National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS66 KPDT 170332
AFDPDT

AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE PENDLETON OR
832 PM PDT THU MAY 16 2013

.UPDATE...CURRENT FORECAST REMAINS ON TRACK WITH LITTLE CHANGES.
UPPER LEVEL TROUGH CONTINUES TO LINGER OVER THE PACIFIC NORTHWEST.
SHOWERS AND A FEW ISOLATED THUNDERSTORMS HAVE RESULTED...AND ARE
EXPECTED AGAIN TOMORROW AFTERNOON AND EVENING.  POPS HAVE BEEN
REDUCED SLIGHTLY FOR THE OVERNIGHT TO EARLY MORNING HOURS AS THE
ATMOSPHERE BRIEFLY STABILIZES.  MODELS ARE STILL TARGETING THE
AFTERNOON INSTABILITY TO BE OVER THE MOUNTAINS OF NORTHEAST OREGON
TOMORROW. THEREFORE SHOWERS AND A SLIGHT CHANCE OF THUNDERSTORMS
REMAIN IN THE FORECAST.  WEBER

&&

.PREV DISCUSSION... /ISSUED 246 PM PDT THU MAY 16 2013/

SHORT TERM...UPDATE...A BROAD UPPER LEVEL TROUGH WILL LINGER OVER
THE WESTERN U.S. THROUGH FRIDAY. WEAK DISTURBANCES ROTATING THROUGH
THE TROUGH WILL KEEP VARYING AMOUNTS OF SHOWERS GOING THROUGH
FRIDAY. BEST CHANCES OF SHOWERS THROUGH TONIGHT WILL BE ACROSS
DESCHUTES COUNTY THIS EVENING, AND OVER CROOK AND GRANT COUNTIES
TONIGHT. A STRAY THUNDERSTORM MAY BE POSSIBLE LATE THIS AFTERNOON
INTO EARLY EVENING OVER THE NORTHERN BLUE MOUNTAINS AND WALLOWA
COUNTY. RAIN FALL HAS BEEN COOLING SURFACE TEMPS IN DESCHUTES
COUNTY, SO DO NOT EXPECT THUNDER THERE AT THIS TIME. BEST CHANCES OF
SHOWERS WILL SHIFT TO THE BLUE MOUNTAINS SOUTH TO GRANT COUNTY AND
EAST INTO WALLOWA COUNTY FRIDAY AS THE LAST WAVE PUSHES THE TROUGH
AXIS EAST TOWARDS IDAHO AND EASTERN NEVADA. THESE AREAS MAY ALSO SEE
ISOLATED THUNDERSTORMS IN THE AFTERNOON AND EVENING. SHOWER CHANCES
WILL DECREASE OVERNIGHT FRIDAY NIGHT INTO SATURDAY MORNING. ANOTHER
TROUGH WILL DIG INTO THE REGION SATURDAY AND SATURDAY NIGHT. THIS
SYSTEM WILL INCREASE SHOWER CHANCES, ESPECIALLY FROM THE BLUE
MOUNTAINS SOUTHWEST INTO CENTRAL OREGON SATURDAY AFTERNOON AND
EVENING. WINDS WILL INCREASE ACROSS THE BASIN, IN THE GORGE AND THE
KITTITAS VALLEY SATURDAY DUE TO THE ARRIVAL OF THIS NEXT TROUGH.
NORTHWEST FLOW WILL KEEP SOME SHOWERS GOING OVER THE MOUNTAINS ON
SUNDAY DUE TO UPSLOPE AFFECTS. OTHERWISE BUILDING HIGH PRESSURE WILL
DRY OUT THE LOWER ELEVATIONS. LOW TEMPS WILL RUN NEAR SEASONAL,
WHILE HIGH TEMPS WILL RUN NEAR OR SLIGHTLY BELOW SEASONAL THROUGH
THE PERIOD. 90

LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...BOTH THE GFS AND ECMWF
ARE FORECASTING AN UPPER RIDGE PATTERN SUNDAY NIGHT WITH FAIR
CONDITIONS ACROSS MOST OF THE CWA. THE EXCEPTION WILL BE OVER THE
EASTERN ZONES WHERE THERE MAY BE SOME CLOUDINESS AND A FEW SHOWERS
FROM A DEPARTING WEATHER SYSTEM. THE HIGH PRESSURE ALOFT IS EXPECTED
TO PERSIST THROUGH MONDAY. AFTER THAT THE NEXT WEATHER SYSTEM WILL
BEGIN TO MOVE INTO THE PACIFIC NORTHWEST. THE GFS MODEL WANTS TO
BRING IN THE TROUGH FIRST WHILE THE ECMWF KEEPS AN UPPER RIDGE OVER
THE CWA ON MONDAY. HOWEVER BOTH MODELS COME INTO PHASE WITH THE
DEVELOPMENT OF A LARGE CLOSED UPPER LOW BY LATE TUESDAY WITH THE GFS
MUCH FURTHER SOUTH THAN THE ECMWF WITH THE POSITION OF THE UPPER
LOW. THE ECMWF HAS BEEN HAVING A BETTER TRACK RECORD DURING THE
RECENT FEW SYSTEMS AND THEREFORE AM LEANING TOWARD THE ECMWF
SOLUTION WITH THE LOW FURTHER NORTH ALONG THE BC COAST. THIS WILL
CAUSE A SOUTHWEST FLOW OVER THE CWA WHICH WILL HELP TO TRANSPORT
MOISTURE AND INCREASING INSTABILITY OVER THE REGION. HOWEVER...BOTH
SOLUTIONS MEANS A COOLING TREND WHICH WILL TAKE PLACE WITH FALLING
HEIGHTS AND THICKNESSES...ESPECIALLY THE GFS AS THE UPPER LOW CENTER
COMES MUCH CLOSER TO THE AREA. THIS PATTERN OF UPPER LOWS WILL
PERSIST THROUGHOUT THE REMAINDER OF THE EXTENDED FORECAST PERIOD...
THOUGH WITH VERY SIGNIFICANT DIFFERENCES IN THE PLACEMENT OF THE
UPPER LOWS BETWEEN THESE TWO MODELS. AS SUCH DID NOT MAKE TOO MANY
CHANGES IN THE EXTENDED FORECAST PERIOD DUE TO THE UNCERTAINTY.
HOWEVER THERE IS BETTER AGREEMENT BETWEEN THE TWO MODELS BY THURSDAY
AND THEN THE MODELS DIVERGE AGAIN FURTHER OUT IN THE EXTENDED
FORECAST PERIOD WITH THE ECMWF BEING MUCH MORE ORGANIZED AND DEEPER
THAN THE GFS AND AM LEANING TOWARD THAT SCENARIO. THE RESULT WILL BE
COOL CONDITIONS WITH PERIODIC SHOWERS. EVEN THOUGH TEMPERATURES WILL
BE ON THE COOL SIDE THEY WILL NOT BE MUCH COOLER THAN NORMAL AND IN
FACT THEY WILL BE CLOSE TO NORMAL FOR THIS TIME OF YEAR. 88

AVIATION...06Z TAFS...VFR CONDITIONS ARE EXPECTED TO PREVAIL OVER
THE NEXT 24 HOURS.  HOWEVER...SOME TAF SITES MAY EXPERIENCE BRIEF
MVFR CONDITIONS DUE TO LOWERED CIGS FROM SHOWERS.  SHOWERS WILL
TAPER OFF OVERNIGHT TONIGHT AND PICK BACK UP TOMORROW LATE MORNING
TO EARLY AFTERNOON.  WINDS WILL BE BREEZY AFTER 21Z AT JUST ABOUT
ALL TAF SITES OTHER THAN KPSC AND KYKM.  EXPECT WINDS 5 TO 15KTS
WITH 20 TO 25KTS AT TIMES.  WEBER

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  50  70  47  68 /  10  20  20  20
ALW  53  72  50  70 /  20  20  20  20
PSC  52  77  49  76 /  10  10  10  10
YKM  47  74  44  72 /  10  10  10  20
HRI  50  75  48  74 /  10  10  10  20
ELN  49  71  48  68 /  20  10  10  20
RDM  42  64  38  63 /  40  20  10  30
LGD  46  64  44  62 /  20  40  30  20
GCD  43  66  41  64 /  40  50  30  20
DLS  53  71  49  68 /  30  10  10  20

&&

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

THREAT INDEX
FRIDAY : GREEN
SATURDAY : GREEN
SUNDAY : 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

$$

89/88/89