620  
FXUS65 KBYZ 271556  
AFDBYZ  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE BILLINGS MT  
956 AM MDT THU JUL 27 2017  
   
UPDATE
 
 
PV MOVING THROUGH THE REGION THIS MORNING WAS GENERATING AN AREA  
OF SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ACROSS THE CENTRAL  
ZONES. ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS ARE  
EXPECTED TO DEVELOP ACROSS THE AREA THROUGH THE DAY AS ENERGY FROM  
AN APPROACHING SHORTWAVE MOVES IN FROM THE WEST AND MONSOONAL  
MOISTURE AND LOW LEVEL MOISTURE ADVECTS INTO THE REGION. MODELS  
HAVE BEEN CONSISTENT IN A MORE ORGANIZED AREA OF CONVECTION  
FORMING ACROSS FAR SE MONTANA DURING THE LATE MORNING/EARLY  
AFTERNOON HOURS, AND MOVING OFF TO THE EAST, WITH RE-DEVELOPMENT  
OVER THE SAME AREA LIKELY TO CONTINUE INTO THE EVENING. A FEW  
STRONG TO POTENTIALLY SEVERE STORMS ARE POSSIBLE ACROSS SE MONTANA  
WHERE MARGINAL SHEAR AND INSTABILITY WILL BE PRESENT. MAIN  
THREATS BEING WIND, AND TO A LESSER EXTENT HAIL. STORMS WILL  
ALSO BE CAPABLE OF PRODUCING HEAVY RAIN WITH PWATS IN EXCESS OF  
AN INCH, AND STORM MOTIONS EXPECTED TO BE FAIRLY SLOW. HAVE  
UPDATED SKY, POPS, AND WINDS TO CURRENT TRENDS. THE REST OF THE  
FORECAST REMAINS ON TRACK AND THE PREVIOUS FORECAST DISCUSSION AND  
AN UPDATED AVIATION DISCUSSION ARE BELOW. STP  
 

 
   
SHORT TERM...VALID FOR TDY AND FRI
 
 
MONSOONAL MOISTURE WILL CONTINUE TO MOVE INTO THE AREA FROM THE  
SOUTHWEST TODAY, ALONG WITH A FEW WEAK DISTURBANCES EMBEDDED IN  
THE SW FLOW ALOFT. NOT A LOT OF FOCUS MECHANISMS TO GRAB ONTO IN  
THIS PATTERN AND MODELS (ESPECIALLY CAMS) ARE GENERATING A LOT OF  
ANOMALOUS VORT CENTERS FROM CONVECTION THAT HASN'T OCCURRED. AS A  
RESULT HARD TO PINPOINT ANY GIVEN PERIOD AS BETTER THAN ANY OTHER  
FOR PRECIPITATION CHANCES. SO, HAVE BROADBRUSHED 20 TO 40 POPS  
ACROSS THE AREA TODAY AND TONIGHT WITH HIGHEST PRECIPITATION  
CHANCES OVER SE MT WHERE SOUTHERLY FLOW HAS INCREASED PRECIPITABLE  
WATER VALUES OVER AN INCH. LIGHT WINDS FROM THE SURFACE TO  
15-20KFT WILL BRING SLOW STORM MOTIONS TODAY AND COMBINED WITH  
HIGH PWATS WILL BRING A CHANCE FOR LOCALLY HEAVY RAINFALL WITH ANY  
STORMS, ESPECIALLY FOR AREAS EAST OF BILLINGS. GIVEN DRY GROUND  
CONDITIONS AND A LACK OF A FOCUS FOR ORGANIZED CONVECTION FLASH  
FLOOD THREAT LOOKS MINIMAL. AS DOES THE THREAT FOR SEVERE STORMS  
AS CAPE VALUES LOOK SUFFICIENT FOR A FEW STRONG STORMS BUT SHEAR  
IS LACKING. TEMPERATURES TODAY WILL BE JUST A BIG COOLER THAN  
YESTERDAY BASED ON MORE SUBSTANTIAL CLOUD COVER, BUT STILL NEAR  
90. NOT MUCH DIFFERENCE IN THE FORECAST BETWEEN TODAY AND FRIDAY  
WITH ISOLATED TO SCATTERED MAINLY LATE DAY SHOWERS AND STORMS AND  
HIGHS NEAR 90. CHAMBERS  
   
