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000
FXUS65 KGGW 201515
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
915 AM MDT MON MAY 20 2013

.SHORT TERM...FOR NORTHEAST MONTANA...TODAY THROUGH WEDNESDAY...
RAINFALL CONTINUES OVER THE EASTERN HALF OF THE CWA THIS MORNING.
MADE A FEW FURTHER ADJUSTMENTS TO THE WESTERN EDGE OF HIGH POPS
WITH EXPECTATION THAT RAIN WILL STAY TO THE EAST OF GLASGOW AND
JORDAN. SIMILAR ADJUSTMENTS ALSO MADE FOR TONIGHT WITH THE UPPER
LOW BEGINNING TO SHIFT EASTWARD. EBERT

6AM UPDATE...THE WESTERN PUSH OF RAIN LOOKS TO FALL SHORT OF
GLASGOW THEREFORE BACKED DOWN THE 100 POPS.    PROTON

PREVIOUS SHORT TERM DISCUSSION...TODAY AND TONIGHT...A VERTICALLY
STACKED LOW PRESSURE SYSTEM SITUATED OVER THE DAKOTAS WILL
CONTINUE TO SIT AND SPIN. AS IT DOES...A SHIELD OF STRATIFORM RAIN
WILL CONTINUE TO RETROGRADE FROM EAST TO WEST THOUGH THE
DAY...BEFORE CRASHING BACK TO THE SOUTHEAST THIS AFTERNOON AND
EVENING AS THE LOW BEGINS TO TRANSLATE EASTWARD. DETERMINING THE
MAXIMUM EXTENT OF THE BACK EDGE OF THE RAINFALL SHIELD WILL
CONTINUE TO BE THE MAIN FORECAST CHALLENGE.

THE LATEST NAM HAD THE PRECIPITATION INITIALIZED A BIT FURTHER TO
THE EAST THAN RADAR OBSERVATIONS SHOWED. THUS...FEEL THE
PRECIPITATION SHIELD SHOULD MAKE IT A BIT FURTHER THAN THIS
SOLUTION IS SUGGESTING. THE 00Z ECMWF AND GFS HAVE A LITTLE BETTER
HANDLE ON IT. WILL ADMIT THAT THE HRRR HAS BEEN AN IMPRESSIVE
INFORMER AS IT CAUGHT ONTO THE IDEA THAT THE SHIELD WOULD STOP
RETROGRADING FOR A FEW HOURS OVERNIGHT BEFORE AGAIN PROCEEDING ITS
MARCH FURTHER WEST TOWARD MORNING AND THIS IS WHAT IS OCCURRING.
LENDING FURTHER SUPPORT TO THE GUIDANCE IS THE OBSERVATION OF
RECENT PRESSURE FALLS ACROSS THE CWA. PRESSURES ARE GENERALLY
FALLING BETWEEN 0.5 AND 1 MB PER HOUR FOR THE LAST FEW HOURS.
THEREFORE...WILL FEEL COMFORTABLE WITH A BLEND OF THE
ECMWF/GFS/HRRR MODEL SOLUTIONS FOR DETERMINING A BEST GUESS AS TO
WHERE THE BACK EDGE WILL REACH BEFORE IT BEGINS TO PUSH BACK TO
THE SOUTHEAST. THIS BRINGS IT TO A LINE FROM ABOUT OPHEIM...EXTENDING
SOUTH THROUGH JUST WEST OF GLASGOW...TO THE JORDAN AREA. TO THE
EAST OF THIS LINE...THERE IS A DECENT CHANCE AT A NICE WETTING
RAIN THROUGH TONIGHT. IN FACT...WOULD NOT BE SURPRISED IF SOME
AREAS SEE ONE TO TWO INCHES OF RAINFALL ACCUMULATION BY THE END OF
TONIGHT AND INCLUDED A MENTION OF HEAVY RAIN IN SOME OF THE
EASTERN ZONES THROUGH THE MORNING. TO THE WEST OF THIS LINE...RAIN
CHANCES WILL ONLY BE SHOWERY IN NATURE WITH A FEW HUNDREDTHS OF AN
INCH OF ACCUMULATION THE ABSOLUTE MOST THAT WOULD OCCUR. PRECISE
RAINFALL AMOUNTS WILL DEPEND UPON THE PRECISE LOCATION OF WHERE
THE BACK EDGE OF THIS RAIN SHIELD WINDS UP...AS WELL AS SOME FINER
MESOSCALE DETAILS THAT ARE DIFFICULT TO DETERMINE WITH MUCH
CONFIDENCE. TEMPERATURES ARE KEPT AROUND OR JUST BELOW SEASONAL
NORMALS DUE TO THE PRESENCE OF THE LINGERING UPPER TROUGH.

