Flash Flooding and Hail in Montana, July 21 to 22, 2001

NORTHEAST MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
255 PM MDT SAT JUL 21 2001

THE CABOOSE ON THE SEVERE WEATHER TRAIN APPEARS TO BE IN SIGHT AND
LOOKS LIKE IT WILL PASS THRU GGW WITH A COLD FRONT ON SUNDAY. UPPER
TROF OVER SW CANADA AND PACIFIC NW EXPECTED TO MOVE INLAND OVER NEXT
COUPLE OF DAYS BRINGING A CHANGE IN THE PATTERN.

UNTIL THEN...CONDITIONS REMAIN FAVORABLE FOR SEVERE THUNDERSTORMS AS
SEVERAL VORT COUPLETS ARE EXPECTED TO MOVE NE ON SW FLOW ALOFT.
AN UPPER TROF WILL SHIFT THE SW FLOW ALOFT TO THE WEST SUNDAY
NIGHT. HOWEVER...THE MAIN UPPER TROF AXIS REMAINS NORTHWEST OF MT
UNTIL LATE MONDAY.

IN THE SHORT TERM...18Z GGW SOUNDING SHOWS A WEAK CAP AT 850 MB THAT
ONLY NEEDS A SFC TEMP OF 86 TO COMPLETELY ERODE. SOUNDING MODIFIED
FOR A SFC TEMP OF 86 AND DEWPOINT OF 61 YIELDS A CAPE OF 2500 J/KG
AND LI OF -8. MORE UNSTABLE THAN FORECASTED BY THE MODELS. STRONGER
CAP TO THE SE AT THIS TIME THAT IS EXPECTED TO GRADUALLY ERODE
TONIGHT. EXPECT CONVECTION TO FIRE OVER NRN PART OF CWA FIRST AND SE
LATER.

SCT THUNDERSTORMS WERE DEVELOPING AT 20Z NEAR QUASI-STATIONARY FRONT
OVER CENT MT. THIS FRONT EXTENDS SOUTH FROM A SFC LOW OVER SW SASK.
EXPECT SOME OF THE STORMS TO TRACK INTO THE WRN PART OF GGW CWA OVER
NEXT FEW HOURS AND INTENSIFY AS IT ENCOUNTERS MORE UNSTABLE AIR.

1000+ J/KG CAPE REMAINS OVER ERN MT TONIGHT AND SUNDAY MORNING WITH
A PEAK OF 3000+ J/KG NEAR GDV AT 06Z. THE VERY UNSTABLE AIR FINALLY
GETS PUSHED EAST WITH COLD FRONT AROUND MIDDAY ON SUNDAY. FORECAST
SHEAR PROFILES AND HODOGRAPHS...ESP IN THE EAST FAVORABLE FOR
SUPERCELLS. WILL MENTION SCT THUNDERSTORMS TONIGHT WITH SEVERE
STORMS POSSIBLE. WILL HAVE LOW CHC POPS FOR THUNDERSTORMS WEST ON
SUNDAY AND HIGHER CHC POPS EAST GIVEN THE LATER IN THE DAY TIMING OF
THE FRONT IN THE EAST.

YESTERDAY'S STORMS SATURATED THE GROUND OVER THE EAST HALF OF THE
CWA. WITH PRECIPTABLE WATER BETWEEN 1.2 AND 1.5 INCHES ABOUT EQUAL
TO THE 1 HR FLASH FLOOD GUIDANCE IN SOME OF THE ZONE...WILL ISSUE
FLASH FLOOD WATCH FOR EASTERN HALF OF CWA TONIGHT.

SHOULD BE IN BETWEEN SYSTEMS SUNDAY NIGHT. WILL MENTION PARTLY
CLOUDY SKIES. MONDAY SHOULD START OUT PT CLOUDY BUT MAIN TROF AXIS
DROPS SOUTH FROM CANADA TOWARDS NE MT MONDAY AFTERNOON. COOLER
AIRMASS BEHIND COLD FRONT AND APPROACHING UPPER TROF ON MONDAY WILL
KEEP HIGHS IN THE 70S AT MOST LOCATIONS...SLIGHTLY WARMER SOUTH.
WILL MENTION A SLIGHT CHANCE OF AFTN SHOWERS NORTH ON MONDAY AND
KEEP THE SOUTH DRY.  FORRESTER

EXTENDED...BROKEN RECORD FOR THE EXTENDED...ECMWF AND CANADIAN GEM
MODELS ARE STARTING TO COME AROUND TO MRF SOLUTION OF ALBERTA TROF
BEING REPLACED BY AN ALASKAN TROF. THIS WILL PUT NE MT UNDER A TROF
ACCORDING TO THE ECMWF. CANADIAN LOOKS ZONAL ACROSS THE AREA...BUT
UNSTABLE WITH TIGHT ISO-HEIGHT PACKING. MRF MORE PROGRESSIVE WITH
THE ALASKAN TROF...BUT NW FLOW FOR FRI AND SAT SPELLS UNSTABLE
ATMOS. WILL BUMP TEMPS DOWN INTO THE 70S FOR TUES AND WED DUE TO
EFFECTS FROM THE UPPER TROF OVER THE AREA. WILL TREND TEMPS CLOSER
TO NORMS FOR THU THROUGH SAT. WITH SAID TROFINESS ACROSS THE AREA
...WILL ALLOW FOR A CHANCE OF DAILY T-STORMS.  JAMBA

KGGW 060/083 055/075 052/075 056/078 057/082 057/082 057/082
      TBBBBBB  794312/7633333
KGDV 063/085 060/079 057/075 058/077 058/083 057/082 056/082
      TBBBBBB  795411/76633333