Forecast Discussions mentioning ACARS, received at FSL on 07/05/99

STLT WTR VAPOR INDICATING CHANNEL OF MID LVL MSTR ALG THE ERN BDR THIS AFTN WITH SFC TROF E OF THE URBAN CORRIDOR AS WELL. CURRENT ACARS SOUNDING INDICATING A GOOD MID LVL CAP ABV H5. THEREFORE CHC FOR TS THIS EVENING SHUD BE ZERO. IF ANY STORMS DO FORM THEY MAY OCCUR OVR EXTREME SRN AND ERN PTNS OF THE CWA THIS EVENING. FOR MONDAY...SFC HIGH WILL SAG S IN THE 12-18Z TIME FRAME WITH FLOW BECOMING ELY BY THE AFTN. AFT 18Z...LOW LVL THETA-E RIDGE STARTS TO REDEVELOP OVR NERN CO. THIS COUPLED WITH WEAK COOLING IN THE MID LVLS...ASSOCIATED WITH A SHORT WAVE MOVING ACRS WY...SHUD REMOVE MID LVL CAP BY 00Z TUE. THEREFORE WL MNTN ISOLD TO WDLY SCT TSTMS FOR LATE AFTN AND EVENING ON MON. LOW LEVEL UPSLOPE WL CONTINUE INTO TUE...WITH FCST SOUNDINGS INDICATING EVEN MORE INSTBY AS LOW LVL MSTR CONTINUES TO INCRS. WITH UPR RIDGE OVHD...TSTM ACTIVITY WL CONTINUE TO BE DURING THE LATE AFTN/OVRNGHT PDS AS TSTM SHUD BE SLOW TO FIRE...UNLESS SOME UPPER LEVEL SUPPORT BRUSHES THE AREA. THESE FTRS ARE DIFFICULT TO ASSESS BEYOND 12 HRS. IN THE EXTENDED ...UPR LVL RIDGE WL CONTINUE WITH SHORT WAVE MOVING ACRS NRN ROCKIES THU INTO FRI...WITH SFC HIGH AND MORE UPSLOPE DVLPG BY FRI AFTN...SO WL KEEP MNTN OF SLGT CHC/CHC OF TSTMS THRU THE PD. COOPER

.DEN...NONE.

...SYNOPSIS... HIGH PRESSURE BUILDING WESTWARD INTO SOUTHERN CALIFORNIA WILL BRING WARMER TEMPERATURES THROUGH TUESDAY WITH LESS EXTENSIVE NIGHT AND MORNING LOW CLOUDS ALONG THE COAST.

...DISCUSSION... SUBSIDENCE FM THE SUBTOPICAL RDG BUILDING WWD INTO SRN CA FM THE SW STATES FINALLY LED TO A FASTER BREAK UP OF THE CSTL STRATUS FIELD SUN. 00Z NKX SOUNDING SHOWED THE BASE OF THE MARINE INVERSION DOWN TO AROUND 2000 FT MSL...DOWN FM ABOUT 3000 FT 24 HOURS EARLIER... WITH AN ACARS SOUNDING FM LAX EARLY SUN EVENING SHOWING THE BASE OF THE INVERSION IN CSTL LOS ANGELES COUNTY DOWN TO AROUND 1000 FT MSL. WHILE MDLS SUPPORT CONTINUED WK CSTL EDDY FORMATION EACH NIGHT THRU WED NIGHT...AREAS OF CSTL NIGHT/MORNING LOW CLOUDS AND FOG SHOULD BE CONFINED TO SRNMOST CSTL SXNS (I.E. SAN COUNTY CST) WITH ONLY PATCHY COVERAGE ORANGE COUNTY CSTL PLAIN AND SAN COUNTY VLYS. STRONG SUBSIDENCE INVERSION SHOULD RESULT IN HAZY CONDITIONS...ESPECIALLY INLAND VLYS. ATMOS CONTINUES TO WARM NEXT TWO DAYS FOR CONTINUED WARMING VLYS INLAND. LOW LVL ONSHR FLOW WEAKENS A LTL TODAY...THEN CHANGES LTL FOR TUE. THIS SHOULD ALLOW CSTL SXNS TO WARM SOME TODAY WITH ONLY SLIGHT ADDITIONAL WARMING FOR TUE.

