081
FXUS65 KBYZ 290828
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
228 AM MDT Mon Apr 29 2024

.DISCUSSION...

Today through Tuesday...

Satellite imagery shows zonal flow thru the PacNW and northern
Rockies, ahead of a low along the BC coast. To our east, the
central plains low has lifted to eastern SD and will reach western
Lake Superior today...i.e. it is out of our picture but has
slowed the progression of the Pacific trof set to arrive late
today. BLX radar shows an area of showers from Livingston and the
Beartooth-Absarokas to near Billings, a result of a weak shortwave
and relatively steep mid level lapse rates. These showers will
continue to spread east and gradually dissipate over the next
several hours. Once these showers have ended, there will be a dry
period of wx until a much greater chance of showers arrives by mid
afternoon.

A shortwave along the WA coast will move thru the northern Rockies
today and be associated with a cold front which is expected to
reach our west by late afternoon. Large scale ascent combined with
modest diurnal instability (100-200 j/kg of sbcape) will produce
showers (60-90% chance) and a few thunderstorms from mid afternoon
thru the evening. Any t-storms will remain weak. Some locations
along our western foothills may see up to 0.25" of rain, but most
areas can expect 0.10" or less. The fropa/convection combo could
yield pockets of enhanced winds between 22-04z (local gusts to 45
mph). Heads up if you have outdoor activities planned. Mountains
will see a period of accumulating snow late this afternoon thru
tonight (until PV axis passes) with 3-6" on west aspects. Snow
levels will actually fall quickly behind the front, enough such
that western foothills locations could see a brief mix with wet
snow. That said, the Pacific front will be followed by downsloping
breezy west winds, so lower elevations will see a quick
transition to drying behind the trof.

Well-mixed gusty west winds will impact the region on Tuesday,
with expectation of widespread 30-45 mph gusts (strongest across
our north), consistent with ~35kt flow at 700mb. It should also be
noted that it will be quite dry tomorrow. Ensembles suggest pwats
falling to 0.20" or lower and this should translate to dewpts in
the teens, and min RHs of 15-25%. Greenup is well underway so no
fire concerns.

Look for temperatures in the 60s today and 50s Tuesday.

A few noteworthy probabilities:
Tue gusts of 30+ mph:  80-95% regionwide
Tue gusts of 40+ mph:  70% BigT to 3HT, 20-50% elsewhere
Tue gusts of 50+ mph:  30% BigT to 3HT, 10% or less elsewhere
Mountain snow of 4+ inches:  40% (western mountains only)

JKL

Tuesday evening through Sunday...

An active and unsettled period is in store for the extended
forecast. With several upper lows and general troughing across the
northern Rockies and southern Canada, rounds of showers and
moisture as well as temperatures slightly below average are
anticipated.

Wednesday, a broad upper low will continue wobbling around in NE
MT and Southern Canada. Precip chances will begin increasing from
the WNW by early afternoon, eventually spreading PoPs across the
area. Highest PoPs exist in the mountains where there is a 50-70%
chance. As for the lower elevations, there is a 20-50% chance for
precip. Temperatures will drop Wednesday night along with snow
levels, as a result, there is a period where precip type becomes
snow or a rain/snow mix in the lower elevations, including
Billings. Little to no snow accumulations are expected below the
foothills, with less than a 10% chance for 0.1" of snowfall. As
for the mountains, several inches of snow will fall through the
extended forecast. The chance for 6 or more inches of snow are
50-70% in the western mountains, 30-60% in the Bighorns, and up to
15% for foothill locations such as Red Lodge and Story, WY.

Beginning Friday, there is uncertainty with the pattern evolution
going into the weekend, some models are showing another low
digging into northern Rockies while others are depicting a
building ridge. The difference between the two would be
temperatures and moisture chances. The current forecast has high
temperatures in the 50s Wednesday thru Friday, 60s on Saturday, and
60s/70s on Sunday.

Matos

&&

.AVIATION...

An area of showers will impact KLVM to KBIL early this morning,
thru around 14z, and local MVFR is possible. Otherwise, there is a
greater chance of showers across the region this afternoon and
evening as a Pacific cold front arrives. Expect local MVFR in the
showers, potentially down to IFR at KLVM where rain could mix w/
snow after 00z. Mountains will be frequently obscured. SW winds
will gust to 30kts along the western foothills before the frontal
passage, then a short period of 20-35kt W-NW wind gusts can be
expected regionwide behind the cold front tonight. JKL

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Tue     Wed     Thu     Fri     Sat     Sun
-------------------------------------------------------
BIL 067 037/056 035/055 037/054 035/054 035/062 040/070
    4/T 52/W    24/W    35/W    25/W    22/W    12/W
LVM 060 029/049 028/049 032/052 032/051 030/060 037/064
    8/T 84/W    35/W    44/W    35/W    22/W    23/W
HDN 069 038/058 034/058 035/055 032/056 032/064 039/074
    3/W 72/W    24/W    45/W    25/W    21/B    12/W
MLS 066 041/057 035/057 036/051 034/054 033/061 041/071
    1/B 72/W    02/W    35/W    23/W    21/B    11/B
4BQ 067 041/057 034/056 036/051 033/055 032/061 041/072
    1/B 51/N    11/B    24/W    13/W    21/B    11/B
BHK 067 038/056 030/057 032/049 030/051 030/058 036/068
    1/U 53/W    02/W    25/W    23/W    22/W    11/B
SHR 068 035/056 030/052 030/051 028/052 030/061 038/071
    2/W 72/W    24/W    45/W    24/W    31/B    12/W

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.

&&

$$
weather.gov/billings