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.

News10 ABC Sacramento 7-Day

Words to Live By

Love the Phil & Teds mottoes: "There's No Such Thing as Bad Weather, Just the Wrong Cover," and "Adapt and Survive." Check it out, courtesy Jose's cool wife.

Marathon Weather

Not a lot of options on the course, but you'd have some balmy early morning temps.

Soggy Slog? Uncertainty Reigns

The new Sacto discussion is posted. Various scenarios are described, ranging from rain on Saturday into Sunday to rain holding off until Sunday afternoon to rain not arriving until Monday. Net result is a forecast for below normal temps and above-normal rain chances with "uncertainty in the timing, coverage and amount of precipitation."

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

...EXTENDED DISCUSSION (FRIDAY NIGHT THROUGH MONDAY)...THE MODELS HAVE VARIOUS SOLUTIONS FOR THE WEEKEND AND INTO NEXT MONDAY BUT EITHER WAY IT WILL MOST LIKELY BECOME COOLER AND WETTER FOR AT LEAST A PORTION OF INTERIOR NORTHERN CALIFORNIA. THE 18Z GFS HAS A LOW COMING DOWN INTO MONTANA FRIDAY NIGHT INTO SATURDAY. THE LOW THEN RETROGRADES TO NEAR THE ORCA BORDER ON SUNDAY NIGHT AND OVER NORTHERN CALIFORNIA ON MONDAY. THIS WOULD BRING COOLER TEMPERATURES AND A CHANCE OF PRECIPITATION TO THE AREA BY SUNDAY AFTERNOON AND INTO MONDAY. THE ECMWF HAS A LOW FROM THE GULF OF ALASKA OFF THE PACIFIC NORTHWEST COAST ON FRIDAY NIGHT AND THEN IT MOVES SOUTH AND COMBINES WITH ANOTHER LOW THAT MOVES EAST FROM 140 WEST SUNDAY NIGHT AND THEN THE SYSTEM MOVES INLAND THROUGH CALIFORNIA ON MONDAY. A MOISTURE PLUME IS EXPECTED WITH THIS SYSTEM WHICH WOULD BRING WETTER WEATHER THAN THE GFS. THE ECMWF SHOWS 500 MB HEIGHTS OF 5300M WITH THIS SYSTEM WHICH IS THREE STANDARD DEVIATIONS BELOW CLIMATOLOGY SO THIS SYSTEM COULD BRING A SIGNIFICANT PRECIPITATION EVENT TO THE AREA. THE GEM MODEL IS BETWEEN THE GFS AND ECMWF AND JUST BRING THE LOW OVER THE PACIFIC NORTHWEST AND THROUGH CALIFORNIA ON SUNDAY. THIS WOULD BRING A CHANCE OF PRECIPITATION SATURDAY INTO SUNDAY. AFTER LOOKING AT THE VARIOUS SOLUTIONS THE FORECAST CURRENTLY LEANS TO BELOW NORMAL TEMPERATURES AND ABOVE CLIMATOLOGY FOR THE POPS BUT THERE IS STILL UNCERTAINTY IN THE TIMING...COVERAGE AND AMOUNT OF PRECIPITATION.

SF NWS: Growing Confidence

Yeah, this is SF, not Sacto, but as I said earlier, the train generally passes through this station on its way to the valley. And moisture and wind are now definitely on board, though it remains far from certain a storm will arrive in the valley before the race. In fact, I'm sensing (hoping?) that it'll hit the capital after we've collected our PRs, finisher medals and high fives.

This discussion relies partly on consultation with the Hydrometeorological Prediction Center—that's the HPC reference—a part of the vast National Oceanic and Atmospheric Administration apparatus that focuses on what's called "quantitative precipitation forecasting." If you read forecasts discussions much you'll come across QPF references frequently. Put simply, it's how much it's going to rain.

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

... IN THE EXTENDED...THIS WEEKEND WILL SEE THE PATTERN UNDERGO A MAJOR SHIFT. BASED ON CHATS WITH HPC AND BETTER RUN TO RUN CONSISTENCY HAVE FOLLOWED THE 12Z ECMWF. WESTERN PACIFIC TYPHOON NIDA CENTERED NEAR 20/137E WILL CONTINUE TO WEAKEN AND SHEAR APART BY THURSDAY MORNING. ENERGY FROM THE TYPHOON WILL EJECT INTO THE WESTERLIES... STRENGTHENING THE EAST ASIAN JET. ON SAT A SHORTWAVE DROPS SOUTH ALONG THE PACIFIC NW COAST...UNDERCUTTING A HIGH AMPLITUDE RIDGE CENTERED OFF THE ALASKA/BRITISH COLUMBIA COAST. THIS SHORTWAVE STALLS OFF THE COAST ALLOWING A BAROCLINIC TO DEVELOP OFF THE COAST. ON SUN THE 12Z ECMWF DEVELOPS A 992 MB LOW ALONG THE FRONT AND MOVES IT TO THE NORTHERN CA COAST...IF THIS VERIFIES SUNDAY THROUGH MONDAY COULD BE WINDY AND WET. HAVE BUMPED UP POPS A BIT...BUT HAVEN`T WENT FULL BORE ON THIS SOLUTION SINCE THE DETAILS ARE STILL IN A BIT OF FLUX (WHEREAS THE OVERALL PATTERN IS SHOWING CONSISTENCY). PER THE 12Z ECMWF...THROUGH THE MIDDLE OF THE FOLLOWING WEEK THE STORM DOOR IS OPEN WITH THE WESTERLIES BRINGING ANOTHER STRONG SYSTEM TO THE COAST
BY WEDNESDAY...

The Race Is Not Today

Still, nice afternoon in Sacramento...

