000
FXUS66 KOTX 071127
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
327 AM PST WED JAN 7 2009
.SYNOPSIS...
A MOIST AND MILD SUBTROPICAL AIRMASS WILL INCREASE THE THREAT OF
SIGNIFICANT VALLEY RAINS...RISING SNOW LEVELS...AND GUSTY WINDS THROUGH
THURSDAY. URBAN AND SMALL STREAM FLOODING IS EXPECTED OVER
PORTIONS OF REGION THROUGH EARLY FRIDAY. DRIER WEATHER IS EXPECTED
FOR FRIDAY INTO THE WEEKEND WITH TEMPERATURES RETURNING TO
SEASONAL LEVELS. THIS WILL DRAMATICALLY LOWER THE THREAT OF
FLOODING.
&&
.DISCUSSION...
TODAY AND TONIGHT...
WET AND WARM WEATHER WILL BE THE RULE DURING THIS PERIOD...AS
SUB-TROPICAL MOISTURE PLUME WILL REMAIN FIXED ON THE INLAND NW.
PRECIPITABLE WATER MOSAICS THIS MORNING SHOW AN EXTENSIVE PLUME OF
MOISTURE EXTENDING FROM WELL WEST OF HAWAII TO THE NE CORNER OF WA
WITH VALUES IN EXCESS OF ONE INCH WEST OF THE CASCADE CREST AND
AROUND .75 INCHES EAST OF THE CREST. REALLY SEE NO REASON FOR THIS
MOIST AND PRIMARILY ZONAL PATTERN TO CHANGE DURING THE NEXT 24
HOURS. HOWEVER THE ORIENTATION WILL BECOME MORE SW- NE LATE
TONIGHT WITH THE APPROACH OF A STRONG UPPER LEVEL TROF.
STRONG LOW-LEVEL ISENTROPIC ASCENT WILL COMBINE WITH SIGNIFICANT
MOISTURE TRANSPORT RESULTING IN CATEGORICAL POPS FOR LOCATIONS
NEAR THE CASCADES AND OVER MOST OF NORTH IDAHO. MEANWHILE...STRONG
WESTERLY FLOW IN THE 850-700 MB LAYER WILL RESULT IN SIGNIFICANT
RAIN-SHADOWING IN THE LEE OF THE CASCADES. IT IS ALWAYS A LITTLE
DIFFICULT TO ASCERTAIN HOW PREVALENT THIS AFFECT WILL BE...HOWEVER
GENERALLY THE STRONGER THE WINDS THROUGH THE LAYER...THE MORE
SLOPOVER THERE WILL BE NEAR THE CREST...WITH THE DRYING EXTENDING
FARTHER EAST TOWARD THE IDAHO PANHANDLE. RADAR IMAGERY OVER THE
PAST 6 HOURS HAS DEPICTED A RATHER STAGNANT PATTERN OF
PRECIPITATION WITH MOST OF IT LOCKED NEAR THE CREST AND SLOPPING
ALMOST TO WENATCHEE. ECHOES HAVE ALSO BEEN FIXED OVER EXTREME
EASTERN WA AND MOST OF THE IDAHO PANHANDLE. THIS PATTERN WILL NOT
CHANGE SIGNIFICANTLY TODAY...HOWEVER AS THE TROF MOVES CLOSER TO
THE COAST TONIGHT...THE SHADOWING WILL BEGIN TO DECREASE AS THE
MEAN 850-700 MB FLOW TURNS MORE SW VS. THE CURRENT W-WNW REGIME.
ALL THIS EQUATES TO SIGNIFICANT PRECIPITATION WITH AMOUNTS RANGING
FROM 1-3 INCHES NEAR THE CASCADE CREST AND 1-2 INCHES OVER NORTH
IDAHO...DROPPING OFF TO A FEW HUNDREDTHS OF AN INCH OVER THE
WENATCHEE AREA AND ONTO THE WESTERN COLUMBIA BASIN. WHILE THE
PRECIPITATION WILL BE HEAVY AT TIMES...THE THREAT OF ADDITIONAL
SNOWFALL IS RAPIDLY WANING. THE LATEST MESOWEST OBSERVATIONS
INDICATE ONLY A FEW OBS BELOW FREEZING THIS MORNING AND THOSE WERE
LOCATED IN EXTREME NE WA AND FAR NORTHERN IDAHO. WITH MOUNTAIN
TEMPS GENERALLY ABOVE FREEZING...THE LIKELY RESULT IS POCKETS OF
LIGHT FREEZING RAIN. A LITTLE COULD ALSO OCCUR IN THE CASCADE
VALLEYS. THE THREAT OF FREEZING PRECIP WILL END BEFORE MIDDAY WITH
TEMPS CLIMBING ABOVE FREEZING. WITH SNOW LEVELS GENERALLY AROUND
6K FEET OVER THE CENTRAL PANHANDLE...WE WILL END THE WINTER STORM
WARNING. DUE TO THE AFOREMENTIONED FREEZING RAIN POCKETS WE WILL
HOLD ONTO THE NE WA AND N ID ZONES UNTIL EARLY THIS MORNING.
