Area Forecast Discussion
Issued by NWS Glasgow, MT

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000
FXUS65 KGGW 040305 AAA
AFDGGW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE GLASGOW MT
905 PM MDT SUN MAY 3 2015

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH TUESDAY...

THE BROAD TROUGH OVER THE PRAIRIE PROVINCES WILL SHIFT EAST
TONIGHT AS THE WESTERN RIDGE CROSSES THE DIVIDE. THE RESULT WILL
BE A RETREATING COLD BOUNDARY. THEREFORE EXPECT A SLIGHTLY WARMER
NIGHT THAN LAST NIGHT. SATELLITE IMAGERY REVEALED INCREASED CLOUDS
ALONG THE BOUNDARY THAT COVER THE SOUTHERN COUNTIES BUT LEAVE THE
NORTHERN TIER CLEAR TONIGHT. MAIN ADJUSTMENT WAS TO EDIT SKY GRIDS.
NO OTHER GRID CORRECTIONS WERE NEEDED. SCT

PREVIOUS DISCUSSION...
THE FORECAST FOR THE NEXT FEW DAYS IS FAIRLY QUIESCENT DUE TO A
MID- LEVEL LONG WAVE RIDGE THAT BUILDS OVER MONTANA FROM THIS
EVENING THROUGH TUESDAY AFTERNOON. APPROACH OF NEXT UPSTREAM
SYSTEM...WHICH IS A LARGE (AND THUS PREDICTABLE) LONG WAVE TROUGH
WILL BEGIN TO IMPACT THE CWA TUESDAY NIGHT WITH SOME SHOWERS
POSSIBLE OUT WEST.

SURFACE TROUGH AHEAD OF THE INCOMING LONG WAVE UPPER TROUGH SETS-
UP EAST OF THE ROCKIES AS EARLY AS MONDAY...LEADING TO
STRENGTHENING SOUTHERLY TO SOUTHEASTERLY SURFACE WINDS MONDAY AND
TUESDAY AFTERNOONS. SINKING AIR WITH THE RIDGE AND WARM SOUTHERLY
FLOW WILL WARM MONDAY AND TUESDAYS HIGHS INTO THE MID TO UPPER
70S.

SOUTHERLY TO SOUTHEASTERLY FLOW ON MONDAY AND TUESDAY WILL
INCREASE BOUNDARY LAYER MOISTURE AND BEGIN TO MAKE THE
ATMOSPHERE LESS STABLE. MOISTURE ADVECTION WILL BE ENHANCED DUE TO
A NOCTURNAL LOW-LEVEL JET MONDAY AND TUESDAY NIGHTS. INITIAL
SHOWERS OUT WEST TUESDAY AFTERNOON ARE EXPECTED HAVE SOME THUNDER
WITH THEM AS NAM FORECASTS CAPE TO 500 J/KG...THOUGH BETTER
INSTABILITY WILL BE FURTHER WEST UNDER THE COLDER AIR ALOFT WITH
THE INCOMING UPPER TROUGH.

GOOD DEEP MIXING MONDAY AND TUESDAY AFTERNOONS IS EXPECTED TO
PRODUCE SURFACE WINDS NEAR 20KTS WITH GUSTS TO 30. WITH IMPROVING
MOISTURE...RELATIVE HUMIDITY IS EXPECTED TO BE SUPPORTED AT AROUND
30% MINIMUM. FIRE WEATHER HEADLINES ARE NOT EXPECTED TO BE
NEEDED...ESPECIALLY WHEN THE VERY GREEN VEGETATION IS TAKEN INTO
ACCOUNT...HOWEVER...20 KTS OF WIND WITH SOME REDUCTION IN
AFTERNOON HUMIDITY GIVES SOME POTENTIAL FOR MORE ACTIVE THAN USUAL
FIRES.

ELEVATED WINDS MONDAY AND TUESDAY AFTERNOONS CREATE A WINDOW FOR
POSSIBLE LAKE WIND ADVISORY FROM 18Z TO 3Z BOTH DAYS. 850MB WINDS
ARE A LITTLE STRONGER ON TUESDAY AT 20 TO 25KTS IN THE NAM
MODEL...THOUGH WEAKER IN THE GFS. PRECISE CONSISTENCY IN SHORT
TERM MODELS IS PRETTY CLEAR FOR MONDAY AFTERNOON...SO ISSUED NPW
FOR THE LAKE FOR MONDAY AFTERNOON. MARTIN


.LONG TERM...TUESDAY NIGHT THROUGH SUNDAY...
MODELS SHOWED HORRIBLE AGREEMENT DURING THIS PERIOD. GFS WAS ALSO
DRIER FOR TUESDAY NIGHT WHILE ECMWF MUCH WETTER. GFS ALSO SHOWED
THAT PERIOD MAY NOT BE AS WET AS INHERITED FORECAST PORTAYED...SO
BACKED OFF ON POPS SLIGHTLY FOR THURSDAY NIGHT AND FRIDAY. WITH COOL
AIRMASS IN PLACE ATMOSPHERE SHOULD BE PRETTY STABLE THEN. TEMPS LOOK
TO BE COOLER THAN NORMAL LATE IN THE WEEK.

