FXUS66 KPDT 150555
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
955 PM PST MON DEC 14 2009
.UPDATE...SNOW HAS MOVED ACROSS THE CASCADES INTO THE YAKIMA AND
KITTITAS VALLEY AND COLUMBIA RIVER GORGE. RAIN STARTED IN REDMOND.
EXPECT PRECIPITATION TO SPREAD ACROSS THE REST OF EASTERN WASHINGTON
AND OREGON THIS EVENING. TEMPERATURES AND DEWPOINTS ARE IN THE 30S
IN CENTRAL OREGON AND NORTH CENTRAL OREGON SO CURRENT FORECAST OF
MIXED RAIN AND SNOW CHANGING TO RAIN OVERNIGHT LOOKS GOOD.
TEMPERATURES ARE IN THE 30 AND 40 IN THE JOHN DAY BASIN AND OCHOCO
JOHN DAY HIGHLANDS...BUT THE DEWPOINTS ARE LOW ENOUGH THAT THE
FORECAST OF MAINLY SNOW IS OK. THE MODIFIED ARCTIC AIR MENTIONED
BELOW HAS KEPT TEMPERATURES IN THE 20S THIS EVENING ACROSS THE LOWER
COLUMBIA BASIN. MIX OF SNOW AND FREEZING RAIN LATER TONIGHT STILL
LOOKS LIKE A GOOD FORECAST AS WELL.
SNOWFALL HAS INCREASED IN YAKIMA. UPGRADED ADVISORY TO WARNING SINCE
EXPECT SNOW TO CONTINUE OVERNIGHT AND REACH WARNING AMOUNTS.
COONFIELD
&&
.AVIATION...06Z TAFS...SNOW SHOWERS CONTINUE ACROSS THE YAKIMA AND
KITTITAS VALLEY. SNOW ACCUMULATIONS AT KYKM ARE ABOUT AN INCH PER
HOUR AND SHOW NO SIGNS OF LETTING UP BEFORE 10Z. SNOW SHOWERS WILL
PICK UP ACROSS KPSC...KALW...AND KPDT ANYTIME AFTER 06Z. EXPECT
FREQUENT CHANGES IN FLIGHT CONDITIONS FROM MVFR TO IFR OVER THE NEXT
18 TO 24 HOUR AS SHOWERS WILL LOWER CIGS AND VISIBILITIES AT ALL TAF
SITES INCLUDING KRDM AND KDLS. WARM AIR ALOFT MAY PROVIDE A PERIOD
OF FREEZING RAIN AT KPDT...KALW...KDLS...AND POSSIBLY KYKM. 76/89
&&
.PREV DISCUSSION... /ISSUED 240 PM PST MON DEC 14 2009/
SHORT TERM...TONIGHT THROUGH TUESDAY NIGHT...THE NEXT PACIFIC STORM
SYSTEM IS CURRENTLY MOVING ONSHORE. THE MAIN PUSH OF THE SYSTEM/S
ENERGY WILL DRIVE INTO BRITISH COLUMBIA...BUT THE WARM FRONT
ASSOCIATED WITH THIS SYSTEM WILL AFFECT THE PACNW THROUGH TUESDAY.
THIS IS A WET SYSTEM SO EXPECT MOST LOCATIONS TO SEE DECENT PRECIP
FROM THIS WARM FRONT. SNOW LEVELS WILL GRADUALLY RISE ACROSS OREGON
TONIGHT AND ACROSS WASHINGTON ON TUESDAY. AS SUCH SHOULD SEE SNOW
CHANGE TO RAIN TONIGHT IN CENTRAL AND NORTH-CENTRAL OREGON.
