Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 260308
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
908 PM MDT SAT JUL 25 2015

.DISCUSSION...
RADAR AT 850 PM SHOWED ONE BAND OF SHOWERS MOVING EAST THROUGH
FERGUS AND BLAINE COUNTIES AND THIS BAND SHOULD BE EAST OF THOSE
COUNTIES BY LATE EVENING. ELSEWHERE RADAR AT 850 PM WAS SHOWING
VERY ISOLATED SHOWERS ROUGHLY IN LINE WITH THE INHERITED FORECAST.
HAVE DOUBTS THERE WILL BE ANY MORE LIGHTNING TONIGHT BUT THERE IS
STILL SOME WEAK INSTABILITY IN THE EAST SO LEFT IN A MENTION OF
THUNDER IN THAT AREA FOR THE REST OF THIS EVENING. MODELS
FORECAST A WEATHER DISTURBANCE TO ROTATE NE THROUGH THE CENTRAL
AND NORTHERN ZONES THE REST OF TONIGHT. LIKE THE INHERITED
FORECAST WHICH SHOWS ISOLATED TO SCATTERED SHOWERS IN THOSE AREAS.
LOWERED SKY COVER OVER A PORTION OF THE NW PLAINS FOR THE REST OF
THIS EVENING IN LINE WITH SATELLITE IMAGERY. ALSO INCREASED
WESTERLY WINDS FOR THE REST OF THIS EVENING OVER THE NW PLAINS.
WITH REGARD TO THE SYSTEM FOR EARLY NEXT WEEK THE LATEST NAM MODEL
CONTINUES ITS TREND OF BEING SLOWER AND FARTHER SOUTH WITH THE TRACK
OF THE UPPER LOW THAN THE OTHER MODELS. WILL HAVE TO WAIT TO SEE
IF THE OTHER MODELS MIGHT MAKE A CHANGE TOWARDS THE NAM BUT OF
LATE THEY HAVE BEEN CONSISTENT IN BEING FASTER THAN THE NAM WITH
THE UPPER LOW. BLANK

&&

.AVIATION...
UPDATED 2350Z.

EXPECT GENERALLY VFR CONDITIONS.A WEAKLY UNSTABLE AIRMASS HAS
RESULTED IN A FEW SHOWERS AND ISOLATED THUNDERSTORMS OVER THE
FORECAST AREA WHICH WILL CONTINUE INTO THIS EVENING. THUNDERSTORMS
SHOULD END BY 04Z BUT A FEW SHOWERS WILL CONTINUE NEAR AND NORTH OF
A LINE THROUGH KGTF AND KLWT AFTER MIDNIGHT AND NEAR AND NORTHWEST
OF A LINE THROUGH KGTF TO KHVR SUNDAY MORNING. THEN SUNDAY AFTERNOON
SCATTERED SHOWERS AND THUNDERSTORMS WILL DEVELOP PRIMARILY OVER
SOUTHWEST AND CENTRAL MONTANA. A FEW THUNDERSTORMS OVER THE EASTERN
PLAINS COULD HAVE WIND GUSTS TO 40 KTS AND MVFR CONDITIONS IN
HEAVIER RAIN. BLANK

