Avalanche in Washington, March 27, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
918AM PDT SUN MAR 27 2011

.SYNOPSIS...A PASSING UPPER LEVEL LOW PRESSURE SYSTEM WILL GIVE
SHOWERS TO WESTERN WASHINGTON TODAY. SHOWERS WILL GRADUALLY DIMINISH
TONIGHT. WEAK HIGH PRESSURE WILL MOVE ACROSS THE AREA MONDAY GIVING
DRIER WEATHER. WET WEATHER IS EXPECTED MONDAY NIGHT AND TUESDAY AS
FRONTAL SYSTEM MOVES ACROSS THE AREA. A MUCH WETTER STORM SYSTEM
COULD AFFECT THE AREA WEDNESDAY AND THURSDAY.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS A VERTICALLY STACKED LOW
CENTERED NEAR 47N 129W THIS MORNING. THIS LOW WILL MOVE ESE ALONG
THE COLUMBIA RIVER THIS AFTERNOON AND INTO SW IDAHO MON MORNING.

A BRIEF AND WEAK RIDGE OF HIGH PRES WILL MOVE ACROSS THE AREA MON.
AS THIS MOVES BY...EXPECT PARTLY SUNNY CONDITIONS MON WITH ONLY
ISOLATED SHOWERS. WITH SOME SUNSHINE...TEMPERATURES WILL RISE INTO
THE MID 50S MOST AREAS WITH SOME UPPER 50S POSSIBLE.

A FRONTAL SYSTEM NOW NEARING 150W WILL PUSH THROUGH THE AREA MON
NIGHT AND WILL BE QUICKLY FOLLOWED BY ANOTHER FRONT TUE NIGHT. THESE
FRONTS WILL LIKELY BEGIN THE TRANSITION TO A MORE ZONAL AND MUCH
WETTER PATTERN BEGINNING MID WEEK.

CURRENT SHORT TERM FORECASTS LOOK GOOD. NO UPDATES ARE NEEDED.
ALBRECHT

.LONG TERM...PREVIOUS LONG RANGE DISCUSSION FOLLOWS...THE 00Z GFS IS
COMING INTO CLOSER AGREEMENT WITH THE PAST COUPLE ECMWF RUNS
REGARDING A STRONGER AND WETTER STORM SYSTEM POSSIBLE BY MIDWEEK.
WARM FRONTAL RAINFALL WILL REACH WRN WA TUESDAY NIGHT INTO WEDNESDAY
BUT BOTH MODELS AGREE THAT INITIALLY THE HEAVIEST RAIN WILL FOCUS
JUST TO THE N OF WA ACROSS CENTRAL/SRN VANCOUVER ISLAND.
HOWEVER...BOTH MODELS AGREE THAT HIGH PRES WILL BEGIN TO FLATTEN
OVER THE PAC NW WEDNESDAY NIGHT ALLOWING THE FRONTAL BAND TO SLOWLY
SAG SWD OVER WA. THERE IS THE POSSIBILITY FOR A RATHER WET PERIOD
FROM THE MID TO LATTER PART OF NEXT WEEK. WILL NEED TO WATCH THIS
CLOSELY. SEE THE HYDRO SECTION BELOW FOR FURTHER DETAILS.

MERCER

&&

.HYDROLOGY...PREVIOUS HYDROLOGY DISCUSSION FOLLOWS...THE 00Z
GFS/ECMWF ARE IS PRETTY GOOD AGREEMENT ON A RATHER WET PATTERN
SETTING UP OVER WA BY MIDWEEK. MODELS SHOW A STRONG FRONTAL BAND
INITIALLY STALLED ACROSS VANCOUVER ISLAND WEDNESDAY. THIS WILL SAG
SWD OVER WRN WA WEDNESDAY NIGHT THROUGH THURSDAY. IF THE CURRENT
MODEL PROGS PAN OUT...24 TO 36 HOUR QPF AMOUNTS OF 3-5 INCHES ARE
NOT OUT OF THE QUESTION ALONG W/SW FACING SLOPES OF THE OLYMPICS AND
ESPECIALLY CASCADES. THIS RAISES SOME CONCERNS FOR RIVER FLOODING
EVEN THOUGH CLIMATOLOGY DOES NOT FAVOR WIDESPREAD RIVER FLOODING
THIS TIME OF YEAR. PREVIOUS MODEL RUNS THE PAST COUPLE DAYS HAVE
VARIED QUITE A BIT WITH SOME MODELS HOLDING THE RIDGE STRONGER OVER
THE AREA KEEPING THE HEAVIEST RAIN JUST TO THE N OF WA. THIS
SCENARIO IS STILL POSSIBLE. IT IS ALSO POSSIBLE THAT MODELS ARE
OVERDOING THE EXTENT OF THE MOISTURE TAP. THIS STORM SYSTEM IS STILL
SEVERAL DAYS OUT SO THERE IS STILL TIME TO ASSESS ANY POSSIBLE FLOOD
THREAT.  MERCER

