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000
FXUS65 KBYZ 070918
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
318 AM MDT Wed Jun 7 2023

.DISCUSSION...

Today through Friday morning...

Persistent pattern remains in place over the region with upper
ridging to the east and troughing to the west. Waves of weak
energy, and moisture advecting in from the south and southeast
will continue to bring daily chances for showers and
thunderstorms.

Showers and thunderstorms are expected to develop over the higher
terrain by this afternoon, moving off onto the lower elevations
during the evening and night. Low-level easterly winds will
continue to support PWATs near or more than an inch. Latest
guidance continues to indicate the easterly winds, along with a
slight increase in heights with the ridge shifting a bit west may
keep a cap in place over portions of the area through much of the
day, which would inhibit the convection. Greatest coverage with storms
today will be near the mountains. CAPE values will approach 1500
J/kg, with only very weak shear in place. Locally heavy rainfall
and flash flooding is possible with any stronger, or persistent
thunderstorms. Heading into Thursday, an upper low currently over
southern California will start to lift north and east into the
Great Basin, advecting some associated vorticity into the region.
PWATs will again be high, with some locations approaching 1.25
inches or more. CAPE values will approach 1500 J/kg, and shear
looks to be slightly better, but not great (20-30 kts).
Thunderstorms will be more widespread given the above, lifting
through the area during the afternoon and evening hours, into the
night. A few of the thunderstorms could be strong. Have gone
ahead and issued a Flood Watch for Thursday afternoon through late
Thursday night for areas from Rosebud County west. Given the very
moist environment, and already saturated soils from recent
rainfall, storms that produce heavy rainfall will have a high
potential to cause flash flooding.

Temperatures will continue to range from the 70s over the west, to
the 80s over the east, with valley locations along the Yellowstone
River approaching the upper 80s. Mild nights will continue with
lows in the 50s to lower 60s. STP

Friday through Tuesday...

The weather pattern in the extended forecast looks similar to the
one we have been in for the past several days, with an upper
trough meandering over the eastern Pacific and western US and
upper air high pressure over northern MT to Alberta/Saskatchewan.
This pattern should facilitate more easterly flow into our area
for the first part of the weekend, which will supply more
moisture-rich air into the area.

Expect more rounds of scattered showers and thunderstorms across
the area Friday (60-90% chance) and Saturday (20-90% chance). A
frontal boundary should be in the area, its exact location
uncertain at this time, that should help to initiate widespread
convection and increase areal coverage of showers and
thunderstorms. There is a localized flood concern especially on
these days given the ample moisture in place (precipitable water
values of 1.00-1.30 inches) and the likelihood for storms to move
slowly.

Then drier air looks to move in from the northeast on
Sunday, with the air getting so dry in southeast MT that it should
prevent showers and thunderstorms from developing there that day.
South central MT and north central WY still look to have adequate
precipitable water values of 0.75-1.00 inches to support more
shower and thunderstorm development on Sunday. The drier air then
looks to exit southeast MT on Monday so that scattered showers and
thunderstorms can occur across the area Monday and Tuesday. For
Sunday into Tuesday, the lower precipitable water values should
help lower the precipitation potential from thunderstorms
somewhat, but if storms were to train over the same areas there
still could be localized flood concerns.

High temperatures will generally be in the 70s and 80s Friday,
Monday and Tuesday, and 70s Saturday and Sunday. Low temperatures
will be in the 50s and 60s Friday night then 50s Saturday night
through Monday night. RMS

&&

.AVIATION...

Scattered showers and isolated thunderstorms will occur from
north central WY to southeast MT, east of KBIL and west of KBHK,
through 12z today. Otherwise, patchy fog is possible through
about 15z today across the area, then VFR should prevail.
Scattered showers and thunderstorms will develop over the
mountains late this morning then expand to the rest of the area
after 18z today. Thunderstorms could produce heavy downpours,
localized MVFR-IFR conditions and gusty winds. Mountains will be
obscured especially in the afternoon and evening. RMS

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Thu     Fri     Sat     Sun     Mon     Tue
-------------------------------------------------------
BIL 081 059/081 058/080 059/073 057/076 056/078 057/077
    3/T 37/T    77/T    78/T    54/T    25/T    46/T
LVM 080 054/076 053/079 053/076 054/073 052/074 052/076
    5/T 39/T    86/T    57/T    57/T    37/T    57/T
HDN 083 059/085 058/081 059/075 056/078 055/081 055/078
    3/T 46/T    68/T    78/T    43/T    14/T    45/T
MLS 088 063/089 064/084 061/075 056/079 056/083 058/082
    2/T 33/T    47/T    75/T    21/U    12/W    24/T
4BQ 087 061/087 061/083 059/072 054/075 054/081 055/079
    3/T 23/T    48/T    77/T    32/T    13/W    35/T
BHK 089 060/088 060/082 057/075 051/077 051/081 054/082
    2/T 22/T    36/T    63/W    10/U    01/U    23/T
SHR 080 054/081 053/079 053/073 052/073 051/076 050/075
    5/T 46/T    48/T    58/T    54/T    15/T    36/T

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Flood Watch in effect from Thursday afternoon through late
      Thursday night FOR ZONES
      29>31-34-40-42-56>58-63>68-138-139-141-169>173-228-235.
WY...Flood Watch in effect from Thursday afternoon through late
      Thursday night FOR ZONES 198-199.

&&

$$
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