Severe Thunderstorm Warning 20, NWS Sacramento, CA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
205 PM PDT FRI JUL 12 2002

VORT MAX SEEN ON WATER VAPOR LIFTING NORTH OF SAC...TAKING
ASSOCIATED MID LEVEL CLOUDS AND MOST ACC WITH IT. ENOUGH DYNAMICS
ACTED ON THE PRESENT ELEVATED STEEP MID LEVEL LAPSE RATES AND DEEP
MOISTURE (ACC CLOUDS) TO PRODUCE SOME BIG RAIN DROPS OVER SAC THIS
MORNING...30DBZ ON THE 88D RADAR. OTHER EASTERLY WAVES IN THE
CLOCKWISE FLOW OF THE UPPER HIGH CENTERED OVER NEVADA ARE PRODUCING
ELEVATED SHOWERS OVER THE EASTERN PACIFIC/NORTH COAST AT THIS HOUR.
SURFACE BASED CONVECTION NOW FIRING UP ALONG THE SIERRA NEVADA CREST
DUE TO STRONG HEATING AND CONVERGENCE ALONG THE CREST IN SRLY FLOW.
IMPRESSIVE OVERSHOOTING TOPS SEEN OUT THE WINDOW. GOES CAPES NOW
NEAR 1000 J/KG. PWS SHOWS TO BE AS HIGH AS 1.4-IN OVER CENTRAL CA.
LAPS SURFACE BASED CAPE OF 800-1200 J/KG FROM SIERRA CREST INTO THE
COASTAL RANGE AND SHASTA MOUNTAINS. SOME OF THESE CELLS COULD PACK A
PUNCH WITH GUSTY WIND AND HEAVY RAIN...MABYE HAIL. STEERING FLOW IS
NOW MOVE SELY THAN EASTERLY SO MUCH OF IT WILL BE CARRIED DUE NORTH.
SPEAKING OF HEATING...DELTA BREEZE WE SAW YESTERDAY HAS DECREASED
(FAIRFIELD 10-14KTS AND MARINE LAYER DOWN TO BELOW 1000 FT AFTER
SHORT WAVE PASSAGE). THIS HAS BROUGHT TEMPS UP TO 100F QUICKLY AGAIN
IN SAC DESPITE THE EXTENSIVE MORNING CLOUDINESS...DOES NOT TAKE MUCH
TO MIX OUT SUCH A WARM AIRMASS. H85 TEMPS SUPPORT 105-110 IN THE
VALLEY WITH NO MARINE INFLUENCE. ELSEWHERE TEMPS ARE SOARING INTO
THE 100S IN THE FOOTHILLS AND WILL RISE QUICKLY AS BAND OF ACC
CONTINUES TO LIFT OUT OF NORTHERN ZONES.

LESS CLOUDS TONIGHT...SO COOLER TEMPS. AVN SHOWS ANOTHER VORT MAX
LIFTING ALONG THE SIERNEV CREST SATURDAY AFTERNOON. EVEN WITH OUT
THIS THE THREAT FOR MOIST CONVECTION CONTINUES NEAR THE CREST AS
FLOW VEERS SLIGHTLY S-SW AND HIGH PW AIR REMAINS ALONG WITH STEEP LAPSE
RATES LINGER. ELSEWHERE H85 TEMPS DROP ONLY ABOUT 1C SO MORE 100 DEG
TEMPS. SOME MARINE AIR WILL STILL MODIFY THE DELTA. DELTA BREEZE
RETURNS SATURDAY NIGHT AS A STRONGER SHORT WAVE SLAMS INTO THE
PACNW. THIS PROVIDES SOME SYNOPTIC COOLING AS WELL BUT NOT ENOUGH TO
KEEP REDDING FROM GOING OVER 100 AGAIN ON SUNDAY. SURFACE PRESSURE RISES
IN THIS SYSTEMS WAKE WILL BATTLE THE DELTA BREEZE ON SUNDAY AND MAY
BE ABLE TO SHUT IT OFF AS ACV-SFO GRADIENT INCREASES TO 4-5MB. THE
MARINE AIR IN THE VALLEY SHOULD BE MIXED OUT LEADING TO MORE CENTURY
MARK TEMPS...ESPECIALLY NORTHERN VALLEY...BUT ALSO POSSIBLE IN SAC
AREA. ETA IS WARMER WITH H85 TEMPS WITH 27C WHILE THE AVN DISPLAYS
25C AT THE MOST.

DRY SW FLOW PREVAILS MONDAY INTO WEDNESDAY WITH SOME SYNOPTIC
COOLING AND STRONGER DELTA BREEZES. WEAK CYCLONIC FLOW/SHORT WAVES
REMAIN TO OUR NORTH IN THE PACNW. WEAK UPPER LOW WILL DRIFT TOWARD
THE CA COAST AND INLAND THURSDAY IF THE AVN (FORMERLY MRF) VERIFIES.
AVN SUGGESTS A WARMING TREND FOR LATE IN THE WEEK...POSSIBLE BACK TO
100 TEMPS. OLD ECMWF IS SIMILAR WITH THIS UPPER LOW FEATURE
THURSDAY. UKMET IS FURTHER SOUTH. BASICALLY THIS LEAVES US IN
SEASONABLE WEATHER. AT THIS TIME WE WILL KEEP FORECAST DRY WITH MUCH
UNCERTAINTY OF THE UPPER LOW TRACK AND MOISTURE INTERACTION.

.STO...NONE.

BLU UU 070/084 068/083 067 65310
RBL UU 072/105 070/103 067 65000
SAC UU 065/100 064/099 063 65000

TARDY