FXUS65 KMSO 052035

Area Forecast Discussion
National Weather Service Missoula MT
235 PM MDT Fri Jun 5 2020

.DISCUSSION...The atmospheric set-up this afternoon going into
this evening is one that will be conducive to producing high-based
thunderstorms across north central Idaho and western Montana.
Thunderstorm initiation will occur in eastern Oregon and eastern
Washington later in the afternoon, with storms then expected to
track eastward into our region through the evening and overnight
hours. Short term high resolution models continue to depict a
period of time where a few stronger, potentially severe
thunderstorms could occur later this evening. Several models
show strong storms tracking along a line from the Camas Prairie
in Idaho, moving northeastward across the Clearwater Mountains,
and then into west central and northwest Montana. Should storms
remain strong enough, they could track across the Mission and
Flathead valleys thereafter.

No matter where storms end up developing, impacts such as hail,
strong winds, lightning, and brief heavy rainfall should be
anticipated. Stronger storms could produce larger hail (up to ping
pong in size) and potentially damaging wind speeds greater than
60 mph. Our confidence is low in the chance for these kinds of
impacts occurring, however with the potential very much in the
picture, it cannot be ignored.

Storms will become more widespread and ease in strength and
intensity by Saturday morning as more steady-state rainfall begins
to fill in across the region. Storms on Saturday could occur
anywhere, however the best focus for development appears to be
over southwest Montana and portions of central Idaho (namely Lemhi

With the cold front expected to cross and rainfall to become
commonplace going into Sunday, snow levels will begin to drop
rather dramatically for early June. By Monday, snow levels across
north central Idaho into western Montana will lower to roughly
5000 feet. The chance for snow accumulations down to 4500-5000
feet is a real concern during this time. Those with outdoor
activities planned, especially those involving recreation in
higher terrain, should prepare for raw, cold, and wet conditions.
Given that Glacier National Park opens on the west side on June
8, those who plan to go into the Park should plan ahead for
unseasonably cold temperatures (on the order of 15 to 20 degrees
colder than normal for this time of year), along with brief snow
accumulations in the higher elevations of the Going-to-the-Sun

Again: anyone traveling into the Northern Rockies backcountry
should take measures to protect themselves from snowfall and a
heightened risk of hypothermia Sunday through Monday.

Precipitation will then exit the region with plenty of cold air
left behind. Daytime high temperatures on Monday will struggle to
get out of the 50s, and by Tuesday the highs will only warm
slightly into the mid 60s. As a result of continued below normal
temperatures, the threat for frost will occur both Monday morning
and Tuesday morning. Protect any sensitive vegetation Sunday night
and Monday night to protect from the threat of frost.


.AVIATION...Clouds will increase within the Northern Rockies air
space this evening, ahead of a surface cold front that will move
from west to east from KGIC (near 06/0000Z) to KBTM (near
06/2200Z). There may be brief thunderstorm activity unrelated to
the cold front along Continental Divide near KBTM 05/2100Z -
06/0200Z. Thunderstorms are anticipated to develop along and ahead
of the cold front, with large hail, reduced visibility/ceiling,
and wind gusts exceeding 50 knots possible in the 06/0000Z -
06/1000Z period within a narrow area encompassing KGIC-KP69-KMLP-
KMSO-KGPI. Lightning potential is anticipated to lessen after
06/1000Z. Episodic rain showers and relatively low ceilings will
linger behind the cold front that will temporarily stall across
KMSO from southwest to northeast on Saturday morning. After
06/1800Z, the surface cold front will continue to march eastward,
with a low, yet non-trivial threat of large hail, wind gusts over
40 knots, and brief low visibility/ceilings (06/2000Z - 07/0200Z).
Most terrain obscurations will be related to the pre-frontal
thunderstorm activity, later followed by widespread rain shower
activity post-frontal.



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