THE THREAT FOR FLOODING ON THE GREEN RIVER REMAINS LOW. MERCER

&&

.AVIATION...UPPER TROUGH OFF THE COAST WITH SOUTHERLY FLOW ALOFT
OVER WA. WEAKENING COLD FRONT TO MOVE INTO WA TODAY SPREADING
MOISTURE INLAND. AIR MASS STABLE AHEAD OF THE FRONT BECOMING
UNSTABLE BEHIND THE FRONT FOR SHOWERS INTO TONIGHT AS UPPER TROUGH
MOVES ONSHORE. WEAK UPPER RIDGE TO BUILD INTO WA MON FOR A BRIEF
DRYING TREND.

CEILINGS WITH PRECIP TO DROP INTO THE MVFR CATEGORY...OUTSIDE OF THE
PRECIP VFR. A MORE SHOWERY REGIME LATER THIS AFTERNOON FOLLOWING THE
FRONT WITH GENERALLY VFR CONDITIONS WITH MVFR CEILINGS POSSIBLE WITH
SHOWERS.

WITH MORE ONSHORE FLOW OVERNIGHT...EXPECT CEILINGS TO DROP INTO THE
MVFR CATEGORY AGAIN BY MON MORNING.

KSEA...CEILINGS TO RUN NEAR 025 WITH PRECIP THEN RISE TO NEAR 040
POST-FRONTAL AROUND 22Z. CEILINGS TO DROP BACK TO AROUND 025 AROUND
MIDNIGHT. SOUTHEAST WINDS 4 TO 8 KNOTS BECOMING MORE SOUTHERLY THIS
AFTERNOON FOR A CONSISTENT AIRCRAFT FLOW PATTERN. BUEHNER

&&

.MARINE...A 993 MB LOW ABOUT 250 NM W OF CAPE FLATTERY WILL MOVE
SOUTHEAST AND WEAKEN OVER THE OFFSHORE WATERS TODAY AND DISSIPATE
TONIGHT. PATTERN TO GIVE SMALL CRAFT ADVISORY WINDS TO THE COASTAL
WATERS EASING BY TONIGHT BUT THE SWELL TO REMAIN IN THE 10 OR 11
FOOT RANGE KEEPING THE SMALL CRAFT ADVISORY INTACT. SMALL CRAFT
ADVISORY WINDS IN THE NORTHERN INLAND WATERS TIL AROUND MIDDAY WHEN
PRESSURE GRADIENTS BEGIN TO EASE.

AFTER A BRIEF BREAK MONDAY MORNING...THE NEXT PACIFIC FRONTAL SYSTEM
WILL APPROACH THE COASTAL WATERS WITH WINDS PICKING UP OVER ALL OF
THE WATERS LATE MONDAY. THE FRONT WILL MOVE THROUGH THE WATERS
LATE MONDAY NIGHT INTO TUESDAY MORNING WITH SMALL CRAFT ADVISORY
WINDS OVER MOST OF THE AREA. ANOTHER FRONTAL SYSTEM IS EXPECTED TO
REACH THE AREA WEDNESDAY WITH SMALL CRAFT ADVISORY WINDS EXPECTED
OVER ALL OF THE WATERS AGAIN. BUEHNER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...

WA...NONE.

PZ...SMALL CRAFT ADVISORY COAST...EAST ENTRANCE TO STRAIT OF JUAN
       DE FUCA...NORTHERN INLAND WATERS AND ADMIRALTY INLET.