087
FXUS65 KBYZ 220347
AFDBYZ

Area Forecast Discussion...Updated
National Weather Service Billings MT
947 PM MDT Mon Jul 21 2025

.KEY MESSAGES...

- Scattered showers and thunderstorms through this evening. A few
  storms could become severe and produce large hail, strong
  winds, and heavy rain.

- Cooler temperatures (70s and 80s) Tuesday and Wednesday with
  continued daily chances of showers and thunderstorms. A few
  thunderstorms could become strong to severe over portions of the
  area both days.

- More typical July weather (warmer and drier) looks to return
  for Thursday into the weekend.

&&

.UPDATE...
Atmosphere still quite unstable across much of the lower
elevations. Jet related forcing fueling lift over our NW zones
(Roundup area) where strong to severe thunderstorms are still
going.

We have updated PoPs for the rest of the evening. Much of Severe
Thunderstorm Watch 535 still in valid until 11 PM. BT

&&

.DISCUSSION...
Through Tuesday Night...

Mid clouds and light showers or virga were moving in from the
southwest early this afternoon as an upper low/trough was situated
over the Pac NW. Temperatures had risen into the upper 70s and
80s, on their way to the 80s to lower 90s. Diffluent southwest
flow, along with ample moisture (PWATs greater than an inch) and
good instability (CAPE values 1000-2000 J/kg) and shear (deep
layer shear of 35-50 kts) will allow for showers and thunderstorms
this afternoon/evening. The showers/thunderstorms will develop
over the mountains this afternoon, spreading north and east
through the evening. Thunderstorms could be strong to severe,
producing large hail, strong wind gusts and heavy rainfall. The SPC
has a marginal to slight risk for severe weather over most of the
area this afternoon and evening.

Tuesday will be a cooler day with highs in the 70s and 80s. A cold
front and shortwave energy moving through the area will bring
shower and thunderstorm chances Tuesday afternoon and evening,
continuing into the night. With CAPE values of 750 to 1500 J/kg),
deep layer shear (35 to 50 knots), and ample moisture (PWATs
greater than an inch), a few thunderstorms could become strong to
severe. Large hail, strong wind gusts and heavy rainfall are the
main threats with the severe thunderstorms. The SPC has a marginal
risk for severe weather for areas mainly from Billings east during
the afternoon and evening. STP



Wednesday through Sunday...

Upper level shortwave troughing will continue to produce showers
and thunderstorms over the region Wednesday. Scattered showers
and thunderstorms from the overnight hours will continue through
the day and into the evening. With the 500 mb jet providing
sufficient shear and with sufficient instability (MUCAPE ~
500-1000J/kg), a few strong to severe thunderstorms are possible.
As high atmospheric moisture remains in place, heavy rain will
continue to be a concern with any strong thunderstorms Wednesday.
Into Thursday, drier air is expected to move in behind departing
troughing, allowing for warmer and drier conditions to build back
in. As southwest flow returns late Thursday, afternoon isolated
showers and thunderstorms will continue through the weekend.

Temperatures will remain cooler into Wednesday with highs near 80
degrees, warming to the 80s to low 90s Thursday, reaching 80s to
mid 90s through the remainder of the period. TS

&&

.AVIATION...


Showers and thunderstorms will continue over portions of the
forecast area this evening. Locations at risk for strong to severe
storms producing MVFR-IFR conditions are KMLS-KBHK-K97M-KRPX
through 06Z. Low stratus producing MVFR conditions begins to
spread in from the northwest late tonight/Tuesday morning.
ANother round of scattered to numerous showers/thunderstorms
are expected Tuesday afternoon/evening. BT

&&

.PRELIMINARY POINT TEMP/POPS...

    Tue     Wed     Thu     Fri     Sat     Sun     Mon
-----------------------------------------------------------
BIL 061/082 060/079 059/089 062/094 061/094 061/092 061/092
    36/T    75/T    21/U    11/U    11/U    10/U    11/U
LVM 052/081 050/082 051/089 053/090 053/091 053/090 053/091
    36/T    54/T    11/U    11/U    11/U    11/U    11/U
HDN 060/084 059/080 057/091 059/094 059/094 060/094 059/092
    44/T    85/T    31/U    11/U    11/U    10/U    11/U
MLS 063/084 061/080 060/090 063/094 063/096 063/092 065/092
    82/T    74/T    31/U    11/U    11/U    21/U    21/U
4BQ 064/085 062/080 061/088 063/091 063/094 064/092 065/091
    31/B    83/T    52/T    21/U    11/U    10/U    21/U
BHK 061/084 058/080 056/085 060/090 060/092 061/088 061/088
    61/B    63/T    41/U    21/U    11/U    21/U    21/U
SHR 057/085 055/081 053/089 056/091 057/091 057/092 057/092
    24/T    65/T    42/T    11/U    11/U    10/U    11/U

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Severe Thunderstorm Watch 535 in effect until 11 PM MDT this
      evening FOR ZONES 29-31>33-36-37-42-58-63-68-172-228.
WY...None.

&&

$$
weather.gov/billings