Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 042109

Area Forecast Discussion
National Weather Service Pocatello ID
209 PM MST Sun Dec 4 2016

.SHORT TERM...Tonight through Wednesday. Vigorous shortwave axis
and associated surface cold front slowly shifting through Idaho
panhandle this afternoon per water vapor satellite imagery.
Consolidated moisture stream ahead of feature producing moderate
snows across portions of East Idaho this afternoon. Snow totals
slowly building up in central mountains with precip shield now
pushing east across the remainder of the region. Strong south
winds along south edge of Snake Plain along interstates continuing
to keep areas dry. HRRR paints winds shifting more southwest
around 02Z, give or take an hour, which should be passage of the
front. Precip enhances along that line during this time frame.
Surface wet bulbs likely cold enough to support snow down the
surface by this point though stronger temperature gradient lags
the wind shift by 4-6 hours, coincident with shortwave axis.
Expect snow to continue shifting focus southeast toward the Bear
Lake area after 06z, but concern shifts to blowing snow in
strengthened gradient behind the front. Have highlighted areas
with gusts > 20kts for areas of blowing snow, which matches well
with current headlines and includes some areas of the Snake Plain.
Limited accumulations in the Snake Plain ahead of the front will
likely limit impact, especially with overnight event. Therefore
will hold off on any headline at this time. Model consensus is to
shift feature out of East Idaho early Monday, with most areas
seeing snow end before or around sunrise. Have kept decreasing
orographic snows along Wyoming border through the day tomorrow but
decreasing trend is clear. Have shifted end of eastern zone
headline to end earlier at 18z, but believe an even earlier
cancellation is likely, perhaps even with next forecast package as
conditions decrease overnight.

Northwest flow stays in place but flow generally dry and anti-
cyclonic through Monday night. Very cold temps begin to shift into
the region behind current system and will likely see several below
zero readings. Next system drives through PacNW and arrives in
central mtns by Tuesday morning. Quite a bit of difference between
GFS/NAM in depth of next shortwave and placement of associated
precipitation. Highest precip chances between 06Z Tue-00Z Wed,
then decreasing afterward. QPF amounts not impressive but
increasingly cold temperatures and higher snow ratios could still
lead to a few inches mainly higher elevations. Remnants of system
could linger into Wednesday but have kept precip chances low. DMH

.LONG TERM...Wednesday night through next Sunday. The GFS and ECMWF
are still several hours apart with the onset of precipitation for
the storm coming in for Thursday and Friday. The GFS still pushes
moisture into the eastern highlands with the EC only into the
western mountains, although the latter has sped up just a bit.
Despite that, it looks like Thursday night and Friday will be WET
AND WINDY across all of eastern Idaho. While we are still a ways
out, the central and eastern mountains will see quite a bit of snow
again along with blowing snow. This storm will eventually turn warm
at lower elevations for at least a mix for a bit, but we might be
looking for some decent snowfall at those locations as well. The
weekend will be drier at lower elevations but showers will be
possible especially in the mountains. Keyes


.AVIATION...We are finally seeing rain and snow affecting valley TAF
sites as of 2pm. Meanwhile, KSUN has been socked in all day with
snow and KDIJ is FINALLY seeing snow and lower ceilings/visibility
developing as downslope effects weaken. Through at least this
evening, we should continue to see conditions worsen at all sites
(except for KSUN which will stay IFR). That means look for IFR
(potentially LIFR) as ceilings and visibility lower. At sites seeing
rain now, that will quickly change to snow as the cold front
arrives, which also may spell blowing snow at KBYI, KPIH, KIDA and
KDIJ.  Strong wind shear should also continue until frontal passage
as well with ~50kt winds within 1000ft of the ground. There will be
an abrupt end to the snow within a couple hours of the front
passing. Timing would be as follows: KSUN (4-6Z), KBYI (4-6z), KPIH
(5-7z) and KIDA (6-8z). KDIJ will likely remain at IFR until around
10-13z) due to snow lingering in northwest flow into the Teton
Valley. Conditions will improve, including diminishing winds through
the day tomorrow. Keyes


Winter Storm Warning until 6 AM MST Monday for IDZ032.

Winter Storm Warning until 5 PM MST Monday for IDZ019-023.

Winter Storm Warning until midnight MST tonight for IDZ018-031.

Winter Storm Warning until 5 PM MST Monday for IDZ025.


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