Severe Thunderstorm Warning 229, NWS Billings, MT

SOUTH CENTRAL AND SOUTHEAST MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
158 PM MDT SUN JUL 22 2001

.MON AND TUE...
BOTH AVN AND ETA SEEMED TO ALIGN RATHER WELL ACCORDING TO THE
WATER VAPOR IMAGERY AT 18Z. ETA DID BETTER WITH THE SURFACE FEATURES AT
THAT TIME.

CONVECTION IS ALREADY FIRING UP OVER SOUTH CENTRAL MONTANA. CAPES IN
AREA ABOUT 1000 J/KG. SOME DIRECTIONAL SHEAR AT LOW LEVELS...BUT WINDS
ABOVE 500 MB LEVEL SOUTHWEST AT 50 KTS OR HIGHER ACCORDING TO AN
AIRCRAFT SOUNDING AT BILLINGS TAKEN SHORTLY AFTER 18Z. GOOD SPEED SHEAR
GOING ON THERE. SEE NO REASON NOT TO MENTION THE POSSIBILITY OF SEVERE
THUNDERSTORMS OVER THE COUNTY WARNING AREA TONIGHT. THE LATEST MESO-
SCALE DISCUSSION FROM THE STORM PREDICTION CENTER SUPPORTS THIS AS
WELL.

BOTH MODELS HAVE THE THETA E RIDGE BASICALLY STRADDLING SOUTHERN
MONTANA AND NORTHERN WYOMING AT THE OUTSET. WITH TIME THE RIDGE SINKS
INTO WYOMING. ETA PLACES THE MAXIMUM THETA E INTO NORTHEAST WYOMING
AND WESTERN SOUTH DAKOTA MONDAY MORNING...WHILE AVN PLACES THIS MORE
OVER NORTH CENTRAL WYOMING. BOTH MODELS...IN ESSENCE...DO NOT HAVE THE
THETA E RIDGE THAT FAR AWAY FROM THE COUNTY WARNING AREA. MOREOVER...
THE UPPER LEVEL TROUGH...WHILE GETTING CLOSER...DOES NOT PASS OVER THE
COUNTY WARNING AREA. THUS...WILL STILL KEEP POPS FOR THUNDERSTORMS FOR
ALL PERIODS.

HIGH TEMPERATURES MAY BE SOMEWHAT TRICKY DUE TO CLOUD DEBRIS FROM
THUNDERSTORM ACTIVITY. CHB

.WED...THU...FRI...SAT...SUN...
MODELS SIMILAR IN  PLACEMENT ACROSS WESTERN NORTH AMERICA BUT DIFFER
IN  TIMING OF TRANSIENT WAVES AND STRENGTH OF THESE WAVES. A GENERAL
WESTERLY FLOW DEVELOPS ACROSS THE  AREA BY  MIDWEEK TRANSITIONING TO
A GENERAL DRY PATTERN WITH ISOLATED  THUNDERSTORMS BY THE END OF THE
WEEK CONTINUING INTO THE WEEKEND. MODELS DEPICT A COLD FRONT TO MOVE
THROUGH THE NORTHERN ROCKIES LATE  INTO THE WEEKEND.  WENT WITH SOME
SCATTERED THUNDERSTORMS WEDNESDAY  AND THURSDAY WHEN  THE ATMOSPHERE
TRANSITIONS TO THE WESTERLY FLOW WITH GENERALLY DRY CONDITIONS AFTER
THAT.  TEMPERATURES WILL BE NEAR NORMAL  THROUGH THE EXTENDED PERIOD
BEFORE COOLING OFF EARLY IN THE WEEK NEXT WEEK. THORICHT

    MON     TUE     WED     THU     FRI     SAT     SUN
-----------------------------------------------------------
BIL 056/083 055/084 058/086 058/087 057/085 056/085 055/080
    44/T    33/T    33/T    33/T    22/B    22/B    22/B
LVM 048/080 048/081 057/087 058/086 058/085 057/084 055/081
    44/T    33/T    33/T    33/T    22/B    22/B    22/B
HDN 053/087 052/088 056/088 057/089 056/086 055/087 053/082
    44/T    33/T    33/T    33/T    22/B    22/B    22/B
MLS 058/087 055/088 060/090 059/090 059/088 058/086 057/082
    33/T    33/T    33/T    33/T    22/B    22/B    22/B
4BQ 058/086 054/087 059/090 058/089 058/087 057/085 056/081
    44/T    43/T    33/T    33/T    22/B    22/B    22/B
BHK 056/082 051/083 057/089 057/088 057/086 057/086 056/081
    33/T    33/T    33/T    33/T    22/B    22/B    22/B
SHR 055/083 053/082 058/088 057/087 056/085 056/084 056/080
    44/T    43/T    33/T    33/T    22/B    22/B    22/B

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