000 FXUS66 KOTX 081216 AFDOTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SPOKANE WA 415 AM PST SUN NOV 8 2009 .SYNOPSIS... THE ACTIVE WEATHER PATTERN WILL CONTINUE TODAY OVER THE PACIFIC NORTHWEST THROUGH THE MIDDLE OF THE WEEK. VALLEY RAIN AND HIGH MOUNTAIN SNOW IS EXPECTED THIS AFTERNOON OVER MUCH OF EASTERN WASHINGTON AND NORTHERN IDAHO. A BREAK IN THE PRECIPITATION IS EXPECTED MONDAY...BEFORE ANOTHER MOIST STORM SYSTEM ARRIVES LATE IN THE DAY. MID WEEK ALSO PROMISES TO BE WET IN THE VALLEYS AND SNOWY IN THE MOUNTAINS. && .DISCUSSION... TODAY AND TONIGHT...THE EARLY MORNING WATER VAPOR LOOP SHOWS ZONAL FLOW CONTINUING INTO THE PACIFIC NORTHWEST. THE UPPER LOW THAT HAS BEEN OVER THE GULF OF ALASKA THE LAST TWO DAYS IS MORE DIFFUSE THAN 24 HOURS AGO...AND THE FLOW OVER THE EASTERN PACIFIC IS CLUTTERED WITH LITTLE SHORTWAVES. IT IS TOUGH TO PICK OUT THESE FAST MOVING WAVES ON SATELLITE...AND THE MODELS HAVE STRUGGLED TO RESOLVE THEM DURING THE LAST COUPLE OF DAYS. A VORTICITY MAX NEARING THE MOUTH OF THE COLUMBIA RIVER (AS OF 10Z) WILL BE THE MAIN PLAYER FOR THE WEATHER OVER EASTERN WASHINGTON AND NORTHERN IDAHO TODAY. BOTH THE 00Z NAM AND 00Z GFS GRABBED ONTO THIS VORTICITY AND GENERATED A GENEROUS BAND OF PRECIPITATION ACROSS THE COLUMBIA BASIN THROUGH THE NORTHERN IDAHO PANHANDLE. LIFT AHEAD OF THIS VORTICITY CENTER SHOULD BE ENHANCED BY MOIST ISENTROPIC ASCENT IN THE 295-300K LAYER COUPLED WITH ELEVATED THETA-E LAPSE RATES APPROACHING 0C. THE BEST PRECIPITATION BAND SHOULD OCCUR FROM 18Z-03Z ALONG THE BEST THERMAL GRADIENT NEAR 700MB. SINCE THE WESTERLY FLOW IN THE 850-700MB LAYER HAS BEEN WEAKENING OROGRAPHIC SNOWS OVER THE PANHANDLE HAVE BEEN DECREASING...SO THE WINTER STORM WARNINGS FOR THE MOUNTAINS WILL BE TAKEN DOWN EARLY THIS MORNING. THE WEAKENING WESTERLY FLOW IN THE MID LEVELS WILL ALSO HELP TO MINIMIZE THE RAIN SHADOW OVER THE BASIN TODAY. THE RAIN AMOUNTS GENERATED BY THE MODELS OF .10-.25 INCHES FROM THE MOSES LAKE AREA THROUGH DEER PARK WILL HAVE A GOOD CHANCE OF VERIFYING. ELEVATIONS ABOVE 3500 FEET IN THIS SWATH OF PRECIPITATION STAND A GOOD CHANCE OF RECEIVING 1-4 INCHES OF SNOW THIS AFTERNOON/EVENING INCLUDING THE MT. SPOKANE AREA THROUGH THE HIGH ELEVATIONS OF KOOTENAI AND BONNER COUNTIES. STRATUS DEVELOPMENT THIS EVENING LOOKS LIKELY IN THE MOSES LAKE...WENATCHEE...AND OMAK AREAS. WEAK SOUTHEASTERLY BOUNDARY LAYER FLOW...MID LEVEL WARMING...AND THE LIKELIHOOD OF WET GROUND DUE TO PRECIPITATION SUGGESTS FOG OR STRATUS. THE SPOKANE AREA AND THE VALLEYS NORTH