Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 051801
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1201 PM MDT THU MAY 5 2016

...AVIATION SECTION CORRECTED...

.DISCUSSION...
HAVE MADE A FEW MINOR ADJUSTMENT TO THE POP GRIDS. REMAINDER OF
FORECAST LOOKS ON TRACK. COLD FRONT APPEARS TO BE MOVING ACROSS THE
INTERNATIONAL BORDER. WINDS HAVE SWITCHED TO A NORTHERLY DIRECTION
BEHIND THE FRONT. MODELS INDICATE THE AIRMASS WILL CONTINUE TO
DESTABILIZE AHEAD OF THE FRONT. SHOWERS AND THUNDERSTORMS WILL
DEVELOP BY MID AFTERNOON. MODELS INDICATE CAPE VALUES OF AROUND 400
J/KG AND BULK SHEAR VALUES 0F 40 KTS WHICH WILL TRANSLATE TO A FEW,
POSSIBLY STRONG, THUNDERSTORMS. CONVECTIVE ACTIVITY SHOULD BE RATHER
SHORT LIVED AND SHOULD END BY EARLY EVENING. TEMPERATURES LOOK GOOD.

&&

.AVIATION...
UPDATED 1801Z.
A COLD FRONT /CURRENTLY MOVING THROUGH KCTB AS OF 18Z/ WILL CONTINUE
TO PUSH SOUTH ACROSS CENTRAL AND PARTS OF SOUTHWEST MONTANA THROUGH
FRIDAY MORNING. ALONG AND BEHIND THE FRONT...SCT SHRA AND GUSTY
NORTH WINDS ARE EXPECTED TO DEVELOP. THE ATMOSPHERE MAY BECOME
UNSTABLE ENOUGH THIS AFTERNOON AND EVENING FOR A FEW TSRA TO DEVELOP
AS WELL. CONFIDENCE IS MODERATE THAT TSRA WILL DEVELOP...BUT LOWER
FOR MOST INDIVIDUAL TAF SITES. FOR THIS REASON...DROPPED TSRA FROM
ALL SITES BUT KHLN THROUGH THIS EVENING. OF NOTE...IF CONFIDENCE IN
TSRA INCREASES AT ANY TAF SITE...FUTURE FORECASTS MAY NEED TO BE
AMENDED TO REFLECT THIS. ANY TS THAT DEVELOPS THIS AFTERNOON/EVENING
COULD HAVE GUSTY WINDS AND SMALL HAIL. OTHERWISE...EXPECT LOWER CIGS
AND MTN OBSCURATIONS ALONG AND BEHIND THE FRONT WITH MVFR CIGS
LIKELY AT KGTF/KLWT. MARTIN

&&

.PREV DISCUSSION...ISSUED 317 AM MDT THU MAY 5 2016

TODAY THROUGH SATURDAY...THE HIGH AMPLITUDE RIDGE WHICH SUPPORTED
WELL ABOVE AVERAGE TEMPERATURES THE PAST FEW DAYS BEGINS TO
COLLAPSE AND MOVE EAST TODAY. A CANADIAN COLD FRONT MOVING THROUGH
CALGARY EARLY THIS MORNING IS EXPECTED TO CROSS INTO MONTANA
BEFORE NOON, THEN PROGRESS THROUGH THE FORECAST AREA BY EARLY
EVENING. A DEEP CLOSED LOW NEARING THE CALIFORNIA COAST IS
EJECTING PACIFIC MOISTURE INTO THE REGION. INSTABILITY DERIVED
FROM RESIDUAL LOW-LEVEL WARMTH AND STEEPENING LAPSE RATES, WILL
COMBINE WITH WEAK SHEAR ALONG AND AHEAD OF THE SURFACE FRONT TO
PRODUCE SCATTERED SHOWERS AND THUNDERSTORMS THIS AFTERNOON. CAPE
COULD REACH 400 TO 900 J/KG WITH AROUND 30 KTS OF SHEAR. WHILE
THERE IS A MINIMAL THREAT FOR SEVERE WEATHER, THIS ENVIRONMENT
DOES SUPPORT SCATTERED THUNDERSTORMS THAT WILL NEED TO BE
MONITORED FOR POTENTIAL HAZARDS. ONCE THE FRONT PASSES EARLY
THURSDAY EVENING, A PERIOD OF LIGHT STRATIFORM RAIN IS EXPECTED TO
MOVE NORTH TO SOUTH THROUGH FRIDAY MORNING. OVERNIGHT RAINFALL
TOTALS SHOULD BE LESS THAN 0.2 INCHES OVER THE NORTH CENTRAL
PLAINS, WITH .25 TO 0.5 INCHES POSSIBLE OVER THE ROCKY MOUNTAINS
AND OVER MUCH OF SOUTHWEST MONTANA. RAIN COULD LINGER THROUGH
SATURDAY OVER THE SOUTHWEST AS THE SURFACE FRONT STALLS IN THE
AREA. TEMPERATURES REMAIN COOL OVER THE SOUTHWEST ON SATURDAY, BUT
REBOUND BACK INTO THE 70S FOR NORTH CENTRAL MT. PN

SATURDAY NIGHT THROUGH THURSDAY...SOUTHWEST MONTANA WILL STILL BE
MOIST SATURDAY NIGHT AND UNDER THE INFLUENCE OF THE LOW PRESSURE TO
THE SOUTH. HOWEVER, THE NORTHERN ZONES WILL BE DRIER AND UNDERNEATH
WEAK HIGH PRESSURE ALOFT. THE CHANCE OF PRECIPITATION WILL INCREASE
OVER THE REGION SUNDAY AS THE TROF DIGS INTO THE PACIFIC NORTHWEST.
THE APPROACHING TROF WILL CAUSE THE AIRMASS TO BECOME QUITE UNSTABLE
SUNDAY AFTERNOON WITH SCATTERED SHOWERS AND THUNDERSTORMS. ALSO, AS
THIS TROF APPROACHES, AN ASSOCIATED COLD FRONT WILL CROSS THE
ROCKIES SUNDAY NIGHT AND BRING COOLER AIR INTO THE REGION. THE
AIRMASS WILL REMAIN VERY MOIST WITH PERIODS OF WIDESPREAD
PRECIPITATION UNDER THE INFLUENCE OF THIS TROF UNTIL DRYING SOMEWHAT
WEDNESDAY NIGHT AS THE TROF MOVES EAST. THE REGION WILL REMAIN
UNSETTLED, HOWEVER, AS A SHORTWAVE MOVING THROUGH THE NORTHWEST FLOW
ALOFT CROSSES THE ZONES. THIS WILL BRING ANOTHER PUSH OF COOLER
CANADIAN AIR INTO THE REGION AND SLOW DOWN ANY QUICK TEMPERATURE
RECOVERIES. TEMPERATURES WILL BE WELL ABOVE SEASONAL NORMALS SUNDAY
BUT COOL TO NEAR AND BELOW SEASONAL AVERAGES MONDAY THROUGH THE END
OF THE PERIOD. ZELZER

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  79  44  61  40 /   0  40  50  20
CTB  70  40  62  37 /  30  60  40   0
HLN  82  46  60  42 /  10  30  50  30
BZN  81  44  61  40 /   0  20  50  40
WEY  68  42  56  38 /  10  30  60  50
DLN  78  46  60  43 /  10  30  60  40
HVR  81  47  69  38 /   0  50  30   0
LWT  81  46  61  40 /   0  30  40  20

&&

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

$$

WEATHER.GOV/GREATFALLS



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