EXTREME SOUTHWESTERN CALIFORNIA AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
AFDSAN 320 AM PDT MON AUG 23 1999
...SYNOPSIS...
A WEAK UPPER TROUGH OF LOW PRESSURE OFF THE CALIFORNIA COAST AND
BROAD HIGH PRESSURE OVER THE INTERIOR WEST WILL BRING WEAK SOUTHERLY
FLOW ALOFT AND WEAK ONSHORE LOW LEVEL FLOW TO SOUTHERN CALIFORNIA
THROUGH MID WEEK. A MINOR SURGE OF MONSOONAL MOISTURE WILL BRING A
CHANCE OF THUNDERSTORMS TO THE MOUNTAINS AND DESERTS TODAY.
...DISCUSSION...
SYNOPTIC PATTERN IMPACTING SRN CA WL CHANGE LITTLE DURG THE NEXT FEW
DAYS WITH A WK UPPER TROUGH OFF THE CA CST WITH BROAD HIGH
PRESSURE OVER THE INTERIOR WEST. THIS WL RESULT IN WK SLY FLOW ALF
OVR SRN CA WITH WK ONSHR FLOW. HOWEVER...SUBSYNOPTIC DETAILS SHOULD
RESULT IN PERCEPTIBLE DAY TO DAY DIFFERENCES.
FIRST ITEM OF CONCERN IS THE INFLUX OF MOSTLY MID LVL MONSOONAL MSTR
INTO SRN CA TODAY. 03Z ETA IS WELL-INITIALIZED AND PREFERRED. MSTR
ASSOCD WITH ONGOING THUNDERSTORMS OVR FAR SW AZ WL REMAIN ALG AND E
OF THE MTNS TODAY. MTSR ASSOCD WITH THUNDERSTORMS OVR NW MEXICO SUN
EVENING WL BE DRAWN NORTHWARD INTO SRN CA TODAY ALG AND W OF THE
MTNS. ETA BRINGS A SWATH OF 70+ PERCENT RH AT 500 MB NORTHWARD
ACROSS SRN CA ALG AND W OF THE MTNS TODAY. WL CHANGE WORDING FOR
CSTL SXNS TODAY TO PARTLY CLOUDY AFTER MORNING LOW CLOUDS TO ACCOUNT
FOR THIS BRIEF INFLUX OF MID LVL MSTR. FOR MTNS AND DESERTS...WL
INCR POPS TO LOW END OF CHANCE CATEGORY TODAY TO ACCOUNT FOR THE
INFLUX OF MSTR...KPG HIGHEST POPS IN THE MTNS. BOTH RUC AND ETA
GENERATE QPF TODAY ALF THE MTNS FROM THE SBD MTNS S. ETA ACTUALLY
GENERATES QPF FOR SAN COUNTY MTNS AS EARLY AS THE LATE MORNING...
HENCE WL REMOVE TIME QUALIFIERS FOR THUNDERSTORMS TODAY FOR THE SAN
COUNTY MTNS. WL LEAVE THUNDERSTORM WORDING FOR TUE UNCHANGED FOR NOW.
MARINE LYR...SUN EVENING ACARS SOUNDINGS/RAOBS SHOWED A MARINE LYR
DEPTH OF AROUND 700 FT LAX...TO 1500 FT NKX. WITH LTL CHANGE IN
HEIGHTS ALF OVR SRN CA THE NEXT FEW DAYS...EXPECT ONLY MINOR DAY TO
DAY CHANGES IN THE MARINE LYR DEPTH THRU MID WEEK. MDLS ARE ABSENT
SYNOPTIC SUPPORT FOR A CSTL EDDY THRU TUE. HIGHER RESOLUTION MDLS
SHOW ONLY WK ONSHR FLOW AND NO CSTL EDDY. EXPECT CONTINUATION OF
LATE NIGHT/EARLY MORNING LOW CLOUDS AND FOG WITH PATCHY DENSE FOG
INLAND ORANGE COUNTY CSTL PLAIN...SAN COUNTY CSTL MESAS...AND LWR
CSTL VLYS OF SAN COUNTY.
