Severe Thunderstorm Warning 28, NWS Billings, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
235 PM MDT TUE JUN 22 2004

.SHORT TERM...VALID FOR WED AND THU...

COLD FRONT WAS SOUTH OF E ZONES THIS AFTERNOON. SHORTWAVE ENERGY AND
RIGHT REAR QUADRANT OF UPPER LEVEL JET WERE PROVIDING SUPPORT FOR AREA
OF CONVECTION SLIDING SE THROUGH FORECAST AREA THIS AFTERNOON. WILL
KEEP CHANCE OF THUNDERSTORMS GOING THROUGH 02Z THEN FADE CHANCES
FROM W TO E THROUGH 06Z. SOME STORMS MAY PRODUCE HAIL AS FREEZING LEVEL
WAS NEAR 11000 FT PER LATEST ACARS DATA.

GFS PICKED UP ON A SHORTWAVE OVER N BC THIS AFTERNOON AND MOVED IT INTO
E ZONES ON WED. ETA DID NOT SHOW THIS WAVE. BOTH MODELS HAD A SHORTWAVE
OVER WESTERN ZONES AND HAD YET ANOTHER BOUNDARY MOVING SOUTH THROUGH THE
E ZONES. LEANED TOWARD GFS SOLUTION AND WENT FOR 20 POPS FAR EAST AND
WEST WED AFTERNOON.

AS NW FLOW CONTINUES WED NIGHT AND THU...BACKDOOR COLD FRONT WILL SLIDE
INTO THE AREA WED NIGHT AND REMAIN OVER THE REGION ON THU. RIGHT REAR
QUADRANT OF 300 MB JET WILL BRING UPPER LEVEL DIVERGENCE TO THE EASTERN
PART OF THE AREA WED NIGHT. INCREASED POPS OVER E ZONES WED NIGHT AND
THU...OTHERWISE DID NOT CHANGE POPS THAT WERE ALREADY IN PLACE.

MADE ONLY MINOR ADJUSTMENTS TO TEMPS THROUGH THE PERIOD. WED WILL BE
WARMER THAN THU DUE TO COLD FRONT SETTLING OVER AREA ON THU. ARTHUR

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

NORTHWEST FLOW WILL CONTINUE THURSDAY NIGHT THROUGH EARLY SATURDAY..WITH
SHORTWAVES MOVING THROUGH THE NORTHWEST FLOW PRODUCING A SLIGHT CHANCE
FOR AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS IN THE SOUTHWEST
ZONES. FUTURE SHIFTS WILL NEED TO MONITOR HOW THE GFS MODEL HANDLES THE
SHORTWAVE MOVING THROUGH FRIDAY NIGHT AND EARLY SATURDAY...AS THIS
VORTICITY MAXIMUM ORIGINATES OVER NORTHEAST WASHINGTON STATE VERY
QUICKLY FRIDAY MORNING. HAVE LEFT THE SLIGHT CHANCE OF PRECIPITATION AS
IS DURING THE FRIDAY EVENING PERIOD AS INSTABILITY WILL BE PRESENT AND
CONVECTION MAY FORM EVEN IF THE GFS MODEL IS OVER-DEVELOPING THE
VORTICITY MAXIMUM.

SATURDAY NIGHT THROUGH TUESDAY NIGHT...AN UPPER LEVEL LOW MOVES ONSHORE
IN WESTERN WASHINGTON STATE DEVELOPING SOUTHWEST FLOW OVER THE
FORECAST AREA. WITH AFTERNOON INSTABILITY IN PLACE AHEAD OF A WEAK
COLD FRONTAL PASSAGE...AN UPPER SHORTWAVE IS EXPECTED TO MOVE INTO THE
SOUTHWEST MOUNTAINS SATURDAY. THIS IS ENOUGH TO LEAVE THE CURRENT
FORECAST FOR A SLIGHT CHANCE FOR CONVECTION SATURDAY EVENING. WITH HIGH
PRESSURE BUILDING INTO EASTERN MONTANA SATURDAY EVENING BEHIND THE
FRONT...WINDS WILL BE MAINLY FROM THE EAST AND SOUTHEAST THROUGH EARLY
MONDAY. AS THE UPPER LEVEL LOW MOVES ONSHORE AND NORTHEAST INTO BRITISH
COLUMBIA MONDAY AND TUESDAY...THE UPPER RIDGE IS PUSHED EAST TO THE
WESTERN DAKOTAS WITH AN INVERTED SURFACE TROUGH ALSO MOVING NORTHEAST
ACROSS THE FORECAST AREA. WILL NOT YET ADD ANY CHANCE OF PRECIPITATION
MONDAY AND TUESDAY...BUT IF THE MODELS CONTINUE TO SHOW THIS PATTERN
THE AREA MAY HAVE A 24-36 HOUR PERIOD OF SOUTHEAST LOW LEVEL FLOW
TO INCREASE MOISTURE ACROSS THE EAST AND PRODUCE AT LEAST SCATTERED
CONVECTION.

MADE ONLY MINOR CHANGES TO WINDS AND TEMPERATURES WITH THIS PACKAGE.
CONTINUE TO LEAN TOWARD THE HIGHER END OF THE GFS ENSEMBLE TEMPERATURE
VALUES...INDICATING A SLOW WARMING TREND THROUGH THE WEEKEND AND INTO
EARLY NEXT WEEK. CARPENTER

&&

.PRELIMINARY POINT TEMP/POPS...

    WED     THU     FRI     SAT     SUN     MON     TUE
-----------------------------------------------------------
BIL 054/083 054/076 052/078 052/078 052/078 054/083 055/084
    40/B    23/T    21/B    10/B    00/B    00/B    00/B
LVM 046/082 046/075 045/075 044/075 045/077 046/078 047/078
    32/T    23/T    22/T    20/B    00/B    00/B    00/B
HDN 054/082 055/077 053/078 051/080 052/081 053/085 054/085
    40/B    33/T    00/B    00/B    00/B    00/B    00/B
MLS 051/078 053/074 052/075 052/079 054/079 055/084 056/084
    40/B    33/T    00/B    00/B    00/B    00/B    00/B
4BQ 053/082 054/073 051/073 050/076 051/079 052/081 054/083
    30/B    34/T    00/B    00/B    00/B    00/B    00/B
BHK 050/076 052/070 044/071 046/072 047/076 051/079 052/081
    42/T    32/W    00/B    00/B    00/B    00/B    00/B
SHR 049/080 050/073 048/075 047/076 047/079 048/080 050/082
    30/B    23/T    12/T    21/B    10/B    00/B    00/B

&&

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

&&

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