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000
FXUS65 KGGW 131521 AAA
AFDGGW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE GLASGOW MT
921 AM MDT MON MAY 13 2013

.SHORT TERM...FOR NORTHEAST MONTANA...TODAY THROUGH WEDNESDAY...
SATELLITE IMAGERY SHOWS HIGH CLOUDS FORMING OFF THE FRONT RANGE
AND SPREADING OVER NORTHEAST MONTANA. EVEN SO...PLENTY OF SUNSHINE
SHOULD MAKE IT THROUGH THE THIN OVERCAST. SO WILL LEAVE PARTLY
CLOUDY IN. THE UPPER TROUGH REMAIN WELL OFF TO THE WEST...BUT THE
EXIT REGION HAS BEEN HIGHLIGHTED FOR SLIGHT CHANCE FOR SEVERE
THUNDERSTORMS BY SPC. THIS AREA EXTENDS WELL INTO THE WESTERN HALF
OF THE CWA. THE DAY SHOULD BE WARM LIKE SUNDAY BUT THE DEW POINTS
SHOULD BE A LITTLE HIGHER INCREASING THE LEVEL OF INSTABILITY. YET
THE COLD FRONT SHOULD ONLY BE POSITIONED ALONG THE FRONT RANGE AT
00Z THIS EVENING AND NOT REACH NORTHEAST MONTANA UNTIL MID
EVENING...WHEN INSTABILITY IS LOSING ITS STRENGTH AROUND SUNSET.
THE MAIN THREAT TO ANY THUNDERSTORM APPEARS TO THE POSSIBILITY OF
STRONG WINDS AS INDICATED BY THE INVERTED-V SOUNDING PROFILE AT
00Z. THE OTHER CONCERN IS A FIRE WX CONCERN THAT HAS DIMINISHED AS
MODELS SUGGEST A SLIGHTLY HIGHER RH FOR THIS AFTERNOON IN THE EAST
WHERE THERE WAS A FIRE WX WATCH UNTIL THIS MORNING. WITH A QUIET
DAY EXPECTED...NOT MANY CHANGES WERE NEEDED TO THE FORECAST. DID
ADJUST THE WIND BASED ON THE LATEST NAM GUIDANCE. THE SKY COVER
WAS INCREASED EARLIER DUE TO THE THIN OVERCAST. WILL REVISIT THE
BIGGER ISSUES WITH THE AFTERNOON FORECAST WITH THE LATEST MODEL
DATA. SCT

PREVIOUS DISCUSSION...
AFTER WATCHING THE LAST SEVERAL MODEL RUNS COME IN OVER THE NEAR
SHORT TERM FORECAST PERIOD...TRENDS HAVE CONSISTENTLY LEANED
TOWARD A SLIGHTLY MORE MOIST AFTERNOON AND EARLY EVENING TODAY
THAN PREVIOUSLY INDICATED. MIN RH VALUES LOOK NOW TO BOTTOM OUT
AROUND 20 TO 25 PERCENT. MEANWHILE...WINDS LOOK TO STRUGGLE TO
CLIMB ABOVE 20 MPH AND THE PEAK SUSTAINED WIND WILL NOT COINCIDE
WITH THE DRIEST PART OF THE DAY EITHER. GIVEN THESE TRENDS AND
LOWER CONFIDENCE...FELT IT WAS BEST TO CANCEL THE FIRE WEATHER
WATCH WHICH WAS PREVIOUSLY ISSUED FOR TODAY.

CONVECTIVE PARAMETERS SHOW GOOD SUPPORT FOR A GENERAL THUNDERSTORM
THREAT ACROSS NORTHEAST MONTANA THIS EVENING AND TONIGHT. SLIGHT
RISK OF SEVERE THUNDERSTORMS OUTLINED BY SPC IS PLACE JUST OUTSIDE
OR TO THE WEST OF OUR CWA. WOULD NOT BE SURPRISE IF A SEVERE
THUNDERSTORM OVER LEWISTOWN DIMINISHES SLIGHTLY AND BRINGS SMALL
HAIL TO OUR CWA TONIGHT. OVERALL SEVERE THUNDERSTORM PARAMETERS
DIMINISH THROUGH NORTHEAST MONTANA THROUGH THE EVENING HOURS. A
GOOD WETTING RAIN CAN BE EXPECTED FOR MOST OF OUR CWA...ALTHOUGH
THE 06Z RUN OF THE NAM EMPHASIZED MORE OUR SOUTH CENTRAL ZONES
WHILE ALL OTHER MODELS PAINT THE RAIN OVER OUR NORTHERN ZONES.
NEXT SHIFT WILL NEED TO WATCH THIS FOR POTENTIAL SHIFTS IN THE
MODEL RAIN BANDS AND ADJUST FORECAST QPF AMOUNTS ACCORDINGLY.

