100
FXUS66 KSGX 270424
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
924 PM PDT WED JUN 26 2019
SYNOPSIS
A PERSISTENT MARINE LAYER WILL HAVE LOW CLOUDS MOVE INLAND INTO
THE VALLEYS EACH NIGHT AND CLEAR BACK TO NEAR THE COAST EACH DAY.
A SLOW WARMING TREND WILL CONTINUE THROUGH THE WEEKEND. SOME MID
AND UPPER LEVEL TROPICAL MOISTURE AND CLOUDS COULD SPREAD ACROSS
PORTIONS OF FAR SOUTHERN CALIFORNIA AROUND SATURDAY. ANOTHER WEAK
TROUGH OF LOW PRESSURE NEAR THE WEST COAST COULD SPREAD SLOW
COOLING INLAND FOR THE EARLY TO MIDDLE PART OF NEXT WEEK WITH
NIGHT AND MORNING COASTAL LOW CLOUDS EXTENDING FARTHER INTO THE
VALLEYS.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
..UPDATE
THE COAST ENDED UP SEEING FULL SUNSHINE THIS AFTERNOON AS THE
MARINE LAYER STRATUS DECK DISSIPATED. IT IS RE-DEVELOPING THIS
EVENING IN PLACES ALONG THE COAST AND WILL CONTINUE TO DO SO AND
SPREAD INTO WESTERN PORTIONS OF THE INLAND VALLEYS OVERNIGHT.
DRIZZLE IS NOT ANTICIPATED TONIGHT AS THE MARINE LAYER WILL BE
RATHER SHALLOW.
WE HAVE BEEN LOOKING AT THE WEEKEND TO SEE IF REMNANT MOISTURE
FROM TROPICAL STORM ALVIN COULD PRODUCE ANY RAINFALL OR ELEVATED
CONVECTION (DRY LIGHTNING). ENSEMBLES SUPPORT A DRY FORECAST.
INSTABILITY ON FORECAST SOUNDINGS IS VERY LOW WITH MUCAPE <50 J/KG.
SO AT THIS TIME, WHILE MID-HIGH LEVEL MOISTURE WILL BE STREAMING
IN FRIDAY NIGHT-SATURDAY, THE MAIN CONSEQUENCE LOOKS TO JUST BE
SOME MID-HIGH LEVEL CLOUDINESS. HOWEVER, WE WILL CONTINUE TO
ASSESS THIS AS THERE WILL BE A GOOD MOISTURE SURGE IN THE MID-
UPPER LEVELS (RESULTING IN PW INCREASING TO 200-250% OF NORMAL,
HIGHEST SE). SEE PREVIOUS DISCUSSION BELOW FOR FURTHER FORECAST
DETAILS.
..PREVIOUS DISCUSSION (ISSUED AT 134 PM PDT WED JUN 26 2019)
THIS AFTERNOON...THE MARINE LAYER LOW CLOUDS HAVE MOSTLY CLEARED
OVER THE COASTAL AND INLAND AREAS EXCEPT FOR PORTIONS OF NORTHERN
SAN DIEGO COUNTY AND SOUTHERN ORANGE COUNTY. THE LOW CLOUDS HAVE
CLEARED MORE THAN YESTERDAY MOST LIKELY DUE TO A WEAKER INVERSION
AND A THINNER CLOUD LAYER. THIS HAS RESULTED IN GENERALLY HIGHER
TEMPS THAN AT THIS TIME YESTERDAY IN THE LOWER ELEVATIONS WEST OF
THE MTNS. ELSEWHERE, TEMPS ARE ABOUT WHAT THEY WERE AT THIS TIME
YESTERDAY OR EVEN A LITTLE LOWER IN SOME AREAS. THE HIGH CLOUDS
FROM THIS MORNING HAVE MOVED OFF TO THE EAST.
FROM PREVIOUS DISCUSSION...
A LARGE LOW PRESSURE SYSTEM OFF THE COAST OF OR WITH A TROUGH
EXTENDING SOUTHWARD OFF THE SOCAL COAST WILL DOMINATE OUR WEATHER
INTO THE WEEKEND. FARTHER TO THE SOUTH, TROPICAL STORM ALVIN HAS
DEVELOPED NEAR 14.7 DEGREES NORTH LATITUDE, 109.4 DEGREES WEST
LONGITUDE.
