Severe Thunderstorm Warning 21, NWS Great Falls, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
915 AM MDT SAT JUN 16 2007

UPDATED ZONES AND STATE BY 1000 AM

.UPDATE...
A RATHER ACTIVE SEVERE WEATHER DAY EXPECTED TO SET UP OVER NORTH
CENTRAL/SOUTHWEST MONTANA LATER THIS AFTERNOON AND EVENING.

A FEW CHANGES TO THE FORECAST FOR THIS MORNING...ONE AREA OF LIGHT
RAIN WAS MOVING THROUGH EAST GLACIER PARK...TOWARDS THE CUT BANK
AREA. POPS HAVE BEEN RAISED IN THIS AREA. TEMPERATURES ALSO LOWERED
A BIT DO TO CLOUDS/PRECIP. ISOLATED LIGHT RAIN SHOWERS FALLING NORTH
OF LEWISTOWN...SO LOW POPS CONTINUE FOR THAT REGION. OTHERWISE...ALL
ELSE IS IN GOOD SHAPE FOR THIS MORNING.

SEVERE THUNDERSTORMS WILL DEVELOP THIS AFTERNOON ALONG A LINE FROM
JUST SOUTH OF EAST GLACIER PARK TO JUST NORTH OF BUTTE BETWEEN 1 PM
AND 3 PM. THESE SEVERE THUNDERSTORMS WILL MOVE EAST-NORTHEAST
THROUGH NORTH CENTRAL/SOUTHWEST MONTANA THROUGH THE REMAINDER OF THE
AFTERNOON AND EVENING HOURS. LARGE HAIL/DAMAGING WINDS WILL BE THE
MAIN THREAT. SPC HAS PLACED MOST OF NORTH CENTRAL MONTANA IN A
MODERATE RISK OF SEVERE THUNDERSTORMS. THIS LOOKS GOOD...AS
WIDESPREAD LARGE HAIL/DAMAGING WINDS WILL OCCUR OVER MUCH OF THIS
REGION. THE THREAT FOR TORNADOES OVER THIS REGION DOES NOT LOOK AS
GOOD AS IT DID YESTERDAY...AS THE DIRECTIONAL SHEAR IS NOT QUITE
THEIR. HOWEVER...DO TO THE HIGH INSTABILITY AND STRONG SPEED SHEAR
ALOFT...AN ISOLATED TORNADO IS STILL POSSIBLE...MAINLY EAST OF GREAT
FALLS. REFER TO THE 1000 AM UPDATED HWO FOR A FEW MORE DETAILS.

FOR TONIGHT AND SUNDAY...SEVERE WEATHER WILL CONTINUE THROUGH THE
EVENING HOURS OVER THE REGION...AS AN UPPER LEVEL TROF MOVES INTO
WESTERN MONTANA BY EARLY SUNDAY MORNING. EXPECT A RATHER COOL AND
SHOWERY DAY OVER MUCH OF THE REGION FOR SUNDAY. BRUSDA

&&

.AVIATION...
UPDATED 1125Z.
SOUTHWEST FLOW ALOFT OVER THE REGION WILL BECOME INCREASINGLY MOIST
THROUGH THE COURSE OF THE DAY. THE AIRMASS WILL BECOME QUITE
UNSTABLE AFTER 18Z AND A SURFACE TROUGH MOVING THROUGH THE AREA WILL
PROVIDE A STARTING POINT FOR CONVECTION. THUNDERSTORMS WILL BECOME
WIDESPREAD OVER THE AREA WITH SOME PRODUCING STRONG GUSTY
WINDS...LARGE HAIL AND PERIODS OF HEAVY RAIN. VFR CONDITIONS WILL
PREVAIL THROUGH 18Z WITH AREAS OF MVFR AND LOCAL IFR IN CONVECTION
THROUGH THE EVENING. LATE IN THE EVENING CONVECTION WILL TAPER OFF
FROM THE WEST...BUT WILL CONTINUE OVER THE EASTERN ROUTES. THOMSON

&&

.PREV DISCUSSION... (ISSUED 525 AM MDT SAT JUN 16 2007)

DISCUSSION...

TODAY THROUGH MONDAY...AN ACTIVE WEATHER DAY SHAPING UP FOR THE
COUNTY WARNING AREA. A CLOSED UPPER LOW PUSHES ONSHORE OVER THE
PACIFIC NORTHWEST THIS MORNING RESULTING IN AN INCREASING
SOUTHWESTERLY FLOW ALOFT OVER THE AREA. THE AIRMASS WILL BECOME
INCREASINGLY UNSTABLE THIS AFTERNOON AS MORE MOISTURE IS ADVECTED
INTO THE AREA. A SURFACE TROF DEVELOPS BY LATE AFTERNOON OVER
EASTERN MONTANA AND THIS WILL HELP FOCUS CONVECTIVE DEVELOPMENT.
SPC HAS MOST OF MONTANA UNDER A SLIGHT RISK. PREDICTIVE SOUNDINGS
INDICATE STEEP LAPSE RATES AND DECENT CAPE VALUES ACROSS THE AREA.
THE SOUNDINGS ALSO INDICATE STRONG SHEAR AND A FAIRLY DEEP MOIST
LAYER. SOME THUNDERSTORMS ARE LIKELY TO BECOME SEVERE WITH
DAMAGING WINDS AND LARGE HAIL THE PRIMARY THREATS. MUCH COOLER AIR
MOVES INTO THE AREA SUNDAY AS THE CLOSED LOW PASSES OVER CENTRAL
MONTANA. WITH THE COLD POOL ALOFT...SCATTERED SHOWERS WILL REMAIN
A POSSIBILITY. NORTHWEST FLOW ALOFT WILL TAKE UP RESIDENCE ON
MONDAY WITH ENOUGH INSTABILITY FOR ISOLATED SHOWERS. TEMPERATURES
WILL BE THE WARMEST TODAY WITH READINGS DROPPING BELOW SEASONAL
AVERAGES ON SUNDAY. TEMPERATURES WILL CLIMB SLIGHTLY ABOVE
SEASONAL AVERAGES ON MONDAY. EMANUEL

