004 
FXUS65 KMSO 271328
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
628 AM MST WED JAN 27 2010

.UPDATE...INCREASED POP AND SNOW AMOUNTS IN PORTIONS OF WESTERN
MONTANA THIS MORNING


&&

.DISCUSSION...RECENT RADAR AND SATELLITE ENHANCEMENTS ARE PRODUCING
LIGHT SNOWS ACROSS PORTIONS OF THE BITTERROOT MOUNTAINS AND WEST
CENTRAL MONTANA. EVEN THOUGH THE SNOWFALL IS LIGHT...ACCUMULATIONS
UP TO AN INCH ARE POSSIBLE OVER THE NEXT FEW HOURS.


&&

.AVIATION...A NEWLY DEVELOPED AREA OF SNOW WILL IMPACT KMSO
THROUGH 27/16Z WITH UP TO AN INCH OF SNOW POSSIBLE. AREAS OF VALLEY
FREEZING FOG IS EXECTED THROUGH THE MORNING HOURS...ESPECIALLY IN
NORTHWEST MONTANA AND THE BITTERROOT VALLEY. EXPECT LOWERING
VISIBILITIES AND CEILINGS. 

&&

.PREV DISCUSSION... /ISSUED 413 AM MST WED JAN 27 2010/ 

DISCUSSION...

FOG HAS DEVELOPED ACROSS MANY OF THE VALLEYS IN THE NORTHERN
ROCKIES AND SHOULD PERSIST THROUGH MID MORNING WHICH WILL IMPACT
THE MORNING COMMUTE. FOG WILL BE MOST EXTENSIVE IN THE LOWER
VALLEYS OF EXTREME NORTHWEST MONTANA WHERE VISIBILITIES MAY BE
BROUGHT DOWN TO 1/4 MILE AT TIMES.  IN ADDITION A WEAK AND SLOW
MOVING WEATHER DISTURBANCE AND WEAK WEST/NORTHWEST FLOW CONTINUES
TO BRING VERY LIGHT SNOW ACROSS CENTRAL IDAHO...WESTERN
MONTANA...AND SOUTHWEST MONTANA. EXPECT WIDESPREAD LIGHT SNOW TO
PERSIST THROUGH MUCH OF THE MORNING WITH ONLY VERY LITTLE SNOW
ACCUMULATIONS. PERHAPS UP TO AN INCH IN THE MOUNTAINS AND A TRACE
TO HALF INCH IN THE VALLEYS AT BEST...WHICH MAY CAUSE SOME
DIFFICULT TRAVEL FROM SLICK ROADS IN AREAS.

THIS MORNING'S WEAK WEATHER DISTURBANCE WILL EXIT THE REGION BY
LATE THIS AFTERNOON AND EVENING. THE REMAINDER OF THE WEEK WILL
THEN BE LARGELY UNDER THE INFLUENCE OF A DEVELOPING RIDGE OVER THE
REGION. THIS WILL BE A DIRTY RIDGE WITH CONSIDERABLE HIGH TO MID
CLOUDS OVER THE REGION. MORNING FOG IS ANTICIPATED UNDER THIS
RIDGE WITH LOW LEVEL MOISTURE IN PLACE. THERE IS SOME UNCERTAINTY
WITH THE POTENTIAL EXTENT OF THE FOG AT THIS TIME WHICH IS
DEPENDENT ON THE PLACEMENT OF THE RIDGE AXIS AND EXTENT OF CLOUD
COVER.

SATURDAY THROUGH MONDAY...UPPER LEVEL TROUGH WILL MOVE INTO THE
PACIFIC NORTHWEST...INTRODUCING SOUTHWEST FLOW AND MOISTURE TO
NORTH CENTRAL IDAHO AND WESTERN MONTANA. BULK OF THE 500MB LOW
ENERGY WILL DIVE INTO THE GREAT BASIN...WITH A WEAKER 500MB WAVE
REMOVED TO THE NORTH. THIS SPLIT FLOW IS TYPICAL OF THE UPPER
LEVEL PATTERN OBSERVED THIS WINTER...AND TYPICAL ESPECIALLY UNDER
EL NINO CONDITIONS. GREATEST PRECIPITATION AMOUNTS WITH THIS
SYSTEM ARE FOCUSED OVER THE CLEARWATER MOUNTAINS IN NORTH CENTRAL
IDAHO AND THE WEST FACING SLOPES OF THE BITTERROOTS. A WEAKER SECONDARY
SHORTWAVE PROGGED TO TRACK BEHIND THIS SYSTEM FOR THE BEGINNING OF
NEXT WEEK. NORTHWEST FLOW REMAINS OVER THE AREA...AS A
PROGRESSIVE...ZONAL FLOW ENCOMPASSES THE REGION.

AVIATION...

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...NONE.
ID...NONE.
&&

$$

SHORT TERM...RPN
LONG TERM....RPN
AVIATION...RPN