Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 300409 AAA
AFDGGW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE GLASGOW MT
909 PM MST THU JAN 29 2015

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

THE MAIN FORECAST CHALLENGE FOR TONIGHT WILL BE THE POSSIBILITY OF
FOG. BUT BUFKIT IS MUCH LESS CERTAIN FOR TONIGHT FOR MOST SPOTS.
HOWEVER...WE HAVE HAD REPORTS OF FOG FROM A FEW AREAS TO THE
NORTH. PLUS FOG IS SHOWING UP ON THE IR IMAGERY IN SOUTHERN
SASKATCHEWAN. SO DECIDED TO REMOVE MENTION OF FOG FOR MOST AREAS
SOUTH OF THE MISSOURI RIVE...BUT KEEP IT GOING FOR THE NORTHERN
COUNTIES. WIND IS GENERALLY LIGHT...BUT MADE A FEW TWEAKS FOR
FAVORED AREAS OF EAST WIND. ALSO ADJUSTED SKY COVER. SCT

PREVIOUS DISCUSSION...
SYNOPTIC SET UP...MULTIPLE ARCTIC AIR-MASS CENTERS ARE MOVING OVER
THE NORTHWEST TERRITORIES AND THE HUDSON BAY. WEAK WARM RIDGING
EXIST OVER THE PACIFIC NORTHWEST AND SOUTHERN BRITISH COLUMBIA.
NORTHEAST MONTANA LIES BETWEEN THESE TWO FEATURES UNDER NORTHWEST
FLOW ALOFT.

TODAY THROUGH FRIDAY...ARCTIC AIR-MASS IS SLIDING OFF TO THE EAST
AND ALLOWING A SHALLOW COLD POOL TO FORM IN MOST OF THE BOUNDARY
LAYER WHICH IS TRAPPING IN MOISTURE FROM SNOWMELT THE LAST FEW
DAYS. FORT PECK LAKE IS ADDING A LITTLE EXTRA MOISTURE TO THIS
FLOW WHICH IS REDUCING VISIBILITY IN THE MILK RIVER VALLEY
PARTICULARLY MORE THAN THE REST OF THE AFFECTED AREAS. THIS EFFECT
MAY REMAIN IN PLACE THROUGH THE OVERNIGHT HOURS AND SHOULD BEGIN
TO EXIT AS WINDS SHIFT TO THE WEST AND INCREASE THROUGH THE
DAYLIGHT HOURS FRIDAY. WEAK REBOUND OF THE RIDGE TO THE WEST WILL
BRIEFLY OCCUR FRIDAY LEADING TO THE WEAK CHINOOK WINDS THAT
AFTERNOON.

FRIDAY NIGHT THROUGH SATURDAY...ONE OF THE COLD AIR CENTERS OVER
THE NORTHWEST TERRITORIES WILL DROP SOUTH INTO CENTRAL MANITOBA
AND REINFORCE THE ARCTIC AIR-MASS IN SASKATCHEWAN WAFFLING THE
PREVIOUS STATIONARY BOUNDARY...BACKDOOR STYLE...INTO AND THROUGH
NORTHEAST MONTANA. MOISTURE RIDING ALONG THE NORTHWEST FLOW IN THE
MID LAYERS WILL RE-ORIENT IN A WAY TO PROVIDE UPGLIDE AND GENERATE
SNOW ON THE EAST SIDE OF THE FRONT.

SNOW WILL SPREAD OVER THE CWA EARLY SATURDAY MORNING INTO THE
AFTERNOON. 1 TO 3 INCHES IS ANTICIPATED WITH THIS PASSAGE. AREAS
OF THE HI-LINE NORTH OF HIGHWAY 2 LOOK TO HAVE THE MOST IMPACT.
WHILE BLOWING SNOW IS NOT OUT OF THE QUESTION...CURRENT BARE
GROUND SHOULD PREVENT LARGE AREAS OF IT. GAH


.LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...
UPDATE...WITH CONTINUED MODEL AGREEMENT ON THE PLACEMENT OF THE
PRECIPITATION...POPS WERE INCREASED SIGNIFICANTLY FOR THE MONDAY
AFTERNOON THROUGH TUESDAY AFTERNOON TIME PERIOD...HOWEVER QPF AND
SNOW AMOUNTS WERE LEFT ALONE AT THIS POINT. THE COLD FRONT THAT
WILL PUSH THROUGH DURING THIS TIME FRAME WILL BE SUBSTANTIAL. THE
AVERAGE 24-HR CHANGE AMONGST THE 850MB TEMPERATURES FROM MONDAY
MORNING AND TUESDAY MORNING IS ABOUT 15 TO 20 DEGREES...EQUATING
TO APPROXIMATELY -13C AND -28C ACROSS NEMONT AFTER THE ARCTIC AIR
MASS HAS ENTERED THE AREA. WITH THAT MENTIONED TEMPERATURES WERE
ALSO LOWERED MONDAY NIGHT THROUGH WEDNESDAY AFTERNOON. AEC

