595
FXUS65 KGGW 171543
AFDGGW

Area Forecast Discussion
National Weather Service Glasgow MT
943 AM MDT Mon Jun 17 2024

.DISCUSSION...
Updated the latest forecast with a blend of the latest and
greatest model data available this morning. One thing noticed was
the increase in pops for mainly the eastern zones today.

Rest of the forecast looked to be in good shape. TFJ

Previous Discussion...
KEY MESSAGES:
- Cool temperatures with widespread rain expected today and
  Tuesday.

- Isolated to scattered thunderstorms this afternoon and tonight
  and again Tuesday afternoon and evening. Marginal risk for
  severe thunderstorms this afternoon and evening along the
  Yellowstone River.

- Warm temperatures starting on Wednesday with frequent chances
  for showers and thunderstorm chances between Wednesday and
  Saturday.

WEATHER PATTERN OVERVIEW:

There will be an upper trough/low moving into western Montana
today while a surface low develops over Wyoming. SW flow aloft
ahead of the trough will bring deep moisture into the forecast
area today which will allow widespread rain showers to develop by
sometime this afternoon with embedded thunderstorms. To the
northeast of the surface low today, an inverted surface trough
along the Yellowstone River will bring somewhat warmer and
more unstable airmass with a marginal risk of severe
thunderstorms. At the same time precipitable water rises to 1.0
to 1.25 inches this afternoon and evening in the east. WPC has a
marginal risk for excessive rain today and tonight and the best
chance for excessive rain would come in any embedded thunderstorms
that develop.

The upper low moves through central Montana tonight and eastern
Montana on Tuesday which will keep the rain going most of the time
until the low moves to the northeast Tuesday night. At this point,
there is a 60-80 percent chance of a half inch of rain and a 20-40
percent chance of an inch of rain today and Tuesday from this
event.

Montana spends the remainder of the week in an unstable WSW to SW
flow aloft which will bring warmer temperatures and frequent
chances for showers and thunderstorms.

FORECAST CONFIDENCE and DEVIATIONS:

For the system today through to Tuesday night, QPF amounts varied
slightly from the previous forecast, with a probability around
70-100% for at least 0.25", 60-80% for 0.50", and 20-40% for 1".

From Wednesday onward confidence is moderate on a gradual warming
trend, but low on precipitation chances. Models agree on a broad
western US and Canada trough with a WSW to SW flow aloft over
Montana but disagree on the timing of waves within the flow aloft.


&&

.AVIATION...

LAST UPDATE: 1540Z

FLIGHT CAT RANGE: VFR becoming MVFR this afternoon and IFR
tonight.

DISCUSSION: Clouds will continue lowering today as rain moves
into northeast Montana. Cloud bases will lower to MVFR levels
between 19z and 23z this afternoon and to IFR levels between 00z
and 03z this evening. Scattered showers develop across the region
this morning with widespread rain and embedded thunderstorms
expected this afternoon, tonight and Tuesday.

WIND: East 5 to 15 knots this morning becoming ENE 10 to 20 knots
and NE to north 10 to 15 knots tonight. TFJ


&&

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

$$

weather.gov/glasgow