169
FXUS66 KMTR 152053
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
153 PM PDT TUE APR 15 2025
..NEW SYNOPSIS, SHORT TERM, LONG TERM
SYNOPSIS
ISSUED AT 146 PM PDT TUE APR 15 2025
COOLER CONDITIONS WILL CONTINUE THROUGH WEDNESDAY, WITH A 20%
CHANCE FOR ISOLATED SHOWERS AND A THUNDERSTORM OR TWO. THEREAFTER,
A WARMING TREND IS ANTICIPATED THROUGH THE WEEKEND.
SHORT TERM
ISSUED AT 146 PM PDT TUE APR 15 2025
(THIS EVENING THROUGH WEDNESDAY NIGHT)
SHORT TERM KEY MESSAGES
*COOL CONDITIONS CONTINUE
*10 TO 15% CHANCE FOR VERY ISOLATED DRY STORMS
*PATCHY COASTAL DRIZZLE
A STUBBORN MARINE LAYER TODAY CONTINUES TO GRADUALLY ERODE AS
SOUTHERLY FLOW ENVELOPS THE REGION. A VEIL OF MID TO UPPER LEVEL
CLOUDS CONTINUES TO LIFT NORTHWARD AHEAD OF A CUTOFF UPPER LOW
PARKED TO OUR SOUTHWEST. THESE INTERMITTENT CLOUDS WILL TRANSLATE
TO PARTLY SUNNY SKIES ACROSS MOST AREAS THIS AFTERNOON, WITH
LITTLE IN THE WAY OF FANFARE ANTICIPATED THIS AFTERNOON. AFTERNOON
ACARS DATA (SOUNDINGS FROM AIRCRAFT) FROM ACROSS THE BAY AREA
INDICATE THAT MOISTURE IS BIFURCATED VERTICALLY AND THIS PAIRS
WELL WITH THE AFOREMENTIONED SATELLITE DISCUSSION. THIS IS
IMPORTANT BECAUSE MOISTURE IS CURRENTLY NOT ALIGNED WITH THE
LOCATION OF THE STEEPEST LAPSE RATES (AT LEAST NOT YET), WHICH IS
NEEDED FOR CONVECTION. I DON'T ANTICIPATE THIS TO CHANGE THIS
AFTERNOON OR TONIGHT ACROSS OUR REGION AND AS A RESULT, THE WORDED
FORECAST FOR THIS TIME PERIOD REMAIN VOID OF ANY RAIN OR STORMS.
IT'S HIGHLY PROBABLE THAT WE'LL CONTEND WITH ANOTHER ROUND OF
MARINE STRATUS LATE TONIGHT AND INTO WEDNESDAY MORNING AS 925MB
FLOW REMAINS LARGELY ONSHORE. SIMILAR TO THIS MORNING, THE VERY
GENTLE ASCENT THROUGH THE COLUMN, THANKS TO THE UPPER LOW TO THE
SOUTH, WILL PROMOTE THE DEVELOPMENT OF DRIZZLE WHERE THE MARINE
LAYER IS DEEPEST/MOST MOIST AND ACROSS AREAS OF TERRAIN. THE
LARGELY ONSHORE FLOW WILL PROMOTE COOL CONDITIONS ACROSS THE AREA.
AS IT PERTAINS TO THE POTENTIAL FOR HIGH BASED CONVECTION, THE
OPPORTUNITY REMAINS AROUND 20%. MOST MODEL GUIDANCE REMAINS IN
AGREEMENT THAT A PLUME OF MOISTURE, CHARACTERIZED BY PRECIPITABLE
WATER VALUES OF AT OR ABOVE 0.75" WILL LIFT NORTHWARD. IN
ADDITION, 700-500MB LAPSE RATES OF 8 C/KM ARE ALSO ADVERTISED. THE
COMBINATION OF THE MOISTURE AND COOLER AIR ALOFT WILL SUPPORT
MUCAPE VALUES OF A FEW HUNDRED J/KG. WHILE THIS MATCHES CONCEPTUAL
MODELS OF INFAMOUS LIGHTNING EVENTS ACROSS THE REGION, IT APPEARS
UNLIKELY (THOUGH NOT ZERO) THAT THERE WILL BE ALIGNMENT OF
SUFFICIENT MOISTURE AND STEEPER LAPSE RATES IN THE VERTICAL TO
WARRANT ANYTHING MORE THAN A 20 POP. FURTHERMORE, A CONSENSUS OF
HIGHER RESOLUTION NWP AND OTHER TOOLS DON'T APPEAR TO NECESSITATE
THE MESSAGING OF A HIGHER END THREAT. FOR NOW, WE'LL CONTINUE TO
MONITOR TRENDS IN SATELLITE, RADAR, AND SUPPLEMENTAL UPPER AIR
OBSERVATIONS.
THE MOST PROBABLE AREA FOR CONVECTION (HIGH BASED SHOWERS AND/OR
DRY THUNDERSTORMS) WILL BE ACROSS EXTREME SOUTHERN PORTIONS OF THE
SOUTH BAY AND INTO THE CENTRAL COAST THROUGH THE DAY ON WEDNESDAY.
