Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 221136
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
536 AM MDT TUE JUL 22 2014

.SHORT TERM...FOR NORTHEAST MONTANA...TODAY THROUGH THURSDAY...

UPDATED FORECAST TO ADD PATCHY FOG FOR THE NORTHEAST PART OF THE
CWA. FOG OR MIST ARE BEING OBSERVED AT A COUPLE OBSERVING SITES
AND SATELLITE IMAGERY SHOWS AREAS OF LOW CLOUDS.  MARTIN

PREVIOUS DISCUSSION...
WITH A HIGH PRESSURE RIDGE OVER THE SOUTHERN ROCKIES AND SOUTHERN
PLAINS REGIONS AND A LOW PRESSURE SYSTEM JUST OFF SHORE OF THE
PACIFIC NORTHWEST...PACIFIC MOISTURE IS BEING FUNNELED OVER THE
NORTHERN ROCKIES AND NORTHERN HIGH PLAINS REGIONS. MULTIPLE
EMBEDDED SHORT-WAVE DISTURBANCES RIDING AMIDST THE OTHERWISE
NEARLY ZONAL OR SLIGHTLY SOUTHWESTERLY FLOW ALOFT CONTINUE TO
PROVIDE SMALL POCKETS OF LIFT CAPABLE OF PRODUCING SOME ISOLATED
OR SCATTERED RAIN SHOWERS AND THUNDERSTORMS ACROSS PORTIONS OF
NORTHEAST MONTANA.

THE MAIN INFLUENCE IN THE SHORT TERM FORECAST PERIOD IS THE AREA
OF LOW PRESSURE APPROACHING THE PACIFIC NORTHWEST AND NORTHERN
ROCKIES REGIONS. MODELS GENERALLY SYNOPTICALLY AGREE IN BRINGING
THIS LOW ONSHORE TONIGHT AND TURNING THE UPPER LEVEL FLOW OVER
NORTHEAST MONTANA MORE SOLIDLY FROM THE SOUTHWEST. ENOUGH MOISTURE
AND INSTABILITY WILL BE PRESENT TO ALLOW SOME STRONG TO SEVERE
THUNDERSTORMS TO DEVELOP ACROSS PORTIONS OF THE NORTHERN HIGH
PLAINS REGION. THIS AFTERNOON AND TONIGHT...THE STRONGER STORMS
ARE EXPECTED NEAR AND SE OF INTERSTATE 94 THROUGH OUR CWA.

FOR WEDNESDAY NIGHT...THE THREAT FOR STRONGER THUNDERSTORMS SEEMS
TO SHIFT MORE OVER OUR PHILLIPS COUNTY. OF GREATEST IMPACT WILL
LIKELY BE NOCTURNAL THUNDERSTORMS DURING THE LATE NIGHT HOURS OF
WEDNESDAY NIGHT AND VERY EARLY THURSDAY MORNING. MODELS CONTINUE
TO TRY TO GATHER AROUND A SOLUTION SHOWING MODERATE TO HEAVY QPF
FOR AN AREA GENERALLY FROM WHITEWATER THROUGH GLASGOW THROUGH WOLF
POINT...BUT THERE STILL EXISTS SOME UNCERTAINTY. TRIED TO SHOW AT
LEAST A LITTLE MORE CONFIDENCE IN THE POPS WHERE THE BEST MODEL
CONSENSUS WAS FOUND.

BY LATE THURSDAY...THE LOW PRESSURE SYSTEM LIFTS NORTHEASTWARD
THROUGH OUR CWA LEAVING A ZONAL UPPER-LEVEL FLOW IN ITS WAKE.
BMICKELSON

.LONG TERM...THURSDAY NIGHT THROUGH TUESDAY...

DUE TO THE IMPACT OF A STRONG SOMEWHAT NEGATIVELY TILTED UPPER LOW
MOVING INTO CANADA JUST NORTH OF MONTANA...POSSIBLY SEVERE CONVECTION
IS EXPECTED TO BE ONGOING AT THE BEGINNING OF THE LONG TERM
FORECAST THURSDAY NIGHT. GFS SHOWS A 75KT 500MB SPEED MAX ROUNDING
THE BOTTOM OF THE LOW THURSDAY NIGHT. THIS DYNAMIC WILL SUPPORT
STRONG QG FORCING OVER EASTERN MT AS WELL AS GENERATE STRONG DEEP
LAYER SHEAR.