&&

.PREV DISCUSSION...
/ISSUED 550 PM MDT SAT JUL 25 2015/

TONIGHT THROUGH MONDAY... WATER VAPOR PIX INDICATE A BROAD UPPER
LEVEL TROF MOVING OVER THE WEST COAST. THE CENTER OF CIRCULATION
CURRENTLY OVER THE NORTHERN COAST OF BRITISH COLUMBIA WILL MOVE OVER
THE PACIFIC NORTHWEST BY  SUNDAY NIGHT. FOR THE REMAINDER OF TODAY,
THE AIRMASS WILL REMAIN UNSTABLE INTO THE EVENING. A WEAK
DISTURBANCE IN THE UPPER LEVEL FLOW IS APPROACHING THE CENTRAL AND
SOUTHWEST ZONES. ALTHOUGH MOISTURE IS SCARCE, THIS DISTURBANCE WILL
AID THUNDERSTORM DEVELOPMENT INTO THE LATE EVENING. WITH THE DRY
LOWER LEVELS, STRONG GUSTS ARE POSSIBLE FROM ANY CONVECTIVE
DEVELOPMENT. UNSETTLED CONDITIONS WILL CONTINUE SUNDAY AS THE UPPER
LEVEL TROF CONTINUES TO MOVE EAST. CENTRAL AND SOUTHWESTERN ZONES
WILL HAVE THE BEST CHANCE OF THUNDERSTORM DEVELOPMENT. A JET AHEAD
OF THE TROF WILL MOVE THROUGH THE UPPER LEVEL FLOW BY AFTERNOON. AN
ASSOCIATED COOL BOUNDARY WILL BE SETTLING ACROSS CENTRAL AND EASTERN
PORTIONS OF THE REGION AND THIS WILL PROVIDE A GOOD FOCUS FOR
CONVECTION...AND GOOD SHEAR COULD DEVELOP FOR THUNDERSTORM SUPPORT.
THE TROF WILL DIG INTO SOUTHERN IDAHO MONDAY AND DYNAMICS ACROSS
CENTRAL AND SOUTHWEST MONTANA WILL STRENGTHEN. THE AIRMASS WILL
MOISTEN RAPIDLY WITH WIDESPREAD PRECIPITATION ACROSS THE REGION.
TEMPERATURES WILL TREND LOWER SUNDAY WITH THE APPROACH OF THE UPPER
LEVEL TROF THEN DROP SIGNIFICANTLY MONDAY. TEMPERATURES OF 20
DEGREES OR MORE BELOW SEASONAL NORMALS ARE EXPECTED. ZELZER

MONDAY NIGHT THROUGH SATURDAY...A RAPIDLY MOVING UPPER TROF WILL
BRING PRECIPITATION IN THE FORM OF SHOWERS AND THUNDERSTORMS TO THE
AREA TO START THE PERIOD. THE BEST CHANCE FOR PRECIPITATION WILL BE
TUESDAY MORNING AND TOTAL QPF VALUES APPROACHING AN INCH WILL BE
POSSIBLE FOR PORTIONS OF NORTHERN MONTANA WHILE VALUES OF THREE-
QUARTERS OF AN INCH ARE POSSIBLE OVER NORTH CENTRAL MONTANA. BY
TUESDAY AFTERNOON, THE TROF WILL BE OVER NORTHEAST MONTANA AND WRAP-
AROUND PRECIPITATION WILL BE ENDING FROM WEST TO EAST. A TIGHT
SURFACE PRESSURE GRADIENT WILL RESULT IN GUSTY WINDS EARLY TUESDAY.
RISING 500MB HEIGHTS AND A DRY NORTHWESTERLY FLOW ALOFT WEDNESDAY
WILL RESULT IN DRY CONDITIONS THROUGH FRIDAY. THE MODELS DIVERGE A
BIT WITH THEIR SOLUTIONS SATURDAY AS THE GFS BRINGS SHORT WAVE
ENERGY ALONG THE INTERNATIONAL BOUNDARY WHILE THE ECMWF MAINTAINS AN
UPPER RIDE. TEMPERATURES WILL BE 15 TO 20 DEGREES BELOW SEASONAL
AVERAGES TUESDAY BUT A WARMING TREND WILL BEGIN WEDNESDAY AND
TEMPERATURES SHOULD REMAIN NEAR SEASONAL AVERAGES FOR THE REMAINDER
OF THE WEEK.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  57  78  53  55 /  30  30  70  70
CTB  54  73  50  59 /  20  20  50  80
HLN  57  81  54  56 /  20  30  60  80
BZN  52  86  54  62 /  20  20  30  60
WEY  41  77  43  62 /  10  20  30  60
DLN  50  83  51  60 /  20  30  50  80
HVR  58  82  56  62 /  20  20  70  70
LWT  54  83  54  60 /  20  30  50  60

&&

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

$$

WEATHER.GOV/GREATFALLS


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