Flash Flood and Hail in Montana, July 14, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
249 PM MDT THU JUL 14 2011

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH SATURDAY...
THUNDERSTORMS ARE BEGINNING TO DEVELOP THIS AFTERNOON ACROSS
SOUTHWEST AND CENTRAL MONTANA...DRIVEN BY AN EMBEDDED DISTURBANCE
IN  A SOUTHWEST FLOW ALOFT. GIVEN EXCELLENT UPPER LEVEL SUPPORT
EXPECT THESE STORMS TO CONTINUE TO INTENSIFY THROUGH THE
AFTERNOON...BRINGING A SEVERE WEATHER OUTBREAK TO NORTHEAST
MONTANA THIS EVENING. A SEVERE THUNDERSTORM HAS BEEN ISSUED
THROUGH 9PM THIS EVENING FOR MUCH OF THE AREA. BY LATE EVENING
AND OVERNIGHT THE BETTER POTENTIAL FOR STORMS WILL LIE ACROSS THE
EASTERN ZONES...AND GIVEN GOOD DYNAMIC SUPPORT EXPECT A ROUND OF
ONGOING NOCTURNAL THUNDERSTORMS.

FRIDAY AFTERNOON AND EVENING THE WARM SOUTHWEST FLOW ALOFT WILL
CONTINUE. ALTHOUGH SUPPORT DOES NOT LOOK AS STRONG...ANOTHER ROUND
OF STRONG TO SEVERE THUNDERSTORMS WILL BE POSSIBLE...MAINLY SOUTH
OF THE MISSOURI RIVER. STORM ACTIVITY WILL AGAIN TAPER OFF SOME
OVERNIGHT FRIDAY NIGHT...HOWEVER AGAIN CAN NOT RULE OUT A
NOCTURNAL STORM OR TWO GIVEN REASONABLE QG FORCING AND MID LEVEL
INSTABILITY/MOISTURE.

SATURDAY UPPER RIDGING WILL BEGIN BUILDING INTO NORTHEAST
MONTANA...HOWEVER SOUTHWEST FLOW ALOFT WILL CONTINUE. THIS WILL
BRING INCREASING TEMPERATURES...AND WILL PUSH THE BEST POTENTIAL
FOR THUNDERSTORMS NORTH OF THE MISSOURI RIVER. GILCHRIST

.LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...
THE EXTENDED PERIOD CONTINUES WITH THE PERSISTENT SOUTHWEST FLOW
ALOFT OVER EASTERN MONTANA THAT IS DRIVEN BY HIGH PRESSURE OVER
SOUTHEASTERN CONUS AND A TROUGH OVER BRITISH COLUMBIA. WITH THE
TROUGH SLOWLY LIFTING FARTHER NORTH THE HIGH PRESSURE CENTER
SPREADS NORTHWEST INTO NEMONT BRINGING IN DRIER AND HOTTER AIR.
GFS MODEL GUIDANCE SUGGESTS TRIPLE DIGITS BY MONDAY...BUT WILL
HOLD OFF DUE TO UNCERTAINTY. AFTERNOON/EVENING INSTABILITY COULD
LEAD TO SOME THUNDERSTORMS DEVELOPING SO ADDED SLIGHT CHANCE POPS
FOR SATURDAY...SUNDAY AND MONDAY EVENINGS. LATE IN THE WEEK THE
WEST COAST TROUGH DEVELOPS A SHORTWAVE THAT WILL BE SPUN OFF TO
THE EAST ACROSS NORTHERN MONTANA. THE MODELS ARE KIND OF DRY ON
THIS ONE BUT THE FRONT COULD INITIATE MORE THUNDERSTORMS. AFTER
THE VERY WARM TEMPERATURES WITH LOW RELATIVE HUMIDITY...FIRE
WEATHER COULD SOON BECOME A CONCERN. SCT

PREVIOUS DISCUSSION...
MODELS CONTINUE TO BE IN GOOD AGREEMENT WITH A SUBTLE PATTERN
CHANGE...A TRANSITION TO MORE OF A MID-SUMMER-LIKE PATTERN. THAT
IS...HOTTER AND DRIER. UPPER HIGH CENTER OVER TX EXPANDS NORTHWARD
AND INTENSIFIES...BECOMING A 600 DM CENTER OVER NE...ABOUT AS
STRONG AS IT EVER GETS. WEAKENING OF THE UPPER TROUGH ALONG THE
WEST COAST...AS A SIGNIFICANT PART OF IT MOVES NE INTO CANADA.
THIS HELPS ALLOW THE HIGH TO EXPAND NW.