THE PRIMARY HAZARDS, AS IS TYPICALLY THE CASE WITH HIGH BASED
CONVECTION, WILL BE FOR ISOLATED LIGHTNING STRIKES AND
GUSTY/ERRATIC OUTFLOW WINDS OVER A CONFINED AREA. THE GOOD NEWS IS
THAT PROXIES FOR FUEL/VEGETATION VOLATILITY SUGGEST THAT WHILE
LIGHTNING-INITIATED FIRE STARTS WILL BE POSSIBLE, THEY SHOULD NOT
EXHIBIT MUCH RESISTANCE TO CONTROL. FURTHERMORE, THE EXTENDED
FORECAST DOES NOT OFFER MUCH IN THE WAY OF ANY *BIG* WIND EVENTS
SHOULD THE COVERAGE OF DRY THUNDERSTORMS EXCEED EXPECTATIONS.
LONG TERM
ISSUED AT 146 PM PDT TUE APR 15 2025
(THURSDAY THROUGH NEXT MONDAY)
LONGER TERM KEY MESSAGES
*WARMING TREND ENSUES
*LITTLE TO NO PRECIPITATION FORECAST
THE LONG TERM FORECAST APPEARS VERY TRANQUIL, WITH REALLY THE
PRIMARY ITEM TO NOTE BEING A WARMING TREND. MEDIUM TO LONG RANGE
ENSEMBLE CLUSTER GUIDANCE INDICATES THAT THE LONG TERM PATTERN
WILL BE LARGELY GOVERNED BY SLIGHT RIDGING OVER THE GULF OF
ALASKA. DOWNSTREAM FROM THIS FEATURE, ZONAL TO SLIGHT TROUGHING IS
ANTICIPATED.
AHEAD OF THIS RIDGING ACROSS THE GULF OF AK WILL BE A LONGWAVE
TROUGH THAT WILL SLIDE SOUTHWARD THROUGH THE GREAT BASIN ON
SATURDAY. AS THIS FEATURE SLIDES SOUTHWARD, IT'LL TIGHTEN THE
SURFACE PRESSURE GRADIENT BETWEEN BUILDING SURFACE HIGH PRESSURE
ACROSS NEVADA AND REMNANT TROUGHING ALONG THE COAST. THESE
OFFSHORE WINDS DON'T APPEAR TERRIBLY STRONG, BUT THE 925MB WINDS
AVERAGE BETWEEN 20 AND 25 KNOTS AND THE TAIL END OF OUR LOCAL WRF
DOES SUPPORT SOME OF THIS MOMENTUM MIXING DOWN TOWARD THE SURFACE.
WE'LL NEED TO BE MINDFUL OF ANY CHANGES TO THE WINDS HERE. OTHERWISE,
IT APPEARS RAIN-FREE FOR THE FORESEEABLE FUTURE AND AS SUCH, THE
CURRENT EXTENDED FORECAST OFFERS NO MEANINGFUL POPS.
AVIATION
(18Z TAFS)
ISSUED AT 1021 AM PDT TUE APR 15 2025
TRICKY FORECAST THIS MORNING AS AMPLE LOW LEVEL MOISTURE REMAINS
(DEEP MARINE LAYER) WITH MID-HIGH LEVEL CLOUDS STREAMING
OVERHEAD. SOME THINNING OF THE STRATUS DECK IS OCCURING, BUT
SLOW, ESPECIALLY WITH HIGH CLOUDS OVERHEAD. DO EXPECT MAINLY VFR
THIS AFTERNOON INTO THIS EVENING. CIGS/MARINE LAYER DO RETURN
TONIGHT WITH IMPACTS FOR THE WED AM RUSH AGAIN. OVERALL CONF IS
LOW TO MODERATE.
VICINITY OF SFO...ACARS PROFILES CONTINUE TO SHOW DEEP MOISTURE
FROM SFC TO 1500-2000 FEET. SATELLITE/CAMS DO SHOW SOME BLUE
POKING THROUGH, BUT WILL LEAVE CIGS THROUGH 19Z. VFR THIS
AFTERNOON. CIGS WILL RETURN TONIGHT.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...CIGS LINGER 19Z AND LOWER CONF THROUGH
20Z. VFR THIS AFTERNOON. CIGS EARLY RETURN TONIGHT.
MARINE
(TODAY THROUGH SUNDAY)
ISSUED AT 349 AM PDT TUE APR 15 2025
LIGHT TO MODERATE WINDS LAST THROUGH MUCH OF THE WEEK. MODERATE
SEAS HOLD THROUGH MIDWEEK OR SO, AND THEN BUILD INTO THE LATTER
PORTION OF THE WORK WEEK. NORTHWESTERLY WINDS LOOK TO BECOME FRESH
FOR THE WEEKEND LEADING TO CONCERNS FOR SMALLER CRAFT.
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...NONE.
SHORT TERM...BAIN
LONG TERM....BAIN
AVIATION...MM
MARINE...MM
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