HAMweather.com Area Forecast Discussion for County Warning Area GGW

Thu, 16 Feb 2012 06:28:51 GMT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
900 PM MST WED FEB 15 2012

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH FRIDAY...
UPDATED THE FORECAST TO LOWER THE OVERNIGHT LOWS DOWN ACROSS MOST
OF THE CWA. LOWS ARE ALREADY DROPPING IN TO THE LOWER 20S AND
UPPER TEENS. WITH THE NEW SNOW PACK AND CLEAR SKIES FORECAST FOR
TONIGHT FEEL LIKE THE OVERNIGHT LOWS WERE A LITTLE TO WARM. MODELS
DATA WASN'T MUCH HELP EITHER SINCE THE OBSERVED DATA WAS ALREADY
COLDER THEN WHAT THE MODELS WERE SHOWING FOR OVERNIGHT LOWS.
DECIDED TO USE TH HRRR MODEL OUTPUT AND THEN ADJUST DOWN TO THE
NEAR OBSERVED EVENING DEW POINTS. RSMITH

PREVIOUS DISCUSSION...WATER VAPOR IMAGERY AND 500 MB HEIGHT FIELD
SHOWS A SOMEWHAT HALTED AND STAGNANT SPLIT UPPER LEVEL FLOW
REGIME. THE SOUTHERN STREAM CONTINUES TO SHOWCASE A SERIES OF
CLOSED UPPER LOW CENTERS MOVING SOUTHWARD OVER THE CASCADES THEN
TURNING SHARPLY EASTWARD THROUGH THE FOUR CORNERS AREA...SPAWNING
THUNDERSTORMS NEAR THE SOUTHERN MISSISSIPPI RIVER VALLEY. THE
NORTHERN STREAM IS CHARACTERIZED MAINLY BY ALTERNATING SHORT WAVE
UPPER LEVEL TROUGHS AND RIDGES. THE NORTHERN STREAM IS CURRENTLY
INFLUENCING NORTHEAST MONTANA MORE THAN THE SOUTHERN STREAM WITH
NORTHWESTERLY FLOW ALOFT.

SATELLITE IMAGERY WITH CLEARING SKIES TODAY REVEALS THE NEW SNOW
FIELD FROM YESTERDAYS STORM. THE MAJORITY OF THE HEAVY SNOW PACK
SEEMS TO BE LOCATED IN PHILLIPS AND VALLEY COUNTIES. TEMPERATURES
THERE ARE TOPPING OUT NEAR OR JUST BELOW THE THAWING OR FREEZING
MARK. TEMPERATURES FURTHER SOUTH OVER BARE GROUND ARE NEARING 40
DEGREES THIS AFTERNOON.

FORECAST CHALLENGES WILL FOCUS MAINLY ON TEMPERATURES AND SLIGHT
CHANCES FOR SNOW THURSDAY NIGHT THROUGH FRIDAY MORNING. TONIGHT
THROUGH THURSDAY AFTERNOON...NORTHEAST MONTANA FINDS ITSELF
SQUARELY IN BETWEEN RIDGING FROM THE SOUTHWEST AND TROUGHING FROM
THE NORTH AND NORTHEAST. NORTHWEST FLOW ALOFT WILL DOMINATE AND A
RELATIVELY DRY ENVIRONMENT WILL PREVENT ANY SUBSTANTIAL
PRECIPITATION THROUGH THIS MIDDLE PORTION OF THE WEEK.

