Rapelje, Montana Weather Forecast Discussion

030
FXUS65 KBYZ 122142
AFDBYZ
Area Forecast Discussion
National Weather Service Billings MT
342 PM MDT Fri Sep 12 2025
.KEY MESSAGES...
- A good chance for precipitation (30-80% chance >0.5 inches from
  Billings east) through Saturday.
- Turning cooler for Saturday (upper 60s to 75).
- Drier and warmer (70s to low 80s) Sunday and Monday.
- Cooler temperatures and wetter conditions with storm system
  Monday night through Wednesday.
&&
.DISCUSSION...
Through Saturday night...
Scattered showers and thunderstorms were lifting through western
areas, and off the Bighorn Mountains and areas to the northeast
this afternoon, as an upper trough approached and a jet max nosed
into the area. Showers and thunderstorms are expected to increase
in coverage over central and eastern areas this afternoon and
evening, with some of the thunderstorms possibly becoming strong
to severe. Instability is modest with MUCAPE up to 1500 J/kg and
shear of 30-40 kts, greatest over the east. The SPC currently has
a marginal risk for severe storms across western and central
areas, with a slight risk over the east. Main threats are strong
wind gusts and large hail, with heavy rain as well.
The best period for precipitation is expected to be overnight
tonight into Saturday morning (50-90% chance) as a mid-level
circulation lifts into the region, with moisture and instability
wrapping back in from the east and northeast. Precipitation
chances begin decreasing Saturday afternoon and evening as the
upper energy shifts north and east. Precipitation totals through
Saturday are forecast to range from near a couple tenths in the
far west, to around an inch near the Dakotas border. Probabilities
for half an inch or more of precipitation range from around 30%
near Billings, to near 80% near the Dakotas border.
Temperatures on Saturday will drop into the upper 60s to lower
70s, below normal for this time of year. STP
Sunday through Thursday...
Troughing is the overall pattern in the longterm forecast period,
although models depict a brief shortwave ridge moving through
Sunday through Monday. The chance for showers and thunderstorms
will be low Sunday into Monday, before increasing with an
approaching upper trough and developing low. There is uncertainty
with this system, despite ensembles showing moderate agreement.
The ECMWF ensemble depicts the trough interacting and merging into
the upper low that moved through Montana to end this week.
Meanwhile, the GEFS shows the two combining into a larger trough
without a distinct upper low. The timing and location of this
system will play a part in the extent of the chance for precip.
Another note about the Monday through Tuesday system is that
850mb temperature anomalies around -5C are depicted by the latest
ensembles. The current forecast depicts light snow accumulations
(up to an inch) on the highest peaks of the Absaroka/Beartooths.
Those with recreations in the high country should be prepared for
cooler and potentially wintry conditions during this timeframe.
The current forecast has a low chance (10-30%) for precipitation
in the southwestern mountains and along the Dakotas border,
Sunday. Monday afternoon and evening the chance increases (30-80%)
across the area, continuing through Tuesday. The threat for
strong thunderstorms in the extended forecast period is low, with
minimal instability and shear.
High temperatures are forecast to be in the 70s and 80sF Sunday
and Monday, cooling into the 60s to around 70F Tuesday, and 70s on
Wednesday. Matos
&&
.AVIATION...
Scattered showers and thunderstorms will lift north and east
through into the evening, becoming more widespread overnight. A
few thunderstorms could be strong to severe this afternoon and
evening over central and eastern areas, with heavy rainfall, wind
gusts to 50 kts and large hail. Showers and isolated
thunderstorms will linger into Saturday as a disturbance moves
through the region. In general, VFR will prevail with MVFR
conditions possible with showers/thunderstorms. STP
&&
.PRELIMINARY POINT TEMP/POPS...
Sat     Sun     Mon     Tue     Wed     Thu     Fri
-----------------------------------------------------------
BIL 056/069 052/080 055/080 054/069 050/073 049/078 052/077
    78/T    11/U    03/W    45/T    32/W    00/U    11/B
LVM 046/069 043/078 046/073 042/068 041/074 043/079 044/075
    35/T    11/U    15/T    55/T    21/U    00/U    11/B
HDN 055/072 048/081 051/082 051/069 047/073 046/079 049/080
    87/T    21/B    01/U    55/T    42/W    10/U    10/B
MLS 059/074 053/077 054/082 054/072 051/072 049/075 051/077
    87/T    21/B    11/U    33/T    42/W    10/U    10/U
4BQ 058/074 053/074 053/081 054/070 050/068 048/074 050/077
    84/T    21/B    11/U    33/T    43/T    11/U    10/U
BHK 057/074 052/074 052/080 051/074 049/071 046/073 047/074
    97/T    33/T    31/B    22/T    42/T    11/U    11/U
SHR 049/073 044/077 047/080 046/067 043/069 042/077 046/079
    84/T    21/B    02/W    46/T    53/W    10/U    01/U
&&
.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.
&&
$$
weather.gov/billings

NWS BYZ Office Area Forecast Discussion