Damaging Wind in Montana, August 17, 2023

Area Forecast Discussion
National Weather Service Billings MT
911 PM MDT Thu Aug 17 2023

.UPDATE...
Early evening satellite imagery shows a moistening southerly flow
extending into south central MT on western periphery of strong
high plains ridge. We are actually seeing some cumulus fields over
our western mountains and foothills. A bit upstream, there is some
weak convection approaching Dillon and Ennis. This activity will
have a difficult time reaching our cwa tonight, w/ no forcing and
a loss of daytime heating, but the mid level moisture may be
enough for a few sprinkles/virga over our far west. Otherwise,
most of our region will be dry tonight as much better chances of
convection begin tomorrow. Tonight will be a very warm night with
lows in the 60s to mid 70s most places (courtesy of increasing
cloud cover and downslope gradients).

Livingston (100F) and Billings (99F) each missed their daily
record high by one degree today. Records will be challenged again
Friday.

JKL

&&

.DISCUSSION...

Through Friday night...

Hot conditions will remain in place over the area through Friday,
with ridging over the region. Highs will reach the 90s to lower
100s, with many locations seeing a moderate chance of reaching or
exceeding 100 degrees Friday (40-60%). The one item that may inhibit
temperatures is smoke filtering through the region. While it's
not expected to reach the surface, it could limit temperatures
by a few degrees. Regardless, it will still be hot, and folks
should stay hydrated and if at all possible, limit outdoor
exposure. Heat advisories remain in effect over portions of the
area today through Friday.

A few high-based showers or virga are possible across
western areas tonight into Friday morning as moisture begins
working into the region from the southwest. Isolated showers and
thunderstorms are expected to move off the mountains during the
afternoon, spreading north and east over the plains through the
evening. Gusty and erratic winds are possible with thunderstorms,
but PWATs approaching 1.25 inches will give thunderstorms the
potential for at least some brief heavy rain. Winds also increase
on Friday ahead of a cold front passage Friday night. The hot
temperatures along with RH down into the teens and 20s in some
areas, as well as breezy westerly winds will bring elevated fire
weather conditions for Friday. RH will increase, with winds
decreasing Friday evening. STP

Saturday through Thursday...

A change in the weather pattern is expected this weekend across
the region with cooler temperatures and increased atmospheric
moisture leading to better chances (20-70%) for wet showers and
thunderstorms.

Saturday and Sunday, the upper air flow pattern will consist of a
strong ridge over the central US, a trough over the West Coast,
and south/southwesterly flow in between these two features over
the Northern Rockies. Tropical Storm Hilary will also be moving
northwestward over the eastern Pacific Ocean during this period,
with its moisture getting drawn northward by the middle and upper
air flow. In the lower levels, easterly flow will advect moist air
from the central US to our area as well. So, altogether, the
atmosphere looks to moisten considerably over our area with
precipitable water values progged to rise to 1.00-1.70 inches,
which is near or above the 99.5th climatological percentile. This
pattern should facilitate the development of scattered showers and
thunderstorms over the area (20-70% chance) in the afternoon and
evening both days this weekend. There is some uncertainty with the
location of this activity at this time though. It is possible
that central locations miss activity due to a capping inversion
there and lack of nocturnal activity. Southeast MT, on the other
hand, could see nocturnal thunderstorms Saturday night and
especially Sunday night, with low-level southeasterly flow in
place there. Any thunderstorms that develop this weekend will be
capable of producing heavy downpours given the ample moisture
available.

Monday through Thursday, the upper air flow pattern is progged to
retrograde a bit, with the ridge building westward over our area.
This pattern will give us a lower chance of showers and
thunderstorms (15-50%) each day but given that we are still
somewhat on the periphery of the ridge it's not a totally dry
pattern. The low- level flow will become more southerly by Monday
which will also cause temperatures to increase from the weekend
readings.

High temperatures will generally be in the 70s to 80s Saturday
and Sunday, then 80s to 90s Monday through Thursday. RMS/Arends

&&

.AVIATION...

Smoke from wildfires to the west will continue to hover in the
skies and slightly reduce slant-range visibility. Surface
visibility will remain above 6SM, as smoke is forecasted to stay
aloft. A disturbance approaching from the southwest will bring a
few high-based showers to western and central areas late tonight
into Friday morning. Isolated showers and thunderstorms are
possible through the afternoon and evening hours Friday, as they
spread from west to east across the area. STP

&&

.PRELIMINARY POINT TEMP/POPS...

    Fri     Sat     Sun     Mon     Tue     Wed     Thu
-----------------------------------------------------------
BIL 072/099 065/083 060/079 062/091 061/093 063/091 064/085
    02/T    11/B    51/E    41/B    21/B    11/U    22/W
LVM 066/094 058/084 054/077 056/086 057/088 057/088 056/083
    12/T    24/T    55/T    74/T    42/T    22/T    24/T
HDN 066/100 061/086 058/085 059/093 058/095 059/092 061/085
    02/T    10/B    51/E    41/B    21/U    11/U    22/W
MLS 067/102 067/085 060/082 063/091 063/094 065/091 065/085
    01/G    20/U    72/W    51/B    11/U    11/U    22/W
4BQ 068/101 067/090 063/087 065/096 064/097 065/093 065/086
    00/G    20/U    61/E    30/B    10/U    20/U    22/T
BHK 063/102 064/087 058/080 060/092 059/092 061/090 062/084
    00/G    10/U    63/T    41/B    10/U    10/U    21/B
SHR 064/098 062/087 058/085 059/093 059/093 060/089 059/084
    02/T    11/B    51/B    31/B    11/U    21/U    23/T

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Heat Advisory remains in effect from 9 AM to 10 PM MDT Friday
      FOR ZONES 29>33-36-37-57-58-138-139-169-170-173-235.
     Red Flag Warning in effect from 10 AM to 9 PM MDT Friday FOR
      ZONE 117.
WY...None.

&&

weather.gov/billings