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