AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
230 PM PDT MON APR 28 2008
.SYNOPSIS...UPPER LEVEL LOW PRESSURE WILL MOVE PAST TO THE NORTH
BRINGING SIGNIFICANT COOLING AND A DEEPENING MARINE LAYER THROUGH
MID WEEK. STRONGER ONSHORE FLOW WILL CAUSE LOCAL GUSTY WINDS IN THE
MOUNTAINS AND DESERTS TUESDAY AND WEDNESDAY. A LITTLE WARMER TOWARD
THE END OF THE WEEK IN DRY NORTHWEST FLOW.
&&
.DISCUSSION...FOR SOUTHWEST CALIFORNIA INCLUDING SAN DIEGO...
ORANGE...SOUTHWEST SAN BERNARDINO AND WEST RIVERSIDE COUNTIES.
.SHORT TERM (TODAY-THU)...THERE WAS VARIABLE HIGH CLOUDINESS TODAY.
EARLY AFTERNOON ACARS SOUNDINGS SHOWED A NEAR SURFACE BASED
INVERSION WITH WEAK ELY WINDS IN THE LOW LEVELS AND NW WINDS ALOFT.
WEAKENING OFFSHORE GRADIENTS.
IT WAS ANOTHER HOT DAY TODAY WITH NEAR RECORD MAX TEMPS BUT THERE
WILL BE 10 TO 20 DEGREES F COOLING IN MOST AREAS W OF THE MOUNTAINS
TUE. AN UPPER TROUGH WILL MOVE PAST TO THE N LATE TUE BRINING LOWER
HEIGHTS AND MUCH STRONGER ONSHORE FLOW. A WEAK EDDY IS EXPECTED LATE
TONIGHT...BECOMING STRONGER WED NIGHT. THIS WILL RESULT IN DEEPENING
OF THE MARINE LAYER AND CONSIDERABLE COOLING TUE...CONTINUING WED.
MAX TEMPS SHOULD DROP BELOW SEASONAL AVERAGES WED. A LITTLE WARMER
THU AS A SHORT WAVE RIDGE MOVES IN FROM THE W AND ONSHORE FLOW
WEAKENS. LOW CLOUDS AND FOG WILL MAINLY BE CONFINED TO THE COASTAL
AREAS TONIGHT AND FOG COULD BE LOCALLY DENSE. STRATUS WILL WILL GET
INTO THE COASTAL MOUNTAIN SLOPES WED MORNING AND THEN DECREASE A BIT
BY WED NIGHT AND THU MORNING. THE STRONGER ONSHORE FLOW WILL CAUSE
LOCAL STRONG GUSTY WINDS IN THE MOUNTAINS AND DESERTS TUE AND WED.
THE STRONGEST WIND GUSTS WILL GET NEAR ADVISORY STRENGTH TUE AND WED
DURING THE AFTERNOONS AND EVENINGS.
&&
.LONG TERM (FRI-MON)...A GRADUAL WARMING TREND AND DECREASING MARINE
LAYER SHOULD CONTINUE FRI AND SAT IN A DRY NW FLOW PATTERN. THERE
COULD BE BRIEF COOLING AND A DEEPER MARINE LAYER SUN AS A SHORT WAVE
TROUGH MOVES THROUGH...BUT MODELS ARE INCONSISTENT THAT FAR OUT.
WARMER BY NEXT MON AS HIGH PRESSURE BUILDS.
&&
.AVIATION...
282030Z...A MOSTLY CLEAR SKY WITH UNRESTRICTED VIS WILL CONTINUE
THROUGH THE EVE. AREAS OF FOG ARE EXPECTED TO DEVELOP ALONG THE
COAST AFTER 10Z AND COULD IMPACT COASTAL AIRPORTS. THIS IS MOST
LIKELY AT SAN WITH CEILINGS AROUND 800 FEET WITH VIS AROUND 3-5SM
LASTING UNTIL AROUND 16Z TUE.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
PUBLIC...DA
AVIATION...MM
AREA FORECAST DISCUSSION
NWS KANSAS CITY/PLEASANT HILL MO
630 PM CDT MON APR 28 2008
...UPDATED AVIATION DISCUSSION...
