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Wednesday, December 2, 2009
Sacto NWS Discussion: Colder, Slight Rain Chance
It hit 61 at Sacramento Executive Airport this afternoon, but that could be it for 60s for a while. The latest Area Forecast Discussion calls for highs to plunge "10 to 20 degrees" over the weekend. Precipitation remains a possibility for Sunday but chances appear small and amounts, if any, would be light. That's because, if I'm reading this correctly, the Saturday/Sunday "storm" appears to be what is often called an "inside slider." In addition to being a very tough pitch to hit, an inside slider is a weather system that moves into California from the north. As such, it doesn't pick up moisture the way the vast bulk of the state's winter storms do when they come in from the Pacific.
As for winds, both direction and force too difficult to say right now—all depends on the precise timing of that upper level low.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
300 PM PST WED DEC 2 2009
... THE RIDGE WEAKENS OVER THE AREA AS AN UPPER LEVEL LOW DROPS DOWN FROM CANADA INTO THE PACIFIC NORTHWEST FRIDAY INTO FRIDAY NIGHT THIS WILL START THE COOLING TREND. THE MODELS STILL VARY WITH THE TIMING...TRACK AND STRENGTH OF THIS LOW WITH THE ECMWF BEING FURTHER WEST AND DEEPER. EITHER WAY THIS WILL BRING SOME COLD CONTINENTAL AIR DOWN OVER NORTHERN CALIFORNIA. HIGH TEMPERATURES WILL DROP AROUND 10 TO 20 DEGREES OVER THE WEEKEND COMPARED TO WHAT WE SAW TODAY. THE GFS REMAINS DRY WITH A MORE EASTERLY TRACK AND THE ECMWF BRINGS SOME PRECIPITATION OVER THE SIERRA SATURDAY INTO EARLY SUNDAY. THE FORECAST LEANS TOWARD A FURTHER WESTERLY TRACK WITH THE LOW FOR A SLIGHT CHANCE TO CHANCE OF SHOWERS OVER THE SIERRA AND SHASTA COUNTY MOUNTAINS SATURDAY INTO EARLY SUNDAY. COLD AIR WILL BE COMING DOWN WITH THIS SYSTEM DROPPING SNOW LEVELS DOWN TO AROUND 3000 FEET IN THE NORTH TO AROUND 4500 FEET SOUTH OF TAHOE. THIS COULD BRING WINTER DRIVING CONDITIONS TO THE MOUNTAIN PASSES SATURDAY NIGHT INTO SUNDAY. ALTHOUGH THE SYSTEM IS FAIRLY DRY SO SNOWFALL ACCUMULATIONS ARE EXPECTED TO BE LESS THAN 6 INCHES AT THE HIGHEST ELEVATIONS AT THIS TIME. AS THE SYSTEM DIGS OUT INTO THE PACIFIC IT WILL BRING A SLIGHT CHANCE OF RAIN AND SNOW OVER THE AREA ON SUNDAY. HSO
As for winds, both direction and force too difficult to say right now—all depends on the precise timing of that upper level low.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
300 PM PST WED DEC 2 2009
... THE RIDGE WEAKENS OVER THE AREA AS AN UPPER LEVEL LOW DROPS DOWN FROM CANADA INTO THE PACIFIC NORTHWEST FRIDAY INTO FRIDAY NIGHT THIS WILL START THE COOLING TREND. THE MODELS STILL VARY WITH THE TIMING...TRACK AND STRENGTH OF THIS LOW WITH THE ECMWF BEING FURTHER WEST AND DEEPER. EITHER WAY THIS WILL BRING SOME COLD CONTINENTAL AIR DOWN OVER NORTHERN CALIFORNIA. HIGH TEMPERATURES WILL DROP AROUND 10 TO 20 DEGREES OVER THE WEEKEND COMPARED TO WHAT WE SAW TODAY. THE GFS REMAINS DRY WITH A MORE EASTERLY TRACK AND THE ECMWF BRINGS SOME PRECIPITATION OVER THE SIERRA SATURDAY INTO EARLY SUNDAY. THE FORECAST LEANS TOWARD A FURTHER WESTERLY TRACK WITH THE LOW FOR A SLIGHT CHANCE TO CHANCE OF SHOWERS OVER THE SIERRA AND SHASTA COUNTY MOUNTAINS SATURDAY INTO EARLY SUNDAY. COLD AIR WILL BE COMING DOWN WITH THIS SYSTEM DROPPING SNOW LEVELS DOWN TO AROUND 3000 FEET IN THE NORTH TO AROUND 4500 FEET SOUTH OF TAHOE. THIS COULD BRING WINTER DRIVING CONDITIONS TO THE MOUNTAIN PASSES SATURDAY NIGHT INTO SUNDAY. ALTHOUGH THE SYSTEM IS FAIRLY DRY SO SNOWFALL ACCUMULATIONS ARE EXPECTED TO BE LESS THAN 6 INCHES AT THE HIGHEST ELEVATIONS AT THIS TIME. AS THE SYSTEM DIGS OUT INTO THE PACIFIC IT WILL BRING A SLIGHT CHANCE OF RAIN AND SNOW OVER THE AREA ON SUNDAY. HSO
Truth and the Forecast
My favorite story involving weather forecasting and big public events is the one about the radio weather guy who got fired for correctly predicting rain at a Rush Limbaugh dittohead gathering in the San Joaquin Valley. This is true. Walter Brasch reported the story back in 1995:
KMJ, which carries the Rush Limbaugh talk show, was sponsoring the Second Annual Dittohead Barbecue and Politically Incorrect Picnic, Saturday, April 15. Since it was already politically incorrect, it was apparently no big deal that it was also Easter and Passover weekend.Ten days later, Broeske canned Boyd, although he denied it was because of the weather guy's unwillingness to shade a forecast.
