092 FXUS66 KPQR 221017 AFDPQR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PORTLAND OR 316 AM PDT THU OCT 22 2015 .SYNOPSIS...CLEARING SKIES BEHIND A DEPARTING FRONT WILL RESULT IN A COOL MORNING WITH AREAS OF FOG. OFFSHORE WINDS WILL DEVELOP THIS EVENING. CLEAR SKIES AND A DRIER ATMOSPHERE WILL LEAD TO COOLER TEMPERATURES LATE TONIGHT WITH SOME INLAND AREAS COOLING INTO THE 30S. WEAK OFFSHORE WINDS WILL CONTINUE FRIDAY AS A LOW PRESSURE SYSTEM APPROACHES THE PACIFIC NORTHWEST. THIS LOW WILL BRING A CHANCE FOR RAIN LATE IN THE WEEKEND. && ...FIRST FROST OF THE FALL POSSIBLE FOR THE NORMALLY COLDER LOWLAND VALLEY LOCATIONS LATE TONIGHT/EARLY FRIDAY MORNING... .SHORT TERM...A WEAKENING FRONT IS OVER THE CASCADES EARLY THIS MORNING. SKIES ARE CLEARING BEHIND THE FRONT...AND EXPECT SOME RADIATION FOG TO DEVELOP ALONG THE COAST AND IN THE INTERIOR VALLEYS THIS MORNING...ESPECIALLY IN AREAS WHERE THE WINDS CALM. THIS FOG WILL LIKELY BE DENSE AND LIMIT VISIBILITIES TO A QUARTER OF A MILE OR LESS AT TIMES. DO NOT EXPECT THIS FOG TO BE WIDESPREAD OR LONG LASTING...WITH PLENTY OF SUNSHINE THIS AFTERNOON. A THERMAL TROUGH OVER CALIFORNIA WILL BUILD NORTHWARD INTO OREGON THIS MORNING...WITH NORTH TO NORTHEAST WINDS HELPING MIX THE LOWER LEVELS OF THE ATMOSPHERE. THE THERMAL TROUGH WILL REMAIN AT OR NEAR THE COAST THROUGH EARLY FRIDAY MORNING...CONTINUING OFFSHORE WINDS. THIS WILL HELP KEEP SKIES MOSTLY CLEAR THIS EVENING...AS WELL AS MIX DRIER AIR ALOFT DOWN TOWARDS THE SURFACE. TEMPERATURES FOR THE CASCADES AND THE INTERIOR VALLEYS WILL RAPIDLY DROP AFTER SUNSET...AND LIKELY LOWER INTO THE 30S EARLY FRIDAY MORNING. THE OFFSHORE WINDS WILL NOT BE STRONG ENOUGH TO PREVENT RADIATION FOG COMPLETELY...BUT THINK THE AREAL EXTENT OF FOG AND LOW CLOUDS WILL BE MINIMAL FRIDAY MORNING. THE WILLAMETTE VALLEY TEMPERATURES WILL BE THE COLDEST IN OUTLYING ...MORE RURAL AREAS. THE COOL START FRIDAY SHOULD LIMIT WARMING SOMEWHAT IN THE AFTERNOON WITH DAYTIME TEMPERATURES REMAINING NEAR SEASONAL CLIMATOLOGY. LIGHT OFFSHORE WINDS WILL CONTINUE FRIDAY EVENING...BUT WITH MORE OF A SOUTHERLY COMPONENT AS A CLOSED LOW APPROACHES THE COAST. THE OFFSHORE WINDS WILL BE WEAKER...ALLOWING FOR ANOTHER OPPORTUNITY FOR OVERNIGHT RADIATION FOG AND/OR COLD TEMPERATURES. WINDS WILL BECOME SOUTHERLY EARLY SATURDAY AS THE LOW NEARS THE COAST. THE SOUTHERLY WIND REVERSAL MAY BRING SOME LOW MARINE CLOUDS AND FOG TO THE CENTRAL OREGON COAST MID MORNING SATURDAY...MOVING NORTH UP THE COAST THROUGH THE DAY. THE MODELS VARY ON THE TIMING OF THE APPROACH WITH GFS THE QUICKEST SOLUTION AND THE OUTLIER. HAVE CONTINUED TO LEAN TOWARDS THE SLOWER SOLUTIONS OF THE AM AND THE ECMWF. SOME HIGH CLOUDS MAY BEGIN TO STREAM OVER THE AREA SATURDAY AFTERNOON AND EVENING...BUT DO NOT EXPECT ANY RAIN FROM THE LOW UNTIL LATER IN THE WEEKEND. TJ .LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY...A CLOSED LOW WILL BRING A CHANCE FOR RAIN SUNDAY. THERE IS A LOT OF MODEL VARIABILITY ON THE TIMING...AREAL EXTENT...AND AMOUNT OF RAIN. THE 00Z MODELS FORECAST THAT THE UPPER RIDGE WITH THE CLOSED LOW WILL SPLIT