Severe Thunderstorm Warning 7, NWS Glasgow, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
848 PM MDT SAT MAY 31 2008

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH MONDAY...
SURFACE TROF HAS DROPPED SOUTH INTO THE NORTHERN PORTION OF THE
CWA FROM SASKATCHEWAN AND HAS PROVIDED ENUF IMPETUS IN AN UNSTABLE
ENVIRONMENT TO GENERATE A FEW THUNDERSTORMS. SUSPECT THAT SUNSET
AND LOSS OF HEATING WILL SUBSTANTIALLY STICK A FORK IN THIS
ACTIVITY. WILL UPDATE TO ADD SOME SMALL POPS TO THE NORTHERN THIRD
OR SO OF THE AREA AND TWEAK A FEW OTHER PARAMETERS TO BETTER
REFLECT CURRENT AND EXPECTED CONDITIONS. OVERALL FORECAST WAS IN
PRETTY GOOD SHAPE AND CHANGES MOSTLY MINIMAL.

PREVIOUS DISCUSSION...
MAIN FORECAST CONCERN IN WILL BE PRECIP CHANCES NEXT SEVERAL DAYS
AS UPPER LOW AND SHORTWAVE ENERGY APPROACH MT. CURRENT WATER VAPOR
SATELLITE SHOWS UPPER LOW JUST OFF COAST OF BC WITH UPPER RIDGE
AXIS OVER WRN MT AND SHORTWAVE ROUNDING BASE OF THE UPPER TROUGH
IN IDAHO. A SURFACE TROUGH IN SOUTHERN SASK IS PRODUCING SOME
CONVECTION NORTH OF THE CWA BORDER WITH MORE CONVECTION OFF HIGHER
TERRAIN IN CENTRAL MT. MORE FAVORABLE ELEVATED INSTABILITY IS
FARTHER WEST WITH HIGHER CAPES AND LOWER LIS AND WILL KEEP BEST
PRECIP CHCS FROM GGW/WEST NORTH INTO EVENING. BY 12Z SUNDAY 1ST
PIECE OF SHORTWAVE ENERGY WILL EJECT INTO WRN MT WITH SECONDARY
ENERGY APPROACHING SRN MT BY 00Z. MODELS INDICATE DECENT LEE
TROUGH DEVELOPING SUN AFTN WHICH WILL INCREASE LOW LEVEL MOISTURE
AND INSTABILITY ACROSS THE CWA. THE BEST MOISTURE CONVERGENCE AND
HIGHER CAPES WILL BE SOUTH AND WEST ALONG ELEVATED TERRAIN...BUT
ANY -TSRA FORMING WILL MOVE INTO NERN MT AS UPPER FLOW BECOMES
SOUTHWEST. HAVE INCREASED POPS SUN AFTN INTO EVENING KEEPING BEST
CHC IN SWRN ZONES. SUNDAY NIGHT INTO 12Z MONDAY THE GFS SEEMS TO
BE OVERDONE WITH QPF IT GENERATES AROUND STRONG 850MB LOW. THERE
IS GOOD SURFACE CONVERGENCE AND MOISTURE ADVECTION ALONG THE WEAK
COLD FRONT BOUNDARY AS IT SHIFTS ACROSS ERN MT MONDAY AFTN BUT
THINK GFS MODEL QPF IS TOO HIGH. HAVE KEPT ALL AREAS IN CHC POPS
INTO MONDAY AFTERNOON AS SHORTWAVE EJECTS INTO ND WITH UPPER LOW
IN WRN MT. HAVE ALSO COOLED MAX TEMPS A BIT ON MONDAY AS AIRMASS
LOOKS A LITTLE COOLER THAN PREVIOUS MODEL RUNS. SLA

.LONG TERM...MONDAY NIGHT THROUGH SATURDAY...
EXITING SHORTWAVE AT THE BEGINNING OF THE EXTENDED CONTINUES TO BE
HANDLED DIFFERENTLY BY THE 12Z MODEL SUITE WITH DIFFERENCES
CONTINUING THROUGH THE REMAINDER OF THE PERIOD.
HOWEVER...UNSETTLED WEATHER WITH SCATTERED AFTERNOON AND EVENING
CONVECTION WILL PREVAIL THROUGH THE EXTENDED FORECAST. AFTER THE
EXITING SHORTWAVE ON TUESDAY GFS AND ECMWF QUICKLY BUILD A
LONGWAVE TROUGH OVER THE WEST COAST. THIS TROUGH SLOWLY PROPAGATES
EASTWARD THROUGH THE REST OF THE WEEK WITH THE ECMWF TAKING IT
FARTHER EAST THAN THE GFS. BOTH MODELS KEEP A SURFACE TROUGH IN
THE VICINITY OF THE CWA. TEMPERATURES WILL AVERAGE BELOW SEASONAL
NORMALS THROUGH THE EXTENDED PERIOD. ONLY CHANGES WERE FOR COORDINATION
PURPOSES AS POPS NEAR CLIMATOLOGY ARE REASONABLE GIVEN THE MODEL
UNCERTAINTY WITH AN UNSETTLED PATTERN. AJZ

PREVIOUS LONG TERM DISCUSSION...
THE EXTENDED PERIOD BEGINS WITH A SHORT WAVE TROUGH TRAVELING OVER
THE NORTHERN PLAINS. MODELS DIFFER ON DETAILS AND TRACK OF
DISTURBANCE FOR TUESDAY. THE ECMWF SENDS THE LOW INTO CANADA WHILE
THE GFS SENDS IT INTO THE CENTRAL PRAIRIE. THE BEST OPTION FOR NOW
IS TO MAINTAIN CHANCE POPS/THUNDER AS INHERITED. ON THE HEELS OF
THE SHORT WAVE ANOTHER UPPER TROUGH WILL SLIDE SOUTH INTO THE
PACIFIC NORTHWEST. THIS LONG WAVE TROUGH WILL SPREAD OVER THE
WESTERN STATES BRINGING COOLER AIR AND UNSETTLED CONDITIONS FOR
MOST OF THE REMAINDER OF THE PERIOD. GFS HAS NOT BEEN CONSISTENT
WITH THIS SYSTEM SO WILL LEAN TOWARDS THE MORE CONSISTENT EXTENDED
MODEL...WHICH IS THE ECMWF FOR NOW. WITH GENERAL TROUGHINESS WILL
MAINTAIN AT LEAST SLIGHT CHANCE POPS AND COOLER THAN NORMAL
TEMPERATURES THROUGH ALL PERIODS. SCT

&&

.AVIATION...
VFR CONDITIONS WILL PREVAIL THROUGH SUNDAY AFTERNOON.  MID LEVEL
CLOUDS WILL INCREASE LATE TONIGHT AND INTO SUNDAY. SHOWERS AND
THUNDERSTORMS WILL DEVELOP SUNDAY AFTERNOON WITH MORE COVERAGE
THAN TODAY. ANY THUNDERSTORMS COULD BRING BRIEF MVFR CONDITIONS TO
THE TERMINALS. WIND WILL BECOME EAST AROUND 10KT SUNDAY AFTERNOON
WITH HIGHER GUSTS IN AND AROUND ANY THUNDERSTORMS...WHICH WOULD BE
VARIABLE IN DIRECTION. AJZ/SIMONSEN

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

WEATHER.GOV/GLASGOW