Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 202247 AAA
AFDPDT

AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE PENDLETON OR
348 PM PDT SAT SEP 20 2014

UPDATED AVIATION DISCUSSION

.SHORT TERM...TONIGHT THROUGH TUESDAY...THE UPPER LEVEL HIGH
PRESSURE RIDGE WILL CONTINUE TO KEEP CONDITIONS FAIR ACROSS THE
PACIFIC NORTHWEST THROUGH SUNDAY. THIS RIDGE WILL BEGIN TO SHIFT
EAST SUNDAY THOUGH IN RESPONSE TO AN UPPER TROUGH OVER THE EASTERN
PACIFIC. OFFSHORE SURFACE FLOW WILL CONTINUE INTO SUNDAY, THOUGH
THIS FLOW WILL BEGIN TO SHIFT TOWARDS ONSHORE LATE IN THE DAY. AN
UPPER LOW OVER CALIFORNIA WILL DRIFT NORTHEAST THROUGH NEVADA INTO
SOUTHERN IDAHO SUNDAY AND SUNDAY NIGHT. SOME OF THE MOISTURE
ASSOCIATED WITH THIS SYSTEM MAY TRY TO MIGRATE NORTH INTO THE PACNW
LATE SUNDAY AND SUNDAY NIGHT. AT THIS TIME EXPECT TO SEE SOME
BATCHES OF HIGHER BASED CLOUDS DRIFT INTO PORTIONS OF THE AREA BUT
DO NOT EXPECT ANY PRECIP THROUGH SUNDAY NIGHT. UPPER FLOW WILL
BECOME SOUTHWESTERLY BY MONDAY, AND WILL CONTINUE AS SUCH INTO
TUESDAY. A WEAK DISTURBANCE MAY TAP THE MOISTURE FROM THE ABOVE
MENTIONED UPPER LOW AND CAUSE A FEW LIGHT SHOWERS OVER CASCADE EAST
SLOPES MONDAY MORNING. STILL APPEARS TO BE ENOUGH INSTABILITY MONDAY
AFTERNOON AND EVENING TO CAUSE A FEW THUNDERSTORMS OVER OUR EASTERN
MOUNTAIN ZONES. ALSO A FEW SHOWERS MAY OCCUR ALONG AND NEAR THE
CASCADE CREST MONDAY AFTERNOON AND EVENING. TUESDAY LOOKS TO BE
GENERALLY DRY, THOUGH A FEW SHOWERS MAY LINGER INTO THE NORTHEAST
MOUNTAIN ZONES AND ALONG THE WASHINGTON CASCADE EAST SLOPES.
TEMPERATURES WILL REMAIN WARMER THAN SEASONAL THROUGH THIS PERIOD.
90

.LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...A DEEP LOW PRESSURE
TROUGH DEVELOPING OFFSHORE WILL GRADUALLY BREAK DOWN THE STRONG HIGH
PRESSURE RIDGE OVER THE PACIFIC NW. THE 12Z ECMWF IS DEEPER WITH THE
OFFSHORE LOW COMPARED TO THE 12Z GFS AND IS ALSO FASTER AT BREAKING
DOWN THE RIDGE. FOR NOW...WILL COMPROMISE BETWEEN BOTH SOLUTIONS AND
INCREASE RAINFALL FROM THE WEST TUESDAY NIGHT AND WEDNESDAY. THE
CHANCE OF PRECIPITATION WILL INCREASE WEDNESDAY NIGHT AND THURSDAY.
THE ECMWF IS ALSO FASTER WITH A SHORTWAVE TROUGH AND ITS ASSOCIATED
WEAK SURFACE COLD FRONT ON THURSDAY. LAPSE RATES WILL STEEPEN ON
THURSDAY THAT WILL BRING A SLIGHT CHANCE OF THUNDERSTORMS TO THE
EASTERN FORECAST AREA. A BROAD UPPER TROUGH WILL REMAIN OVER WA/OR
FRIDAY FOR CONTINUED SHOWERS. MARGINALLY UNSTABLE CONDITIONS ARE
EXPECTED...AND THE THREAT OF THUNDERSTORMS IS MINIMAL. BY THE END OF
SEPTEMBER...THE AMOUNT OF DAYLIGHT DECREASES TO UNDER 12 HOURS WITH
LESS TIME FOR SURFACE HEATING SO IT`S HARD TO ANTICIPATE
THUNDERSTORM ACTIVITY WITH THIS TYPE OF PATTERN IN LATE SEPTEMBER.
THE ECMWF AND GFS DIFFER SIGNIFICANTLY IN DAY 7. IF THE ECMWF
VERIFIES...SHOWERS WILL CONTINUE UNDER A BROAD CYCLONIC FLOW ALOFT
NEXT SATURDAY. THE GFS PUSHES THE TROUGH EASTWARD FOLLOWED BY A
STRENGTHENING HIGH PRESSURE RIDGE FOR DRY AND WARMER CONDITIONS.
BOTH THE ECMWF AND GEFS ENSEMBLES HAVE A HIGH DEGREE OF SPREAD LATE
IN THE PERIOD...SO WILL KEEP POPS AND TEMPERATURES NEAR CLIMATOLOGY.
WISTER

&&

.AVIATION...00Z TAFS...CLEAR SKIES AND WINDS LESS THAN 15 KTS WILL
CONTINUE THROUGH MIDNIGHT.  THIN HIGH CIRRUS CLOUDS WILL SPREAD EAST
OF THE CASCADES SUNDAY MORNING ALONG WITH FEW-SCT ALTOCUMULUS CLOUDS
DURING THE DAY.  WINDS ON SUNDAY WILL REMAIN AOB 15 KTS.  WISTER

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  53  88  57  85 /   0   0   0  10
ALW  58  88  63  86 /   0   0   0  10
PSC  52  89  56  87 /   0   0   0  10
YKM  53  86  56  83 /   0   0   0  10
HRI  49  90  54  88 /   0   0   0  10
ELN  49  90  57  85 /   0   0  10  10
RDM  43  89  48  83 /   0   0   0  10
LGD  44  87  51  84 /   0   0   0  20
GCD  48  88  51  84 /   0   0  10  20
DLS  55  90  59  84 /   0   0   0  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
&&

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

$$

90/85/85






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