High Wind Watch 11, NWS Great Falls, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1155 AM MDT THU AUG 13 2015

AVIATION SECTION UPDATED.

.UPDATE...INCREASED CLOUD COVER AND ADDED SMOKE TO THE GRIDS TO
ACCOUNT FOR SMOKE FROM PACIFIC NORTHWEST WILDFIRES PASSING OVER
NORTH-CENTRAL MT. ALSO INCREASED WINDS ACROSS NORTH-CENTRAL MT FOR
THE REST OF TODAY THROUGH FRIDAY PER LATEST OBS AND CONSIDERING THE
EVENTUAL COLD FRONTAL PASSAGE LATER TOMORROW. OTHERWISE, THE REST OF
THE FORECAST LOOKS GOOD. STILL EXPECT A FEW THUNDERSTORMS TO DEVELOP
OVER HIGHER TERRAIN THIS LATE AFTERNOON/EARLY EVENING, ESPECIALLY
OVER SOUTHWEST MT. MPJ/JASZKA

AVIATION SECTION UPDATED

...INCREASED RISK OF CRITICAL FIRE WEATHER CONDITIONS FRIDAY AND
FRIDAY NIGHT...
...STRONG WINDS POSSIBLE ALONG THE ROCKY MOUNTAIN FRONT FRIDAY
NIGHT INTO SATURDAY MORNING...

.DISCUSSION...

TODAY THROUGH SATURDAY...ONE MORE RELATIVELY QUIET DAY WILL GIVE
WAY TO A MORE ACTIVE FRIDAY AND SATURDAY. HIGH PRESSURE ALOFT
WILL KEEP THE AREA HOT AND DRY INTO FRIDAY. TEMPERATURES WILL
WARM INTO THE 90S FOR MOST OF THE AREA. SOME LOCATIONS ACROSS
NORTH CENTRAL MONTANA WILL APPROACH RECORD HIGHS, AND A FEW MAY
EVEN REACH 100 DEGREES. A FEW STORMS MAY ALSO DEVELOP OVER THE
MOUNTAIN AREAS THIS AFTERNOON AND EVENING AND PRODUCE GUSTY WINDS.
SMOKE FROM THE THOMPSON AND REYNOLDS CREEK FIRES WILL ALSO LINGER
OVER THE NORTHERN ROCKY MOUNTAIN FRONT AND ADJACENT PLAINS THROUGH
THE DAY ON FRIDAY. FORECAST MODELS HAVE CONTINUED TO SLOW THE
PROGRESSION OF A WEATHER SYSTEM INTO THE PACIFIC NORTHWEST.
REGARDLESS, A MOIST AND UNSTABLE DIFFLUENT SOUTHWESTERLY FLOW
ALOFT AHEAD OF THIS SYSTEM WILL BRING A GOOD CHANCE OF A MIX OF WET
AND DRY THUNDERSTORMS TO THE AREA ON FRIDAY. A JET MAX IN THIS FLOW
MAY CAUSE SOME OF THESE STORMS TO BECOME QUITE STRONG WITH FREQUENT
LIGHTNING AND STRONG ERRATIC WIND GUSTS TO NEAR 50 MPH AT TIMES.
PRECIPITABLE WATER VALUES WILL EXCEED 1 INCH FOR MUCH OF THE AREA,
MAKING BRIEF HEAVY RAIN AND SMALL HAIL ALSO POSSIBLE. SOUTHERLY
WINDS WILL ALSO INCREASE ON FRIDAY AHEAD OF AN APPROACHING PACIFIC
COLD FRONT. FRONTAL PASSAGE FRIDAY NIGHT WILL CAUSE WINDS TO SHIFT
MORE WESTERLY AND STRENGTHEN, ESPECIALLY ALONG THE ROCKY MOUNTAIN
FRONT. FORECAST MODELS INDICATE 700 MB WINDS THERE OF AROUND 60 MPH
WITH A STRONG SURFACE GRADIENT, MAKING HIGH WIND CRITERIA WIND
POSSIBLE THERE. HOWEVER, WITH THE RECENT UNCERTAINTY WITH THE MODEL
TIMING, WILL HOLD OFF ON A HIGH WIND WATCH FOR NOW. AS THE PACIFIC
SYSTEM EXITS THE AREA ON SATURDAY, THE WINDS AND SHOWERS/STORMS WILL
DIMINISH, COOLING TEMPERATURES MOSTLY INTO THE 70S IN ITS WAKE WITH
LESS DRY CONDITIONS.  COULSTON