.DISCUSSION...
HIGH PRESSURE ORIGINATING OVER CANADA WILL DROP SOUTH INTO THE CWA
TONIGHT. UNSEASONABLY COLD AIR WILL OVERSPREAD THE REGION WITH
RECORD OR NEAR RECORD LOW TEMPERATURES. INCREASING WARM ADVECTION
HIGH CLOUDS NOW OVER THE NORTHERN AND CENTRAL HIGH PLAINS WILL
SPREAD INTO THE WESTERN CWA LATE THIS EVENING...AND INTO THE EASTERN
CWA AFTER MIDNIGHT. THIS CLOUD COVER WILL HELP SLOW DOWN THE
LONGWAVE RADIATIONAL COOLING AND SHOULD RETARD FROST FORMATION BY
SEVERAL HOURS OVER THE WESTERN CWA. MADE A MINOR ADJUSTMENT TO THE
FROST ADVISORY BY EXTENDING IT TO 14Z.
OTHERWISE...WITH A SOUTHEASTERLY BOUNDARY LAYER WIND NOT BEING A
WARMING WIND HAVE TRIMMED BACK MAX TEMPERATURES FOR TUESDAY BY A FEW
DEGREES...AND I MAY NOT HAVE BEEN AGGRESSIVE ENOUGH. THE BETTER
WARMUP WILL ARRIVE ON WEDNESDAY AS MID LEVEL RIDGE PASSES THROUGH
AND ALLOWS A TRUE SOUTHERLY WIND. MADE FEW IF ANY CHANGES TO
WEDNESDAY FORECAST.
MJ
MEDIUM RANGE (THURSDAY-MONDAY)...
A HIGHER AMPLITUDE BLOCKY PATTERN WILL PREDOMINATE THROUGH THE
MEDIUM RANGE PERIOD...WITH THE EVOLUTION OF AN UNSEASONABLY DEEP
CLOSED LOW (GREATER THAN 2 NORMALIZED STANDARD DEVIATIONS)
PROGRESSING FROM THE CNTRL PLAINS INTO THE UPPER MIDWEST INTERACTING
WITH A RETROGRADING STRONG BLOCKING RIDGE (GREATER THAN 3 NORMALIZED
STANDARD DEVIATIONS) OVER ERN CANADA. WILL CONTINUE TO GIVE MOST
WEIGHT TOWARDS GFS ENSEMBLE MEANS...THOUGH WITH MORE CONSIDERATION
TO THE 00Z ECMWF (WHICH HAS TRENDED SIGNIFICANTLY TOWARDS THE
ENSEMBLE MEANS)...AND A SLIGHTLY LESS DEEP VERSION OF THE
OPERATIONAL 12Z GFS. OVERALL OPERATIONAL MODEL TRENDS HAVE BEEN
SLIGHTLY SLOWER IN INITIALLY EJECTING THE UPPER LEVEL ENERGY INTO
THE PLAINS THURSDAY AFTERNOON...THOUGH STILL NOT AS SLOW AS THE
MAJORITY OF THE GFS ENSEMBLE MEMBERS. GIVEN HISTORICAL MODEL
BIASES...FEEL FUTURE FORECASTS MAY CONTINUE THE SLOWER
TREND...THOUGH ANALYSIS OF A 110+KT JET STREAK PROPAGATING THROUGH
THE SRN SIDE OF A NEGATIVELY TILTED TROUGH MAKES IT DIFFICULT TO
ARGUE FOR A SIGNIFICANTLY SLOWER OUTCOME. FOR THE WEEKEND AND
BEYOND...MODELS ARE UNDERSTANDABLY HAVING A VERY DIFFICULT TIME
RESOLVING THE MOVEMENT OF THIS CUTOFF LOW FEATURE...WITH THE HIGH
AMPLITUDE BLOCK IN ITS WAY. 00Z ECMWF AND 06Z GFS ATTEMPTED TO
RETROGRADE A NORTH ATLANTIC VORTEX WESTWARD OVER THE RIDGE
AXIS...THEN CREATE A FUJIWHARA CYCLE ABOUT THE GREAT LAKES.
