702  
FXUS65 KBYZ 272121  
AFDBYZ  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BILLINGS MT  
321 PM MDT MON MAR 27 2017  
   
SHORT TERM...VALID FOR TUE AND WED
 
 
AN UPPER TROUGH WAS APPROACHING THE AREA TO THE WEST AND WAS  
GENERATING SCATTERED SHOWERS WEST OF BILLINGS. THESE SHOWERS WILL  
BECOME MORE NUMEROUS AS THE TROUGH APPROACHES. RAISED POPS FOR  
TONIGHT. MODELS HAVE BEEN ROBUST ON QPF AMOUNTS SOUTH OF BILLINGS  
INTO SHERIDAN COUNTY THROUGH TUESDAY MORNING FOR THIS EVENT WITH  
THE GFS HEAVIEST. HAVE MAINTAINED THE WINTER WEATHER ADVISORY FOR  
THE BIGHORN MOUNTAINS, WITH THE HEAVIEST SNOW BEING LATE TONIGHT  
THROUGH TUESDAY MORNING. 850MB TEMPERATURES STAY FAIRLY WARM  
THROUGH THE NIGHT, BUT DO FALL TO AROUND 1C ALONG THE FOOTHILLS  
LATE TONIGHT. RAIN COULD MIX WITH SOME WET SNOW OVER THE WESTERN  
FOOTHILLS. KEPT ACCUMULATIONS DOWN DUE TO WARM DAY TODAY AND THE  
LACK OF DYNAMIC FORCING, BUT SHOULD BE ABLE TO PUT AN INCH,  
POSSIBLY TWO, DOWN AT RED LODGE OVERNIGHT.  
 
THE SYSTEM WORKS SOUTHEAST THROUGH THE DAY OVER SOUTH CENTRAL  
ZONES AND SHERIDAN COUNTY, BUT THE FORCING GETS HELD UP OVER AN  
INVERTED SURFACE TROUGH OVER SOUTHEAST MONTANAN DURING THE DAY  
TUESDAY. HAVE RAISED POPS TUESDAY FOR THE SOUTHEAST, AS THE GFS  
WAS PRODUCING AROUND A HALF INCH OF RAINFALL OVER CARTER COUNTY.  
THE REST OF THE AREA WILL DRY OUT TUESDAY AFTERNOON.  
 
TUESDAY NIGHT AND WEDNESDAY WILL BE A DRYING PERIOD FOR THE  
FORECAST AREA AS LOW LEVEL DOWNSLOPE FLOW TAKES OVER. TEMPERATURES  
WILL BE HELD IN THE MID 40S TO MID 50S TUESDAY, WITH CLOUDS AND  
SHOWERS AROUND, BUT WILL BE ALLOWED TO MODIFY INTO THE 60S ON  
WEDNESDAY WITH MORE SUNSHINE. TWH  
   
LONG TERM...VALID FOR THU...FRI...SAT...SUN...MON
 
 
AN ACTIVE WEATHER PATTERN WILL CONTINUE THROUGH THE EXTENDED  
PERIOD...ESPECIALLY DURING THE BEGINNING OF THE WEEK.  
TEMPERATURES WILL GENERALLY BE NEAR OR JUST ABOVE NORMAL THROUGH  
THE WEEK.  
 