12Z ECMWF BACKED OFF ON A SYSTEM NEXT WEEKEND THAT THE 00Z RUN HAD
WRAPED UP AND COMBINED WITH A COLD AIRMASS DROPPING SW OUT OF
CENTRAL CANADA (MEANING SNOW WAS POSSIBLE). WET-BULB TEMPERATURES
NEXT SUNDAY ARE PROGGED TO BE ABOUT -4 TO -6 IN PLENTYWOOD SO THAT
WHITE STUFF MAY FALL SOMEWHERE BUT MOST LIKELY IN THE DAKOTAS AT
THIS POINT. TFJ

PREVIOUS DISCUSSION...
SOUTHWEST FLOW ALOFT WILL PREVAIL FROM TUESDAY NIGHT INTO THE
WEEKEND. THERE WILL BE AN UPPER RIDGE TO THE EAST AND AN UPPER
TROUGH/LOW TO THE WEST.

THE UPPER TROUGH/LOW WILL DIG OVER THE PACIFIC NW TUESDAY NIGHT
AND WEDNESDAY. A SHORTWAVE TROUGH IN THE SW FLOW ALOFT WILL MOVE
THROUGH EASTERN MONTANA TUESDAY NIGHT AND WEDNESDAY. AT THE SAME
TIME...THE LOW PRESSURE SYSTEM AND COLD FRONT ALSO MOVES THROUGH
THE FORECAST AREA WHICH WILL BRING A GOOD CHANCE OF THUNDERSTORMS.
THE COLD FRONT GRADUALLY MOVES INTO THE DAKOTAS DURING THE DAY ON
WEDNESDAY BUT THE MOIST SOUTHERLY FLOW ALOFT CONTINUES. UPPER LOW
TO THE WEST CONTINUES TO MOVE SOUTH TOWARDS CALIFORNIA. MODELS
HINT AT A POSSIBLE DRY SLOT WHICH WILL REDUCE PRECIP CHANCES BUT
AT THE SAME TIME... THE ATMOSPHERE IS EXPECTED TO BE UNSTABLE.
WILL MAINTAIN A CHANCE OF THUNDERSTORMS.

ON THURSDAY...THE TROUGH/UPPER LOW TO THE WEST DIVES SOUTH INTO
CALIFORNIA AND KEEPS A MOIST SOUTHERLY TO SOUTHWEST FLOW ALOFT
GOING OVER EASTERN MONTANA. MEANWHILE...THERE WILL BE A SURFACE
HIGH OVER ALBERTA AND SASKATCHEWAN WHICH WILL BRING A DRIER LOW
LEVEL NORTHERLY WIND INTO NORTHEAST MONTANA. MODELS DIFFER ON HOW
WELL THE DRIER LOW LEVEL FLOW WILL LIMIT PRECIP CHANCES.
ALSO...WEAK SHORTWAVE TROUGHS ARE EXPECTED WITHIN THE SW FLOW
ALOFT. WILL MAINTAIN A CHANCE OF SHOWERS AND THUNDERSTORMS SOUTH
AND SLIGHT CHANCE NORTH. TEMPERATURES WILL BE COOLER WITH THE
COLD FRONT WELL TO THE EAST.

ON FRIDAY...THERE IS A SHORTWAVE RIDGE EXPECTED IN THE SW FLOW
ALOFT AND SURFACE HIGH WILL BE OVER SASKATCHEWAN AND EASTERN
MONTANA. AT THIS POINT...THIS DAY HAS THE BEST CHANCE OF BEING DRY
IN THE EXTENDED PERIOD. HOWEVER...ATMOSPHERE IS EXPECTED TO REMAIN
MOIST IN SOUTHERN MONTANA AND WYOMING. WILL MAINTAIN A SLIGHT
CHANCE OF SHOWERS IN THE SOUTH.

THE UPPER LOW LIFTS NORTHEAST ON FRIDAY AND WILL MOVE ACROSS
MONTANA AND WYOMING SATURDAY AND SUNDAY BRINGING DEEP MOISTURE
INTO THE FORECAST AREA. MODELS DIFFER ON WHETHER TO TURN THE LOW
INTO AN OPEN TROUGH (GFS) OR MAINTAIN THE CLOSED LOW (ECMWF) AS
IT MOVES THROUGH THE AREA. EITHER WAY... IT IS LOOKING COOL AND WET
FOR NEXT WEEKEND. WILL MENTION A CHANCE OF SHOWERS FOR NOW.
FORRESTER


&&

.AVIATION...
VFR CONDITIONS WILL PREVAIL INTO MONDAY.

A SURFACE LOW PUSHES INTO WESTERN MONTANA MONDAY DRIVING SOUTHEAST
WINDS OUT AHEAD OF OVER EASTERN MONTANA. OTHERWISE...LIGHT WINDS
WITH CLEAR SKIES ARE EXPECTED TONIGHT. TFJ

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
LAKE WIND ADVISORY FROM NOON TO 9 PM MDT MONDAY FOR FORT PECK
LAKE FOR CENTRAL AND SOUTHEAST PHILLIPS...CENTRAL AND SOUTHERN
VALLEY...GARFIELD...MCCONE...PETROLEUM.

&&

$$

WEATHER.GOV/GLASGOW







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