WEAK TROUGH CONDITIONS ALONG THE W COAST...SW FLOW ALOFT IS OVER
OUR AREA STILL...BUT WEAKER AS WELL, THERE WILL BE WEAK
SHORTWAVES...BUT EXPECT THUNDERSTORM ACTIVITY TO BE QUITE LIMITED
...SUB-ISOLATED UNDER 15 PCT POPS MOST PERIODS.

THICKNESSES ARE IN THE 575 DM TO 585 DM RANGE MOST OF THE TIME.
MODELS INDICATE MONDAY TO BE THE HOTTEST... AS 850 MB TEMPS CLIMB
TO 28-32C OVER OUR AREA. THIS WILL PUSH HIGHS TO NEAR THE 100
DEGREE MARK.

MODELS DISAGREE SOME LATE IN THE PERIOD. THIS IS DUE TO HANDLING OF
THE W COAST UPPER TROUGH THAT IN RE-INFORCED BY A NEW UPPER LOW
FROM AK. PREFER THE PATTERN OF LATE...WHERE PART OF TROUGH MOVES
INLAND...BUT PART REMAINS ALONG W COAST. SOME MODELS AND SOME GFS
ENSEMBLES MEMBERS SHOWING THE WHOLE TROUGH MOVING INLAND...WHICH
SEEMS LEAST LIKELY...ESPECIALLY IN JULY. ALSO PREFER THE SLOWER
COLD FRONT ARRIVAL TUE/TUE NIGHT AS WELL. SIMONSEN

&&

.AVIATION...
THE PERSISTENT LOW ALONG THE WEST COAST WILL CONTINUE TO FEED A
MOIST SOUTHWESTERLY FLOW INTO MONTANA TODAY. IN ADDITION THE LEE
SURFACE TROUGH HAS SHIFTED EAST INTO A POSITION OVER NORTHEAST
MONTANA. THIS WILL BRING IN SCATTERED TO BROKEN CLOUD LAYERS
BETWEEN 5K AND 12K FT AGL LATER TODAY.

THE 12Z UPPER AIR SOUNDING FROM KGGW THIS MORNING INDICATED A VERY
UNSTABLE ENVIRONMENT. WITH THIS INSTABILITY...THUNDERSTORM
ACTIVITY WILL INCREASE IN AREA COVERAGE LATER THIS AFTERNOON AND
EVENING. SOME THUNDERSTORMS MAY BECOME SEVERE. THERE IS THE
POTENTIAL FOR LARGE HAIL AND WINDS GUSTS UP TO 50KT WITH ANY
SEVERE STORM. THE STRONGER STORMS WILL ALSO HAVE HEAVY SHOWERS
THAT COULD DROP VISIBILITIES AND CEILINGS TO MVFR/IFR TEMPORARILY.
SCT

&&

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

&&

WEATHER.GOV/GLASGOW

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GLASGOW MT
359 PM MDT THU JUL 14 2011

MTZ016>027-059>062-151200-
CENTRAL AND SOUTHEAST PHILLIPS-CENTRAL AND SOUTHERN VALLEY-
DANIELS-SHERIDAN-WESTERN ROOSEVELT-PETROLEUM-GARFIELD-MCCONE-
RICHLAND-DAWSON-PRAIRIE-WIBAUX-NORTHERN PHILLIPS-
SOUTHWEST PHILLIPS-NORTHERN VALLEY-EASTERN ROOSEVELT-
359 PM MDT THU JUL 14 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHEAST
MONTANA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

SCATTERED THUNDERSTORMS CAN BE EXPECTED THIS AFTERNOON AND
EVENING. THREATS WITH STORMS INCLUDE LARGE HAIL...STRONG DAMAGING
WINDS...AND HEAVY RAIN THAT COULD CAUSE LOCALIZED FLASH FLOODING.
A SEVERE THUNDERSTORM WATCH IS IN EFFECT UNTIL 9 PM FOR
PHILLIPS...VALLEY...DANIELS...SHERIDAN...ROOSEVELT...
PETROLEUM...GARFIELD...AND MCCONE COUNTIES.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

STRONG TO SEVERE THUNDERSTORMS WILL AGAIN BE POSSIBLE ON
FRIDAY...MAINLY SOUTH OF THE MISSOURI RIVER.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.