Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 052036
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
136 PM PDT THU MAY 5 2016

.SHORT TERM...TONIGHT THROUGH SATURDAY NIGHT...ACTIVE WEATHER
PATTERN CONTINUES WITH A LARGE UPPER LOW OFF THE COAST AND A
DEVELOPING CLOSED LOW OVER SOUTHERN CALIFORNIA. AN UPPER RIDGE IS
MOVING TO THE NORTHEAST AND OUT OF THE REGION. THERE IS ABUNDANT
MOISTURE AND INSTABILITY BEING PULLED NORTHWARD IN A SOUTHERLY FLOW
ALOFT INTO THE FORECAST AREA. SO FAR THIS AFTERNOON CLOUDS HAVE KEPT
CONVECTION TO A MINIMUM WITH SOME WEAK STORMS SOUTH OF THE CWA IN
LAKE AND KLAMATH COUNTIES. EXPECT AS AFTERNOON HEATING CONTINUES
THUNDERSTORMS WILL BEGIN TO DEVELOP...ESPECIALLY OVER THE EASTERN
AND NORTHEAST MOUNTAINS WHERE TEMPERATURES ARE THE WARMEST AND THERE
ARE THE FEWEST CLOUDS. IN ADDITION THE EASTERN AND NORTHEAST
MOUNTAINS IS WHERE THE BEST DYNAMICS ARE TO PRODUCE FORCING TO
TRIGGER THUNDERSTORM DEVELOPMENT. SHEAR VALUES ARE AROUND 40-50 KTS
WITH PWAT WATER VALUES NEAR OR JUST OVER AN INCH. IN
ADDITION HELICITY VALUES ARE AROUND 300 M2/S2 AND NEGATIVE LI`S FROM
-2 TO -5 C. THESE ARE ALL VERY FAVORABLE PARAMETERS FOR THE
DEVELOPMENT OF THUNDERSTORMS...SOME POSSIBLY SEVERE WITH ORGANIZED
ROTATION TO THEM. DUE TO THE HIGH WATER CONTENT OF THE ATMOSPHERE
HAVE A FLASH FLOOD WATCH IN EFFECT FROM THE OCHOCO-JOHN DAY
HIGHLANDS NORTHEAST THROUGH THE NORTHEAST MOUNTAINS AND WALLOWA
COUNTY THROUGH THIS EVENING. IN PARTICULAR CONCERN IS THE BURN SCAR
FROM LAST YEARS CANYON CREEK FIRE IN SOUTHERN GRANT COUNTY. ELSEWHERE
THERE MAY POSSIBLY BE MUD OR ROCK SLIDES DUE TO VERY HEAVY RAINFALL
IN STEEP TERRAIN. THUNDERSTORMS WILL DISSIPATE THIS EVENING AFTER
DARK WITH THE LOSS OF SURFACE HEATING. ON FRIDAY THE UPPER LOW OVER
SOUTHERN CALIFORNIA WILL SHIFT EASTWARD INTO THE SOUTHERN GREAT
BASIN. THIS WILL CAUSE A WRAP AROUND NORTHEAST FLOW OVER THE
FORECAST AREA. WHILE THIS IS NOT ALWAYS CONDUCIVE FOR THUNDERSTORM
DEVELOPMENT...THERE COULD STILL BE THUNDERSTORM DEVELOPMENT DUE TO
THE AMOUNT OF LINGERING INSTABILITY AND ABUNDANT MOISTURE IN THE
ATMOSPHERE. HAVE THUNDERSTORMS IN FRIDAY`S FORECAST FOR THE
SOUTHEAST THIRD OF THE CWA FOR FRIDAY AFTERNOON AND EVENING. THE
UPPER LOW WILL CONTINUE TO MOVE TO THE EAST SATURDAY AND SATURDAY
NIGHT WHICH WILL CAUSE A GRADUAL DECREASE IN CONVECTIVE DEVELOPMENT
AND STABILIZATION OF THE ATMOSPHERE. IT WILL WARM UP AGAIN ON FRIDAY
AND SATURDAY COMPARED TO TODAY`S HIGHS SO FAR WITH LOW ELEVATION
TEMPERATURES IN THE LOWER TO MID 80S...WITH 60S AND 70S IN THE
MOUNTAINS. WINDS WILL INCREASE THIS AFTERNOON AND IT WILL BECOME
LOCALLY BREEZY AND THEN THEY WILL BECOME LIGHT OVERNIGHT AND THEN
INCREASE AGAIN ON FRIDAY AND SATURDAY AFTERNOONS AND EVENINGS. 88

.LONG TERM...SUNDAY THROUGH THURSDAY...MODELS ARE IN GOOD AGREEMENT
WITH RESPECT TO BRINGING ANOTHER UPPER LEVEL LOW OVER PORTIONS OF
THE FORECAST AREA SUNDAY. THIS SYSTEM IS EXPECTED TO MAINLY AFFECT
SOUTHEAST WASHINGTON AND NORTHEAST OREGON AS IT SLOWLY SLIPS INTO
IDAHO AND MONTANA MONDAY NIGHT.  BY TUESDAY...DRIER NORTHERLY UPPER
LEVEL FLOW IN THE WAKE OF THE AFOREMENTIONED LOW SHOULD RESULT IN
DRIER WEATHER OVER THE REGION.  BY WEDNESDAY...THE MODELS BEGIN TO
DIFFER IN THEIR HANDLING OF THE UPPER LEVEL PATTERN.  GFS TRIES TO
BRING A DISTURBANCE OVER THE AREA WHILE ECMWF KEEPS DRIER
NORTHWESTERN FLOW.  AT THIS TIME...PREFER THE DRIER ECMWF FORECAST
SO WILL LEAN TOWARDS IT.  DAYTIME HIGH TEMPERATURES ARE EXPECTED TO
REMAIN ABOVE NORMAL THROUGH THE PERIOD.  EARLE

&&

.AVIATION....AVIATION...00Z TAFS...VFR CONDITIONS SHOULD PREVAIL
OVER THE NEXT 24 HOURS. ANOTHER ROUND OF CONVECTIVE WEATHER IS
EXPECTED ACROSS THE REGION TONIGHT. KBDN, KRDM, KPDT AND KALW WILL
HAVE THE GREATEST CHANCE OF THUNDERSTORMS THROUGH THIS EVENING. SOME
OF THE STRONGER STORMS COULD PRODUCE BRIEF MVFR CONDITIONS.  AREAL
COVERAGE WILL DECREASE TOMORROW AS THE SYSTEM MOVES FARTHER AWAY
FROM THE AREA.  WINDS WILL GENERALLY BE LESS THAN 15 KTS. WINDS WILL
DECREASE OVERNIGHT AND INCREASE TO 10-20 KTS BY FRIDAY AFTERNOON.
WINDS COULD BE VARIABLE AND GUSTY NEAR THUNDERSTORMS. EARLE

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  56  79  56  81 /  30  20  10  10
ALW  55  80  55  82 /  20  20  10  10
PSC  56  84  56  86 /  20  10  10   0
YKM  53  85  53  86 /  20  10  10   0
HRI  53  82  53  85 /  20  10  10  10
ELN  50  82  50  83 /  20  10  10   0
RDM  42  74  42  80 /  50  20  30  10
LGD  46  74  46  77 /  60  40  30  20
GCD  49  71  49  77 /  70  50  40  20
DLS  53  85  53  88 /  20  10  10   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...FLASH FLOOD WATCH UNTIL 10 PM PDT THIS EVENING FOR ORZ049-050-
     502-503-505-506.

WA...NONE.

&&

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

$$

88/81/81



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