Castro Valley, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

317
FXUS66 KMTR 200435
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
935 PM PDT Wed Aug 19 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 147 PM PDT Wed Aug 19 2026

 - Compressed marine layer today, increases Thursday into the weekend

 - A gradual cooling kicks off Thursday and continues into the
   weekend

 - Elevations above about 1000 feet will have warm temperatures
   and RH values in the teens Thursday morning and afternoon

&&

.SHORT TERM...
Issued at 147 PM PDT Wed Aug 19 2026
(This evening through Thursday night)

Little change to the forecast as we shift from quasi-ridging to more
zonal flow in the upper levels over the next day. An upper level low
will slowly advance towards the West Coast, nudging the Desert
Southwest high slightly eastward. This will allow a cooling tend to
start on Thursday, in addition to the marine layer deepening and
onshore flow increasing. The marine layer should get to 1000-1200ft
by Thursday morning, leading to another night with wide spread
stratus, patchy fog, and patchy coastal drizzle. Elevations above
the marine layer, wont` be as lucky and will continue to be warm and
dry above it. Clouds begin to clear by early to mid morning, with
the stratus retreating to the coast by late morning. High clouds
look to return to the forecast tomorrow which should leave us with
partly to mostly cloudy skies. High temperatures will likely be a
couple of degrees cooler than Wednesday.

&&

.LONG TERM...
Issued at 147 PM PDT Wed Aug 19 2026
(Friday through next Tuesday)

The upper level low continues to track towards the West Coast, with
the trough elongating southwards and the shortwave or closed low
moving towards the PacNW by Saturday. Troughing holds over the
region through early next week, which will lead to temperatures
being anywhere from 5 to 15 degrees below their seasonal normal.
Stratus looks promising each night through at least Saturday
morning, with the marine layer potentially compressing Saturday
night into Sunday morning. Models suggest it could deepen again
Sunday night into Monday morning, which may lead to more widespread
stratus.

&&

.AVIATION...
(06Z TAFS)
Issued at 935 PM PDT Wed Aug 19 2026

Currently LIFR-VFR. Persistence forecast on tap with moderate to
high confidence in IFR ceilings returning to all terminals tonight.
Further deterioration to LIFR is expected at coastal terminals and
STS. If the marine layer undergoes compression, conditions will
further deteriorate with less inland extent expected. VFR is
expected by the afternoon (except for HAF) with IFR stratus
sticking close to the coast. Diurnal winds will prevail.

Vicinity of SFO...Currently VFR with westerly flow. High confidence
in an IFR ceiling returning tonight with VFR by late-morning.
Diurnal winds will prevail.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently IFR with westerly flow at MRY and
IFR with northwesterly flow at SNS. High confidence in conditions
deteriorating to LIFR. At least a brief period of VFR is expected by
tomorrow afternoon. Diurnal winds will prevail.

&&

.MARINE...
(Tonight through next Tuesday)
Issued at 935 PM PDT Wed Aug 19 2026

Moderate to fresh northwesterly breezes will prevail through
Friday, increasing to become fresh to strong over the weekend.
Hazardous conditions for small craft are expected across the outer
waters and along the coastal jet regions into Friday. Rough seas
in the outer waters will slowly abate with moderate seas
prevailing by Friday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Friday for Pt Arena to Pt
     Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Pinos to Pt
     Piedras Blancas 0-10 nm.

     Small Craft Advisory from 3 PM to 9 PM PDT Thursday for Pigeon
     Pt to Pt Pinos 0-10 nm.

&&

$$

SHORT TERM...KR
LONG TERM....KR
AVIATION...Sarment
MARINE...Sarment

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