502
FXUS65 KGGW 150808
AFDGGW

Area Forecast Discussion
National Weather Service Glasgow MT
208 AM MDT Thu Aug 15 2024

.DISCUSSION...

KEY MESSAGES:

 - Surface smoke moving in from the northern Canadian Prairie
   wildfires today will lead to a hazier and smokier conditions
   across Montana.

 - 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.

 - Omega Block-like pattern will increase heights across the
   region from Saturday, leading to the return of 90 degree heat.

WEATHER PATTERN OVERVIEW:

A 500 hPa trough in the Gulf of Alaska will move south in the next
24 hrs, and 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- like 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 NW`ern half of the CWA, and 20% to 40%
south and east of Glasgow. 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 noticeably higher as we`ve had
relatively smokeless skies in the last 7 days.

Latest HREF run and its associated members are not really strongly
signaling morning fog. Will continue to monitor, but felt
justified in removing fog wording this morning.

With respect to high temperatures from Sunday onward, the
probability of reaching 100F for max temperatures area 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


&&

.AVIATION...

UPDATED: 0800Z

FLIGHT CAT: Mostly VFR (Brief MVFR conditions in the thickest of
surface wildfire smoke)

DISCUSSION: Mostly clear skies are expected today. At the same
time, wildfire smoke will in from Canada, leading to brief areas
of reduced visibility, but mostly remaining above 7SM.

Winds: Winds will primarily be from the northwest, at 5 to 10 kts
west of KGGW and as high as 10 to 15 kts for KGDV, KOLF, and KSDY.
Winds become light and variable tonight.

-Enriquez


&&

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

$$

weather.gov/glasgow