THE BIG WEATHER STORY OF THE EXTENDED PERIOD IS A LARGE UPPER  
LEVEL LOW. THIS LOW WILL APPROACH THE WESTERN US THURSDAY AND  
THEN STRENGTHEN AND DIVE TOWARDS THE FOUR CORNERS REGION BY  
FRIDAY AFTERNOON. AS THIS UPPER LEVEL LOW MOVES SOUTHEAST THURSDAY  
AFTERNOON RAIN AND HEAVY MOUNTAIN SNOW WILL BEGIN TO OVERSPREAD  
THE REGION AS GOOD UPPER LEVEL SUPPORT FORMS AN AREA OF LOW  
PRESSURE OVER WYOMING. RAIN AND MOUNTAIN SNOW AMOUNTS ARE HIGHLY  
UNCERTAIN NOW GIVEN THE FACT THE MODEL DIFFERENCES IN THE STRENGTH  
OF THE LOW PRESSURE. THE GFS IS STRONGER WITH THIS LOW AND WITH  
THE UPPER LEVEL SUPPORT, SO PRECIPITATION AMOUNTS ARE HIGHER WITH  
THIS SOLUTION. ON THE OTHER HAND THE EC AND CANADIAN SOLUTIONS ARE  
WEAKER WITH THIS LOW PRESSURE AND MUCH FURTHER SOUTH WITH THE  
PARENT UPPER LEVEL LOW, SO THEY ARE A LITTLE BIT DRIER. RIGHT NOW  
THE FORECAST CALLS FOR NEAR AN INCH OF PRECIPITATION IN THE  
MOUNTAINS (AMOUNTING TO 8-12 INCHES OF SNOW), AND ABOUT 0.5 INCHES  
OF RAIN IN THE LOWER ELEVATIONS. FOOTHILLS WILL SEE A MIX OF RAIN  
AND SNOW, WITH PRECIPITATION AMOUNTS NEARING 0.75 INCHES. FORECAST  
PRECIPITATION AMOUNTS WILL CHANGE AS THE MODELS COME INTO BETTER  
AGREEMENT SO BE SURE TO STAY UP TO DATE WITH THE FORECAST.  
 
WHILE PRECIPITATION AMOUNTS VARY, MOST MODEL SOLUTIONS ARE IN  
AGREEMENT THAT THINGS WILL CLEAR OUT OVERNIGHT FRIDAY WITH A NICE  
BEGINNING TO THE WEEKEND POSSIBLE ON SATURDAY. AFTER THAT, MODEL  
SOLUTIONS BEGIN TO QUICKLY DIVERGE SO LEFT RAIN CHANCES IN THE  
FORECAST ON SUNDAY AND MONDAY UNTIL MODEL AGREEMENT IMPROVES.  
DOBBS  
 

 
   
AVIATION
 
 
A DISTURBANCE WILL WORK IN TONIGHT AND PRODUCE AN AREA OF SHOWERS  
OVER WESTERN LOCATIONS (KLVM). THESE SHOWERS WILL SPREAD INTO  
CENTRAL LOCATIONS (KBIL/KSHR) OVERNIGHT TONIGHT AND CONTINUE INTO  
TUESDAY MORNING. THE HEAVIER SHOWERS WILL LOWER CONDITIONS TO MVFR  
NEAREST THE MOUNTAINS AND FOOTHILLS. SOME WET SNOW WILL MIX IN  
WITH THE RAIN OVER ELEVATIONS ABOVE 4500 FEET AND CAUSE LOCAL IFR  
TO LIFR CONDITIONS. THE EAST (KMLS/KBHK) WILL REMAIN VFR THROUGH  
THE NIGHT. THE MOUNTAINS WILL BE OBSCURED WITH AREAS OF MODERATE  
TO HEAVY SNOW. TWH  
 

 
   
PRELIMINARY POINT TEMP/POPS
 
 
TUE WED THU FRI SAT SUN MON  
-----------------------------------------------------------  
BIL 041/055 035/063 041/061 042/052 033/057 038/062 040/061  
66/W 10/B 13/R 65/R 21/U 11/B 12/W  
LVM 032/054 029/060 038/055 034/049 029/057 035/061 036/058  
93/W 11/N 25/R 53/O 11/U 11/B 22/W  
HDN 039/053 032/064 038/065 041/054 032/059 035/063 036/063  
56/W 10/B 13/R 55/R 31/B 10/B 12/W  
MLS 041/056 036/064 040/068 044/054 035/058 037/064 040/064  
26/W 30/B 11/E 44/R 31/B 10/B 12/W  
4BQ 041/050 035/062 038/067 042/054 035/055 036/062 039/064  
38/W 61/B 01/B 46/R 61/B 10/B 12/W  
BHK 037/055 036/061 037/068 040/055 034/055 034/060 037/061  
26/W 71/B 01/B 35/R 51/B 10/B 02/W  
SHR 035/046 030/058 034/062 038/051 032/055 033/060 035/061  
68/W 20/B 02/R 76/R 41/B 10/B 12/W  
 

 
   
BYZ WATCHES/WARNINGS/ADVISORIES
 
 
MT...NONE.  
WY...WINTER WEATHER ADVISORY IN EFFECT UNTIL 9 PM MDT TUESDAY FOR  
ZONE 98.  
 

 
 

 
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