Flash Flood in Montana, June 2, 2023

Area Forecast Discussion
National Weather Service Billings MT
209 PM MDT Fri Jun 2 2023

.DISCUSSION...

Rest of Today through Sunday Night...

Heavy rain continues! Stratiform rain is strengthening along the
Beartooth foothills west of Billings as deep upslope flow and
upper-level divergence increases across the. In a move similar to
upslope snow events we get during the winter, this rain looks to
persist in this manner through the evening and overnight. While
those locations from Red Lodge through Big Timber aren't expected
to get much for storm activity, the persistent rain will add up,
with additional amounts 0.75-1.5" expected across the area.

At, north, and east of Billings will have some brief clearing this
afternoon before another round of storms passes through. Some
convective initiation is already observed across northern Rosebud
County, and this activity will increase through the afternoon. As
it's been the past couple weeks, the environment is a low-shear
one once again, meaning severe potential is low (only a small
chance for quarter size hail), but small hail pea size to half
inch in diameter can be expected with any storm. If no hail
occurs, these slow moving storms will once again produce heavy
rain, and can result in flash flooding if over 1 to 2" of rain
occurs. Most areas can still soak up a decent amount of rain which
will assist in waning off flash floods, but the area from
Billings and north through western Wheatland County and Roundup
receiving pockets of very heavy rain (2-4") yesterday evening, and
their soils are very saturated. Any storms that occur there will
take much less to result in flash flooding. Do not attempt to
cross any flooded roads, whether via walking or in a vehicle!

The weekend will see reduce rain potential, but doesn't
completely remove it. While PWATs slightly decrease, they still
remain ~2 standard deviations above normal, and we still see a
marginal excessive rainfall outlook for south-central MT. While
dry air does try to move in over the mountains, a persistent
southeast flow at the low-levels will keep moisture from the Gulf
of Mexico moving into the area. Shear still stays low, hence while
storms are still possible each day, the severe potential remains
very low (though again, small hail is likely with all these
storms). The lingering rain threat occurs with these still above
normal pwats, and slow moving nature that is expected of any
storms that occur. Vertz

Monday through Friday...

Showers and thunderstorms will continue for the extended period,
with convection mainly in the afternoon and evening each day.
Highest chances for precipitation will range generally from
50%-80% each afternoon from around KBIL to KSHR W...with lower
chances E of KBIL. Chances will be a bit lower Monday afternoon
and evening with 30-60% PoPs from around KBIL to KSHR W, as an
upper level ridge will be over the area. Ridging will persist over
the region through the period with energy moving underneath the
ridge. PWAT's will be around 1 inch from around KBIL E. Thus the
possibility of heavy rainfall with thunderstorms will continue
through Friday. Regarding severe weather, SREF showed MLCAPE of
500-1000 J/kg with little shear on Monday, and CWASP's had lower
50s in some areas through the rest of the period. Therefore, some
stronger storms are possible through the extended. High temps will
be in the 70s and 80s through Friday. Arthur

&&

.AVIATION...

MVFR/IFR or lower conditions will prevail in showers and
thunderstorms through late evening over the area. Patchy fog is
also expected W of KMLS through early Saturday morning.
Precipitation will taper off E and S of KBIL late tonight, but
MVFR/IFR conditions will continue across the entire area. Showers
and thunderstorms will once again overspread the area from W to E
during Saturday with MVFR/IFR or lower conditions. Widespread
mountain obscurations will continue through Saturday. Arthur

&&

.PRELIMINARY POINT TEMP/POPS...

    Sat     Sun     Mon     Tue     Wed     Thu     Fri
-----------------------------------------------------------
BIL 056/071 056/075 057/081 059/083 060/082 060/083 060/080
    87/T    45/T    23/T    35/T    44/T    46/T    56/T
LVM 051/066 049/073 051/079 052/079 054/079 055/079 055/077
    99/T    45/T    45/T    37/T    46/T    57/T    57/T
HDN 056/075 056/078 055/083 057/086 058/085 059/086 060/082
    76/T    35/T    23/T    23/T    33/T    35/T    45/T
MLS 058/080 060/083 062/087 063/088 064/088 065/088 065/085
    72/T    32/T    21/U    22/W    22/T    23/T    44/T
4BQ 056/079 058/081 058/084 060/086 061/086 062/087 061/084
    63/T    34/T    21/U    12/T    12/T    23/T    45/T
BHK 056/082 059/083 058/085 059/086 060/086 060/086 060/084
    41/B    22/T    11/U    12/W    11/U    12/T    34/T
SHR 050/073 051/075 051/080 053/081 054/082 055/081 055/078
    87/T    36/T    23/T    23/T    24/T    35/T    46/T

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Flood Watch in effect until midnight MDT tonight FOR ZONES
      29>32-34-40-42-56>58-63>68-138-139-141-169>173-228-235.
WY...Flood Watch in effect until midnight MDT tonight FOR ZONES
      198-199.

&&

weather.gov/billings

Preliminary Local Storm Report
National Weather Service Billings, MT
614 PM MDT Fri Jun 02 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0530 PM     Heavy Rain       7 SW Billings           45.71N 108.65W
06/02/2023  M5.50 inch       Yellowstone        MT   Public

0600 PM     Heavy Rain       5 W Melville            46.10N 110.05W
06/02/2023  M1.00 inch       Sweet Grass        MT   Co-Op Observer

&&

TS