THURSDAY NIGHT THROUGH FRIDAY MORNING...AN UPPER LEVEL TROUGH
FROM SASKATCHEWAN PROVIDES SOME WEAK LIFT WHICH MAY COOPERATE JUST
ENOUGH WITH THE EXPECTED PACIFIC MOISTURE TO BRING SOME LIGHT SNOW
OVER OUR SOUTHWESTERN ZONES. DO NOT EXPECT MUCH FROM IT. FRIDAY
UPPER LEVEL RIDGING RETURNS AND CUTS OFF THE MOISTURE. THE
TEMPERATURE FORECAST IN THE SHORT TERM WILL BECOME HIGHLY
DEPENDENT ON THE SLOWLY ERODING NEW SNOW PACK OVER CENTRAL AND
NORTHWESTERN PORTIONS OF OUR CWA. COLDER MAX TEMPS OVER THE SNOW
CAN BE EXPECTED OVER THE NEXT FEW DAYS AS THE SNOW PACK MELTS TO
BARE GROUND FROM THE SOUTH. BMICKELSON

.LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY...
MODELS ARE SHOWING A WEAKENING TREND WITH A DISTURBANCE MOVING
THROUGH THE AREA LATE SUNDAY INTO EARLY NEXT WEEK...SO LOWERED
POPS ACCORDINGLY. OTHERWISE... TEMPS WERE LOWERED A BIT FRIDAY
NIGHT MAINLY ACROSS THE NORTHERN ZONES WITH THE FRESH SNOWCOVER
PRESENTLY IN PLACE. REST OF FORECAST LOOKS GOOD. JAMBA

PREVIOUS DISCUSSION... 
LONG TERM FORECAST PERIOD BEGINS WITH AN UPPER LEVEL RIDGE OVER
ALL OF CENTRAL MONTANA. FRIDAY NIGHT INTO SATURDAY AFTERNOON AN
APPROACHING UPPER LEVEL LOW MOVES ONSHORE OVER THE PACIFIC
NORTHWEST PUSHING THE UPPER RIDGE EASTWARD INTO THE NORTHERN
PLAINS. THIS UPPER LOW BECOMES MORE OF AN OPEN WAVE WHICH WILL
SPLIT AND SEND THE MORE ACTIVE PART OF THE SYSTEM OVER THE CENTRAL
ROCKIES. THE NORTHERN PART OF THIS OPEN WAVE WILL CROSS THE
NORTHERN ROCKIES AND IT WILL TRIGGER SOME LIGHT SNOW SHOWERS
ACROSS NEMONT SATURDAY NIGHT THROUGH SUNDAY NIGHT. LOOKS LIKE
ANOTHER INCH OR TWO OF SNOW WILL BE POSSIBLE BUT KEPT POPS IN THE
LOWER CHANCE RANGE FOR NOW.

MODELS TAKE THE SOUTHERN PART OF THIS UPPER WAVE INTO THE CENTRAL 
PLAINS BY MONDAY AND IT BECOMES VERTICALLY STACKED. IT LOOKS AS
THOUGH THIS SYSTEM WILL BE TOO FAR TO THE SOUTH TO EFFECT WEATHER
ACROSS EASTERN MONTANA. 

GENERALLY THE UNSETTLED WEATHER PATTERN WILL CONTINUE FOR THE
REST OF THE EXTENDED AND NORTHEAST MONTANA SEEMS PINNED BETWEEN A
RIDGING INFLUENCE FROM THE SOUTHWEST AND CONTINUED TROUGHING OVER
THE GREAT LAKES. THIS MEANS EASTERN MONTANA WILL BE IN THE NORTHWEST
FLOW WITH DISTURBANCES MOVING THROUGH THIS FLOW FROM MONDAY
THROUGH THURSDAY NIGHT. MODELS ARE ALL DIFFERENT ON TIMING OF
THESE WAVES BUT TUESDAY NIGHT INTO WEDNESDAY LOOKS LIKE A PERIOD
THAT THE MODELS ARE IN SOME AGREEMENT FOR MORE LIGHT SNOWFALL. SO
ADDED SOME SLIGHT CHANCE POPS TO THIS TIME FRAME. RSMITH

.AVIATION...
VFR. MAINLY CLEAR SKIES ARE EXPECTED TONIGHT BUT LOW VFR CLOUDS
WILL DRIFT SOUTHEAST ACROSS THE AREA INTO THURSDAY AS AN UPPER
DISTURBANCE SPINS UP OVER SOUTHERN SASKATCHEWAN. WINDS WILL BE
LIGHT FROM THE NORTHWEST. JAMBA/PROTON

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