FOR THURSDAY INTO THE WEEKEND, THE AXIS OF THE LOW PRESSURE
TROUGH WILL EXTEND FROM THE PACIFIC NORTHWEST COAST TO A POSITION
OFF THE SOUTHERN CALIFORNIA COAST ALONG 130W. THIS WILL KEEP THE HIGH
PRESSURE RIDGE TO THE SOUTHEAST EXTENDING FROM BAJA, ACROSS
NORTHERN MEXICO, AND NEW MEXICO, INTO THE CENTRAL AND SOUTHERN
PLAINS. SOUTHERN CALIFORNIA WILL BE IN BETWEEN WITH SOUTHWEST FLOW
ALOFT AND CONTINUING ONSHORE FLOW.
OVER TIME, THE TROUGH WILL WEAKEN AND HEIGHTS WILL RISE. THIS WILL
CAUSE THE MARINE LAYER TO BECOME A LITTLE SHALLOWER WITH NIGHT
AND MORNING COASTAL LOW CLOUDS NOT EXTENDING AS FAR INLAND. THIS
WILL ALSO BRING SLOW WARMING FOR THURSDAY THROUGH THE WEEKEND.
HOWEVER, IF MID AND HIGH LEVEL TROPICAL MOISTURE AND CLOUDS FROM
THE REMNANTS OF ALVIN MOVES ACROSS PORTIONS OF THE AREA AROUND
SATURDAY, HIGH TEMPERATURES COULD BE A LITTLE LOWER FOR THOSE
AREAS ON SATURDAY. THERE IS ALSO SOME POTENTIAL FOR ELEVATED
CONVECTION ACROSS PORTIONS OF THE AREA ON SATURDAY, MAINLY FOR THE
AREAS CLOSER TO NORTHERN BAJA. IF THE TROUGH IS A LITTLE FARTHER
EAST, THE MOISTURE WOULD MOSTLY STAY JUST SOUTH OF SOUTHWESTERN
CALIFORNIA AS IT MOVES INTO ARIZONA. EVEN IF THE MID AND HIGH
CLOUDS DO MATERIALIZE, CURRENT NUMERICAL MODEL GUIDANCE INDICATES
THAT A LACK OF INSTABILITY AND FORCING WILL MAKE IT UNLIKELY FOR
THERE TO BE SIGNIFICANT PRECIPITATION.
FOR THE EARLY TO MIDDLE PART OF NEXT WEEK, ANOTHER WEAKER TROUGH
OF LOW PRESSURE WILL APPROACH THE WEST COAST. THIS WOULD KEEP THE
HIGH PRESSURE RIDGE SUPPRESSED TO THE SOUTHEAST. SLOW COOLING
WOULD SPREAD INLAND WITH STRENGTHENING ONSHORE FLOW. THE MARINE
LAYER WOULD ALSO DEEPEN WITH NIGHT AND MORNING COASTAL LOW CLOUDS
AGAIN EXTENDING FARTHER INTO THE VALLEYS.
AVIATION
270345Z...COAST/VALLEYS...SCT015-020 NEAR THE COAST THIS EVENING
BECOMING BKN-OVC015-020 TOPS 030 AND MOVING 20 MILES INLAND THROUGH
15Z THURSDAY. SKIES CLEARING BACK TO THE COASTAL TAF SITES THROUGH
21Z. VIS RESTRICTIONS OF 2-5 MILES AT KONT AND KSBD FROM 13Z-18Z.
MOUNTAINS/DESERTS...CLEAR SKIES WITH UNRESTRICTED VISIBILITY
THROUGH THURSDAY.
MARINE
NO HAZARDOUS MARINE CONDITIONS THROUGH MONDAY.
SKYWARN
SKYWARN ACTIVATION IS NOT REQUESTED. HOWEVER WEATHER SPOTTERS ARE
ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS.
SGX WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...NONE.
PUBLIC...GREGORIA (UPDATE)/PG (PREV DISCUSSION)
AVIATION/MARINE...MOEDE
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