687
FXUS65 KBYZ 220009
AFDBYZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
609 PM MDT THU MAY 21 2026
KEY MESSAGES
- 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
HIGH ELEVATION SNOW IN THE BIGHORNS HAS TAPERED TO LIGHT SNOW
SHOWERS AND FLURRIES, AND HAVE CANCELLED THE WINTER WEATHER
ADVISORY. SNOTELS SHOW 4-8" ACCUMULATIONS IN THE BIGHORNS TODAY.
AREA OF PRECIP HAS LIGHTENED CONSIDERABLY OVER THE PAST FEW HOURS,
AS IT CONTINUES TO SHIFT EASTWARD. THERE IS STILL ENERGY LIFTING
OUT OF EASTERN WY SO EXPECT SHOWERS TO SPREAD INTO OUR FAR EAST
THIS EVENING, BUT BAROCLINICITY IS FADING AND PRECIP AMOUNTS WILL
BE LIGHTER THAN EXPECTED EARLIER (UP TO 0.10-0.20"). ADDITIONALLY,
THE INSTABILITY AXIS HAS SHIFTED INTO THE WESTERN DAKOTAS SO THE
T-STORM RISK IN OUR FAR EAST HAS ENDED. TO THE WEST, WE ARE SEEING
ISOLATED WEAK DIURNAL CONVECTION ON THE BACK SIDE OF THE TROF,
WHERE MESOANALYSIS SHOWS UP TO ~200 J/KG OF CAPE UNDER THE COLDER
AIR ALOFT. THIS WILL PERSIST INTO THE EARLY EVENING BUT SHOULD
TAPER OFF BY SUNSET. SHOWERS NEAR THE DAKOTAS BORDER MAY LINGER
INTO EARLY FRIDAY MORNING, OTHERWISE IT WILL BE A QUIET NIGHT OF
WEATHER WITH LOW TEMPS DROPPING TO THE 30S. IN FACT, THE RECORD
LOW FOR MAY 22 AT LIVINGSTON IS 27F AND COULD BE CHALLENGED. JKL
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
00Z DISCUSSION...
AN AREA OF RAIN WILL CONTINUE TO MOVE EASTWARDS WHICH WILL RESULT
IN SITES SUCH AS KMLS/KSHR OCCASIONALLY DIPPING TO MVFR THROUGH
04Z. FATHER EAST TOWARDS KBHK, TRANSIENT MVFR CONDITIONS WILL
CONTINUE THROUGH MOST OF THE PERIOD. KBIL/KLVM WILL SEE SCATTERED
SHOWERS THROUGH ROUGHLY THE SAME TIME (04Z). THESE SHOWERS ARE
CONVECTIVE IN NATURE AND THUS ERRATIC WINDS NEAR THESE SHOWERS
SHOULD BE ANTICIPATED. A STRAY STRIKE OF LIGHTNING CANNOT BE RULED
OUT. WINDS WILL REMAIN LIGHT ACROSS ALL SITES FOR THE DURATION OF
THE PERIOD WITH A NW COMPONENT. MOUNTAINS WILL BE FULLY OBSCURED
THROUGH 06Z AND PARTIALLY OBSCURED THROUGH 15Z. WMR
PRELIMINARY POINT TEMP/POPS
FRI SAT SUN MON TUE WED THU
-----------------------------------------------------------
BIL 039/068 043/078 050/086 054/090 056/087 054/078 052/079
10/U 00/U 00/U 00/U 12/T 44/W 22/T
LVM 030/065 038/075 046/082 048/084 049/078 045/071 044/073
22/W 10/U 00/U 01/U 15/T 56/T 34/T
HDN 036/068 039/078 046/087 050/090 053/088 053/078 050/081
20/U 00/U 00/U 00/U 11/B 44/W 23/T
MLS 039/068 040/077 047/086 052/091 059/091 057/080 054/082
20/U 00/U 00/U 00/U 01/N 23/W 22/T
4BQ 038/064 039/075 046/085 052/090 059/089 056/078 053/079
50/U 01/U 00/U 00/U 01/N 33/T 32/T
BHK 037/064 036/075 043/085 052/091 058/089 056/079 052/079
72/W 00/U 00/U 00/U 00/N 24/W 33/T
SHR 030/064 034/072 039/081 044/086 047/086 046/075 044/078
40/U 01/U 00/U 01/U 01/N 45/T 33/T
BYZ WATCHES/WARNINGS/ADVISORIES
MT...NONE.
WY...NONE.
WEATHER.GOV/BILLINGS
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