Severe Thunderstorm Warning 91, NWS Glasgow, MT

NORTHEAST MONTANA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE GLASGOW MT
255 PM MDT WED JUL 18 2001

...WILL ISSUE FLASH FLOOD WATCH FOR ERN ZONES TONIGHT...

UPPER LOW OVER CENTRAL ALBERTA WITH AN UPPER TROF OVER THE PACIFIC
COAST WILL REMAIN IN PLACE THROUGH FRI. WITH UPPER RIDGE OVER THE
CENTRAL US...SW FLOW ALOFT WILL CONTINUE OVER MT WITH SEVERAL
SHORTWAVES EXPECTED TO AFFECT NE MT INTO THE WEEKEND.

IN THE SHORT TERM...DRY LINE BOUNDARY EAST OF NEAR OLF AND CIRCLE
BRINGING SOMEWHAT DRIER AIR INTO THE REGION THIS AFTERNOON.
MESOETA AND AVN MOVES THIS DRYLINE TO THE NODAK BORDER THIS EVENING
BUT DEW POINTS ARE REMAINING IN THE LOWER 50S BEHIND THIS DRY LINE
WITH ENOUGH INSTABILITY TO FIRE CONVECTION. AHEAD OF THE DRY
LINE...DEW POINTS ARE NEAR 60 AND THE LAPS ANALYSIS SHOWS CAPE AS
HIGH AS 2400 J/KG AROUND GDV WITH LI OF -7. CONDITIONS FAVORABLE FOR
SEVERE CONVECTION THIS EVENING...ESP EAST OF THE DRY LINE. WILL
MENTION SCT THUNDERSTORMS ALL ZONES WITH THE HIGHEST POPS IN THE
EAST. GROUND OVER ERN ZONES REMAINS SATURATED FROM LAST NIGHTS RAIN.
ANY THUNDERSTORM THAT DEVELOPS COULD DEPOSIT A QUICK INCH OR TWO OF
RAIN. WILL ISSUE A FLASH FLOOD WATCH FOR TONIGHT FOR ERN PART OF
CWA.

ON THURSDAY...MODELS HAVE THE BEST INSTABILITY OVER SE MT.
HOWEVER...THE MAIN SHORTWAVE ENERGY TRACKS OVER NE MT. MESOETA
BRINGS A VORT COUPLET THROUGH NE MT BETWEEN 18Z AND 21Z. MESOETA HAS
UNSTABLE AIR FORECASTED EAST OF THE VORT TRACK WHICH IS THRU
JDN...OLF AND PLENTYWOOD WHICH IS CLOSE TO A MESOETA DRY LINE
BOUNDARY THAT SEPARATES DEW POINTS IN THE 40S FROM DEW POINTS IN THE
60S. CAPE IS FORECASTED TO PEAK AROUND 2000 J/KG ALONG AND EAST OF
THE YELLOWSTONE RIVER AROUND 18Z. MESOETA FORECASTS PRECIPTABLE
WATER AS HIGH AS 1.60 INCHES BETWEEN GDV AND WIBAUX AT 21Z ON THU.
ANY THUNDERSTORMS THAT DO DEVELOP IN THE ERN HALF OF GGW CWA COULD
ONCE AGAIN BE A FLASH FLOOD CONCERN WITH SATURATED GROUND.

THU NIGHT AND FRIDAY...WITH UNSTABLE AIR REMAINING OVER ERN MT AND
SHORTWAVES CONTINUING TO TRACK OVER NE MT...WILL KEEP A CHANCE OF
THUNDERSTORMS IN THE FORECAST. MESOETA DOES BRING ANOTHER VORT
COUPLET THROUGH THE NW PART OF GGW CWA BETWEEN 12Z AND 15Z FRIDAY
WITH A FEW WEAKER VORTS BEFORE AND AFTER.

EXTENDED...MEDIUM RANGE MODELS IN DISAGREEMENT WITH THE WESTERN
CONUS BEYOND DAY 4 (SUNDAY). THE CLOSED LOW OVER WESTERN CANADA
LIFTS OUT ACCORDING TO THE MRF/CANADIAN AND ECMWF SUNDAY...BUT THE
CANADIAN AND THE ECMWF BUILD A REX BLOCK (HIGH OVER LOW) OVER
BRITISH COLUMBIA/PAC NW WHILE THE MRF BUILDS A BROAD RIDGE INTO MT.
DIFFERENCES ARE GREATEST ON DAY 7. WILL THEREFORE KEEP WITH A
PERSISTENCE FORECAST THROUGH THE EXTENDED.  JAMBA

KGGW 060/085 063/085 058/083 056/085 058/084 061/085 061/085
      TTBBBBB  793433/7633333
KGDV 061/085 061/086 057/085 058/085 058/084 060/084 060/084
      TTBBBBB  794433/7633333

.GGW...FLASH FLOOD WATCH TONIGHT FOR ZONES 019-020-022>027-062.