747
FXUS65 KBYZ 212038
AFDBYZ
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT
238 PM MDT THU MAY 21 2026
KEY MESSAGES
- LOWER ELEVATION RAIN AND MOUNTAIN SNOW SHIFTS EAST REST OF
TODAY; EXPECT SCATTERED THUNDERSTORMS CAPABLE OF PRODUCING SMALL
HAIL AND LOCALIZED DOWNPOURS LATE TODAY NEAR THE DAKOTAS
BORDER.
- WARMING TREND AND MOSTLY DRY FRIDAY THROUGH MONDAY; EXPECT
MOUNTAIN SNOW MELT TO INCREASE RIVER FLOWS.
- CHANCE OF THUNDERSTORMS BY MIDDLE OF NEXT WEEK.
UPDATE
THE WINTER STORM WARNING FOR THE BEARTOOTHS AS BEEN CANCELLED.
DESCENDING AIR HAS MOVED INTO THE AREA BEHIND THE UPPER TROUGH
AXIS BRINGING WIDESPREAD SNOW OVER THE HIGH COUNTRY TO AN END.
EXPECT ISOALTED TO SCATTERED RIAN.SNOW SHOWERS OVER SOUTH CENTRAL
MT THROUGH THE AFTERNOON DUE TO DIURNAL INSTABILITY.
MODERATE TO HEAVY SNOW WILL CONTINUE TO IMPACT THE BIG HORNS
REGION THROUGH THE DAY. A WINTER WEATHER ADVISORY REMAINS IN
EFFECT FOR THE PRYORS/NORTHERN BIGHORNS THROUGH 9 PM. BT
DISCUSSION
NEXT 7 DAYS (THROUGH NEXT WEDNESDAY)...
DYNAMIC UPPER TROUGH AXIS CURRENTLY EXTENDS FROM CENTRAL MT
INTO WESTERN WY. ENERGY ROUNDING THE BOTTOM WILL CAUSE TROUGH TO
START SWINGING MORE EASTERLY TONIGHT AND EVENTUALLY LIFT
EAST/NORTHEAST INTO THE DAKOTAS TOMORROW MORNING. IN THE
MEANTIME, UPPER FORCING AND DEEP UPSLOPE WILL CONTINUE TO AFFECT
THE NORTH FACING SLOPES OF THE BEARTOOTHS/PRYORS/BIGHORNS. AS
TROUGH SLOWLY SLIDES EAST, PRECIPITATION WILL BEGIN TO DECREASE
FROM WEST TO EAST AS DESCENDING AIR MOVES IN BEHIND THE TROUGH
AXIS. WINTER STORM WARNING FOR THE BEARTOOTHS SET THROUGH 6 PM
THIS EVENING LOOKS REASONABLE...AS DOES THE 9 PM ENDING TIME FOR
THE WINTER WEATHER ADVISORY OVER THE PRYORS/BIGHORNS. WE DO HAVE A
SLIGHT THREAT OF THUNDERSTORMS LATE TODAY INTO THE EVENING ALONG
THE MT/DAKOTA BORDER IN THE WARM SECTOR AHEAD OT THE TROUGH.
MARGINAL SHEAR AND CAPE COULD PRODUCE HEAVY DOWNPOURS AND SMALL
HAIL, BUT BELIEVE BEST CHANCE OF THIS IS EAST IN THE DAKOTAS. ONE
MORE NOTE, THERE IS A 30-60% CHANCE OF DROPPING UNDER 32F TONIGHT
IN OUR FOOTHILLS AND NEARBY PLAINS
(LIVINGSTON/COLUMBUS/HARLOWTON/SHERIDAN). THOSE WITH FRAGILE
PLANTS OR YOUNG LIVESTOCK SHOULD BE PREPARED FOR A LIGHT FROST IN
THESE AREAS.
AS TROUGH SLIDES EAST A SURFACE LOW DEVELOPS OVER WESTERN SOUTH
DAKOTA THIS EVENING. STEEP HEIGHT FALLS AND LOW LEVEL CONVERGENCE
IS PROGGED OVER OUR EASTERN BORDER COUNTIES AND SHOULD PRODUCE
A STEADY BAND OF MODERATE PRECIPITATION OVERNIGHT AND INTO FRIDAY
MORNING. CHANCE OF AT LEAST 0.25" OF LIQUID IS >50% FOR MUCH OF
CARTER AND FALLON COUNTIES, AND A LITTLE LESS FOR PORTIONS OF
CUSTER AND POWDER RIVER. PRECIPITATION MAY LINGER RIGHT ALONG THE
DAKOTA BORDER INTO MIDDAY FRIDAY BEFORE FINALLY ENDING. OTHERWISE,
FRIDAY LOOKS WARMER AND DRIER WITH TEMPS BACK TO THE 60S. A WEAK
SHORTWAVE WITHIN THE NW FLOW ALOFT MAY BE ENOUGH TO PRODUCE WEAK
DIURNAL CONVECTION IN THE AFTERNOON AND EARLY EVENING...MAINLY
OVER THE BEARTOOTH/ABSAROKA RANGES.
