 |
Forecast Discussion:Western Washington
930 PM PDT WED MAR 17 2010SYNOPSIS
SURFACE HIGH PRESSURE JUST OFFSHORE WILL BUILD EAST ACROSS BRITISH COLUMBIA AND ALBERTA THROUGH THURSDAY. AN UPPER LEVEL RIDGE WILL BUILD OVER THE REGION. DRY WEATHER WITH COOL NIGHT TIME LOW TEMPERATURES CAN BE EXPECTED...WHILE DAYTIME HIGHS WARM THROUGH SATURDAY. A COLD FRONT WILL REACH THE AREA SUNDAY WITH A COOL UPPER TROUGH MONDAY. &&
SHORT TERM
THE EVENING SLP ANALYSIS SHOWS A 1038MB HIGH CENTERED JUST OFF VANCOUVER ISLAND. SATIMG IS MOSTLY CLEAR. THE TIME HEIGHT CROSS SECTION FROM THE NAM MODEL THIS EVENING NICELY SHOWS THE NW FLOW ALF AND COOL AIR MASS GRADUALLY WARMING THRU SAT MORNING AS THE UPPER RIDGE OFFSHORE SHIFTS OVER THE AREA. 500MB HEIGHTS RISE INTO THE 560S...AND THE RIDGE AXIS REACHES THE COAST FRIDAY NITE WITH A 570DM CONTOUR TO KAST. THE NAM HAS SOME LOW LEVEL MOISTURE FOR A FEW HOURS THU AND FRI MORNING...PATCHY FOG OR LOW CLOUDS POSSIBLE. AFTER THE UPPER RIDGE SHIFTS INLAND AN UPPER TROF AND COLD FRONT APPROACH THE AREA SUN. UNTIL THEN 850MB TEMPS WARM FROM -4C THIS EVENING TO MAYBE AS WARM AS +9C SATURDAY...AND WITH THE SFC HIGH PRES BUILDING THRU SW CANADA AND THEN SAGGING SOUTHEAST INLAND OFFSHORE FLOW WILL DEVELOP...PROBABLY STRONGEST SATURDAY MORNING AS THERMALLY INDUCED LOW PRES OVER NRN CALIF ON FRI SPREADS OUT AND MERGES WITH WHAT LOOKS LIKE A BIT OF A WARM FRONT JUST OFFSHORE SAT. THE FCST LOOKS FINE...WE MAY SEE SOME CIRRUS SAT...BUT OTHERWISE FAIR SKIES AND WARMING DAYTIME HIGHS AFTER A COUPLE OF FROSTY MORNINGS IN ALL THE NORMAL COOL SPOTS. 19
LONG TERM
A COMPACT UPPER LOW WILL ROTATE NEAR THE QUEEN CHARLOTTES ON SUNDAY. A WARM FRONT MAY BRUSH THE COAST AND NORTHERN INTERIOR WITH SOME LIGHT RAIN BEGINNING SATURDAY NIGHT AND LIFTING BY ON SUNDAY. THE COLD FRONT COMES THROUGH SUNDAY EVENING. MODELS SEEM TO BE BACK TO THE IDEA OF A COLD UPPER LOW OVER THE AREA SUNDAY NIGHT AND MONDAY...WITH LOW SNOW LEVELS AND SHOWERS. SHORTWAVE RIDGING WILL TRY TO BUILD IN BRIEFLY TUESDAY AND TUESDAY NIGHT BEFORE ANOTHER SYSTEM APPROACHES FROM THE WEST ON WEDNESDAY. DAMICO &&
HYDROLOGY
THE FLOOD RISK ACROSS WESTERN WASHINGTON AND THE GREEN RIVER IS LOW THROUGH THE NEXT 10 DAYS. A STRONG UPPER LEVEL RIDGE BUILDING OFFSHORE TONIGHT WILL PROVIDE DRY WEATHER THROUGH SATURDAY. A SYSTEM APPROACHING FROM THE WEST WILL PRODUCE LIGHT AMOUNTS OF PRECIPITATION SATURDAY NIGHT AND SUNDAY. HEAVIER PRECIPITATION SUNDAY EVENING/NIGHT WILL BE ACCOMPANIED BY LOW SNOW LEVELS. A COLD SHOWERY PATTERN WILL PERSIST THROUGH TUESDAY. A SERIES OF COOL AND QUICK MOVING SYSTEMS WILL AFFECT THE AREA LATER IN THE WEEK. A WARMER...WETTER STORM IS POSSIBLE GOING INTO THE FOLLOWING WEEKEND...ALTHOUGH UNCERTAINTY IS HIGH THIS FAR OUT. DAMICO &&
AVIATION
HIGH PRES ALOFT WILL BUILD OFFSHORE TONIGHT THROUGH THURSDAY WITH DRY NORTHWESTERLY FLOW ALOFT OVER THE AREA. SURFACE GRADIENTS LIGHT WITH FOG...CIGS BELOW 500 FEET VISIBILITIES BELOW 1 SM...A POSSIBILITY IN THE USUAL LOCATIONS LIKE KOLM 10Z-17Z THURSDAY MORNING. CLEAR SKIES FOR THE REMAINDER OF THE AREA THROUGH THURSDAY EVENING. KSEA...CLEAR SKIES WITH NORTH NORTHEAST WIND 6-10 KNOTS THROUGH THURSDAY EVENING. FELTON &&
MARINE
SURFACE HIGH PRES OVER THE COASTAL WATERS WILL BUILD INTO SOUTHERN BRITISH COLUMBIA TONIGHT INTO THURSDAY MORNING. THE HIGH WILL REMAIN IN PLACE THROUGH FRIDAY WITH INCREASING OFFSHORE FLOW THURSDAY NIGHT INTO FRIDAY AS SURFACE PRESSURE LOWERS ALONG THE COAST. OFFSHORE FLOW WILL WEAKEN ON SATURDAY WITH THE FLOW SWITCHING BACK TO ONSHORE ON SUNDAY AS THE HIGH PRES EAST OF THE CASCADES DISSIPATES. SWELL ALONG THE COAST IN THE 10 TO 13 FOOT RANGE TONIGHT WILL SUBSIDE BELOW 10 FEET THURSDAY MORNING AND REMAIN BELOW 10 FEET INTO THE WEEKEND. FELTON &&
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE. PZ...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS IS IN EFFECT FOR THE COASTAL WATERS AND WEST ENTRANCE TO THE STRAIT OF JUAN DE FUCA. A SMALL CRAFT ADVISORY FOR ROUGH BAR GRAYS HARBOR BAR CONDITIONS REMAINS IN EFFECT TIL 9 AM THU. $$ WWW.WEATHER.GOV/SEATTLE FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION PLEASE SEE WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML (ALL LOWERCASE).