Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 211555 AAA
AFDPIH

Area Forecast Discussion...UPDATED
National Weather Service Pocatello ID
955 AM MDT SAT MAY 21 2016

.UPDATE...
Adjusted precip chances for the rest of today based on latest
trends, with the main adjustment being to increase chances across
the Upper Snake Highlands and Eastern Highlands. Remainder of the
forecast looks on track. Divergence associated with the left exit
region of the upper jet wrapping around a closed low centered over
Oregon, along with another mid/upper-level shortwave rounding the
upper low, will continue to force a roughly north/south oriented
precip band across these areas late this morning into early this
afternoon. This more organized band of precip is expected to
eventually slide east/northeast into WY and MT later this
afternoon, however additional scattered to numerous showers and
embedded thunderstorms will continue across southeast Idaho this
afternoon as the closed upper low trudges very slowly
east/northeast. If we see some pockets of clearing this afternoon,
sufficient localized instability may again develop to support a
few strong storms given the strong winds aloft and resultant
enhanced deep layer shear.

KB

&&

.PREV DISCUSSION... /issued 301 AM MDT SAT MAY 21 2016/

SHORT TERM...Today through Monday night. The upper level low
responsible for our recent stretch cool and unsettled weather
remains centered over southeast Oregon at this time, and will
remain there much of today. Thus, SE Idaho will be within moist
southwest flow today. Embedded in this flow will be weak
disturbances that will aid in lift. Just enough instability
combined with favorable environmental conditions may result in the
development of an isolated strong thunderstorm this afternoon
across the Eastern Snake Plain eastward to the Wyoming border,
with small hail and gusty winds possible. Otherwise, a band of
showers will be ongoing early this morning across the Snake Plain.
Periods of showers will continue across the Central Mountains
today with snow showers above roughly 7,000 feet. The Upper Low
swings northeastward through Idaho tonight and skips into
Montana/Southern Alberta Sunday, placing SE Idaho in a somewhat
drier SW flow. Nonetheless, showers and isolated thunderstorms
will develop once again, best chances across highland areas. A few
inches of snow are still expected at mid and upper slopes across
the Central Mountains. Breezy SW winds across the Snake Plain
Sunday may be strong enough to warrant a Lake Wind Advisory for
the American Falls Reservoir. More showers and isolated
thunderstorms are expected Monday, particularly in the afternoon
and early evening hours. Temperatures will remain well below
average through the period...with near record low daytime highs
across the Central Mountains this weekend. There is a chance for
pockets of frost or freezing nighttime temperatures across the
Snake Plain, particularly Sunday morning and perhaps Monday
morning. This will be dependent upon the amount of clearing and
strength of the winds, but at this time think widespread
frost/freeze conditions will be avoidable. AD/Hedges

LONG TERM...Tuesday through Saturday night. The story does not
change much thru the extended period with both GFS and ECMWF showing
the Pac NW dominated by upper closed lows thru Saturday. This
results in scattered aftn/early eve showers and tstms and isolated
activity overnight thru morning. The highest probabilities will be
over the mtns. Cool temps continue. Hedges

AVIATION...A persistent upper low continues to dominate the region
with sct showers and isold aftn/eve tstms. Breezy sw winds also
expected this aftn. Precip should quiet down tonight. Hedges

&&

.PIH Watches/Warnings/Advisories...
None.
&&

$$



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