TEMPERATURES...WITH MDTLY HIGH HEIGHTS ALF AND VRY WK ONSHR FLOW...
HIGH TEMPERATURES SHOULD BE SEASONABLY HOT FM THE VLYS INLAND WITH
COOLER HIGH TEMPERATURES CONFINED TO AREAS CLOSE TO THE CST.
SAN 000
.SAN...NONE.
MARTIN
AREA FORECAST DISCUSSION
NWS SEATTLE WA
AFDSEW 250 AM PDT MON AUG 23 1999
06Z SURFACE ANALYSIS HAS THERMALLY INDUCED LOW RIGHT ALONG THE COAST.
THIS AGREES WITH FOG/STRATUS SATELLITE IMAGERY WHICH SHOWS STRATUS
DECK STILL AT LEAST 20 MILES OFFSHORE EXCEPT ALONG THE EXTREME NORTH
COAST. MODELS CONSISTENT IN MOVING THERMALLY INDUCED LOW INLAND
TODAY. CURRENT ACARS SOUNDINGS HAVE 850 MB TEMPS OVER KSEA +19C RIGHT
NOW WHICH VERIFIES WELL 09Z AVN 850 MB TEMP FIELD. LITTLE FLOW ALOFT
TO MIX THIS WARM AIR ALL THE WAY TO THE SURFACE BUT KSMP IS 13
DEGREES WARMER THAN LAST NIGHT. JOHNSON STUDY USING LAST NIGHTS DATA
AND ESTIMATING MORNING TEMPS FOR NEVILLE STUDY BOTH GIVE MAX NEAR 85
FOR SEATTLE TODAY. THERMALLY INDUCED LOW SHIFTS EAST OF THE CASCADES
TONIGHT BUT SURFACE HIGH OFF THE COAST NOT VERY STRONG AND ONLY A
LITTLE COOLING ALOFT TUESDAY MORNING COMBINING TO KEEP MARINE LAYER
SHALLOW OVER THE INTERIOR. ONSHORE PRESSURE GRADIENTS SLOWLY INCREASE
AS THE DAY GOES ON PROVIDING 5 TO 10 DEGREES OF COOLING FOR THE MAX
TEMPS ON TUE.
.EXTENDED...STRONG FLOW ACROSS THE NORTHERN PACIFIC WITH 110 KT JET
JUST EAST OF THE DATELINE AT 50N ON THE MODELS ACTUALLY UNDERDONE
WITH MULTIPLE AIREPS INDICATING 120-140 KT WINDS AT 300 MB. WITH SUCH
STRONG FLOW IN AUGUST AND OLD WESTERN PACIFIC TYPHOON MOISTURE SOON
TO BE EMBEDDED IN THE FLOW DONT HAVE MUCH CONFIDENCE IN THE EXTENDED
MODELS RIGHT NOW. HAVING SAID THAT...BOTH MRF AND EURO KEEP A
MAJORITY OF THE ENERGY FROM THE SYSTEM DUE TO REACH THE BC COAST WED
WELL TO THE NORTH OF WASHINGTON AND 500 MB HEIGHTS ALTHOUGH DROPPING
...REMAIN ABOVE 574DM. ON THU THE 4 CORNERS HIGH REBUILDS NORTH AND
BY FRI A STRONG UPPER LEVEL RIDGE IS OVER THE AREA. MRF MUCH STRONGER
WITH THERMALLY INDUCED SURFACE LOW ON FRI ALONG THE COAST WHILE EURO
KEEPS LOW FURTHER SOUTH AND HAS FLAT GRADIENTS ACROSS WESTERN WA.
BOTH MODELS HAVE HIGH HEIGHTS OVER THE AREA. WILL SHOW IMPROVING
TREND ON THU WITH FRI BEING SIMILAR TO YESTERDAY ( SUNDAY ). FELTON
UIL 011 SEA 000 OLM 000
.KATX...VCP32/CSR32...OPERATIONAL.
.SEW...NONE.