Severe Thunderstorm Warning 3, NWS Pendleton, OR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
337 PM PDT MON MAY 18 2009

UPDATED AVIATION DISCUSSION

.SHORT TERM...TONIGHT THROUGH WEDNESDAY.  A COLD FRONT IS
APPROACHING THE COAST THIS AFTERNOON...AND MOISTURE AHEAD OF THE
FRONT IS INCREASING ACROSS CENTRAL OREGON.  THIS IS EVIDENT BY
CUMULUS CLOUDS ON VISIBLE.  RIGHT NOW...THE CAP IS PRETTY STRONG AND
THERE HAS BEEN LITTLE VERTICAL DEVELOPMENT OF THE CLOUDS.  THE
QUESTION THAT REMAINS IS WHETHER THE CAP WILL BREAK LEADING TO
CONVECTION AND WILL THESE STORMS BE STRONG OR SEVERE.  BELIEVE
ADDITIONAL DAYTIME HEATING ALONG WITH A VERY WEAK DISTURBANCE OVER
SOUTH CENTRAL OREGON AS SEEN ON WATER VAPOR LOOPS WILL BREAK THE CAP
AND LEAD TO LATE AFTERNOON AND EVENING THUNDERSTORMS.  THE MODERATE
VERTICAL SHEAR WILL HELP SUSTAIN UPDRAFTS FOR THE POTENTIAL OF
STRONG THUNDERSTORMS...AND ONE OR TWO OF THE STORMS COULD PRODUCE
LARGE HAIL AND/OR STRONG OUTFLOWS.

THE COLD FRONT WILL SWEEP EAST OF THE CASCADES LATE TONIGHT AND
TUESDAY.  THERE COULD BE ISOLATED THUNDERSTORMS AHEAD OF THE FRONT
IN AREAS EAST OF THE BLUE MOUNTAINS.  OTHERWISE...THE MAIN IMPACT
FROM THIS FRONT WILL BE WINDS.  TIGHT PRESSURE GRADIENTS WILL LEAD
TO WINDY CONDITIONS AND PATCHY BLOWING DUST ACROSS THE COLUMBIA
BASIN AND SURROUNDING VALLEYS.  CONFIDENCE IS HIGH THAT WINDS IN THE
KITTITAS VALLEY WILL BE 30-40 MPH WHICH WARRANTS A WIND ADVISORY.
THE WIND ADVISORY WILL BE ISSUED DURING THE AFTERNOON PACKAGE.
WINDS WILL DECREASE OVERNIGHT.  TEMPERATURES ON TUESDAY WILL BE MUCH
COOLER THAN TODAY...ABOUT 20-25 DEGREES COOLER.  TEMPERATURES
TUESDAY NIGHT ARE EXPECTED TO BE IN THE LOWER 30S TO MID 40S...SO
MANY PEOPLE WILL BE CHANGING FROM AIR CONDITIONERS TODAY TO HEATERS
TUESDAY NIGHT. AT THIS TIME...IT DOES NOT APPEAR THAT TEMPS IN THE
BASIN AND ADJACENT VALLEYS WILL FALL TO BELOW FREEZING.

NO MAJOR WEATHER CONCERNS ARE EXPECTED ON WEDNESDAY.  THE AREA WILL
BE UNDER A DRY WESTERLY FLOW WITH NEAR SEASONAL TEMPERATURES.
JOHNSON

.LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY...MODELS ARE IN GOOD
AGREEMENT TOWARD THE END OF THE WEEK. A WESTERLY FLOW WILL BE OVER
THE REGION WITH DRY AND WARM CONDITIONS. MAXIMUM TEMPERATURES WILL
WARM TO THE MID TO UPPER 70S FOR THE LOWER ELEVATIONS BY FRIDAY WITH
UPPER 60S TO LOWER 70S IN THE HIGHER ELEVATIONS. DURING THE
WEEKEND...THE MODELS DIVERGE IN THE DETAILS...THOUGH BOTH MODELS ARE
KEEPING THE REGION DRY INTO NEXT WEEK. THE GFS MODEL BRINGS A
SHORTWAVE TROUGH THROUGH THE PACIFIC NORTHWEST FRIDAY NIGHT AND
SATURDAY WHILE THE EUROPEAN MODEL KEEPS A WESTERLY FLOW. HAVE LEANED
MORE TOWARD THE EUROPEAN AS IT HAS BEEN MORE CONSISTENT. THIS WILL
KEEP THE REGION UNDER A DRY WESTERLY FLOW THROUGH THE WEEKEND. DMH

&&

.AVIATION...00Z TAFS...CUMULUS WILL CONTINUE TO DEVELOP ACROSS
CENTRAL OREGON AND THE MOUNTAINS OF NORTHEAST OREGON AS WELL AS
ALONG THE CENTRAL WASHINGTON CASCADES. ISOLATED THUNDERSTORMS ARE
POSSIBLE LATER THIS AFTERNOON AND EVENING IN CENTRAL OREGON AND
ALONG THE BLUE MOUNTAINS. SURFACE WINDS WILL BE BREEZY THIS
AFTERNOON AT KDLS AND KPDT BEFORE DECREASING OVERNIGHT. A COLD FRONT
WILL BRING AN INCREASE IN LOW CLOUDS AND A CHANCE OF SHOWERS EARLY
TUESDAY MORNING. SURFACE WINDS WILL INCREASE BY TUESDAY AFTERNOON
FOR ALL TAF SITES. DMH

&&

.HYDROLOGY...A FLOOD WATCH WAS ISSUED EARLIER FOR THE NACHES RIVER
NEAR NACHES.  THE RIVER IS WELL ABOVE BANKFUL AND IS FORECAST TO
RISE TO FLOOD STAGE BY TUESDAY MORNING.  HYDROLOGIC STATEMENTS HAVE
ALSO BEEN ISSUED FOR THE YAKIMA RIVER AND GRANDE RONDE RIVER.  SNOW
MELT RUNOFF CONTINUES TO CAUSE HIGH WATER LEVELS...AND LEVELS WILL
REMAIN HIGH THROUGH MOST OF THE WEEK.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  57  69  43  69 /  10  30  10   0
ALW  59  69  46  70 /  10  30  10   0
PSC  59  76  45  73 /   0  10  10   0
YKM  52  67  41  70 /  10  20  10   0
HRI  58  72  44  72 /  10  20  10   0
ELN  52  63  41  68 /  10  20  10   0
RDM  48  63  30  69 /  10  20  10   0
LGD  53  62  40  66 /  20  30  20   0
GCD  53  63  39  67 /  20  20  10   0
DLS  56  64  44  73 /  10  30  10   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...WIND ADVISORY FROM 10 AM TO 10 PM PDT TUESDAY FOR WAZ026.
     FLOOD WATCH FOR TUESDAY THROUGH WEDNESDAY FOR THE NACHES RIVER
      NEAR NACHES IN WAZ027.

&&

TI:YGG

FOR ADDITIONAL WEATHER INFORMATION, CHECK OUR WEB SITE AT...
WWW.WEATHER.GOV/PENDLETON

85/84/84

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