Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 221735 AAA
AFDPDT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
1035 AM PDT FRI MAY 22 2015

UPDATED AVIATION DISCUSSION

.UPDATE...ABUNDANT MOISTURE CONTINUES TO RAP AROUND A LOW PRESSURE
SYSTEM OVER CALIFORNIA AND INTO OUR AREA. COMBINING THIS WITH
DAYTIME HEATING WILL CONTINUE TO PRODUCE SHOWERS AND THUNDERSTORMS
THIS AFTERNOON. PWAT REMAINS HIGH AND SOME OF THE STORMS MAY BECOME
STRONG AND PRODUCE HEAVY RAIN ESPECIALLY OVER THE EASTERN HALF OF
THE REGION THAT INCLUDES THE BLUE/WALLOWA MTNS ALONG WITH THE JOHN
DAY HIGHLANDS WHERE A FLASH FLOOD WATCH REMAINS IN EFFECT. IN
ADDITION SOME MODIFICATIONS WERE DONE TO AFTN TEMPS AND THE PRESENT
SHORT TERM FORECAST APPEARS ON TRACK FOR NOW.

&&

.AVIATION...18Z TAFS. IT WILL PREDOMINANTLY REMAIN VFR FOR THE NEXT
24 HOURS...BUT CIGS WILL BE 3500-8000 FEET AGL AND THERE MAY BE
PERIODS OF MVFR WITH SHOWERS AND THUNDERSTORMS.  WEB CAMS NEAR KRDM
AND KBDN ARE SHOWING LOW LYING SCUD CLOUDS WITH BASES AROUND 1500
FEET.  TOWERING CUMULUS AND/OR CB CLOUDS WILL LIKELY DEVELOP AS THE
DAY PROGRESSES...AND THERE MAY BE IN CLOUD LIGHTNING OR CTG
LIGHTNING. WINDS WILL HAVE A WESTERLY COMPONENT THIS AFTERNOON AT 5-
15 KT...EXCEPT 15 TO 25 KT AT KDLS.  WISTER

&&

.PREV DISCUSSION... /ISSUED 300 AM PDT FRI MAY 22 2015/

SHORT TERM...TODAY THROUGH SATURDAY NIGHT...A BROAD UPPER LEVEL
TROUGH WILL REMAIN OVER THE REGION THROUGH MUCH OF THIS PERIOD. THE
AIR MASS ACROSS THE REGION WILL REMAIN MOIST AND UNSTABLE TODAY.
INCREASING WEST FLOW FROM THE GORGE SOUTH INTO CENTRAL OREGON WILL
INCREASINGLY LIMIT SHOWER AND THUNDERSTORM CHANCES IN THESE AREAS
LATE THIS AFTERNOON INTO THE EVENING. ELSEWHERE SCATTERED TO
WIDESPREAD SHOWERS WITH ISOLATED TO SCATTERED THUNDERSTORMS WILL BE
POSSIBLE, ESPECIALLY IN THE AFTERNOON AND EVENING. STORM MOTION WILL
BE RELATIVELY SLOW AND DECENT RAINFALL WILL BE POSSIBLE, ESPECIALLY
FROM THUNDERSTORMS. AS THE MAIN SHOWER AND STORM FOCUS LOOKS TO BE
OVER THE EASTERN MOUNTAIN ZONES WILL CONTINUE THE FLASH FLOOD WATCH
COVERING THE OCHOCO-JOHN DAY HIGHLANDS NORTH TO THE BLUE MOUNTAINS
AND NORTHEAST TO WALLOWA COUNTY. A WEAK LOW LOOKS TO SLIDE SOUTH-
SOUTHEAST ACROSS THE REGION TONIGHT. AS A RESULT A DEFORMATION
PRECIP BAND MAY DEVELOP NORTH AND EAST OF THE LOW. AS SUCH WILL KEEP
40-60 PERCENT POPS GOING FROM SOUTH CENTRAL WASHINGTON INTO
NORTHEAST AND EAST CENTRAL OREGON TONIGHT. WESTERLY LOW LEVEL FLOW
WILL CONTINUE TO INCREASE SATURDAY. THUS THE AIR MASS OVER THE
REGION WILL BECOME A BIT DRIER, LIMITING THE AREAS TO BE AFFECTED BY
SHOWERS AND THUNDERSTORMS SATURDAY AFTERNOON AND EVENING. AT THIS
TIME EXPECT SHOWERS/STORMS TO BE MAINLY OVER SOUTH CENTRAL
WASHINGTON AND THE EASTERN MOUNTAIN ZONES. 90

LONG TERM...SUNDAY THROUGH FRIDAY...AN OVERALL DRYING TREND WILL
OCCUR ON SUNDAY WITH NWLY FLOW REGIME BECOMING AT LEAST BRIEFLY
ESTABLISHED OVER THE AREA. THERE WILL STILL BE A SLIGHT CHANCE FOR
AFTERNOON THUNDERSTORMS OVER THE FAR EAST AND ALONG THE WASHINGTON
CASCADE EAST SLOPES. ON MONDAY AN UPPER LOW WILL DROP SWD FROM
BRITISH COLUMBIA INTO WASHINGTON AND BRING A SLIGHT CHANCE FOR
AFTERNOON THUNDERSTORMS EASTERN MOUNTAINS AND WASHINGTON CASCADES.
FROM TUESDAY ONWARD THE MEDIUM RANGE MODELS DIVERGE ON THE HANDLING
OF THE UPPER LOW. THE GFS MEANDERS THE LOW OVER THE FORECAST AREA
KEEPING A CHANCE FOR SHOWERS AND A SLIGHT CHANCE FOR THUNDERSTORMS
EACH DAY THROUGH FRIDAY...WHEREAS THE ECMWF MOVES THE LOW OUT AND
REPLACES IT WITH DRY NW FLOW. FOR NOW HAVE TRENDED THIS FORECAST
UPDATE TOWARD THE GFS WHICH IS IN LINE WITH THE PREVIOUS FORECAST TO
MAINTAIN CONTINUITY. TEMPERATURES WILL BE WARM THROUGH THE PERIOD
WITH HIGHS UPPER 70S TO MID 80S LOWER ELEVATIONS WITH 60S TO LOWER
70S MOUNTAINS.



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  74  54  73  51 /  50  40  40  20
ALW  76  56  75  55 /  50  50  30  20
PSC  83  58  80  54 /  40  40  30  10
YKM  78  59  79  55 /  60  40  40  20
HRI  80  57  78  53 /  50  40  30  10
ELN  79  56  78  54 /  60  40  40  20
RDM  68  44  68  39 /  40  20  20  10
LGD  69  54  68  50 /  80  60  40  30
GCD  68  49  69  45 /  80  60  30  20
DLS  76  57  70  54 /  20  20  20  10

&&

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

WA...FLASH FLOOD WATCH THROUGH THIS EVENING FOR WAZ030.

&&

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

$$

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