A MORE DISTINCT AND VIGOROUS COLD FRONT WILL PASS THROUGH THE CWA
LATE TONIGHT AND VERY EARLY TUESDAY MORNING. STRONG SUBSIDENCE
AND COLD AIR ADVECTION BEHIND THE FRONT WILL ALLOW STRONG AND
ENHANCED WINDS BEHIND THE FRONT TO PERSIST THROUGHOUT MOST OF THE
DAY ON TUESDAY AS ISOLATED SHOWERS LINGER OVER THE CANADIAN
BORDER. CRITICAL FIRE WEATHER CONDITIONS LOOK MORE LIKELY ON
TUESDAY WITH WIDESPREAD SUSTAINED WINDS IN EXCESS OF 25 TO 20
KNOTS. SEE FIRE WEATHER DISCUSSION.

SOME VERSION OF ZONAL FLOW WILL PERSIST THROUGH THE REMAINDER OF
THE FORECAST PERIOD. BMICKELSON


.LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY...
EXTENDED PERIOD OPENS WITH DRY ZONAL FLOW OVER MONTANA. BY
THURSDAY MORNING FLOW BEGINS TO TURN INCREASINGLY SOUTHWEST WITH
UPPER TROF PUSHING ACROSS THE WEST COAST AND INTO THE GREAT BASIN.
MODELS IN GOOD AGREEMENT WITH SLOWLY LIFTING THIS TROF INTO THE
NORTHERN PLAINS OVER THE WEEKEND THEN FORMING A CLOSED LOW IN THE
UPPER MIDWEST EARLY NEXT WEEK. SOME INDICATION OF THE FIRST GOOD
LOW LEVEL JET FROM THE GULF INTO THE NORTHERN PLAINS DEVELOPING ON
THURSDAY. THIS WILL INCREASE THE MOISTURE AVAILABLE FOR THE
INCOMING SYSTEM...WHICH ALREADY WILL CONTAIN MID TO HIGH LEVEL
PACIFIC MOISTURE...LEADING TO THE POTENTIAL FOR SIGNIFICANT
RAINFALL FOR MUCH OF THE REGION SOMETIME OVER THE WEEKEND. EBERT

&&

.AVIATION...
VFR. TODAY WILL BRING BKN-OVC HIGH CLOUDS ALONG WITH WESTERLY
WINDS AT 15 TO 25KTS. THE APPROACH OF A STRONG COLD FRONT
TONIGHT WILL BRING THE POTENTIAL FOR A FEW THUNDERSTORMS DURING
THE EVENING WITH GUSTY WINDS AND BRIEF REDUCED FLIGHT CONDITIONS
TO MVFR. WIND ARE EXPECTED TO INCREASE SIGNIFICANTLY BEHIND THE
FRONTAL PASSAGE EARLY TUESDAY MORNING...LASTING THROUGH THE DAY ON
TUESDAY. RAE/GILCHRIST

&&

.FIRE WEATHER...

A WEAK FRONT MOVING THROUGH EASTERN MONTANA THIS MORNING WILL
BRING SOME INCREASED WINDS BY THIS AFTERNOON...BUT WITH RELATIVE
HUMIDITY STRUGGLING TO DROP BELOW 25 PERCENT...CRITICAL FIRE
WEATHER CONDITIONS SEEM LESS LIKELY TODAY.

A MORE VIGOROUS COLD FRONT WILL SLIDE THROUGH THE REGION LATE
TONIGHT. STRONG SUBSIDENCE AND COLD AIR ADVECTION WILL SUSTAIN
STRONG AND GUSTY WIND FROM THE WEST THROUGH THE ENTIRE DAY TUESDAY.
ALTHOUGH COOLING TEMPERATURES WILL RESULT IN HIGHER HUMIDITY...THE
MUCH STRONGER WINDS WILL MAINTAIN THE POTENTIAL FOR CRITICAL FIRE
CONDITIONS THROUGH TUESDAY EVENING. A FIRE WEATHER WATCH IS IN
EFFECT.

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH FROM TUESDAY MORNING THROUGH TUESDAY EVENING
FOR MTZ120-122-134>137.

&&

$$

WEATHER.GOV/GLASGOW