Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 151941

Area Forecast Discussion
National Weather Service Pocatello ID
141 PM MDT Thu Mar 15 2018

.SHORT TERM...Tonight through Saturday night.

Large low pressure system off the coast of Oregon continues to
spread moisture into central and east Idaho this afternoon.
Residual snow showers will become more isolated as we head into
the overnight hours. Snow amounts tonight look light, generally
less than an inch. On Friday, the low moves onshore. Expect to see
light rain and snow move into the Magic Valley and central Idaho
mountains during the afternoon. Expect to see the coverage and
intensity increase during the evening and through the overnight
hours. Looks like a band of wet heavy snow may develop around
Hailey and extend northeastward through Howe and to near Spencer.
This would include Carey, Bellevue, Ketchum, Arco and Mackay.
Around the Sun Valley area, this band may produce 6 to 12 inches
between Friday night and Saturday with higher amounts along the
ridges. Amounts may be somewhat less around Arco and Mackay,
perhaps closer to 4 to 8 inches. Am issuing a winter storm watch
effectively for the stretch of Highway 75 extending from near the
Picabo area to Stanley. If amounts hold, expect the Mackay/Arco
area and possibly the Spencer area to fall under an advisory. The
models are a strong uptick in snowfall amounts on today`s model
runs, so there`s still some uncertainty in the forecast. Across
the Magic Valley, Snake Plain and the southeast highlands,
probably looking at 1 to 3 inches of snow as the low moves through
the area on Saturday. Higher elevations and bench areas could see
up to 6 inches. There will be some warm air in the system and
expect a rain/snow mix in the lower valleys Saturday afternoon.
However, much of the snow may pass through the Magic Valley and
lower Snake Plain by Saturday morning. Most of the widespread snow
will exit the region Saturday afternoon, leaving isolated to
scattered snow showers for Saturday night.


.LONG TERM...Sunday through Thursday. Broad low centered over Idaho
shifts east into the central Plains Sunday into Sunday night, with
deep low still centered off CA coast. East Idaho stuck under ridge
trying to build ahead of Pacific low, but there are still signs of
shortwave activity trying to drop south into the northern Rockies.
So, as with previous several days, models are still struggling to
find some consensus on the details. Held on to precip chances Sunday
during the day, gradually decreasing Sunday night into Monday. We
kept with the trend toward decreasing showers through Tuesday based
on model blends. However, we did starting increasing the chance of
showers sooner on Wednesday and kept with higher numbers beyond
that. We start out with temperatures 5-10 degrees below average, but
warm up to above average by late next week as flow turns southwest.


.AVIATION...Any confidence in TAFs for the next 24 hours is going to
be...well on the low side. Several "waves" are moving eastern Idaho
during this period, making it much harder to pinpoint when/where
showers will be throughout the period. We did take out VCSH at most
sites overnight, but would be surprised at all if that changes.
There is so much moisture around that any weak "push" could pop off
rain or snow. Also with that, that also means if we do get any
prolonged "dry" periods, stratus and fog could quickly develop.
Ceilings will vary greatly in this pattern, from VFR to IFR.
Visibilities should remain VFR unless an airport sees heavier
showers or fog. The idea is to definitely check these forecasts
often if you are flying. Keyes


Winter Storm Watch from Friday evening through Saturday
afternoon for IDZ018-031.


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