MONSOONAL MSTR...ETA/AVN DIFFER IN HOW FAR W THEY BRING MID LVL MONSOONAL MSTR TUE FROM AZ INTO SRN CA WITH THE ETA FARTHER W AND THE AVN KPG MOST FOR THE MSTR CONFINED ALG AND E OF THE LWR CO RIVER VLY. THE DIFFERENCE APPEARS TO BE THE RESULT OF DIFFERENCES IN HOW THE MDLS HANDLE TWO SMALL SCALE CIRCULATIONS...ONE CNTRD NR 28N/125W AT 00Z AND A SECOND OVR THE NRN GULF OF CA. THE AVN APPEARS TO HAVE THE SUPERIOR INITIALIZATION AND HANDLING OF THESE FEATURES AND IS THUS PREFERRED IN LIMITING THE WWD MIGRATION OF THE MONSOONAL MSTR INTO SRN CA THRU TUE. THE TROUGH MOVG INLAND INTO THE PAC NW ON WED SHOULD INCR SWLY FLOW ALF OVR CA SUFFICIENTLY TO NUDGE THE MONSOONAL MSTR EASTWARD INTO AZ FOR WED. AS THE UPR TROUGH MOVES FARTHER INLAND ON THU...THE SUBTROPICAL RDG WL BEGIN TO BUILD BACK WWD INTO SRN CA WITH A MINOR INTRUSION OF 500-700MB MEAN RH SHOWN FOR THE SOUTHEASTERN HALF OF SRN CA FOR THU THRU THE WEEKEND.

EXTENDED...MDLS IN GENERAL AGREEMENT WITH THE SYNOPTIC FEATURES N OF 40N WITH AN UPR RDG ALG THE BRITISH COLUMBIA CST...AN UPR TROUGH OVR THE NORTHEASTERN PAC...AND A SECOND UPR TROUGH OVR THE NRN PLAINS AND GREAT LAKE STATES. MDLS MAINTAIN AN ELONGATED SUBTROPICAL RDG TO THE S OF THE AFOREMENTIONED MID AND HIGH LATITUDE FEATURES...BUT DIFFER IN THE DETAILS. AS MENTIONED ABV...THE MRF WOULD BRING A MINOR INTRUSION OF MID LVL MSTR INTO THE SOUTHEASTERN HALF OF SRN CA FOR THU THRU THE WEEKEND WITH A LEAST A SLIGHT CHANCE OF DIURNAL THUNDERSTORMS FOR SRN MTNS AND SRN AND ERN DESERTS.

SAN 000

.SAN...NONE.

MARTIN

LOW CLOUDS HAVE BEEN PUSHED WELL SOUTH AND WEST OF THE DISTRICT THIS EVENING AS THE UPPER RIDGE BUILDS IN WITH THE MARINE LAYER SHRINKING RAPIDLY. LATEST ACARS/PROFILER SOUNDINGS SHOW SIGNIFICANT WARMING IN LOW LEVELS DURING THE PAST 24 HOURS WITH THE MARINE LAYER SHRINKING DOWN TO NEAR 1200 TO 1500 FEET. OFFSHORE TREND IN THE GRADIENTS CONTINUE THIS EVENING WHICH PROBABLY AT LEAST PARTLY EXPLAINS WHY THE LOW CLOUDS WERE PUSHED OFFHSORE. 18Z MESO-ETA SUGGESTS NOT MUCH RETURN IN THE LOW CLOUDS OVERNIGHT. SOME PATCHY LOW CLOUDS AND DENSE FOG MAY DEVELOP LATE TONIGHT OVER THE CENTRAL COAST OF SLO/SBA COUNTIES AND THE SANTA YNEZ VALLEY. SOME LOW CLOUDS MAY ALSO RETURN LATE TONIGHT OVER LAX COUNTY COAST...OTHERWISE SKIES WILL BE CLEAR THROUGHOUT THE DISTRICT.

