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000 FXUS66 KSTO 210507 AFDSTO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SACRAMENTO CA 955 PM PDT SAT SEP 20 2008 .DISCUSSION... SHORT WAVE THAT HAS MOVED OVER NORCAL TODAY MAINTAINED ONSHORE FLOW AND BROUGHT COOLER THAN NORMAL MAX TEMPS TO THE INTERIOR...SOME 8 TO 10 DEG BELOW NORMAL IN THE VLY. UPWARD MOTION FROM THE SHORT WAVE HAS LIFTED/ERODED MUCH OF THE MARINE LAYER ALONG THE CA COAST... EXCEPT INTO AND NEAR THE SFO BAY AREA. WITH WATER VAPOR AND MODELS INDICATING RELATIVELY WEAK SHORT WAVES OVER THE ERN PAC MOVING ACROSS NORCAL ON SUN...WE EXPECT ONSHORE FLOW TO CONTINUE WITH THE MARINE LAYER OFF THE SFO COAST CONTINUING TO PROVIDE MUCH COOLER THAN NORMAL MAX TEMPS THROUGH THE DELTA INFLUENCE AREAS. LOOKS LIKE FURTHER AWAY FROM THE MARINE INFLUENCE MOST SITES SHOULD SEE SOME WARMING ON SUN BASED ON THE FORECAST 850 MBS TEMPS AND LOW TO MID LEVEL THICKNESSES...PERHAPS 2 TO 6 DEG OF WARMING. CLOUDINESS ALONG AND N OF 40N EXPECTED TO SPREAD INLAND ACROSS THE NRN ZONES ON SUN WITH WEAK INSTABILITY NOTED ACROSS THE NRN MTNS AND NE PLATEAU. THERE IS SOME UPPER LEVEL DIVERGENCE NOTED ACROSS THE AREA FROM THE INDIRECT CIRCULATION OF THE INBOUND JET SUN AFTN. THE SHORT WAVES CONSOLIDATE AS THE TROF DEEPENS SLIGHTLY AS IT MOVES INTO THE GREAT BASIN ALLOWING THE ERN PAC RIDGE TO BUILD INTO NORCAL SLIGHTLY ON MON. ADDITIONAL WARMING OF SOME 4 TO 6 DEG IS EXPECTED BASED ON THE FORECAST 850 MBS TEMPS AND LOW TO MID LEVEL THICKNESSES. SO THE FIRST DAY OF FALL WILL STILL SEEM A LITTLE SUMMERY...AS THE AUTUMNAL EQUINOX OCCURS ON 9/22 AT 1544Z (0844 PDT). ADDITIONAL WARMING EXPECTED ON TUE WITH TEMPS RETURNING TO NORMAL AS THE RIDGE OF HIGH PRESSURE FROM THE DESERT SW EXPANDS SLIGHTLY NWD. JHM && .EXTENDED DISCUSSION (TUESDAY NIGHT THROUGH SATURDAY)... HI PRESSURE DEVELOPS NEAR THE MEXICO BORDER IN THE DESERT SOUTHWEST AS 500 MB HEIGHTS BECOME ZONAL ACROSS NORTHERN CALIFORNIA. SOME WEAK SHORTWAVES MAY PASS TO THE NORTH OF CALIFORNIA WEDNESDAY THROUGH FRIDAY. TEMPERATURES ARE EXPECTED TO FLUCTUATE NEAR NORMAL WITH THURSDAY AND FRIDAY BEING THE WARMEST DAYS AS RIDGING EXPANDS NORTHWARD...GENERALLY 2-4 DEGREES ABOVE NORMAL. TEMPS WILL BEGIN A COOLING TREND...JUST BELOW NORMAL...BY SATURDAY AS A LOW PRESSURE SYSTEM APPROACHES THE CANADIAN COASTLINE AND ITS ASSOCIATED TROUGH DIGS SOUTHWARD OVER CALIFORNIA. HAVE KEPT FORECAST DRY DURING TROUGH PASSAGE SINCE MODELS SHOW PRECIPITATION STAYING TO THE NORTH OR ALONG THE COAST. JBB && .AVIATION... VFR CONDS WITH STRATUS EXPANDING OVER SFO BAY AREA WITH IFR/MVFR CIGS. APPROACHING SHORT WAVE ON SUN WILL SPREAD HIGH BASED CLOUDINESS OVER INTERIOR NORCAL...ESPECIALLY NRN MTNS ON SUN WITH CHANCE OF ISOLD RW-/TRW- SUN AFTN. && .STO WATCHES/WARNINGS/ADVISORIES...NONE. && $$