Severe Thunderstorm Warning 6, NWS Billings, MT

SOUTH CENTRAL AND SOUTHEAST MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
153 PM MDT SAT MAY 26 2001

.SUN AND MON...
PER ETA MODEL...RIDGE AXIS HOLDS IN PLACE WITH SERIES OF UPPER LEVEL
DISTURBANCES MOVING UP IN SW FLOW. THESE DISTURBANCES MOVE INTO AN AREA
OF DIFFLUENCE ALONG/NEAR THE SW MTNS AND WHEN COMBINED WITH DEVELOPING
EASTERLY FLOW FROM SFC TO 700MB UPSLOPE CONDITIONS RESULT. OMEGA AND RH
VALUES STEADILY INCREASE FROM SFC TO 500MB TONIGHT THROUGH MONDAY WHICH
WILL AID IN RAIN DEVELOPMENT IN THESE FAVORED AREAS. AIR MASS REMAINS
FAIRLY STABLE TO THE EAST OF BIL TONIGHT...HOWEVER INCOMING DISTURBANCE
AS SEEN FROM SAT IR PICS WILL TRANSLATE EAST ALONG MT/WY BORDER AND
EXPECT ISOLATED SHOWERS/THUNDER TO DEVELOP DURING THE EVENING HOURS AND
DISSIPATE BY MIDNIGHT. TEMPS WILL BE ABOUT 3-5 DEGREES COOLER MONDAY AS
EAST FLOW BECOMES MORE DOMINANT AND LINGERING CLOUD COVER FROM EXPECTED
SHOWERS TONIGHT HOLDS IN PLACE. AVN MODEL PLACES UPCOMING DISTURBANCES
IN SLIGHTLY DIFFERENT LOCALES BUT OVERALL PATTERN IS THE SAME WITH
DIFFLUENT FLOW SHOWING UP ALONG/NEAR SW MTNS FOR SCT SHOWERS/THUNDER
NEXT COUPLE OF DAYS. AS A RESULT WILL GO WITH A BLEND OF THE TWO MODELS
AND SIMILAR TO WHAT GOING FCST HAS TRENDED. ONLY AREA OF QUESTIONABLE
PRECIP WILL BE THE SE CORNER TONIGHT DEPENDING ON ACTUAL TRACK OF UPPER
LEVEL DISTURBANCE WHICH ETA/AVN CANNOT AGREE UPON. WILL INTRODUCE ISOLD
POPS THERE AS FAIR WEATHER CU ARE POPPING AS SEEN FROM SAT VIS PICS.
WILL GO CLOSER TO FAN GUIDANCE FOR HIGHS WHICH TRENDS BETTER WITH THE
SLIGHTLY COOLER READINGS FOR MON GOING INTO THE EXTENDED. SPRINGER

.TUE...WED...THU...FRI...SAT...
ECMWF...CANADIAN...MRF...AND NEW AVN RUNS PRESENT VERY DIFFERENT IDEAS
ON THE COMING SCENARIO. THE FIRST THREE TRACK THE UPPER LEVEL LOW
FARTHER NORTH AT LEAST INITIALLY...WHILE THE NEW AVN TRACKS THE SYSTEM
INTO MONTANA...ENDING THURSDAY AT 12Z WITH THE UPPER LOW OVER NORTHERN
WYOMING. ALONG WITH THE CANADIAN RUN AND THE ECMWF...IT IS ON THE SLOW
SIDE. MRF IS THE FASTEST OF THE RUNS CONSULTED. DUE TO THE VARIETY OF
SCENARIOS...CONFIDENCE IS LIMITED. AVN DOES LINE UP WITH THE ETA RUN
TO A BETTER DEGREE FOR 60 HOURS.  THUS WILL AT LEAST START OUT WITH IT
IN MIND. AM LOOKING HOWEVER...TO KEEP THE UPPER LEVEL SYSTEM IN CANADA
FOR THE MOST PART.  AM HAVING PROBLEMS WITH ACCEPTING THE VERY LOW
THICKNESS VALUES THAT AVN PRESENTS DURING MID WEEK. DO LIKE THE SLOWER
PROGRESS THAT IT PRESENTS WITH THE FEATURES AND WILL NOT BE AS HASTY
IN CLEARING OUT PRECIPITATION. TOWARD THE END OF THE PERIOD...MRF
SUGGESTS A RETURN TO SOUTHWEST FLOW AND SURFACE LOW DEVELOPMENT OVER
MONTANA. AGAIN...THINK THAT THIS PROGRESSION IS TOO FAST CONSIDERING
THE RECENT HISTORY OF SYSTEMS PASSING THROUGH HERE. CHB.

    SUN     MON     TUE     WED     THU     FRI     SAT
-----------------------------------------------------------
BIL 050/080 050/075 049/069 040/068 043/071 049/074 051/077
    22/T    33/T    43/T    33/W    22/E    22/B    22/B
LVM 048/075 048/072 045/067 039/065 041/069 048/074 050/076
    42/T    33/T    43/T    33/W    22/E    22/B    22/B
HDN 050/080 048/076 047/071 038/070 040/073 047/075 049/078
    22/T    33/T    43/T    33/W    22/E    22/B    22/B
MLS 050/080 050/075 052/074 043/071 045/073 048/076 052/079
    20/B    33/T    44/T    33/W    22/E    22/B    22/B
4BQ 049/081 049/077 050/072 041/068 043/070 047/075 051/078
    20/B    33/T    44/T    33/W    22/E    22/B    22/B
BHK 049/078 048/073 050/070 039/067 041/069 045/073 049/075
    20/B    33/T    44/T    33/W    22/E    22/B    22/B
SHR 047/078 048/074 048/069 038/066 042/070 047/y074 049/076
    32/T    33/T    44/T    33/W    22/E    22/B    22/B