000
FXUS66 KOTX 032333
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
333 PM PST WED DEC 3 2008
.SYNOPSIS...HIGH PRESSURE WILL KEEP THE INLAND NORTHWEST DRY AND COOL
THROUGH THURSDAY. A PACIFIC STORM SYSTEM WILL BEGIN TO SPREAD
MOISTURE INTO THE AREA ON FRIDAY THROUGH THE WEEKEND...WITH THE
BEST CHANCE OF PRECIPITATION ON SUNDAY. A BRIEF BREAK WILL OCCUR
ON MONDAY BEFORE ANOTHER WET PACIFIC STORM MOVES INTO THE AREA ON
TUESDAY.
&&
...SNOW IN THE MOUNTAINS THIS WEEKEND AND ANOTHER STORM SYSTEM
EARLY NEXT WEEK...
.DISCUSSION...
TONIGHT AND TOMORROW...COOL AND DRY AIR CONTINUES TO FILTER INTO
EASTERN WASHINGTON AND NORTHERN IDAHO THIS AFTERNOON. A 21Z
SURFACE CHART SHOWS AN EXPANSIVE CENTER OF HIGH PRESSURE SPANNING
FROM THE NORTHWEST TERRITORIES DOWN THROUGH THE HIGH PLAINS OF
MONTANA AND WYOMING. SURFACE DEWPOINTS OVER EASTERN WASHINGTON AND
NORTHERN IDAHO ARE IN THE TEENS AND LOW TWENTIES...AND FOR THE
FIRST TIME IN DAYS THE AFTERNOON VISIBLE IMAGERY SHOWS NO FOG OR
STRATUS OVER THE COLUMBIA BASIN. WE WILL SEE A DECREASE IN CLOUDS
THIS EVENING AS A THE NOSE OF A 250MB JET MAX TRANSLATES FROM
SOUTHERN BRITISH COLUMBIA THIS AFTERNOON TOWARD SOUTHERN IDAHO BY
TOMORROW MORNING. CLEARING SKIES...LOW DEWPOINTS...AND LIGHT
NORTHEAST WINDS WILL ALLOW TEMPERATURES TO FALL QUICKLY OVERNIGHT.
SOME OF THE COLDEST READINGS SO FAR THIS SEASON ARE EXPECTED
TOMORROW MORNING...WITH TEENS AND LOW TWENTIES COMMON OVER THE
SPOKANE FORECAST AREA. THEN TOMORROW...THE CHILLY CONDITIONS WILL
CARRY OVER INTO THE AFTERNOON. DESPITE SUNNY SKIES...TEMPERATURES
WILL ONLY TOP OUT IN THE 30S. SOME MODERATION IN TEMPERATURES IS
EXPECTED THURSDAY NIGHT INTO FRIDAY AS THE UPPER LEVEL RIDGE
FLATTENS AND 850MB TEMPERATURES SURGE WELL ABOVE 0C. THE MOST
MARKED WARM UP WILL BE OVER THE CASCADE MOUNTAINS...WHILE THE REST
OF THE FORECAST AREA WILL EXPERIENCE SUBTLE WARMING UNDER AN
INCREASING LOW LEVEL INVERSION. /GKOCH
FRIDAY AND SATURDAY...LARGE RIDGE OVER THE AREA HAS A BIT OF A
POSITIVE TILT AS IT PUSHES UP AND OVER A SYNOPTIC SCALE CLOSED
LOW OFF THE CALIFORNIA COAST THAT CUTS OFF UNDER THE RIDGE OVER
THE WEEKEND. GENERAL CONUS LONGWAVE PATTERN OF A RIDGE IN THE
WEST WITH A ROBUST AND ACTIVE TROF IN THE EAST WILL NOT CHANGE
DURING THIS TIME PERIOD. WHAT LOOKS TO HAPPEN IS A LARGE GYRE OFF
THE COAST AND TO THE SOUTH OF THE ALEUTIANS WILL SWEEP A
BAROCLINIC BAND WITH SIGNIFICANT TAP INTO SUBTROPICAL MOISTURE...
