Forecast Discussions mentioning ACARS, received at FSL on 05/20/00

CLOUDS HAVE CLEARED OUT JUST ABOUT EVERYWHERE IN OUR CWA AND EVEN IN SRN ZONES ITS PARTLY CLOUDY...BUT LOW AND MID CLOUDS LINGER JUST SOUTH AND WEST OF OUR AREA. WITH DEW PT TEMPS IN MAINLY IN THE 30S AND 20S TO THE NORTH...LOW TEMPS SHOULD BE ABOUT AS LOW AS LAST NIGHT WITH READINGS IN THE 30S EXCEPT SOME UPPER 20S IN THE NORMALLY COLDER MOUNTAIN VALLEY LOCATIONS. ACARS 0RD->BTV SOUNDING SHOWS TEMPS DOWN TO 34 DEGREES AT 4000 FT.

18Z ETA KEEPS CLOUDS TO OUR SOUTH AND WEST THROUGH 18-21Z TOMORROW SO HAVE INDICATED THAT IN THE CENTRAL AND SOUTHERN ZONES. TEMPERATURES WILL BE VERY CLOSE TO NORMAL IN THE MID TO UPPER 60S.

PS

.BTV...NONE.



PATCHY STRATUS AND DENSE FOG WHICH AFFECTED IMDT CSTL SXNS OF SRN VTU AND L.A. COUNTIES EARLIER THIS EVENING HAS PUSHED TO THE S AND DISSIPATED...AS HAVE LOW CLDS ALG THE CNTRL CST OF SLO/SBA COUNTIES. AS A RESULT...THE ENTIRE FCST AREA WAS CLEAR ATTM. DEWPOINTS WERE STILL QUITE HIGH NEAR THE IMDT CST...AND WITH VERY SMALL TEMP/DEW POINT SPREAD...AND A LOW INVERSION BLV SOME DENSE FOG MAY DEVELOP IN CSTL SXNS OVERNIGHT. XPCT ANY DENSE FOG TO BE CONFINED TO WITHIN A COUPLE OF MILES...AT MOST...OF THE BEACHES. WL INCLUDE PTCHY DENSE FOG NEAR THE BEACHES TONIGHT/EARLY SAT IN AN EVENING ZONE UPDATE.

ONSHR COMPONENT OF PRES GRADS WAS GENERALLY WK AND TRENDING WKLY OFHSR. N-S COMPONENTS WERE A BIT STRONGER...BUT WERE IN THE PROCESS OF DECRSG. THEREFORE...ALTHOUGH SOME GUSTY NLY WINDS ARE XPCTD BLO PASSES AND CYNS OF SRN SBA CNTY...WNDS WL MOST CERTAINLY STAY BELOW ADVISORY CRITERIA.

UPR RDG IN THE PROCESS OF BLDG INTO CA ATTM. BROAD SCALE SUBSIDENCE ASSOCD WITH THE RDG HAS CAUSED SIGNIFICANT WARMING TO SPRD INTO LOWER LVLS OF THE ATMOS...AND HAS CAUSED MARINE INVERSION TO LOWER AND STRENGTHEN. IN FACT...THANKS TO KSAN FOR POINTING OUT A PARTICULAR ACARS SOUNDING FROM KLAX SHOWING AN INVERSION TOP TEMP OF 83 DEGS F AT ARD 1000 FT! WHILE SUCH A STRONG INVERSION CAN TYPICALLY RESULT IN SLOW CLEARING...BLV THERE WILL NOT BE ENOUGH OF A LOW CLD FIELD FOR THIS TO POSE A PROBLEM ON SAT. CONTD RISES IN THICKNESSES AND H85 TEMPS SHOULD LEAD TO SEVERAL DEGS OF WARMING IN MOST AREAS ON SAT. HAVING THE ADVANTAGE OF NOW KNOWING THE HIGH TEMPS ACRS THE AREA ON TODAY... WL BUMP TEMPS UP IN MOST AREAS FOR SAT. STRONG AND SHALLOW INVERSION WILL LIKLEY RESULT IN A VERY SHARP TEMP GRADIENT FROM THE BEACHES TO THE LOWER VLY LOCATIONS ON SAT.