WITH LITTLE TO NO RAIN FOR THE PORTLAND FORECAST AREA. HAVE NOT JUMPED ONTO THIS SOLUTION QUITE YET...BUT WITH THE RECENT HISTORY OF SPLITTING TROUGHS...THINK IT IS A REASONABLE FORECAST. A SHORTWAVE UPPER RIDGE SHOULD KEEP MONDAY AND TUESDAY MOSTLY DRY....DEPENDING ON HOW THE WEEKEND UPPER TROUGH SPLITS. THIS RIDGE WILL SLOW THE PROGRESSION OF THE NEXT SYSTEM...AND POSSIBLY EVEN STRETCH AND SPLIT THIS SECOND UPPER TROUGH. THIS SYSTEM MAY ENTRAIN MOISTURE FROM THE REMNANTS OF HURRICANE OLAF AND PRODUCE DECENT RAIN SOMEWHERE ALONG THE WEST COAST. TJ && .AVIATION...WIDE VARIETY OF FLYING CONDITIONS IN PLACE ACROSS THE FORECAST AREA THIS MORNING. HIGH CLOUDS ASSOCIATED WITH A DEPARTING COLD FRONT ARE CLEARING OUT...WHICH WILL INCREASE THE RISK OF FOG TOWARDS SUNRISE. HOWEVER THE LOW-LEVEL AIR MASS IS SLIGHTLY BETTER MIXED THAN WED MORNING...SO THE TENDENCY THUS FAR HAS BEEN FOR MVFR STRATUS TO DEVELOP RATHER THAN FOG. EXPECT THIS TREND TO CONTINUE THIS MORNING...WITH MVFR STRATUS BECOMING MORE WIDESPREAD BY 12Z AND LINGERING THROUGH 18Z-20Z BEFORE CLEARING. ONCE THESE CIGS CLEAR...EXPECT VFR CONDITIONS TO PREVAIL THIS AFTERNOON AND EVENING. VALLEYS WHICH REMAIN CLEAR THROUGH 13Z WILL HAVE AN INCREASED RISK OF LOCALLY DENSE FOG AND LIFR CONDITIONS. GREATEST CHANCE OF FOG THIS MORNING WILL BE IN THE WESTERN WILLAMETTE VALLEY AS WELL AS COASTAL VALLEYS. ANY FOG SHOULD SLOWLY LIFT AFTER 16Z...WITH CIGS/VSBYS IMPROVING TO MVFR BY 17Z THEN CLEARING TO VFR BY 20Z. KPDX AND APPROACHES...VFR CONDITIONS WILL LIKELY DETERIORATE TO MVFR BY 13Z...WITH SOME PATCHY IFR POSSIBLE. THERE IS A 20 PERCENT CHANCE OF IFR/LIFR FOG DEVELOPING IN AND AROUND KPDX THIS MORNING. EITHER WAY...CIGS ARE EXPECTED TO CLEAR AROUND 19Z WITH VFR THEREAFTER. WEAGLE && .MARINE...MODERATE NORTHERLY FLOW EXPECTED ACROSS THE COASTAL WATERS TODAY WITH HIGH PRESSURE BUILDING INTO THE PAC NW AND A THERMAL TROUGH ALONG THE S OREGON COAST. A FEW GUSTS TO 25 KT ARE POSSIBLE FOR THE SOUTHERN WATERS...ESPECIALLY NEAR CAPES. HOWEVER THESE ARE EXPECTED TO BE TOO LOCALIZED TO WARRANT A SCA FOR WIND. W-NW SWELL FROM AN EARLIER GULF OF ALASKA LOW WILL ARRIVE MIDDAY...PUSHING SEAS TO 10-12 FT AND PROMPTING A SCA FOR SEAS ALL WATERS THIS AFTERNOON INTO TONIGHT. SEAS SHOULD FALL BACK BELOW 10 FEET FRI MORNING. HIGH PRESSURE WILL SLOWLY WEAKEN FRI...WITH WINDS VEERING NE-E-SE FRI-SAT AS LOW PRES NOW NEAR 155W APPROACHES THE OREGON COAST. FORECAST MODELS CONTINUE TO SHOW A GREAT DEAL OF UNCERTAINTY AS TO HOW STRONG THIS LOW WILL BE AS IT REACHES THE COASTAL WATERS SAT NIGHT/SUN...PROJECTING ANYTHING FROM LIGHT SE FLOW TO NEAR-GALE CONDITIONS. FOR NOW KEPT WINDS FAIRLY MODERATE OVER THE WEEKEND BUT WILL NEED TO MONITOR THIS SYSTEM CLOSELY. WEAGLE && .PQR WATCHES/WARNINGS/ADVISORIES... OR...NONE. WA...NONE. PZ...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM NOON TODAY TO 6 AM PDT FRIDAY FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT 60 NM. SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 11 AM THIS MORNING TO 6 AM PDT FRIDAY. && $$ 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.