Severe Thunderstorm Warning 63, NWS Great Falls, MT

SOUTHWEST AND NORTH CENTRAL MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
300 PM MDT SAT JUL 21 2001

ACCORDING TO MODELS LOOKS LIKE THERE WILL BE A CHANGE TO CURRENT
PATTERN OF SW FLOW ALOFT WITH SEVERE WEATHER EPISODES E OF THE
CONTINENTAL DIVIDE. FOR TONIGHT...AIRMASS IS UNSTABLE ONCE AGAIN
OVER AREA AND EVEN A LITTLE MORE UNSTABLE THAN EARLY FRI AFTERNOON.
MSAS DATA INDICATES A MOISTURE CONVERGENCE AREA FROM SW TO N
CENTRAL MT AT 19Z. APPEARS TO BE ENOUGH SHEAR FOR ORGANIZED STORMS
BUT NOT NECESSARILY SUPERCELLS. THE PROBLEM LIKE FRIDAY NIGHT IS
THAT MODELS DO NOT INDICATE ANY SIGNIFICANT SHORTWAVES AFFECTING
FORECAST AREA. STILL WITH QUITE AN UNSTABLE AIRMASS WILL GO WITH HIGH
SCATTERED TO LOW LIKELY POPS OVER MOST OF AREA. IN THE FAR NW
WILL GO WITH SLIGHT CHANCE POPS AS THAT AREA IS FORECAST TO BE
IN A DRIER AIRMASS. FOR SUNDAY...ETA AND AVN DIFFER SIGNIFICANTLY
WITH REMNANTS OF PAC NW UPPER TROUGH MOVING THROUGH THE AREA. PREFER
THE SLOWER AND WEAKER ETA AS THE AVN/MRF HAS HAD A TENDENCY TO BE TOO
STRONG AND FAST WITH SHORTWAVES MOVING TOWARDS AN UPPER RIDGE. WILL
GO WITH 20 AND 30 PCT POPS AS MOISTURE AND LIFT AHEAD OF FEATURE ARE
NOT VERY IMPRESSIVE. FORECAST SOUNDINGS STILL INDICATE SOME
INSTABILITY DURING THE AFTERNOON BUT IT IS QUITE A BIT LESS THAN THAT
OF TODAY. FOR MONDAY...BOTH ETA AND AVN FORECAST A STRONGLY
POSITIVELY TILTED SHORTWAVE FROM SW SASK THROUGH NW MT TO ERN OREGON.
AREA IS MAINLY UNDER WLY CONFLUENT FLOW ALOFT WITH LITTLE IN THE WAY
OF SHORTWAVE ACTIVITY. AIRMASS IS ALSO NOT ALL THAT MOIST. WAS
TEMPTED TO GO DRY BUT MODELS DO INDICATE SOME WEAK INSTABILITY SO
WILL GO WITH BROADBRUSH 20 PCT POPS. AVN QPF FOR MON LOOKS OVERDONE.
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.EXTENDED...
ON TUESDAY THE TROUGH CONTINUES OVER THE WESTERN US WITH MINOR SHORT
WAVES MOVING THROUGH THE MEAN SW FLOW. THE TROUGH LOOKS LIKE IT
WILL MOVE EAST ON WEDNESDAY WITH YET ANOTHER TROUGH MOVING THROUGH
SOUTHERN CANADA ON THU/FRI. THOUGH THE FLOW ALOFT BECOMES MORE
WESTERLY BY THURSDAY...THE SHORTWAVE MOVING THROUGH ON THU/FRI WILL
KEEP A CHANCE OF AFTERNOON/EVENING STORMS IN FORECAST THROUGH FRI.
WITH NORTHWEST FLOW BY SAT...SHOULD BE DRYING OUT THEN.

CCF NUMBERS
GTF BB 055/078 050/078 048 04522
CTB BB 050/075 047/075 045 04221
HLN BB 054/080 051/080 050 04522
BZN BB 051/080 047/080 047 04431
WEY BB 046/075 042/076 042 04432
DLN BB 049/077 043/077 044 04421
HVR EB 060/088 054/088 052 04532
LWT EB 056/077 048/077 046 04632=

MTZ011>015-047-050>055-212230-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1030 AM MDT SAT JUL 21 2001

...STRONG THUNDERSTORMS POSSIBLE AGAIN THIS AFTERNOON AND EVENING
FOR CENTRAL MONTANA...

HAIL AND GUSTY WINDS WILL AGAIN BE POSSIBLE WITH THUNDERSTORMS IN AN
AREA EAST OF A LINE FROM HAVRE TO GREAT FALLS TO HELENA TO DILLON.
SOME THUNDERSTORMS...MAINLY OVER BLAINE...FERGUS...JUDITH
BASIN...AND MEAGHER COUNTIES COULD SEE HAIL TO 1 INCH IN
DIAMETER...WIND GUSTS TO 60 MPH...AND BRIEF HEAVY RAIN.

A VERY UNSTABLE AIRMASS CONTINUES OVER CENTRAL MONTANA. ONCE AGAIN
THUNDERSTORMS WILL DEVELOP OVER CENTRAL AND SOUTHWEST MONTANA THIS
AFTERNOON AND SPREAD NORTHEAST OVERNIGHT. DUE TO A LACK OF A
SIGNIFICANT WEATHER DISTURBANCE ALOFT...ANY SEVERE THUDNERSTORMS
THAT DEVELOP THIS AFTERNOON AND EVENING SHOULD BE ISOLATED.

ANYONE WITH OUTDOOR ACTIVITIES PLANNED THIS AFTERNOON AND EVENING
OVER CENTRAL MONTANA SHOULD LISTEN TO NOAA WEATHER RADIO...OR
ANOTHER MEDIA OUTLET...TO KEEP POSTED ON ANY WATCHES OR WARNINGS
THAT MAY BE ISSUED.

THIS INFORMATION CAN ALSO BE OBTAINED FROM OUR WEB SITE AT:
HTTP://WWW.WRH.NOAA.GOV/GREATFALLS

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