Severe Thunderstorm Warning 25, NWS Great Falls, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1020 AM MDT MON JUL 6 2009

.DISCUSSION...

CONTINUE TO EXPECT AN ACTIVE THUNDERSTORM PATTERN THIS AFTERNOON
WITH SEVERE THUNDERSTORMS VERY POSSIBLE. SPC CONTINUES WITH A SLIGHT
RISK OVER THE STATE. HAVE MADE MINOR UPDATES TO THE GRIDS AND WILL
ISSUE ANOTHER SET OF ZONES. EMANUEL

&&

.AVIATION...
UPDATED 1800Z.
VFR CONDITIONS WILL PREVAIL AT ALL SITES AHEAD OF A COLD FRONT
LIKELY TO PRODUCE THUNDERSTORMS. THE FRONT WILL START TO MOVE OVER
THE AREA EARLY IN THE AFTERNOON AND BECOME MORE ORGANIZED AS IT
MOVES EASTWARD. THUNDERSTORMS WILL LIKELY PRODUCE GUSTY ERRATIC
WINDS AND BRIEF HEAVY RAINFALL. SOME HAIL IS EXPECTED WITH THESE
STORMS ALONG WITH THE POSSIBILITY OF WINDS IN EXCESS OF 60 MPH.
BRIEF INTRUSIONS INTO MVFR AND IFR ARE POSSIBLE WITH THESE STORMS.
AFTER THE STORMS PASS...SOME HIGHER CEILINGS ARE EXPECTED BUT
CONDITIONS SHOULD QUICKLY REVERT TO IFR CONDITIONS. SUK

&&

.PREV DISCUSSION...ISSUED 429 AM MDT MON JUL 6 2009

...SEVERE WEATHER EVENT EXPECTED THIS AFTERNOON AND EVENING...

TODAY AND TONIGHT...A STRONG WEATHER DISTURBANCE ALOFT NEAR THE
CASCADES THIS MORNING WILL MOVE INTO THE AREA WEST OF THE
CONTINENTAL DIVIDE THIS AFTERNOON THEN SWEEP THROUGH THE FORECAST
AREA THIS EVENING. THE ASSOCIATED COLD FRONT WILL MOVE THROUGH THE
EAST SLOPES THIS AFTERNOON AND BE EAST OF A GREAT FALLS-CUT BANK
LINE BY 6 PM MDT. THIS COLD FRONT THEN SHOULD REACH A
HAVRE-LEWISTOWN LINE BY MID-EVENING. THE COLD FRONT WILL PROVIDE A
FOCUS AND TRIGGER FOR A LINE OF THUNDERSTORMS. INSTABILITY AND WIND
SHEAR APPEAR GREAT ENOUGH FOR SOME SEVERE THUNDERSTORMS TO BE
EMBEDDED IN THIS LINE. IN FACT CONDITIONS ARE SUCH THAT THERE IS A
THREAT OF TORNADOES OVER NORTH CENTRAL MONTANA. DRIER AIR WILL MOVE
IN BEHIND THE FRONT AND NOT ONLY END THE THREAT OF SEVERE
THUNDERSTORMS BUT ALSO THE THREAT OF ANY SHOWERS.

TUESDAY THROUGH WEDNESDAY...ON TUESDAY THERE WILL BE SOME RESIDUAL
INSTABILITY FOR SOME AFTERNOON SHOWERS AND THUNDERSTORMS. SEVERAL
WEATHER DISTURBANCES ALOFT WILL AFFECT THE FORECAST AREA TUESDAY
NIGHT INTO WEDNESDAY. MODELS DEVELOP A ROUGHLY EAST-WEST BAND OF
PRECIPITATION OVER THE FORECAST AREA DURING THE PERIOD OF TUESDAY
NIGHT THROUGH WEDNESDAY BUT DIFFER ON ITS PLACEMENT. SO FOR NOW WILL
GENERALLY KEEP THE CHANCES OF PRECIPITATION IN THE CHANCE RANGE.
BLANK

