628
FXUS65 KMSO 231828
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
1228 PM MDT Sun Jun 23 2024

.DISCUSSION...A trough moving over the region today will set up
zonal (west to east) flow for tomorrow. Overall, the impact of
this pattern is breezy conditions in the valleys with stronger
winds gusting near 30 or 40 mph at some mountain locations. Along
with the increased winds, the region is under a very dry air mass,
so relative humidity will be dropping down below 20 percent at
most low elevation locations.

Monday through Wednesday a ridge builds in over the region,
causing some of the hottest and driest conditions we`ve seen so
far this summer. For several days, many valley locations will have
relative humidity drop below 20 percent. Also, under the influence
of the ridge a phenomena called thermal belts will intensify.
Thermal belts cause low humidity to persist on the mid-slopes and
sometimes the upper slopes in the mountains.

While land management agencies are currently still reporting fire
danger at moderate levels across the northern Rockies, these are
the weather conditions that start the transition to a drier time
of the Summer. And the end of June and early July is a very
typical time of year for this to occur.

A recent change in the models has been to show the ridge starts
breaking down late Wednesday into Thursday. Previously, even the
ensembles weren`t indicating a breakdown starting until Thursday.
But the timing has been trending earlier with successive model
runs the last few days. This will bring more wind again, cooler
temperatures, and the chance for lightning later this week. The
probability of a good, wetting rain with this system has been
trending down. So while portions of northwest Montana still have a
roughly 50 percent chance of getting 0.10 inches or more of rain
Thursday or Friday, most of the rest of the region less than a 25
percent chance of picking up that much moisture.

&&

.AVIATION...A trough moving over the region today and tonight will
bring gusty westerly winds this afternoon and increasing cloud
cover. There is a slight chance of thunderstorms this evening, but
dry air moving in from the west is really making just virga much
more likely with more thunderstorms east of the Continental
Divide.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&

$$