Heavy Rain in Washington, September 29, 2005

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 AM PDT THU SEP 29 2005

.SYNOPSIS...A COLD FRONT WILL STALL OVER SOUTHERN WASHINGTON TODAY
PRODUCING RAIN AT TIMES SOUTH AND SHOWERS OVER THE NORTH. SNOW
LEVELS IN THE MOUNTAINS WILL DROP TO 5000 FEET BY LATE IN THE DAY AS
COLDER AIR FILTERS IN.  SHOWERY AND COOL CONDITIONS WILL PERSIST
INTO SAT...FOLLOWED BY ANOTHER SYSTEM ON SUNDAY PRODUCING MORE RAIN
ACROSS THE AREA.  A SERIES OF SYSTEMS WILL CONTINUE THE UNSETTLED
WEATHER PATTERN THROUGH MUCH OF NEXT WEEK.

&&

.SHORT TERM...LATEST SURFACE OBSERVATIONS INDICATE THE FRONT HAS
SAGGED SWD TO NEAR SEATTLE EARLY THIS MORNING.  RADAR IMAGERY SHOWS
CONTINUED MODERATE AND OCCASIONAL HEAVY RAIN SOUTH OF PUGET SOUND
EXTENDING NE INTO THE CASCADES.  RAINFALL AMOUNTS HAVE BEEN AIDED
BY VERY STRONG WLY H850 FLOW AND UPPER LEVEL DIFFLUENCE OVER THE
AREA.  SATELLITE IMAGERY ALMOST IMPLIES A LACK OF MOISTURE AND LIFT
WITH LITTLE CLOUD TOP BRIGHTENING ON THE IR IMAGE.  HOWEVER...IT
APPEARS THE OROGRAPHICS HAVE REALLY MADE UP FOR ANY LACK OF DYNAMICS
WITH WIDESPREAD 3-5 INCH AMOUNTS IN THE MOUNTAINS AND EVEN ONE
REPORT OVER 7 INCHES SW SIDE OF THE OLYMPICS.  MODELS INDICATE A
LULL IN PRECIP OVER CENTRAL AND NRN PARTS OF THE CWA BUT AN
APPROACHING WAVE SHOULD REGENERATE PRECIP FROM THE CENTRAL SOUND
SWD.  THE OLYMPIC PENINSULA AND NRN INTERIOR SHOULD STAY IN THE POST
FRONTAL SHOWERY AIRMASS...WITH COOLER AIR SLOWLY FILTERING IN
THROUGH THE DAY.  IN FACT...SNOW LEVELS ARE STILL EXPECTED TO FALL
TO AT LEAST 5000 FEET BY THIS EVENING WITH SOME LIGHT SNOW IN THE
MOUNTAINS OVERNIGHT INTO SAT. STEADY PRECIP SHOULD END FRI NIGHT AND
SAT BUT SHOWERS WILL CONTINUE WITH AN UNSTABLE AIRMASS MOVING
OVERHEAD.  THE GFS STILL IMPLIES THUNDERSTORMS ARE POSSIBLE WITH
LIS DOWN TO -3 C ALONG THE COAST SAT AND SUN.

THE GFS STILL BRINGS THE MAIN UPPER LOW AND ASSOCIATED SURFACE
TROUGH THROUGH ON SUN.  THIS SHOULD RENEW PRECIP WITH INCREASING
COVERAGE OF SHOWERS.  AGAIN...WE COULD SEE SOME EMBEDDED LIGHTNING
BUT PROBABLY REMAINING ISOLATED. NOTHING ADDED TO THE FORECAST AT
THIS TIME BUT MAY NEED TO BE LATER TODAY IF THE NEXT MODELS RUNS
STILL LOOK THIS UNSTABLE.  MODELS MOVE THE TROUGH E ON MON WITH
GRADUALLY DECREASING SHOWERS.  THE NEXT SYSTEM QUICKLY APPROACHES
FROM THE W ON TUE WITH WEAK RIDGING OVER WA.  IT REMAINS SOMEWHAT
UNCLEAR HOW MUCH BREAK WE WILL END UP WITH AS WARM FRONTAL MOISTURE
COULD SNEAK IN HERE QUICKER THAN THE MODEL CURRENTLY SHOWS.  THE
SYSTEM BECOMES WELL DEVELOPED AND SHOULD BRING A RATHER VIGOROUS
COLD FRONT THROUGH THE AREA TUE NIGHT AND WED FOR MORE RAIN.
EXTENDED MODELS MAINTAIN A MOIST WLY FLOW THROUGH THE REST OF NEXT
WEEK WITH ADDITIONAL SYSTEMS LIKELY.  LOOKS LIKE THE WET PATTERN IS
HERE TO STAY.  MERCER

&&

.AVIATION...THE MAIN COLD FRONT HAS MOVED S AND E THIS MORNING AND
EXTENDS FROM A LITTLE S OF KAST...ARCING UP OVER THE CENTRAL WA
CASCADES. LATEST 06Z NAM INDICATES A FAST MOVING WAVE APPROACHING
FROM OFFSHORE WILL STILL RE-INVIGORATE THE FRONT TODAY...BUT OVER
THE SW INTERIOR AND S CASCADES. DESPITE SOME LIFTING CIGS OVER THE N
INTERIOR AND BETWEEN KSHN-KHQM...LOTS OF LOW LEVEL MOISTURE LEFT
OVER AROUND PUGET SOUND. GRADIENTS HAVE WEAKENED RAPIDLY AS EXPECTED
SO NOT MUCH HELPFUL MIXING THIS MORNING. THUS CIGS BELOW 2000 FT
WILL PERSIST THROUGH THE MORNING...FOLLOWED BY MORE IMPROVEMENT THIS
AFTERNOON. ISOLATED VIS BELOW 1SM MAY STILL DEVELOP BECAUSE OF ALL
THE MOISTURE. KSEA WINDS...N WINDS HAVE PUSHED S AS FAR AS KBFI AND
SHOULD REACH KSEA BY 12Z. EXPECT KSEA WINDS TO BECOME N 3-6 KT BY
12Z THEN BECOME LIGHT AND VARIABLE LATER THIS MORNING. SW WINDS 4-7
KT SHOULD RETURN THIS AFTERNOON. KAM

&&

.SEW WATCHES/WARNING/ADVISORIES...
.FLOOD WARNING FOR THE SNOQUALMIE RIVER NEAR FALLS UNTIL 800 AM FRI
MORNING.
.SMALL CRAFT ADVISORY COAST FOR HAZARDOUS SEAS.

&&

.KATX...VCP21/CSR21 OPERATIONAL.

&&