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October 2014
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Ana’s Remnants

Posted: October 27th, 2014
IMG_20141027_073903686_HDR red sky 2

Sailors take warning? This morning’s sunrise.

 

 

The remnants of Hurricane Ana will pass by the region tonight, and while the City and Watersheds will be spared from the worst of the passing storm, a fair amount of rainfall is expected overnight into tomorrow. After a break from precipitation on Wednesday, another frontal system will roll through and keep Thursday and Friday mostly wet. Forecast models currently disagree on whether this weekend will be showery or dry.

 

Citywide, the NWS currently predicts 0.65″ in the 12-hours ending at 5 AM tomorrow, followed by 0.22″ the rest of the day, then 0.04″ on Wednesday, 0.88″ on Thursday, and 0.34″ on Friday. The UW WRF-GFS and ECMWF are in general agreement with the above. Lowland winds may gust to 25 midday tomorrow; otherwise should remain mostly weak.

 

Over SPU’s mountain reservoirs, similar rainfall amounts to the lowlands are expected overnight and much of the week, but a big difference is expected for Thursday: at the moment over 1.50″ is expected in the 24-hour period ending at 11 PM. Southerly winds should not be problematic throughout the forecast period, and snow levels will rise to above 6000-7000′ through at least Thursday.

 

Excerpts from this morning’s NWS Area Forecast Discussion (emphasis added):

 

RAIN WILL OVERSPREAD THE REST OF THE CWA THIS EVENING AHEAD OF A WARM FRONT AND IT WILL ALSO BECOME WINDY OVER THE COAST AND NORTHWEST INTERIOR. THE WIND ADVISORY THAT WAS ISSUED EARLIER WAS EXPANDED TO INCLUDE WESTERN SKAGIT COUNTY AND THE ADMIRALTY INLET AREA.

SIGNIFICANT RAIN IS POSSIBLE WITH THE SYSTEM OVERNIGHT WITH THE REMAINS OF HURRICANE ANA EMBEDDED IN THE FLOW. THE HEAVIEST RAINS ARE EXPECTED OVER THE SOUTHWEST SLOPES OF THE OLYMPICS DUE TO 850 MB SOUTHWEST WINDS TO 45 KNOTS ENHANCING OROGRAPHIC LIFT.

THE COLD FRONT IS ANTICIPATED TO SWEEP ACROSS THE AREA ON TUESDAY. THIS WILL BRING AN END TO THE STEADY RAIN. SATELLITE IMAGERY DID NOT SHOW A VERY IMPRESSIVE COLD POOL BEHIND THE FRONT…SO RAINFALL AMOUNTS WITH THE SHOWERS WILL BE LOW. SOME DRYING WILL OCCUR TUESDAY NIGHT INTO WEDNESDAY MORNING IN RESPONSE TO A WEAK UPPER RIDGE MOVING OVER THE AREA.

EXTENDED MODELS CONTINUED WITH THE IDEA OF SHOWING THE FRONT FROM TUESDAY MORNING MOVING SOUTHEAST AND OUT OF THE AREA FOR A COUPLE OF DAYS BUT THEN GETTING RE-ENERGIZED AND MOVING BACK NORTH OVER THE AREA ON THURSDAY. WILL KEEP RAIN IN THE FORECAST FOR WEDNESDAY NIGHT INTO THURSDAY. GOOD CONSISTENCY CONTINUED THURSDAY NIGHT AND FRIDAY WITH A DEEP UPPER LEVEL TROUGH OFFSHORE KEEPING RAIN IN THE FORECAST. THE TROUGH AXIS WILL MOVE THROUGH FRIDAY NIGHT.

MODEL SOLUTIONS START TO DIVERGE OVER THE WEEKEND WITH THE ECMWF BRINGING ANOTHER SYSTEM INTO THE AREA ON SUNDAY WHILE THE GFS WAS SLOWER WITH THIS FEATURE. THE 00Z RUN OF BOTH MODELS WAS STRONGER AND MORE INTACT WITH THIS FEATURE VERSUS PREVIOUS RUNS. WILL WAIT FOR ANOTHER RUN OR TWO BEFORE INCREASING POPS FOR SUNDAY.

 

– JRH

 

References:

 

NWS Area Forecast Discussion
NWS Forecast Table Interface