Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
335 AM PDT MON MAY 25 2015

.SYNOPSIS...A RIDGE OFFSHORE WILL MAINTAIN LOW LEVEL ONSHORE FLOW 
ACROSS WESTERN WASHINGTON THROUGH TUESDAY...KEEPING SKIES MOSTLY 
CLOUDY. WEAKER ONSHORE FLOW FROM MID WEEK ONWARD ALONG WITH HIGHER 
PRESSURE BUILDING OVER THE REGION WILL ALLOW MORE AFTERNOON SUNSHINE 
AND A WARMING TREND. THE AIR MASS OVER THE CASCADES WILL CONTINUE TO 
BECOME SLIGHTLY UNSTABLE LATE IN THE DAY FOR A CHANCE OF SHOWERS 
NEAR THE CREST. 

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS UPPER LEVEL LOW HAS MOVED INTO 
SOUTH CENTRAL BRITISH COLUMBIA EARLY THIS MORNING. OVER WESTERN 
WASHINGTON MORE OF THE SAME WITH CLOUDY SKIES ACROSS THE AREA. 
TEMPERATURES AT 3 AM WERE IN THE UPPER 40S TO MID 50S.

LITTLE CHANGE IN THE FORECAST THIS MORNING. LOW LEVEL ONSHORE FLOW 
CONTINUING TODAY KEEPING SKIES CLOUDY ACROSS THE AREA. TOPS OF THE 
MARINE LAYER BETWEEN 5000 AND 6000 FEET SO ONCE AGAIN NO REAL 
BREAKOUT EXPECTED THIS AFTERNOON. MODELS HAVE THE LOW DRIFTING SOUTH 
THIS MORNING AND GIVEN THE DEEP MARINE LAYER A LITTLE EXTRA LIFT 
COULD RESULT IN SOME LOCAL DRIZZLE. BY 00Z TUESDAY UPPER LEVEL LOW 
OVER THE NORTHERN PORTION OF EASTERN WASHINGTON. AIR MASS OVER THE 
CASCADES BECOMING SLIGHTLY UNSTABLE THIS AFTERNOON. THIS ADDED ON TO 
SOME WRAP AROUND MOISTURE FROM THE LOW WILL KEEP A CHANCE OF SHOWERS 
IN THE FORECAST. HIGHS IN THE LOWLANDS WILL CONTINUE TO BE A LITTLE 
BELOW NORMAL...UPPER 50S TO MID 60S.

UPPER LEVEL LOW NOT MOVING MUCH TONIGHT AND TUESDAY WITH THE LOW 
CENTER MODELED TO BE NEAR PASCO BY 00Z WEDNESDAY. WITH THE LOW IN 
THE VICINITY THIS WILL KEEP THE THREAT OF SHOWERS GOING IN THE 
CASCADES. FOR THE LOWLANDS ONSHORE FLOW CONTINUES TONIGHT AND 
TUESDAY BUT BEGINS TO WEAKEN A TOUCH TUESDAY AFTERNOON INCREASING 
THE CHANCES FOR A LITTLE SUN LATE IN THE DAY ON TUESDAY. WITH PLENTY 
OF CLOUD COVER TONIGHT LOW TUESDAY MORNING WILL BE IN THE UPPER 40S 
TO MID 50S. LOW LEVEL ONSHORE FLOW TUESDAY WILL KEEP HIGHS IN THE 
UPPER 50S TO MID 60S. 

UPPER LEVEL LOW KICKS OUT SLOWLY TO THE SOUTHEAST TUESDAY NIGHT AND 
WEDNESDAY WITH AN UPPER LEVEL RIDGE BUILDING OFFSHORE. THE SLOW 
TREND OF WEAKENING ONSHORE FLOW WILL CONTINUE ON WEDNESDAY RESULTING 
IN A LITTLE SUNSHINE IN THE AFTERNOON. TEMPERATURES ALOFT DO NOT 
WARM MUCH WITH THE 850 MB TEMPERATURES ONLY RISING FROM AROUND PLUS 
8 ON TUESDAY TO PLUS 10 ON WEDNESDAY. ONSHORE FLOW STILL STRONG 
ENOUGH FOR PLENTY OF CLOUD COVER TUESDAY NIGHT INTO AT LEAST EARLY 
WEDNESDAY AFTERNOON FOR THE INTERIOR WITH THE CLOUDS HANGING TOUGH 
ALONG THE COAST WEDNESDAY AFTERNOON. MOS SEEMS A LITTLE OVER 
AGGRESSIVE WITH THE WARM UP WITH THE ONSHORE FLOW STILL PRESENT 
WEDNESDAY AFTERNOON. WILL UNDERCUT THE GUIDANCE BY A COUPLE OF 
DEGREES GOING FOR 60S AND LOWER 70S INLAND WHILE KEEPING HIGHS IN 
THE LOWER 60S ALONG THE COAST. EVEN WITH THE RIDGE BUILDING OFFSHORE 
THE AIR MASS OVER THE CASCADES WILL ONCE AGAIN BECOMING SLIGHTLY 
UNSTABLE LATE IN THE DAY FOR A CHANCE OF SHOWERS...MAINLY NEAR THE 
CREST.

