256
FXUS65 KGGW 171954
AFDGGW

Area Forecast Discussion
National Weather Service Glasgow MT
154 PM MDT Tue Sep 17 2024

.DISCUSSION...

KEY MESSAGES:

1) Scattered severe thunderstorms can be expected mainly this
evening in a south to north corrider mainly east of a Glasgow-
Jordan line. Damaging wind and large hail will be major threats,
but heavy rain cannot be ruled out.

3) Western zones could see a significant rain event tonight
through Thursday morning. Lower amounts for eastern zones. A
Hydrologic Outlook was issued today for this plus the threat for
higher stream runoff from central Montana (i.e. Flatwillow Creek).


WEATHER PATTERN OVERVIEW:
An upper low near the Wasatch of northern Utah will lift into
eastern Montana later tonight and become vertically stacked. This
structure will only allow it to drift slowly northeastward, not
exiting Montana until Wednesday Night. The unusaully high humidity
for this time of year (current dewpoints have reached the upper
50s to lower 60s!) to materilize into heavy rain for much of
central Montana through Wednesday Night.

SPC continues to have most of the CWA in a Slight Risk, but the
corridor east of Glasgow to Jordan line looks to have the highest
chance at this point for hail. Wind looks to be scattered across
the CWA. Timing looks to be best in the evening as the storms move
north.

The DESI Grand Ensemble showed a 40 to 60 percent chance of 2
inches of total rainfall for SW Phillips and Petroleum counties.
This promped the issuance of a Hydrologic Outlook. Another concern
are the streams that feed from central Montana, particularly the
Flatwillow Creek.
The SW zones could see strong winds from about 6 pm Wednesday
till about 6 pm Thursday with a tight surface gradient on the SW
side of the surface low. At this point, winds speeds will likely
stay below High Wind Warning criteria but a Lake Wind Advisory is
likely for Fort Peck Lake.

Temperatures closer to seasonal average will settle across the
region behind the front starting on Wednesday. The upper level low
will depart to the northeast on Thursday taking the rain with it.
Temperatures will remain close to average through the end of the
weekend.

FORECAST CONFIDENCE & DEVIATIONS:

There is moderate confidence of strong to severe storms occurring
late this afternoon through early Wednesday morning.

High confidence of rainfall greater than 1" occurring in
Phillips and Petroleum counties, with low to medium confidence of
1" of rain further east. TFJ

&&

.AVIATION...
Last Updated: 2000Z

CATEGORY: VFR then MVFR late tonight.

DISCUSSION: Scattered showers and thunderstorms, some of which
could be strong to severe with large hail and damaging wind will
move north this evening. Ceilings then will lower to MVFR levels
later tonight and remain there except for KSDY Wednesday. Lower
ceilings (IFR) can be expected over central and southeast
Montana.

WINDS: E or SE at generally 10 kts or less, but higher at KSDY
with speeds at 20-25kts. TFJ

&&

.GGW WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

weather.gov/glasgow