LONG TERM...VALID FOR SAT...SUN...MON...TUE...WED
 
 
A WEAK FLOW UNDER AN UPPER RIDGE WILL BE OVER THE REGION THROUGH  
THE PERIOD. MODELS WERE IN GOOD AGREEMENT WITH THE OVERALL  
SYNOPTIC PATTERN, BUT OVERALL, ECMWF SHOWED MORE QPF THAN THE  
GFS. WEAK ENERGY MOVES THROUGH THE RIDGE THROUGH THE PERIOD. FOR  
SATURDAY, KEPT THUNDERSTORM CHANCES CONFINED TO MAINLY THE  
MOUNTAINS. MORE ENERGY AND MONSOONAL MOISTURE SURGES INTO THE AREA  
ON SUNDAY, WHICH WILL SUPPORT MORE WIDESPREAD PRECIPITATION  
CHANCES. THE MOISTURE WILL SLIDE INTO SE MT ON MONDAY FOR  
PRECIPITATION CHANCES THERE. KEPT CHANCES OVER THE MOUNTAINS TUE.  
AND WEDNESDAY. E FLOW OVERTAKES THE AREA TUESDAY, THEN THE GFS  
SHOWS A LOW-LEVEL JET SETTING UP IN THE E ON WED., WHILE THE ECMWF  
DOES NOT HAVE THIS FEATURE. WENT WITH CLIMO POPS WED. EVENING DUE  
TO THIS DISCREPANCY. THURSDAY LOOKS LESS ACTIVE SO WENT DRY IN  
THE AFTERNOON. SO, DESPITE OVERALL AGREEMENT IN THE LARGE-SCALE  
PATTERN, SMALL MODEL DIFFERENCES COULD MAKE A DIFFERENCE IN WHERE  
THE STORMS WILL BE LOCATED. STABILITY AND SHEAR PARAMETERS DID NOT  
SUPPORT STRONG THUNDERSTORMS AT THIS POINT. TEMPERATURES WILL BE  
IN THE LOW TO MID 90S. ARTHUR  
 

 
   
AVIATION
 
 
ISOLATED SHOWERS/TSTMS WILL IMPACT AREAS BETWEEN KBIL AND KMLS  
THIS MORNING. VFR WILL PREVAIL. BY MIDDAY, EXPECT SCATTERED  
THUNDERSTORMS TO DEVELOP FROM KMLS-K4BQ EASTWARD. SOME OF THESE  
STORMS COULD BE STRONG AND PRODUCE HEAVY RAINFALL AND LOCAL MVFR  
OR LOWER FLIGHT CONDITIONS THROUGH THE AFTERNOON AND EVENING.  
ISOLATED TO SCATTERED THUNDERSTORMS WILL ALSO IMPACT WESTERN AREAS  
FROM MID AFTERNOON THROUGH THE EVENING. A FEW MOUNTAIN  
OBSCURATIONS ARE POSSIBLE. JKL  
 

 
   
PRELIMINARY POINT TEMP/POPS
 
 
TDY FRI SAT SUN MON TUE WED  
-------------------------------------------------------  
BIL 090 064/092 064/093 064/094 065/094 064/091 063/091  
3/T 32/T 21/U 12/T 21/U 11/U 11/U  
LVM 086 057/084 055/090 055/091 055/090 054/091 054/090  
2/T 22/T 21/U 12/T 11/U 11/U 11/U  
HDN 090 064/093 065/095 063/096 063/095 061/093 062/094  
3/T 32/T 21/U 12/T 21/U 11/U 11/U  
MLS 091 066/094 068/096 067/097 068/097 065/094 065/094  
4/T 41/B 21/U 11/U 21/U 11/U 11/U  
4BQ 087 064/092 065/094 065/094 065/094 063/092 063/093  
4/T 42/T 21/B 11/U 22/T 11/U 11/U  
BHK 088 065/090 065/093 062/094 064/094 061/092 059/091  
4/T 42/T 31/U 11/U 22/T 11/U 11/U  
SHR 084 061/087 061/091 058/091 058/090 057/090 057/090  
3/T 32/T 22/T 12/T 21/B 11/U 11/U  
 

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

 
 

 
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