.LONG TERM...EXTENDED MODELS WHICH HAVE BEEN IN GOOD AGREEMENT THE 
LAST COUPLE OF NIGHTS HAVE LOST A BIT OF CONSISTENCY BOTH AMONG THE 
INDIVIDUAL MODELS AND RUN TO RUN. GFS SHOWING UPPER LEVEL RIDGE 
MOVING INTO WESTERN WASHINGTON ON THURSDAY. THE ECMWF IS WEAKER WITH 
THIS FEATURE BECAUSE OF YET ANOTHER UPPER LEVEL LOW MOVING INTO 
CENTRAL BRITISH COLUMBIA. THE GFS IS WEAKER AND FURTHER NORTH WITH 
THIS FEATURE. BOTH MODELS STILL HAVE DECENT 500 MB HEIGHTS OVER 
WESTERN WASHINGTON...MID 570 DMS AND WEAK LOW LEVEL ONSHORE FLOW. 
WILL STAY WITH THE IDEA OF CONTINUING THE WARMING TREND ON THURSDAY 
WITH PLENTY OF HIGHS IN THE 70S OVER THE INTERIOR. ECMWF CONTINUES 
TO DROP THE LOW SOUTH ON FRIDAY INDUCING A STRONGER ONSHORE PATTERN 
VERSUS THE GFS WHICH HAS THE LOW MUCH FURTHER NORTH. THE ECMWF DOES 
KEEP THE PRECIPITATION WITH THE LOW NORTH OF THE BORDER. ON SATURDAY 
THE ECMWF MOVES THE LOW BACK TO THE NORTHEAST WHILE THE GFS SOLUTION 
CONTINUES TO PUT THE LOW FURTHER TO THE NORTH AND EAST. MODELS ARE 
IN GENERAL AGREEMENT WITH ANOTHER WEAK UPPER LEVEL LOW DEVELOPING 
NEAR HAIDA GWAII ON SUNDAY. CURRENT FORECAST FOLLOWS THE WARMER...BY 
ABOUT 5 DEGREES...GFS SOLUTION FOR FRIDAY THROUGH SUNDAY WITH HIGHS 
IN THE LOWER TO MID 60S ON THE COAST AND MID 60S TO MID 70S OVER THE 
INTERIOR WITH THE WARMEST DAY BEING FRIDAY. WITH THE NEWER SOLUTIONS 
IN THE EXTENDED RUNS THIS MORNING WILL LET THE CURRENT FORECAST RIDE 
FOR ANOTHER FORECAST PACKAGE. FELTON

&&

.AVIATION...A WEAK UPPER LEVEL LOW WILL SLOWLY MOVE SOUTHEAST  
ACROSS MAINLY EASTERN WASHINGTON THROUGH TUESDAY. LIGHT NW FLOW 
ALOFT. AIR MASS IS MOIST IN THE LOWER LEVELS AND SOMEWHAT MOIST 
ALOFT. STABLE CONDITIONS EXCEPT SLIGHTLY UNSTABLE ALONG THE CASCADE 
CREST. 

THE UPPER LOW WILL DEEPEN THE MARINE LAYER AND WEAK LIFT MAY PRODUCE 
PATCHY DRIZZLE THIS MORNING. WIDESPREAD MVFR IS LIKELY THIS MORNING 
WITH PATCHY IFR CONDITIONS WHERE DRIZZLE DEVELOPS. MVFR CEILINGS 
WILL BRIEFLY SCATTER THIS AFTERNOON AND EVENING BUT SHOULD FILL BACK 
IN OVERNIGHT.

 KSEA...CEILING AROUND 1-3K FT WILL RISE TO 4K FT IN THE AFTERNOON. 
DRIZZLE IS POSSIBLE THIS MORNING. THE DEEP MARINE LAYER WILL REMAIN 
INTACT. SW WIND 6-10 KT. CHB

&&

.MARINE...HIGH PRES WILL REMAIN OFFSHORE WITH LOWER PRES INLAND. 
SMALL CRAFT ADVISORY STRENGTH WINDS OF 15 TO 25 KT WILL EACH EVENING 
THROUGH TUESDAY NIGHT AS ONSHORE FLOW INCREASES. ONSHORE FLOW WILL 
WEAKEN WEDNESDAY THROUGH FRIDAY. CHB

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY CENTRAL AND EAST STRAIT.

&&

$$

WWW.WEATHER.GOV/SEATTLE

YOU CAN SEE AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION AT 
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML






National Weather Service Glossary of Abbreviations