Freeze Warning 2, NWS Missoula, MT

252 
WWUS75 KMSO 171432
NPWMSO

URGENT - WEATHER MESSAGE
National Weather Service Missoula MT
832 AM MDT Sun Sep 17 2017

MTZ003-171545-
/O.EXP.KMSO.FZ.W.0002.000000T0000Z-170917T1500Z/
Flathead/Mission Valleys-
832 AM MDT Sun Sep 17 2017

...FREEZE WARNING WILL EXPIRE AT 9 AM MDT THIS MORNING...

* Impacts/Timing: Temperatures have warmed to near freezing for
  most locations and will continue to moderate this morning with 
  mild temperatures expected this afternoon.

* Locations impacted include: Flathead Valley, Mission Valley, 
  and Polson

$$

Area Forecast Discussion
National Weather Service Missoula MT
414 AM MDT Sat Sep 16 2017

...Frost/freeze threat this weekend...
...Cold & wet weather to persist into next week...

.DISCUSSION...The low pressure system that brought all the rain
and snow to the Northern Rockies is slowing moving off to the
northeast. However, light snow is still falling across
southwestern Montana, including Butte. Elsewhere across western
Montana and north-central Idaho, the valley rain and mountain snow
has largely ended. Things will finally begin to dry out for
southwestern Montana by late morning.

For areas that have seen clearing skies overnight, like
northwestern Montana and north-central Idaho, temperatures have
dipped to below freezing and in some cases into the mid 20s. This
is the first time many areas across extreme northwestern Montana
have seen a freeze this season, therefore the Freeze Warning
remains in place for Lincoln County. High temperatures today will
be on the order of 10-15 degrees below normal for many locations
across the Northern Rockies, feeling much like fall. More
widespread clearing is expected overnight tonight, so those that
didn't see the frost like temperatures (west-central Montana),
will possibly see them Sunday morning. Sunday will be a very
pleasant day, with highs in the mid to upper 60s for the valleys
of western Montana, and the low 70s for the lower elevations of
north-central Idaho.

However the warmer "normal" conditions of Sunday will be brief as
yet another cold, upper level low pressure system is expected to
dig into the Pacific Northwest and swing through the Northern
Rockies early next week. Colder temperatures, gusty winds and
precipitation will accompany a strong cold frontal passage Monday
afternoon. While not overly likely, a few rumbles of thunder
could even be heard given the sharp dynamics along the cold front.
Of greater concern, though, will be the chance for rapidly
lowering snow levels creating brief bursts of snow at area passes.
Monday night snow levels will fall even farther, conservatively
residing between 4500 and 5000 feet by daybreak Tuesday. While mid
level winds are expected to remain too weak to support organized
shower activity, numerous disorganized rain/snow/graupel showers
are likely throughout much of Tuesday across parts of Central
Idaho and West Central Montana with the snow level hovering around
5500 feet much of the day. All this being said, there are a few
outlier solutions which present stronger mountain top winds which
could be sufficient to promote organized shower activity and
perhaps a period of banded showers. If bands do develop, snow
and/or graupel could be possible to much lower elevations,
including valley locations (Missoula, Bitteroot, Mission). But
it's far too early to pin down the timing and location of such a
micro scale meteorological phenomena.

There really won't be much of a break between this area of low
pressure and the next, seemingly stronger weather system that's
forecast to move into the Northern Rockies late Tuesday night.
Minimal warm air advection seems likely with this second storm
being so close to the exiting first storm and thus snow could
present an even greater concern across North Central Idaho and
West Central Montana on Wednesday into Thursday. Thereafter the
models do diverge some, although the commonalities point towards
various degrees of continued troughing into the weekend. Thus
below normal temperatures with better than normal changes for
precipitation seem likely at this point with a better than average
degree of forecast confidence.

&&

.AVIATION...Light snow continues to fall in southwestern Montana,
including KBTM. Visibility reductions and low ceilings will
gradually improve by late morning as the low pressure center moves
off to the northeast. However, mountain obstructions due to
lingering mid-level moisture will remain into the afternoon hours.
All other terminals across western Montana and north-central Idaho
will see minimal to no impacts in visibility and low ceilings.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Warning until 6 AM MDT early this morning ABOVE
     6000 FEET for the Bitterroot/Sapphire Mountains...
     Butte/Blackfoot Region...Potomac/Seeley Lake Region.

     Freeze Warning until 10 AM MDT this morning Kootenai/Cabinet
     Region.

ID...Winter Storm Warning until 6 AM MDT early this morning ABOVE
     6000 FEET for the Eastern Lemhi County.

&&