Severe Thunderstorm Warning 57, NWS Glasgow, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
805 PM MDT SAT JUL 31 2004

.UPDATE...QUIET EVENING AT THE MOMENT WITH CLEAR SKIES ACROSS
NORTHEAST MONTANA WITH SURFACE HIGH PRESSURE RIDGING INTO THE AREA
FROM CENTRAL ALBERTA. FRONTAL BOUNDARY EXTENDING FROM NORTH CENTRAL
MONTANA NEAR CUT BANK TO THE SE CORNER OF THE STATE IS SEPARATING
DEW POINTS IN THE 50S NORTH FROM DEW POINT IN THE 30S SOUTH. SOME
THUNDERSTORMS DEVELOPED THIS AFTERNOON NEAR THIS FRONT IN THE
ROCKIES IN SOUTHERN ALBERTA AND WERE MOVING EAST ALONG THE
MT/ALBERTA BORDER BETWEEN SHELBY AND LETHBRIDGE AT 02Z. CURRENT
MOVEMENT HAS THESE STORMS REACHING PHILLIPS COUNTY BETWEEN 05 AND
06Z. A WEAK SHORTWAVE MOVING EAST WITH THE STORMS MAY BE ENOUGH KEEP
THE STORMS TOGETHER INTO NE MONTANA OVERNIGHT.

THE FRONT SHOULD REMAIN STATIONARY OVERNIGHT. ETA AND GFS BOTH SHOW
FRONTOGENESIS DEVELOPING LATE TONIGHT INTO SUNDAY COMBINED WITH
OVERRUNNING THAT COULD ENHANCE ANY PRECIP THAT DEVELOPS.
HOWEVER...THE BEST OVERRUNNING IS EXPECTED TO REMAIN NORTH OF THE
BORDER IN SASKATCHEWAN. GOING CHANCE POPS FOR LATE TONIGHT AND
SUNDAY MORNING STILL LOOK REASONABLE. WILL UPDATE FORECAST TO TRIM
POPS THIS EVENING AND ADJUST WIND FORECAST AS MOST AREAS ALREADY
HAVE NE WINDS. FORRESTER

&&

.PREV DISCUSSION...
.SHORT TERM...FOR NORTHEAST MONTANA TONIGHT THROUGH MONDAY...
A FEW CUMULUS CLOUDS ARE STARTING TO DEVELOP ACROSS THE AREA.
SURFACE BOUNDARY STILL FLOATING AROUND AREA.  SO WITH MODELS
INDICATING BETTER LIFT...HAVE LEFT TONIGHT ALONE AS SOME OF THE
CUMULUS COULD FORM INTO THUNDERSTORMS.

MODELS ARE IN GENERAL AGREEMENT FOR THE SHORT TERM.  UPPER PATTERN
OF NORTHWEST FLOW REMAINS AS A RIDGE STARTS TO BUILD TO THE WEST OF
THE AREA.  HOWEVER...THE MODELS DO NOT AGREE AT ALL WITH THE DETAILS
OF WHAT WILL HAPPEN.  THE GFS AND ETA MODELS BOTH SHOW SHORTWAVES
AND LIFT MOVING THROUGH NORTHEAST MONTANA AT DIFFERENT TIMES THROUGH
SUNDAY.  SO WILL LEAVE PRECIPITATION ALONE IN THE FIRST COUPLE
PERIODS.   MODELS AGREE THAT SUNDAY NIGHT INTO MONDAY WILL HAVE
LITTLE DYNAMICS TO DEVELOP STORMS SO HAVE LOWERED POPS FOR THESE
PERIODS.  TLSJR

.LONG TERM...MONDAY NIGHT THROUGH SATURDAY...
MEDIUM RANGE MODELS REMAIN IN OVERALL GOOD AGREEMENT NEXT WEEK WITH
THE LONGWAVE PATTERN.  THE SUBTROPICAL RIDGE WILL BUILD NORTH INTO
THE PLAINS. AN UPPER TROUGH WILL PUSH ACROSS THE NORTHERN ROCKIES
AND INTO THE NORTHERN PLAINS TOWARD THE END OF THE FORECAST PERIOD.
TEMPERATURES WILL AVERAGE NEAR TO A BIT ABOVE NORMAL MUCH OF THE
WEEK WITH A COOLER AIRMASS TO WORK INTO THE AREA BY NEXT WEEKEND.
THE BEST CHANCE OF CONVECTION LOOKS TO BE EARLY IN THE PERIOD
ASSOCIATED WITH A QUASI STATIONARY FRONTAL BOUNDARY ACROSS THE
AREA...AND AGAIN TOWARD THE END OF THE PERIOD AS A STRONG COLD FRONT
WORKS ACROSS THE AREA.

