320
FXUS65 KGGW 142109
AFDGGW

Area Forecast Discussion
National Weather Service Glasgow MT
309 PM MDT Wed May 14 2025

.DISCUSSION...

KEY MESSAGES:

- Storm system now tracking through southern Montana today will
  eventually move into the Dakotas tonight and become stacked with
  a surface low pressure center on Thursday.

- With models finally honing in on the track of this storm,
  expected rainfall amounts have been adjusted to reflect more
  rain east of MT-Highway 13 and less rain west of MT-Highway 13.

WEATHER PATTERN OVERVIEW:

Current large-scale storm circulation seems to now be centered
over southern Montana. In a general sense, this kind of storm
track usually favors NE MT with precipitation; and indeed
rainfall has begun to accumulate for most NE MT locations, albeit
with lesser than expected amounts, due to some dry air being
pulled into the storm system. NBM and other majority blended
consensus models had not cued into this dry slot; but today, the
dry slot has shown up in most model depictions, allowing us to
fine tune the precipitation forecast with (hopefully) more
accuracy moving forward.

As the entire storm system matures and stalls over the Dakotas
tonight through Thursday night, quite gusty wrap-around surface
winds from the NW will stream through NE MT. This will be enough
to warrant us issuing a Lake Wind Advisory. Expect NW winds of 25
to 35 mph and stronger gusts from Thursday morning through late
Thursday night.

Another matter of concern especially for tomorrow is how the
backside wrap-around precipitation will behave. With the dry slot
expected through our central and western CWA, most of this
encroaching rain from North Dakota will reach as far as MT-Highway
13. West of this line though, any additional rainfall with this
storm system will be very light. This drastic gradient of expected
rainfall ranges from near nothing for Malta up to 1.50 inches for
Sidney.

Finally on Friday, the effects of this storm system move far
enough eastward to allow short-wave ridging to take over and
provide a drier period.

Saturday and beyond, another Pacific trough moves inland and
increases rainfall chances for us, although, it should be noted
that the NBM forecast for chance of precipitation is probably erroneously
high.

FORECAST CONFIDENCE & DEVIATIONS:

Low confidence in timing specific rain showers today. High
confidence in the more rainfall in the east late tonight and
Thursday, and low confidence in any showers to the west of the
main rain band.

Strong deviation from NBM today through Day 3 of the forecast to
more accurately reflect the dry slot and the resultant reduced
rainfall amounts, blending the best model consensus of short-term,
high resolution models. Kept NBM for the remainder of the
forecast.



&&

.AVIATION...

LAST UPDATE: 2107Z, Wednesday afternoon, May 14th

FLIGHT CAT RANGE: Mainly VFR, becoming mainly MVFR later today
and mainly IFR tonight only for KSDY.

DISCUSSION: Most areas are expected to have MVFR ceilings later
this afternoon, with some areas of low VFR mixed in. Ceilings
will lower further to IFR in most areas this evening and continue
into Thursday with frequent rain showers, which may only be
realized in KSDY

WIND: This afternoon and evening from the NE and N around 10 kts
with a few stronger gusts. Thursday morning from the NW around 10
to 15 kts. Thursday late morning through Thursday late night, from
the NW at 25 kts gusting up to 40 kts.


&&

.GGW WATCHES/WARNINGS/ADVISORIES...
Lake Wind Advisory from 9 AM Thursday to 4 AM MDT Friday for
Central and Southeast Phillips-Central and Southern Valley-
Garfield-McCone-Petroleum.

&&

$$

weather.gov/glasgow