THE RAINFALL AMOUNTS ALONE COULD POTENTIALLY CAUSE MINOR HYDRO
PROBLEMS...HOWEVER COMBINING THIS PRECIP WITH MELTING SNOW WILL
LEAD TOWARD WIDESPREAD HYDRO ISSUES. SNOW-MELT MAY OCCUR SWIFTER
THAN PREVIOUSLY ANTICIPATED AS TEMPS HAVE WARMED SIGNIFICANTLY
WITH THE PASSAGE OF A WARM FRONT. A FEW LOCATIONS SUCH AS
WENATCHEE...MOSES LAKE...PULLMAN...AND EVEN SPOKANE HAVE NEARED OR
EVEN EXCEEDED THE PREVIOUSLY FORECAST HIGH TEMP VALUES AND THAT
WAS SHORTLY AFTER MIDNIGHT. ALL SHORT-RANGE MODELS ARE UNDER
FORECASTING THE MIXING AND SUBSEQUENT WARMING WITH ONE
EXCEPTION...THE LOCAL WRF MODEL. THIS MODEL PEGGED THE DEVELOPMENT
OF A MESO-LOW OVER THE WESTERN BASIN AND SUBSEQUENT HIGH WIND
EVENT IN THE WENATCHEE AREA. IT ALSO PEGGED THE WARMING. WE WILL
GENERALLY USE THIS GUIDANCE THROUGH THE DAY AND INTO THE
NIGHT. THIS SUGGESTS MOST VALLEY LOCATIONS WILL SURGE INTO THE
40S TODAY...WITH 50S COMMON SOUTH OF I90. THIS WARMING WILL
COMBINE WITH MODERATE WINDS RESULTING IN A PRIME SNOW-MELTING
PATTERN...ESPECIALLY AS THE SNOW PACK RIPENS THROUGH THE DAY.
THE WARMING OF THE DAY DOES NOT SUBSIDE TONIGHT EITHER AS THE
WINDS BACK TOWARD MORE OF A SOUTHWESTERLY ORIENTATION. WRF MODEL
GUIDANCE FORECASTS LOWS IN THE 40S. THIS COMBINED WITH AN
INCREASING THREAT OF RAIN...WILL RESULT IN VERY RAPID RUNOFF FOR
MANY VALLEY LOCATIONS. HYDRO HEADLINES FOR URBAN AND SMALL STREAM
FLOODING WILL CONTINUE. GIVEN THE SIGNIFICANT PRECIPITATION IN THE
LEE OF THE CASCADES WITH THE SLOPOVER WE HAVE EXPANDED THE HYDRO
HEADLINES INTO THAT AREA AS WELL. WE WILL ALSO NEED TO WATCH FOR
ICE DAM BREAKUPS AS THE RUNOFF WILL OVERWHELM ANY THAT HAVE
FORMED. OF NOTE...THE HANGMAN CREEK GAGE IN SPOKANE HAS DROPPED BY
2 FEET OVERNIGHT A GOOD INDICATION OF A SIGNIFICANT ICE DAM
SOMEWHERE UPSTREAM.
AS FOR WINDS...WE WILL LET THE CURRENT BATCH OF ADVISORIES AND
WARNINGS CONTINUE INTO EARLY MORNING. LOOKS LIKE THE PEAK HAS
LIKELY OCCURRED IN THE WENATCHEE AREA...AND WINDS ELSEWHERE WILL
SLOWLY SUBSIDE. LOOKING AT THE NAM12 AND WRF SOLUTIONS...WE WILL
LIKELY NEED ANOTHER BATCH OF WIND ADVISORIES LATE TONIGHT FOR THE
PALOUSE AND SPOKANE AREA AS A SIGNIFICANT 850 MB SW JET DEVELOPS
AFTER 06Z. FX
THURSDAY THROUGH FRIDAY...MODELS IN GOOD AGREEMENT WITH A COLD FRONT
POSITIONED OVER CENTRAL WASHINGTON EARLY THURSDAY MORNING MOVING
EAST INTO MONTANA IN THE AFTERNOON. HEAVY RAIN AND MELT WILL
REMAIN A CONCERN OVER EASTERN WASHINGTON AND NORTHERN IDAHO UNTIL
THE COLD FRONT PASSES. HEAVY RAIN WILL THEN COME TO AN END BUT
BREEZY AFTERNOON WINDS BEHIND THE FRONT AND RESIDUAL RUNOFF WILL
LEAD TO FLOOD CONCERNS THROUGH FRIDAY AFTERNOON. THUS THE FLOOD
WARNINGS AND ADVISORIES FOR EASTERN WASHINGTON AND NORTH IDAHO
REMAIN IN EFFECT THROUGH THIS TIME FRAME. THEN A SHORT WAVE DROPS
DOWN IN NORTHWEST FLOW THURSDAY AFTERNOON AND EVENING. STRONG
WESTERLY FLOW AND COLD AIR ADVECTION IN THE LOWER LEVELS WILL
RESULT IN VERY PRONOUNCED PRECIP SHADOWING IN THE LEE OF THE
CASCADES WITH THE BEST PRECIP THREAT BEING IN THE IDAHO PANHANDLE
AND CAMAS PRAIRIE. SNOW LEVELS AS THIS WAVE DROPS IN WILL HAVE
LOWERED TO AROUND 3500 FEET WHERE LIGHT MOUNTAIN ACCUMULATIONS ARE
EXPECTED. THEN A SHORT WAVE RIDGE BUILDS IN ON FRIDAY FOR DRIER
CONDITIONS OVER ALL THE AREA. MAIN PROBLEM MAY BE FOG AND STRATUS
AND RESIDUAL MOISTURE IN THE BOUNDARY LAYER MAY HAVE A HARD TIME
DISSIPATING AS THE SHORT WAVE RIDGE BRINGS MORE MIXING POTENTIAL
ON FRIDAY. A COMBINATION OF POOR MIXING AND EXPECTED STRATUS WILL
LEAD TO MUCH COOLER TEMPS ON FRIDAY...BUT VALUES THAT ARE MORE
TYPICAL FOR JANUARY.
