436
FXUS65 KBYZ 140001
AFDBYZ

Area Forecast Discussion...Updated
National Weather Service Billings MT
601 PM MDT Sat Jul 13 2024

.UPDATE...

Severe Thunderstorm Watch 525 has been issued for Rosebud, Custer,
Fallon and Carter counties through midnight tonight. Main threats
are large hail and damaging winds. For Rosebud County, the severe
threat will remain north of I-94. Have updated PoPs and weather
to latest trends. STP

&&

.DISCUSSION...

Through Monday night...

Several concerns this forecast period. One was the strong cluster
of thunderstorms moving E through S. Saskatchewan. Models varied
in their solutions of whether the cluster would impact the eastern
forecast area and if it does, they also differed on timing. HREF
brings it SE through the area, mostly E of Rosebud County from
about 00Z thru 08Z tonight. GFS/WRF keep it NE of the forecast
area. ECMWF clips NE zones while weakening the system. If it comes
in, HREF showed a few fairly strong helicity tracks and strong
wind gusts. KBHK sounding showed 1000-1500 J/kg of MUCAPE and Bulk
Effective Shear up to 60 kt, as well as several hundred m2/sec2 of
helicity. Thus, if this cluster moves into the eastern zones,
strong gusty winds, large hail and a possible tornado would be the
main threats. SPC has an enhanced threat area NE of KMLS and over
Fallon County. Slight risk includes KMLS and Ekalaka, with
marginal further W to Hysham. Given the uncertainty in track, had
a 30% PoP over Fallon/NE Custer County through 06Z with 20% PoPs
to the S. Kept a 20% PoP over Powder River and Carter Counties
after midnight MDT. System pushes a backdoor cold front into the E
tonight.

Also for late this afternoon through 03Z tonight, monsoonal flow
will bring a 20% chance of thunderstorms to the southern mountains
and adjacent areas. Included the KBIL area based on CAMS. Low
temps will range from the upper 50s W to the mid 60s E.

On Sunday, a weak wind shift front will push SE through the area.
A cold front will push S through the area Sun. night or Monday.
Raised wind gusts toward the NBM 90th percentile Sunday and
Monday afternoon into the early evening given good mixing and
signals from ECMWF ensemble meteograms. Other forecast concerns
included the heat on Sunday and fire weather concerns. High temps
will be around 100 degrees with lows in the mid to upper 60s
central and E. Heat Advisory was in good shape and set to end Sun.
evening. Temps on Monday will be lower...in the upper 80s to
around 90 degrees. For fire concerns on Sunday...hot temps and
RH`s in the teens, along with gusty winds in the far W and far E
are concerning. Fuels are not quite ready in the W. Will have
another round of monsoonal thunderstorms over the southern
mountains extending to KBIL and KSHR again. HDW showed around a
50% chance of exceeding the 90th percentile over a small portion
of the E. Have no PoPs in the east, so will continue the
headlines, highlighting the concerns. Monsoonal moisture will
affect the area again for Mon. afternoon through Mon. night.
Arthur

Tuesday through Saturday...

Clusters were in good agreement with strong upper ridging
prevailing over the region through the extended. Another period
of above normal temperatures is in store for the region with highs
in the 90s. Chances of temps hitting 100 degrees are 10% or less
through Saturday. Period will also be quite dry. PoPs each
afternoon and evening were highest in the SW mountains at around
40%. Otherwise had 20% PoPs adjacent to the mountains Chances for
QPF reaching 0.10 inches were highest in the high elevations of
the SW in the teens to 20%. Fosberg was low thru the period for
fire weather concerns. CWASP values for severe potential were also
low. Arthur

&&

.AVIATION...

VFR conditions will prevail over the next 24 hours with only
slight reductions to slant range visibility from smoke. A cluster
of thunderstorms, some strong to severe look to track through/near
KMLS and KBHK this evening, generally between 01Z to 05Z. With
these storms, strong erratic winds and large hail are the main
threats, with heavy rain temporarily reducing visibility. Weak
showers and thunderstorms also exist along and near the MT/WY
border this evening. The main threat with this activity is erratic
winds. Sunday will start out quiet before another round of
showers and thunderstorms (15-45% chance) moves mainly along the
MT/WY border once again. Arends

&&

.PRELIMINARY POINT TEMP/POPS...

    Sun     Mon     Tue     Wed     Thu     Fri     Sat
-----------------------------------------------------------
BIL 064/100 066/090 063/094 064/094 065/096 065/095 065/094
    22/T    20/U    11/U    01/U    11/U    11/B    12/T
LVM 058/097 058/092 056/092 056/092 056/094 059/094 058/092
    11/B    11/U    12/T    12/T    12/T    12/T    12/T
HDN 062/100 064/090 060/095 060/094 061/098 062/097 062/095
    22/T    20/U    11/U    11/U    11/U    11/U    11/U
MLS 065/099 065/087 061/092 062/089 063/094 065/093 064/092
    30/U    10/U    10/U    10/U    10/U    11/U    11/U
4BQ 066/100 069/089 062/092 062/089 063/094 063/093 062/092
    20/U    20/B    11/U    11/U    11/U    12/T    11/U
BHK 062/098 062/084 057/085 056/086 058/091 060/090 060/090
    31/U    10/U    11/U    10/U    10/U    11/U    11/U
SHR 060/100 064/089 058/091 055/091 057/093 059/093 059/090
    22/T    22/T    22/T    12/T    11/U    12/T    12/T

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Heat Advisory in effect until 9 PM MDT Sunday FOR ZONES
      29>34-36-37-40-42-56>58-63>66-138-139-141-169-170-172-173-228-235.
     Severe Thunderstorm Watch 525 in effect until midnight MDT
      tonight FOR ZONES 31>33-37-58.
     Red Flag Warning in effect until midnight MDT tonight FOR
      ZONE 117.
WY...Heat Advisory in effect until 9 PM MDT Sunday FOR ZONE 199.

&&

$$
weather.gov/billings