Area Forecast Discussion
Issued by NWS Glasgow, MT

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000
FXUS65 KGGW 232042
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
242 PM MDT TUE SEP 23 2014

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

SYNOPTIC SET UP... SHORT TERM BEGINS WITH A LARGE HIGH PRESSURE
RIDGE OVER THE WESTERN HALF OF THE US AND THE CANADIAN PLAINS. AN
EQUALLY LARGE TROUGH IS DEVELOPING OVER THE NORTHEAST PACIFIC
EXTENDING FROM OFF THE COAST OF THE PACIFIC NORTHWEST INTO THE
GULF OF ALASKA.

THIS AFTERNOON THROUGH THURSDAY... HIGH PRESSURE RIDGE OVER
NORTHEAST MONTANA IS EXPECTED TO REMAIN IN PLACE. THIS WILL CREATE
STABLE DRY CONDITIONS ACROSS THE AREA AS WELL AS ADD TO A WARMING
TREND. TEMPERATURES WILL BE WELL ABOVE NORMAL WITH POTENTIAL
NEAR RECORD HIGHS POSSIBLE WEDNESDAY AND RECORD BREAKERS HIGHLY
POSSIBLE ACROSS THE AREA ON THURSDAY. CONFIDENCE IN THESE PERIODS
ARE HIGH.

LOWER TO MID 90S FOR HIGHS AND LIGHT WINDS WILL MAKE FOR A
GREAT RECREATIONAL DAY ON THE LAKE OR JUST OUTDOORS. GAH


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

AFTERNOON UPDATE...
SYNOPTIC SET UP... A LARGE HIGH PRESSURE RIDGES RUNS FROM THE
DESERT SOUTHWEST THROUGH UTAH... WYOMING... EASTERN MONTANA AND
THEN CURVES BACK OVER WESTERN ONTARIO. AN EQUALLY LARGE COOL CORE
TROUGH RUNS FROM THE CALIFORNIA COAST TO BRITISH COLUMBIA. SOUTH
TO SOUTHWEST FLOW ALOFT DIVIDES THESE TWO LARGE FEATURES FROM
CENTRAL CALIFORNIA THROUGH IDAHO AND WESTERN MONTANA. MEANWHILE...
THE COLDEST AIR OF THE NORTHERN HEMISPHERE IS BOTTLED UP IN THE
ARCTIC DIPPING AS FAR SOUTH AS THE NORTHWEST TERRITORIES.

THURSDAY NIGHT THROUGH FRIDAY...HIGH PRESSURE WILL SLOWLY EXIT TO
THE EAST. THESE WILL BE THE LAST HIGH CONFIDENCE DAYS WITH DRY
CONDITIONS. TEMPERATURES WILL DROP SLIGHTLY AS WEAK A COLD FRONT
FORMS UP OUT OF THE LEE SIDE MOUNTAIN TROUGH.

FRIDAY NIGHT THROUGH SUNDAY... TROUGH IS EXPECTED TO CONTINUE ITS
EVOLUTION THROUGH THE 48 HOURS BY SPLITTING INTO TWO PARTS. THE
SOUTHERN PART WILL BARREL THROUGH THE FOUR CORNERS AND DRIVE THE
REMAINING WARM AIR FROM THE DESERT SOUTHWEST UP NORTH INTO EASTERN
MONTANA. THIS SHOULD FORM A BRIEF RIDGE BY SUNDAY WITH SOUTHERN
FLOW. ISOLATED THUNDERSTORMS WILL BE POSSIBLE SATURDAY AFTERNOON
AND EVENING RIGHT BEFORE THE WARM AIR ARRIVES. HOWEVER... BY SUNDAY
PLACEMENT OF NORTHEAST MONTANA IN THE NORTHERN WEAK HALF OF THE
SPLIT FLOW AND THE WARM AIR WILL PROBABLY STABILIZE OUT THE
ATMOSPHERE AND KILL ANY CHANCE FOR RAIN SHOWERS. MODEL SHIFT FROM
PREVIOUS RUNS IS VERY MUCH DRY ACROSS MULTIPLE MODELS WHICH
DECREASES FORECAST CONFIDENCE. CONFIDENCE AT THIS POINT IS AVERAGE
FOR THE LONG RANGE.

