High Wind in Washington, November 11 to 12, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
909 AM PST TUE NOV 11 2014

.SYNOPSIS...AN EARLY SEASON ARCTIC COLD FRONT WILL PUSH ACROSS MUCH
OF THE FORECAST AREA EARLY TODAY. THE WIND WILL BECOME MUCH STRONGER
TODAY AND TONIGHT...ESPECIALLY IN EAST-WIND PRONE AREAS. COLD AIR
EAST OF THE CASCADES WILL SUPPORT A STRONG EAST WIND PATTERN THROUGH
LATE WEDNESDAY. A PACIFIC FRONT IS EXPECTED TO OVERRUN THE COLD AIR
MASS WEDNESDAY NIGHT AND THURSDAY...WITH WINTRY PRECIPITATION LIKELY
IN THE COLUMBIA GORGE AND HOOD RIVER VALLEY...AND POSSIBLY ACROSS THE
PORTLAND/VANCOUVER METRO AREA AND NORTH OREGON COAST RANGE. THE
PACIFIC FRONT WILL BRING MILDER AIR TO OUR SOUTHERN ZONES...BUT
TEMPERATURES ARE EXPECTED TO REMAIN BELOW NORMAL NORTH AND EAST OF
SALEM. A FRONTAL ZONE WILL LINGER WITH OCCASIONAL PRECIPITATION
THROUGH THE WEEKEND.

&&

.SHORT TERM...TODAY THROUGH THURSDAY...AN EARLY SEASON TASTE OF
WINTER FOR MOST AREAS OVER THE NEXT COUPLE OF DAYS. THIS WILL BE A
VERY COMPLEX...CHALLENGING AND MULTI-FACETED FORECAST FOR THE SHORT
TERM...WITH PRECIPITATION TYPE BEING THE MOST DIFFICULT PART. THE
FIRST PHASE OF THE PATTERN...THE WIND...IS COMING TOGETHER NICELY.
16Z KTTD-KDLS GRADIENT AT -8.5 MB...PRETTY CLOSE TO WHAT YESTERDAYS
12Z NAM INDICATED. THE MORE SIGNFICANT GRADIENT IS KPDX-KTTD...WHICH
WAS AT -0.9 MB. THIS HAS RESULTED IN STRONGER WIND AT KPDX COMPARED
TO KTTD. CROWN POINT HAS ALREADY HAD GUSTS TO 66 MPH...AND LARCH MT
IN SW WA HAS HIT 58 MPH.

THE DEPTH OF THE COLD AIR IS AT LEAST 4000 FEET MSL...IF NOT A LITTLE
DEEPER. WANDERERS PEAK...AT 4350 FT...WAS 29 DEG WITH GUSTS 30-40 MPH
THIS MORNING. COLD HIGH PRESSURE WILL CONTINUE TO STRENGTHEN OVER THE
NRN ROCKIES AND ERN WA TODAY...RESULTING IN STRONGER LOW-LEVEL
PRESSURE GRADIENTS. MEANWHILE...LEE-SIDE TROUGHING IS DEVELOPING DUE
TO DOWNSLOPE WINDS ALONG THE COAST...TO FURTHER ENHANCING E-NE
PRESSURE GRADIENTS ACROSS SOUTHWEST WASHINGTON AND NORTHWEST OREGON.
00Z MM5-NAM TIME-HEIGHT SECTION FOR KTTD STILL QUITE IMPRESSIVE
SHOWING EAST WIND AT 50 KT JUST ABOVE THE SURFACE FROM 00Z WED THRU
AT LEAST 15Z. THE STABLE FLOW-REVERSAL DEPICTED BETWEEN 750 AND 700
MB THROUGH TONIGHT...INDICATING MORE OF A MOUNTAIN WAVE EVENT.
THUS...THE LARGER-SCALE GRADIENTS WILL BE OF MORE SIGNIFICANCE VERSUS
THE LOCAL...MICRO-SCALE...GRADIENTS. KOTH-KGEG AT -21.3 MB AT
16Z...AND IS EXPECTED TO PUSH -25 MB OR MORE BY TONIGHT. LOCAL
STUDIES HAVE SHOWN THAT A KOTH-KGEG GRADIENT OF -20 TO -21 MB
RESULTED IN A DAMAGING DOWNSLOPE EAST WIND EVENT FOR EASTERN CLARK
AND CLACKAMAS COUNTIES IN DEC 2003. THIS EVENT HAS THE POTENTIAL TO
BE STRONGER AND MORE WIDESPREAD. IT APPEARS THE DOWNSLOPE MOUNTAIN
WAVE SITUATION TRANSFORMS INTO MORE OF A GAP WIND SITUATION SOMETIME
WED...AS THE INVERSION LOWERS. THE LATEST NAM SHOWS A KTTD-KDLS
GRADIENT OF AT LEAST -11 MB 15Z WED. BASED ON LOCAL STUDIES...THIS
WOULD YIELD WIND GUSTS OF 75-85 MPH AT THE WEST END OF THE
GORGE...AND POSSIBLY CLOSE TO 100 MPH AT VISTA HOUSE. CURRENT
WIND HIGHLIGHTS LOOK GOOD...BUT WILL LIKELY NEED TO EXTEND THE ONES
OUTSIDE THE GORGE THROUGH WED AFTERNOON.

