ECMWF vs. GFS

Runners, you gotta know a few geeky weather terms. Just a few. ECMWF is European Center for Medium-Range Weather Forecasts, an organization that uses computer modeling based on six equations to issue 10-day forecasts (among other "products"). GFS, which stands for Global Forecast System, is an American-based computer model and because it's freeware a lot of the weather Web sites like Weather Underground, Weather Channel, etc. rely heavily on it for their forecasts. I'm sure you'll want to delve into the GFS atmosphereic model description here. The GFS runs out to 16 days but nobody really trusts it past about a week.

So what we have now, according to the National Weather Service offices in both the Bay Area and Sacramento, is a disagreement between the ECMWF and GFS. The Euro sees rain hitting Northern California late Sunday; the GFS sees it holding off until later in the week. Either way we win, right?

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
904 PM PST MON NOV 30 2009

.DISCUSSION...AS OF 9:00 PM PST MONDAY...THE MAIN FOCUS IS THE MAJOR PATTERN CHANGE...WHICH MAY DEVELOP BY THE END OF THE UPCOMING WEEKEND.

... THE 12Z ECMWF DEVELOPS A MAJOR PRECIP EVENT ACROSS NEARLY THE ENTIRE STATE OF CALIFORNIA FROM LATE SUNDAY THROUGH MONDAY. THE 00Z GFS..ON THE OTHER HAND...HOLDS OFF WITH THE INITIAL SALVO OF RAIN AND WIND UNTIL THE MIDDLE OF NEXT WEEK...WITH MORE RAIN FORECAST TO QUICKLY FOLLOW. THE MESSAGE AT THIS POINT IS THIS: CONFIDENCE IS HIGH REGARDING THE UPCOMING MAJOR PATTERN CHANGE AND THE POTENTIAL FOR AN EXTENDED PERIOD OF WET WEATHER. BUT THE TIMING REMAINS UNCERTAIN... ESPECIALLY FOR THE INITIAL EVENT. FOR PLANNING PURPOSES...POTENTIALLY HEAVY RAINFALL AND STRONG WINDS MAY ARRIVE AS EARLY AS SUNDAY NIGHT...OR AS LATE AS THE MIDDLE OF NEXT WEEK. AND...WET AND BLUSTERY WEATHER WILL LIKELY PERSIST OFF AND ON FOR SEVERAL DAYS ONCE IT STARTS. HAZARDOUS WEATHER OUTLOOKS/SPECIAL WEATHER STATEMENTS WILL BE ISSUED ONCE THERE IS A CLEARER IDEA ON THE TIMING.


AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
930 PM PST MON NOV 30 2009

... BOTH THE GFS AND ECMWF SHOW BREAK DOWN OF THE RIDGE...BUT DIFFER SIGNIFICANTLY ON HOW WET IT MAY BE IN NORCAL. WHILE THE GFS BRINGS A COLD AIR LOW DOWN FROM THE ARCTIC...THE ECMWF BRINGS IT IN FROM THE GULF OF AK...AND IS MUCH WETTER AS MOISTURE FROM TYPHOON NIDA CURRENTLY NEAR 140E MAY BECOME ENTRAINED INTO THE UNDERCUTTING FLOW. THEREFORE THERE IS A HIGH DEGREE OF UNCERTAINTY INVOLVED IN THE THE FORECASTS FOR THE UPCOMING WEEKEND.