Forecast Discussions mentioning ACARS, received at FSL on 04/27/00

BLOCKY PATTERN CONTINUES IN THE MID LEVELS...WITH CUT OFF UPPER LOW OVER PENNSYLVANIA AND 500 MB RIDGE POKING INTO THE JAMES BAY AREA. AT THE SURFACE...HIGH PRESSURE RIDGE EXTENDS FROM QUEBEC SOUTHWEST ACROSS THE GREAT LAKES AND INTO THE SOUTHERN PLAINS. MAIN FORECAST CONCERNS ARE PRECIP CHANCES WITH SHORT WAVE DROPPING SOUTHEAST OUT OF DAKOTAS FRIDAY...AND TEMPERATURES THROUGH THE PERIOD.

GOES WATER VAPOR LOOP SHOWS CIRCULATION ASSOCIATED WITH SHORT WAVE TROF MOVING INTO THE WESTERN DAKOTAS AT 19Z...WITH TROF EXTENDING SOUTH INTO THE PLAINS. REGIONAL RADAR PICS SHOW AREA OF RAIN AND THUNDERSTORMS FROM THE DAKOTAS SOUTH INTO OKLAHOMA AHEAD OF THIS FEATURE. 12Z MODEL RUNS ARE SIMILAR IN DEVELOPING RIDGE OVER THE ROCKIES BY 36 HOURS...FORCING SHORT WAVE SOUTHEAST INTO IOWA AND SOUTHERN ILLINOIS THROUGH 00Z FRIDAY. THIS RESULTS IN BEST LOW LEVEL MOISTURE AND THERMAL ADVECTION PASSING TO SOUTH AND WEST OF OUR FORECAST AREA. FAN/FWC POPS HAVE CONTINUED TO LOWER WITH EACH MODEL RUN...DROPPING BELOW 30 PERCENT FOR RFD. MODEL TIME SECTIONS PRETTY DRY...WITH LARGE SURFACE DEWPOINT GRADIENTS BETWEEN NORTHEAST ILLINOIS AND THE MISSOURI VALLEY. WITH GUIDANCE POPS SO LOW AND MOISTURE RETURN LIMITED BY CURRENT SURFACE RIDGE AXIS...WILL DROP MENTION OF PRECIP THURSDAY FOR ROCKFORD AREA. BETTER CHANCE FOR PRECIP MAY BE FRIDAY AFTERNOON AND FRIDAY NIGHT...AS SECOND SHORT WAVE DROPS SOUTHEAST PER AVN FORECASTS. STILL...ONLY LOW POPS WARRANTED.

TEMPERATURE WISE...WEAK SUBSIDENCE INVERSION SEEN JUST BELOW 900 MB IN AFTERNOON ACARS SOUNDINGS OUT OF ORD. TEMPS A BIT BELOW GUIDANCE NUMBERS FOR THIS AFTERNOON. WITH MORE MID/HIGH CLOUDS AND VERY SIMILAR 850 MB TEMPS THURSDAY PREFER GOING ZFP NUMBERS...WHICH ARE A BIT LOWER THAN THE FAN/FWC GUIDANCE. WEAK GRADIENT WILL KEEP AREAS NEAR LAKE MICHIGAN COOLER NEXT FEW DAYS.

.CHI...NONE

RATZER



...SYNOPSIS... A TROUGH OF LOW PRESSURE MOVING INLAND ALONG THE WEST COAST TODAY AND FRIDAY WILL BRING A COOLING TREND TO SOUTHERN CALIFORNIA WITH MORE EXTENSIVE NIGHT AND MORNING LOW CLOUDS AND FOG WEST OF THE MOUNTAINS THROUGH SATURDAY WITH BREEZY CONDITIONS IN THE MOUNTAINS AND DESERTS FRIDAY AND SATURDAY. FAIR AND A LITTLE WARMER SUNDAY AND MONDAY. ...DISCUSSION... LIMITED NEW DATA DUE TO EARLIER NATIONAL AWIPS DATA OUTAGE...AN OUTAGE CONTINUING IN A MORE LIMITED FORM WITH MUCH OF 00Z GRAPHICAL MDL DATA STILL UNABVL. FOG PRODUCT FROM WESTERN REGION SATELLITE FEED SHOWS LOW STRATUS COVERING MUCH OF SAN COUNTY CST EXTENDING LCLLY INTO SAN COUNTY VLYS AND DEVELOPING NORTH ALG THE IMDT ORANGE COUNTY CST CONSISTENT WITH THE EXPECTED CSTL EDDY. EARLY WED EVENING ACARS SOUNDINGS FM LGB/SNA SHOWED THE BASE OF THE MARINE INVERSION ALG THE CST AROUND 700 TO 750 FT...UP ABOUT 100 FT FM 24 HOURS AGO. THE INVERSION BASE IN THE INLAND EMPIRE WAS AROUND 1500 FT. GRADUAL SLOW DEEPENING OF THE MARINE LYR IS EXPECTED TO CONTINUE THRU MID MORNING WITH PATCHY LOW CLOUDS AND DENSE FOG REACHING THE INLAND EMPIRE NR OF JUST AFTER DAYBREAK. WITH GRADUAL DEEPENING...DENSE FOG SHOULD NOT PERSIST AT ANY ONE LOCATION FOR AN EXTENDED PERIOD THIS MORNING...HENCE DENSE FOG ADVISORIES ARE UNLIKELY THIS MORNING.

