Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 230140
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
740 PM MDT FRI MAY 22 2015

.UPDATE...
HAVE MADE SOME ADJUSTMENTS TO POPS TONIGHT BASED ON LATEST TRENDS
IN SATELLITE AND RADAR DATA. SCATTERED SHORT-LIVED SHOWERS AND
ISOLATED THUNDERSTORMS HAVE DEVELOPED OVER CASCADE...CHOUTEAU AND
SOUTHERN BLAINE COUNTIES WHERE POPS WERE INCREASED THIS EVENING AS
THIS ACTIVITY CONTINUES TO PUSH SLOWLY WESTWARD. SHOULD SEE A
GENERAL DISSIPATING TREND AFTER 04Z...BUT SOME SHOWERS COULD
LINGER THROUGH THE NIGHT ACROSS JUDITH BASIN...FERGUS AND BLAINE
COUNTIES AS A WEAK DISTURBANCE ROTATES AROUND THE BROAD UPPER LOW
CENTERED OVER THE GREAT BASIN INTO EASTERN PORTIONS OF CENTRAL MT
LATE TONIGHT. HOENISCH

&&

.AVIATION...

UPDATED 2326Z.

CENTRAL AND SOUTHWEST MONTANA WILL REMAIN UNDER THE INFLUENCE OF A
WEAK UPPER LEVEL LOW PRESSURE TROF THROUGH SATURDAY. THE AIRMASS
WILL REMAIN RATHER MOIST AT MID-LEVELS ACROSS SOUTHWEST MONTANA
TONIGHT. THIS MOISTURE WILL CREEP FARTHER NORTH SATURDAY AND PUSH
INTO THE HILINE BY AFTERNOON. ISOLATED THUNDERSTORMS WILL END THIS
EVENING BUT A CHANCE OF THUNDERSTORMS WILL DEVELOP AGAIN SATURDAY
AFTERNOON. LOCAL MVFR CIGS ARE POSSIBLE NEAR SHOWERS AND
THUNDERSTORMS BUT ELSEWHERE VFR CONDITIONS WILL PREVAIL THROUGH THE
NEXT 24 HOURS.

&&

.PREV DISCUSSION...
/ISSUED 528 PM MDT FRI MAY 22 2015/
CURRENT RADAR/SATELLITE IMAGERY SHOWING SCATTERED SHOWERS AND A FEW
SMALL THUNDERSTORMS DEVELOPING MAINLY FROM THE LITTLE BELT AND SNOWY
MTNS SOUTH TO THE MT/ID BORDER.  EXPECT PRECIPITATION COVERAGE TO
INCREASE OVER THE SOUTHWEST COUNTIES AND EXTEND INTO PARTS OF
CASCADE/CHOUTEAU/FERGUS/JUDITH BASIN COUNTIES BY LATE AFTN AS
ADDITIONAL MOISTURE ARRIVES FROM IDAHO/WYOMING.  MOISTURE PUSH IS
DRIVEN BY A SLOW-MOVING UPPER-LEVEL LOW PRESSURE AREA PRESENTLY
CENTERED AT THE CA/NV/AZ BORDER.  FORECAST MODELS REMAIN IN VERY
GOOD AGREEMENT THAT THE LOW WILL TRACK GRADUALLY TO THE NORTHEAST
THROUGH THE GREAT BASIN OVER THE WEEKEND, REACHING EASTERN WYOMING
BY MIDDAY SUNDAY.  AS IT MOVES, EAST-SOUTHEAST WINDS ON THE
FRONTSIDE OF THE LOW`S CIRCULATION WILL BRING BOTH PACIFIC AND SOME
GULF OF MEXICO MOISTURE INTO MT, PRODUCING SCATTERED SHOWERS AND
THUNDERSTORMS EACH AFTERNOON AND EVENING THROUGH SUNDAY. NO STRONG
OR SEVERE STORMS ARE EXPECTED AT THIS TIME, AS INSTABILITY AND WIND
SHEAR PARAMETERS ARE FORECAST TO BE WEAK FOR THE NEXT COUPLE DAYS.
CONVECTIVE ACTIVITY WILL DISSIPATE OVER MOST OF THE FORECAST AREA
EACH EVENING NEAR/AFTER SUNSET.

LATEST MODELS ARE ALSO INDICATING A BETTER CHANCE OF SHORT-TERM DRY
CONDITIONS ON MONDAY AS OUR REGION WILL BE BETWEEN THE EXITING
WEEKEND WEATHER SYSTEM AND THE NEXT SHORTWAVE TROF MOVING INTO THE
PACIFIC NORTHWEST. ISOLATED SHOWERS AND THUNDERSTORMS WILL BE
POSSIBLE ALONG THE ROCKY MTN FRONT AND PARTS OF SOUTHWEST MT MON
AFTN/EVE AS THE TROF TAPS INTO RESIDUAL MOISTURE OVER WESTERN MT,
WHILE LOCATIONS GENERALLY ALONG/EAST OF THE INTERSTATE 15 CORRIDOR
REMAIN PRECIP FREE.
WARANAUSKAS

MONDAY NIGHT THROUGH FRIDAY...MODELS CONTINUE TO BE IN AGREEMENT
IN A GENERAL SENSE WITH PRECIPITATION TRENDS AT LEAST INTO
MIDWEEK. THAT IS SHOWER ACTIVITY SHOULD BE MAINLY ISOLATED
MONDAY NIGHT THEN PICK UP SOME INTO MIDWEEK. WITHIN A PARTICULAR
MODEL THERE IS GENERAL CONSISTENCY FROM RUN-TO-RUN BUT THE GFS AND
ECMWF CONTINUE TO EXHIBIT DIFFERENCES BETWEEN EACH OTHER WITH
THEIR FORECASTS ALOFT. LIKE LAST NIGHT THE ECMWF TAKES AN UPPER
LOW NEAR VANCOUVER ISLAND SUNDAY NIGHT SOUTHEAST AND WEAKENS IT AS
IT MOVES INTO CENTRAL MONTANA BY MID-WEEK. THE GFS TAKES THE UPPER
LOW SOUTHEAST EVER SO SLOWLY AND THEN FOR A PERIOD HAS IT QUASI-
STATIONARY BEFORE WEAKENING IT AND MOVING IT INTO MONTANA ON
FRIDAY. DUE TO MODEL DIFFERENCES WITH DETAILS OF THEIR
PRECIPITATION FORECASTS WILL GO WITH THE BROADBRUSH IDEA FROM
TUESDAY ON OF SCATTERED SHOWERS EXCEPT ISOLATED SHOWERS TOWARDS
THE CANADIAN BORDER. OVER THE FORECAST AREA THERE WILL BE ISOLATED
THUNDERSTORMS DURING THE LATE AFTERNOON AND EARLY EVENING BUT DO
NOT ANTICIPATE ANY SEVERE STORMS AT THIS TIME.
BLANK

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  47  64  43  65 /  50  40  20  20
CTB  42  67  38  67 /  10  20  10  10
HLN  48  64  45  67 /  40  70  40  20
BZN  42  61  41  62 /  20  60  40  40
WEY  34  57  33  57 /  60  60  40  30
DLN  44  62  41  63 /  30  50  30  30
HVR  42  70  41  71 /  20  20  10  20
LWT  45  61  42  61 /  50  50  20  20

&&

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

$$

WEATHER.GOV/GREATFALLS


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