EXTREME SOUTHWESTERN CALIFORNIA AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
AFDSAN 315 AM PDT WED MAY 9 2001
...SYNOPSIS...
A WEAK UPPER TROUGH OF LOW PRESSURE WILL DEVELOP OVER THE
EASTERN PACIFIC DURING THE NEXT FEW DAYS. IN RESPONSE...A SLOW
COOLING TREND WILL DEVELOP INLAND FROM THE COAST TODAY THROUGH
SATURDAY WITH SLOWLY INCREASING NIGHT AND MORNING COASTAL LOW CLOUDS
AND FOG.
...DISCUSSION...
A GRADUAL SLOW COOLING TREND WL BEGIN TO SPREAD INLAND FM THE CST
TODAY THRU SAT AS A WK TROUGH OF LOW PRESSURE DEVELOPS OVR THE ERN
PAC...POSSIBLY MOVG INLAND NEXT WEEK. TUE EVENING ACARS SOUNDINGS
SHOWED A SHALLOW MARINE INVERSION (INVERSION BASE 700 TO 900 FT ALG
THE CST) CAPPED BY A VERY STRONG INVERSION. MINOR COOLING WL SPREAD
A LTL FARTHER INLAND TODAY WITH SOME CLOUDS ONCE AGAIN LINGERING NR
THE BEACHES. WK CSTL EDDY AND SLOW DEEPENING OF THE MARINE LYR WL
SPREAD LOW CLOUDS A LTL FARTHER INLAND TONIGHT WITH COOLING
SPREADING INLAND TO ALL AREAS W OF MTNS THU WITH SOME ADDITIONAL
COOLING FRI AND SAT. WL SHOW COOLING IN LINE WITH MRF MOS.
LATEST SATELLITE IMAGERY SHOWS WK CSTL EDDY WITH NARROW SLIVER OF
STRATUS SPREADING NORTHWARD ALG THE SRN CA CST. STRENGTH AND
SHALLOWNESS OF THE MARINE INVERSION WILL LIMIT INLAND PENETRATION OF
CSTL STRATUS ONCE AGAIN THIS MORNING. HOWEVER...DENSE FOG IS
POSSIBLE THIS MORNING NR THE MESAS...HIGHER CSTL TRRN...AND LWR CSTL
VLYS IN SAN COUNTY AND NR HIGHER CSTL TRRN IN ORANGE COUNTY.
NOWCASTS WL BE ISSUED...AS NECESSARY...TO HIGHLIGHT AREAS OF LWR
VISIBILITY DURG THE MORNING COMMUTE. TRENDS OF 06Z ETA APPEAR
REASONABLE IN SHOWING GREATER STRATUS COVERAGE...SOME MARINE LYR
DEEPENING...AND GREATER INLAND PENETRATION OF CSTL STRATUS TONIGHT
INTO THU MORNING.
SAN 000
.SAN...NONE.
MARTIN
AREA FORECAST DISCUSSION
NWS CHICAGO IL
AFDCHI 310 AM CDT WED MAY 9 2001
FORECAST CONCERNS INCLUDE LINGERING PRECIP OVER SOUTHERN COUNTIES OF
FORECAST AREA THIS MORNING...THEN PRECIP CHANCES AND TIMING LATE
TONIGHT THROUGH FRIDAY AS NEXT FRONTAL SYSTEM APPROACHES.
CURRENT RADAR SHOWS SCATTERED SHOWERS/TSTORMS GENERALLY SOUTH OF
I-80 AND EAST OF I-55. THIS IN ASSOCIATION WITH WEAK SHORT WAVE SEEN
IN GOES WATER VAPOR LOOP MOVING INTO CENTRAL ILLINOIS. RUC AND ETA
HANDLE THIS BEST...AND CONTINUE TO WEAKEN THIS FEATURE THIS MORNING.
TROF AXIS THEN SHIFTS EAST OF THE AREA WITH WEAK RIDGING ALOFT THIS
AFTERNOON. SHOULD BE ANOTHER DAY WITH GOOD MIXING GIVEN STEEP LOW
LEVEL LAPSE RATES...AND GUIDANCE HIGHS AROUND 80 LOOK GOOD WHEN
COMPARED TO ACARS SOUNDINGS AND MODEL 850 MB TEMPS. BREEZY AGAIN
TODAY ESPECIALLY NORTHWEST WHERE GRADIENT STRONGER...BUT NOT AS
WINDY AS TUESDAY.
ATTENTION THEN SHIFTS TO SERIES OF SHORT WAVES ADVANCING ACROSS THE
NORTHERN PLAINS IN FLAT WESTERLY UPPER FLOW PATTERN. INITIAL WAVE IN
EASTERN MONTANA THIS MORNING DEVELOPS SURFACE LOW OVER NORTHERN
MINNESOTA BY THIS EVENING...WITH COLD FRONT EXTENDING INTO THE
WESTERN HIGH PLAINS. GOOD MOISTURE ADVECTION INTO IOWA...MINNESOTA
AND WESTERN WISCONSIN AHEAD OF THIS FEATURE...AND SHOULD RESULT IN
THUNDERSTORM DEVELOPMENT ACROSS THAT AREA LATER TODAY AND TONIGHT.
WITH FAST WESTERLY FLOW ALOFT...EASTERN PORTION OF BOUNDARY SHOULD
MOVE MORE QUICKLY INTO THE UPPER GREAT LAKES...SLOWING SOUTHEASTWARD
PROGRESSION TOWARD ILLINOIS. CURRENT FORECAST HAS LOW CHANCE OF
PRECIP INTO ROCKFORD AREA TOWARD MORNING...AND THIS STILL LOOKS OK.
LATER PERIODS BECOME LESS CLEAR AS DIFFERENCES IN FRONTAL POSITION
AND RESOLUTION OF SHORT WAVES BECOME EVIDENT IN THE MODEL FORECASTS.
WITH LOW LEVEL BOUNDARY BECOMING MORE PARALLEL TO UPPER FLOW...FAVOR
SLOWER ETA MOVEMENT OF SURFACE FRONT. THIS WOULD KEEP BEST CHANCES
OF PRECIP OVER NORTHERN/NORTHWEST SECTIONS OF THE FORECAST AREA
THURSDAY...WITH BEST SURFACE MOISTURE CONVERGENCE AND INSTABILITY.
BETTER CHANCES FOR ENTIRE FORECAST AREA THURSDAY NIGHT INTO
FRIDAY...AS SURFACE FRONT SAGS INTO ILLINOIS. POTENTIAL FOR HEAVY
RAINS ESPECIALLY NORTHWEST SECTIONS THURSDAY NIGHT.
WITH SLOWER ETA PROGRESSION OF FRONT FAVORED THURSDAY...EXPECT MAX
TEMPS PERHAPS A CATEGORY ABOVE MOS NUMBERS ESPECIALLY SOUTHERN
SECTIONS. WINDS TURN N/NE BEHIND THE FRONT FRIDAY...WITH COOLER
TEMPS ESPECIALLY VICINITY OF LAKE MICHIGAN.
.CHI...NONE.
RATZER