000 FXUS66 KSEW 132313 AFDSEW AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SEATTLE WA 310 PM PST MON FEB 13 2012 .SYNOPSIS...SPLIT UPPER FLOW WILL PERSIST THROUGH THE WORK WEEK... ONLY ALLOWING WEAK WEATHER DISTURBANCES TO IMPACT THE AREA. A WEAK LOW PRESSURE SYSTEM OFFSHORE WILL HEAD SOUTH INTO NORTHERN OREGON ON TUESDAY...FOLLOWED BY RIDGING ON WEDNESDAY. A WEAK FRONTAL SYSTEM WILL REACH WESTERN WASHINGTON ON THURSDAY...FOLLOWED ONCE AGAIN BY A BUILDING RIDGE AND DRY WEATHER ON FRIDAY. A THIRD SYSTEM WILL REACH THE AREA SATURDAY. && .SHORT TERM...SHORTWAVE RIDGING IS BEGINNING TO MOVE INTO THE COASTAL WATERS...REPLACING THE STRETCHED TROUGH THAT PASSED THROUGH WESTERN WASHINGTON EARLIER TODAY. SHOWERS HAVE ENDED EXCEPT FOR A FEW LINGERING SPRINKLES...BUT THE CLOUD COVER REMAINS EXCEPT AROUND WESTERN WHATCOM COUNTY...THE NW TIP OF THE OLYMPIC PENINSULA AND HIGHER TERRAIN WHERE DRIER AIR HAS MOVED IN ALOFT WITH NORTHERLY FLOW. SURFACE WINDS WILL BACK TO THE SOUTHWEST TONIGHT IN ADVANCE OF THE NEXT LOW OFFSHORE...OFFERING LITTLE OPPORTUNITY FOR CLEARING. THE WEAK RIDGE QUICKLY BREAKS DOWN AS IT PASSES INLAND TUESDAY MORNING AND IS FOLLOWED BY ANOTHER SPLITTING TROUGH. AN UPPER LOW FROM THE SOUTHERN BRANCH WILL DIVE SOUTHEAST TOWARD THE WA/OR BORDER TUESDAY AFTERNOON. PRECIPITATION WITH THIS SYSTEM WILL BE HEAVIEST OVER THE CENTRAL COAST AND SOUTH INTERIOR...WITH LESS PRECIPITATION OVER THE NORTHERN HALF. WRFGFS 4KM SHOWS VERY LITTLE PRECIPITATION NORTH OF EVERETT...AND HAVE MAINTAINED CHANCE POPS FOR NORTHERN AREAS. SNOW LEVELS WILL FALL TO AROUND 2000 FEET TUESDAY...BUT THE LOW IS UNABLE TO PULL DOWN SLIGHTLY COLDER AIR BOTTLED UP OVER BRITISH COLUMBIA. SHOWERS WILL TAPER FROM NORTH TO SOUTH TUESDAY AFTERNOON/EVENING AS THE LOW PULLS INTO OREGON. A STRONGER RIDGE WILL BUILD JUST OFFSHORE ON WEDNESDAY...WITH 500 MB HEIGHTS AROUND 560 DM OVERHEAD BY MIDDAY WEDNESDAY. THE NEXT FRONTAL SYSTEM APPROACHING FROM THE WEST WILL RUN INTO THE RIDGE ON THURSDAY...AND WEAKEN AS IT PASSES THROUGH. A STRONGER RIDGE WILL BUILD OVER THE AREA ON FRIDAY WITH OFFSHORE FLOW AT THE SURFACE. POPS HAVE BEEN REMOVED...AND TEMPERATURES SHOULD RISE INTO THE LOWER TO MID 50S. DAMICO .LONG TERM...MODEL DISAGREEMENT CONTINUES FOR THE WEEKEND AND BEYOND. THE GFS MAINTAINS THE IDEA OF A SPLIT PATTERN...TAKING THE SOUTHERN PORTION OF A SPLITTING TROUGH IN A FAMILIAR TRACK INTO THE WA/OR BORDER SATURDAY. THE LATEST ECMWF HAS A STACKED LOW MOVING DIRECTLY OVER WESTERN WA SATURDAY. SATURDAY`S FORECAST WAS TRENDED TOWARD THE GFS...WITH HIGHER POPS FOR THE COAST AND SOUTHERN PORTIONS SINCE THE GFS HAS HANDLED THE SPLIT FLOW BETTER THAN THE ECMWF AS OF LATE. DUE TO UNCERTAINTY PAST SATURDAY...CLIMO POPS WERE USED. DAMICO && .HYDROLOGY...FLOODING IS UNLIKELY DURING THE NEXT 7 DAYS. && .AVIATION...A TRANSITORY UPPER RIDGE WILL PREVAIL OVER WRN WA THRU MUCH OF TONIGHT. NLY FLOW ALOFT WILL BECOME WLY LATER TONIGHT. WEAK SFC PRES GRADIENTS WILL SLOWLY TIGHTEN OVERNIGHT. THE LOWER BOUNDARY LAYER REMAINED QUITE MOIST AND THIS COMBINED WITH LIGHT WINDS WITHIN THE LAYER WAS MAKING IT VERY DIFFICULT FOR THE CLOUDS TO SCATTER OUT. THE UPCOMING FORECAST PACKAGE WILL INDICATE GENERALLY MVFR CIGS /1-3K FT/ THRU TONIGHT. KSEA...CIGS SHOULD REMAIN NEAR 2500 FT RANGE THRU TONIGHT. IT IS POSSIBLE THAT CIGS MAY BRIEFLY POP UP TO NEAR 5K FT THIS EVENING. && .MARINE...AN OCCLUDED FRONT WELL OFFSHORE WILL CONTINUE TO MOVE SE... RESULTING IN GRADUALLY INCREASING SE FLOW OVERNIGHT. THE 1012 MB LOW AND ASSOCIATED OCCLUDED FRONT WILL MOVE ACROSS THE COASTAL WATERS ON TUE. WEAK ONSHORE FLOW WILL PREVAIL ON WED. ANOTHER FRONTAL SYSTEM WILL AFFECT THE AREA ON THU. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...NONE. PZ...SMALL CRAFT ADVISORIES FOR HAZARDOUS SEAS ARE IN EFFECT FOR THE COASTAL WATERS AND WEST ENTRANCE TO THE STRAIT OF JUAN DE FUCA. SMALL CRAFT ADVISORY FOR ROUGH BAR UNTIL 6 PM PST TUESDAY FOR THE GRAYS HARBOR BAR. && $$ YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML. WWW.WEATHER.GOV/SEATTLE