Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 231539 AAA
AFDGGW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE GLASGOW MT
939 AM MDT SAT AUG 23 2014

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

RADAR RETURNS CONFIRM WIDESPREAD RAIN THIS MORNING AND GUIDANCE
SUGGESTS MORE OF THE SAME THROUGH THE DAY. THE MAIN QUESTION
CONTINUES TO BE THE EXPECTED QPF AMOUNTS. THE RADAR RETURNS
SUGGEST MORE OF A STEADY RAIN THAN PERIODS OF HEAVY RAIN. A LOOK AT
6 HR FLASH FLOOD GUIDANCE SUGGESTS THAT SOME FLOODING COULD
OCCUR...ESPECIALLY WHERE DRAINAGE IS POOR. SEE HYDRO DISCUSSION
FOR MORE INFORMATION. THE CURRENT GRIDS LOOK GOOD FOR FEW CHANGES.
HOWEVER DID BACK OFF FROM TS MENTION FOR ALL BUT FAR EASTERN
PORTIONS OF THE CWA TODAY. ALSO INCLUDED POSSIBILITY OF HEAVY RAIN
FOR THE SOUTHWESTERN PORTIONS OF THE CWA. THE INVERTED TROUGH HAS
NUDGED INTO NORTHEAST AND NORTH-CENTRAL MONTANA PUTTING UP A
STRONG SURFACE GRADIENT RESULTING IN STRONG GUSTY WIND. THE LAKE
WIND ADVISORY FOR FORT PECK LAKE REMAINS IN EFFECT. SCT

PREVIOUS DISCUSSION...
SYNOPTIC SET UP...SHORT TERM BEGINS WITH A LARGE TROUGH RUNNING
FROM ALBERTA THROUGH WESTERN MONTANA INTO THE INTER-MOUNTAIN WEST
AND TERMINATING OVER THE FOUR CORNERS. THIS HAS BUSTED UP MOST OF
THE HOT HIGH PRESSURE ACROSS THE DESERT SOUTHWEST WITH ITS
REMNANTS LINGERING IN CALIFORNIA. THE TROUGH HAS ALSO TAPPED INTO
THE MONSOONAL MOISTURE FROM THIS REGION AND IS PROVIDING AN
EXPRESS LANE NORTH FOR IT TO FILTER ACROSS THE COLD FILTERING IN.
TO THE WEST... A WEAK RIDGE RUNS UP THE COAST OF THE PACIFIC
NORTHWEST AND INTO BRITISH COLUMBIA.

TODAY THROUGH SUNDAY... COLD HIGH PRESSURE WILL FILTER INTO THE
REGION NEAR THE SURFACE DIRECTLY BEHIND A WIND UP LOW THAT TRAVELS
NORTH INTO EASTERN MONTANA. MONSOONAL MOISTURE WILL OVERRUN THIS
AIR ALLOWING FOR STRATIFORM RAIN TO FORM AND PROVIDE A QUITE A BIT
OF QPF ACROSS THE AREA OVER THE NEXT 36 HOURS. USING A MULTI MODEL
BLEND VALUES AS HIGH AS 3 TO 4 INCHES HAVE APPEARED OVER THE
MISSOURI BREAKS DURING THIS TIME... HOWEVER WISDOM HERE SHOULD
PREVAIL. MONTHLY TOTAL AUGUST RECORDS USUALLY DO NOT EXCEED 4 TO
6 INCHES AND QPF FROM MODEL OUTPUT IS TYPICALLY DOUBLE WHAT REALLY
OCCURS ACROSS EASTERN MONTANA. GUT FEELING PUSHES THE TOTALS FOR
MOST OF THE AREA TO AROUND 2 INCHES TOTAL. HOWEVER THESE TOTALS AND
LOCALLY HIGHER VALUES MAY STILL PRODUCE FLOODING OF SOME FORM AND
THEREFORE A FLOOD WATCH HAS BEEN ISSUED THROUGH SUNDAY.

