SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
847 PM PDT SAT MAY 22 1999
UPPER LOW SITTING AND SPINNING OVER THE SOUTHERN DESERTS THIS
EVENING. THERE WAS ENOUGH MOISTURE AND INSTABILITY ASSOCIATED WITH THE
SYSTEM FOR WIDELY SCATTERED SHOWERS AND THUNDERSTORMS TO DEVELOP MAINLY
EAST AND SOUTH OF THE DISTRICT DURING THE AFTERNOON AND EARLY EVENING
ALTHOUGH SOME MEASURABLE RAIN WAS NOTED IN THE SAN GABRIEL VALLEY. NOT
MUCH HAPPENING AT THIS TIME. MID LEVEL CLOUDIENSS CONTINUES TO MOVE
INTO THE DISTRICT FROM THE NORTHEAST AND EAST IN THE CIRCULATION AROUND
THE UPPER LOW. GIVEN CURRENT TRENDS IT IS DIFFICULT TO DETERMINE IF ANY
MORE SHOWERS OR THUNDERSTORMS WILL DEVELOP OVERNIGHT...BUT CONSIDERING
WHAT HAPPENED LAST EVENING (THUNDERSTORMS DEVELOPED JUST OFF THE L.A.
COUNTY COAST) AND THE POSITION OF THE UPPER LOW WILL KEEP MENTION OF A
SLIGHT CHANCE OF A SHOWER OR THUNDERSTORM IN THE FORECAST OVERNIGHT.
LOW CLOUDS ALSO LINGERING IN SOME AREAS. EXPECT THE LOW CLOUDS TO
INCREASE IN COVERAGE AGAIN OVERNIGHT SINCE GOOD ONSHORE GRADIENTS
CONTINUE WITH A SOUTHERLY LOW LEVEL FLOW AND SUPPORT FROM 18Z MESO ETA.
ACARS SOUNDINGS SHOW THE MARINE LAYER AROUND 4200 FEET OVER LAX. NKX
00Z SOUNDING SHOWED THE MARINE LAYER NEAR 5000 FEET.
00Z ETA/NGM IN BASIC AGREEMENT ON MOVEMENT OF UPPER LOW VERY SLOWLY
NWD AND EWD AND INTO NERN AZ BY MON AFTERNOON. PROXIMITY OF UPPER LOW
COMBINED WITH SOME MOISTURE AT LOWER AND MID LEVELS ON SUN WARRANTS
MENTION OF A SLIGHT CHANCE OF A SHOWERS OR THUNDERSTORMS INTO THE L.A.
COUNTY VALLEYS. THE SLIGHT CHANCE SHOULD LINGER INTO EARLY SUN EVENING.
WILL UPDATE ZONES BY 930 PM AND MAKE THE ABOVE MENTIONED CHANGES.
EXTENDED...MEDIUM RANGE MODELS SIMILAR IN MOVING OUT UPPER LOW FROM
SOCAL TUE WITH WEAK RIDGING FOR WED/THU. DRY WEATHER THRU THE PERIOD
WITH THE USUAL COASTAL LOW CLOUDS. TEMPERATURES CLOSER TO SEASONAL
NORMS THRU PERIOD.
LAX 2100. SIRARD.
.LAX...NONE.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
230 PM PDT SAT MAY 22 1999
UPPER RIDGE ALONG 130 W BUILDS PER SATELLITE SHRINKING MARINE LAYER
BELOW 15 KFT PER ACARS AND SURFACE FEATURE SPREADS OVER WA WHILE A
TROUGH EXTENDS N ALONG THE OREGON COAST PER METAR. ALL MODELS SIMILAR
THROUGH MON AM. THEY PROGRESS AN UPPER RIDGE INTO WA SUN AND BEYOND
MON SO THAT A SURFACE TROUGH DEVELOPS OVER THE WRN WA THROUGH SUN
NIGHT IN CONCERT WITH A WARMING TREND. AN IMMEDIATE PROBLEM IS SEA
BREEZE STRENGTH PUGET SOUND DUE TO DIABATIC HEATING S. METAR
GRADIENTS SUPPORT WINDS JUST BLO THE 20 KTS SHOWN BY NGM. A WAVE ON
FRONT NEAR 40 N 150 W PER ANALYSIS SHOULD AID TROUGH GROWTH ALONG
COAST SUN FOR PEAK TEMPS THERE FOLLOWED BY A STRONG SEA BREEZE.
ADIABATIC WARMING INTERIOR SHOULD EASE WIND A BIT. WILL SHOW TEMPS
ABOVE MOS INTERIOR DAY 2 DUE TO EARLY PRESENCE OF THERMAL TROUGH.
ALTHOUGH AVN AGREES THAT A MARINE LAYER WILL BE PRESENT W OF CASCADES
MON AFTERNOON ITS DEPTH AND ARRIVAL TIME ARE QUITE UNCERTAIN.
.EXTENDED PROBLEM IS STRENGTH OF FRONT AND ASSOCIATED UPPER TROUGH
THAT INITIATES THE PUSH. MOST MODELS DAMP THE TROUGH BEFORE IT
REACHES WA. WE EXPECT THAT THEY WILL STRENGHEN ONSHORE FLOW MON NIGHT
AND LEAD TO CHC SHOWERS BY TUE.EXPECT PRECIP TO BE DRIZZLE AT FIRST
THEN LIGHT SHOWERS AS MARINE LAYER DEEPENS BUT MOISTURE AND STRENGTH
LIMITED FOR MUCH ELSE AND DRIER CONDITIONS LIKELY AGAIN BY THU.
UIL 0000 SEA 0000 OLM 0000 KIERULFF
.KATX...VCP32/CSR31...OPERATIONAL
.SEW...SCA COAST.