Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 222000

Area Forecast Discussion
National Weather Service Pocatello ID
200 PM MDT Tue Oct 22 2019

.SHORT TERM...Tonight through Wednesday. Vigorous shortwave
dropping through East Idaho today, dragging surface cold front
southeast across the region. Winds are beginning to pick up close
to advisory criteria across portions of the Snake Plain but
remaining below. Cloud cover and light shower activity likely
planning a role in keeping wind speeds below criteria for now.
Area of showers continues to sag south through the forecast area,
with satellite imagery showing clearing behind the shortwave axis,
which could induce a brief period of mixing later this afternoon
across southern portions of the Snake Plain. Any potential
increase into low-end advisory criteria will be very brief so will
continue to keep Wind Advisory headline off the table. Snow
levels are still relatively warm for this system, so snow amounts
remain light and confined to higher elevations with little impact
to the region. After passage of this shortwave feature, cool
northwest flow remains in place. Weak impulses continue to drive
through the flow helping to maintain weak orographic precipitation
mainly along the Wyoming border and the Divide region tonight
into Wednesday. DMH

.LONG TERM...Wednesday night through Tuesday. Amplified high
pressure builds along the coastal states Wednesday night into
Thursday. Resulting northerly flow across the region maintains
cool temperatures but dry conditions through the early portions of
the extended. Quick moving upper trough pushes into the PacNW by
late Friday, shunting high pressure south and leaning into a more
zonal flow across East Idaho Friday and Friday night. Temperatures
warm slightly but conditions remain dry. Low deepens as stronger
shortwave trough drops through the panhandle into East Idaho
Saturday and Saturday night. Expect frontal passage on Saturday
with another windy day and another drop off in temperatures into
Sunday. Temperature trends look cold enough to drop snow levels to
valley floors Saturday night, so snow forecast will be very
dependent on timing of the precipitation as well as how much
liquid can be realized with the system.

Beyond that, though, all bets are off. GFS and GEFS have moved to
a deep trough over the Rockies/Plains, leaving East Idaho in
northwest flow. The ECMWF and ensembles shift toward pinching the
base of the trough off into a low over the Great Basin, leaving
East Idaho in northerly flow. Both solutions could be
precipitation producers, but likely favoring light amounts over
high elevations. Ensemble temperature spreads are fairly drastic,
but remaining on the cold side following the trough axis Sunday.
Will stick with the blended solutions. DMH


.AVIATION...A band of rain and snow is shifting southeast this
afternoon across central and eastern Idaho. The only sites really
being impacted is DIJ/PIH/BYI where MVFR/IFR conditions are
ongoing. We should a little bit of improvement late this
afternoon, but still likely hitting MVFR conditions. Elsewhere it
has remained VFR with gusty winds impacting BYI, IDA, and PIH.
Speeds in the 25-35kt range for gusts will persist until around
sunset with winds dropping off, especially after midnight. The
question then turns to fog and stratus potential. The high
resolution data indicates definitely stratus (down to IFR/LIFR
ceilings) impacting PIH, IDA and BYI. DIJ is a bit of a question
mark, but enough confidence is there for now to drop them down
that far. Fog is a little dependent on wind overnight. There MAY
be enough to keep fog out of these TAF sites, or at least patchy
enough to not predominantly impact them. However, high resolution
guidance suggests otherwise. Confidence is NOT HIGH ENOUGH here to
include it for now. This is expected to form late evening, but
really ramp up at 9z...with things dissipating by 18z tomorrow.
SUN will not see any of this and will remain VFR for the entire
period. After that, VFR weather with lighter winds are
anticipated. Keyes



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