Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 231751
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1151 AM MDT THU APR 23 2015

.DISCUSSION...

TODAY...THE COLD FRONT HAS MOVED EAST OF THE ZONES AND THE
SHOWERS HAVE MOVED EAST AS WELL. THE AIRMASS WILL BECOME SLIGHTLY
UNSTABLE THIS AFTERNOON AND DEVELOPMENT OF SHOWERS AND
THUNDERSTORMS ARE AGAIN EXPECTED MAINLY OVER PORTIONS OF
SOUTHWEST MONTANA. UPDATED TO FRESHEN POPS AND WX. ZELZER

&&

.AVIATION...
UPDATED 1751Z.

WEAK INSTABILITY WILL DEVELOP OVER PORTIONS OF SOUTHWEST MONTANA
THIS AFTERNOON WITH A SLIGHT CHANCE FOR SHOWERS AND THUNDERSTORMS.
THIS WILL INCLUDE KBZN AND EVENING SHOWERS ARE ALSO POSSIBLE NEAR
KLWT. AN APPROACHING LOW PRESSURE SYSTEM WILL KEEP THE AIRMASS
UNSETTLED AND BRING A ANOTHER PERIOD OF SHOWERS AND THUNDERSTORMS TO
CENTRAL AND SOUTHWEST MONTANA FRIDAY. LOCAL MVFR CONDITIONS ARE
POSSIBLE NEAR SHOWERS AND THUNDERSTORMS. ELSEWHERE...VFR CONDITIONS
WILL PREVAIL THROUGH THE NEXT 24 HOURS.

&&

.PREV DISCUSSION...
/ISSUED 555 AM MDT THU APR 23 2015/
THURSDAY THROUGH SATURDAY... BY AFTERNOON THE SHOWER
ACTIVITY ASSOCIATED WITH THE COLD FRONTAL PASSAGE WILL HAVE THE LEFT
THE AREA TO THE EAST AND CONDITIONS WILL DRY OUT AS THE UPPER LEVEL
RIDGE BUILDS BACK INTO THE AREA. THESE WARM AND DRY CONDITIONS WILL
CONTINUE AGAIN ON FRIDAY WITH THE ONLY POTENTIAL FOR SHOWERS SHOULD
BE OVER THE HIGHER TERRAIN...MAINLY OVER SOUTHWEST MONTANA. BY
SATURDAY AN UPPER LEVEL LOW OFF THE COAST OF WASHINGTON WILL BEGIN
TO MOVE INLAND AND SOME INSTABILITY AND MOISTURE WILL BE EJECTED OUT
IN FRONT OF IT. THIS WILL LEAD TO SHOWERY CONDITIONS ON SATURDAY
WITH AN INCREASED CHANCE OF THUNDERSTORMS WITH AFTERNOON HEATING.
ONCE AGAIN THE BEST CHANCES FOR MOISTURE WILL BE OVER THE HIGHER
TERRAIN AND ADJACENT PLAINS AND VALLEYS. TEMPERATURES WILL REMAIN
NEAR OR ABOVE SEASONAL AVERAGES. SUK

SATURDAY NIGHT THROUGH THURSDAY...THE PERIOD BEGINS WITH AN UPPER
TROF APPROACHING WESTERN MONTANA. A STRONG DIFFLUENT SOUTHWESTERLY
FLOW ALOFT AHEAD OF THE TROF WILL BRING MOISTURE AND INSTABILITY
ACROSS THE AREA. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL
LIKELY DEVELOP SATURDAY NIGHT. THE TROF BEGINS TO SPLIT AS IT
CROSSES THE CONTINENTAL DIVIDE EARLY SUNDAY BUT ENOUGH ENERGY
REMAINS WITHIN THE NORTHERN BRANCH TO CONTINUE SHOWER ACTIVITY
ACROSS SOUTHWEST AND CENTRAL MONTANA. THE AIRMASS DRIES OUT SUNDAY
NIGHT AND MONDAY AS A POSITIVE TILT UPPER RIDGE BUILDS ACROSS THE
AREA. DRY AND STABLE CONDITIONS CONTINUE TUESDAY THOUGH THE MODELS
BEGIN TO DIVERGE WITH THEIR SOLUTIONS. THE GFS AND CANADIAN MODELS
KEEP THE RIDGE AXIS ALONG THE CONTINENTAL DIVIDE WHILE THE ECMWF
PUSHES THE AXIS FURTHER EAST IN RESPONSE TO AN UPPER TROF MOVING
INTO THE PACIFIC NORTHWEST. WEDNESDAY REMAINS DRY AS THE GFS
MAINTAINS THE RIDGE OVER THE AREA AND THE CANADIAN AND ECMWF...WHILE
BRINGING SHORTWAVE ENERGY ACROSS SOUTHERN CANADA...STILL HAVE HIGH
500 MB HEIGHTS OVER THE AREA. MODELS IN POOR AGREEMENT THURSDAY
BUT WILL LEAN TOWARD THE GFS SOLUTION WHICH DEVELOPS SOUTHWEST
FLOW ALOFT ON THE BACK SIDE OF THE UPPER RIDGE AND DEVELOPS
SHOWERS ACROSS PORTIONS OF SOUTHWEST MONTANA. TEMPERATURES WILL BE
NEAR SEASONAL AVERAGES TO START THE PERIOD BUT WILL CLIMB ABOVE
SEASONAL AVERAGES MONDAY THROUGH THURSDAY.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  62  43  57  38 /   0  10  20  40
CTB  58  39  55  34 /   0  10  20  10
HLN  63  38  56  34 /  10  10  40  40
BZN  61  36  60  35 /  20  10  40  70
WEY  55  29  52  28 /  30  20  40  50
DLN  62  35  55  32 /  20  10  40  80
HVR  62  42  63  42 /  10  10  20  30
LWT  59  39  58  37 /  10  10  40  70

&&

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

$$

WEATHER.GOV/GREATFALLS


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