033
FXUS65 KGGW 152046
AFDGGW

Area Forecast Discussion
National Weather Service Glasgow MT
246 PM MDT Thu Aug 15 2024

.DISCUSSION...

KEY MESSAGES:

 - Surface smoke moving in from Canadian wildfires has prompted a
   Dense Smoke Advisory and Air Quality Alert through Friday afternoon.

 - A wetter Friday is in store for much of northern Montana, with
   the greatest chances for a wetting rain highest across Phillips
   County (40% to 60% chance of exceedance).

 - Hint of a line of storms developing across the island ranges
   Friday afternoon with severe wind gusts being the biggest
   concern.

 - A slight warming trend through the weekend brings the return of
   widespread highs in the 90s.

WEATHER PATTERN OVERVIEW:

A 500 hPa trough in the Gulf of Alaska will move south in the next
24 hrs, parking itself off the Washington coastline, cutting off
from the jet stream, while a shortwave trough traverses the Great
Plains and parking itself in the ECONUS, setting up an Omega
Block pattern.

Being downstream of the western-most cutoff low pressure will
lead to enhanced upper-level divergence and increased PoP chances
across northern Montana on Friday. The probability of a wetting
rain (at least a tenth of an inch of rainfall) on Friday ranges
from 40% to 60% across the western half of the CWA, and 20% to
40% south and east of Glasgow. For Friday afternoon and evening,
some CAMs are hinting of a line of showers and thunderstorms
(possibly with some bowing hinted in the 16th 00Z HRRR run).
Latest RAP13 forecast soundings in our western zones show
relatively dry low and mid- levels, indicative of severe wind gust
concerns. Will have to monitor this trend carefully.

By Saturday, 500 hPa heights increase, leading to drier conditions
and temperatures increasing as high as the mid-90s, as per the NBM
mean.

FORECAST CONFIDENCE & DEVIATIONS:

Main change from the NBM in the short term forecast is adding in
the latest HRRR/RAP13 surface smoke guidance into the Weather and
Visibility grids. The source of the smoke for this next batch of
smoke and haze today and into Friday comes from the wildfires
across the far northern Canadian Prairie. The concentration of the
particulate matter will be much higher than recent days and is not
being captured well without a concentration formula adjustment
based on current observations.

With respect to high temperatures from Sunday onward, the
probability of reaching 100F for max temperatures is highest for
locations in lower elevations of adjacent river valleys, though
these probabilities of exceedance do not go above a 20% chance. We
will have to carefully monitor the trends for the 500 hPa high
pressure and how much heights increase in subsequent model runs
and to see if we creep back up to the 100s.

-Enriquez/Zanker

&&

.AVIATION...

UPDATED: 2000Z

FLIGHT CAT: Mainly MVFR - IFR

DISCUSSION: Mostly clear skies are expected through Friday morning
above wildfire smoke filtering in from Canada. This will lead to
periods of IFR visibility, particularly after sunrise on Friday
after some improvement this evening. By 00Z Saturday, the next
round of scattered thunderstorms will approach the TAF sites from
the west.

WINDS: North at 10-15 knots becoming east at 5-10 knots around 06Z.

&&

.GGW WATCHES/WARNINGS/ADVISORIES...
Dense Smoke Advisory until 6 PM MDT Friday for Central and
Southeast Phillips-Central and Southern Valley-Daniels-Dawson-
Eastern Roosevelt-Garfield-McCone-Northern Phillips-Northern
Valley-Petroleum-Prairie-Richland-Sheridan-Southwest Phillips-
Western Roosevelt-Wibaux.

&&

$$

weather.gov/glasgow