AND EAST OF THE METRO MAY ALSO BE PLAGUED BY STRATUS OVERNIGHT. /GKOCH MONDAY THROUGH WEDNESDAY...THE LARGE SCALE FLOW PATTERN CONTINUES TO EXHIBIT SIMILAR PATTERNS TO THOSE EXHIBITED BY THE MODELS DURING THIS PORTION OF THE FORECAST FOR THE LAST SEVERAL DAYS. IN GENERAL...A RIDGE POPPING UP OVER CENTRAL MONTANA AND A DEEPENING LONG WAVE TROUGH OFF THE PACIFIC COAST OF NORTH AMERICA LEAVE THE FORECAST AREA IN THE TRANSITION ZONE BETWEEN THE TWO REGIMES EARLY IN THE WEEK. THE RESULT IS BROAD SOUTHWESTERLY FLOW ALOFT WITH A STRONG WEST-TO-EAST SURFACE PRESSURE GRADIENT BECOMING INCREASINGLY ESTABLISHED ACROSS THE AREA ON MONDAY. THIS SETUP GRADUALLY MIGRATES EASTWARD BY MONDAY NIGHT AND TUESDAY...BRINGING A RATHER IMPRESSIVE SHORT WAVE ACROSS THE AREA WITH A VERY STRONG COLD FRONT. DOWNSLOPE DRYING BEHIND THE FRONT QUICKLY ENVELOPES THE AREA BY MID-WEEK...BEFORE LARGE CHANGES AGAIN OCCUR LATER IN THE WEEK. THE PRESSURE GRADIENT SETUP ON MONDAY PER THE MODEL CONSENSUS SHOULD ALLOW FAIRLY IMPRESSIVE EASTERLY SURFACE FLOW TO CONCENTRATE DOWNSLOPE DRYING FROM THE LEWISTON AREA...THROUGH THE PALOUSE AND INTO THE SPOKANE/CDA AREA ON MONDAY. WITH MEAGER LAYER RH VALUES ABOVE THE BOUNDARY LAYER...CLEAR TO PARTLY CLOUDY SKIES SHOULD BE THE RULE THROUGH AT LEAST THE FIRST HALF OF THE DAY ACROSS FAR EASTERN WA AND PORTIONS OF THE ID PANHANDLE. THE LONE EXCEPTION WILL BE ALONG THE CANADIAN BORDER WHERE A NORTHWARD ADVANCING WARM FRONT WILL LIKELY STILL BE STRADDLING THE BORDER THROUGH 18Z OR SO ON MONDAY. WHILE A BIT OF PRECIP ALONG THIS FRONT IS POSSIBLE MONDAY MORNING...UNIMPRESSIVE ISENTROPIC OMEGAS AROUND 295K AND FAIRLY HIGH CONDENSATION PRESSURE DEFICITS PER THE GFS SEEM TO INDICATE THAT CHANCE IS FAIRLY SMALL. HOWEVER...BY MONDAY AFTERNOON AND MONDAY NIGHT...WITH THE OFF SHORE SHORT WAVE ADVANCING TOWARD THE COAST...LAYER RH VALUES WILL INCREASE RAPIDLY FROM WEST TO EAST. AS THEY DO...DEEP LAYER ISENTROPIC LIFT WILL DO LIKEWISE. MIXING RATIOS APPROACHING 4 G/KG AND STRONG SOUTHWEST TO NORTHEAST MOISTURE TRANSPORT ON THE 295K SURFACE WILL INCREASE THE CHANCES OF PRECIPITATION PROGRESSIVELY INTO MONDAY EVENING. WITH THE FLOW BECOMING INCREASINGLY SOUTHERLY FROM EASTERLY...SNOW LEVELS WILL ALSO BEGIN TO RISE. BY MONDAY AFTERNOON...850 MB TEMPERATURES ACROSS THE ENTIRE AREA AWAY FROM THE EAST SLOPES OF THE CASCADES WILL BE IN THE 2 TO 7C RANGE...WITH WET BULB ZERO HEIGHTS GENERALLY IN THE VICINITY OF 4500 TO 5500 FEET. AS A RESULT...SNOW LEVELS SHOULD BE HIGH ENOUGH EVEN WITH IMPRESSIVE LIFT AND FAIRLY