Four days before the Dittoheads were to meet, (Sean) Boyd forecast a chance of showers, based upon reports of the National Weather Service. (Program Director John) Broeske possibly didn't think that anyone, including the clouds, had a right to rain upon his plumped-up sizzling raucous barbecued hotdogs. After all, the station, which sends 5,000 screaming watts of conservative thinking into one of the state's biggest media markets, had something of an investment in making sure thousands showed up to celebrate the Biggest Mouth That Roars, even if the Chief Dittohead himself had no plans to attend. So, Broeske strongly suggested that Boyd revise the forecast. After all, you never know with California weather. It could have been a wonderful day in the neighborhood.
"Do you want me to change all the forecasts?" Boyd asked, then sarcastically suggested that the program director could just write down what he thought the weather should be, "and I'll tell it just the way you have asked." The program director might have thought about the temptation to move a few clouds but declined. Boyd stuck with his weather report. About 3 p.m. that Sunday, rain began falling upon the char-smoked Dittoheads....
Ideal Conditions?
In 2008, just before the London Marathon, the guys at Science of Sport explored the research on what weather conditions are conducive to high performance. The whole piece, which is not especially long, is worth reading, but the upshot is that 41-59F (5-15C) is the sweet spot for fast times. Generally, ambient temperature trumps sky conditions as a predictor of performance, but if temps are below ideal—say, 32-41F (0-5C)—runners seem to do better if the sun in shining than they do under cloudy skies. As Jonathan Dugas said in a comment to the post: "[E]ven though the guys are running at very high metabolic rates, when the ambient temp is 0-5 C and there is no sunshine even they tend to get cold and uncomfortable and suffer from the conditions."
Morning Roundup
National Weather Service
Saturday night in Folsom shows a slight chance of rain, rising to a chance of rain on Sunday. Morning low around 37. For Sacramento Sunday, a chance of rain, mostly cloudy, high 53.
AccuWeather
Around 37 degrees and dry in Folsom at the start. Clouding up through the morning, chance of rain increasing, heading toward a high of 51 in Sacramento.
Weather Channel
Partly cloudy overnight Saturday in Folsom, with a 20 percent chance of rain, morning low around 35. South winds at 5 mph. For Sacramento for Sunday, times of sun and clouds. Highs in the mid 50s. 10 percent chance of rain.
Wunderground
For Folsom Sunday morning, mostly cloudy, 20 percent chance of rain at 4 a.m. rising to 50 percent chance at 10 a.m. Temp around 36 at sunrise. Light winds shifting from west to south/southeast.
Tuesday, December 1, 2009
Chilly, Yes; Not so Much Rain or Wind?
OK, the Bay Area NWS has moved the pattern-change thinking ahead quite a bit tonight, at least according to this amateur's interpretation of the fresh forecast disucssion. It's not going to be very wet in the Sacramento-Folsom corridor Sunday morning, if at all, but it will be chilly. The middle of next week California will be slammed with heavy rain and strong winds.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
910 PM PST TUE DEC 1 2009
...NO SIGNIFICANT WEATHER EXPECTED THROUGH SATURDAY. A MAJOR PATTERN CHANGE BY EARLY NEXT WEEK WILL PRODUCE A PERIOD OF STORMY WEATHER WITH A CHANCE FOR HEAVY RAINFALL.