MONDAY NIGHT THROUGH THURSDAY NIGHT...MODELS ARE STARTING TO COME
INTO BETTER ALIGNMENT ON EXTENDED SO CONFIDENCE IN THE FORECAST HAS
INCREASED FROM LAST NIGHT. STILL...WENT WITH CONSERVATIVE CHANGES
TOWARD THE GFS (AND NEWER ECMWF) SOLUTION AND WILL SEE WHAT TOMORROW
NIGHT BRINGS BEFORE MAKING BIGGER CHANGES. MODELS ARE NOW BOTH
INDICATING AN UPPER LEVEL RIDGE BUILDING INTO THE REGION BY TUESDAY
NIGHT. RIDGE DOMINATES THROUGH THURSDAY BEFORE GETTING PUSHED
EASTWARD AS THE NEXT PACIFIC LOW MARCHES TOWARD THE PACIFIC
NORTHWEST AND SOUTHERN BRITISH COLOMBIA. FLOW THROUGH THE RIDGE
SHOULD BE JUST DIRTY ENOUGH FOR SOME AFTERNOON AND EVENING
CONVECTION SO ONLY LOWERED POPS A LITTLE. ALSO WARMED TEMPERATURES
SLIGHTLY...AGAIN BEING CONSERVATIVE WITH MY CHANGES FOR NOW. THOMSON

FRIDAY THROUGH SATURDAY...MODELS CONTINUE WITH A LONG WAVE TROUGH
OVER THE EASTERN PACIFIC AND A BROAD UPPER LEVEL RIDGE OVER THE
UPPER MIDWEST. THUS...MONTANA WILL BE UNDER A RATHER MOIST AND
UNSTABLE SOUTHWEST FLOW ALOFT. TEMPERATURES WILL RUN WARMER THAN
SEASONAL AVERAGE ALONG WITH ISOLATED/SCATTERED
THUNDERSTORMS...ESPECIALLY OVER THE MOUNTAINS. WILLIAMSON DC

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  78  50  66  43 /  40  70  30  30
CTB  68  48  62  40 /  40  60  40  30
HLN  83  52  70  45 /  40  70  30  20
BZN  84  50  69  40 /  40  50  40  30
WEY  77  42  64  35 /  30  30  20  30
DLN  83  49  72  38 /  30  20  20  20
HVR  79  54  67  45 /  20  70  40  40
LWT  76  52  65  42 /  30  70  40  40

&&

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

&&

WEATHER.GOV/GREATFALLS

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE GREAT FALLS MT
1000 AM MDT SAT JUN 16 2007

MTZ008>015-044>055-171200-
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-
1000 AM MDT SAT JUN 16 2007

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

.DAY ONE...TODAY AND TONIGHT

THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF NORTH
CENTRAL MONTANA THIS AFTERNOON AND EVENING...WHILE A SLIGHT RISK OF
SEVERE THUNDERSTORMS IS EXPECTED OVER MUCH OF SOUTHWEST MONTANA.

WIDESPREAD THUNDERSTORMS WILL DEVELOP BETWEEN 1 PM AND 3 PM THIS
AFTERNOON BETWEEN EAST GLACIER PARK AND BUTTE. THESE THUNDERSTORMS
WILL QUICKLY BECOME SEVERE AS THEY MOVE EASTWARD TOWARDS THE
HELENA...GREAT FALLS...AND BOZEMAN AREAS. THESE SEVERE THUNDERSTORMS
WILL CONTINUE TO MOVE EASTWARD AND AFFECT MUCH OF CENTRAL
MONTANA...INCLUDING THE HAVRE AND LEWISTOWN AREAS THROUGH THIS
EVENING. THE MAIN THREAT FROM THE SEVERE THUNDERSTORMS TODAY WILL BE
DAMAGING WINDS...LARGE HAIL AND PERIODS OF HEAVY RAINFALL. THE BEST
TIME FRAME FOR ANY SEVERE STORMS TO OCCUR IS FROM 2 PM TO 10 PM.

LISTEN TO NOAA WEATHER RADIO OR YOUR LOCAL MEDIA OUTLETS FOR ANY
UPDATED FORECASTS...WATCHES...OR WARNINGS THAT COULD BE ISSUED LATER
TODAY ON THIS DEVELOPING SEVERE WEATHER EVENT.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.SPOTTER INFORMATION STATEMENT...

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