Lightning Strikes in Washington, September 5, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
350 AM PDT THU SEP 5 2013

.SYNOPSIS...AN UPPER LEVEL LOW OFF THE SOUTHERN OREGON COAST WILL
MOVE INTO WESTERN OREGON TODAY THEN TURN NORTH REACHING CENTRAL
WASHINGTON FRIDAY MORNING. SHOWERS AND THUNDERSTORMS EMBEDDED IN THE
SOUTHERLY FLOW ALOFT WILL CONTINUE TO MOVE THROUGH THE AREA TODAY
AND THIS EVENING. AS THE LOW APPROACHES FRIDAY MORNING THE SHOWER
ACTIVITY WILL GIVE WAY TO RAIN. THERE IS THE POTENTIAL FOR EXCESSIVE
RAINFALL OVER PARTS OF THE AREA TONIGHT INTO FRIDAY. THE LOW WILL
REMAIN OVER CENTRAL WASHINGTON SATURDAY THEN KICK OUT TO THE EAST ON
SUNDAY. AN UPPER LEVEL RIDGE WILL BUILD OVER THE AREA FOR DRIER AND
WARMER WEATHER FOR AT LEAST THE FIRST HALF OF NEXT WEEK.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS UPPER LEVEL LOW FINALLY ON THE
MOVE WITH THE LOW MOVING SOUTHEAST IN THE LAST FEW HOURS TO ABOUT
200 NM W OF NORTH BEND OREGON. MOIST SOUTHERLY FLOW ALOFT OVER
WESTERN WASHINGTON THIS MORNING. DOPPLER RADAR PICKING UP SHOWERS
AND THUNDERSTORMS OVER THE SOUTHERN PORTION OF THE AREA AND OVER THE
CASCADES.

LITTLE CHANGE IN THE PATTERN TODAY WITH THE LOW CONTINUING TO MOVE
SLOWLY TOWARD THE OREGON COAST. MOIST SOUTHERLY FLOW ALOFT
CONTINUING WITH THE AIR MASS REMAINING SOMEWHAT UNSTABLE. EXPECT
MORE SHOWERS AND THUNDERSTORMS TO DEVELOP AND MOVE THROUGH THE AREA.
AS THE LOW MOVES INLAND OVER SOUTHERN OREGON LATER THIS AFTERNOON
FLOW ALOFT OVER WESTERN WASHINGTON WILL BECOME MORE SOUTHEASTERLY.
THIS WILL INCREASE THE CHANCE OF CONVECTION DEVELOPING OVER THE
CASCADES AND THEN DRIFTING OUT OVER THE LOWLANDS.

UPPER LEVEL LOW MOVING NORTH NORTHEAST OVERNIGHT WITH THE LOW ENDING
UP SOMEWHERE BETWEEN THE DALLES AND PENDLETON BY 12Z FRIDAY. ALL OF
THE MODEL SOLUTIONS ARE PRETTY CONSISTENT THAT A DEFORMATION ZONE
WILL DEVELOP NORTHWEST OF THE LOW CENTER TONIGHT. AMSU IMAGERY NOT
AS IMPRESSIVE AS IT WAS LAST NIGHT WITH THE TPW VALUES AROUND THE
LOW THIS MORNING STILL PEAKING OUT AROUND 1.5 INCHES BUT FOR THE
MOST PART TPW VALUES AROUND 1 INCH WITH THE LOW. STILL...THESE
VALUES COMBINED WITH THE SLOW MOVEMENT OF THE LOW WILL CREATE THE
POTENTIAL FOR HEAVY RAINFALL WHERE THE DEFORMATION ZONE SETS UP
TONIGHT. THE CURRENT FORECAST TRACK OF THE LOW WOULD PUT THE
DEFORMATION ZONE OVER THE CENTRAL AND SOUTHERN CASCADES INTO THE
CENTRAL PUGET SOUND REGION.

LOW CONTINUING TO SLOWLY MOVE NORTH NORTHEAST FRIDAY MORNING. THE
SLOW MOVEMENT OF THE LOW FRIDAY MORNING WILL ONCE AGAIN KEEP THE
POTENTIAL OF HEAVY PRECIPITATION WITH THE DEFORMATION ZONE OVER THE
CENTRAL CASCADES INTO THE THE CENTRAL PUGET SOUND AREA. IN A
REVERSAL OF WHAT NORMALLY HAPPENS AS STORMS MOVE INTO WESTERN
WASHINGTON ITS VERY LIKELY THAT THE NORTH COAST WILL BE THE DRIEST
LOCATION IN THE NEXT 36 HOURS.

MODEL SOLUTIONS ARE PRETTY SIMILAR WITH THE LOW STALLING OVER
CENTRAL WASHINGTON FRIDAY NIGHT INTO SATURDAY WITH THE PRECIPITATION
ASSOCIATED WITH THE LOW DRYING UP BY SATURDAY MORNING. STILL PLENTY
OF LOW LEVEL MOISTURE AROUND SO EVEN WITH THE RAIN COMING TO AN END
NOT MUCH IN THE WAY OF SUNSHINE IN THE FORECAST.