... ECMWF AND GFS ARE NOW COMING INTO BETTER AGREEMENT ON HOW THE PATTERN WILL INITIALLY EVOLVE FROM DRY TO WET. BOTH MODELS INDICATE THAT A PIECE OF ENERGY FROM THE SYSTEM CURRENTLY BETWEEN 140 AND 150W WILL BREAK OFF AND MOVE OVER THE TOP OF THE RIDGE DURING THE NEXT 48 HOURS...INGEST SOME COLD CANADIAN AIR...AND FORM A CLOSED UPPER LOW OVER OR NEAR THE PAC NW BY FRIDAY AFTERNOON. MEANWHILE A WETTER AND MORE POWERFUL SYSTEM IS POISED TO BREAK UNDER THE RIDGE AND APPROACH CA FROM THE DUE WEST BY LATE IN THE WEEKEND. MOST RECENT MODEL OUTPUT INDICATE THAT THE COLD SYSTEM OVER THE PAC NW WILL SAG FAR ENOUGH SOUTH TO DEFLECT MOST OF THE MOISTURE FEEDING IN FROM THE WEST...AND THAT SOUTHERN CALIFORNIA WILL GET THE BRUNT OF THE PRECIP FROM THE FIRST SYSTEM EARLY NEXT WEEK. WE`LL LIKELY SEE SCATTERED SHOWERS SOMETIME LATE IN THE WEEKEND AND INTO MONDAY. FOR OUR AREA... THE HIGHEST RAINFALL TOTALS WITH THIS FIRST SYSTEM WILL LIKELY BE ACROSS OUR SOUTHERN-MOST COUNTIES...THE AREA CLOSEST TO THE BEST MOISTURE INFLUX. BUT RAINFALL AMOUNTS DO NOT LOOK OVERLY IMPRESSIVE ANYWHERE IN OUR AREA THROUGH MONDAY. MUCH MORE SIGNIFICANT RAINFALL IS LIKELY TO FOLLOW FROM THE MIDDLE OF NEXT WEEK ONWARD AS A STRONG AND WET FLOW ACROSS THE PACIFIC BREAKS FULLY THROUGH AND DELIVERS PERIODIC RAIN EVENTS (LIKELY HEAVY) FROM TUESDAY NIGHT OR WEDNESDAY ONWARD. PERIODS OF STRONG WIND AND HEAVY SEAS WILL OCCUR AS WELL BEGINNING AROUND THE MIDDLE OF NEXT WEEK. THE HAZARDOUS WEATHER STATEMENT WILL BE UPDATED SHORTLY TO MORE ACCURATELY REFLECT THE MOST RECENT FORECAST GUIDANCE.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
910 PM PST TUE DEC 1 2009
...NO SIGNIFICANT WEATHER EXPECTED THROUGH SATURDAY. A MAJOR PATTERN CHANGE BY EARLY NEXT WEEK WILL PRODUCE A PERIOD OF STORMY WEATHER WITH A CHANCE FOR HEAVY RAINFALL.
... ECMWF AND GFS ARE NOW COMING INTO BETTER AGREEMENT ON HOW THE PATTERN WILL INITIALLY EVOLVE FROM DRY TO WET. BOTH MODELS INDICATE THAT A PIECE OF ENERGY FROM THE SYSTEM CURRENTLY BETWEEN 140 AND 150W WILL BREAK OFF AND MOVE OVER THE TOP OF THE RIDGE DURING THE NEXT 48 HOURS...INGEST SOME COLD CANADIAN AIR...AND FORM A CLOSED UPPER LOW OVER OR NEAR THE PAC NW BY FRIDAY AFTERNOON. MEANWHILE A WETTER AND MORE POWERFUL SYSTEM IS POISED TO BREAK UNDER THE RIDGE AND APPROACH CA FROM THE DUE WEST BY LATE IN THE WEEKEND. MOST RECENT MODEL OUTPUT INDICATE THAT THE COLD SYSTEM OVER THE PAC NW WILL SAG FAR ENOUGH SOUTH TO DEFLECT MOST OF THE MOISTURE FEEDING IN FROM THE WEST...AND THAT SOUTHERN CALIFORNIA WILL GET THE BRUNT OF THE PRECIP FROM THE FIRST SYSTEM EARLY NEXT WEEK. WE`LL LIKELY SEE SCATTERED SHOWERS SOMETIME LATE IN THE WEEKEND AND INTO MONDAY. FOR OUR AREA... THE HIGHEST RAINFALL TOTALS WITH THIS FIRST SYSTEM WILL LIKELY BE ACROSS OUR SOUTHERN-MOST COUNTIES...THE AREA CLOSEST TO THE BEST MOISTURE INFLUX. BUT RAINFALL AMOUNTS DO NOT LOOK OVERLY IMPRESSIVE ANYWHERE IN OUR AREA THROUGH MONDAY. MUCH MORE SIGNIFICANT RAINFALL IS LIKELY TO FOLLOW FROM THE MIDDLE OF NEXT WEEK ONWARD AS A STRONG AND WET FLOW ACROSS THE PACIFIC BREAKS FULLY THROUGH AND DELIVERS PERIODIC RAIN EVENTS (LIKELY HEAVY) FROM TUESDAY NIGHT OR WEDNESDAY ONWARD. PERIODS OF STRONG WIND AND HEAVY SEAS WILL OCCUR AS WELL BEGINNING AROUND THE MIDDLE OF NEXT WEEK. THE HAZARDOUS WEATHER STATEMENT WILL BE UPDATED SHORTLY TO MORE ACCURATELY REFLECT THE MOST RECENT FORECAST GUIDANCE.
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