SATURDAY NIGHT THROUGH THURSDAY. EXTENDED RANGE FORECAST MODELS
NOW IN BETTER AGREEMENT FOR THIS PERIOD THAN DISCUSSED YESTERDAY.
PERIOD BEGINS WITH A WEAK, QUICK-MOVING DISTURBANCE TRACKING ALONG
THE US/CAN BORDER DURING THE DAYTIME HOURS ON SUN. ISOLATED
SHOWERS AND A THUNDERSTORM OR TWO MAY DEVELOP ALONG THE HILINE SUN
AFTN, PERHAPS AS FAR SOUTH AS CHOUTEAU AND NORTHERN FERGUS
COUNTIES, WHILE REST OF REGION REMAINS DRY. THAT SYSTEM EXITS SUN
NIGHT, WITH WEAK RIDGING AND DRY CONDITIONS TO FOLLOW ON MON. BY
TUES MORNING, THE NEXT PACIFIC SHORTWAVE TROF COMES ASHORE IN
WA/OR. BOTH GFS AND ECMWF MODELS BRING THE LOW PRESSURE CENTER
TOWARD MT ON TUES WITH THE GFS TAKING IT ON SOMEWHAT MORE DIRECT
AND QUICKER PATH. PLUMES OF MOISTURE IN THE SOUTHWEST FLOW ALOFT
AHEAD OF THE TROF AXIS WILL GENERATE SCATTERED THUNDERSTORMS
MAINLY OVER THE ROCKY MTN FRONT AND CENTRAL MT TUES AFTN/EVE. THE
GFS MODEL TAKES THE TROF INTO EASTERN WY BY MIDDAY WED WITH DRY
CONDITIONS FOR WED-THURS. MEANWHILE, THE ECMWF HAS THE TROF AXIS
ONLY JUST EAST OF THE CONTINENTAL DIVIDE WITH PRECIPITATION
CONTINUING ALONG/EAST OF A DILLON-LEWISTOWN-GLASGOW LINE INTO WED
AFTN AND A SECONDARY TROF SWEEPING ACROSS THE HILINE/CENTRAL MT
COUNTIES WITH ANOTHER ROUND OF SHOWERS THRU MIDDAY THURS. GIVEN
THAT THE GFS SOLUTION HAS SHOWN BETTER RUN-TO-RUN CONSISTENCY,
CURRENT FORECAST FAVORS ITS GENERALLY DRIER CONDITIONS. EXCEPT FOR
A WARMUP INTO THE LOW-MID 80S ON MON AHEAD OF THE PACIFIC TROF,
HIGH TEMPS EACH DAY WILL BE A BIT COOLER THAN NORMAL, REACHING
ONLY THE LOW-MID 70S ON SUN AND TUES AND MID-UPPER 70S ON WED AND
THURS. WARANAUSKAS

&&

.AVIATION...

UPDATED 1755Z. VFR CONDITIONS PREVAIL THROUGH THE PERIOD WITH MOSTLY
CLOUD FREE SKIES. VISIBLE SATELLITE REVEALS ELEVATED LAYERS OF SMOKE
CROSSING THE STATE. SMOKE FROM THE REYNOLDS FIRE IN GLACIER NP MAY
CAUSE VISIBILITY REDUCTIONS AT KCTB THIS AFTERNOON WITH MOUNTAIN
OBSCURATION POSSIBLE. TEMPERATURES NEAR 100 DEGREES WILL INCREASE
DENSITY ALTITUDES. SOUTHWESTERLY FLOW ALOFT STRENGTHENS TODAY. A
DEEPLY MIXED SURFACE LAYER WILL ADD GUSTY WINDS THIS AFTERNOOON AT
KHVR/KGTF. MOISTURE MOVING NORTH FROM IDAHO REACHES SOUTHWEST MT
LATE THIS AFTN GIVING CHANCE FOR ISOLATED -TSRA AROUND
KBZN/KDLN/KWYS. NUTTER

&&

.FIRE WEATHER...

TODAY...HOT AND DRY CONDITIONS WILL CONTINUE TODAY, AS HUMIDITY
VALUES FALL INTO THE 10 TO 20 PERCENT RANGE. A FEW STORMS MAY
DEVELOP OVER THE MOUNTAINS THIS AFTERNOON AND EVENING, BUT THEY
SHOULD BE FAIRLY WEAK WITH ONLY ERRATIC WIND GUSTS POSSIBLE.

FRIDAY AND FRIDAY NIGHT...DRY CONDITIONS WILL CONTINUE INTO FRIDAY
WITH WIDESPREAD 15 TO 20 PERCENT AFTERNOON HUMIDITY. SCATTERED
WET AND DRY THUNDERSTORMS WILL ALSO DEVELOP DURING THIS TIME. SOME
STORMS MAY BECOME STRONG WITH FREQUENT LIGHTNING AND STRONG
ERRATIC WIND GUSTS POSSIBLY UP TO 50 MPH. THIS WILL INCREASE THE
THREAT OF NEW FIRE STARTS AND THE SPREAD OF NEW AND EXISTING
FIRES. ALSO, SOUTHERLY WINDS WILL INCREASE AHEAD OF A PACIFIC COLD
FRONT, COMBINING WITH THE DRY CONDITIONS TO POTENTIALLY CREATE
CRITICAL FIRE WEATHER CONDITIONS. HAVE THEREFORE ISSUED A FIRE
WEATHER WATCH FOR FRIDAY AFTERNOON THROUGH FRIDAY NIGHT. STORMS
WILL PERSIST INTO FRIDAY NIGHT, AND THE COLD FRONT WILL SHIFT
WINDS MORE WESTERLY AND INCREASE THEM QUITE A BIT.

SATURDAY THROUGH SUNDAY...SHOWERS, STORMS AND WINDS WILL DECREASE
ON SATURDAY AS THE SYSTEM EXITS THE AREA. THIS WILL LEAVE THE AREA
COOLER AND NOT NEARLY AS DRY.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  98  66  95  60 /  10  10  40  30
CTB  97  60  92  56 /  10  10  40  40
HLN  97  61  95  55 /  10  10  40  30
BZN  94  57  94  52 /  10  10  30  20
WEY  84  43  83  45 /  20  20  30  30
DLN  90  58  90  51 /  10  20  30  30
HVR 100  65 100  61 /  10  10  30  30
LWT  94  65  94  58 /  10  10  20  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH FROM FRIDAY AFTERNOON THROUGH LATE FRIDAY
NIGHT FOR MTZ112>118.

&&

WEATHER.GOV/GREATFALLS