THE EAST WINDS WILL EASILY USHER IN THE COLDEST AIR THUS FAR THIS
SEASON. SINCE IT IS SO EARLY IN THE SEASON...THIS AIR MASS IS NOT AS
COLD AS WOULD BE IN DECEMBER OR JANUARY...WHEN ARCTIC COLD WOULD HAVE
A CHANCE TO INCUBATE OVER NORTHERN CANADA...THE SOURCE REGION OF THIS
AIR MASS. THIS IS AN IMPORTANT DISTINCTION...AND WILL HAVE
SIGNIFICANT IMPACTS ON PRECIPITATION TYPE AS A FRONTAL SYSTEM BEGINS
TO OVERRUN THE COLD AIR MASS WITH PACIFIC MOISTURE WED NIGHT/EARLY
THU. THIS BECOMES THE BIGGEST FORECAST CHALLENGE IN THE SHORT TERM.

IF THIS WERE DECEMBER OR JANUARY...THIS OVERALL PATTERN WOULD BE
NEARLY PERFECT FOR LOWLAND SNOW...WITH LOW PRESSURE APPROACHING FROM
THE SOUTHWEST AND A ROBUST COLD AIR MASS IN PLACE ACROSS THE PAC NW.
FOR SNOW TO OCCUR IN THE WILLAMETTE VALLEY THERE WILL NEED TO BE
SIGNIFICANT WET-BULB EFFECTS...WHICH WOULD REQUIRE A FAIRLY HEAVY
BATCH OF PRECIPITATION TO MOVE INLAND WED NIGHT/EARLY THU. LATEST NAM
BRINGS PRECIP INTO THE FAR SW PART OF THE FORECAST AREA BETWEEN 06Z
AND 09Z THU...AND NOT TO KPDX AND THE COLUMBIA GORGE UNTIL AT LEAST
15Z. SLOWER MAY BE BETTER NEAR THE GORGE AS THE INCOMING MOISTURE
WILL BE FIGHTING SUCH A STRONG EAST WIND AND VERY DRY LOWER PART OF
THE AIR MASS. IF THE NAM MODEL SOUNDINGS WERE TAKEN AT TOTAL FACE
VALUE...KPDX WOULD SEE SEVERAL HOURS OF SNOW THU BEFORE TURNING TO
-FZRA. EVEN THE KSLE NAM MODEL SOUNDING PROVIDES A 3-6 HR PERIOD OF
-FZRA BEFORE CHANGING TO RAIN. THE COLUMBIA GORGE IS LIKELY TO GET
SUBSTANTIAL SNOWFALL. THE 00Z WRF-GFS SHOWS AT LEAST 5-10 INCHES OF
SNOWFALL 12Z THU TO 00Z FRI FOR THE GORGE. THE OFFSHORE LOW-LEVEL
FLOW IN THE COLUMBIA GORGE NEVER COMPLETELY ENDS...BUT DOES WEAKEN
CONSIDERABLY FRI. LOTS OF THINGS TO MULL OVER...BUT EXPECT WINTER
STORM WATCHES TO BE ISSUED FOR THE AFTERNOON FORECAST. WEISHAAR

.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS...THURSDAY NIGHT
THROUGH MONDAY...MODELS ENTER THE EXTENDED UNDER FAIRLY GOOD
AGREEMENT ON THE LARGE SCALE PICTURE. THE BROAD ARCTIC TROUGH STILL
WILL EXHIBIT INFLUENCE EAST OF THE CASCADES FOR THE LOWER COLUMBIA
BASIN. SOUTHERLY WINDS ON ON FRIDAY SHOULD SERVE TO WARM UP A LARGE
PART OF THE FORECAST AREA BUT SOUTHERLY WINDS WILL LIKELY SKIP ACROSS
THE GORGE WITHOUT MUCH MIXING BELOW THE GORGE RIM. THIS WILL STILL
ALLOW COLDER DENSE AIR TO SEEP THROUGH THE COLUMBIA GORGE AND
SEVERELY LIMIT TEMPERATURE RISES THROUGH THE WEEKEND. THE REINFORCED
COLD AIR IS ALSO INDICATED VIA MSLP FIELDS FROM THE MEDIUM RANGE
MODELS. IN FACT...THE DGEX AND	ECMWF ARE IN REMARKABLE AGREEMENT
BEGINNING SATURDAY WITH ANOTHER ROUND OF STRONG EAST WIND GRADIENTS
ACROSS THE MT HOOD/MT ADAMS GAP. THIS GIVES ADDED CONFIDENCE THE
COLDER AIR WILL SEEP TOWARD THE WESTERN GORGE AND EAST METRO AT A
MINIMUM.