00Z ETA/NGM CONTINUE TO SHOW THE UPPER RIDGE BUILDING INTO THE FOUR CORNERS AND EXTEND INTO SOCAL RIGHT THRU TUE. RISING HEIGHTS/ THICKNESSES OVER THE DISTRICT WILL ALLOW FOR A SIGNIFICANT WARM UP ALL INLAND AREAS THRU TUE. AFTERNOON ONSHORE GRADIENTS WILL KEEP CONDITIONS PLEASANTLY MILD AT THE BEACHES. SOME LOW CLOUDS NEAR THE BEACHES POSSIBLE MON NITE AND TUE OTHERWISE MOSTLY CLEAR SKIES TO CONTINUE.

UPDATED THE ZONES AT 910 PM MAINLY TO SCALE BACK ON LOW CLOUD FORECAST IN SOME AREAS...WITH OTHER MINOR MODIFICATIONS.

IN THE EXTENDED...UPPER HI OVER OR NEAR THE FOUR CORNERS REGION LINGERS WED THRU FRI. STILL SLIGHT CHANCE OF AFTERNOON CONVECTION CANNOT BE RULED OUT OVER THE MOUNTAINS AND DESERTS WITH MOISTURE MAINLY ABOVE 700 MB STILL FORECAST TO MOVE INTO THOSE AREAS. INTERESTINGLY ENOUGH...00Z ETA RUN AT 48 HOURS (TUE AFTERNOON) BRINGS IN SOME MOISTURE AT 700 MB (50 PERCENT RH) WITH 0.04 INCH OF RAINFALL FORECAST OVER THE IMPERIAL VALLEY TUE AFTERNOON. AT ANY RATE...IT LOOKS LIKE OTHER THAN THE SLIGHT CHANCE OF AFTENROON THUNDERSTORMS OVER THE MOUNTAINS AND DESERTS...CONDITIONS DURING THE EXTENDED PERIOD SHOULD REMAIN WARM TO HOT AND DRY OVER SOCAL.

LAX 0000. SIRARD

.LAX...SMALL CRAFT ADVISORY...SEE LAXCWFLAX.

MAIN QUESTION WITH THIS FORECAST PACKAGE WILL BE HOW LONG THE HEAT AND HUMIDITY WILL LAST.

LATEST WATER VAPOR LOOP SHOWING THE UPPER LEVEL RIDGE CONTINUING TO DOMINATE THE REGION. SATELLITE ALSO INDICATES THAT THIS UPPER LEVEL RIDGE IS STARTING TO BREAK DOWN SOME IN THE NORTHERN PLAINS DUE TO A STRONG SHORTWAVE MOVING THROUGH MONTANA. THE MODELS PROJECT THIS SHORTWAVE TO MOVE EAST TO THE GREAT LAKES BY 48 HOURS AND HELP FLATTEN THE RIDGE OVER THE OHIO VALLEY. UNFORTUNATELY...THIS WILL GIVE VERY LITTLE RELIEF FROM THE HEAT AND HUMIDITY...BUT IT MAY INCREASE THE RISK FOR A SHOWER OR THUNDERSTORM TUESDAY AS A WEAK FRONTAL BOUNDARY APPROACHES FROM THE NORTHWEST.

FOR TODAY...LATEST ACARS DATA FROM SDF SHOWS LOTS OF CAP BETWEEN 750 AND 650 MB WHICH WILL ONCE AGAIN BE THE LIMITING FACTOR FOR ANY CONVECTION TODAY WITH ONLY SCATTERED CU AROUND. AS A RESULT... TEMPERATURES WILL ONCE AGAIN BOOST TO AROUND 95 WITH DEWPOINTS REMAINING IN THE MID 70S WHICH YIELDS HEAT INDICES BETWEEN 105 AND 110. THEREFORE...WE WILL CONTINUE TO MENTION THE HEAT ADVISORY THIS AFTERNOON.

