Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 232029

Area Forecast Discussion
National Weather Service Missoula MT
229 PM MDT Tue Jul 23 2019

.DISCUSSION...Mostly sunny conditions throughout much of the day
have lead to temperatures thus far running about 5 to 20 degrees
above yesterday`s readings. Meanwhile, an abundance of low and mid
level moisture has remained throughout the Northern Rockies as
given by widespread dew point temperatures in the 50s and low
60s. This has resulted in an environment that is ripe for
convective potential once our cap (inversion) is broken. And this
appears to have begun as evident by several cumulus and
cumulonimbus build ups which have developed this past hour.
Meanwhile, yet another slug of monsoonal moisture has been pushing
north through Idaho and has moved into Western Montana this past
hour, adding to the deep moisture and instability profile while
also bringing a little more lifting to our environment.

All these factors will ultimately lead to the development of
widespread showers and thunderstorms this afternoon which are
expected to persist through the evening and quite likely well
into the early AM hours of Wednesday morning. The threat for some
storms with large (quarter sized) hail will be there, albeit the
areal coverage of the stronger cells still appears to be
insufficient to warrant a Severe Thunderstorm Watch box. However,
the abundant atmospheric moisture coupled with only modest forward
storm motion very well may lead to an enhanced threat for very
heavy rain and flash flooding.

Convection will likely begin to wane some after about 10 pm with
only isolated cells persisting until after midnight. But the
latest high resolution guidance appears to be hinging upon the
passage of another upper level disturbance that`s presently
enacting convection along far western Nevada. The conjunction of
this feature, coupled with additional vertical wind shear
courtesy of an approaching west coast trough and cold front
appear to initiate an early morning convective complex over the
panhandle of North Central Idaho. Some guidance would suggest that
this area of storms may possess our best potential for a severe
storms, likely due to the additional shear working in an
environment of untapped convective potential.

A strong cold front will move through the Northern Rockies on
Wednesday, bringing gusty winds to many areas. But especially
across NW Montana, Flathead Lake and Glacier National Park. As
such a Lake Wind Advisory has been issued to highlight sustained
winds of 15 to 25 mph gusting to 40 mph at times resulting in
quite choppy conditions on Flathead. Gusts up to around 50 mph
are possible across the higher terrain and at Logan Pass in
Glacier National Park.

Temperatures will warm back into the upper 80s and approach 90 on
Thursday and Friday under westerly flow. Models are hinting that
Lemhi County and SW Montana may get brushed by another wave of
monsoonal moisture (slight chance of thunderstorms) from the
Desert Southwest. But then a drier, seasonably warm pattern sets
in place for the weekend and is expected to carry into at least
early next week.


.AVIATION...Showers and thunderstorms are expected again today.
The storms are expected to come in two waves, the first will
affect the Bitterroot Valley and Missoula east through Butte and
Ovando this afternoon. This wave is started early this afternoon
and will affect terminals KSMN, KMSO, and KBTM through the early
evening. A second wave will move southwest to northeast later
tonight through central Idaho and northwest Montana. Model
guidance suggests the best chance for severe thunderstorms will be
in NW Montana around 06Z to 09Z tonight, which is just ahead of a
shortwave and cold front moving into the region for Wednesday. The
focus for severe weather will be west of terminal KGPI, though
some strong thunderstorms may affect the terminal too.



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