PREVIOUS DISCUSSION...PERSISTENT WEST COAST RIDGE TOGETHER WITH
HUDSON BAY LOW LEAVES REGION BENEATH NORTHWEST FLOW ALOFT
THROUGH PERIOD. UPPER RIDGE RETROGRESSES SATURDAY NIGHT AS HUDSON
BAY LOW DEEPENS ALLOWING COLDER CANADIAN AIR TO PUSH INTO MONTANA
FROM THE NORTHEAST. SEVERAL SHORT WAVE DISTURBANCES ROTATE AROUND
LOW BRINGING INCREASED MOISTURE AT LOW AND MID LEVELS THROUGH
REMAINDER OF WEEKEND AND NEXT WEEK. GFS AND ECMWF DIFFER SLIGHTLY
IN PLACEMENT AND TIMING OF THESE DISTURBANCES...SO WILL SIMPLY GO
WITH SLIGHT CHANCE SHOWERS THROUGH PERIOD. TEMPERATURES WILL
REMAIN NEAR OR SLIGHTLY BELOW NORMAL FOR THE ENTIRE EXTENDED
FORECAST PERIOD. SURFACE PRESSURE GRADIENTS DO NOT SUPPORT
GENERATION OF STRONG WINDS...SO EXPECT ONLY OCCASIONALLY BREEZY
WINDS OVER NORTHEAST MONTANA. BRITTON

&&

.AVIATION...
FLIGHT CATEGORY: IFR TO VFR... BECOMING ALL VFR MIDDAY FRIDAY.

SYNOPSIS: THE EDGE OF AN ARCTIC AIR-MASS HAS SET IN ACROSS THE
REGION TODAY AND IS PROVIDING A VERY SHALLOW LAYER ALONG WITH
MOISTURE POOLING UP IN IT FROM THE LAST FEW DAYS SNOW MELT INTO
THE EAST SIDE OF THE BOUNDARY. TERMINALS UNDERNEATH THIS LAYER
WILL BE AT RISK FOR FOG FROM THIS AFTERNOON UNTIL FRIDAY MORNING.
WEST WINDS FRIDAY AFTERNOON SHOULD MOVE THE BOUNDARY LAYER OUT AND
WITH IT...THE THREAT FOR FOG. TIMING WILL BE A TRICKY THING WITH
THIS BOUNDARY AS THERE ARE BREAKS IN THE CLOUDS VISIBLE FROM
SATELLITE. MAINLY CLEAR TERMINALS COULD QUICKLY SOCK IN AND VFR
HOLES MAY RANDOMLY APPEAR IN TERMINALS WITH PERSISTENT DENSE FOG.
SO HEAVY UNCERTAINTY EXISTS WITH THESE TAF ISSUANCES. AMENDMENTS
ARE TO BE EXPECTED THROUGH THE NEXT 12 TO 18 HOURS OF THE CYCLE.

WIND: OUT OF THE SOUTH AT LESS THAN 10 KTS...VEERING TO THE WEST
AFTER MIDNIGHT AND INCREASING THROUGH THE AFTERNOON FRIDAY.

GAH

&&

.HYDROLOGY...
DUE TO THE RECENT RECORD SETTING WARM TEMPERATURES SOME OF THE
CREEKS AND SMALL STREAMS ARE RUNNING. MINOR FLOODING WAS REPORTED
AT 7 MILE CREEK NEAR GLENDIVE AND BEAVER CREEK NEAR WIBAUX...WHICH
PROMPTED THE ISSUANCE OF SMALL STREAM FLOOD ADVISORIES. THE
ADVISORY FOR BEAVER CREEK WAS CANCELLED SINCE THE WATER HAS
RETURNED WITHIN ITS BANKS AND NO LONGER FLOODING THE SURROUNDING
AREAS.

TEMPERATURES ARE EXPECTED TO REMAIN ABOVE AVERAGE THROUGH
FRIDAY...RETURNING TO NEAR NORMAL ON SATURDAY...WHICH WILL BEGIN
TO LIMIT ANY FURTHER FLOODING. AEC

&&

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

&&

$$

WEATHER.GOV/GLASGOW




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