Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 010237
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
737 PM PDT SAT APR 30 2016

.UPDATE...A WEAK WEATHER DISTURBANCE OVER NORTHEAST OREGON...
SOUTHEAST WASHINGTON AND NORTHERN IDAHO IS CAUSING SOME WRAP AROUND
MOISTURE AND INSTABILITY OVER THE EXTREME NORTHEAST PORTION OF THE
CWA. THERE ARE A FEW SHOWERS AS A RESULT BUT THEY ARE WEAK AND ARE
NOT PRODUCING ANY LIGHTNING. THESE SHOULD DECREASE RAPIDLY AFTER
DARK. WILL UPDATE THE FORECAST TO REMOVE PRECIPITATION FROM THE
FORECAST LATER THIS EVENING FOR TONIGHT. A HIGH PRESSURE RIDGE ALOFT
WILL BUILD OVER THE REGION LATE TONIGHT AND ON SUNDAY FOR FAIR
WEATHER AND A WARMING TREND FOR SUNDAY WITH DRY CONDITIONS. THIS
WILL PERSIST THROUGH SUNDAY NIGHT AND MONDAY MORNING. THEN THE FLOW
WILL BECOME SOUTHERLY MONDAY AFTERNOON AS THE UPPER RIDGE MOVES OFF
TO THE NORTHEAST AND AN UPPER TROUGH OFF THE COAST MOVES TOWARD THE
COAST. MOISTURE AND INCREASING INSTABILITY WILL WORK ITS WAY INTO
CENTRAL OREGON MONDAY AFTERNOON AND EVENING. THERE WILL BE A CHANCE
OF SHOWERS AND A SLIGHT CHANCE OF AFTERNOON AND EVENING
THUNDERSTORMS OVER CENTRAL OREGON AS A RESULT...MAINLY ALONG THE
CASCADE EAST SLOPES. CONDITIONS WILL BECOME INCREASINGLY UNSTABLE
WITH MOISTURE IN A SOUTHERLY FLOW ALOFT FURTHER INTO THE COMING WEEK
WITH SHOWERS AND THUNDERSTORMS BECOMING MORE WIDESPREAD. THIS
SCENARIO IS COVERED WELL IN THE CURRENT FORECAST. IT WILL ALSO BE
WARMER ON MONDAY AND TUESDAY WITH MOSTLY LIGHT WINDS. 88

&&

.AVIATION...06Z TAFS...VFR CONDITIONS WITH MOSTLY CLEAR SKIES WILL
PREVAIL FOR THE NEXT 24 HOURS AT ALL TAF SITES WITH WINDS
BECOMING LIGHT AFTER DARK THIS EVENING AT ALL TAF SITES. 88

&&

.PREV DISCUSSION... /ISSUED 545 PM PDT SAT APR 30 2016/

SHORT TERM...A NORTHERLY FLOW WILL CONTINUE TO BRING CLOUDS ACROSS
SOUTHEAST WASHINGTON AND NORTHEAST OREGON THROUGH EARLY THIS EVENING
AND THEN DECREASE IN CLOUD COVER AND SHOWERS LATE THIS EVENING. AN
UPPER RIDGE WILL BUILD IN ON SUNDAY WITH SUNNY SKIES AND WARMER
TEMPERATURES. THIS HIGH PRESSURE WILL CONTINUE ON MONDAY WITH A
WARMING TREND CONTINUING. HOWEVER THE FLOW ALOFT ON MONDAY WILL
BEGIN TO BECOME SOUTHERLY RESULTING IN AN INCREASE IN MOISTURE AND
INSTABILITY TO CENTRAL OREGON FOR A SLIGHT CHANCE OF AFTERNOON
THUNDERSTORMS THERE...MAINLY ALONG THE OREGON CASCADE EAST SLOPES.
THEN ON TUESDAY THE FLOW ALOFT WILL BECOME STRONGER SOUTHERLY AS THE
UPPER RIDGE MOVES TO THE NORTHEAST AND AN UPPER TROUGH OFF THE COAST
MOVES TO THE COAST. THIS WILL RESULT IN MOISTURE AND INSTABILITY TO
BE PUMPED NORTHWARD INTO ALL OF THE CWA FOR A CHANCE OF SHOWERS AND
A SLIGHT CHANCE OF AFTERNOON THUNDERSTORMS AREA WIDE. 88

LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...TUESDAY EVENING A DEEP
TROUGH WILL BE LOCATED OFFSHORE WITH AN ELONGATED FRONT APPROACHING
THE COAST. A WARM MOIST SOUTHERLY FLOW WILL DEVELOP OVER EASTERN
WASHINGTON AND OREGON TUESDAY...INCREASING THE CHANCE FOR SHOWERS
AND THUNDERSTORMS. INSTABILITY WILL DECREASE WITH THE LOSS OF
DAYTIME HEATING...SO THUNDERSTORMS WILL DECREASE OVERNIGHT...THEN
REDEVELOP WEDNESDAY AFTERNOON/EVENING. WEDNESDAY NIGHT THE TROUGH
WILL SPLIT AND MOVE INLAND. A CLOSED LOW WILL DEVELOP IN THE
SOUTHERN HALF OF THE TROUGH AS IT MOVES INLAND THURSDAY. THE GFS
ENSEMBLE MODELS SHOW A WIDE VARIATION IN LOCATION OF THE LOW (OREGON
TO SOUTHERN CALIFORNIA) BY FRIDAY MORNING. I BASED THE FORECAST FOR
THURSDAY AND FRIDAY ON THE MAIN ENERGY SHIFTING SOUTH AND SHOWER AND
THUNDERSTORM ACTIVITY ENHANCED BY DIURNAL HEATING/COOLING AND
OROGRAPHIC TERRAIN EFFECTS. EXPECT SHOWERS TO PERSIST OVER THE AREA
WITH THE BROAD TROUGH BUT THUNDERSTORMS COVERAGE SHOULD BE LIMITED
TO CENTRAL TO NORTHEAST OREGON. FRIDAY NIGHT AND SATURDAY SOUTHEAST
FLOW AROUND THE LOW IN CALIFORNIA WILL KEEP SHOWERS CENTRAL TO
NORTHEAST OREGON...BUT DRIER CONDITIONS WILL DEVELOP IN EASTERN
WASHINGTON AS THE LOW MOVES FARTHER SOUTHEAST.  COONFIELD

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  44  75  44  79 /  10   0   0  10
ALW  47  76  48  79 /  10   0   0  10
PSC  45  80  44  84 /  10   0   0   0
YKM  44  79  44  82 /   0   0   0   0
HRI  43  79  43  83 /  10   0   0   0
ELN  43  77  42  80 /   0   0   0   0
RDM  35  73  37  78 /   0  10   0  10
LGD  43  70  40  74 /  10   0   0  10
GCD  38  71  37  75 /  10  10  10  10
DLS  46  81  46  84 /   0   0   0   0

&&

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

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

$$

88/76/88



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