.LONG TERM...ALL OF THE EXTENDED MODELS IN GOOD AGREEMENT THIS
MORNING WITH THE LOW KICKING OUT TO THE EAST ON SUNDAY WITH AN UPPER
LEVEL RIDGE BUILDING INTO WESTERN WASHINGTON. THE ECMWF IS MUCH
FLATTER WITH THE RIDGE AND BRINGS A WEAK SHORTWAVE OVER THE TOP OF
THE RIDGE ON MONDAY. THE GFS DOES NOT HAVE THIS FEATURE. WILL
ACCOUNT FOR THE SHORTWAVE WITH JUST SOME MORNING CLOUDS MONDAY. BOTH
THE GFS AND THE ECMWF HAVE THE UPPER LEVEL RIDGE SOLIDLY ENTRENCHED
OVER WESTERN WASHINGTON TUESDAY AND WEDNESDAY. 500 MB HEIGHTS IN THE
MID 580 DMS BY 00Z THURSDAY. LOW LEVEL FLOW NEVER TURNS OFFSHORE SO
NOT EXPECTING A BIG HEAT WAVE. MOS TEMPERATURES LOOK TO BE GIVING
CLIMATOLOGY TOO MUCH RESPECT TUESDAY AND WEDNESDAY KEEPING HIGHS
NEAR NORMAL. CURRENT FORECAST OF HIGH TEMPERATURES 5 DEGREES OR SO
ABOVE NORMAL...70S AND LOWER 80S...LOOKS GOOD AT THIS POINT. FELTON

&&

.HYDROLOGY...FLOOD WATCH FOR THIS AFTERNOON THROUGH FRIDAY WILL
CONTINUE WITH THE THREAT OF HEAVY PRECIPITATION STILL INTACT.
EVERYTHING DEPENDS ON WHERE THE DEFORMATION ZONE SETS UP. THIS WILL
BE A VERY NARROW FEATURE WITH A DIFFERENCE OF ONLY A FEW MILES
MAKING A BIG DIFFERENCE IN THE AMOUNT OF RAIN IN THE NEXT 36 HOURS.
RIGHT NOW THE CENTRAL PUGET SOUND AREA INTO THE CENTRAL AND SOUTHERN
CASCADES HAS THE BEST CHANCES OF SEEING HEAVY PRECIPITATION. THE
MONTHLY NORMAL RAINFALL FOR SEPTEMBER IN SEATTLE IS 1.50 INCHES. ITS
CERTAINLY POSSIBLE THAT SEATTLE COULD GET ITS NORMAL MONTHLY
RAINFALL IN THE NEXT 36 HOURS WITH THE HEAVIEST RAINFALL RATES
TONIGHT INTO FRIDAY MORNING. IN GENERAL...1 TO 2 INCHES OF RAIN IS
POSSIBLE IN THE LOWLANDS WITH 2 TO 4 INCHES POSSIBLE IN THE CENTRAL
AND SOUTHERN CASCADES BY 00Z SATURDAY. FELTON

&&

.AVIATION...AN UPPER LEVEL LOW JUST OFF THE OREGON COAST WILL SHIFT
INLAND OVER WA AND OREGON TONIGHT AND FRIDAY. SOUTHERLY FLOW ALOFT
WILL TURN MORE EASTERLY TODAY. SCATTERED SHOWERS THIS MORNING WILL
TRANSITION TO AREAS OF RAIN LATER THIS AFTERNOON OR EVENING AND RAIN
IS LIKELY TO FALL TONIGHT THROUGH FRIDAY MORNING. THE HEAVIEST RAIN
TONIGHT WITH LOWEST CIGS AND VSBY IS LIKELY TO BE FROM THE I-5
CORRIDOR EAST INTO THE CASCADES. THERE IS A CHANCE OF
THUNDERSTORMS...ESPECIALLY OVER THE CASCADES.

KSEA...LIGHT AND VARIABLE WIND...GRADIENTS ARE PRETTY FLAT.
SCATTERED SHOWERS ACROSS WESTERN WA TODAY WILL TURN TO RAIN TONIGHT.
THERE IS A CHANCE OF THUNDERSTORMS...SO TODAY WILL BE A DAY TO WATCH
THE RADAR AND LIGHTNING DETECTION PLOTS.
&&

.MARINE...THERE IS A 1017 MB LOW OVER THE OREGON OFFSHORE WATERS BUT
THAT LOW WILL DISSIPATE AS IT MOVES INTO SW OREGON TODAY. LOW
PRESSURE EAST OF THE CASCADES AND HIGH PRESSURE CENTERED NEAR 50N
130W WILL GIVE INCREASING ONSHORE FLOW THROUGH TONIGHT AND FRIDAY.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WATCH IN EFFECT FOR MUCH OF THE AREA FROM THURSDAY
     AFTERNOON THROUGH FRIDAY AFTERNOON.

PZ...NONE.

&&

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