Heat in Washington, May 17, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT SAT MAY 17 2008

.SYNOPSIS...A WARM UPPER LEVEL RIDGE OVER THE PACIFIC NORTHWEST WILL
WEAKEN THROUGH SUNDAY. MARINE AIR WILL PUSH ONTO THE COAST THIS
AFTERNOON AND INTO THE INTERIOR OF WESTERN WASHINGTON THIS EVENING.
A COOL UPPER LEVEL TROUGH WILL MOVE OVER THE AREA TUESDAY.

&&

.SHORT TERM...WARM UPPER RIDGE WEAKENS THROUGH SUNDAY. THE THERMALLY
INDUCED SURFACE LOW PRESSURE TROUGH OVER WESTERN WASHINGTON THIS
MORNING SHIFTS TO THE EAST SLOPES OF THE CASCADES MID AFTERNOON.
MARINE PUSH STARTS UP THIS AFTERNOON. GRADIENTS ARE PRETTY FLAT THIS
MORNING WITH HQM-SEA STILL SLIGHTLY OFFSHORE AND -2MB THRU THE
STRAIT SO THE NAM MIGHT BE A FEW HOURS TOO FAST AND A MILLIBAR TOO
STRONG WITH THE ONSHORE GRADIENTS THIS AFTERNOON. OTH-SEA IS STILL
ONLY +2MB...SO THERE IS ENOUGH TIME TO LAY DOWN A RECORD HIGH TEMP
FOR SEA-TAC TODAY BEFORE THE MARINE AIR STARTS TO COOL THINGS OFF
LATE THIS AFTERNOON. OUR FCST MAX TEMPS ON THE COAST WILL PROBABLY
BE A NOTCH TOO LOW...ALTHOUGH THE HIGHS FOR THE DAY WILL LIKELY
OCCUR THIS MORNING THEN TEMPS WILL DROP THIS AFTERNOON AS THE BREEZE
OFF THE PACIFIC KICKS IN. WITHOUT A RESERVOIR OF MARINE STRATUS
OFFSHORE THE LOW CLOUDS AND FOG WILL HAVE TO FORM IN PLACE...AND
THAT IS WHAT THE MM5NAM 0-3KFT MIXING RATIO FORECAST SHOWS...AROUND
06Z TONIGHT LOW CLOUDS FORM ON THE COAST...PUSH INTO KOLM AROUND
12Z...AND THEN INTO KSEA TO KPAE AROUND 15Z. BUT IT DOESNT LOOK
VERY EXTENSIVE...SO I WILL PROBABLY REWORD THE FCST FOR SUNDAY AS
AREAS OF LOW CLOUDS AND LOCAL FOG OTHERWISE MOSTLY SUNNY...AND I MAY
ADD A FEW DEGREES TO THE TEMPS ON THE AFTERNOON PACKAGE. WE ARE
SHOWING 20 DEGREES OF COOLING FOR THE PASSES...THAT MAY BE A BIT TOO
MUCH SINCE THE STRATUS WONT BE TOO DEEP AND PROBABLY WILL NOT PUSH
NEARLY AS FAR AS THE CASCADES. THE AIR MASS WILL CONTINUE TO COOL
MONDAY...AND SOME AREAS OF LIGHT PRECIP WITH THE INCOMING UPPER TROF
AND ASSOCIATED COLD FRONT REACH WESTERN WA MONDAY EVENING. 19

.LONG TERM...TUESDAY LOOKS LIKE A RATHER CHILLY DAMP DAY IN THE
LATEST PROGS. THE 12Z NAM SUGGESTS HIGHER POPS THAN THE CURRENT
FORECAST...SHOWERS OR RAIN LIKELY FOR ALL OF WESTERN WA. THERE IS
ROOM IN THE FORECAST TO MOVE TUE/WED COOLER AND WETTER AND SHOW A
LITTLE MORE IMPROVEMENT INTO THE END OF THE WEEK. 19

&&

.AVIATION...UPPER LEVEL HIGH PRESSURE WILL FLATTEN AND SHIFT EAST
TODAY.  THIS WILL ALLOW A THERMALLY INDUCED LOW PRESSURE ALONG THE
COAST TO SHIFT INLAND OVER PUGET SOUND BY 20Z...THEN SHIFT OVER THE
CASCADES AFTER 00Z. LIGHT SLY WIND ALOFT BECOMING LIGHT-MODERATE
SWLY AFTER 00Z. AMS DRY AND SOMEWHAT UNSTABLE INLAND.

