Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 200249

Area Forecast Discussion
National Weather Service Glasgow MT
849 PM MDT Thu Sep 19 2019


Evening update...
Going forecast was mostly in good shape. Main POP changes were to
make things a little drier for roughly the western 2/3rds of the
CWA. Also had to account for the storms that formed over Garfield
County that are moving through McCone County now (830 pm MDT):
these are in place about 3-4 hours early vs. hi res models.

MUCAPE values still forecast to surge overnight, with the RAP13
forecast sounding at KSDY peaking out at 2998 J/kg at 6z; others
in our east generally peaking out in the neighborhood of 2000
J/kg, so still some concern for severe hail potential tonight.


Previous Discussion...
A surface low will move slowly north and northeast through
Eastern Montana this evening through much of tonight, entering
western North Dakota early Friday morning. This will trigger
showers and storms late tonight (chances start to increase after
midnight) across far eastern Montana. A large inversion will be in
place, but there will still be ample MUCAPE available on the
order of 1500 to 2000 J/Kg. If storms are able to stay isolated,
there will be a threat for large hail. Otherwise, the main threat
will be heavy rain, which could lead to some localized flooding.
The best timeframe for these storms will be from 2 AM through 8
AM. The storms will eventually move east into North Dakota Friday

Additional storms will develop Friday afternoon and increase in
coverage Friday night as a large upper-level trough moves through
the area. With the front already being east of the area by peak
heating, the threat for additional severe storms Friday afternoon
and evening is small, but cannot be ruled out as there will still
be some lingering moisture across far eastern areas.

Rain will begin to diminish from west to east on Saturday as a
ridge of high pressure begins to build into western Montana. Total
rainfall amounts through Saturday will range from around 0.10 inch
in northern Phillips County to upwards of an inch towards Sidney
and Glendive.

The ridge will keep us dry Sunday, but another trough will be
moving into the area for the first part of next week. Limited
moisture should help to keep things fairly dry through Tuesday,
but a round of Pacific moisture will increase precipitation
chances towards mid-week.

High temperatures will be in the 60s and 70s through the forecast
period with lows generally in the 40s.




WINDS: northwest at all TAF locations except KSDY 5 to 10 kts
overnight. Winds shift to the west at KSDY after 9z and become
more northwest by 12z. Winds tomorrow will be northwest to north 5
to 15 kts at all TAF sites.

SYNOPSIS: Low pressure at the surface will move through the
region through tonight. This will trigger showers and
thunderstorms late tonight with the best chances near the North
Dakota border. Stronger storms are possible near KGDV & KSDY
through Friday morning with primarily a hail threat. Additional
isolated severe storms are possible Friday afternoon in similar
areas. Potential for some wind shear through the overnight hours
as the front passes through the area.





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