FXUS66 KOTX 290012
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
410 PM PST SAT NOV 28 2009
.SYNOPSIS...
PRECIPITATION...MAINLY IN THE FORM OF SNOW...WILL INCREASE THIS
EVENING ACROSS NORTHERN WASHINGTON AND FAR NORTHERN IDAHO.
ACCUMULATIONS OF SNOW WILL GENERALLY BE LIGHT...WITH THE MOUNTAINS
NORTH OF SPOKANE AND INTO NORTH IDAHO SEEING THE MOST SIGNIFICANT
ACCUMULATIONS. FOLLOWING TONIGHT...HIGH PRESSURE WILL BE THE DOMINANT
WEATHER FEATURE OVER THE PACIFIC NORTHWEST FOR MOST OF NEXT WEEK.
LOOK FOR MAINLY DRY WEATHER AND CHILLY TEMPERATURES.
&&
.DISCUSSION...
TONIGHT...ABOVE WHATS LEFT OF THE NEAR-SFC STRATUS DECK...WE'VE
SEEN A STEADY THICKENING OF THE MID- CLOUD CANOPY AND A MOISTENING
OF THE MID- LEVEL DRY LYR AS STRATIFORM PCPN TIED TO MOIST
ISENTROPIC ASCENT ALONG A WRMFNT SLOWLY SATURATES THE LYR. THE
DEPTH OF THIS DRY LYR HAS DECREASED TO 4-5K FT FOR MOST TOWNS N OF
A LINE FROM KELLOGG TO SPOKANE AND KOMK...SUFFICIENT TO PRODUCE
FLURRIES EVEN FOR LOWER ELEVS. ITS UNCERTAIN AS TO HOW MUCH
SEEDING OF THE STRATUS DECK WILL OCCUR...BUT WE'VE INCLUDED LIGHT
SNOW IN THE FCST FOR TONIGHT FOR ALL OF THE ID PANHANDLE...AND
FROM SPOKANE N TO BC BORDER. ACCUMULATIONS WILL BE LIGHT WITH THE
MAJORITY OF THE SNOW FALLING IN THE MTNS ABOVE 3.5K FT MSL ACROSS
THE NE WA AND N ID MTNS. NO MAJOR CHANGES TO THE FCST FOR LOW
TEMPS AND FOG RE-DEVELOPMENT. BZ
SUNDAY THROUGH TUESDAY...MODELS IN GOOD AGREEMENT FOR SUNDAY AND
MONDAY AS THE UPPER LEVEL RIDGE REMAINS OVER THE PACIFIC
NORTHWEST. THE RIDGE WILL FLATTEN ON MONDAY AS A FRONT APPROACHES
THE WEST COAST. ECMWF SHOWS THE FRONT SPLITTING AS A CUTOFF LOW
APPROACHES OREGON AND WE WOULD REMAIN IN DRY NW FLOW AS A RIDGE SETS UP
ALONG THE COAST. MEANWHILE THE NAM...GFS AND CANADIAN ALL SHOW THE
FRONT MOVING THROUGH THE INLAND NORTHWEST LATE MONDAY/EARLY
TUESDAY WITH JUST VERY LIGHT QPF EXPECTED. LOOKING AT AMSU TPW IN
THE PACIFIC WHERE THIS FRONT IS FORMING...PRECIPITABLE WATER IS
CURRENTLY VERY UNIMPRESSIVE...SO MODELS DEPICTION OF JUST LIGHT
PRECIP IS VALID. AFTER THE FRONT PASSES VERY DRY AIR MOVES IN FROM
CANADA. BY TUESDAY AN UPPER LEVEL RIDGE WILL EXTEND ALONG THE
WEST COAST. A SURFACE HIGH WILL MOVE SOUTH OUT OF CANADA BRINGING
A REINFORCING SHOT OF COOLER NORTHEASTERLY FLOW TO THE FORECAST
AREA. FORECAST CHANGES WERE TO LOWER CLOUD COVER AFTER THE FRONT
PASSES...DECREASE POPS FURTHER AFTER THE FRONT ESPECIALLY IN THE
VALLEYS AND ALONG THE CASCADES. KEPT MENTION OF FOG FOR SUNDAY
NIGHT ACROSS THE VALLEYS. TEMPERATURES FOR THE PERIOD WILL START
OUT ABOVE AVERAGE AND THEN TREND TO AVERAGE READINGS BY TUESDAY AS
THE COLD AIR MOVES IN. /NISBET
TUESDAY NIGHT THROUGH SATURDAY...IN ONE FORM OR ANOTHER...THE
LONGWAVE PATTERN FEATURES A RIDGE OF HIGH PRESSURE ACROSS THE
EASTERN PACIFIC AND PORTIONS OF THE WESTERN CONUS TUES NT/WED
WHICH EVENTUALLY BECOMES SQUASHED...REDEVELOPING WESTWARD
ACROSS THE EASTERN PACIFIC...OPENING THE DOOR TO COOLER
TEMPERATURES AND SLIGHT CHANCE FOR SNOW BY THE WEEKEND.