WEDNESDAY NIGHT THROUGH SATURDAY NIGHT...FORECAST PERIOD BEGINS WITH
A SHORTWAVE TROUGH EXITING THE REGION WITH ISOLATED SHOWERS AND
THUNDERSTORMS LINGERING THROUGH WEDNESDAY NIGHT BEFORE DIMINISHING.
A LOW AMPLITUDE RIDGE BUILDS ON THURSDAY WHICH WILL YIELD QUIETER
CONDITIONS ALONG WITH COOLER THAN AVERAGE TEMPERATURES...HOWEVER
KEPT SLIGHT CHANCE POPS WITH TERRAIN-INDUCED SHOWERS AND
THUNDERSTORMS POSSIBLE OVER THE MOUNTAINS. MODELS DIVERGE ON FRIDAY
AS ANOTHER SERIES OF SHORTWAVES CROSSES THE FORECAST AREA UNDER WEAK
FLOW. GIVEN THE MODEL UNCERTAINTY AND TYPICAL DAYTIME
INSTABILITY...KEPT SLIGHT CHANCE POPS WITH SLIGHTLY COOLER THAN
AVERAGE TEMPERATURES. BY SATURDAY...TEMPERATURES WILL CLIMB
CLOSER TO SEASONAL AVERAGES WITH TRANQUIL CONDITIONS ANTICIPATED.
MLS

SUNDAY THROUGH MONDAY...MODELS ARE IN FAIR AGREEMENT DURING THIS
PERIOD...WITH SOME DIFFERENCES IN TIMING OF FEATURES. A WEAK UPPER
LEVEL RIDGE MOVES EAST OF THE REGION SUNDAY MORNING. BEHIND THIS
SYSTEM...AN UPPER LEVEL LOW PRESSURE SYSTEM APPROACHES FROM THE
NORTHWEST COAST WITH AN ASSOCIATED WEAK COLD FRONT MOVING ACROSS THE
FORECAST AREA MONDAY. LIMITED MOISTURE IN A SOMEWHAT UNSTABLE
SOUTHWESTERLY FLOW ALOFT WILL RESULT IN ISOLATED SHOWERS AND A FEW
MAINLY AFTERNOON AND EVENING THUNDERSTORMS. SHOWERS AND
THUNDERSTORMS WILL BE A LITTLE MORE NUMEROUS OVER THE MOUNTAINS.
TEMPERATURES ARE EXPECTED TO TO BE NEAR SEASONAL AVERAGES SUNDAY
BEFORE COOLING SEVERAL DEGREES MONDAY. EK

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  83  51  78  50 /  60  30  20  50
CTB  73  47  72  45 /  80  20  20  20
HLN  86  48  80  52 /  60  30  30  50
BZN  90  45  84  50 /  20  30  20  40
WEY  76  39  73  40 /  20  30  10  20
DLN  81  42  77  47 /  30  20  20  40
HVR  86  52  80  50 /  40  70  20  40
LWT  83  49  76  48 /  30  70  20  60

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

SHORT TERM...EMANUEL/BLANK
LONG TERM...MLS/KURDY
AVIATION...SUK

WEATHER.GOV/GREATFALLS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GREAT FALLS MT
737 AM MDT MON JUL 6 2009

MTZ008>015-044>055-071345-
BEAVERHEAD-NORTHERN ROCKY MOUNTAIN FRONT-EASTERN GLACIER-HILL-
CASCADE-CHOUTEAU-CENTRAL AND SOUTHERN LEWIS AND CLARK-MADISON-
TOOLE-LIBERTY-EASTERN PONDERA-BLAINE-
SOUTHERN ROCKY MOUNTAIN FRONT-EASTERN TETON-JUDITH BASIN-FERGUS-
JEFFERSON-BROADWATER-MEAGHER-GALLATIN-
737 AM MDT MON JUL 6 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL
MONTANA...NORTH CENTRAL MONTANA AND SOUTHWEST MONTANA.

