537  
FXUS65 KBYZ 140258  
AFDBYZ  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE BILLINGS MT  
858 PM MDT TUE APR 13 2021  
   
UPDATE
 
 
SOME MID LEVEL CONVERGENCE HAS SHIFTED A LITTLE FARTHER SOUTH AND  
WAS BRUSHING THE NORTHERN TIER OR ZONES WITH SOME LIGHT SNOWFALL  
FORM JUDITH GAP TO JUST NORTH OF ROUNDUP. HAVE EXTENDED POPS  
FARTHER SOUTH TO GATHER THIS. ALSO, UPSLOPE FLOW WAS PRODUCING A  
MORE PERSISTENT BAND OF LIGHT SNOW ALONG THE FOOTHILLS AND RED  
LODGE WEBCAM WAS SHOWING A LITTLE ACCUMULATION ON THE ROADWAYS.  
MODELS WEAKEN THIS SOME OVERNIGHT AS WINDS LIGHTEN BUT DECIDED TO  
RAISE POPS TO LIKELY THERE AS LIGHT SNOW SHOULD CONTINUE FOR  
SEVERAL MORE HOURS BEFORE TAPERING OFF LATE TONIGHT. TWH  
 

 
   
DISCUSSION
 
 
TONIGHT THROUGH WEDNESDAY NIGHT...  
 
SATELLITE IMAGERY SHOWS AN UPPER LOW OVER MN, AND ANOTHER TO OUR  
WEST OVER OR, LEAVING US WITHIN THE QUIET COL REGION. MAIN AREA OF  
ASCENT IS TO OUR NORTH, AND THIS IS WHERE COLD CLOUD TOPS AND  
HEAVIER PRECIP HAVE BEEN, BUT SHALLOW/MOIST INSTABILITY EXTENDING  
INTO THE DENDRITIC LAYER IS RESULTING IN SOME LIGHT SNOW SHOWERS  
AND FLURRIES IN OUR FORECAST AREA TODAY. NOTICE THE FLURRIES IN  
BILLINGS AT 225 PM. ALSO NOTE THE VERY CELLULAR LOOK TO THE BROKEN  
CLOUD FIELD IN SOUTHEAST MT. THE POTENTIAL FOR LIGHT SNOW SHOWERS  
OR FLURRIES WILL CONTINUE THRU THE NIGHT, WITH FOCUS SHIFTING  
WEST OVER TIME AS WE BECOME MORE UNDER THE INFLUENCE OF EVOLVING  
LOW OVER THE NORTHERN GREAT BASIN. ONE OTHER ISSUE FOR TONIGHT:  
ADVECTION OF LOW LEVEL MOISTURE FROM WHERE PRECIP IS FALLING TO  
OUR NORTH, AND UPSLOPE WINDS, SHOULD RESULT IN A DEVELOPING  
STRATUS FIELD AS THE NIGHT WEARS ON.  
 
WEDNESDAY SHOULD BE A MOSTLY DRY DAY AS MID LEVELS BECOME WARMER  
AND SHALLOW INSTABILITY BECOMES EVEN MORE SHALLOW. CYCLONIC  
EASTERLY MID LEVEL WINDS WILL BE ENOUGH FOR AREAS OF LIGHT SNOW  
ALONG OUR WESTERN FOOTHILLS. TEMPS TOMORROW WILL REMAIN CHILLY  
WITH HIGHS IN THE 30S TO LOW 40S, OR PRETTY CLOSE TO TODAY.  
UPSLOPE STRATUS MAY AFFECT TEMPS SOMEWHAT.  
 
SNOW CHANCES WILL INCREASE WEDNESDAY NIGHT AS UPPER LOW MOVES TO  
NORTHERN UT AND A VORT MAX LIFTS THRU WY. HEAVIER PRECIP WILL BE  
TO OUR SOUTH IN WY, WHERE MAIN REGION OF BAROCLINICITY WILL EXIST,  
BUT WITH DEEPENING MOISTURE AND ASCENT THE CYCLONIC EASTERLY FLOW  
WILL PRODUCE PRECIP IN OUR WESTERN AND SOUTHERN UPSLOPE AREAS,  
ESPECIALLY AS THE DENDRITIC LAYER AGAIN BECOMES MORE INVOLVED.  
OVERALL SNOW ACCUMS WILL BE LIGHT OVER THE NEXT 36 HOURS, W/ 1-2  
INCHES AT MELVILLE AND RED LODGE BY EARLY THURSDAY. JKL  
 
THURSDAY THROUGH TUESDAY...  
 