SURFACE TROUGH AHEAD OF THE SYSTEM WILL BE CO-LOCATED WITH A
DRYLINE AND WILL BE MOVING INTO NORTH DAKOTA BY THURSDAY NIGHT
WITH STORMS EXPECTED TO HAVE FORMED ALONG AND AHEAD OF THE
DRYLINE. THERE IS STILL SOME UNCERTAINTY AS TO THE LOCATION AND
TIMING OF MOVEMENT OF THE DRYLINE...BUT IT IS ANTICIPATED THAT
EASTERN PARTS OF THE CWA WILL HAVE CONVECTION MOVING EASTWARD OUT
OF THE AREA BY THURSDAY NIGHT...PER SPC DAY3 OUTLOOK. COMBINATION
OF SHEAR AND INSTABILITY IS QUITE GOOD WITH FORECAST SOUNDINGS
SHOWING 2000 TO 3000 J/KG OF CAPE AND 45KTS OF BULK SHEAR.
SOMEWHAT LARGE DEWPOINT DEPRESSIONS AND PWAT VALUES BELOW 1 INCH
SUGGEST THE POSSIBILITY OF LOW PRECIPITATION SUPERCELLS WITH LARGE
HAIL AND MICROBURSTS POTENTIALLY THE MAIN RISKS. THE MAXIMUM CAPE
IS ALSO AROUND THE -20C LEVEL IN FORECAST SOUNDINGS...ENHANCING
HAIL GROWTH.

FOLLOWING PASSAGE OF THE THURSDAY NIGHT SYSTEM...THERE WILL ONLY
BE AN OUTSIDE CHANCE SATURDAY FOR A SHOWER IN THE EXTREME
NORTHEAST PART OF THE CWA ON THE BACK SIDE OF THE UPPER LOW AS IT
TAKES A TURN AN DIGS SOUTHEAST FROM MANITOBA TOWARDS IOWA. FROM
SATURDAY NIGHT ONWARD...RIDGE GROWS OVER THE GREAT DIVIDE LEADING
TO BENIGN WEATHER WITH CLEAR SKIES...WARM TEMPERATURES...AND LIGHT
WINDS THROUGH TUESDAY. THERE IS PRETTY STRONG MODEL AGREEMENT ON
THE PRESENCE OF THE WESTERN US RIDGE ALL THE WAY THROUGH TUESDAY.

MARTIN

&&

.AVIATION...
AREA WILL BE IN BETWEEN STORM SYSTEMS WITH HIGH PRESSURE
DOMINATING THE WEATHER FOR THE NEXT 24 HOURS. WINDS WILL BE LESS
THAN 10KTS AND GENERALLY EASTERLY OR VARIABLE THROUGH WEDNESDAY
MORNING. THERE IS SOME MOISTURE AT MID-LEVELS BUT ANY CEILINGS
WILL BE ABOVE FL100.

THERE IS A CHANCE FOR AN ISOLATED THUNDERSTORM TUESDAY
AFTERNOON...BUT ANY CONVECTIVE ACTIVITY WILL BE VERY ISOLATED AND
PREVAILING CONDITIONS WILL BE VFR. MARTIN


&&

.FIRE WEATHER...

WEDNESDAY AND THURSDAY CONTINUE TO FAVOR THE DEVELOPMENT FOR
MARGINALLY CONCERNING FIRE WEATHER CONDITIONS. WEDNESDAY IS A BIT
MORE UNCERTAIN. WHILE THE RELATIVE HUMIDITIES DROP TO NEAR 20
PERCENT FOR THE WEST END OF THE CMR AND PETROLEUM COUNTY...THE
SOUTHEAST WINDS ARE ONLY AROUND 10 TO 15 MPH. THE STRONGER WINDS
ARE NORTH AND EAST OF THERE BUT THE RELATIVE HUMIDITIES WILL BE
IN THE LOWER 30S. RH RECOVERY OVERNIGHT IS PRETTY POOR AS WELL
WITH READINGS IN THE 50S OVERNIGHT.

THURSDAY...AFTER A FRONTAL PASSAGE...WINDS WILL SHIFT FROM THE
NORTHWEST AN INCREASE INTO THE 20G30 MPH RANGE. RELATIVE
HUMIDITIES WILL DROP TO NEAR 15 PERCENT FOR THE SAME AREA.

OVERALL...THE BIGGEST CONCERN FOR FIRE WEATHER IS
LIGHTNING...POTENTIALLY DRY LIGHTNING...WITH STORMS ON WEDNESDAY
AFTERNOON/EVENING AND THEN LOW HUMIDITIES AND SHIFTING WINDS
SHIFTING INCREASING LATE THURSDAY.

FRANSEN/BMICKELSON

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

WEATHER.GOV/GLASGOW




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