234
FXUS65 KGGW 202017
AFDGGW

Area Forecast Discussion
National Weather Service Glasgow MT
217 PM MDT Thu Jun 20 2024

.DISCUSSION...

KEY MESSAGES:
- Shower and thunderstorm chances increase through Friday, when
  stronger storms and a more widespread wetting rain is expected.

- A few isolated severe cells Friday late afternoon and evening
  are possible, with wind and hail the primary threats.

- A slow warm up is expected through Sunday when some 90s for
  highs likely appear.

WEATHER PATTERN OVERVIEW:
Scattered rain showers and isolated thunderstorms are increasing
in coverage this afternoon and looking to be mainly south of the
Missouri River. SPC`s HREF is pointing toward some gusty winds
with these cells upward of 50 mph by 6pm this evening amidst
increased updraft helicity, but isolated and focused to the
southwest over higher terrain.

However, a shortwave arriving Friday afternoon does look like it
has the chance for a isolated severe cell or two with about 1000
J/kg CAPE, bulk shear around 40-50 kts, and precipitable water
over 1 inch. The one problem with this environment appearing in forecast
soundings and that is a cooler than average surface layer with
cloud cover, which will keep most convection elevated rather than
surface based. This may prevent strong winds initially. That being
said, CAMs point towards strong cells embedded in light shower
activity which could form their own environments and CAMs also
point towards a couple 50-65 mph gusts that could occur with the
strongest cells. The chance of at least one case of severe weather
in the GGW CWA Friday late afternoon and early evening is about
60%, with the chance of a single point getting hit by it less than
10%. Rain totals with this passage vary from a tenth to a half
inch over the CWA, with locally higher amounts where storms train.
Afterward, a ridging pattern will favor seasonably warm and drier
conditions from Sunday into the middle of next week.

FORECAST CONFIDENCE and DEVIATIONS:
There is high confidence (60-80%) in general thunder with minimal
chances (10%) for severe weather at a particular point Friday
afternoon and evening. Confidence is medium to high for the
general conditions remaining slightly warmer and drier than normal
through much of next week.

-Zanker/GAH

&&

.AVIATION...

LAST UPDATE: 2000Z

FLIGHT CAT RANGE: VFR - MVFR

DISCUSSION: SCT/BKN mid level cumulus is developing into
scattered showers and isolated thunderstorms late this afternoon
and evening, especially south of the Missouri River. Mainly KSDY
and KGDV will be impacted with medium (40%) confidence for brief
MVFR conditions. More widespread shower activity with embedded
stronger storms arrive after 18Z Friday.

SFC WIND: Calming to less than 10 kts tonight, then east around 10
kts Friday afternoon. Expect gusty and erratic winds near any
thunderstorm.

&&

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

$$

weather.gov/glasgow