VIRTUALLY NO ENSEMBLE MEMBER INDICATED SUCH AN INTERACTION...AND NOW
THE 12Z OPERATIONAL GFS HAS REVERTED BACK TO PREVIOUS FORECASTS (AND
IN MORE AGREEMENT WITH ENSEMBLES) KEEPING THE COLD CORE LOW MORE
ISOLATED AND FILLING OVER THE GREAT LAKES INTO EARLY NEXT WEEK.
MAIN FORECAST EMPHASIS WILL BE ON THE STRONG WAVE THURSDAY ENTERING
THE PLAINS STATES. ALL MODELS CONTINUE TO SHOW A DEFINITE NEGATIVE
TILT TO THIS SYSTEM WITH A 110+KT JET STREAK OVERSPREADING THE WARM
SECTOR...PLACING MUCH OF EASTERN KANSAS AND FAR WESTERN MISSOURI IN
THE HIGHLY DIFFLUENT LEFT FRONT REGION. ACCORDINGLY...DEEP LAYER
SHEAR WILL INCREASE MARKEDLY (0-6KM BULK SHEAR 40-60KT)...WITH LOW
LEVEL WINDS BACKING AND INCREASING (0-3KM SRH AROUND 400 M2/S2)
THROUGHOUT THE PREFRONTAL WARM SECTOR. STILL CONSIDERABLE
UNCERTAINTY EXISTS REGARDING THE QUALITY OF MOISTURE RETURN
THURSDAY...AS MODELS STILL SHOW MIXING RATIOS OF 12-13 G/KG RAPIDLY
SURGING NORTH BY THURSDAY AFTERNOON. GIVEN LOWER 40 DEWPOINTS AND
NLY WINDS ARE ALREADY PUSHING THROUGH THE TEXAS GULF COAST...WITH
MID TO UPPER 50 DEWPOINTS OBSERVED BY NORTH GULF BUOYS...ALONG WITH
SFC PRESSURE RIDGING FORECAST TO HANG ALONG THE TEXAS COAST UNTIL
WEDNESDAY EVENING...THE MODEL FORECAST MAGNITUDE OF MOISTURE RETURN
ALMOST SEEMS UNREASONABLE (ALTHOUGH CERTAINLY NOT TOTALLY OUT OF THE
REALM OF POSSIBILITY). WILL CONSIDER MOISTURE RETURN OF 11-12 G/KG A
LITTLE MORE CERTAIN AND REASONABLE...WHICH WOULD STILL YIELD
1500-2000 J/KG SB CAPES (VERSUS 2500-3000 J/KG FOR 12-13 G/KG).
REGARDLESS...INSTABILITY AND SHEAR PARAMETERS STILL REMAIN QUITE
FAVORABLE FOR A SIGNIFICANT SEVERE WEATHER EPISODE WITH ROTATING
SUPERCELLULAR STORM STRUCTURE SUPPORTING ALL MODES OF CONVECTIVELY
SEVERE WEATHER. ASIDE FROM THE UNCERTAIN MOISTURE QUALITY (WHICH MAY
ALSO AID IN MORE ELEVATED LCL/S FOR LOWER BOUNDARY LAYER
DEWPOINTS)...ONE OTHER SAVING GRACE MAY BE SLIGHTLY SLOWER MOVEMENT
TO THE UPPER WAVE...WHICH WOULD ALLOW CONVECTIVE INITIATION AND THE
MOST SIGNIFICANT SEVERE THREAT TO REMAIN JUST WEST OF THE FORECAST
AREA. REGARDLESS...EVEN IF THE SYSTEM WERE SLOWER...AND CONVECTION
DEVELOPED FURTHER WEST...ALL SEVERE WEATHER TYPE PARAMETERS REMAIN
FAVORABLE FOR CONTINUED ROTATING SUPERCELLS IN A NOCTURNAL REGIME.