FRIDAY NIGHT THROUGH TUESDAY...FLAT RIDGE OFF THE COAST WILL
RESULT IN A NORTHWEST FLOW ALOFT. GFS AND ECMWF SHOW A SYSTEM
DROPPING DOWN IN THE NORTHWEST FLOW LATE SATURDAY INTO SUNDAY BUT
WITH THE BEST ENERGY REMAINING NORTH AND EAST OF THE AREA. HOWEVER
UPSLOPE FLOW IN COMBINATION WITH THE PASSING WAVE INTO N IDAHO
WILL LEAD TO A GOOD CHANCE FOR PRECIPITATION. FOR NOW OPTED TO NOT
MAKE CHANGES AND LEAVE IN CHANCE POPS AND LET DAY SHIFT EVALUATE
FURTHER. BY TUESDAY ECMWF AND TO A GREATER DEGREE GFS AMPLIFY THE
RIDGE JUST OFF THE COAST ALONG 130W WHICH WOULD RESULT IN DRY
CONDITIONS FOR ALL OF THE INLAND NW. HOWEVER GIVEN UNCERTAINTY IN
THAT THIS IS DAY 7 LEFT A CHANCE OF MOUNTAIN SNOW SHOWERS IN THE
FORECAST. JW
&&
.AVIATION...
A WSW FLOW AND MOISTURE FEED ACROSS THE INLAND NW WILL ALLOW
SOME RAIN TO DEVELOP OVERNIGHT INTO EARLY WEDNESDAY. THIS IS
PROJECTED TO DEVELOP IFR/LCL MVFR CIGS OVERNIGHT INTO WEDNESDAY
MORNING OVER EASTERN TAF SITES. STEADIER PRECIPITATION IS
EXPECTED TO DEVELOP AFTER 18-01Z IN THESE AREAS. KEAT-KMWH ARE
EXPECTED TO SEE MVFR/LCL IFR CONDITION...WITH A MORE INTERMITTENT
PRECIP RISK. LOOK FOR LOCALLY WINDY CONDITIONS IN KEAT/KPUW/KGEG
...AND BREEZY CONDITIONS AT THE OTHER TAF SITES...THROUGH 15-20Z.
SOME LLWS IS ALSO A RISK. /JCOTE
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 48 41 43 27 30 23 / 60 90 80 20 10 10
COEUR D`ALENE 47 41 42 29 31 22 / 70 90 100 30 10 10
PULLMAN 50 44 44 28 34 26 / 80 100 100 50 10 10
LEWISTON 54 47 48 33 39 30 / 30 50 70 20 10 10
COLVILLE 42 36 43 26 29 19 / 60 90 70 10 10 10
SANDPOINT 43 40 41 30 30 17 / 100 100 100 30 10 10
KELLOGG 46 40 40 29 30 24 / 100 100 100 60 20 10
MOSES LAKE 51 39 46 24 33 20 / 20 30 30 10 0 10
WENATCHEE 52 38 46 28 35 20 / 20 30 20 10 0 10
OMAK 42 36 45 23 29 16 / 20 50 20 10 10 10
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...WIND ADVISORY UNTIL 10 AM PST THIS MORNING FOR COEUR D`ALENE
AREA...IDAHO PALOUSE.
WINTER STORM WARNING UNTIL 10 AM PST THIS MORNING ABOVE 3000
FEET FOR NORTHERN PANHANDLE.
WA...WIND ADVISORY UNTIL 10 AM PST THIS MORNING FOR EAST SLOPES
NORTHERN CASCADES...WATERVILLE PLATEAU.
WIND ADVISORY UNTIL 10 AM PST THIS MORNING FOR LOWER GARFIELD
AND ASOTIN COUNTIES...SPOKANE AREA...UPPER COLUMBIA BASIN...
WASHINGTON PALOUSE.
WINTER STORM WARNING UNTIL 10 AM PST THIS MORNING ABOVE 3000
FEET FOR NORTHEAST MOUNTAINS.
HIGH WIND WARNING UNTIL 10 AM PST THIS MORNING FOR WENATCHEE
AREA.
&&
$$
