National Weather Service National Headquarters

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

000
FXUS66 KPDT 211200 AAA
AFDPDT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
459 AM PDT TUE MAY 21 2013

UPDATED SHORT TERM DISCUSSION

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT...A LARGE UPPER LEVEL
LOW PRESSURE TROUGH SEEN ON SATELLITE WATER VAPOR LOOP DIGGING
SOUTHWARD NEAR QUEEN CHARLOTTE ISLAND WILL DEVELOP RAPIDLY INTO A
CLOSED MID/UPPER LEVEL LOW PRESSURE SYSTEM TODAY WITH THE CENTER OF
THE LOW REACHING THE OREGON COAST BY LATE THIS AFTERNOON. THIS COLD
LOW WILL PUSH A COLD FRONT THROUGH THE FORECAST AREA TODAY. THE
FRONT WILL MOVE EASTWARD ACROSS THE WESTERN SECTIONS THIS MORNING
WITH SHOWERS MOVING INTO THE TRI-CITIES AND HERMISTON BY LATE THIS
MORNING. MARGINAL INSTABILITY AHEAD OF AND ALONG THE COLD FRONT WILL
FAVOR ISOLATED THUNDERSTORMS POSSIBLE THIS AFTERNOON AND THIS
EVENING IN THE BLUE MOUNTAINS AND GRANT COUNTY EASTWARD INTO IDAHO.
THE UPPER LOW WILL LINGER OVER THE REGION THROUGH WEDNESDAY NIGHT
FOR PERIODS OF RAIN SHOWERS AT LOWER ELEVATIONS WITH SNOW SHOWERS IN
THE MOUNTAINS. SNOW LEVELS WILL LOWER LATE TONIGHT TO AROUND
2800-3500 FEET FOR LIGHT SNOW SHOWERS OCCURRING AT PASS LEVELS IN
THE MOUNTAINS OF CENTRAL AND NE OREGON AND THE BLUE MOUNTAINS IN
WASHINGTON. SNOW ACCUMULATIONS OF 2-3 INCHES ARE EXPECTED IN THE
BLUE MOUNTAINS OVERNIGHT INTO WEDNESDAY MORNING. AN LATE SNOW
SEASON/OFFSEASON SNOW ADVISORY MAY BE NEEDED FOR THE BLUE MOUNTAINS
FOR LATE TONIGHT, BUT WILL DEFER TO THE DAY SHIFT FOR A DECISION.
SNOW LEVELS WILL LOWER TO 3500-4200 FEET BY LATE WEDNESDAY NIGHT.
POLAN

.LONG TERM...THURSDAY THROUGH TUESDAY...A LARGE AND PERSISTENT UPPER
LOW PRESSURE SYSTEM WILL LINGER OVER THE PACIFIC NORTHWEST THROUGH
MUCH OF THE EXTENDED PERIOD. THERE WILL BE WAVES OF ENERGY ROTATING
AROUND THIS SYSTEM WITH EACH ONE BRINGING A CHANCE OF RAIN SHOWERS
AND POSSIBLE AFTERNOON THUNDERSTORMS TO THE FORECAST AREA. ANY
THUNDERSTORMS THAT DO FORM WILL MAINLY BE CONCENTRATED FROM THE BLUE
MOUNTAINS EASTWARD AND SOUTHWARD INCLUDING CENTRAL OREGON AROUND THE
DESCHUTES PLATEAU. THIS SYSTEM HAS THE POTENTIAL TO PRODUCE
SIGNIFICANT RAINFALL TO SOME AREAS...MAINLY IN THE MOUNTAINS...WHICH
WILL HELP EASE THE CURRENT DRY SPELL THAT THE CWA IS EXPERIENCING.
THE LONG RANGE MODELS BEGIN TO DIVERGE SIGNIFICANTLY BY SATURDAY
MORNING WITH THE ECMWF AND GFS MODELS PLACING THE CENTER OF THE
UPPER LOW ABOUT 500 MILES APART WITH THE ECMWF POSITIONED OF THE BC
COAST AND THE GFS CENTERED OVER NORTH CENTRAL WASHINGTON. THE
DIVERGENCE BETWEEN THESE TWO LONG RANGE MODELS INCREASES BUT BOTH
KEEP A GENERAL TROUGH LIKE PATTERN OVER THE CWA THROUGH THE EXTENDED
PERIOD AND THEREFORE WILL NOT MAKE ANY CHANGES AFTER DAY 5
(SATURDAY). TEMPERATURES WILL BE COOL THROUGH THE PERIOD AND A
LITTLE BELOW NORMAL DUE TO THE CLOUDS AND LOWER HEIGHTS AND 850 MB
TEMPERATURES.

&&

.AVIATION...12Z TAFS...VFR CONDITIONS WILL PREVAIL THROUGH THE
PERIOD. HOWEVER CONDITIONS WILL DETERIORATE AS A LARGE WEATHER
SYSTEM AND UPPER LOW PRESSURE SYSTEM MOVES INTO THE REGION. THIS MAY
RESULT IN BRIEF PERIODS OF MVFR CONDITIONS BY 19Z...ESPECIALLY AT
KRDM...KBDN AND KDLS. THESE DETERIORATING CONDITIONS WILL REACH THE
REST OF THE TAF SITES BY 00Z. WINDS WILL BEGIN LIGHT BUT THEY WILL
INCREASE TO 20 TO 30 KTS AT KDLS AND 15 TO 25 KTS IN THE LOWER
COLUMBIA BASIN AND BLUE MOUNTAIN FOOTHILLS BY 18Z AS THE WEATHER
SYSTEM MOVES INTO THE REGION. THE BREEZY TO WINDY CONDITIONS WILL
PERSIST THROUGH AT LEAST 12Z WEDNESDAY. 88

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  64  40  59  39 /  60  70  50  20
ALW  68  43  60  43 /  60  70  50  20
PSC  71  44  65  39 /  50  60  40  20
YKM  65  38  63  37 /  50  20  30  20
HRI  67  42  65  38 /  40  70  40  20
ELN  62  42  58  39 /  60  20  40  30
RDM  59  31  54  32 /  50  50  40  30
LGD  71  39  54  37 /  60  50  50  30
GCD  69  36  56  35 /  50  40  40  20
DLS  63  44  61  42 /  70  30  50  40

&&

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

THREAT INDEX
TODAY : YELLOW
WEDNESDAY : GREEN
THURSDAY : 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

$$

99/88/88