639
FXUS65 KGGW 220623
AFDGGW

Area Forecast Discussion
National Weather Service Glasgow MT
1223 AM MDT Mon Jun 22 2026

.KEY MESSAGES...

- Expect showers and thunderstorms starting early this morning in
  the west and spreading east through the day.

- A marginal risk exists for today and some storms could become
  severe with large hail in the afternoon over the Yellowstone
  Valley.

- A slow warm up is expected Tuesday through Friday. Another
  system will arrive around Friday with ample rain possible
  through the weekend.





&&

.DISCUSSION...

WEATHER PATTERN OVERVIEW:
A weak low level jet is expected to kick in this morning, and with
only a small amount of elevated capping overnight in the southern
part of the area, a strong thunderstorm or two is possible across
the Yellowstone Valley. Gusts up to 50 mph and hail are the main
hazards. The cooler surface temperatures will allow the hail to
stay together instead of melting right away on its way down to the
ground. Strongest cell look to occur between Noon and 6PM.

The upper trough will slowly break down and move east through
Wednesday. So, a weak ridge will be able to build in by Friday.
The northeast part of the area will be in the periphery of the
trough, so there are still chances for showers and storms through
Wednesday afternoon. A weak round of showers and storms is
expected to make its way in for Thursday & Friday as the trough
starts to rebuild.

By Friday night the ridge exits and a new PCNW trough arrives.
With this arrival will be ample precipiation through the weekend
and possibly into early next week. THere is also a chance for the
start of this passage to contain severe weather as it first moves
in and breaks down the ridge.


FORECAST CONFIDENCE & DEVIATIONS:
Only deviations from NBM were to remove 6-hour jagged edges from
hourly PoPs in the NBM PPI01 and creat a more seamless transition
from hour to hour.

There is MODERATE to LOW confidence in low clouds in fog this
coming morning.

There is HIGH confidence is regional storms today and MODERATE
confidence of strong storms occurring in the southeast this
afternoon.

There is MODERATE confidence in showers and storms over the
weekend.

/GAH

&&

.AVIATION...
LAST UPDATE: 0620Z

FLIGHT CAT RANGE: VFR - MVFR

DISCUSSION: A stalled boundary oriented N/S over KGGW has allowed
for low clouds to form east of it. At higher elevations these
clouds may sneak in as fog and briefly drop of to IFR Between
09Z-15Z Monday morning.

Another round of showers and thunderstorms are expected across
the region moving west to east and will begin impacting KGGW at
09Z and gradually spread east to all terminals by 18Z. MVFR
Visibility may be possible in heavy downpours. Showers and
thunderstorms should exit around 04 to 05Z this evening. There is
a chance (5-20%) for an isolated Severe cell with large hail at
KGDV from 18 to 00Z this afternoon. But, this is not high enough
to include in the TAFs directly yet.

WIND: Light and variable through this morning. Becoming N ands
then NW at 10 kts or less through the afternoon. Gusty erratic
winds are possible near any thunderstorms. Backing NW to W at less
than 10 kts Monday night.

GAH


&&

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

$$

weather.gov/glasgow