MONDAY NIGHT & TUESDAY...CLOSED UPPER RIDGE IN NORTHERN TEXAS
CONTINUES TO BUILD NORTH INTO EASTERN MONTANA. A SURFACE FRONT WILL
REMAIN NEARLY STATIONARY FROM NORTHWEST TO SOUTHEAST ACROSS THE CWA.
ALONG AND TO THE EAST OF THE FRONTAL BOUNDARY THE ATMOSPHERE WILL
BE UNSTABLE WITH LIS PROGGED PER THE GFS AS LOW AS -7C WITH
SURFACE BASED CAPE VALUES IN EXCESS OF 2000 J/KG TUESDAY AFTERNOON.
THE DEEPER MOISTURE WILL REMAIN ACROSS THE DAKOTAS WHERE THERE WILL
BE STRONGER RETURN FLOW...BUT LOOKS LIKE THERE MAY BE ENOUGH
MOISTURE AND INSTABILITY TO GENERATE A FEW THUNDERSTORMS.

TUESDAY NIGHT & WEDNESDAY...NO BIG CHANGE TO THE PATTERN AS THE
QUASI STATIONARY FRONTAL BOUNDARY ONLY VERY SLOWLY INCHES OFF TO THE
EAST. THE ATMOSPHERE REMAINS UNSTABLE ALONG AND EAST OF THE
BOUNDARY FOR A CONTINUED THREAT OF THUNDERSTORMS. THE UPPER RIDGE
AXIS WILL BE ACROSS EASTERN MONTANA DURING THIS TIME WHICH WILL HELP
TO KEEP THE ATMOSPHERE CAPPED AND SHOULD HELP TO LIMIT THE
THUNDERSTORM COVERAGE FROM BECOMING ALL THAT GREAT. ANY STORMS THAT
DO FIRE UP WOULD HAVE THE POTENTIAL OF BECOMING STRONG TO SEVERE.

WEDNESDAY NIGHT & THURSDAY...THE FRONTAL BOUNDARY WILL REMAIN ACROSS
OUR EASTERN ZONES...BUT WITH CONTINUED WARMING AT LOW AND MID LEVELS
AS THE THERMAL RIDGE WORKS INTO EASTERN MONTANA CONTINUED WOULD BE
LESS FAVORABLE FOR THUNDERSTORM DEVELOPMENT. AN UPPER TROUGH WILL
BEGIN TO PUSH INTO THE PACIFIC NORTHWEST BY LATE IN THE THURSDAY.

FRIDAY & FRIDAY NIGHT...THE UPPER TROUGH CONTINUES TO PUSH EAST AND
ACROSS THE NORTHERN ROCKIES. SOME DIFFERENCES BETWEEN THE ECMWF AND
GFS. THE ECMWF LIFTS A PORTION OF THE TROUGH THROUGH SOUTHWEST
CANADA WITH A PIECE OF THE TROUGH LINGERING BACK IN WASHINGTON
STATE. THE GFS BRINGS A STRONG TROUGH ACROSS SOUTHERN CANADA LATE
FRIDAY AND FRIDAY NIGHT WHICH WOULD SEND A STRONG COLD FRONT ACROSS
THE AREA. DURING RECENT WEEKS THE TREND HAS BEEN FOR THESE STRONGER
TROUGHS AND COLD FRONTS TO PUSH ACROSS THE AREA...SO PLAN TO LEAN
CLOSER TO THE GFS SOLUTION ALTHOUGH FEEL THAT THE TIMING MAYBE A BIT
TOO QUICK. IN COORDINATION WITH SURROUNDING OFFICES HAVE INTRODUCED
A CHANCE OF THUNDERSTORMS TO THE FORECAST FRIDAY AFTERNOON...AND WILL
GRADUALLY SHIFTS THE POPS EAST FRIDAY NIGHT.

SATURDAY...BASED ON THE ABOVE THINKING THE UPPER TROUGH SHOULD PUSH
EAST SATURDAY FOR COOLER WEATHER.  WILL LINGER SOME SHOWERS ACROSS
OUR EASTERN ZONES TO ACCOUNT FOR POSSIBLE SLOWER TIMING. PLAN TO
LOWER TEMPERATURES A FEW DEGREES BEHIND THE FRONT. SHOULD LATER RUNS
CONTINUE TO LOOK SIMILAR TO THE CURRENT GFS WOULD LIKELY NEED TO
KNOCK TEMPERATURES BACK INTO THE 70S WHICH IS WHAT HAS BEEN
OCCURRING BEHIND THE COLD FRONTAL PASSAGES MUCH OF THE SUMMER. CB

&&

.KGGW WATCHES/WARNINGS/ADVISORIES...NONE.

&&