THROUGH THE END OF THE WEEK CONTINUES TO LOOK COLD AND WET. STILL  
WATCHING FOR A CUT OFF LOW TO TRACK JUST SOUTH OF THE AREA. ALONG  
WITH PRODUCING SOME GOOD UPSLOPE FLOW FOR THE FOOTHILLS AND  
MOUNTAINS, BUT IT WILL ALSO ALLOW FOR A GOOD MOISTURE TAP FROM THE  
CENTRAL PLAINS. AREAS ON THE NORTHEAST SIDE OF THE BIGHORN  
MOUNTAINS ARE AREAS AROUND RED LODGE COULD SEE A FEW INCHES OF  
ACCUMULATION. FRIDAY ANOTHER WAVE DROPPING OUT OF CANADA WILL  
PHASE WITH THE LOW IN THE CENTRAL ROCKIES, WHICH WILL SHIFT WINDS  
TO BE MORE NORTHWESTERLY WHICH WILL REDUCE THE UPSLOPE FLOW SOME  
FOR THE BIG HORNS AND RED LODGE.  
 
THINGS SHOULD DRY OUT AND WARM UP FOR SATURDAY INTO SUNDAY, AS  
SOME RIDGING MOVES DOWN INTO THE AREA. THIS WILL BE FAIRLY SHORT-  
LIVED AS ANOTHER CLIPPER SYSTEM DROPS INTO THE AREA SUNDAY NIGHT  
INTO MONDAY. THE LATEST RUNS HAVE COME IN WITH FAIRLY GOOD  
AGREEMENT THAT THIS COULD BE A DECENT PRECIPITATION EVENT. WILL  
MONITOR AND IF THIS CONSISTENCY CONTINUES, WILL NEED TO TREND THE  
FORECAST UPWARD. REIMER  
 

 
   
AVIATION
 
 
AREAS OF LIGHT SNOW WILL PERSIST ACROSS THE FORECAST AREA TONIGHT  
WITH VFR TO MVFR CONDITIONS PREVAILING THIS EVENING, DIMINISHING  
TO MVFR TO IFR OVERNIGHT AS SNOW INTENSIFIES FROM THE SOUTHWEST BY  
MORNING. UPSLOPE EAST/NORTHEAST WINDS WILL ALSO BRING THE  
POTENTIAL FOR FOG TO AREAS EAST OF BILLINGS WITH LOCAL LIFR  
CONDITIONS POSSIBLE (KBHK, KMSL, K4BQ). EXPECT MOUNTAIN  
OBSCURATION TO BE PREDOMINANT FOR ALL MOUNTAIN RANGES TONIGHT  
THROUGH WEDNESDAY. CHAMBERS  
 

 
   
PRELIMINARY POINT TEMP/POPS
 
 
WED THU FRI SAT SUN MON TUE  
-----------------------------------------------------------  
BIL 024/038 027/041 032/047 030/055 033/062 034/051 030/060  
22/S 36/S 63/O 11/B 01/B 33/O 11/U  
LVM 023/037 027/039 029/045 028/056 032/061 034/052 030/060  
23/S 45/S 42/O 10/U 01/B 22/O 11/U  
HDN 021/040 027/043 031/047 028/055 029/062 032/051 028/060  
21/E 26/O 74/O 11/B 01/B 33/O 11/U  
MLS 022/040 025/043 029/046 025/052 029/061 031/049 026/057  
32/S 02/O 42/S 00/B 01/B 21/B 11/U  
4BQ 021/040 026/041 030/042 026/048 028/058 031/047 026/055  
20/E 15/O 64/O 11/B 01/U 22/O 11/U  
BHK 018/037 022/041 026/041 023/047 026/058 026/046 022/053  
22/S 02/S 53/O 11/B 01/B 21/B 11/U  
SHR 018/039 024/038 027/039 024/047 025/056 028/046 023/054  
23/S 78/S 86/O 22/O 01/U 33/O 11/U  
 

 
   
BYZ WATCHES/WARNINGS/ADVISORIES
 
 
MT...NONE.  
WY...NONE.  
 

 
 

 
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