Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 302045
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
245 PM MDT SAT MAY 30 2015

.DISCUSSION...
THE MAIN MESSAGE IS UNSETTLED WEATHER WILL CONTINUE. ONE WEATHER
DISTURBANCE ALOFT WILL BE MOVING THROUGH THE FORECAST AREA THE
REMAINDER OF SATURDAY AFTERNOON. ASSOCIATED SHOWERS AND A FEW
THUNDERSTORMS WILL BE MOVING OUT THE EASTERN PLAINS BY LATE
AFTERNOON. ANOTHER WEATHER DISTURBANCE ALOFT OVER NORTHWEST
MONTANA EARLY SATURDAY AFTERNOON WILL MOVE TO THE EAST SLOPES
LATE THIS AFTERNOON BUT WEAKEN AS IT MOVES FARTHER EAST. A LINE OF
SHOWERS AND THUNDERSTORMS WILL BE ASSOCIATED WITH THIS LATTER
FEATURE BUT IS EXPECTED TO DISSIPATE AS IT MOVES TOWARDS CENTRAL
MONTANA DUE TO THE WEAKENING OF THE WEATHER DISTURBANCE AND LOSS
OF HEATING. EXPECT A MOSTLY DRY PERIOD AFTER MIDNIGHT WITH PARTLY
CLOUDY TO CLEAR SKIES IN THE NORTH. THIS WILL AID IN THE
DEVELOPMENT OF PATCHY FOG OVER THE EASTERN PLAINS. AN UPPER RIDGE
WILL BUILD INTO THE FORECAST AREA ON SUNDAY. EVEN WITH THIS RIDGE
THE AIRMASS WILL BECOME UNSTABLE ENOUGH FOR SCATTERED SHOWERS AND
THUNDERSTORMS MAINLY OVER THE MOUNTAINS. SOUTHWEST FLOW ALOFT WILL
DEVELOP OVER WESTERN MONTANA MONDAY AND BRING INCREASED MOISTURE.
IN ADDITION A WEATHER DISTURBANCE ALOFT WILL MOVE INTO SOUTHWEST
OR POSSIBLY CENTRAL MONTANA DURING THE AFTERNOON. LIFT ASSOCIATED
WITH THIS DISTURBANCE ALONG WITH THE INCREASED MOISTURE AND A MORE
UNSTABLE AIRMASS WILL RESULT IN NUMEROUS SHOWERS WITH SCATTERED
THUNDERSTORMS. INGREDIENTS CONTINUE TO POINT TO A THREAT OF
STRONGER THUNDERSTORMS MONDAY AFTERNOON SO WILL INCLUDE THE
MENTION OF HAIL AND GUSTY WINDS. BLANK

MONDAY NIGHT THROUGH FRIDAY...A SHALLOW LOW PRESSURE TROF WILL
MOVE OVER THE PACIFIC NORTHWEST AND MOVE TOWARDS THE ROCKIES
EARLY TUESDAY. THE ASSOCIATED COLD FRONT WILL CROSS THE AREA
TUESDAY AND COOL MOST TEMPS ACROSS THE FORECAST AREA. THE WESTERN
US WILL REMAIN UNDERNEATH A BROAD AREA OF CYCLONIC FLOW, A VERY
SHALLOW TROF, AND THE AIRMASS WILL REMAIN COOL AND SOMEWHAT MOIST.
ANOTHER LOW PRESSURE SYSTEM WILL MOVE OVER THE WEST COAST AND INTO
THE CYCLONIC FLOW ALOFT THURSDAY. THIS TROF WILL DEEPEN OVER THE
WESTERN US AND INFLUENCE THE WEATHER OVER CENTRAL MONTANA THROUGH
FRIDAY NIGHT. THE ECMWF BEGINS TO DIFFER A BIT FROM THE GFS ON
THURSDAY BY DEEPENING ITS TROF OVER THE PACIFIC NORTHWEST AND
CALIFORNIA. BY FRIDAY, THE ECMWF PLACES A CLOSED LOW OVER
CALIFORNIA. OVERALL, THE TROF IS DEEPER THAN THE GFS BUT HEIGHTS
OVER THE FORECAST AREA ARE NOT THAT MUCH DIFFERENT BETWEEN THE
TWO MODELS. BY EARLY SATURDAY, THOUGH, THE GFS IS ALREADY
BEGINNING TO CREATE A RIDGE OVER THE ZONES WHILE THE ECMWF
CONTINUES THE TROF. THE GFS SOLUTIONS WILL BRING A COLD FRONT
ACROSS CENTRAL MONTANA FRIDAY, AND WITH QUITE UNSTABLE CONDITIONS,
STRONG THUNDERSTORMS WOULD BE EXPECTED. THE ECMWF, HOWEVER, WOULD
KEEP FORECAST AREA UNDER A MORE STABLE AIRMASS. TIMING IS A
PROBLEM WITH THESE DIFFERING SOLUTIONS AND WILL TREND TOWARDS A
BLEND...WILL MENTION THUNDERSTORMS ON FRIDAY BUT WITH THE TIMING
ISSUES, WILL WAIT BEFORE STRESSING ANY STRONG DEVELOPMENT.
TEMPERATURES WILL REMAIN NEAR OR JUST BELOW NORMALS THROUGH
THURSDAY. THE GFS SOLUTION WOULD BRING COOLER TEMPS ON FRIDAY BUT
WITH THE DIFFERENCES BETWEEN THE GFS AND ECMWF, WILL HOLD BACK ON
ANY STRONG COOLING. ZELZER

&&

.AVIATION...

UPDATED 1740Z.

THERE WILL BE SCATTERED TO NUMEROUS SHOWERS THIS AFTERNOON WITH
SCATTERED THUNDERSTORMS. A FEW OF THESE THUNDERSTORMS WILL HAVE
BRIEF MVFR/IFR CEILINGS AND VISIBILITIES IN HEAVY RAIN. ALSO THERE
COULD BE LOCAL GUSTY WINDS TO NEAR 40 KTS WITH THE THUNDERSTORMS.
THIS ACTIVITY WILL DIMINISH EARLY THIS EVENING WITH SKIES GENERALLY
CLEARING. THEN EXPECT CEILINGS NEAR AND ABOVE 15000 FT SPREADING
NORTHEAST LATE TONIGHT. CEILINGS WILL LOWER OVER SOUTHWEST MONTANA
SUNDAY MORNING BUT STILL LIKELY REMAIN VFR AS SCATTERED SHOWERS
DEVELOP. ALTHOUGH NOT MENTIONED IN THE TAFS DUE TO LOW CONFIDENCE
THERE WILL BE A THREAT OF IFR CEILINGS AND VISIBILITIES IN FOG NEAR
AND NORTHEAST OF A LINE FROM KCTB TO KLWT LATE TONIGHT AND EARLY
SUNDAY MORNING.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  50  78  54  76 /  20  20  10  70
CTB  46  76  48  73 /  20  10  10  50
HLN  52  78  56  75 /  30  40  20  70
BZN  50  76  53  77 /  30  30  20  50
WEY  41  69  45  70 /  40  40  30  40
DLN  51  77  52  73 /  40  30  20  60
HVR  45  80  51  82 /  40  20  20  30
LWT  49  75  54  77 /  50  30  30  70

&&

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

$$

WEATHER.GOV/GREATFALLS



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