www.weather.gov | www.weather.gov |
 |
 |
 |
||
 |
|
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 071809 AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SEATTLE WA 935 AM PST SAT NOV 7 2009 .SYNOPSIS...A BROAD UPPER LEVEL TROUGH WITH COOL MOIST UNSTABLE AIR WILL CONTINUE TO DIRECT SHOWERS...THUNDERSTORMS AND BREEZY WEATHER INTO WESTERN WASHINGTON THROUGH SUNDAY MORNING (image). A WARM FRONT WILL MOVE THROUGH THE AREA SUNDAY NIGHT...FOLLOWED BY A COLD FRONT ON MONDAY. A WEAKER COLD FRONT SHOULD CROSS THE AREA TUESDAY FOLLOWED BY SHOWERS FROM AN UPPER LEVEL TROUGH ON WEDNESDAY. A WEAK UPPER LEVEL RIDGE ON THURSDAY SHOULD LOWER THE CHANCE OF RAIN...BUT ANOTHER FRONTAL SYSTEM WILL PROBABLY REACH THE AREA FRIDAY OR SATURDAY. && .SHORT TERM...A BROAD UPPER TROUGH WILL CONTINUE OVER THE ERN PAC INTO THE MIDDLE OF NEXT WEEK. THIS TYPICALLY SPELLS ACTIVE AND UNSETTLED WEATHER FOR THE PAC NW. FOR TODAY...SATELLITE IMAGERY STILL SHOWS A LOT OF COLD CONVECTIVE CLOUD TOPS FOR A LONG DISTANCE UPSTREAM OFF THE COAST...ALLOWING THE COLD AND CONVECTIVE PATTERN TO CONTINUE THROUGH TONIGHT AND INTO SUNDAY MORNING (image). VERY COLD AIR ALOFT (500 MB TEMPS AT OR BELOW -30C) CONTINUES TO SUPPORT AN UNSTABLE ATMOSPHERE ALONG WITH SHOWERS AND SCATTERED THUNDERSTORMS. WITH SNOW LEVELS AROUND 3000 FEET...THIS WILL EQUATE TO BURSTS OF HEAVY SNOW IN THE MOUNTAINS...WHERE A WINTER STORM WARNING IS IN EFFECT. COLD AIR ALOFT WILL CONTRIBUTE TO GENEROUS SNOW RATIOS...AGAIN SUPPORTING THE NOTION OF HEAVY SNOW IN THE MTNS. LOOKS LIKE A SHORTWAVE IS CURRENTLY SPREADING ACROSS WRN WA...ENHANCING LIFT AND CONVECTION. UNLIKE EARLY YESTERDAY AFTERNOON WHEN THERE WERE SEVERAL DISCRETE CELLS ON RADAR...SOME WITH ROTATION...PRECIP ON RADAR RIGHT NOW LOOKS A LITTLE MORE SPREAD OUT WITHOUT SO MANY DISCRETE CELLS. COLD AIR ALOFT AND DEPTH OF THE CONVECTION WILL CONTINUE TO SUPPORT PROLIFIC AMOUNTS OF SMALL HAIL IN THUNDERSTORMS. LOOKS LIKE A SHORTWAVE DROPPING INTO THE BACK SIDE OF THE ERN PAC TROUGH WILL AMPLIFY THE LONGWAVE PATTERN A BIT LATER SUNDAY. THIS WILL TURN THE FLOW ALOFT MORE SOUTHERLY ON SUNDAY NIGHT. AT FIRST...A WEAK WARM FRONT WILL LIFT ACROSS THE AREA ON SUNDAY NIGHT. CONSIDERING THE CURRENT ATMOSPHERIC INSTABILITY...THE ADDED STABILITY MAY ACTUALLY DO MORE TO INHIBIT PRECIP THAN WILL BE ADDED BY ISENTROPIC LIFT. STILL...LOWERING OF POPS OVER THE INTERIOR INTO THE CHANCE CATEGORY LATE SUN NIGHT IS APPROPRATE. A COLD FRONT WILL THEN MOVE INLAND LATER ON MONDAY AND EAST OF THE CASCADES ON MON NIGHT...BRINGING ANOTHER ROUND OF MODERATE TO HEAVY RAIN FOR SEVERAL HOURS. HANER .LONG TERM...FROM PREVIOUS DISCUSSION...GFS AND ECMWF REMAIN IN GOOD AGREEMENT REGARDING THE OVERALL PATTERN THROUGH THE END OF NEXT WEEK...BUT AFTER WEDNESDAY BEGIN DIVERGING ON TIMING...WITH THE GFS FASTER. THE OVERALL PATTERN REMAINS PROGRESSIVE AS THE PARADE CONTINUES. MODELS HAVE GOOD AGREEMENT WITH ANOTHER COLD FRONT TUESDAY...FOLLOWED BY AN UPPER LEVEL TROUGH WEDNESDAY. MINOR BREAK THURSDAY WITH A RIDGE BRIEFLY OVERHEAD...BUT THE GFS KEEPS SOME LIGHT PRECIP IN THE AREA. ANOTHER FRONTAL SYSTEM ARRIVES EITHER FRIDAY OR FRIDAY NIGHT. KAM && .HYDROLOGY...NO SIGNIFICANT