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National Weather Service meteorologists use a wide variety of tools such as observations, satellite imagery, radar imagery, and computer models to aid in making forecasts. The Enhanced Area Forecast Discussion is intended to provide additional insight into our traditional Area Forecast Discussion (AFD) by including embedded links to some of the key tools used in the forecast process. These links are specific to the forecast issue of the day and are updated as the forecast discussion is updated. For comments or feedback please contact the Seattle WFO Webmaster For more information on the terms used in the Enhanced AFD, please see Frequently Asked Questions (updated 20 May, 2008). For help decoding the image legends, please see Legends Help. Previous Version ZCZC SEAGPHAFD ALL TTAA00 KSEA 270420 AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SEATTLE WA 900 PM PDT SAT MAY 26 2012 .SYNOPSIS...ONSHORE FLOW IS INCREASING AS AN UPPER LEVEL LOW OVER NORTHEAST NEVADA LIFTS INTO WESTERN MONTANA (image). LOW CLOUDS WILL SPREAD INLAND TONIGHT THROUGH EARLY SUNDAY. A WEAK FRONT AND AN APPROACHING UPPER LEVEL TROUGH WILL KEEP CLOUDS AND A CHANCE OF SHOWERS ACROSS THE AREA SUNDAY NIGHT THROUGH MEMORIAL DAY. A WEAK RIDGE OF HIGH PRESSURE WILL BRING DRIER WEATHER TO THE AREA ON TUESDAY. A SERIES OF FRONTAL SYSTEMS WILL GIVE CLOUDS AND A CHANCE OF PRECIPITATION DURING THE LATTER HALF OF NEXT WEEK. && .SHORT TERM...THE BROAD UPPER LEVEL LOW OVER THE INTERMOUNTAIN WEST CONTINUES TO SLOWLY SHIFT EAST (image). SHORTWAVE RIDGING IS DEVELOPING OUT AROUND 130W. INTERIOR WESTERN WA EXPERIENCED A PLEASANT DAY WITH HIGH TEMPERATURES IN THE LOWER TO MID 70S DESPITE 500 MB LEVEL HEIGHTS ONLY AROUND 560 DM THANKS TO NORTHERLY FLOW AND ABUNDANT SUNSHINE. HOWEVER...THE MARINE PUSH HAS ALREADY BEGUN IN EARNEST AND MARINE STRATUS STUCK ALONG THE COAST (image) WILL PUSH INLAND OVERNIGHT. ISO-SCT MOUNTAIN SHOWERS AND THUNDERSTORMS (MAINLY OVER LEWIS CO AT 9 PM) TRAVELING SOUTH ALONG THE ELEVATED TERRAIN WILL WANE QUICKLY THIS EVENING. THE MARINE PUSH WILL CONTINUE LOCALLY BREEZY SW WINDS FOR THE SOUTHERN SOUND AND HOOD CANAL...AS WELL AS BREEZY W/NW WINDS ALONG THE STRAIT OF JUAN DE FUCA/ADMIRALTY INLET AREA AND SAN JUANS FOR THE FIRST HALF OF TONIGHT. ON SUNDAY...LOW CLOUDS MAY LIFT AND SCATTER ENOUGH IN THE AFTERNOON TO ALLOW FOR A PARTLY SUNNY AFTERNOON OVER THE INTERIOR. HOWEVER...A WEAKENING AND STRETCHING FRONT SEEN OFFSHORE WILL SLOW AND TRY TO PUSH ADDITIONAL MOISTURE INLAND TOMORROW COMPLICATING THE CLOUD FORECAST. THE CHANCE OF SHOWERS WILL BE GREATEST ALONG THE COAST AND OLYMPICS. AN UPPER TROUGH AXIS EXTENDING FROM THE NE PACIFIC (image) WILL APPROACH THE AREA ON MONDAY WITH CONTINUED ONSHORE FLOW. QPF WITH THIS FEATURE STILL