Area Forecast Discussion
Issued by NWS Portland, OR

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207
FXUS66 KPQR 221121
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND
421 AM PDT FRI MAY 22 2015

.SYNOPSIS...THE MARINE LAYER WILL DEEPEN FRIDAY AND MOVE
THE THREAT FOR THUNDERSTORMS OVER AND EAST OF THE CASCADES BY FRIDAY
EVENING. STRONG ONSHORE FLOW WILL CONTINUE THROUGH SATURDAY...THEN
WEAKEN A LITTLE SUNDAY. ANOTHER UPPER LOW LOOKS LIKE IT WILL APPROACH
THE AREA EARLY NEXT WEEK...GENERALLY BRINGING CONTINUED SHOWER
CHANCES.

&&

.SHORT TERM (UPDATED)...OBSERVATIONS SHOW LOW STRATUS HAS MOVED IN
ACROSS THE FORECAST AREA EARLY THIS MORNING...SIGNALING THE ARRIVAL
OF THE MARINE LAYER WHICH WILL MAKE IT DIFFICULT TO GET ANY FURTHER
THUNDER. IN ADDITION...LATEST RADAR TREND SHOWS WEAKENING SHOWERS
ALTHOUGH DO NOT EXPECT THEM TO COMLETELY DISSIPATE. HAVE ELIMINATED
THUNDER FROM THE FORECAST FOR THE LOWLANDS TODAY BUT WILL KEEP A
SLIGHT CHANCE IN FOR THE CASCADES THIS AFTERNOON.

THERE WILL BE LITTLE CHANGE IN THE WEATHER PATTERN FRIDAY NIGHT AND
SATURDAY AS THE UPPER LOW REMAINS OVER THE REGION. A DEEP MARINE
LAYER WILL MAINTAIN CLOUDY SKIES AND POSSIBLY PRODUCE DRIZZLE
SATURDAY MORNING. THE LOW WILL MOVE FURTHER INLAND SATURDAY
AFTERNOON...BUT STILL MAY PRODUCE SOME MOUNTAIN SHOWERS.

MODELS STILL SHOWING LARGE DIFFERENCES SUNDAY AND BEYOND.
IF THE ECMWF IS CORRECT...THERE WOULD BE STRONGER ONSHORE FLOW SUN
WITH LESS AFTERNOON SUN. THE GFS AND NAM HAVE LESS ONSHORE FLOW. IN
ANY EVENT...GENERAL CONDITIONS LOOK STABLE...WITH ANY SHOWER THREAT
CONFINED TO NRN CASCADES. BOWEN/TJ

.LONG TERM...NO SIGNIFICANT CHANGES. PREVIOUS DISCUSSION
FOLLOWS...SUNDAY NIGHT THROUGH THURSDAY...GFS AND ECMWF BOTH SHOW AN
UPPER LEVEL LOW OR TROUGH SITTING OVER OREGON AND WASHINGTON THROUGH
TUE. MAIN MODEL DIFFERENCE IS THAT THE GFS MAINTAINS A CLOSED
FEATURE...KEEPING IT OVER SW WA...WHILE THE ECMWF HAS MORE OF AN OPEN
TROUGH A LITTLE MORE EAST THAN THE GFS. REGARDLESS OF WHICH MODEL
VERIFIES BEST...THE MAIN SENSIBLE WEATHER FOR THE CWA WOULD BE
CONTINUED ONSHORE LOW-LEVEL FLOW WITH THE BEST THREAT OF
SHOWERS...ALBEIT SMALL...OVER THE CASCADES. THE GFS HOLDS THE UPPER
LOW SOMEWHERE OVER SE WA WED...WHILE THE ECMWF HAS A MORE PROGRESSIVE
NWLY FLOW ALOFT. HAVE GONE WITH SLIGHT CHANCE POPS FOR THE CASCADES
WED...BUT IF THE GFS IS MORE RIGHT...THEN IT WOULD BE DRY. TOO MUCH
UNCERTAINTY TO TOTALLY DISREGARD ANY PRECIP THREAT. WEISHAAR

&&

.AVIATION...AS ONSHORE FLOW CONTINUES...THE LOW END MVFR TO IFR CIGS
ALONG THE COAST ARE EXPECTED TO SLOWLY LIFT UP INTO AN MVFR CIG
TODAY. EXPECT THE MVFR CIGS TO SPREAD INTO INLAND VALLEYS THIS
MORNING...AFFECTING VALLEY TAF SITES BY 12Z. THE INLAND CLOUDS ARE
LIKELY TO BREAK UP INTO A SCATTERED CLOUD LAYER BETWEEN 20Z AND 22Z
LEAVING INLAND AREAS VFR. MVFR CIGS ARE LIKELY TO REMAIN ALONG THE
COAST THROUGH 10Z TONIGHT...AND SPREAD BACK INTO INLAND VALLEYS
AGAIN AFTER 09Z.

KPDX AND APPROACHES...MVFR CIGS EXPECTED TO SPREAD IN BETWEEN 09Z
AND 11Z THIS MORNING...THEN BREAK UP AGAIN TO VFR CONDITIONS BETWEEN
20Z AND 22Z THIS AFTERNOON. ONSHORE FLOW WILL AGAIN SPREAD MARINE
CLOUDS WITH MVFR CIGS BACK INLAND AFTER 09Z TONIGHT.

&&

.MARINE...PERSISTENT HIGH PRES WELL OFFSHORE WILL KEEP BELOW SMALL
CRAFT WINDS OUT OF THE NW THROUGH EARLY NEXT WEEK. A FRESH SWELL OF
5 TO 6 FT WILL ALSO CONTINUE OUT OF THE WNW.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...NONE.

&&

$$

INTERACT WITH US VIA SOCIAL MEDIA
WWW.FACEBOOK.COM/NWSPORTLAND
WWW.TWITTER.COM/NWSPORTLAND

THIS DISCUSSION IS FOR NORTHWEST OREGON AND SOUTHWEST WASHINGTON
FROM THE CASCADE CREST TO 60 NAUTICAL MILES OFFSHORE. THE AREA IS
COMMONLY REFERRED TO AS THE FORECAST AREA.



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