FLOODING IS EXPECTED IN WESTERN WASHINGTON DURING THE NEXT WEEK. THIS INCLUDES THE GREEN RIVER. FOR THIS WEEKEND...SNOW LEVELS OF 2500 TO 3000 FEET WILL ELIMINATE THE POTENTIAL FOR EXCESSIVE RUNOFF OVER MOUNTAIN HEADWATERS. SNOW LEVELS WILL RISE TO NEAR 5000 FEET IN ADVANCE OF A WET COLD FRONT ON MONDAY...BUT THE FRONT WILL BE MOVING QUICKLY...LIMITING THE DURATION OF HEAVY RAINFALL. LIMITED DURATION TENDS TO REDUCE THE RISK OF EXCESSIVE RUNOFF. MORE PRECIPITATION IS EXPECTED ON TUESDAY AND WEDNESDAY...BUT SNOW LEVELS WILL AGAIN BE BACK DOWN NEAR 3000 FEET. DRY WEATHER IS POSSIBLE ON THURSDAY AND FRIDAY BEFORE ANOTHER WET BUT FAST-MOVING COLD FRONT ARRIVES EARLY NEXT WEEKEND. AGAIN...THE RISK OF MAINSTEM RIVER FLOODING DURING THE NEXT WEEK IS VERY LOW. HANER && .AVIATION...UNSETTLED WEATHER WILL CONTINUE ACROSS WESTERN WASHINGTON TODAY. A STRONG UPPER LEVEL LOW CONTINUES TO SPIN OFF OF THE ALASKA PANHANDLE WITH CYCLONIC FLOW ALOFT ACROSS THE PACIFIC NORTHWEST. IR SATELLITE SHOWS AN EXTENSIVE CUMULUS FIELD OVER THE OCEAN DRIFTING INLAND. A BAND OF SHOWERS IS MOVING THROUGH THE PUGET SOUND AREA THIS MORNING (image). AN UPTICK IN ACTIVITY IS ANTICIPATED THIS AFTERNOON AS A SURFACE TROUGH MOVES INLAND. SCATTERED THUNDERSTORMS WILL BE POSSIBLE ALONG WITH SMALL HAIL... SOME LIGHTNING ALREADY ALONG THE COAST. SHOWERS WILL DECREASE TONIGHT. CEILINGS WILL RANGE FROM NO CEILING TO MVFR IN SHOWERS...INCLUDING MVFR VISIBILITY. KSEA...SEE ABOVE...NO REASON TO THINK KSEA WILL BE DIFFERENT. GUSTY SOUTH WINDS 10-20 KT WITH GUSTS TO 30 KT...BECOMING MORE SOUTHWEST IN THE AFTERNOON. WINDS EASE TONIGHT. CHB && .MARINE...GALE WARNING POSTED FOR COAST AS MARGINAL GALE SEEMS LIKELY. SMALL CRAFT ADVISORY SOUTHWEST WINDS WILL CONTINUE THE REST OF TODAY AND INTO THE EVENING AND HAVE EXTENDED THE END TIME OF THE ADVISORIES UNTIL MIDNIGHT TONIGHT. THERE WILL BE SOMETHING OF A LULL (image)...INLAND AT LEAST...ON SUNDAY AS WASHINGTON IS BETWEEN SYSTEMS. NEXT SYSTEM SUNDAY NIGHT AND MONDAY LOOKS LIKE A STRONG GALE ON THE COAST AND AT THE WEST ENTRANCE...POSSIBLY PUSHING STORM FORCE WINDS (image). GALES MOST OTHER WATERS INDICATED AS WELL. FRONT PASSES MONDAY AFTERNOON FOR A BURST OF WESTERLIES DOWN THE STRAIT. PATTERN OF LOW PRES OFFSHORE WITH SE WINDS QUICKLY RESUMES AS ONE SYSTEM AFTER ANOTHER MOVES TOWARD WASHINGTON. MEANWHILE...LARGE WESTERLY SWELLS UP TO 25 FT CONTINUE ACROSS THE COASTAL WATERS TODAY...WILL CONTINUE THE HIGH SURF WARNING FOR THE BEACHES. SWELLS WILL GRADUALLY DECAY TO 20 FT ON SUN. CHB && .SEW WATCHES/WARNINGS/ADVISORIES... WA...WINTER STORM WARNING FOR THE CENTRAL AND NORTH CASCAES UNTIL 4 AM PST SUNDAY... WINTER WEATHER ADVISORY FOR THE OLYMPICS UNTIL 10 PM PST TONIGHT. HIGH SURF WARNING FOR THE COAST THROUGH 4 PM TODAY. PZ...GALE WARNING COAST. SMALL CRAFT ADVISORY ALL OTHER WATERS. SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR. $$ WWW.WEATHER.GOV/SEATTLE FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION...PLEASE SEE WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML. |
||
|
|
||
|
Webmaster |
Disclaimer Information Quality Credits Glossary |
Privacy Policy Freedom of Information Act About Us Career Opportunities |