LOOKS LIGHT BUT WITH MORE WIDESPREAD SHOWER ACTIVITY COMPARED TO SUNDAY. TEMPERATURES FOR MEMORIAL DAY WILL STRUGGLING TO REACH THE LOWER 60S (image). SHORTWAVE RIDGING FOR TUESDAY NOW LOOKS MORE ZONAL WITH ONSHORE FLOW AT THE SURFACE. STILL...TUESDAY SHOULD BE A MODEST IMPROVEMENT OVER MONDAY...WITH TEMPERATURES CLIMBING BACK INTO THE MID 60S WITH PARTLY SUNNY SKIES IN THE AFTERNOON. DAMICO .LONG TERM...FROM PREV DISCUSSION...LONG TERM MODELS ARE IN REASONABLE AGREEMENT THAT A FRONTAL SYSTEM WILL PASS ACROSS THE AREA ON WEDNESDAY. THE ECMWF IS WETTER THAN THE GFS...AND IT APPEARS MORE REASONABLE AS HEMISPHERIC COMPOSITE IMAGERY SHOWS TROPICAL MOISTURE FROM REMNANTS OF TROPICAL STORM SANVU IN THE WEST PACIFIC GETTING ENTRAINED INTO THE WESTERLIES. THE ECMWF IS ALSO STRONGER WITH ANOTHER MOIST FRONTAL SYSTEM...AGAIN WITH SOME WEST PACIFIC TROPICAL MOISTURE...COMING INTO THE AREA THE END OF NEXT WEEK. WITH THE CALENDAR SOON FLIPPING OVER TO JUNE...POPS AND QPF WERE NUDGED UPWARD IN THE DIRECTION OF THE ECMWF AND TEMPERATURES WERE NUDGED DOWNWARD A BIT WITH THE INCREASE IN CLOUDS AND MOISTURE. IF TRENDS CONTINUE...LATER EXTENDED POP FORECASTS MAY NEED TO BE BUMPED INTO THE LIKELY CATEGORY. ALBRECHT && .AVIATION...AN ONSHORE PUSH IS IN PROGRESS THIS EVENING. WIDESPREAD MARINE STRATUS ON THE COAST WILL SPREAD INLAND THROUGH ALL OF WESTERN WASHINGTON TONIGHT. LIGHT NLY FLOW ALOFT BECOMING LIGHT WLY FLOW SUNDAY. THE LOW LEVEL AIR MASS WILL REMAIN MOIST THROUGH MIDDAY SUNDAY...THE STRATUS MAY LIFT AND THIN IN THE AFTERNOON FOR SOME AREAS OF PARTIAL CLEARING. THE LOWER SLOPES OF THE OLYMPICS AND WEST SLOPES OF THE CASCADES WILL BECOME OBSCURED IN MARINE STRATUS. HERE IS THE NAM TIME HEIGHT CROSS SECTION OF WIND RH AND TEMP FOR SEATTLE THE MARINE STRATUS CORRESPONDS TO THE HIGH RH LOW LEVEL PURPLE AREA SUNDAY MORNING (image). 19 KSEA...CURRENT 03Z TAF LOOKS GOOD...NO CHANGES EXPECTED WITH MARINE STRATUS THROUGH MIDDAY SUNDAY...MAYBE SOME CLEARING IN THE LATE AFTERNOON AND EVENING HOURS. 19 && .MARINE...A PRETTY STRONG MARINE PUSH IS ONGOING THIS EVENING. UIL-BLI WAS 4MB (image) SO IT SHOULD BLOW GALE IN THE STRAIT. CURRENT FORECASTS LOOK GOOD WITH SMALL CRAFT ADVISORIES FOR THE REST OF THE WATERS...EXCEPT ON THE COASTAL WATERS WHERE THE STRATUS IS ALREADY IN PLACE AND GRADIENTS ARE LIGHT. IN ADDITION TO THE MARINE LAYER...A WEAK FRONT WILL MOVE INTO REGION LATER SUN...AND BEHIND THAT FRONT LATER SUNDAY THROUGH MONDAY ONSHORE FLOW WILL INCREASE AGAIN. 19 && .SEW WATCHES/WARNINGS/ADVISORIES... WA...NONE. PZ...GALE WARNING CENTRAL AND EAST STRAIT OF JUAN DE FUCA. SMALL CRAFT ADVISORY NORTHERN INLAND WATERS...ADMIRALTY INLET...AND PUGET SOUND/HOOD CANAL. && $$ YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML. |
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