FXUS65 KGGW 150332
AFDGGW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
832 PM MST MON DEC 14 2009
.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH WEDNESDAY...
THE WIND CHILL ADVISORY HAS BEEN EXTENDED TO 4AM TONIGHT.
FOR TONIGHTS UPDATE... TEMPERATURES AND WINDS ARE THE MAIN
CONCERNS. WINDS ACROSS THE REGION HAVE BEEN BOUNCY IN TERMS OF 10
MPH CRITERIA WIND CHILL AND ARE EXPECTED TO CONTINUE INTO THE EARLY
MORNING HOURS AS LOCALIZED MESO HIGHS/LOWS GAIN INTENSITY AND
MAINTAIN THE PRESSURE GRADIENT DRIVING WINDS ACROSS THE REGION. IN
ADDITION... TEMPERATURES ACROSS THE REGION ARE RAPIDLY APPROACHING
PREVIOUS NIGHT TIME LOWS WITH CLEAR SKIES AND MULTIPLE MORE HOURS
OF DARKNESS LEFT. THEREFORE LOWS ACROSS MOST VALLEY REGIONS HAVE
BEEN READJUSTED TO CLOSER TO 30 BELOW. GAH
PREVIOUS SHORT TERM DISCUSSIONS...
UPDATED THE SHORT TERM FORECAST TO ADD A WIND CHILL ADVISORY FOR
THIS EVENING FOR MOST OF THE REGION. THE ARCTIC AIR MASS IN PLACE
IS COMBINING WITH WIND SPEEDS BETWEEN 6 MPH AND 12 MPH. EXPECT
THIS TO LAST UNTIL AROUND 9 PM WHEN A SURFACE HIGH WILL DROP THE
WIND DOWN UNDER 6 MPH ACROSS THE NORTHEAST MONTANA. THE REST OF THE
SHORT TERM LOOKS GOOD. RSMITH
TEMPERATURES WILL BE THE MAIN FORECAST CHALLENGE OVER THE NEXT FEW
DAYS AS THE ARCTIC HIGH CURRENTLY MOVING INTO NORTHEAST MONTANA
EXITS TO THE EAST AND UPPER RIDGE BUILDS INTO THE NORTHERN
ROCKIES.
FINAL LOBE OF THE POLAR VORTEX PUSHING THROUGH EASTERN MONTANA
WITH A BAND OF SNOW AHEAD OF IT IN THE YELLOWSTONE VALLEY. THIS
SNOW SHOULD EXIT THE REGION BY LATE AFTERNOON WITH SKIES CLEARING
QUICKLY. WITH THE CLEAR SKIES AND FRESH SNOW COVER...AS WELL AS
LIGHT WINDS AND COLD AIRMASS UNDER THE ARCTIC HIGH...EXPECT
TEMPERATURES TO DROP TO AT LEAST 20 BELOW ZERO IF NOT COLDER IN
MOST PLACES OVERNIGHT.
EVEN WITH THE VERY COLD TEMPERATURES EXPECTED TONIGHT...WARMER AIR
IS MOVING IN ALOFT AS AN UPPER RIDGE BUILDS INTO THE NORTHERN
ROCKIES. THIS WILL SLOWLY ERODE THE DEEP ARCTIC AND BRING WARMER
TEMPERATURES TO THE REGION FOR TUESDAY AND WEDNESDAY. BIGGEST
ISSUES WILL BE HOW QUICKLY THE ARCTIC ERODES...AS POOR MIXING IS
EXPECTED WITH THE SHALLOW STABLE AIRMASS. THUS WOULD EXPECT THE
COLD AIR TO LINGER IN THE VALLEYS OF THE NORTHEAST HALF OF THE
CWA WHILE THE HIGHER TERRAIN TO THE SOUTHWEST WARMS. A FEW SURGES
OF MOISTURE EXPECTED TO LIFT ACROSS THE COLD DOME...ONE LATE ON
TUESDAY WITH ANOTHER ON WEDNESDAY. NOT EXPECTING MUCH
PRECIPITATION WITH EITHER OF THESE WAVES WITH GOOD DOWNSLOPE OFF
THE MOUNTAIN...BUT COULD BE A LITTLE SNOW IN THE FAR NORTHEAST
WHERE THE MOISTURE WILL ENCOUNTER A SLIGHTLY DEEPER INVERSION.
EBERT
.LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY...