MARINE STRATUS WILL FORM ALONG THE COAST AFTER 03Z THIS
EVENING...WITH A PARTIAL STRATUS PUSH INLAND OVERNIGHT AND SUNDAY
MORNING. AREAS OF LOW MVFR STRATUS ARE POSSIBLE OVER PUGET SOUND
AFTER 12Z SUNDAY MORNING...INCLUDING THE KSEA/KBFI TERMINALS BUT
CONFIDENCE IS LOW.

KSEA...S WIND 5-9 KT BECOMING VARIABLE AFTER 18Z...THEN BECOMING
SW 9-14 KT AFTER 22Z. ANY STRATUS OR FOG WILL LIKELY WAIT UNTIL
AFTER 12Z SUNDAY MORNING. DTM

&&

.MARINE...OFFSHORE FLOW WILL SWITCH TO ONSHORE ALONG THE COAST BY
18Z AS THERMALLY INDUCED LOW PRESSURE BEGINS TO MOVE INLAND. WILL
MAINTAIN SMALL CRAFT ADVISORIES FOR THE COAST AND THE WEST ENTRANCE
OF THE STRAIT TODAY...AND WILL MAINTAIN THE GALE WARNING FOR THE
CENTRAL AND EAST STRAIT OF JUAN DE FUCA LATE THIS AFTERNOON AND
TONIGHT. WLYS ARE PROBABLY STRONG ENOUGH TO GIVE ADMIRALTY INLET
SMALL CRAFT WINDS SO THAT AREA WILL BE ADDED.

ONSHORE FLOW WILL GENERALLY PREVAIL THROUGH MONDAY...BUT WILL
STRENGTHEN TUE IN THE WAKE OF A COLD FRONT THAT CLIPS THE NORTHERN
PORTIONS OF THE WATERS LATE MON. DTM

&&

.AVALANCHE...WITH TEMPERATURES RUNNING INTO THE 70 AND 80 DEGREE
RANGE YESTERDAY IN THE MOUNTAINS AND EARLY MORNING TEMPERATURES
TODAY EVEN RUNNING A FEW DEGREES HIGHER...EXPECT FURTHER DANGEROUS
SLIDE ACTIVITY TODAY AND GENERALLY HIGH DANGER TO
CONTINUE...ESPECIALLY ABOVE ABOUT 4 TO 5000 FEET. SOME RECENT SLIDES
HAVE RELEASED TO GROUND WITH SLAB DEPTHS REACHING 15 TO 20
FEET...AND DEBRIS INVOLVING MUD...ROCKS AND MATURE TIMBER. WHILE THE
SKIES ARE CLEAR AND THE AIR IS HOT...THIS IS NOT A GOOD TIME FOR
MOUNTAIN RELATED FUN. BETTER TO WAIT UNTIL THIS MAJOR SPRING SLIDE
CYCLE CONCLUDES. ALTHOUGH SOME COOLING...INCREASED RIDGETOP WINDS
AND SOME HIGH CLOUDS SUNDAY SHOULD BEGIN TO DECREASE SNOW MELT...A
WEAK SNOWPACK SHOULD PERSIST THROUGH THE WEEKEND. MORE SIGNIFICANT
REDUCTION IN THE DANGER EXPECTED EARLY NEXT WEEK. SEE NWAC.US FOR
MORE DETAILS. MOORE

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
.FLOOD WATCH REMAINS IN EFFECT FOR THE RIVERS IN KING...
LEWIS...AND PIERCE COUNTIES THRU SUNDAY EVENING.

.GALE WARNING CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA LATE
THIS AFTERNOON AND TONIGHT.
.SMALL CRAFT ADVISORY COAST...WESTERN STRAIT OF JUAN DE FUCA...AND
ADMIRALTY INLET.
.SMALL CRAFT ADVISORY FOR ROUGH BAR CONDITIONS ON THE GRAYS HARBOR
BAR.

WEATHER.GOV/SEATTLE