EVIDENT IN PRECIPITABLE WATER VALUES NEAR 1.5 INCHES RUNNING
THROUGH ITS CORE....UP AND INTO THE WESTERN US RIDGE. INCREASE IN
POPS IS RESOLVED FOR FRIDAY NIGHT INTO SATURDAY TO SHOW BAROCLINIC
BAND APPROACH AS IT EXTENDS QUITE A BIT TO THE NORTH AND WRAPS UP
INTO THE OFFSHORE GYRE. END RESULT IS THIS FEATURE TRANSLATES INTO
THE AREA WITH A NORTHWEST TO SOUTHEAST TRAJECTORY. WARM
OVERRUNNING STRATIFIED STABLE PRECIPITATION IS THE EXPECTED
SCENARIO. PROG SOUNDINGS SHOWING TEMPERATURES WARMING TO +3 TO +4
CELSIUS AT 750MB AS THE MOISTURE MOVES IN WHICH WOULD ALLOW FOR
MELTING THEN RE-FREEZING AS TEMPERATURES CROSS OVER THE ZERO
DEGREE ISOTHERM AT ABOUT 800MB AND BACK INTO FREEZING. WITH RE-
FREEZING LAYER NEAR THE SURFACE ABOUT 2000-3000 FEET DEEP THERE IS
A POSSIBILITY OF AN UGLY WINTRY MIX OVER THE NORTHERN THIRD OF THE
FORECAST AREA WHICH WOULD INCLUDE FREEZING RAIN AND SLEET. POPS
REMAIN IN THE HIGH CHANCE CATEGORY AT THE MOMENT TO ACCOMMODATE
TEMPERATURE AND TIMING DIFFERENCES BETWEEN THE WARMER ALOFT GFS
AND SOMEWHAT COOLER ALOFT ECMWF...WITH THE ECMWF SUGGESTING A MORE
SNOWY SOLUTION AND MINIMAL SLEET/FREEZING RAIN...SITUATION IS
STILL A LOW CONFIDENCE SCENARIO BUT STILL CLOSE ENOUGH IN THE NEAR
TERM TO ADD ADDITIONAL REMARKS/MENTION IN THE HAZARDOUS WEATHER
OUTLOOK PRODUCT. /PELATTI
SATURDAY NIGHT THROUGH WEDNESDAY...MODEL AGREEMENT ON
SOUTHWESTERLY FLOW AND PERSISTENT ISENTROPIC LIFT DEVELOPING
ACROSS THE EASTERN HALF OF THE CWA IS WELL ESTABLISHED THROUGH THE
FIRST 24 HOURS OR SO OF THE EXTENDED FORECAST. HOWEVER...THE
SPREAD OF PRECIPITATION ACROSS THE AREA AS WELL AS THE TIMING ON
ITS PRECISE ARRIVAL IS LESS THAN STELLAR STILL AT THIS LATE TIME.
NAM PRECIPITATION SPREAD IS MUCH MORE AGGRESSIVE INTO THE CWA FROM
CANADA THAN THE GFS AND ESPECIALLY THAN THE CANADIAN OR ECMWF. THE
ECMWF AND CANADIAN WAIT UNTIL SUNDAY TO DROP ANY MOISTURE IN
ASSOCIATION WITH A LONG FETCH PACIFIC FEED INTO THE CWA. WHILE THE
MODELS DO NOT AGREE ON EXACT TIMING FOR ARRIVAL...THEY DO AGREE ON
A COLD FRONTAL PASSAGE ON SUNDAY. BEHIND THE FRONT...COLD
ADVECTION AGAIN KICKS INTO GEAR OVER THE CWA...WITH BRIEF DRYING
ON TAP FOR MONDAY BEFORE ANOTHER VERY WET SYSTEM MOVES IN FOR
TUESDAY.
WITH THE TRANSITION FROM ISENTROPIC ASCENT TO PRE-COLD FRONTAL
LIFT...FRONTOGENETICAL FORCING BECOMES THE DRIVING MECHANISM
BEHIND PRECIPITATION CHANCES BY SUNDAY. WITH A STRONG TRANSVERSE
FRONTAL CIRCULATION MOVING THROUGH IN ACCORDING WITH IMPRESSIVE
AND DEEP UPWARD INCREASING PVA...VERY STRONG OMEGAS SHOULD BE
GENERATED ON SUNDAY. ADDITIONALLY...WITH THE COLD FRONT...SNOW
LEVELS WILL FALL PRECIPITOUSLY BY EVENING ACROSS THE CWA. AS THEY
DO SO...LOW LEVEL FLOW WILL TURN WEST TO NORTHWESTERLY PER THE GFS
AND ECMWF. WITH THIS FLOW DIRECTION...UPSLOPE SNOWS WILL BE A
POSSIBILITY INTO THE BLUES AND CAMAS PRAIRIE AS WELL AS THE
CENTRAL PANHANDLE...DEPENDING ON THE EVENTUAL WIND FLOW DIRECTION.
