442
FXUS65 KMSO 021933
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
133 PM MDT Tue Jul 2 2024

...Increasing Confidence for a July 5-12 Heatwave...

.DISCUSSION...Disturbances continue to pass through the
northwesterly flow aloft, and combined with above-average
atmospheric moisture, they will bring chances of showers and
thunderstorms today and Wednesday. The main focus for storms this
afternoon is in Flathead and Lake counties and in the Glacier
Region, where radar projections show storms clustering at least
through this evening. Some storms are expected to linger
overnight.

On Wednesday, thunderstorm coverage will expand to include all of
western Montana and the Clearwater Mountains. Model guidance
indicates a more defined shortwave trough passage, bringing modest
atmospheric instability (CAPE 100-250 J/kg) and lift for shower
and storm development. Similar to today, the primary focus for
shower and storm activity will be in Flathead County and Glacier
Park, with 24-hour probabilities for 0.25 inches of precipitation
reaching 60%.

On Independence Day, Thursday, a general drying trend is expected
across the area, with isolated showers and storms developing
along the divide. Highs will warm into the 70s and 80s across
western Montana and into the lower 90s in the lower valleys of
north-central Idaho under mostly clear skies.

Confidence is high for a hot and dry pattern from Friday into the
weekend and beyond. Ensemble models strongly agree (>90% of
members) that a high-amplitude ridge will move across the Pacific
Northwest from Friday into Sunday, with the ridge axis shifting
over the Northern Rockies by next week. Ensembles have been
indicating a longer-duration heatwave across the lower elevations
of Idaho, where excessive heat watches are now in effect. This
trend is well-reflected in the NBM guidance, with probabilities
for temperatures of 100F or greater exceeding 80% in Orofino and
Riggins each day between July 6 and 10. Several days of
temperatures between 90-95F or greater will also impact valley
areas of western Montana.


&&

.AVIATION...
Satellite imagery this afternoon reveals cumulus buildups in the
Northern Rockies and thunderstorms passing through northwest
Montana. Radar projections indicate most thunderstorms this
afternoon and evening will concentrate near KGPI and extend south
and east through the Glacier Region. The strongest storms are
expected to produce heavy rain.

The next shortwave trough is on track to reach the region
overnight, bringing additional showers and thunderstorms,
particularly to northwest Montana. The extra rain today will
increase the chance of fog, especially at KGPI on Wednesday
morning. This disturbance, combined with above-average atmospheric
moisture, is expected to increase thunderstorm coverage across
most of western Montana on Wednesday afternoon.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...Excessive Heat Watch from Sunday afternoon through Tuesday
     evening for Lower Hells Canyon/Salmon River Region...
     Orofino/Grangeville Region.

&&

$$