Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 191044

Area Forecast Discussion
National Weather Service Pocatello ID
344 AM MST Sun Nov 19 2017

.SHORT TERM...Tonight through Tuesday night.

Considerable amount of high cloud is drifting through the region
this morning and low stratus continues to hang on to the upper Snake
Highlands north of Ashton. Think we`ll see a break in the cloud
cover everywhere this afternoon before the next storm system
arrives. We expect this system to arrive in the central Idaho
mountains late tonight, then overspread the region during the day on
Monday. Models continue to act as a pendulum in terms of coverage
and amounts. Latest models have trended somewhat wetter and have
adjusted precipitation chances and amounts consequently. Snow levels
begin at the valley floors Monday morning. By afternoon we will see
warmer air begin to work into central Idaho but may not see those
snow levels get off the valley floors across much of eastern Idaho
Monday afternoon. The strongest push of moisture will arrive Monday
afternoon and exit the region Monday evening. Potentially could see
an inch, maybe two in the valley floors on Monday. Areas above 6000
feet above Ketchum to Stanley and areas around Island Park and
Driggs could see 2 to 5 inches. Will not issue any headlines at this
time for a couple reasons. First, amounts are highly uncertain
because of model run to run inconsistency. This leads into the second
problem involving questionable impacts across the region which at
this point look minor.

Snow levels will continue to rise Monday night, possibly getting
above 7 or 8 thousand feet by Tuesday. Looks like moisture will
continue to move through the region Monday night through Tuesday,
although precipitation will be mainly confined to the Highway 75
corridor from Ketchum to Stanley and along the Tetons. Additional
amounts Tuesday through Tuesday night look light, 1 to 3 inches and
generally above 7000 feet.


.LONG TERM...Wednesday Through Sunday.
The long-term forecast continues to feature a large-scale pattern of
eastern US troughing/western US upper-level ridging, with several
weak systems progged for ID. We also continue to grapple with above
normal uncertainty, but still see no strong indications of
significant/high-impact wx for this busy holiday travel week. The
entire period looks mild, with highs above freezing each day almost
everywhere and upper 40s/low 50s across the Snake Plain.

Stepping through the period, models continue to slowly trend toward
a drier forecast under dirty ridging Wed/Thurs. For Wed, have
reduced PoPs leaving the eastern Magic Valley and Snake Plain dry
and confining low chances of showers to the Sawtooth and Pahsimeroi
region, Upper Snake Highlands, and WY border zone. For Thanksgiving,
we now feel comfortable cautiously pulling the trigger on a dry
forecast everywhere except the Central Mtn region. Snow levels by
this time are projected to be 8,000-9,000 feet, suggesting all
rain with perhaps a few flakes at the highest passes. Any showers
should also be light. Bottom line, no travel impacts foreseen at
this time. With drier weather, high temps have been nudged up a
few degrees. In fact, Thurs could end up being the warmest day
next week with upper 50s possible near Pocatello west into the
Magic Valley. Stay tuned for updates as we continue to monitor
model trends!

Fri features differences between the EC/GFS on placement of shower
activity, but the day looks wetter than Thurs. Guidance consensus
also continues to suggest gusty winds, especially afternoon/eve. We
continue to undercut wind guidance in the official forecast due to
this being 5 days out and below average confidence in the models.
Right now winds do look below wind advisory criteria.

A chance of showers continues next weekend ahead of a pronounced
trough/low pressure system approaching the west coast. Have kept
PoPs high enough to trigger a mention of showers everywhere.
Forecast confidence remains low. - KSmith/Valle


.AVIATION...High pressure remains in control across SE Idaho
today, resulting in solid VFR conditions with dry weather, clear
to partly cloudy skies, light winds, and no anticipated impacts
for aviation. Fog/low stratus potential this AM looks very low
with nothing noted on satellite/sfc obs at this hour. High clouds
will begin to stream into the region tonight ahead of our next
storm system, with a few showers possibly approaching KSUN by Mon
morning. - KSmith/Valle



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