Severe Thunderstorm Warning 86, NWS Glasgow, MT

NORTHEAST MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
222 PM MDT TUE JUL 17 2001

CLOSED UPPER LOW CENTERED OVER SRN BC WILL MIGRATE NE INTO CENTRAL
ALBERTA THE NEXT 2 DAYS. ETA SLIGHTLY EAST OF THE AVN WITH THE UPPER
LOW CENTER AFTER 00Z THU. SEVERAL SHORTWAVES IN SW FLOW AFOFT AHEAD
OF THIS LOW WILL AFFECT NE MT THE NEXT SEVERAL DAYS.

MODELS BRING ONE SHORTWAVE OVER NE MT THIS EVENING AND ANOTHER WED
MORNING. ETA SLIGHTLY SLOWER WITH WED MORNING WAVE (15Z) THAN THE
AVN (12Z). WITH BOTH WAVES...MODELS SET UP A DRY-LINE BOUNDARY NEAR
GGW AND JDN WITH A WEAK THETA-E RIDGE JUST EAST OF THE DRY LINE.
AIRMASS PROGGED TO BE UNSTABLE TO THE EAST OF THIS DRY-LINE WITH THE
MOST UNSTABLE AIR OVER SW ND AND SE MT WHERE THERE IS A STRONGER
THETA-E RIDGE. ETA FORECAST CAPES OF 2000-2500 J/KG COVERS THE SE
PART OF GGW CWA THIS EVENING INCLUDING SDY AND GDV WITH THE 1000+
J/KG CAPE AS FAR WEST AS SCOBEY...OLF AND TERRY UNTIL WED MORNING
SHORTWAVE PASSES.

THE FIRST WAVE THIS EVENING WILL HAVE DAYTIME HEATING AND STRONG
UPWARD OMEGA TO HELP SUPPORT IT. THE WED MORNING WAVE WILL HAVE THE
LEFT FRONT QUADRANT OF 70 KNOT UPPER JET FOR ADDITIONAL SUPPORT.
WITH NOT BEING ABLE TO PINPOINT WHERE THE CONVECTION WILL BE AT THIS
TIME...WILL MENTION SCT THUNDERSTORMS FOR BOTH TONIGHT AND WED FOR
ALL ZONES. WILL HAVE 30 PCT CHANCE IN THE WEST AND 40 PCT IN THE
EAST WITH THE BETTER MOISTURE AND INSTABILITY IN THE EAST.

AFTER WED MORNING'S WAVE PASSES...THE MAIN INSTABILITY SHIFTS TO THE
EAST UNTIL ANOTHER SFC TROF DEVELOPS OVER ERN MT ON THU. WEAK
SHORTWAVES WITH SW FLOW ALOFT WILL KEEP A 20 PCT CHANCE OF
SHOWERS AND THUNDERSTORMS OVER GGW CWA WED NIGHT.

THE UNSTABLE AIR RETURNS ON THU...ESP ALONG AND EAST OF THE SFC TROF
AXIS WHICH MODELS PLACE NEAR GGW AND MLS. WILL NOT SPECIFIC WITH
TIMING OF ANY WAVES ON THU. MESOETA FORECAST CAPE AROUND 2000 J/KG
WITH LI OF -8 OVER MLS AND GDV THU AFTERNOON WILL NEED TO BE WATCHED
BY FUTURE SHIFTS. WILL MENTION A CHANCE OF THUNDERSTORMS.

AS FOR TEMPS...WILL FOLLOW WARMER FWC.  FORRESTER

EXTENDED...UPPER LOW REMAINS OVER ALBERTA UNTIL SAT WHEN IT MOVES
EAST AS AN OPEN TROF. THEN AN UPPER TROF DEVELOPS OVER WEST COAST
OVER THE WEEKEND THAT CONTINUES INTO EARLY NEXT WEEK. EXCEPT FOR A
BRIEF PERIOD ON SUNDAY...ERN MT IS IN SW FLOW ALOFT FOR THE ENTIRE
EXTENDED PERIOD WITH FREQUENT SHORTWAVES. GIVEN THE UNSETTLED
PATTERN...WILL NEED TO MENTION A CHANCE OF THUNDERSTORMS EACH DAY.
FORRESTER

KGGW 062/084 060/085 062/082 058/083 056/085 058/084 061/085
      TTTBBBB  793323/7933333
KGDV 063/085 061/085 061/085 057/085 058/085 058/084 060/084
      TTTBBBB  794423/7933333