IMPRESSIVE QPF TO PRECLUDE WINTER STORM HIGHLIGHTS FOR THE MOUNTAINS. THE SYSTEM FROM MONDAY NIGHT SHIFTS EASTWARD QUICKLY BY TUESDAY NIGHT...WITH WESTERLY FLOW INCREASING AND COLD ADVECTION AT ALL LAYERS TAKING HOLD. TEMPERATURES AT 850 MB FALL OFF TOWARD THE 0 TO -2C RANGE BY WEDNESDAY MORNING...WITH WBZ HEIGHTS DROPPING TO AROUND 3500 FEET. WEDNESDAY NIGHT THROUGH THE EXTENDED FORECAST...WITH COLD ADVECTION THE MAIN PLAYER BY WEDNESDAY NIGHT ACROSS THE AREA...ANOTHER DEEPER SYSTEM IS SET TO TAKE SHAPE OFF SHORE. THE 00Z MODEL GUIDANCE HAS REALLY COME INTO MUCH BETTER AGREEMENT ON CLOSING OFF A DEEP MID-LEVEL SYSTEM AROUND 535 DAM ACROSS WESTERN WASHINGTON AND SHIP IT SOUTHEASTWARD FROM THAT POINT WEDNESDAY NIGHT. IMPRESSIVE Q-VECTOR CONVERGENCE AND IMPRESSIVE DIFFERENTIAL PVA SET THE STAGE FOR A DECENT BATCH OF PRECIPITATION AHEAD OF THIS SYSTEM. HOWEVER...DEPENDING ON THE DEPTH AND TRACK OF ANY LOW LEVEL FEATURE ASSOCIATED WITH IT...THE BOUNDARY LAYER THERMAL PROFILE IS LIKELY TO BE STARKLY DIFFERENT ACROSS THE FORECAST AREA. AT THE MOMENT...THE MODELS ARE FAVORING A MUCH COLDER BOUNDARY LAYER BY THURSDAY NIGHT AND INTO THE NEXT WEEKEND SUCH THAT SNOW IN ASSOCIATION WITH THIS SYSTEM SEEMS LIKELY BY THURSDAY NIGHT ACROSS MOST VALLEY LOCATIONS. HOWEVER...THIS WILL LIKELY CONTINUE TO EVOLVE AS THE WEEK GOES ON...SO STAY TUNED. /FRIES && .AVIATION... A BAND OF PRECIPITATION IS EXPECTED TO DEVELOP OVER THE COLUMBIA BASIN AROUND 17Z AND SPREAD EAST THROUGH SPOKANE AND INTO THE NORTHERN IDAHO PANHANDLE BY 22Z. RAIN WILL BRING CEILINGS DOWN TO IFR OR MVFR AT KEAT...KGEG...KSFF...AND KCOE. CEILINGS PROBABLY WON`T IMPROVE MUCH AS THE RAIN ENDS FROM WEST TO EAST BETWEEN 20Z-02Z. WEAK LOW LEVEL WINDS AND INCREASINGLY LOW LEVEL STABILITY WILL PROVIDE FAVORABLE CONDITIONS FOR THE DEVELOPMENT OF STRATUS AT THE AIRPORTS MENTIONED ABOVE. LOW CEILINGS WILL LIKELY LINGER THROUGH MOST OF THE NIGHT...ESPECIALLY AROUND WENATCHEE. /GKOCH && .PRELIMINARY POINT TEMPS/POPS... SPOKANE 43 33 49 37 47 33 / 60 20 0 80 30 20 COEUR D`ALENE 44 33 49 35 46 32 / 60 20 0 80 40 20 PULLMAN 47 33 54 38 49 34 / 30 10 0 70 20 20 LEWISTON 53 37 57 43 54 40 / 10 10 0 40 20 10 COLVILLE 45 35 48 35 48 32 / 70 40 10 80 30 20 SANDPOINT 43 35 46 34 43 31 / 60 50 0 80 50 30 KELLOGG 40 32 47 34 41 33 / 50 30 0 70 80 30 MOSES LAKE 48 33 48 35 52 30 / 60 10 20 80 0 10 WENATCHEE 43 35 43 38 50 34 / 50 10 30 70 0 10 OMAK 44 33 44 33 48 28 / 60 30 40 90 0 10 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...NONE. WA...NONE. && $$