FXUS65 KGGW 250415 AAA
AFDGGW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE GLASGOW MT
915 PM MST THU DEC 24 2009

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH SATURDAY...
THE MAJOR WINTER STORM MOVING NORTH ACROSS THE CENTRAL PLAINS IS
BEGINNING TO BACK UP INTO THE EASTERN ZONES OF OUR CWA THIS
EVENING. LOW CEILINGS OF AROUND 3K FT HAVE SPREAD WEST OVER THE
EASTERN COUNTIES EARLY THIS EVENING AND HAVE BROUGHT SNOW WITH
IT. LOW QPF WILL NOT PRODUCE MUCH ACCUMULATION...BUT DID BEEF UP
POPS A BIT AND EXPANDED SKY COVER. THE OTHER CHALLENGE CONCERNS
TMINS FOR TONIGHT WHICH HAVE BEEN ADJUSTED LOWER ONCE ALREADY. A
SURFACE HIGH NUDGING SOUTH FROM SASKATCHEWAN WILL KEEP WESTERN
ZONES MOSTLY CLEAR TONIGHT WITH LIGHT WINDS. EXPECT TEMPERATURES
IN THOSE AREAS TO PLUNGE INTO THE MINUS 20S. ADJUSTED TEMPERATURES
WHERE CURRENT TEMPERATURES ARE CLOSELY APPROACHING THE FORECASTED
LOWS. NW WINDS OF 10 TO 20 MPH IN THE EAST WILL CONTINUE TO
SUPPORT THE WIND CHILL ADVISORY TONIGHT. SCT

PREVIOUS DISCUSSION...
THE CLOSED UPPER LEVEL WILL SLIP INTO NORTHWESTERN SOUTH DAKOTA
BY 00Z. HOWEVER THE SURFACE GRADIENT REMAINED UP UP OVER THE
EASTERN PART OF THE CWA. THE SURFACE HIGH WILL BEGIN TO RETREAT
BACK TO THE NORTH INTO SASKATCHEWAN AFTER 12Z ON FRIDAY. WILL GO
AHEAD AND EXTEND THE WIND CHILL ADVISORY FOR THE EASTERN AND
CENTRAL COUNTIES THIS EVENING AND OVERNIGHT. CONTINUED STRONGER
NORTHWESTERLY SURFACE WINDS AND THE CONTINUED 850MB TEMPERATURES
BETWEEN -18*C TO AROUND -14*C THROUGH FRIDAY MORNING WILL KEEP THE
WIND CHILL CONCERNS ACROSS THE EASTERN PART OF THE CWA.

FRIDAY AND SATURDAY...WENT WITH A WINTER WEATHER ADVISORY FOR SNOW
AND BLOWING SNOW FOR THE EASTERN ZONES OF THE CWA STARTING AT 12Z
FRIDAY MORNING. UPPER CLOSED LOW THAT MOVED THROUGH EASTERN
MONTANA WILL COMBINE WITH SOUTHERN CLOSED LOW OVER EASTERN
NEBRASKA AND WESTERN IOWA AND BECOMES A STACK SYSTEM OVER SOUTHERN
MINNESOTA DURING THE DAY ON FRIDAY. THE SURFACE LOW AND THE 700 MB
LOW NUDGE WESTWARD AND PUSH A TROWAL OVER NORTHERN NORTH DAKOTA
WHICH WILL PRODUCE WRAP AROUND SNOW INTO EASTERN MONTANA. THE
SURFACE GRADIENT WILL INCREASE ACROSS EASTERN MONTANA BETWEEN THE
SURFACE LOW OVER SOUTHERN MINNESOTA AND THE SURFACE HIGH MOVING
BACK INTO SASKATCHEWAN. WIND WILL PICK UP FROM THE NORTHWEST AND
SHOULD START TO BLOW AND DRIFT THE SNOW ACROSS EASTERN MONTANA.
THESE CONDITIONS WILL LAST INTO SATURDAY SO LEFT THE WINTER
WEATHER ADVISORY UP THROUGH SATURDAY EVENING. NEW SNOW FALL WILL
BE BETWEEN 2 AND 3 INCHES ACROSS THE EASTERN ZONES. WIND CHILLS
WILL ALSO BE A PROBLEM ON FRIDAY WITH WIND CHILL READING BETWEEN
-20*C TO -30*C. THE SNOW WILL COME TO AN END AS THE LOW PRESSURE
SYSTEM MOVES TO THE EAST. RSMITH

.LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...
MAIN FORECAST IMPACT IN THE EXTENDED WILL BE WRAP AROUND LINGERING
PCPN IN EXTREME EAST SATURDAY NIGHT AND TEMPS. 12Z GFS HAS A
STRONGER TROWAL PATTERN EDGING INTO THE SE MT ZONES WITH THE
THETA-E AS THE STACKED UPPER LOW EJECTS INTO GREAT LAKES AREA.
THIS SHOULD KEEP A LINGERING THREAT OF PCPN IN SOUTHEAST MT INTO
SUNDAY MORNING BEFORE THE MAIN JET MAX MOVES AROUND THE BASE OF
THE TROUGH. BY SUN AFTN THE UPPER RIDGE AXIS WILL BE OVER MT WITH
THICKNESS VALUES RISING AND 850MB TEMPS WARMING TO -1C. WITH SNOW
COVER IN PLACE THE TEMPS WILL STILL REMAIN BELOW NORMAL SO HAVE
KEPT MAX TEMPS NEAR OR BELOW GUIDANCE. THE GFS AND ECMWF THEN HAVE
SOME DIFFERENCES WITH TIMING OF SHORTWAVE FEATURES ON TUES INTO
WED. BOTH DO BRING A SHORTWAVE SOUTH AND ANOTHER ARCTIC BOUNDARY
INTO NE MT WITH OVERRUNNING MOISTURE IN THE WEST...BUT ECMWF
STRONGER WITH THIS FEATURE THAN GFS. ENSEMBLES DO POINT AT A
BOUNDARY TOWARD THURSDAY BUT WILL KEEP THE TREND ON KEEPING
CURRENT TEMPS AND POPS THE SAME. SLA

&&

.AVIATION...
VFR CONDITIONS WILL PREVAIL AT KGGW AND KOLF THRU THE WEEKEND.
SOME BROKEN MID CLOUDS MAY INTERMITTENTLY MOVE THRU IN FLOW AROUND
A MONSTER UPPER LOW PRESSURE SYSTEM AFFECTING MUCH OF THE MIDWEST
AND PLAINS. KSDY AND KGDV WILL REMAIN JUST INSIDE THE EDGE OF THE
CLOUDS AND LIGHT SNOW ROTATING AROUND THE AFOREMENTIONED
SYSTEM...RESULTING IN PREVAILING MVFR CONDITIONS WITH SOME
OCCASIONAL IFR CONDITIONS INTO OR THRU MUCH OF SATURDAY. A
NORTHWEST WIND WILL PREVAIL AT ALL SITES THRU SATURDAY WITH SPEEDS
AT KGGW AND KOLF GENERALLY AROUND 10 KT OR LESS. KSDY AND KGDV
WILL BE UNDER A TIGHTER PRESSURE GRADIENT WITH RESULTANT SPEEDS OF
GENERALLY 15 TO 20 KT WITH OCCASIONAL GUSTS OF 25 TO 30 KT.  

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY UNTIL 5 AM MST FRIDAY FOR CENTRAL AND 
SOUTHERN VALLEY-DANIELS-SHERIDAN-WESTERN ROOSEVELT-GARFIELD-
MCCONE-RICHLAND-DAWSON-PRAIRIE-WIBAUX-NORTHERN VALLEY-EASTERN 
ROOSEVELT.

WINTER WEATHER ADVISORY FROM 5 AM FRIDAY TO 5 PM MST SATURDAY 
FOR RICHLAND-DAWSON-PRAIRIE-WIBAUX-EASTERN ROOSEVELT.

&&

$$

WEATHER.GOV/GLASGOW