Weather Service Report


429 
FXUS65 KGGW 210914
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
314 AM MDT TUE APR 21 2015

.SHORT TERM...FOR NORTHEAST MONTANA...TODAY THROUGH THURSDAY...
NW FLOW ALOFT WILL CONTINUE OVER MONTANA WITH UPPER RIDGE TO THE
WEST AND UPPER LOW TO THE EAST. A SHORTWAVE TROUGH MOVING FROM
MANITOBA THROUGH THE DAKOTAS TODAY IS BRINGING A BACK DOOR COLD
FRONT FROM THE NORTHEAST INTO THE FORECAST AREA THIS MORNING. THIS
FRONT WILL BRING SOMEWHAT COOLER TEMPERATURES MAINLY TO THE
EASTERN HALF OF THE FORECAST AREA AND TURN WINDS TO AN EASTERLY
DIRECTION. THE MUCH COLDER AIR WILL STAY TO THE EAST. THE HIGH
PRESSURE SYSTEM WILL BUILD INTO THE DAKOTAS THIS AFTERNOON AND
BRING MAINLY DRY WEATHER TO NORTHEAST MONTANA.

THE HIGH PRESSURE SYSTEM IN THE DAKOTA WILL KEEP SKIES CLEAR TO
PARTLY CLOUDY TONIGHT. 

THE UPPER RIDGE MOVES INTO WESTERN MONTANA WEDNESDAY MORNING AND
CENTRAL MONTANA WEDNESDAY AFTERNOON. THIS WILL BRING WARMER AIR
INTO THE REGION WITH DRY WEATHER CONTINUING. AT THE SAME TIME...A
SURFACE TROUGH DEVELOPS OVER CENTRAL MONTANA DURING THE DAY TIGHTENING
THE SURFACE GRADIENT WHICH WILL INCREASE THE SPEED OF THE EAST TO
SE WINDS BY WEDNESDAY EVENING. 

MODELS DEVELOP DIFFERENCES STARTING WEDNESDAY NIGHT AS THEY TRACK
AN UPPER TROUGH MOVING INLAND ACROSS BRITISH COLUMBIA AND PACIFIC
NW DIFFERENTLY ONCE IT REACHES ALBERTA AND NW MONTANA ON THURSDAY. 

THE EC IS WANTS TO SEND THIS TROUGH WITH A SHORTWAVE AHEAD OF IT
TO THE EAST WITH A BAND OF MOISTURE ACROSS THE RIDGE ON THURSDAY. THE GFS
KEEPS THE SYSTEM TO THE WEST ALTHOUGH IT DOES WANT TO DEVELOP
CONVECTION ALONG THE SURFACE TROUGH. THE NAM IS SOMEWHERE BETWEEN
THE EC AND GFS. WILL MAINTAIN A SLIGHT CHANCE OF SHOWERS OVER THE
WESTERN HALF OF THE FORECAST AREA FOR NOW AND WAIT TO SEE IF THE
MODELS COME INTO BETTER AGREEMENT IN FUTURE RUNS. FORRESTER


.LONG TERM...THURSDAY NIGHT THROUGH TUESDAY...
THE LATEST 00Z GUIDANCE CONTINUES TO HAVE SOME DIFFERENCES
ALTHOUGH CONFIDENCE IS INCREASING ON A SORT OF PROGRESSIVE WEATHER
PATTERN THAT WILL BE EVOLVING. THURSDAY NIGHT WILL FEATURE A
TROUGH OVER THE PACIFIC NORTHWEST WHICH WILL PUSH SOUTHWEST FLOW
ALOFT ACROSS NORTHEAST MONTANA FOR LATE IN THE WEEK. 

VARIOUS SHORTWAVES EMBEDDED IN THE UPPER FLOW PATTERN WILL PROVIDE
OPPORTUNITIES FOR RAIN SHOWERS...BUT GIVEN THE PROGRESSIVE NATURE
OF THIS PATTERN AND DIFFERENCES IN THE OPERATIONAL GFS/ECMWF IN
TIMING/PLACEMENT OF THESE FEATURES...PREDICTABILITY IS NOT AS HIGH
AS WOULD BE IDEAL. FOR INSTANCE...BY EARLY NEXT WEEK THE GFS
BUILDS A RIDGE OVER THE NORTHERN HIGH PLAINS AND HAS IT TRANSLATE
EAST OVER THE DAKOTAS AS A NEW PACIFIC TROUGH BECOMES ESTABLISHED
MIDWEEK. THE ECMWF ESTABLISHES A HIGHLY AMPLIFIED RIDGE OVER THE
WESTERN CONUS WITH A DEEP TROUGH CLOSED LOW OVER THE EASTERN U.S.
LEADING TO NORTHWEST FLOW ALOFT OVER THE FORECAST REGION. THESE
MARKED DIFFERENCES ILLUSTRATE THE DIFFICULTY IN OFFERING MUCH
DETAIL IN THE EXTENDED. FOR NOW DECIDED TO HAVE SLIGHT CHANCE TO
NEAR CLIMO POPS IN THE GRIDS THROUGH MUCH OF THE EXTENDED PERIOD
TO COVER THE UNCERTAINTY. MALIAWCO

&&

.AVIATION...
VFR CIGS AND VSBYS WILL PREVAIL TODAY WITH DEVELOPING LIGHT
EASTERLY WINDS. MALIAWCO

&&

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

&&

$$

WEATHER.GOV/GLASGOW



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