AT THE SAME TIME...THE REGION WILL REMAIN UNDER A MOISTURE LADEN
BAROCLINIC BAND. MODELS HAVE BEEN WAVERING WITH THE NORTH-SOUTH
POSITION OF THE BAND BUT GENERALLY KEEP PRECIPITATION FALLING OVER
THE NORTHERN PART OF THE CWA FOR THE BULK OF THE WEEKEND THOUGH
DRIFTING SOUTH AT TIMES. MAIN CONCERN WILL BE FOR A CONTINUED THREAT
OF MIXED RAIN/SNOW ACROSS THE NEAR GORGE AREA AND ESPECIALLY SO FOR
THE CENTRAL GORGE. BOTTOM LINE IS FOLKS PLANNING ON TRAVEL TOWARD
EAST OF THE CASCADES THIS WEEKEND AND EARLY NEXT WEEK SHOULD BE
PREPARED FOR WINTER TRAVEL. /JBONK

&&

.AVIATION...VFR CONDITIONS TO CONTINUE WITH A DRY AIR MASS IN A
STRONG OFFSHORE FLOW. TURBULENT DOWNSLOPE WINDS TODAY INTO TONIGHT
ALONG AND TO THE W OF CASCADES WITH WINDS GUSTING 40 TO 55 KT.
STRONG POTENTIAL FOR 50 KT SUSTAINED E WINDS WITHIN 2000 FT AGL OVER
CASCADES FOOTHILLS TODAY TO WED.

KPDX AND APPROACHES...HIGH PRES WITH CLEAR SKIES THROUGH WED AM.
STRONG E WINDS TODAY AND TONIGHT GUSTING TO 40 KT...WITH GUSTS TO
AROUND 50 KT WITHIN A FEW THOUSAND FEET OF GROUND LEVEL.
&&

.MARINE...HIGH PRES INLAND WILL BRING STRONG OFFSHORE WINDS TO THE
COASTAL WATERS TODAY INTO WED MORNING...STRONGEST ACROSS THE
NORTHERN WATERS WHERE A GALE WARNING WILL CONTINUE. WITH GENERALLY A
SMALL ABOUT 4 TO 5 FT SWELL OUT OF THE W THROUGH WED...THE STRONG
WINDS WILL GENERATE STEEP WIND DRIVEN SEAS THAT ARE LIKELY TO BE
LIMITED MORE THAN USUAL FOR SUCH STRONG WINDS DUE TO A SHORT FETCH.
ACROSS THE SOUTHERN WATERS WINDS AND SEAS ARE LIKELY TO BE A LITTLE
LESS...SO SMALL CRAFT FOR WINDS APPEARS LIKELY TO SUFFICE TODAY INTO
WED.

OFFSHORE FLOW WILL EASE THU AS A LOW PRES APPROACHES FROM THE SW.
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...HIGH WIND WARNING UNTIL NOON PST WEDNESDAY FOR GREATER PORTLAND
     METRO AREA-NORTHERN OREGON CASCADE FOOTHILLS.

     HIGH WIND WARNING FROM 2 PM THIS AFTERNOON TO 6 PM PST
     WEDNESDAY FOR WESTERN COLUMBIA RIVER GORGE.

WA...HIGH WIND WARNING UNTIL NOON PST WEDNESDAY FOR GREATER
     VANCOUVER AREA-SOUTH WASHINGTON CASCADE FOOTHILLS.

     HIGH WIND WARNING FROM 2 PM THIS AFTERNOON TO 6 PM PST
     WEDNESDAY FOR WESTERN COLUMBIA RIVER GORGE.

PZ...GALE WARNING UNTIL NOON PST WEDNESDAY FOR COASTAL WATERS FROM
     CAPE SHOALWATER WA TO CASCADE HEAD OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR WINDS UNTIL NOON PST WEDNESDAY FOR
     COASTAL WATERS FROM CASCADE HEAD OR TO FLORENCE OR OUT 60 NM.

&&

INTERACT WITH US VIA SOCIAL MEDIA
WWW.FACEBOOK.COM/NWSPORTLAND
WWW.TWITTER.COM/NWSPORTLAND

THIS DISCUSSION IS FOR NORTHWEST OREGON AND SOUTHWEST WASHINGTON
FROM THE CASCADE CREST TO 60 NAUTICAL MILES OFFSHORE. THE AREA IS
COMMONLY REFERRED TO AS THE FORECAST AREA.