Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 300141 AAA

Area Forecast Discussion...UPDATED
National Weather Service Glasgow MT
741 PM MDT Sat Apr 29 2017

.SHORT TERM...for northeast Montana...tonight through Mon...

The forecast remains on track.  The upper short-wave trough
kicking through the lee-side surface trough has produced
scattered rain showers and isolated general thunderstorms this
evening. The grids covered this well enough for only a minimal
update. Adjusted overnight temperatures a bit based on 18Z CON
guidance. Winds were also tweaked using near term guidance.


Previous Discussion -
Synoptic Setup: Short term begins with a large scale trough over
the western half of the CONUS with its axis running up the
front range from New Mexico to Montana. To the west a ridge has
set up over thew California coast running north into Oregon and
then curving back east into southern Idaho. Zonal flow runs from
Washington to western Montana.

This afternoon into tonight: A lee side mountain trough has laid
down across far western zones and this is becoming the focal point
for afternoon showers and isolated thunderstorms. The big sheep
hills are also acting as a focal point for light shower activity
near the Yellowstone Valley and southern Garfield county that is
showing up on radar as of 130PM. A shortwave in the zonal flow to
the west will move across the lee surface trough and latch on
moving it eastward late this afternoon into the evening hours.
Most of the activity should die off as sunlight wanes this evening
but a shift towards more northern zones is very likely with the
overall diminishing.

Western river valleys that experience any rainshowers in the
evening including the Milk and Missouri River will be focal points
for potential fog development overnight and during the morning
hours due to excess moisture.

Sunday: Conditions should be clear by the morning hours Sunday as
a meso ridge one the backside of the exiting shortwave grows and
pulls in and amplifies the ridge over southern Idaho. However, as
the axis of this ridge pass through eastern Montana this
afternoon chances for rain showers with isolated thunderstorms
will again increase. GAH

Sunday Night to Monday: An unsettled northwest flow aloft will
continue unsettled weather, and cool temperatures. Monday breezy
northwest winds may necessitate the issuance of a Lake Wind
Advisory for Fort Peck Lake. Gilchrist

.LONG TERM...Mon night through Sat...
Afternoon update: The discussion below stands. Looks like a nice
warmup is in store for Wednesday through Friday. Only tweaks made
were to trend toward the latest model consensus. Gilchrist

Previous discussion: Upper trof over the central state will
continue to shift east with the strengthening of the Hudson Bay
low. East Pacific ridge will gradually drift onshore and across
the Rockies through next week.

One last shortwave slides into the trof bringing showers to
eastern Montana on Tuesday. Midweek will feature warmer and drier
conditions with the ridge building into the state. Showers are
possible again across central Montana by Friday afternoon with
next trof pushing into the Pacific NW. Ebert




SYNOPSIS: Showers will gradually dissipate after sunset this
evening. Otherwise sct-bkn mid level clouds are all that is
anticipated in the next 24 hours.

FOG: Any showers that pass over the river valleys this evening
after the sun sets and before diminishing will provide enough
extra moisture to generate a threat for FOG. Currently KGGW looks
to be the most likely to be impacted, but chances are still below
50/50. So Confidence is low and it has not been included in the
TAF yet.

WIND: South to southwest at 5 to 15 kts.





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