SUNDAY NIGHT THROUGH MONDAY... STACKED LOW WILL EXIT THE AREA TO THE
NORTHEAST. CHANCES FOR RAIN WILL QUICKLY DECREASE OVERNIGHT
LEADING TO CLEARING AND COOL CONDITIONS AS HIGH PRESSURE SETTLES
IN TUESDAY AFTERNOON. GAH

.LONG TERM...MONDAY NIGHT THROUGH SATURDAY...
LOOK FOR SPLIT FLOW ALOFT MONDAY NIGHT THROUGH WEDNESDAY.
NORTHEAST MONTANA WILL BE IN THE DRIER NORTHERN STREAM. THERE WILL
BE A SURFACE HIGH PRESSURE SYSTEM MONDAY NIGHT AND TUESDAY WHICH
WILL KEEP MOST OF THE AREA DRY. AN UPPER TROUGH IN THE SPLIT FLOW
ALOFT WILL MOVE THROUGH THE AREA TUESDAY AND TUESDAY NIGHT. THE
STRONGER SOUTHERN TROUGH WILL STAY TO THE SOUTH BUT THE NORTHERN
EDGE OF ITS MOISTURE MAY REACH THE SOUTHERN ZONES FOR A CHANCE OF
SHOWERS... POSSIBLY THUNDERSTORMS.

AN UPPER RIDGE BUILDS INTO THE AREA WEDNESDAY AND THURSDAY WITH A
WARMING TREND AND DRY WEATHER. THE RIDGE IS EXPECTED TO LINGER
INTO NEXT WEEKEND ALTHOUGH THE ECMWF WANTS TO FLATTEN THE RIDGE
WITH SOME SHORTWAVES MOVING ACROSS SOUTHERN CANADA WHILE THE GFS
MAINTAINS THE RIDGE. EITHER WAY... IT LOOKS DRY AND WARM. FORRESTER

&&

.AVIATION...

FLIGHT CATEGORY: MVFR TO IFR WITH MODERATE TO HEAVY RAIN AT TIMES
WITH A LARGE RAIN SHIELD OVER THE REGION. THE RAIN WILL MOVE TO
THE NORTHEAST DURING THE DAY ON SUNDAY.

SYNOPSIS: A STACKED LOW PRESSURE SYSTEM WILL MOVE OVER FAR EASTERN
MONTANA THROUGH PERIOD.

WINDS: FROM THE EAST AND NORTHEAST AT 15 TO 25 KNOTS TODAY TURNING
MORE NORTHERLY TONIGHT AND NORTHWEST BY SUNDAY MORNING.
HICKS/BMICKELSON


&&

.HYDROLOGY...

A VERY WET AND SLOW MOVING LOW PRESSURE SYSTEM WILL BRING 2 TO 4
INCHES OF RAIN TO THE AREA THROUGH SUNDAY. THE EXPECTED RAIN
TOTALS PROMPTED THE WEATHER PREDICTION CENTER TO PLACE NORTHEAST
MONTANA AT A MODERATE RISK FOR EXCESSIVE RAINFALL...AND
SOUTHWESTERN PORTIONS AT HIGH RISK FOR EXCESSIVE RAINFALL. AS A
RESULT FLASH FLOOD WATCH REMAINS IN EFFECT THROUGH SUNDAY.

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
FLOOD WATCH THROUGH SUNDAY AFTERNOON FOR CENTRAL AND SOUTHEAST
PHILLIPS...CENTRAL AND SOUTHERN VALLEY...DANIELS...DAWSON...
EASTERN ROOSEVELT...GARFIELD...MCCONE...NORTHERN PHILLIPS...
NORTHERN VALLEY...PETROLEUM...PRAIRIE...RICHLAND...SHERIDAN...
SOUTHWEST PHILLIPS...WESTERN ROOSEVELT...WIBAUX.

LAKE WIND ADVISORY UNTIL MIDNIGHT MDT TONIGHT FOR FORT PECK LAKE
FOR CENTRAL AND SOUTHEAST PHILLIPS...CENTRAL AND SOUTHERN
VALLEY...GARFIELD...MCCONE...PETROLEUM.

&&

$$

WEATHER.GOV/GLASGOW





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