Winter Storm in Idaho, November 13 to 14, 2014

Area Forecast Discussion
National Weather Service Missoula MT
402 AM MST THU NOV 13 2014

.DISCUSSION...Confidence has increased a little with the much
advertised winter storm to impact central Idaho, southwest and
west central Montana. The increased confidence is due to model
consistency over the last few runs. The low pressure associated
with this storm is expected to move ever so slightly south but
enough to diminish precipitation/snow potential from about the
Camas Prairie in west central Idaho to Missoula and Ovando
northward.

HOWEVER, This has not changed the snow and snow amount potential
for central and east central Idaho. Confidence is high for snow in
these regions however there is some uncertainty where the
potential for the heaviest snow may occur. Nevertheless
significant accumulating snow is still expected to impact the
following areas:

IN CENTRAL IDAHO, late this afternoon through midday Friday:

VALLEYS are expected anywhere from 2 to 5, locally 6 inches, late
this afternoon and tonight.

MOUNTAIN PASSES, especially Lost Trail and Whitebird grade could
receive anywhere from 4-8 inches, possibly higher depending on the
track of the surface low pressure.

IN WEST CENTRAL MONTANA, tonight and Friday:
Snow is expected to impact the central and southern Bitterroot
Valleys, including STEVENSVILLE AND HAMILTON. Amounts are more
uncertain for these areas again dependent on the track of the
surface low moves even just 50 miles south or north. Right now 2
to 3 inches of snow is expected, but just a 50 mile shift of the
surface low either way may have lesser or greater impacts for
travel along US 93 in the Bitterroot Valley. It is looking more
now that MISSOULA and LOLO may receive only an inch which may be
optimistic. North of Missoula little if any snow is expected.

Another arctic intrusion is forecast to impact western Montana
Saturday morning. More cold air and gusty winds will create
dangerous wind chills once again in the favored east to west
facing canyons and gaps of the Missoula/Flathead valleys and along
the Continental Divide.

After the next arctic passes stable conditions will set up for
this weekend. Cold is expected to continue into next week with
strong radiation cooling to cause high valley locations to have
lows well below zero. A few weak shortwaves under northerly flow
continue to show up in model guidance for the beginning of next
week. Though model guidance agree that moisture will increase
somewhat with these waves they continue to show a dry forecast.
The cold air mass, that will be in place while these waves pass,
will be prone to light snow and cloud cover so chances for
precipitation remain in the extended forecast with a slow
moderation in temperatures through the middle of the week. There
are signs that temperatures will return to near normal for the
second half of the week, but any of the low valleys that develop
strong inversions will have a tough time warming.

&&

.AVIATION...Cold temperatures and breezy winds will continue this
morning in the terrain and in a few valleys. Low pressure
currently showing up on satellite loops is just making landfall
on the Oregon coast. Moisture from this low will spread cloud
cover through Idaho and Monday through today. Snow will begin to
fall this afternoon in north central Idaho and spread into west
central and southwest Montana overnight. Low cloud decks and
limited visibility will be observed under a wide swath of snow
that has best chances to set up from around Grangeville, through
Hamilton, Salmon, and Dillon. There are indications that the north
end of the snow focus will be near Missoula and Butte Friday
morning so lowered ceilings and visibility will be possible in
these locations as well. Snow will decrease and wind will increase
with the next arctic that is forecast to pass on Saturday.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...ID...WINTER STORM WATCH from this afternoon through Friday morning
     Lower Hells Canyon/Salmon River Region...
     Orofino/Grangeville Region...Southern Clearwater Mountains.

     WINTER STORM WATCH from this afternoon through Friday morning
     Eastern Lemhi County...Western Lemhi County.

&&