Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 230948
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
348 AM MDT SAT MAY 23 2015

.DISCUSSION...

TODAY THROUGH MONDAY...A BROAD UPPER LEVEL LOW IS CURRENTLY
POSITIONED OVER UTAH AND DRIFTING SLOWLY NORTHEAST. THIS SYSTEM IS
DRAWING MOISTURE NORTHWARD ALONG THE ROCKY MOUNTAINS INTO MONTANA.
NOCTURNAL RAIN SHOWERS CONTINUED OVERNIGHT ACROSS PORTIONS OF NORTH
CENTRAL MONTANA. THESE APPEARED TO INITIATE OVER ELEVATED
TERRAIN...MAINLY THE BEARS PAW MOUNTAINS...WITH WEAK INSTABILITY
INDICATED IN FORECAST SOUNDINGS AND LAST EVENINGS 00Z KGTF RAOB.
FURTHERMORE...WATER VAPOR IMAGERY SUGGESTS A MINOR LOBE OF VORTICITY
POSITIONED OVER NORTH-CENTRAL MONTANA THAT APPEARS TO BE HELPING
MAINTAIN THESE SHOWERS. THESE OBSERVED TRENDS SUPPORT SHORT-TERM
MODEL FORECASTS INDICATING AN EARLIER AND MORE WIDESPREAD
DEVELOPMENT OF SHOWERS AND THUNDERSTORMS OVER CENTRAL MONTANA TODAY.
NOT EVERYONE WILL ENCOUNTER RAIN TODAY...BUT THOSE ENJOYING OUTDOOR
ACTIVITIES SHOULD BE PREPARED TO RESPOND TO SLOW MOVING SHOWERS AND
THUNDERSTORMS. AS WITH THE LAST FEW DAYS...SHEAR AND ENVIRONMENTAL
INSTABILITY REMAIN WEAK AND SEVERE STORMS ARE NOT EXPECTED. TODAYS
TEMPERATURES WILL BE A FEW DEGREES COOLER THAN FRIDAY DUE TO MORE
EXTENSIVE CLOUD COVER. RAIN SHOWER ACTIVITY TRENDS LOWER ON SUNDAY
AND MONDAY AS THE PRIMARY UPPER LOW MOVES AWAY TO THE EAST AND SHORT
WAVE RIDGING DEVELOPS AHEAD OF THE NEXT PACIFIC TROUGH. NUTTER

MONDAY NIGHT THROUGH SATURDAY...THE LATEST GFS AND ECMWF MODEL RUNS
ARE IN BETTER AGREEMENT IN THEIR HANDLING OF AN UPPER LOW THAT IS
OVER WASHINGTON MONDAY NIGHT. THE GFS MOVES THE UPPER LOW VERY
LITTLE INTO TUESDAY NIGHT WHILE THE ECMWF WEAKENS THE UPPER LOW AS
IT MOVES VERY SLOWLY EAST. BY THURSDAY BOTH MODELS HAVE AN UPPER
TROUGH OVER WESTERN MONTANA THROUGH SOUTHERN IDAHO. DUE TO THIS
BETTER AGREEMENT HAVE RAISED CHANCES OF PRECIPITATION THROUGH
MIDWEEK AND ESPECIALLY TUESDAY OVER THE WESTERN MOUNTAINS THROUGH
SOUTHWEST MONTANA. LATER IN THE WEEK THE ECWMF IS FASTER MOVING THE
UPPER TROUGH EAST AND HAVING AN UPPER RIDGE MOVE OVER WESTERN
MONTANA. BY SATURDAY THE GFS STILL HAS THE UPPER RIDGE OVER IDAHO.
THESE DIFFERENCES LEAD TO THE ECMWF BEING RELATIVELY DRIER THAN THE
GFS. DUE TO THE DIFFERENCES WILL CONTINUE WITH THE IDEA OF
PRECIPTATION RANGING FROM BEING SCATTERED OVER SOUTHWEST MONTANA TO
ISOLATED TOWARDS THE U.S. ROUTE 2 AREA. HIGH TEMPERATURES ARE
EXPECTED TO CHANGE LITTLE FROM DAY TO DAY DURING THE 5 DAY PERIOD.
BLANK

&&

.AVIATION...

UPDATED 0416Z.

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.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  61  44  66  42 /  40  20  20  10
CTB  66  39  68  40 /  40  40  10   0
HLN  63  45  67  44 /  70  50  20  10
BZN  59  41  60  39 /  70  40  30  30
WEY  56  34  57  32 /  60  50  20  20
DLN  62  43  62  40 /  40  20  20  20
HVR  71  42  71  44 /  20  10  10  10
LWT  62  43  59  42 /  40  20  30  30

&&

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

$$

WEATHER.GOV/GREATFALLS


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