EXTREME SOUTHWESTERN CALIFORNIA AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
AFDSAN 330 AM PDT FRI AUG 27 1999
...SYNOPSIS...
MONSOONAL MOISTURE WILL BRING A FEW AFTERNOON THUNDERSTORMS TO THE
MOUNTAINS AND DESERTS TODAY...WITH MORE WIDESPREAD THUNDERSTORMS
SATURDAY AS MOISTURE ASSOCIATED WITH THE REMNANTS OF "BRET" ARRIVES.
CONTINUED HOT AND HUMID THROUGH THE WEEKEND. DRIER WEATHER WITH A
RETURN TO NEAR NORMAL TEMPERATURES FOR EARLY NEXT WEEK AS AN UPPER
TROUGH OF LOW PRESSURE DEVELOPS ALONG THE WEST COAST.
...DISCUSSION...
AS DISCUSSED BY THE PREVIOUS SHIFT...THE UPR LVL LOW EJECTING INLAND
INTO CNTRL CA IS EXERTING A GREATER INFLUENCE INTO SRN CA THAN WAS
EXPECTED YESTERDAY WITH THE DEMARCATION BETWEEN SWLY AND ELY FLOW
ALOFT FARTHER TO THE SOUTHEAST THAN PREVIOUSLY EXPECTED (I.E. ACROSS
EXTREME SE CA VERSUS LOS ANGELES). WATER VAPOR IMAGERY SHOWS A
SINGLE COMPACT CENTER WITH THIS SYS...SIMILAR TO THAT SHOWN BY THE
AVN/NGM. THE ETA...WITH TWO VORT CENTERS...IS NOT PREFERRED WITH
THIS SYS. AS THE UPR LOW MOVES INLAND AND TO THE NORTHEAST TODAY...
THE SWLY FLOW ALF OVR SRN CA WL BEGIN TO RELAX THIS AFTERNOON WITH
THE DEMARCATION LINE BETWEEN SWLY AND ELY FLOW ALF SHIFTING SLOWLY
BACK TO THE NW. WAS LEANING TOWARD TRIMMING BACK POPS SIGNIFICANTLY
FOR MTNS AND DESERTS TODAY. HOWEVER...SFC DEWPOINTS OVR THE LWR
DESERTS ARE HIGHER THAN 24 HOURS AGO. EVEN THOUGH THE ETA MAINTAINS
SWLY FLOW ALF LONGER THAN THE AVN/NGM DUE TO THE PRESENCE OF AN
ERRONEOUS SECOND SHORTWAVE ROUNDING THE BASE OF THE TROUGH THIS
MORNING...ETA PW'S CONTINUE TO GRADUALLY INCR OVR THE LWR DESERTS
THRU THE FORECAST PD...THOUGH STABILITY MAY INCR MARGINALLY TODAY AS
TEMPERATURES WARM SLIGTHLY IN THE MID LVLS. K/F ETA GENERATES
CONVECTIVE PRECIPITATION IN ROUGHLY THE SAME AREAS THAT HAD
THUNDERSTORMS YESTERDAY. THUS...EXPECT SIMILAR OR SLIGHTLY REDUCED
COVERAGE TODAY COMPARED TO THU WITH CONVECTION TIED MORE CLOSELY TO
THE HIGHER TERRAIN TODAY.
THE REMANTS OF "BRET" STILL LOOM IN THE FUTURE FOR SRN CA. HERE...
THE ETA INITIALIZATION IS PREFERRED...WITH THE ETA INITIALIZING A
VORT CNTR REPRESENTING THE REMNANTS OF "BRET" OVR NRN MEXICO JUST TO
S OF SERN AZ. THE EFFECT OF THE INLAND PROGRESSION OF THE UPR LOW
INTO CNTRL AND NRN CA TODAY...AND THE NRN ROCKIES SAT...HAS BEEN TO
TEMPORARILY DELAY THE WWD PROGRESSION OF "BRET". HOWEVER...AS THE
UPR LOW EJECTS INLAND..."BRET" IS FREE TO RESUME THE WWD MOTION...
WITH THE ETA BRINGING THE REMANTS INTO SERN CA SAT. ELY FLOW ALF AND
LOW AND MID LVL MSTR SHOULD RETURN AND BECOME BETTER ESTABLISHED
INTO SWRN CA FOR SAT...AND HENCE HIGHER POPS IN THE MTNS AND DESERTS
SEEM WARRANTED AT THAT TIME. HOWEVER...WITH AN UPR TROUGH AMPLIFYING
OFF THE PAC NW CST SAT...THE NW EDGE TO THE ELY FLOW AND ASSOCD MSTR
SHOULDN'T EXTEND TOO FAR PAST THE IMDT FORECAST AREA. 03Z ETA BRINGS
A SURGE OF LOW AND MID LVL MSTR INTO MUCH OF THE ERN DESERTS OF SRN
CA EARLY THIS EVENING. HENCE WL NOT CONFINE THUNDERSTORM WORDING FOR
MTNS/DESERTS TONIGHT ONLY TO THE EVENING PD SHOULD ANY THUNDERSTORMS
DEVELOP OVERNIGHT.
PATCHY STRATUS HAS DEVELOPED NR THE CST WITH A WK CSTL EDDY EVIDENT.
ACARS SOUNDINGS EARLY THU EVENING SHOWED THE BASE OF A STRONG MARINE
INVERSION NR 1000 FT LAX/SNA TO 1400 FT SAN. SUCH AN INVERSION
HEIGHT WOULD USUALLY FAVOR DENSE FOG INLAND FM THE IMDT CST NR THE
MESAS. HIGH TEMPERATURES MAY BE SLIGHTLY COOLER NR THE CST
TODAY...OTHERWISE LTL CHANGE FM THU. SLIGHTLY LWR HIGH TEMPERATURES
FOR SAT WL BY COMPENSATED BY A CORRESPONDING INCR IN HUMIDITY.
EXTENDED...MRF AND EURO MDLS ARE NOW ALL ADVERTISING A TROUGH ALG
THE ENTIRE W CST BY MON. THIS WOULD SHUNT THE MONSOONAL MSTR E OF
SRN CA AND BRING SOME COOLING TO AREAS W OF THE MTNS WITH STRONGER
ONSHR FLOW AND A DEEPER MARINE LYR.
SAN 000
.SAN...HEAT ADV...REFER TO LAXNPWSAN.
MARTIN