A CSTL EDDY IS ONCE AGAIN EXPECTED TONIGHT...BUT WITH SYNOPTIC SUPPORT FOR AN EDDY A LTL WK THAN AT PRESENT. STRONGER SUPPORT FOR A CSTL EDDY ONCE AGAIN FRI NIGHT INTO SAT MORNING. WHILE THE MARINE LYR IS EXPECTED TO CONTINUE GRADUALLY DEEPENING THRU SAT MORNING...DEEPENING MAY NOT YET BE SUFFICENT FOR STRATUS TO REACH LWR CSTL SLOPES BY FRI MORNING...SO HAVE TRIMMED BACK SUCH WORDING IN MTN ZONES A LTL. THIS WL CHANGE FRI NIGHT INTO SAT MORNING AS STRONGER CSTL EDDY...MDT ONSHR FLOW...AND CONTINUED LWRG OF HEIGHTS ALF FM INLAND PROGRESSION AND AMPLIFICATION OF THE UPR TROUGH ALLOWS THE MARINE LYR TO DEEPEN SUFFCIENTLY TO REACH THE LWR CSTL SLOPES. DEEPENING OF MARINE LYR MAY ALSO BE SUFFICIENT FOR "PARTIAL AFTERNOON CLEARING OR PARTLY CLOUDY AFTERNOON" WORDING FOR AREAS W OF THE MTNS. MDLS STILL NOT IN PERFECT AGREEMENT WITH PLACEMENT OF UPR FEATURES IMPACTING SRN CA FOR SUN/MON...BUT POSITION OF WK UPR LOW VCNTY AZ AND WK SHORTWAVE RDG OVR SRN CA WOULD SUPPORT WK LCL OFSHR WINDS THRU AND BLO PASSES AND CANYONS AND SUPPORT WK CSTL EDDY AFFECTING S CST.

SAN 000

.SAN...NONE.

MARTIN



LOTS OF PROBLEMS TONIGHT. FIRST, LCL COMMS PROBS PTLY RESOLVED...YET STILL HAVING DIFFICULTY WITH TRANSMISSION. THANKS PDX FOR BACKUP. INITIALIZATION OF MDLS PREFER AVN FM 12Z/26TH COMPARING IR IMAGERY TO VORT MAX OFF OR CST...AND...ACARS WNDS TO 120KT JET. COMPLEX LOW OFF WA CST SPLITTING AGAIN WITH INITIAL SURGE OF ENERGY MOVG INLND THIS AFTERNOON...FOLLOWED BY CRUX OF ENERGY TONIGHT/FRI MORNING. SECOND PROBLEM CONCERNS MOUNTAIN CONVECTION THIS AFTERNOON. INCRG SE FLOW AHD OF INITIAL ENHANCING OROGRAPHICS WITH 85H THERMAL TROF FLIRTING WITH NRN CASCDS 18Z-24Z. LI'S ONLY +2... YET WITH ADDITIONAL FORCING WILL HANG ON TO ISOLD TSTORMS THERE. MARINE PUSH NR 24Z TO CHOKE OFF CONVECTIVE FEED. 3RD PROBLEM IS TEMP FCSTS WITH MIN LOWS IN MID 50S THIS MORNING. THAT WITH VARIABLE MORNING SUN AND 85H T'S +5C TO +10C AT 18Z COMPARED TO 00Z LAST NIGHT WILL BOOST T'S 3-5F OR SO INLAND ZONES ONLY. FORTH PROBLEM CONCERNS INSTBY ASSOCD WITH TROF FRI. COLD AIR ADVECTION AND SHEAR SIGNIFICANT LATE TONIGHT YET TIMING POOR. MAIN CONCERN EVOLVES FRI WITH CLEARING BHD TROF AND INCRG INSTBY WITH DAYTIME SFC HEATING. CAPES HEALTHY WITH SUB ZERO LI'S SO WILL ADD CHC CONVECTION TO ZONES FRI. 5TH ISSUE IS CONVERGENCE ZONE FRI AND SUPPORTED LIFT. .XTNDD...ONLY NOGAPS AND CANADIAN GEM CAME IN. NOGAPS PROGRESSIVE WITH LOWER AMPLITUDINAL WAVES MOVG INTO PAC NW MON. COMPARING THAT WITH GLOBAL COMPOSITE WV IMGRY ACRS PACIFIC APPEARS SOURCE REGION FOR POLAR COLD AIR ADVECTION IS BEING CUT OFF IN A MORE ZONAL OR EVEN WSWLY FLOW BTWN 35-40N. THUS NOGAPS FASTER SOLN WITH LESS AMPLIFICATION MIGHT BE ON. BEING MY FIRST NIGHT BACK AND LACK OF OTHER DATA... WILL DELAY IN ANY CHANGES... YET SOMETHING TO KEEP IN MIND RMDR OF WEAK. ALL IN ALL...LOOKS LIKE NICE BEGINNING TO WEEKEND WITH CHANGES DVPG LATE SUN. QUERCIAGROSSA UIL 999 SEA 487 OLM 587

.KATX...VCP21/CSR31...OPERATIONAL

.SEW...GALE CST...W ENTRANCE... SCA ELSEWHERE... N