WARMING TREND CONTINUES THIS WEEKEND AND INTO MONDAY AS FLOW
ALOFT TURNS ZONAL AS WE SIT OVER TOP OF A BUILDING RIDGE OF HIGH
PRESSURE. LOOK FOR 70S SATURDAY, AND 80S SUNDAY. AGAIN, THESE
WILL BE MOSTLY DRY DAYS, BUT CANNOT RULE OUT SOME WEAK DIURNAL
SHOWERS ESPECIALLY CLOSE TO THE MOUNTAINS. WE WILL ALSO SEE SOME
INCREASING WIND (15-30 MPH) IN OUR WESTERN ZONES (FOOTHILLS AND
NEARBY PLAINS) SUNDAY.
UPPER FLOW BACKS TO THE SW MONDAY AHEAD OF THE NEXT UPPER TROUGH
MOVES INTO THE PACIFIC NW. TEMPS WILL BE IN THE 80S, AND THE
PATTERN COULD EVEN CAUSE TEMPS TO PUSH NEAR 90F ON MEMORIAL DAY
FOR MANY LOCATIONS (30-70% CHANCE BILLINGS EASTWARD). BEYOND
MONDAY, MODELS DIVERGE ON HOW TO SOLVE THE PACIFIC NW
TROUGH...CUTTING IT OFF OVER OREGON, OR KEEPING AN OPEN WAVE
MOVING INTO THE NORTHERN ROCKIES. EITHER OF THESE PATTERNS DOES
RESULT IN SOME INCREASE IN PRECIP WATER ADVECTING INTO OUR EASTERN
PLAINS AT LEAST TO SOME DEGREE. SO WHAT WE CAN SAY WITH SOME
CONFIDENCE, EXPECT SEASONABLY WARM TEMPS WITH A CHANCE OF
SHOWERS/THUNDERSTORMS AS WE HEAD INTO MID WEEK. BT
AVIATION
PRECIPITATION WILL CONTINUE TO MOVE INTO SOUTHEAST MT THROUGH THE
AFTERNOON WITH A FEW ISOLATED THUNDERSTORMS POSSIBLE. MFVR AND
BRIEF IFR CONDITIONS ARE POSSIBLE UNDER ANY PRECIPITATION.
MOUNTAIN OBSCURATIONS WILL GRADUALLY CLEAR FROM WEST TO EAST THIS
EVENING AND OVERNIGHT. TS
PRELIMINARY POINT TEMP/POPS
TDY FRI SAT SUN MON TUE WED
-------------------------------------------------------
BIL 057 039/068 043/078 050/086 054/090 056/087 054/078
3/W 10/U 00/U 00/U 00/U 12/T 44/W
LVM 053 030/065 038/075 046/082 048/084 049/078 045/071
3/T 20/B 10/U 00/U 01/U 15/T 56/T
HDN 056 036/068 039/078 046/087 050/090 053/088 053/078
7/W 20/U 00/U 00/U 00/U 11/B 44/W
MLS 058 039/068 040/077 047/086 052/091 059/091 057/080
7/W 20/U 00/U 00/U 00/U 01/N 23/W
4BQ 054 039/064 039/075 046/085 052/090 059/089 056/078
7/W 80/U 01/U 00/U 00/U 01/N 33/T
BHK 061 037/064 036/075 043/085 052/091 058/089 056/079
7/T 93/W 00/U 00/U 00/U 00/N 24/W
SHR 046 030/062 034/072 039/081 044/086 047/086 046/075
+/W 50/U 01/U 00/U 01/U 01/N 45/T
BYZ WATCHES/WARNINGS/ADVISORIES
MT...WINTER WEATHER ADVISORY IN EFFECT UNTIL 9 PM MDT THIS EVENING
FOR ZONE 171.
WY...WINTER WEATHER ADVISORY IN EFFECT UNTIL 9 PM MDT THIS EVENING
FOR ZONE 198.
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