FWIW: History

According to the race Web site:

During the CIM's 26 year history (1983-2008), 22 CIM's have had perfect running conditions—no rain, very light winds and temperatures that range in the low 40s at the start to upper 50s/low 60s at the finish. There were four CIMs with noticeable rain and two of those rain days were described as storm conditions with gusting winds.

Using National Weather Service statistics that include what would have been CIM dates in the 10 years before 1983, the chance of rain is 11% (4/35) and the chance of a storm is 5%.

There's also a page on the CIM site with lots of great personal stories about the 1987 race, aka "CIM Stormathon." This is widely accepted as the worst weather in the race's history, with rain and winds gusting as high as 50 mph.

Eureka Office in Agreement on Pattern Change

Mets along the far north coast of California in accord with SF and Sacto forecasters that dry gives way to wet sometime over the weekend into early next week. Key question: Exactly when?

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
322 AM PST MON NOV 30 2009

...THE RIDGE IS FORECAST TO REMAIN OVER THE WEST COAST UNTIL THE WEEKEND, CONTINUING THE DRY WEATHER AND ABOVE NORMAL INLAND TEMPERATURES. MODELS ARE STARTING TO INDICATE A PATTERN CHANGE OVER THE WEEKEND. BUMPED UP POPS ABOVE CLIMO FOR SUNDAY, BUT EXPECT THEM TO NEED TO BE RAISED FURTHER IF THE MODELS COME INTO BETTER AGREEMENT WITH THE TIMING AND STRENGTH OF THE PATTERN CHANGE. STROZ

NWS Bay Area Discussion: Another Perspective

Earlier I posted the National Weather Service Area Forecast Discussion that came out of the Sacramento office this morning. Now here's the discussion from the San Francisco Bay Area office (which is actually located in the Monterey Bay Area, go figure). I like to check in on it to see how the mets at that office might have a different take on things than those in the Sacto office. And of course, pretty much any Pacific-hatched weather that's going to happen in Sacramento has to pass first through the SF forecast area (which extends from Monterey County north through Mendocino County).

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
920 AM PST MON NOV 30 2009

A CHANGE IN THE PATTERN BEGINS OVER THE WEEKEND AS THE WESTERLIES BEGIN TO UNDERCUT THE RIDGE ALONG THE COAST. THE MODELS CONTINUE TO STRUGGLE WITH THE DETAILS OF THIS PATTERN...BUT IT APPEARS THAT ENERGY FROM TYPHOON NIDA IN THE WESTERN PACIFIC WILL ENERGIZE THE EAST ASIAN JET...WHICH WILL THEN UNDERCUT THE RIDGE. THE 12Z GFS IS SLOWER THAN ITS PREVIOUS RUN...AND IS SLOWER THAN THE 00Z ECMWF. WILL WAIT FOR THE 12Z ECMWF BEFORE MAKING ANY CHANGES/UPDATES TO THE FORECAST. MORE ON THIS DEVELOPING PATTERN CHANGE IN THE AFTERNOON DISCUSSION.

NWS Sacramento Office Discussion: Trending Wet

Weather geeks know that especially several days out, the only place to get a good sense of where the conditions are headed is to read the Weather Service "Area Forecast Discussion," available online. This is where the mets explain what they're seeing from the computer models they use, the doubts they have and their sense of how conflicting information might sort itself out. The discussion of the extended period from the Sacramento office this morning picks up on a theme from earlier discussions—that we're likely to see a shift from the dry weather of this week to a wet period next week. Questions remain, however; the models are hardly in full agreement, and at the very least there is uncertainty as to whether rain will be falling before, say, noon on Sunday, or won't arrive until later.

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
955 AM PST MON NOV 30 2009

EXTENDED DISCUSSION (FRIDAY THROUGH MONDAY)...
GFS AND GEM MODELS SHOW A HIGH AMPLITUDE RIDGE DEVELOPING NEAR THE WEST COAST ON FRIDAY. THE ECMWF MODEL IS STILL AN OUTLIER AS IT SHOWS A CUT-OFF LOW MOVING INTO THE PAC NW/NORCAL ON FRIDAY...DESPITE RIDGING. HAVE LEANED MORE TOWARDS THE GFS/GEM SOLUTION FOR FRIDAY AND SATURDAY KEEPING DRY WEATHER IN THE EXTENDED FORECAST. BY SUNDAY...THE GFS AND GEM SHOW A LOW PRESSURE CELL DROPPING SOUTHWARD FROM CANADA AND RETROGRADING INTO CALIFORNIA...WHILE THE ECMWF MODEL SHOWS THE FRIDAY LOW LINGERING ALONG THE WEST COAST. ALL THREE MODELS INDICATE A WET PATTERN SUNDAY AS A SLUG OF MARINE MOISTURE SLAMS INTO CALIFORNIA. ON MONDAY...THE GEM MOVES THE LOW QUICKLY EAST OF OUR REGION AND INDICATES A DRIER PATTERN DEVELOPING. HAVE CHOSEN TO MAINTAIN THE WETTER PATTERN FOR SUN/MON AS INDICATED BY THE GFS/ECMWF FOR THE FAR EXTENDED FORECAST.
JBB

Weather.com: Chance of Showers

"Chance of showers. Highs in the upper 50s and lows in the upper 30s."

Accuweather: Dry

"Times of cloud and sun."

Morning lows in the mid-30s.

Afternoon high 56.

Wet Sam, Dry Sam, Nervous Sam

Bee run-blog overlord Sam McManis is sounding a bit bedraggled, buffeted by changing forecasts. Sunday it was "Looks Like Rain, Folks"; today it's "Uh, Maybe No Rain After All."