SHALLOW...MODIFIED ARCTIC AIR HAS SPILLED INTO THE COLUMBIA
BASIN...THOUGH IT APPEARS SHALLOW IN THE OREGON PORTION OF THE
BASIN. STILL AS THE SNOW LEVELS RISE COULD SEE WARM AIR NOSING OVER
THE COLD AIR AT THE SURFACE IN THE BASIN. THUS SHOULD SEE SNOW
CHANGE TO SLEET AND/OR FREEZING RAIN OVER THE NEXT 18 HOURS OR
SO...ESPECIALLY IN THE GORGE AND THE LOWER COLUMBIA BASIN. THE
POTENTIAL FOR FREEZING PRECIP ALONG THE BLUE MOUNTAIN FOOTHILLS WILL
BE LIMITED AS THE COLD AIR MASS IS SHALLOW AND SHOULD MIX OUT
TONIGHT (IN OREGON FIRST THEN IN WASHINGTON). WILL BE CONTINUING ALL
CURRENT WARNINGS AND ADVISORIES...AND WILL BE ADDING SNOW ADVISORIES
OR SNOW AND ICE ADVISORIES FOR MOST OF THE REMAINING ZONES. BY
TUESDAY NIGHT ONLY EXPECT WINTRY TYPE PRECIP TO LINGER OVER THE
CENTRAL WASHINGTON CASCADE EAST SLOPES...THE YAKIMA VALLEY AND THE
KITTITAS VALLEY. MOST OTHER LOCATIONS SHOULD RAIN WITH SNOW LEVELS
GENERALLY 4500 FEET OR HIGHER AS YET ANOTHER PACIFIC SYSTEM MOVES
THROUGH. WINDS WILL GENERALLY BE LIGHT THOUGH WINDY CONDITIONS CAN
BE EXPECTED IN THE GRANDE RONDE VALLEY THROUGH THE PERIOD. THIS WIND
SHOULD CAUSE THE BLOWING AND DRIFTING OF ANY SNOW THAT FALLS. 90
LONG TERM...WEDNESDAY THROUGH SATURDAY NIGHT. A SERIES OF
DISTURBANCES WILL RACE ACROSS THE TWO STATE AREA KEEPING OUR AREA IN
AN UNSETTLED WEATHER PATTERN INTO THE WEEKEND. THE STRONGEST STORM
SYSTEM WILL PUSH INTO THE AREA THURSDAY AND THURSDAY NIGHT. THE
CHALLENGE WILL BE WITH TEMPERATURES. A SW FLOW ALOFT SHOULD KEEP
TEMPS SLIGHTLY ABOVE FREEZING. HOWEVER A WEDGE OF COLD ALONG ALONG
THE EAST SLOPES OF THE WA CASCADES MAY KEEP SNOW IN THE FORECAST IN
THE YAKIMA AND KITTITAS VALLEYS AND IN THE AREA MOUNTAINS. A BRIEF
BREAK IN BETWEEN SYSTEMS EARLY FRIDAY SHOULD GIVE WAY TO A WARM
FRONT AND ANOTHER STORM THAT IS EXPECTED TO MOVE INTO THE REGION
FRIDAY AFTERNOON AND NIGHT WITH CLOUDS AND SHOWERS. 5H/LOW PRESSURE
WILL NEAR THE PACNW SATURDAY KEEPING SHOWERS IN THE FORECAST FOR THE
BEGINNING OF THE WEEKEND AND BREEZY CONDITIONS ARE POSSIBLE.
SUNDAY AND MONDAY...MODELS NOT IN GOOD AGREEMENT DURING THIS TIME.
MOST CONSISTENT MODELS APPEAR TO HAVE A RIDGE OF HIGH PRESSURE OVER
THE INLAND PACIFIC NORTHWEST AND A TROUGH OF LOW PRESSURE OFF THE
COAST. THIS WOULD LEAD TO A DRY FORECAST FOR THE EAST PORTION OF THE
FORECAST AREA AND PERHAPS SOME PRECIPITATION CLOSER TO THE CASCADES.
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 30 39 36 38 / 80 80 70 50
ALW 27 40 36 40 / 80 80 70 50
PSC 29 33 32 39 / 80 70 70 40
YKM 22 31 27 36 / 90 60 70 50
HRI 29 36 33 39 / 80 70 70 50
ELN 24 31 27 34 / 90 80 80 60
RDM 33 43 34 44 / 90 70 60 60
LGD 30 39 34 37 / 80 90 60 50
GCD 29 40 33 37 / 80 90 60 50
DLS 30 36 34 40 / 100 80 80 70
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY UNTIL 10 AM PST TUESDAY FOR ORZ041.
WINTER WEATHER ADVISORY UNTIL 4 PM PST TUESDAY FOR ORZ049-050-
502-503-506.
WINTER WEATHER ADVISORY UNTIL NOON PST TUESDAY FOR ORZ044-504-
505.
WINTER WEATHER ADVISORY UNTIL 6 AM PST TUESDAY FOR ORZ501.
WA...WINTER STORM WARNING UNTIL 6 PM PST TUESDAY FOR WAZ026-027-501.
WINTER WEATHER ADVISORY UNTIL 10 AM PST TUESDAY FOR WAZ024-502.
WINTER WEATHER ADVISORY UNTIL 4 PM PST TUESDAY FOR WAZ030.
WINTER WEATHER ADVISORY UNTIL NOON PST TUESDAY FOR WAZ028.
WINTER WEATHER ADVISORY UNTIL 6 AM PST TUESDAY FOR WAZ029.
&&
THREAT INDEX
TUESDAY : RED
WEDNESDAY : GREEN
THURSDAY : GREEN
GREEN: NONE OR LIMITED NEED FOR WATCHES, WARNINGS, OR ADVISORIES.
YELLOW: A FEW WATCHES, WARNINGS, OR ADVISORIES POSSIBLE OR IN EFFECT.
RED: NUMEROUS WATCHES, WARNINGS, OR ADVISORIES POSSIBLE OR IN EFFECT.
FOR ADDITIONAL WEATHER INFORMATION, CHECK OUR WEB SITE AT...
WWW.WEATHER.GOV/PENDLETON
$$
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