Hail in Montana, July 18, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
940 AM MDT FRI JUL 18 2008

.SHORT TERM...FOR NORTHEAST MONTANA...TODAY THROUGH SUNDAY...
12Z KGGW SOUNDING SHOWED WARMING BELOW 700 MB OF UP TO 6C PAST 24
HOURS...RESULTING IN A MORE UNSTABLE AIRMASS THIS MORNING. MODELS
SHOWING WEAK SHORTWAVES IN STRONG WSW FLOW ALOFT...105 KT
JET...MOVING OVER THE AREA TODAY RESULTING IN AN EARLY START TO
CONVECTION. VWP SHOWING SE FLOW UP TO 10K FT MSL WHICH SHOULD
CONTINUE TO MOISTEN THE AIRMASS AS FORECAST TODAY WITH SURFACE LOW
OVER CENTRAL MT. MINOR UPDATE TO MORN POPS...WHILE REST OF FORECAST
LOOKS GOOD. SIMONSEN

PREVIOUS SHORT TERM...FOR NORTHEAST MONTANA...TODAY THROUGH
SUNDAY...ALL INDICATIONS ARE THAT THE CURRENT TREND OF THE
FORECAST IS A GOOD ONE...AND NOT A LOT OF CHANGES WILL BE MADE FOR
THIS UPCOMING SHORT TERM PERIOD. SHORTWAVE RIDGE OVER THE AREA NOW
BEGINNING TO MAKE ITS EXIT TO THE EAST WITH UPPER LOW PRESSURE
CENTERED OVER CENTRAL BRITISH COLUMBIA CARVING A TROF SOUTH THRU
THE PACIFIC NORTHWEST. THUS THE UPPER FLOW OVER EASTERN MONTANA TO
BECOME SOUTHWEST BY LATER THIS MORNING. AT THE SURFACE A TROF IS
DEEPENING OVER CENTRAL MONTANA...WITH HIGH PRESSURE OVER THE
DAKOTAS MAKING AN ATTEMPT TO HOLD STAUNCH. THIS RESULTING IN A
TIGHTENING PRESSURE GRADIENT OVER THE AREA CAUSING AN INCREASE IN
EAST TO SOUTHEAST SURFACE WIND. THIS WILL BRING IN MORE MOIST LOW
LEVEL AIR TO EASTERN MONTANA AS TIME GOES ON TODAY. THE SURFACE
TROF IS EXPECTED TO DRIFT SLOWLY EAST TODAY WHILE A STRONG
SHORTWAVE APPROACHES THE REGION IN THE UPPER FLOW. BY MID-
AFTERNOON LAPSE RATES STEEPEN CONSIDERABLY OVER THE AREA WHICH
COUPLES WITH AFTERNOON HEATING TO RESULT IN AT LEAST MODERATE
INSTABILITY. FORECAST SOUNDINGS INDICATE MORE THAN ADEQUATE SHEAR
TO MAKE FOR A GOOD SEVERE WEATHER THREAT LATER THIS AFTERNOON AND
EVENING. ALTHO TORNADIC STORMS CANNOT BE RULED OUT...IT DOES
APPEAR THE FAR BIGGER THREAT IS FOR LARGE HAIL AND VERY STRONG
WIND. ALL PARTS OF THE CWA WILL BE UNDER THAT THREAT. THE
SHORTWAVE EXITS AFTER MIDNIGHT TONIGHT SO EXPECT ACTION TO START
TO TAPER OFF AFTER MIDNIGHT FROM WEST TO EAST WITH AN INTERLUDE OF
CLEARING OCCURRING AT LEAST IN THE WESTERN COUNTIES. SATURDAY
BRINGS THE PASSAGE OF A WEAK COLD FRONT BEING PUSHED BY THE
AFOREMENTIONED UPPER LOW CURRENTLY OVER CENTRAL BRITISH COLUMBIA.
SO MORE SHOWERS AND STORMS POSSIBLE...WITH BEST INSTABILITY AND
CAPE NEAR THE NORTH DAKOTA BORDER...SO SEVERE WEATHER ONCE AGAIN A
THREAT FOR AT LEAST THE COUNTIES BORDERING NORTH DAKOTA...AND
PERHAPS A LITTLE FARTHER WEST DEPENDING ON EXACTLY HOW THIS SYSTEM
PASSAGE EVOLVES. SURFACE HIGH PRESSURE MOVES IN SUNDAY...WITH
PERHAPS A WEAK UPPER RIDGE AS WELL. WITH WIND SHIFTING AROUND TO
WEST TO NORTHWEST...DEWPOINTS LOWER CONSIDERABLY AND LOW LEVEL
MOISTURE WANES. LOOKS LIKE A NICE DAY SUNDAY WITH PLEASANT
TEMPERATURES AND LOWER HUMIDITY. AFTERNOON CUMULUS SHOULD DOT THE
SKY. TEMPERATURES TODAY AND SATURDAY LIKELY A DEGREE OR TWO BELOW
NORMAL FOR MOST.

.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...
THE UPPER LEVEL PATTERN WILL TRANSITION TO ONE MORE TYPICAL OF
MID-SUMMER AS AN UPPER RIDGE STEADILY BUILDS OVER THE CENTRAL UNITED
STATES THROUGH NEXT WEEK. THEREFORE...THE EXTENDED PERIOD SHOULD
TREND TOWARD DRIER CONDITIONS AND WARMER THAN NORMAL TEMPERATURES.
THE 00Z SUITE OF MODELS AGREE FAIRLY WELL ON THE LONGWAVE
FEATURES...WITH SOME DIFFERENCES ON PLACEMENT AND HANDLING OF FINE
SCALE FEATURES. ECMWF IS INITIALLY LESS AMPLIFIED...WHICH IS
SIMILAR TO THE GFS ENSEMBLES...WHICH DEPART FROM THE MORE
AMPLIFIED OPERATIONAL GFS AND CANADIAN. THE FEATURE THAT BRINGS
THE BEST CHANCE FOR THUNDERSTORMS WILL BE A CLOSED LOW INITIALLY
OFF THE CALIFORNIA COAST MONDAY NIGHT. THIS CLOSED CIRCULATION
BECOMES AN OPEN WAVE AND LIFTS NORTHEAST ON THE BACK SIDE OF THE
RIDGE. MODELS STRUGGLE WITH HOW QUICKLY OR SLOWLY TO BRING THIS
WAVE TOWARD NORTHEAST MONTANA. CURRENTLY TUESDAY NIGHT/WEDNESDAY
SEEMS TO BE THE BEST TIMING...ALTHOUGH CONFIDENCE IS LOW. TRENDED
HIGHER WITH TEMPERATURES TOWARD THE END OF THE PERIOD AS
CONFIDENCE IS FAIRLY HIGH. AJZ

&&

.AVIATION...
A STRONG UPPER LEVEL SYSTEM WILL BRING SCATTERED THUNDERSTORMS TO
THE REGION TODAY AND TONIGHT. VFR CONDITIONS WILL PREVAIL
THE MAJORITY OF THE TIME WITH MVFR CONDITIONS OR LOWER ALONG WITH
LARGE HAIL AND STRONG WIND GUSTS POSSIBLE IN ANY THUNDERSTORMS.
THE PREVAILING WIND WILL BE OUT OF THE SOUTHEAST AROUND 10 TO 15KT
WITH STRONGER GUSTS OF VARIABLE DIRECTION IN AND AROUND
THUNDERSTORMS. AJZ

&&

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

&&

WEATHER.GOV/GLASGOW