TONIGHT AND TUESDAY THE MODELS PROJECT THE REMANENTS OF THE SHORTWAVE TO MOVE THROUGH PARTS OF THE LOWER OHIO VALLEY WITH A WEAK FRONTAL BOUNDARY MOVING THROUGH THE CENTRAL SECTIONS OF IN AND IL BY 48 HOURS. NGM LOOKS TO BE A LITTLE QUICK WITH THIS SCENARIO...WHILE THE ETA IS THE SLOWEST. WE ELECTED TO FOLLOW THE SLOWER ETA DUE TO THE RIDGE BREAKING DOWN SLOWLY. SOME HIGH CLOUDS MAY MAKE INTO PARTS OF NORTHERN KY AND SOUTHERN IN BY 48 HOURS. HOWEVER...DUE TO LACK OF LOW LEVEL CONVERGENCE ALONG THE BOUNDARY AND VERY LITTLE UPPER LEVEL SUPPORT...THE CHANCES FOR ANY CONVECTION LOOKS TO BE WIDELY SCATTERED AT BEST. THEREFORE...WE WILL NOT MENTION ANY POPS ATTM. WE LOWERED TEMPERATURES A COUPLE DEGREES DUE TO THE HIGH CLOUDS MOVING IN WHICH WAS IN THE BALL PARK OF THE FWC NUMBERS. WITH THE LOWERING OF THE TEMPERATURES DUE TO THE CLOUDS WE WILL NOT MENTION THE HEAT ADVISORY ON TUESDAY.

.SDF...HEAT ADVISORY FOR CENTRAL KENTUCKY AND SOUTH CENTRAL INDIANA TODAY. COX

LOOKING AT MORNING SOUNDINGS THERE IS SIGNIFICANT WARMING OF THE ATMOSPHERE COMPARED TO 24 HOURS AGO. H85 TEMPS FOR KOAK ARE UP 7C. SIMILAR WARMING IS SEEN ON ARB AIRCRAFT SOUNDINGS. WITH A WEAK ONSHORE FLOW SEEN ON MSAS SURFACE ANALYSIS WOULD EXPECT MAX TEMPERATURES TO RUN MUCH WARMER THAN YESTERDAY. LATEST NGM MOS GUIDANCE WOULD CONCUR WITH THIS. MODELS ALSO SHOW STRONG 500MB RIDGING TODAY TO 588DM WITH H85 TEMPS CLIMBING TO AROUND 23C. CURRENT THINKING IS THAT FORECAST MAY BE TOO LOW BY 5 DEGREES SOME PLACES.

UPPER TROF NEAR 135W IS FORECAST TO DIG SLIGTHLY TODAY AND THEN LIFT OUT BY TUESDAY NIGHT. THIS WILL RESULT IN AN INCREASE ONSHORE FLOW AND LOWEING HEIGHTS FOR MIDWEEK. TROF AXIS AND RIGHT ENTRANCE REGION OF UPPER JET IS PROGGED TO CLIP NORTHERN CALIFORNIA WITH LITTLE MOISTURE. MONSOON MOISTURE IS SEEN INCHING WESTWARD ON WATER VAPOR. 12Z ETA SUGGESTS HIGHER PRECIPITABLE WATER WILL REACH NO FURTHER NORTH THAN YOSEMITE BY LATE TUESDAY...IF THAT...AND NOT AFFECT OUR CWA AS TROF SHUNTS IT EASTWARD.

EXTENDED MODELS STILL ADVERTISE HOT WEATHER STARTING LATE WEEK AND CONTINUING INTO THE NEXT WEEK AS SOUTHWEST HIGH TAKES OVER.

.STO...NONE.

TARDY