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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 152357 AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SEATTLE WA 350 PM PST WED FEB 15 2012 .SYNOPSIS...A WEAKENING FRONTAL SYSTEM WILL MOVE THROUGH THE AREA ON THURSDAY BRINGING CLOUDS AND AREAS OF LIGHT RAIN. A STRONGER FRONTAL SYSTEM WILL MOVE ACROSS THE AREA LATE FRIDAY AFTERNOON INTO FRIDAY NIGHT. A COLD UPPER TROUGH OF LOW PRESSURE WILL GIVE SHOWERS TO THE AREA ON SATURDAY. THE SHOWERS WILL GRADUALLY DIMINISH SATURDAY NIGHT AND SUNDAY AS THE TROUGH MOVES OFF TO THE SOUTHEAST. A SERIES OF FRONTAL SYSTEMS WILL GIVE UNSETTLED CONDITIONS NEXT WEEK. && .SHORT TERM...LONG WAVE UPPER RIDGING SITS ALONG ABOUT 130W WHILE TROUGHS SIT OVER THE GREAT PLAINS AND OVER THE PACIFIC AROUND 170W (image). A FRONTAL SYSTEM EXTENDING FROM THE GULF OF ALASKA SOUTHWARD ALONG ABOUT 140W IS MOVING STEADILY EASTWARD AND IS EXPECTED TO WEAKEN AS IT MOVES EAST THROUGH THE RIDGE AND ACROSS WESTERN WASHINGTON ON THURSDAY. A VIGOROUS SHORT WAVE TROUGH NEAR 170W (image) IS FORECAST BY ALL MODELS TO RAPIDLY DEVELOP AND DEEPEN TO ABOUT 988 MB LOW NEAR 50N 133W FRIDAY THEN SHIFT ESE INTO SOUTHWESTERN WASHINGTON OR NORTHERN OREGON AS A VERTICALLY STACKED AND DECAYING LOW SATURDAY AFTERNOON AND EVENING. ITS ASSOCIATED FRONT WILL MOVE THROUGH THE AREA LATE FRIDAY AFTERNOON THROUGH FRIDAY NIGHT. WEATHER EXTREMES ARE NOT ANTICIPATED THROUGH THE WEEKEND OVER THE AREA. MODEL GUIDANCE IN THE SHORT TERM HAS SHOWN RATHER GOOD CONSISTENCY AND CONTINUITY OVER THE PAST FEW RUNS AND SHORT TERM FORECAST CONFIDENCE IS RELATIVELY HIGH. HIGH PRESSURE THAT IS GIVING DRY WEATHER TO THE AREA THIS AFTERNOON (image) WILL SHIFT EAST OF THE CASCADES OVERNIGHT AS A WEAKENING FRONT OFFSHORE APPROACHES. MODELS SHOW CLOUDS RAPIDLY INCREASING AHEAD OF THE FRONT AFTER MIDNIGHT TONIGHT (image). THE FRONT WILL BE RAPIDLY WEAKENING AS IT MOVES THROUGH THE AREA (image). SO RAIN WILL BE LIKELY IN THE MORNING ALONG THE COAST BUT CHANCES IN THE INTERIOR WILL LIKELY NOT INCREASE A GREAT DEAL WITH THE FRONT REALLY WEAKENING QUICKLY AS IT MOVES THROUGH THE MEAN RIDGE POSITION. PRECIPITATION CHANCES DECREASE SIGNIFICANTLY THURSDAY EVENING INTO EARLY FRIDAY...BUT CLOUDS AND AT LEAST SOME RAIN THREAT WILL REMAIN AS A VERY WEAK SHORT WAVE TROUGH AND MID LEVEL VORTICITY LOBE MOVES ACROSS THE AREA. THE 18Z NAM12 IS DRIER WITH THE FEATURE FRIDAY MORNING THAN THE 12Z SOLUTION AND THE 12Z GFS IS DRY. THE 12Z ECMWF SHOWS SOME LIGHT PRECIPITATION WITH THE PASSING SHORT WAVE TROUGH. AT THIS TIME WILL MAINTAIN 20 POPS LATER THU NIGHT INTO EARLY FRI. PRECIPITATION CHANCES INCREASE LATER FRI AFTERNOON AHEAD (image) OF A FRONTAL SYSTEM ASSOCIATED WITH THE LOW