DEEP COLD CORE SYSTEM WILL CUTOFF FROM THE PRIMARY FLOW ALOFT BY
FRIDAY...AND MEANDER SOMEWHERE ABOUT THE MIDWEST THROUGH THE
WEEKEND. WITH AFOREMENTIONED MODEL UNCERTAINTIES TAKEN INTO
ACCOUNT...FEEL THE PROXIMITY OF THE COLD CORE ALOFT...IN COMBINATION
WITH DAYTIME HEATING AND STEEP LOW LEVEL LAPSE RATES...WILL SUPPORT
AT LEAST SCT SHOWERS FRIDAY (AND POSSIBLY EVEN SATURDAY). ALSO NOT
OUT OF THE QUESTION TO SEE AN ISOLATED LOW TOPPED THUNDERSTORM
FRIDAY AS WELL...THOUGH THESE CHANCES ARE HIGHLY DEPENDENT ON THE
EVENTUAL POSITION OF THE MIDLEVEL LOW AND COLD CORE. MORE OF A
CERTAINTY IS COOLER THAN AVERAGE TEMPERATURES THROUGH THE WEEKEND
(AROUND 1 STANDARD DEVIATION BELOW)...WITH H8 TEMPS FALLING BELOW 0C
AND SPORADIC DIURNAL SC DEVELOPMENT. ON A POSITIVE NOTE
HOWEVER...DRIER AIR AND TRANQUIL WEATHER WILL HAVE ADVECTED EAST AS
THE UPPER LOW PULLS NORTH AND FILLS BY SUNDAY. COULD SEE ANOTHER
WAVE MOVE INTO THE PLAINS LATER MONDAY...THOUGH CONFIDENCE IN THE
TIMING AND PLACEMENT OF ANY SUCH WAVE IS EXTREMELY LOW.
21
&&
.AVIATION...
FOR THE 00Z TAFS...COLD CANADIAN HIGH PRESSURE WILL SETTLE ACROSS
THE TERMINALS EARLY THIS EVENING ALLOWING WINDS TO BECOME LIGHT AND
VARIABLE.
COULD SEE A FEW FROSTY AIRCRAFT OVERNIGHT AS TEMPERATURES FALL INTO
THE UPPER 20S AND LOWER 30S ACROSS THE TERMINALS. OTHERWISE...VFR
CONDITIONS TO PREVAIL WITH INCREASING HIGH CLOUDS AND WINDS
GRADUALLY BECOMING SOUTHEAST BEFORE DAYBREAK. SPEEDS WILL INCREASE
TO 10-12 KNOTS BY LATE MORNING.
BOOKBINDER
&&
.EAX WATCHES/WARNINGS/ADVISORIES...
MO...FROST ADVISORY FROM MIDNIGHT TUESDAY TO 9 AM TUESDAY FOR MOZ001-
MOZ002-MOZ003-MOZ004-MOZ005-MOZ006-MOZ007-MOZ008-MOZ011-
MOZ012-MOZ013-MOZ014-MOZ015-MOZ016-MOZ017-MOZ020-MOZ021-
MOZ022-MOZ023-MOZ024-MOZ025-MOZ028-MOZ029-MOZ030-MOZ031-
MOZ032-MOZ033-MOZ037-MOZ038-MOZ039-MOZ040-MOZ043-MOZ044-
MOZ045-MOZ046-MOZ053-MOZ054.
KS...FROST ADVISORY FROM MIDNIGHT TUESDAY TO 9 AM TUESDAY FOR KSZ025-
KSZ057-KSZ060-KSZ102-KSZ103-KSZ104-KSZ105.
$$
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