AFTER ONE SHORTWAVE RIDES UP AND OVER THE RIDGE TUESDAY...THE
RIDGE WILL TEMPORARILY RE-STRENGTHEN OVER THE REGION WITH
GENERALLY DRY CONDITIONS THROUGH THURSDAY AND TEMPERATURES CLOSE
TO SEASONAL READINGS. MODELS ARE IN DECENT AGREEMENT THROUGH
WEDNESDAY WITH THE BIGGEST FORECAST UNCERTAINTY BEING FOG/LOW
CLOUD POTENTIAL AND RESULTANT TEMPERATURE IMPACTS. THURSDAY
THROUGH THE WEEKEND...CONFIDENCE QUICKLY GOES INTO THE GUTTER AS
MODEL GUIDANCE BECOMES A WIDELY SCATTERED SPAGHETTI PLOT OF
SOLUTIONS. NOT ONLY ARE THE MODEL FAMILIES NOT DEMONSTRATING ANY
CONSISTENCY RUN TO RUN...BUT NOW THE MAIN OPERATIONAL MODELS WE
TEND TO TREND WITH...IE THE GFS/ECMWF...HAVE FLIP-FLOPPED
SOLUTIONS FROM NEARLY 24 HRS AGO. IT IS LITTLE SURPRISE THE MODELS
ARE STRUGGLING WITH THE DETAILS DUE TO THE COMPLEXITY OF PATTERN
WHICH FEATURES A BARRAGE OF ENERGY OVER THE NORTHERN
PACIFIC...RIDGE IN PLACE OVER THE WEST...AND DEEP TROUGH OF THE
EASTERN TWO-THIRDS OF THE US STARTING THURSDAY. BY FRIDAY AND
SATURDAY...EACH MODEL FAMILY BRINGS THE NORTHERN PACIFIC ENERGY
CRASHING INTO THE WEST COAST RIDGE...TEMPORARILY SQUASHING THE
RIDGE...THEN REDEVELOPING THE RIDGE OFF THE COAST WITH A STRONG
COLD NORTH/NORTHEASTERLY PUSH OF ARCTIC AIR OVER THE REGION AS A A
DEEP UPPER-LEVEL DIGS SW INTO THE EASTERN FLANK OF THE LONGWAVE
RIDGE I THINK WE CAN EXPECT INCR PRECIPITATION CHANGES AND MUCH
COOLER AIRMASS WITH TEMPERATURES DIPPING WELL BELOW
NORMAL...HOWEVER...THE DETAILS ARE FAR FROM BEING IRONED OUT AS MODEL
GUIDANCE DIFFERS NEARLY 48 HRS WITH THE TIMING OF THE
AFOREMENTIONED PATTERN AND FELT THE BEST APPROACH TO THIS
AFTERNOON'S FORECAST PACKAGE...IN AGREEMENT WITH SURROUNDING
OFFICES WAS TO MAKE VERY LITTLE CHANGES UNTIL HIGHER CONFIDENCE IS
ACHIEVED. /SB
&&
.AVIATION...
MID AND UPPER-LEVEL MOISTURE WILL CONTINUE TO SPILL OVER
A RIDGE OF HIGH PRESSURE ANCHORED OVER THE INLAND NW WITH
VERY LIGHT PCPN FALLING ALONG THE NORTHERN MTNS AND AT TIMES
EXTENDING INTO THE SPOKANE-COEUR D'ALENE CORRIDOR. EXPECT
THE LIGHT PCPN WILL ACT TO SEEDER-FEEDER THE LINGERING
STRATUS OVER THE SPOKANE AREA AT TIMES THIS EVENING BOUNCING
FROM SCT-BKN020-030...HOWEVER AS PCPN BANDS MOVE OFF AFT
10Z...EXPECT MVFR/IFR STRATUS TO REDEVELOP. GENERALLY VFR
CONDITIONS NOTED FOR THE REMAINING TERMINALS. /SB
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 31 40 34 43 30 37 / 20 0 0 0 10 0
COEUR D'ALENE 31 38 36 43 31 38 / 20 10 0 0 10 0
PULLMAN 30 42 33 45 35 38 / 0 0 0 0 10 0
LEWISTON 32 46 36 48 39 45 / 0 0 0 0 10 0
COLVILLE 32 41 34 42 27 39 / 20 10 10 10 20 0
SANDPOINT 30 38 32 39 27 34 / 30 20 10 10 20 0
KELLOGG 30 40 35 40 32 34 / 20 20 10 10 20 10
MOSES LAKE 30 43 37 44 32 42 / 0 0 0 0 0 0
WENATCHEE 30 45 36 46 33 42 / 0 0 0 0 0 0
OMAK 31 42 35 45 30 42 / 10 0 0 0 10 0
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
WA...NONE.
&&
$$
