Flash Flood in Montana, August 22, 2002

SOUTH CENTRAL AND SOUTHEAST MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
228 AM MDT THU AUG 22 2002

.SHORT TERM...VALID FOR TDY AND FRI...

THE UPPER LEVEL LOW SPINNING NEAR THE TRIPLE POINT OF IDAHO/OREGON/WASH
THIS MORNING IS SHOWING INDICATIONS OF A BIT OF RETROGRESSION. IR
SATELLITE IMAGERY SHOW MOST CONVECTIVE ACITIVTY IS DISSIPATING WITH THE
STRONGER STORMS DEVELOPING OVER SOUTH DAKOTA. NEW ETA SHOWS THE LOW IS
ACTUALLY ELONGATING AND FILLING...BECOMING POSITIVELY TILTED ALONG A
KFCA-KEKA AXIS. THIS MAINTAINS THE SOUTHWEST FLOW ALOFT BUT THE
EASTERLY LOW LEVEL FLOW IN THE AREA WILL BE WEAK. THUNDERSTORMS ARE
EXPECTED TO DEVELOP TODAY DUE TO MODERATE CAPES AND STEEP LAPSE RATES
BUT ORGANIZING SHEAR WILL BE LIMITIED AND EXPECT MOST CELLS TO MOVE
SLOWLY AND PRODUCE HEAVY RAIN. EXPECT BULK OF ACTIVITY TO BE DIURNAL
WITH INITIATION OVER THE HIGHER TERRAIN DUE TO WEAK UPSLOPE AND THEN
ADVANCING INTO THE PLAINS DURING THE LATE AFTERNOON AND EVENING.
CURRENT FORECAST SUPPORTS THIS WITH A SLIGHTLY LOWER POPS OVER THE
SOUTHEAST THIS AFTERNOON. FRIDAY LOOKS VERY SIMILAR BUT BUFKIT
SOUNDINGS DO SHOW A SLOW DRYING OF THE LOWER LAYERS INDICATIVE OF THE
WEAKENING RETURN FLOW DUE TO THE LACK OF LEE SIDE TROFING OVER
WYOMING. AS THE UPPER LOW CONTINUES TO FILL ON FRIDAY IT SLOWLY MOVES
WESTWARD BUT LOOSES ITS POSITIVE TILT AND MODEL SHOWS A BIT MORE
SHORTWAVE ENERGY MOVING INTO THE AREA THAN TODAY. AFTERNOON AND
EVENING THUNDERSTORMS WILL AGAIN BE THE RULE FAVORING OROGRAPHIC
INITIATION BUT WOULD EXPECT CELL MOVEMENT TO BE EVEN SLOWER AND WITH
700MB FLOW BECOMING SOUTHEASTERLY OVER THE AREA IT IS POSSIBLE THAT
SOUTHEAST MONTANA WILL SEE LESS ACITIVITY AS THE FAVORED CELL TRACKS
WILL MOVE AWAY FROM THAT AREA. AS EVIDENCED BY TODAY...TEMPERATURES
WILL BE FICKLE DUE TO TIMING OF CONVECTION AND UPSLOPE KEEPING AREAS
OF CLOUDS AROUND IN THE MORNING HOURS. ONLY A FEW TWEAKS TO LOWER POPS
ON FRIDAY IN THE SOUTHEAST. BORSUM

.LONG TERM...VALID FOR SAT...SUN...MON...TUE...WED...

BOTH SHORT TERM MODELS SHOW THE REMNANTS OF THE UPPER LOW BECOMING A
NEGATIVELY TILTED TROF ACROSS THE AREA THOUGH PATTERN STILL IS NOT
EVOLVING VERY QUICKLY. THIS CAUSES A SURFACE PRESSURE TROF TO FORM OVER
WYOMING AND SOUTHEAST SURFACE FLOW IS MAINTAINED HELPING KEEP HIGHER
DEWPOINTS IN THE AREA. CONVECTION IS FAVORABLE ON SATURDAY BUT SUNDAY
MAY OFFER A LULL AS THE TROF AXIS WORKS ITS WAY NORTH OF THE AREA AND
LAPSE RATES ARE LOWER THAN PREVIOUS DAYS. ALSO LOW LEVEL FLOW BECOMES
WESTERLY AND WOULD PULL THE HIGHER DEWPOINTS OUT OF THE AREA. THUS
DESPITE WEAK CYCLONIC FLOW OVER THE AREA ON MONDAY AND TUESDAY
CONVECTIVE CHANCES LOOK LOW DUE TO THE AIRMASS BEING DRIER. CURRENT
FORECAST LOOKS GOOD AND DO NOT ANTICIPATE ANY CHANGES. BORSUM

    TDY FRI     SAT     SUN     MON     TUE     WED
-------------------------------------------------------
BIL 083 054/084 052/086 054/086 053/083 051/082 050/083
    3/T 33/T    33/T    33/T    30/E    00/B    00/B
LVM 078 050/082 048/083 048/084 047/081 045/080 045/081
    3/T 33/T    33/T    33/T    30/E    00/B    00/B
HDN 083 052/087 050/088 052/088 050/085 048/084 047/084
    3/T 33/T    33/T    33/T    30/E    00/B    00/B
MLS 083 056/085 055/087 057/087 056/083 054/082 053/083
    2/T 22/T    23/T    33/T    30/E    00/B    00/B
4BQ 083 055/084 054/086 056/086 055/082 053/081 053/081
    2/T 22/T    23/T    33/T    30/E    00/B    00/B
BHK 079 053/083 052/084 053/084 053/080 051/079 050/079
    2/T 22/T    23/T    33/T    30/E    00/B    00/B
SHR 082 051/084 051/085 050/084 049/080 047/079 046/079
    3/T 33/T    33/T    33/T    30/E    00/B    00/B

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