Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 050917
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
317 AM MDT THU MAY 5 2016

.DISCUSSION...

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

&&

.AVIATION...
UPDATED 0540Z.

CLOUDS WILL INCREASE OVERNIGHT AS SOUTHWEST FLOW INCREASES AHEAD
OF AN APPROACHING TROUGH OF LOW PRESSURE AND ASSOCIATED SURFACE COLD
FRONT. WINDS SHIFT TO THE NORTH WITH LOWERING CIGS AS THE COLD FRONT
PASSES THROUGH NORTH CENTRAL MT THURSDAY AFTERNOON. SHOWERS AND
THUNDERSTORMS ARE EXPECTED IN THE WARMER UNSTABLE AIR AHEAD OF THE
FRONT, POSSIBLY AFFECTING KCTB/KHLN/KGTF TERMINALS. CONFIDENCE IS
LOWER ON HOW FAR EAST THE SHOWERS AND THUNDERSTORMS WILL SPREAD BY
00UTC FRIDAY. VFR CONDITIONS ARE EXPECTED AT ALL TAF SITES THROUGH
THURSDAY AFTERNOON, WITH MVFR CONDITIONS LIKELY IN OR NEAR SHOWERS
AND THUNDERSTORMS. PN

&&

.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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