to increase through the week, but cigs should
remain primarily VFR.
TAX

&&

.FIRE WEATHER...A sub-tropical disturbance will lift north out of
the SRN Sierra into SW Idaho today producing scattered showers and
thunderstorms across the south-cntrl mountains and Twin Falls
District late this afternoon. This activity will likely produce
wetting rains along with elevated afternoon humidity levels. Further
north, along the NRN periphery of the cloud cover across the Salmon
NF, we will likely see scattered dry-ish thunderstorm development at
least initially this afternoon but moistening up quickly this
evening. Here we have issued a Red Flag Warning for scattered
thunderstorms where afternoon humidity levels are still expected to
remain in the teens to lower 20s today. All that changes by tomorrow
as the region should be solidly under a deep layer, moist southerly
monsoon flow which should persist through the weekend and into
Monday of next week resulting in periods of vigorous diurnal
(afternoon) thunderstorm activity with wetting rains. Southwesterly
flow increases across the region with drier conditions eventually
filtering into the area about mid-week next week. Huston


&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 2 PM MDT to 10 PM MDT this evening for
IDZ475.

$$


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