.DAY ONE...TODAY AND TONIGHT

SEVERE THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON AND EVENING. A
SHARP COLD FRONT WILL PUSH THROUGH THE REGION DURING THE AFTERNOON
AND EVENING HOURS...TRIGGERING NUMEROUS STRONG TO SEVERE
THUNDERSTORMS. DANGEROUS LIGHTNING...HAIL IN EXCESS OF 1 INCH IN
DIAMETER...AND DAMAGING WINDS IN EXCESS OF 60 MPH ARE LIKELY WITH
THE STRONGEST STORMS. THERE IS A SLIGHT RISK OF TORNADOES POSSIBLE
WITH THE STRONGEST STORMS. THE THREAT OF SEVERE WEATHER WILL BE
SOMEWHAT LESS OVER BEAVERHEAD...MADISON...AND GALLATIN COUNTIES.
THE THREAT OF SEVERE WEATHER WILL REACH CUT BANK BY MID-
AFTERNOON...GREAT FALLS AND LEWISTOWN AND BOZEMAN BY LATE
AFTERNOON...AND HAVRE BY EARLY EVENING. THE THREAT OF SEVERE
WEATHER WILL DIMINISH AT CUT BANK AND GREAT FALLS AND BOZEMAN
DURING THE EARLY EVENING...LEWISTOWN BY MID-EVENING AND HAVRE BY
MIDNIGHT. ANYONE PLANNING TRAVEL OR OUTDOOR ACTIVITIES THIS
AFTERNOON AND EVENING SHOULD KEEP TRACK OF CONDITIONS VIA
TELEVISION AND RADIO STATIONS AND NATIONAL WEATHER SERVICE RADIO
AND WEB SITES.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS SHOULD BE PREPARED TO SAFELY OBSERVE AND PROVIDE
TIMELY REPORTS OF SIGNIFICANT WEATHER CONDITIONS TO THE NATIONAL
WEATHER SERVICE OFFICE IN GREAT FALLS OR LOCAL LAW ENFORCEMENT
AGENCIES THIS AFTERNOON AND EVENING.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREAT FALLS MT
115 PM MDT MON JUL 6 2009

MTZ052-062000-
JEFFERSON MT-
115 PM MDT MON JUL 6 2009

...SIGNIFICANT WEATHER ADVISORY FOR WESTERN JEFFERSON COUNTY UNTIL
200 PM MDT...

AT 114 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED THAT
A THUNDERSTORM WAS RAPIDLY DEVELOPING 5 MILES NORTH OF WALKERVILLE...
OR 7 MILES NORTH OF BUTTE...MOVING NORTHEAST AT 25 MPH.

HAIL UP TO THE SIZE OF PENNIES AND WIND GUSTS UP TO 40 MPH ARE
EXPECTED WITH THIS STORM...ALONG WITH HEAVY RAIN AND FREQUENT
DANGEROUS LIGHTNING.

* LOCATIONS IMPACTED INCLUDE...
   BASIN...

IF THREATENING WEATHER APPROACHES YOUR AREA...TAKE SHELTER IN A
STURDY BUILDING.

IN ADDITION...THIS STORM MAY INTENSIFY...SO BE CERTAIN TO MONITOR
LOCAL RADIO AND TV STATIONS...AS WELL AS LOCAL CABLE TV OUTLETS...FOR
ADDITIONAL INFORMATION AND POSSIBLE WARNINGS FROM THE NATIONAL
WEATHER SERVICE.

LAT...LON 4633 11253 4635 11249 4633 11247 4639 11241
      4639 11236 4642 11233 4642 11227 4633 11210
      4605 11247 4616 11253 4618 11259 4622 11260
TIME...MOT...LOC 1915Z 218DEG 20KT 4611 11257

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREAT FALLS MT
157 PM MDT MON JUL 6 2009

MTZ050-051-062045-
FERGUS MT-JUDITH BASIN MT-
157 PM MDT MON JUL 6 2009

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL JUDITH BASIN AND WESTERN
FERGUS COUNTIES UNTIL 245 PM MDT...

AT 156 PM MDT...STORM SPOTTERS REPORTED A STRONG THUNDERSTORM NEAR
STANFORD...MOVING NORTHEAST AT 20 MPH.

HAIL UP TO THE SIZE OF PENNIES AND WIND GUSTS UP TO 40 MPH ARE
EXPECTED WITH THIS STORM...ALONG WITH HEAVY RAIN AND FREQUENT
DANGEROUS LIGHTNING.

* LOCATIONS IMPACTED INCLUDE...
   BENCHLAND...
   DENTON...

IF THREATENING WEATHER APPROACHES YOUR AREA...TAKE SHELTER IN A
STURDY BUILDING.

LAT...LON 4743 10988 4724 10964 4697 11016 4711 11034
TIME...MOT...LOC 1957Z 229DEG 18KT 4710 11015

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