BOTH MODELS ARE IN AGREEMENT WITH A SHORTWAVE PUSHING A COLD FRONT
THROUGH EASTERN MONTANA WEDNESDAY NIGHT INTO THURSDAY...AND BOTH MODELS
ARE ON THE DRY SIDE WITH THE PASSAGE OF THIS FEATURE. THE MAIN
SHORTWAVE LOOKS LIKE IT WILL PASS THROUGH THE REGION THURSDAY
NIGHT. THE MODELS SEEMS TO DISAGREE WITH THE OVERALL SPEED AND
DEVELOPMENT OF THIS SHORTWAVE AT THE TIME OF PASSAGE. THE GFS
PUSHES THE SHORTWAVE THROUGH QUICKLY WITH THE OVERALL SHAPE
REMAINING FLAT. THE ECMWF BRING THE SHORTWAVE THROUGH AROUND THE
SAME TIME BUT IS MUCH SLOWER WITH THE EASTWARD PROGRESSION. THE
FEATURE ON THE ECMWF BECOMES WIDER AND SPREADS OUT OVER THE
CENTRAL ROCKIES. EITHER WAY NEMONT SHOULD REMAIN RELATIVELY DRY
DURING ITS PASSAGE.
THE UPPER RIDGE THAT FOLLOWS ALSO LOOKS SOMEWHAT DIFFERENT ON BOTH
MODELS. THE OVERALL PATTERN WILL HAVE A RIDGE TO THE WEST WITH AN
UPPER LOW OVER THE GREAT LAKES ALONG WITH AN UPPER TROF OVER THE
THE EASTERN US. THE RIDGE ON THE ECMWF IS MUCH SHARPER THEN WHAT
THE GFS INDICATES BUT EASTERN MONTANA WILL REMAIN UNDER NORTHWEST
FLOW ALOFT. OVERALL THE ARCTIC AIR SHOULD REMAIN OVER THE DAKOTAS WITH
THE AIRMASS MODIFYING SOMEWHAT OVER CENTRAL AND EASTERN MONTANA.
IF WE KEEP MOST OF THE SNOW ON THE GROUND THINGS ARE NOT GOING TO
WARM UP TOO MUCH. EXPECT MID 20S TO THE MID 30S ACROSS THE CWA
WITH THE WARMER TEMPERATURES ACROSS CENTRAL MONTANA. AFTER THE
WEEKEND THE MODELS ARE OUT OF PHASE SO LEFT THE EXTENDED FORECAST
PAST SUNDAY NIGHT AS THEY WERE. RSMITH
PREVIOUS DISCUSSION...SHORTWAVE PASSES THROUGH MONTANA ON
THURSDAY WITH A COLD FRONT. THE MAIN EFFECT OF THE FRONT WILL BE
TO LIMIT THE AMOUNT OF WARMING THAT WILL COME TO EASTERN MONTANA
LATE IN THE WEEK. LIMITED MOISTURE IS EXPECTED WITH THIS SYSTEM.
WILL MENTION A SLIGHT CHANCE OF SNOW OVER PARTS OF THE AREA
THURSDAY AND THURSDAY NIGHT.
THE MODELS GENERALLY HAVE AN UPPER RIDGE OVER THE WESTERN U.S. AND
AN UPPER TROUGH/LOW TO THE EAST FOR THE REMAINDER OF THE PERIOD.
HOWEVER...THERE ARE DIFFERENCES IN THE PLACEMENT OF THE
RIDGE...TROUGH AND UPPER LOW ALTHOUGH AT THE MOMENT...THE MODELS
AGREE ON HAVING EASTERN MONTANA IN NORTHWEST FLOW ALOFT BETWEEN
THE RIDGE AND THE TROUGH MOST OF THE TIME. THE MODELS ALSO HAVE
VARIED THEIR FORECAST FROM RUN TO RUN WHICH LIMITS PLACING ANY
CONFIDENCE IN ANY MODEL. AT THE MOMENT...BOTH THE GFS AND ECMWF
PLACE A STATIONARY FRONT STARTING ON FRIDAY NEAR HAVRE AND
BILLINGS WHICH IS A CLIMATOLOGICALLY FAVORED LOCATION FOR A LEE
SIDE FRONT DURING THIS TIME OF YEAR. THE FRONT STAYS NEAR THAT
LOCATION FOR THE REST OF THE PERIOD. AT THE SAME TIME...THEY KEEP
THE VERY COLD AIR TO THE EAST. WILL KEEP TEMPERATURES CLOSE TO
SEASONAL AVERAGES FOR NOW. FORRESTER
&&
.AVIATION...
VFR. THE SKY HAS BECOME CLEAR OVER ALL TERMINALS WITH NORTHWEST
WINDS RANGING FROM AROUND 10 TO 15KTS .
&&
.GLASGOW WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY UNTIL 4 AM MST TUESDAY FOR CENTRAL AND
SOUTHEAST PHILLIPS-CENTRAL AND SOUTHERN VALLEY-DANIELS-SHERIDAN-
WESTERN ROOSEVELT-GARFIELD-MCCONE-RICHLAND-DAWSON-PRAIRIE-WIBAUX-
NORTHERN PHILLIPS-NORTHERN VALLEY-EASTERN ROOSEVELT.
&&
$$
WEATHER.GOV/GLASGOW
