246
FXUS65 KBYZ 162144
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
344 PM MDT Fri May 16 2025

.KEY MESSAGES...

- Scattered showers and a few thunderstorms over the west half of
  our forecast area today and Saturday.

- Another spring weather system is expected to bring lower
  elevation rain and mountain snow, cooler temperatures, and windy
  conditions back across the region Sunday through Monday.

- Heavy rain Sunday into Monday may cause localized flooding in
  areas with saturated ground. Water rises and increased stream
  flows on area waterways can also be expected early next week.

&&

.DISCUSSION...
Through Sunday Night...

Low pressure system over the upper midwest was slowly sliding
east today. This has pulled the stronger winds and precipitation
east with it. Thus, winds and rain coverage have decreased across
our eastern border counties. Ths High Wind Warning for
Fallon/Carter counties were allowed to expire at 100 pm. In the
meantime, we have had some Pacific moisture moving into our
western forecast zones with assoicated perturbation and
instability. This has produced some scattered showers with a few
rumbles of thunder, particularly over and near the high country.
Some of this activity will linger into the evening as it slowly
migrates east overnight. Skies should mostly clear out in our far
east overnight allowing for temps to drop to the lower to mid 30s
across Fallon and Carter Counties resulting in a threat of light
frost and local fog (The probability of reaching 32F is about 25%,
while there is a 60% chance of dropping to 35F or lower). Temps
elsewhere will be in the 40s.

We should see a period of mainly dry conditions late tonight and
Saturday morning. By Saturday afternoon we start to introduce
height falls in response to next approaching upper trough. There
should be enough diurnal heating to achieve a bit more instability
than tomorrow (300-500 j/kg of SBCAPE), but any convection should
remain below severe limits...and may be limited to the higher
terrain in our west thanks to some induced capping from easterly
surface winds. By evening, we may see increased showers and
t-storms over the western half of our CWA and some isolated
activity on the eastern plains as height falls and difluent flow
start to affect our region with the upper trough progged to dig
into the Rockies. Look for highs in the 60s Saturday and lows in
the 40s Saturday night.

Sunday/Sunday night...Upper trough moves slowly across our region
Sunday into Monday spreading precipiation and cooler temps over
the area. As cooler air moves into the western zones (highs in
the 50s), we will still see a warm sector Sunday from Billings
eastward with highs in the 60s to near 70 degrees. PWAT values
will broach .80 inches with decent upper forcing and instability.
We could see a few stronger thunderstorm cells develop capable of
heavy rain and small hail. Due to recent rainfall the past week or
so, grounds may be close to saturated in some areas, especially
around the Big Horns region where two to four inches of rainfall
in the past 10 days has been observed. Local flooding is a
concern, including the Elk fire burn scar where heavy rain in
short time could cause debris flows.

Heavy rainfall potential and impacts...As this early week storm
system moves over the region late Sunday through Monday there is a
potential for heavy rainfall with over an inch of precipitation in
many areas. Snow levels are expected to be relatively high (above
8500 ft) on Sunday, droppng to around 6500-7500 ft by Monday. The
high country could see 5-10 inches of new snow, with wet snow
rain mix in the higher foothills. Some rain on snow is possible,
but overall rainfall and saturated ground soils are currently the
biggest concern, especially around the Big Horns region. Models
are still bouncing around with placement of heaviest precip, with
latest trends pointing to upper Musselshell region (Wheatland,
Musselshell Counties) picking up half to one inch of liquid Sunday
night. However, models have consistently placed over an inch of
liquid over the Big Horns region Sunday through Monday.
Therefore, we will issue a Flood Watch for the Big Horns, Sheridan
Foothills and Southern Big Horn County from noon Sunday to 6 PM
Monday with the aforementioned concerns for this area. We will
monitor other areas across the CWA to possibly expand this Flood
Watch, but for now our greatest concern in these areas. BT

Monday through Friday...

Into Monday, an upper level low set to move across Wyoming will
continue to bring precipitation to the region. Precipitation will
gradually diminish eastward as the low tracks into the Dakotas
Tuesday morning. There still remains uncertainty of the exact
track of the low and where the heaviest precip amounts will occur.
Much of the region has moderate chance for at least an inch of
precipitation Sunday through Monday. Through Monday and Tuesday,
continued rises on waterways can be expected downstream of where
any heavy precipitation occurred. No minor flooding is expected at
this time. With regards to snowfall, snow levels will drop to
around 6-7,000 ft Monday morning, taking away concerns for any
rain on snow potential. Ensembles continue to hint at unsettled
weather with lagging lower heights to our north dragging some weak
energy through the area Tuesday night into Wednesday. Additional
waves are possible later in the week, but ensembles are differing
too much to give decent timing.

Temperatures will remain around average with highs expected to be
in the 50s Monday, warming into the 60s for the remainder of the
week. TS

&&

.AVIATION...

Breezy NW winds of 25-30 kts will continue to decrease through
the afternoon for KMLS and KSHR. Isolated showers will continue
across south-central MT through the early morning hours mainly
for KLVM and KBIL. There is about a 20% chance of fog development
over southeast MT tonight after midnight lasting through 15Z. TS

&&

.PRELIMINARY POINT TEMP/POPS...

    Sat     Sun     Mon     Tue     Wed     Thu     Fri
-----------------------------------------------------------
BIL 045/068 049/064 043/051 042/067 044/068 047/068 045/067
    31/B    29/T    97/W    45/W    54/T    35/T    33/T
LVM 040/064 043/054 038/056 038/064 039/067 042/064 039/065
    52/T    6+/T    85/W    35/T    53/T    35/T    34/T
HDN 043/070 049/069 044/052 041/066 043/068 045/069 044/069
    32/T    29/T    99/W    55/W    54/T    35/T    44/W
MLS 040/068 047/067 043/052 040/062 042/068 045/069 044/068
    01/B    26/T    99/W    64/W    34/W    24/W    43/W
4BQ 039/067 047/068 042/048 040/059 041/066 045/067 045/066
    01/B    26/T    99/W    64/W    34/T    23/W    33/W
BHK 033/064 040/056 038/050 037/056 036/065 040/067 041/066
    10/U    25/T    98/W    74/W    34/W    23/W    42/W
SHR 037/068 043/068 039/048 037/063 038/067 041/069 040/065
    21/B    19/T    99/W    55/W    45/T    24/T    33/T

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Flood Watch in effect from Sunday afternoon through Monday
      afternoon FOR ZONES 138-169-171.
WY...Flood Watch in effect from Sunday afternoon through Monday
      afternoon FOR ZONES 198-199.

&&

$$
weather.gov/billings