000 FXUS66 KSTO 100452 AFDSTO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SACRAMENTO CA 852 PM PST THU FEB 9 2012 .SHORT TERM DISCUSSION... A VERY WEAK SYSTEM OFF TO THE WEST WILL MOVE ALONG THE INTERIOR COASTAL RANGE LATE TONIGHT AND SATURDAY MORNING WITH SOME LIGHT RAIN EXPECTED FROM AROUND THE NORTH BAY NORTHWARD. AS THE LOW MOVES INLAND DURING THE DAY THERE WILL BE A CHANCE OF SHOWERS...MAINLY TO THE NORTH OF SACRAMENTO IN THE VALLEY AND NORTH OF US-50 IN THE MOUNTAINS DURING THE DAY. THERE WILL BE A WEAK WAVE THAT DEVELOPS OVER THE SOUTHERN END OF THE LOW THAT WILL MOVE OVER THE NORTHERN SAN JOAQUIN VALLEY LATE FRIDAY NIGHT AND SATURDAY MORNING THAT WILL KEEP THE THREAT OF SOME SHOWERS AROUND THE INTERIOR. AS THE LOW MOVES EASTWARD SATURDAY NIGHT THE THREAT OF ANY SHOWERS GOES AWAY. THE AMOUNT OF MOISTURE IS VERY LIMITED THROUGHOUT THIS TIME PERIOD SO NOT MUCH RAINFALL IS EXPECTED...EVEN FOR THE MOUNTAINS AND GENERALLY LESS THAN A TENTH OF AN INCH. WEAK RIDGING WILL OCCUR FOR SUNDAY AHEAD OF ANOTHER SYSTEM THE WILL BE A LITTLE WETTER AND MUCH COLDER AND MOVE INTO THE AREA SUNDAY NIGHT AND MONDAY MORNING. IN ADDITION TO BEING A LITTLE WETTER THIS SYSTEM LOOKS FAIRLY UNSTABLE AND COULD BRING SOME THUNDERSTORMS TO THE INTERIOR ON MONDAY. .EXTENDED DISCUSSION (MONDAY THROUGH THURSDAY) MODEL CONSENSUS INDICATES A CLOSED UPPER-LEVEL LOW WILL BE TRACKING OVER NORCAL ON MON BRINGING AT LEAST A GOOD CHANCE TO LIKELY PROBABILITY OF PRECIP TO INTERIOR NORCAL. THE LOW IS FORECAST TO BE A NEGATIVE 1 TO 2 STANDARD DEVIATION ANOMALY AS IT MOVES INLAND RESULTING IN STRONG CAA...STEEPENING LAPSE RATES AND GOOD INSTABILITY...AND A COOL/SHOWERY DAY OVER NORCAL. A BAND OF SHOWERS IS EXPECTED ALONG AND BEHIND THE COLD FRONT AS IT MOVES OVER THE FORECAST AREA DURING THE MORNING. 700 MBS TEMPS FROM THE GFS ARE FORECAST TO BE AROUND -10 DEG C...CORRELATING WITH SNOW LEVELS AROUND 3500 FT...AND POSSIBLY AS LOW AS 2000 TO 3000 FEET AND INTO THE HIGHER FOOTHILLS. DEPTH OF MOISTURE IS FORECAST TO BE THE GREATEST AHEAD OF THE FRONT WITH MID LEVEL DRYING OCCURRING BEHIND THE FRONT. THE FAST MOVING SPEED OF THE LOW AND LIMITED DEPTH OF MOISTURE DOES NOT MAKE THIS A VERY WET SYSTEM...BUT IT SHOULD BE WETTER THAN THE LAST SYSTEM OVER THE SIERNEV WHERE A COUPLE OF INCHES OF SNOW IS POSSIBLE. QPFS UP TO AROUND A HALF INCH ARE POSSIBLE IN THE SIERNEV WITH UP TO QUARTER INCH AMOUNTS IN THE VALLEY ARE SHOWN IN THE QPF GRIDS. BACKWASH CLOUDS AND SCATTERED SHOWERS MAY OCCUR MAINLY OVER THE SIERNEV MON NITE AND EARLY TUE. THERE WAS BETTER CONSENSUS IN THE EXTENDED MODELING FOR THE MIDWEEK PERIOD UNTIL THE 18Z GFS CAME IN. THE LATER RUN NOT ONLY SHOWED LESS INSTABILITY ON MON THAN THE 12Z RUN...BUT ALSO A SECOND LOW DROPPING SWD OVER THE SIERNEV ON WED WHILE THE GFS AND ECMWF TRANSITIONED FROM CYCLONIC TO ANTICYCLONIC FLOW AND RIDGING. THIS IS A BIG CHANGE FROM EARLIER RUNS...AND IS MET WITH SKEPTICISM AT THIS TIME. RIDGING ALOFT AND NLY FLOW IS EXPECTED TO RETURN ON THU FOR A MILD/SEASONABLY WARM DAY. AS THE RIDGE FLATTENS LATER THU AND FRI...SOME WAA PRECIP MAY MAKE ITS WAY INTO THE NRN MTNS. JHM && .AVIATION... VFR CONDITIONS THIS EVENING ACROSS INTERIOR NORTHERN CALIFORNIA. PATCHY MVFR/IFR BR POSSIBLE TONIGHT BETWEEN 10-18Z MAINLY NEAR SACRAMENTO AREA AND KSCK TAF SITES. MID CLOUDS WILL INCREASE AFTER 12Z TONIGHT AS A WEAK FRONTAL SYSTEM MOVES THROUGH THE AREA. SCATTERED -SHRA MAY BE POSSIBLE AFTER 18Z FRIDAY...MAINLY KSAC AND NORTHWARD. GENERALLY VFR/MVFR CONDITIONS EXPECTED IN -SHRA. LIGHT WINDS EXPECTED IN THE VALLEY THROUGH FRI. SOUTHWEST WIND GUSTS UP TO 35 KT POSSIBLE ALONG SIERRA RIDGETOPS FRIDAY. DANG && .STO WATCHES/WARNINGS/ADVISORIES...NONE. && $$