UPR RDG WILL CONT TO STRENGTHEN ACRS THE AREA ON SUN. ADDITIONAL RISES IN THICKNESSES AND H85 TEMPS WILL LIKELY SEND TEMPS TO NEAR RECORD LVLS ACRS THE MTNS...DSRTS AND VLYS ON SUN. MESO ETA AND AVN HINT AT A VERY SHALLOW EDDY CRCLN JUST OFF THE COAST SAT NIGHT/SUN AND MESO SHOWS AN INCRS IN LOW LVL RH FIELDS...MAINLY OVER SRN CSTL SXNS OF L.A. CNTY. THIS WOULD SUGGEST THE POTENTIAL FOR SOME LOW CLDS/PATCHY DENSE FOG SAT NIGHT/EARLY SUN...SO WL ADD THAT TO FCST. WITH CONTD STRONG INVERSION...A MORE XTNSV CLD FIELD AND WK SLY LOW LVL FLOW FOR SUN... THERE IS THE THREAT THAT LOW CLDS COULD BE STUBBORN ALG THE BEACHES OF L.A. AND POSSIBLY VTU COUNTIES ON SUN. ALSO...IF A WK EDDY CRCLN DOES DVLP...IT MAY INDUCE SOME COOLING AT LEAST TO INLAND SNXS OF THE CSTL PLAIN SUN. WL LEAVE THOSE POSSIBILITIES FOR LATER SHIFTS TO EVALUATE.

RDG WL CONT TO KEEP HEIGHTS VERY HIGH ACRS THE FCST AREA THRU TUE OR WED...SO MOST LIKELY SCENARIO WOULD BE FOR SHALLOW MARINE LAYER TO CONT...WITH NIGHT THRU MORNING LOW CLDS AND FOG CONFINED TO THE CSTL PLAIN...AND WELL ABOVE NORMAL TEMPS CONTG IN THE MTNS...DSRTS AND VLYS. ONLY POSSIBLE FLY IN THE OINTMENT...IS VRY WK H5 LOW SPINNING TO THE S AND SW OF THE FCST AREA LATE SUN THRU TUE. ODDS FAVOR THAT THIS SYSTEM WL BE TOO WEAK AND TOO FAR S TO HAVE ANY IMPACT ON THE FCST AREA. HWVR...IT WILL BE IN A PRECARIOUS POSITION...LOCATED SUCH TO ALLOW FOR POSSIBLE DEEPENING OF THE MARINE LYR WHICH COULD SPREAD COOLING INTO THE VLYS. IN ADDITION...WK SELY FLOW ALF COULD HELP STEER SOME MID AND HIGH LVL MSTR INTO THE MTNS AND DSRTS BY MONDAY... SO HAVE TO KEEP EYES TO THE SE OF THE FCST AREA AS WELL.

LAX 0000. BRUNO.

.LAX...SMALL CRAFT ADVISORY (SEE LAXCWFLAX).



HIGH PRESSURE RIDGE OVER NORTHEAST ILLINOIS WILL REMAIN THROUGH SUNDAY AFTERNOON. THE LOW CLOUDS ARE ERODING VERY SLOWLY. THE RUC AND AVN MODELS KEEP HIGH RELATIVE HUMIDITIES IN THE LOW LEVELS THROUGH 12 UTC SATURDAY. ACARS SOUNDINGS SHOW THE INVERSION AT 831 MB AND 741 MB. THE CLOUDS SEEM TRAPPED BY THE LOWER INVERSION. TO BREAK THAT INVERSION A TEMPERATURE OF 74 DEGREES IS NEEDED. WILL FORECAST MOSTLY CLOUDY SKIES THIS MORNING FOR THE CHICAGO AREA AND ROCKFORD AND PARTLY SUNNY TODAY. WITH THE CLOUDS AROUND TEMPERATURES MAY NOT REACH ABOVE GUIDANCE.

THE 500 MB TROUGH OVER NEBRASKA AND IOWA IS FORECASTED BY THE AVN AND ETA MODELS TO BRING POSITIVE VORTICITY ADVECTION INTO NORTHEAST ILLINOIS BY SUNDAY AFTERNOON. MODELS MOVEMENT OF THE TROUGH IS CLOSE BUT A LITTLE FASTER THAT EXTRAPOLATION OF ANALYSIS AT 500 MB AND WATER VAPOR LOOPS. LARGE CAPES ARE FORECASTED OVER WESTERN ILLINOIS AS WELL AS MODERATE WARM AIR ADVECTION AT 850 MB. WILL ADD PROBABILITIES FOR SHOWERS AND THUNDERSTORMS SUNDAY NIGHT AND MONDAY.

.CHI...NONE WHW