Severe Thunderstorm Warning 130, NWS Billings, MT

SOUTH CENTRAL AND SOUTHEAST MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
246 PM MDT SAT AUG 31 2002

.SHORT TERM...VALID FOR SUN AND MON...

UPPER LEVEL TROF CURRENTLY OVER NORTH CENTRAL MONTANA PUSHING
SOUTHEASTWARD ACROSS THE STATE WITH A WEAK FRONTAL BOUNDARY MOVING
AHEAD OF IT ACROSS CENTRAL MONTANA. ONE STRONG THUNDERSTORM HAS HAD A
LONG TRACK ALONG THE NORTH EDGE OF THE BEARTOOTH/ABSAROKA MOUNTAINS
WITH SOME INDICATION OF ROTATION. MORNING RUNS UNDERESTIMATED CAPES
ACROSS THE CENTRAL AND EASTERN SECTIONS WITH LAPS DATA SHOWING 1200-
1600 CAPES WITH TEMPS INTO THE MID 80S AND STILL CLIMBING ACROSS THE
SOUTHEAST. MAY BE MAKING LAST MINUTE ADJUSTMENTS TO THE FORECAST DUE
TO CURRENT CONVECTIVE TRENDS. BEHIND THE TROF AIRMASS IS BARELY
SUPPORTING ISOLATED ACTIVITY WITH MOST OF THIS ACTIVITY EXPECTED TO
DISSIPATE AFTER DARK.

SUNDAY A STRONG JET STREAK PUSHES ACROSS NORTHERN MONTANA PUTTING
SOUTHERN MONTANA IN THE RIGHT EXIT REGION OF JET AND SUBSIDENCE AND
LACK OF INSTABILITY SHOULD KEEP THE DAY DRY. TEMPS WILL BE A FEW
DEGRESS WARMER IN THE WESTERN SECTIONS BECAUSE CLOUDS CAME IN EARLY
TODAY BUT A FEW DEGREES COOLER IN THE EAST WHERE TEMPS WARMED STRONGLY
TODAY. WINDS WILL BE ON THE INCREASE AS A SURFACE WAVE MOVES ACROSS
ALBERTA INTO SASKETCHEWAN AND TIGHTENS DOWNSLOPE GRADIENTS.  ON MONDAY
WARM AIR ADVECTION AT 700 MB MOVES INTO SOUTHERN MONTANA WHILE STRONGER
NORTHWESTLY FLOW ALOFT CONTINUES OVER THE NORTHERN PART OF THE STATE.
THIS COMBINATION OF LIFT AND CONVERGENCE SHOULD GENERATE A MID LEVEL
DECK OF CLOUDS WHICH WILL SUPRESS TEMPERATURES. COOL SURFACE HIGH
PRESSURE SLIDES OVER THE AREA BRINGING A DECREASE TO THE WINDS AND A
STRONG CAP WHICH LIMITS ANY STORMS. BORSUM

.LONG TERM...VALID FOR TUE...WED...THU...FRI...SAT...

TUE & WED...FORECAST AREA WILL BE UNDER A RIDGE OF HIGH PRESSURE AS A
TROUGH IS LOCATED NORTH OF THE GREAT LAKES WITH A MUCH LARGER
TROUGH OFF THE COAST OF BRITISH COLUMBIA. THE GREAT LAKES TROUGH WILL
MOVE EAST ALLOWING THE NEXT TROUGH TO MOVE ONTO THE PACIFIC NORTHWEST
COAST. HOWEVER...THE TROUGH DOES NOT MAKE ITS WAY ONSHORE MUCH AS IT
SLOWLY SINKS SOUTH TOWARDS NORTHERN CA. AS A RESULT...SOUTHWEST FLOW
ALOFT WILL ONCE AGAIN BE OVER THE FORECAST AREA. ALTHOUGH THIS IS A GOOD
PATTERN FOR CONVECTIVE-TYPE PRECIPITATION...CONDITIONS LOOK TO BE
PARTLY CLOUDY AND DRY THROUGH WED NIGHT.
THU THROUGH SAT...TROUGH BEGINS TO MOVE ONTO THE PACIFIC NORTHWEST COAST
AND WHICH CONTINUES THE SOUTHWEST FLOW. TROUGH WILL SWEEP ACROSS ID AND
WESTERN MT WHICH WILL BRING A CHANCE OF SHOWERS AND THUNDERSTORMS
FRIDAY AND SATURDAY. TROUGH WILL THEN MOVE ACROSS THE NORTHERN BORDER
OF THE STATE FRIDAY NIGHT AND SATURDAY WHICH WILL BRING A MORE ZONAL
FLOW TO THE AREA WITH DRY CONDITIONS RETURNING. AS THE TROUGH MOVES
THROUGH...TEMPERATURES WILL BE COOLER THURSDAY. 700MB TEMPERATURES
CONTINUE TO COOL FRIDAY AND SATURDAY BRINGING TEMPERATURES DOWN INTO
THE LOWER TO MIDDLE 70S IN MOST LOCATIONS.  HOOLEY

    SUN     MON     TUE     WED     THU     FRI     SAT
-----------------------------------------------------------
BIL 054/085 053/082 053/088 054/084 054/077 052/071 049/074
    20/U    00/B    00/U    00/B    02/T    22/T    00/B
LVM 046/082 047/078 043/081 044/079 048/073 044/068 044/074
    20/U    00/B    00/U    00/B    03/T    32/T    00/B
HDN 053/087 049/081 052/086 053/085 058/079 053/073 053/079
    20/U    00/B    00/U    00/B    02/T    22/T    00/B
MLS 057/087 054/080 055/090 056/088 056/080 053/074 048/076
    30/U    00/B    00/U    00/B    01/B    21/E    00/B
4BQ 055/086 053/080 054/088 055/087 058/080 053/074 053/080
    30/U    00/B    00/B    00/B    01/B    11/B    00/B
BHK 055/085 051/078 055/086 056/085 058/079 054/073 054/077
    30/U    00/B    00/B    00/B    00/B    11/E    00/B
SHR 051/087 051/079 048/088 049/085 050/079 050/073 044/073
    30/U    00/B    00/U    00/B    02/T    21/B    00/B

.BYZ...
MT...NONE.
WY...NONE.