SUNDAY NIGHT ONWARD... CONFIDENCE AT THIS POINT DROPS OFF TO BELOW
AVERAGE. BEST GUESS IS FOR THE REMAINDER OF THE WARM AIR TO BE
KICKED OFF WEST AND ANOTHER LARGER SHORTWAVE TO ENTER AND PROVIDE
A CHANCE FOR RAIN SHOWERS. IN ADDITION MODELS ARE HINTING AT THE
ARCTIC AIR FINALLY MAKING A HALF HEARTED PLUNGE THROUGH THE
CANADIAN PRAIRIES. IF THIS OCCURS TEMPERATURES COULD EASILY DROP
OFF BY TUESDAY WITH LOWER 60S FOR HIGHS.  GAH


PREVIOUS LONG TERM DISCUSSION...
THE EXTENDED PERIOD BEGINS THURSDAY EVENING WITH A LONG-WAVE
TROUGH OFF TO THE WEST AND A LONG-WAVE RIDGE TO THE EAST.
NORTHEAST MONTANA WILL BE UNDER A SOUTHWEST FLOW ALOFT THAT WILL
SEND WARM AIR INTO THE REGION. THICKNESS HEIGHTS WILL BE GREATER
THAN 580DM OVER NEMONT SO TEMPERATURES WILL REMAIN WELL ABOVE
NORMAL INTO FRIDAY. RAW GUIDANCE FOR FRIDAY SAYS HIGHS IN THE 90S.
BIASED HIGHS A LITTLE COOLER.

THE LONG-RANGE EC AND GFS HAVE BEEN HAVING TROUBLE AGREEING AS TO
WHEN THE COLD FRONT FROM THE WESTERN TROUGH WILL SLIDE EAST OVER
NORTHEAST MONTANA. THE 00Z GFS IS STILL QUICKER THAN THE 12Z EC BY
AROUND 24 HOURS. IN ADDITION...THE GFS CLOSES OFF THE LOW OVER THE
GREAT BASIN REGION ON SATURDAY...WHEREAS THE EC DOES NOT. THE BASE
OF THE GFS TROUGH SENDS A SIGNIFICANT AMOUNT OF MOISTURE NORTH INTO
EASTERN MONTANA BY LATE SATURDAY AFTERNOON. THE CLOSED LOW THEN
WORKS ITS WAY NORTH TOWARD NEMONT AS ANOTHER LARGER LOW BEGINS TO
MOVE ACROSS CANADA. THE GFS IS QUITE WET THROUGH THE REMAINDER OF
THE EXTENDED PERIOD. THE EC HOLDS THE OPEN TROUGH TO OUR WEST BUT
STILL SENDS MOISTURE OUR WAY FROM ITS BASE...BUT WITH MUCH LESS
QPF. THEREFORE BOTH MODELS SHOW A SIGNIFICANT COOLING AND WETTING
RAINS FOR OUR AREA IN THE SECOND HALF OF THE EXTENDED PERIOD.
THOUGHT THE BEST CHOICE FOR POPS WAS A BLEND INCLUDING HPC
GUIDANCE. GENERAL THUNDERSTORMS CAN BE EXPECTED NEAR THE FRONTAL
PASSAGE BEGIN FRIDAY EVENING OR SATURDAY EVENING DEPENDING ON
WHICH MODEL WINS OUT.


&&

.AVIATION...
FLIGHT CATEGORY: VFR

SYNOPSIS: CONTINUED HIGH PRESSURE WILL BRING CLEAR SKIES OR
A FEW HIGH CLOUDS TO THE REGION THROUGH THE TAF CYCLE.

AREA WINDS: WIND WILL GENERALLY BE LIGHT AND OUT OF THE WEST. KGGW
WILL EXPERIENCE NOCTURNAL SOUTHEAST COMPONENT.

GAH


&&

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

&&

$$

WEATHER.GOV/GLASGOW







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