Flash Flood Warning 5, NWS Billings, MT

Area Forecast Discussion...Updated
National Weather Service Billings MT
431 PM MDT Fri May 26 2023

.UPDATE...

A Severe Thunderstorm Watch has been issued for Rosebud, Treasure,
Big Horn (MT), and Sheridan (WY) Counties eastward to the Dakota
border until midnight MDT tonight. Thunderstorms could produce
large hail, strong wind gusts to 60 mph and heavy rain. RMS

&&

.DISCUSSION...

Through Saturday night...

An upper trough is over the western US this afternoon with
disturbances moving through the flow around the trough. A
disturbance is facilitating development of scattered showers and
thunderstorms over the region that should move northeastward into
this evening. Low level easterly winds are supplying moisture but
are also facilitating the development of cloud cover that is
holding temperatures down especially over south central MT. Cloud
cover is much lower over southeast MT/north central WY where
temperatures have climbed into the upper 60s to middle 70s. This
set-up should produce mixed layer CAPE values of 1000-1500 J/kg
over southeast MT to Sheridan County, WY later this afternoon into
this evening. Farther west over south central MT, the cloud cover
and lower surface temperatures likely will produce lower CAPE
values of 500-1000 J/kg. In addition, the vertical wind shear is
around 30 kt mainly from Yellowstone- Musselshell Counties
eastward to southeast MT. The combination of the instability and
shear suggests that the greatest threat of severe thunderstorms is
over southeast MT, east of Billings, and over Sheridan County,
WY, though a severe storm cannot be ruled out over south central
MT. Severe thunderstorms today could produce large hail and
strong wind gusts to 60 mph.

In addition, the moist air that has been in our area over recent
days persists this afternoon with precipitable water values around
0.75 to 1.10 inches. We have continued the Flood Watch for
Musselshell-Yellowstone-Big Horn (MT) Counties eastward to the
Dakota border due to heavy rain potential from thunderstorms on
saturated soil. Storms could train over the same areas in a short
period of time, which would pose the greatest risk of producing
flash flooding. Be prepared for severe weather if you have outdoor
plans. Depending on what rain falls this evening, the flood watch
could be extended into Saturday.

Later this evening into the overnight, showers and thunderstorms
should decrease to more isolated activity with the loss of
instability.

On Saturday, another round of showers and thunderstorms is
expected as more disturbances rotate over the area. Shear looks
much lower over south central MT but appreciable values of 30-40
kt will be over southeast MT and Sheridan County, WY. Instability
looks appreciable again with CAPE near or over 1000 J/kg
especially from Musselshell-Yellowstone Counties eastward. Given
this setup with the shear and instability, SPC has a marginal risk
of severe thunderstorms east of Billings and a slight risk over
far southeast MT, mainly affecting Powder River and Carter
Counties. Storms again could produce heavy rainfall given the
moist air in place.

Shower and thunderstorm activity should again decrease later
Saturday evening.

Low temperatures will generally be in the 40s and 50s tonight and
Saturday night. High temperatures on Saturday will range from the
60s in Wheatland County to the lower 80s over Fallon and Carter
Counties. RMS

Sunday through Friday...

Sunday will see some showers and thunderstorms in the area before
we turn a little drier for the early to middle part of the week.
The low pressure system over the west coast will dissipate and
another low will spin up farther to the south. This low will
cutoff from the main flow putting us in for westerly flow and the
850mb winds will shift keeping the Gulf moisture further to the
east. There will still be decent PWATS around providing some
moisture for afternoon convection these days. By Thursday next
week, the ridging to our east will swing west slightly putting us
back into southwesterly flow. 850mb winds will also shift to
become more easterly bringing the Gulf moisture back into the
region. This will bring our next best chance at more widespread
and heavier precipitation for Thursday and into the weekend.

Temperatures will remain much above average as the pattern over
the next week remains fairly stationary. Sunday will start out
with widespread 70s before the rest of the week warms up. Monday
through Friday locations in southeastern Montana look to be in the
80s with locations west of Billings remaining in the 70s.
Torgerson

&&

.AVIATION...

Scattered showers and thunderstorms will move northeastward across
the area this afternoon and evening. Thunderstorms could produce
large hail, strong wind gusts to 50 kt, torrential rainfall, and
MVFR conditions. Isolated showers are then expected late tonight
into Saturday morning. Low clouds look to produce MVFR conditions
mainly over south central MT and north central WY tonight into
Saturday morning. Scattered showers and thunderstorms are expected
again Saturday afternoon-evening. Mountains will be obscured. RMS

&&

.PRELIMINARY POINT TEMP/POPS...

    Sat     Sun     Mon     Tue     Wed     Thu     Fri
-----------------------------------------------------------
BIL 055/074 053/075 054/078 055/081 056/083 057/079 058/078
    88/T    55/T    23/T    23/T    24/T    36/T    57/T
LVM 048/071 046/072 047/075 049/078 049/080 051/076 051/075
    58/T    57/T    26/T    25/T    25/T    37/T    57/T
HDN 054/075 051/076 052/080 052/082 055/084 056/081 056/079
    +7/T    55/T    23/T    23/T    24/T    36/T    57/T
MLS 057/077 055/075 055/080 056/082 058/086 061/084 062/083
    85/T    54/T    22/T    32/T    12/T    24/T    45/T
4BQ 055/077 053/074 053/080 055/081 056/086 060/083 059/082
    85/T    55/T    22/T    22/T    12/T    24/T    45/T
BHK 056/081 053/075 052/079 054/082 055/084 058/083 059/082
    56/T    65/T    32/T    22/T    11/U    23/T    44/T
SHR 049/073 047/072 047/076 049/078 050/081 052/077 052/075
    97/T    46/T    13/T    23/T    14/T    36/T    57/T

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Flood Watch in effect until midnight MDT tonight FOR ZONES
      29>33-36-37-57-58-138-173-235.
     Severe Thunderstorm Watch 242 in effect until midnight MDT
      tonight FOR ZONES 30>33-36-37-57-58-138-169-171.
WY...Severe Thunderstorm Watch 242 in effect until midnight MDT
      tonight FOR ZONES 198-199.

&&

weather.gov/billings

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