WITH THE COOLING BEHIND THE FRONT...THE THERMODYNAMIC PROFILE OF
THE ATMOSPHERE WILL ALSO BECOME MORE CONDUCIVE TO DENDRITIC GROWTH
THROUGH SUNDAY NIGHT. THE MAXIMUM OMEGA STRIPE GETS INTERCEPTED BY
THE -12C ISOTHERM OVERNIGHT SUNDAY NIGHT WITH NORTHWESTERLY FLOW
PERSISTING...SO SEVERAL INCHES OF SNOWFALL ARE POSSIBLE IN THE
BLUES...CAMAS PRAIRIE...AS WELL AS IN THE CENTRAL PANHANDLE
MOUNTAINS. THESE SNOW SHOWERS WILL LIKELY CONTINUE INTO MONDAY
UNDER NORTHWESTERLY FLOW...WHILE ELSEWHERE...DRIER AIR WILL
CONTINUE TO INVADE BEHIND THE FRONT RESULTING IN MUCH COLDER
CONDITIONS...ESPECIALLY AT NIGHT ACROSS THE CWA.
BY TUESDAY...THE NEXT SYSTEM THAT WILL ARRIVE TO DAMP DOWN THE OFF
SHORE RIDGE BEGINS TO AFFECT THE AREA. HERE AGAIN...ISENTROPIC
PRECIPITATION WILL LIKELY OVERSPREAD THE AREA TUESDAY.
HOWEVER...IN ADVANCE OF TUESDAY`S SYSTEM...MEAN LAYER TEMPERATURES
LOOK TO BE MUCH COLDER ON THE GFS AND ECMWF. THE COLD AIR IN PLACE
IS QUICKLY ADVECTED OUT AS WARMER AIR AGAIN INVADES OFF THE
PACIFIC...BUT NOT BEFORE THE OUTBREAK OF PRECIPITATION ON BOTH
MODELS. AS A RESULT...SNOW CHANGING TO RAIN SEEMS LIKE THE MOST
LIKELY SCENARIO ON TUESDAY.
NORTHWESTERLY FLOW AGAIN BECOMES DOMINANT AFTER TUESDAY`S SYSTEM
DEPARTS WITH OFF SHORE RIDGING AGAIN THE MAIN PLAYER IN THE
FORECAST AND TEMPERATURES TRENDING ABOVE NORMAL YET AGAIN. /FRIES
&&
.AVIATION...
GENERALLY...CIRRUS IS THE MAIN LIMITER TO SEEING COMPLETELY BLUE SKY
THIS AFTERNOON...AND THE CIRRUS WILL BE ON THE WANE AFTER 06Z.
OVERNIGHT...CLEAR SKIES AND NEARLY CALM WINDS ARE EXPECTED AT ALL
TAF SITES BEFORE JUST A FEW CIRRUS CLOUDS MOVE IN AGAIN THURSDAY.
VFR CONDITIONS ARE EXPECTED AT ALL TAFS UNDER COLD CONDITIONS FOR
THE NEXT 24 HOURS. /FRIES
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 19 32 19 34 24 38 / 0 0 0 0 10 30
COEUR D`ALENE 22 34 22 39 25 40 / 0 0 0 0 20 40
PULLMAN 22 36 25 42 28 43 / 10 0 0 0 10 20
LEWISTON 28 39 27 44 30 45 / 10 0 0 0 10 20
COLVILLE 17 34 19 33 22 32 / 0 0 0 0 40 50
SANDPOINT 22 33 19 33 22 33 / 0 0 0 0 40 50
KELLOGG 22 33 22 36 26 38 / 10 0 0 10 20 40
MOSES LAKE 19 36 21 38 24 41 / 0 0 0 0 10 20
WENATCHEE 27 36 24 38 27 41 / 0 0 0 0 10 20
OMAK 19 34 21 35 24 34 / 0 0 0 0 20 30
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
WA...NONE.
&&
$$
