000 
FXUS65 KMSO 160945
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
345 AM MDT WED APR 16 2008

.DISCUSSION...TODAY THROUGH THURSDAY NIGHT...MODELS IN GOOD
AGREEMENT THAT BREEZY...COOL AND SHOWERY WEATHER WILL CONTINUE TO
SLOWLY TAPER OFF THROUGH THE MIDDLE OF OF THE WEEK AS HIGH
PRESSURE BUILDS OVER THE PACIFIC NORTHWEST.

THE LATEST RUN OF THE ECMWF AND GFS SHOW A DEEPENING 500MB CLOSED
LOW OVER THE PACIFIC NORTHWEST ON SATURDAY AND SUNDAY. THIS
FORECAST PATTERN IS HIGHLY COMPLEX WITH EACH RUN OF THE MODELS
HANDLING THE VARIOUS FINNER SCALE FEATURES...SUCH AS FRONTS AND
DYNAMICS...SLIGHTLY DIFFERENT. HOWEVER COMMONALITIES WITHIN THE
MODELS LEAD ME TO BELIEVE A COLD FRONT WILL PASS THROUGH IDAHO AND
MONTANA FROM THE NORTHWEST BEGINNING LATE FRIDAY AND SLOWLY
PROGRESS TO THE SOUTHEAST OVERNIGHT INTO SATURDAY. AS THE 500MB
LOW DEEPENS OVER WASHINGTON IT WILL BECOME CUTOFF FROM THE MAIN
WESTERLY FLOW ALOFT...EFFECTIVELY SLOWING AND POSSIBLY EVEN
STALLING THE FRONTAL PASSAGE OVER WEST CENTRAL OR SOUTHWEST MONTANA
DURING THE DAY ON SATURDAY. AS STATED EARLIER...FORECAST
CONFIDENCE IN THESE SPECIFIC FEATURES IS AT THIS TIME LOW. BUT A
STALLED FRONTAL BOUNDARY COULD PRODUCE A PROLONGED WIND EVENT
ACROSS WEST CENTRAL AND/OR SOUTHWEST MONTANA AND ACT AS A LIFTING
MECHANISM FOR ENHANCED PRECIPITATION.

SATURDAY AFTERNOON A CIRCULATION IN THE MID LEVEL FLOW DEVELOPS IN
BOTH THE GFS AND ECMWF OVER SOUTHWEST MONTANA RESULTING THE
FORMATION OF A 700MB LOW. CLEARLY AND CONFIDENTLY SECURING THE
LOCATION OF THIS FEATURE WILL UNDOUBTEDLY LEAD TO BETTER DEFINITION OF
WHERE THE HEAVIEST PRECIPITATION WILL OCCUR. BUT AT THIS TIME HAVE
CHOSEN TO CONTINUE THE BROAD BRUSH APPROACH TO THE FORECAST AS
CONFIDENCE IS LACKING IN EXACT PLACEMENT OF THE 700MB CIRCULATION AND
ASSOCIATED AREA OF DEFORMATION (ATMOSPHERIC WEAKNESS WHICH LEADS
TO ENHANCED LIFTING). HOWEVER...THE LIKELIHOOD TOWARDS THE
HEAVIEST PRECIPITATION BEING OVER SOUTHWEST MONTANA LATE SATURDAY
INTO SUNDAY MORNING IS GROWING AND WILL CONTINUE TO HIGHLIGHT THIS
REGION IN A HAZARDOUS WEATHER OUTLOOK.

TEMPERATURES WILL BE MUCH COLDER THAN NORMAL THIS WEEKEND...BUT
PINNING THE COLDEST DAY IS COMPLETELY RELIANT UPON THE PROGRESSION
OF THE 500MB LOW. ONCE THE LOW BEGINS TO MOVE EAST IT WILL DRAW A
COLD...CANADIAN AIRMASS OVER THE REGION CAUSING TEMPERATURES TO
FALL TOWARDS RECORD LEVELS DURING THE MORNING HOURS EARLY NEXT
WEEK. FORECAST MODELS KEEP MUCH OF THE WESTERN STATES UNDER THIS
COLDER REGIME THROUGH AT LEAST MID WEEK WITH THE CHANCE FOR
SHOWERS CONTINUING THROUGH THE PERIOD.

&&

.AVIATION...SHOWERS AND BREEZY RIDGE TOP WINDS WILL IMPACT AIR
TRAVEL OVER THE NEXT 24 HOURS. MOUNTAINS AND PASSES WILL BE
OBSCURED AT TIMES.

&&

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

$$

SHORT TERM...STEGEMILLER
LONG TERM...DICKERSON 
AVIATION...STEGEMILLER