THE OTHER CONCERN TODAY WILL BE STRONG GUSTY WINDS DUE TO A SHARP
PRESSURE GRADIENT IN ASSOCIATION WITH THE SURFACE LOW ACROSS THE
DAKOTAS. AM EXPECTING THAT THE TIGHT PACKING OF THE ISOBARS COULD
SUPPORT NORTHERLY WINDS ON THE ORDER OF 20 TO 30 MPH WITH SOME
GUSTS EXCEEDING 40 MPH THIS AFTERNOON AND EVENING. WILL HOIST A
LAKE WIND ADVISORY FROM NOON UNTIL 9PM DUE TO THIS CONCERN. THIS
MAY ALSO LEAD TO WIND DRIVEN RAINS IN SOME LOCATIONS WHICH COULD
POSE AS HAZARDS TO TRAVELERS AND PEDESTRIANS ALIKE.

TONIGHT THROUGH WEDNESDAY...THE LOW PRESSURE SYSTEM OVER THE
DAKOTAS VERY GRADUALLY TRANSLATES EASTWARD...SO CONTINUED TO TREND
POPS DOWN AND HAVE PRECIPITATION SHUTTING OFF FROM WEST TO EAST.
WILL LEAVE ONLY A SLIGHT CHANCE OF RAIN SHOWERS IN THE EXTREME SE
ZONES BY LATE TUESDAY NIGHT. ON WEDNESDAY...ANOTHER UPPER TROUGH
WITH CLOSED LOW MOVES INTO THE PACIFIC NORTHWEST AS IT DOES
SO...DIFFLUENT SOUTHWEST FLOW ALOFT IS EXPECTED TO DEVELOP ACROSS
THE CWA. THIS MAY LEAD TO CONVECTIVE SHOWERS ON WEDNESDAY...MAINLY
ACROSS THE SW ZONES. SOME OF THE SOUNDINGS IN THE NAM BUFKIT JUST
WEST OF THE CWA ARE SHOWING TOTAL TOTALS APPROACHING 50 AND LI
BECOMING NEGATIVE. DID NOT INSERT A MENTION OF THUNDER JUST YET DUE TO THE
FACT THAT THE PRIMARY FOCUS WAS ON THE CURRENT RAINFALL SITUATION
AND LAKE WIND POTENTIAL. HOWEVER...FUTURE SHIFTS MAY WANT TO
EVALUATE THE POTENTIAL FOR ANY CONVECTIVE INITIATION TOWARD THE
MIDDLE OF THE WEEK. MALIAWCO

.LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY...
THE EXTENDED FEATURES MORE SOUTHWEST FLOW THROUGH THE PERIOD. MOST
DAYS SLIGHT CHANCES OF THUNDERSTORMS SLIDING OFF THE CENTRAL
MONTANA MOUNTAINS INTO THE PLAINS FOR HIGHER POPS WEST AND LOW
POPS EAST. FOR THE WEEKEND THE UPPER LOW BREAKS A GOOD WAVE OFF
AND DRIVES IT THROUGH NORTHEAST MONTANA FOR A BETTER CHANCE OF
THUNDERSTORMS THEREFORE BUMPED UP POPS A TAD FOR THOSE PERIODS.

TEMPERATURES WILL HOLD IN NEAR NORMAL THROUGH THE PERIOD.

MODEL TRENDS ARE SHOWING LOWERING HEIGHTS ON THE GFS FOR NORTHEAST
MONTANA WHICH LEADS TO THE UPPER LOW MOVING TOWARDS THE EAST. IF
THE TREND CONTINUES THEN LIKELY POPS ARE A GOOD BET FOR THE
WEEKEND WITH ELEVATED CONFIDENCE. RMOP/ENSEMBLES ARE SHOWING THAT
ITS A GOOD BET THAT AT SOME POINT THIS UPCOMING WEEKEND FOR A
STRONG THUNDERSTORM EVENT ACROSS EASTERN MONTANA. PROTON

&&

.AVIATION...
MVFR VISIBILITY FROM RAIN WITH MVFR/IFR CEILINGS FOR THE EASTERN
AREAS INCLUDING KSDY AND KGDV THROUGH THE PERIOD AS THEY ARE
CLOSER TO THE LOW OVER SOUTHEASTERN NORTH DAKOTA WHICH IS WRAPPING
AROUND MOISTURE INTO THE LOWER YELLOWSTONE RIVER VALLEY. THIS
TREND LOOKS TO CONTINUE THROUGH THE PERIOD.

VFR FOR WESTERN AREAS INCLUDING KGGW AND KOLF THROUGH THE PERIOD
THE MVFR/IFR CEILING SHIELD LOOKS TO STAY JUST OFF TO THE EAST.
FOR NOW WILL STAY WITH VFR CEILINGS.

WIND WILL BE MORE OF AN ISSUE FOR THE EASTERN SITES WITH THE WINDS
STAYING UP ABOVE 20 KNOTS THROUGH THE END OF THE TAF PERIOD.
PROTON/SCT


&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
LAKE WIND ADVISORY UNTIL 9 PM MDT THIS EVENING FOR FORT PECK
LAKE FOR CENTRAL AND SOUTHEAST PHILLIPS...CENTRAL AND SOUTHERN
VALLEY...GARFIELD...MCCONE...PETROLEUM.

&&

$$

WEATHER.GOV/GLASGOW