THAT WILL BE PEAKING AROUND 50N 134W...AND CONTINUE INTO THE EVENING HOURS WITH THE FRONT. A COOL AND SHOWERY REGIME TAKES OVER LATER FRI NIGHT (image) INTO SAT NIGHT (image) OR SUN AS THE VERTICALLY STACKED OFFSHORE LOW MOVES SLOWLY INLAND AND WEAKENS. THE PASSING FRONT FRI NIGHT AND POST FRONTAL SHOWER ACTIVITY SAT INTO SAT NIGHT WILL LIKELY GIVE ADVISORY LEVEL SNOWFALL AMOUNTS TO THE MOUNTAINS. ALBRECHT .LONG TERM...A SERIES OF DISTURBANCES WILL MOVE OVER THE TOP OF A RATHER FLAT LONG WAVE RIDGE NEAR 135W SUN NIGHT (image) THROUGH WED (image). THE HIGHEST POPS WILL BE MON NIGHT INTO TUE NIGHT OR WED. THE AIR MASS WILL BE RATHER MILD WITH LONG WAVE RIDGING JUST OFFSHORE...BUT THERE WILL LIKELY BE ABUNDANT CLOUDS AND SOME LIGHT PRECIPITATION AT TIMES. ALBRECHT && .HYDROLOGY...FLOODING IS NOT EXPECTED OVER THE NEXT 7 DAYS. ALBRECHT && .AVIATION...AN UPPER RIDGE OVER THE REGION WILL MOVE E OVERNIGHT... ALLOWING AN UPPER TROF TO APPROACH FROM THE W. INCREASING WLY FLOW ALOFT (image) AND LOW LEVEL SLY FLOW. THE LOWER CLOUD DECK WAS STUBBORN TO BURN OFF ACROSS MUCH OF THE AREA TODAY (image). HOWEVER VFR CONDITIONS PREVAILED ACROSS MOST PLACES THIS AFTERNOON. ANTICIPATE CIGS TO GRADUALLY LOWER OVERNIGHT AS A FRONTAL SYSTEM STILL WELL OFFSHORE BEGINS TO AFFECT THE AREAS. EXPECT AREAS OF CIGS PRIMARILY IN THE 2-3K FT RANGE LATE TONIGHT...PARTICULARLY OVER THE COAST. KSEA...VFR CONDITIONS ARE EXPECTED TO PERSIST THE REMAINDER OF TONIGHT AND WINDS WILL BE LIGHT. && .MARINE... A FRONTAL SYSTEM WELL OFFSHORE WILL WEAKEN AND MOVE ACROSS THE ON THU. A STRONG LOW AND ASSOCIATED FRONTAL SYSTEM WILL IMPACT THE AREA THE END OF THIS WEEK FOR LARGE WAVES ON THE COASTAL WATERS AND THE POSSIBILITY OF GALE FORCE WINDS ACROSS ALL WATERS. THE TRACK OF THE SURFACE LOW THAT WILL AFFECT THE AREA THE END OF THIS WEEK WAS STILL UNCERTAIN. SOME MODELS TAKE THE SURFACE LOW ACROSS THE NORTHERN OR CENTRAL WASHINGTON COASTAL WATERS WHERE OTHERS TAKE IT INTO THE OREGON COASTAL WATERS. THIS WILL HAVE AN IMPACT ON THE WIND FORECAST. REGARDLESS OF WHERE THE LOW TRACKS... WAVES OF 19 TO 23 FT ARE STILL ANTICIPATED TO ARRIVE ON SATURDAY. THIS WILL RESULT IN HAZARDOUS SEAS ON THE COASTAL WATERS AND HIGH SURF ON THE BEACHES. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...NONE. PZ...SMALL CRAFT ADVISORY UNTIL 6 PM PST THURSDAY FOR THE COASTAL WATERS AND WEST ENTRANCE TO THE STRAIT OF JUAN DE FUCA. SMALL CRAFT ADVISORY FOR WINDS FROM 6 AM TO 6 PM PST THURSDAY FOR THE ADMIRALTY INLET...EAST ENTRANCE TO THE STRAIT OF JUAN DE FUCA...AND NORTHERN INLAND WATERS. SMALL CRAFT ADVISORY FOR ROUGH BAR UNTIL 6 PM PST THURSDAY 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 |
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