Santa Clara, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

503
FXUS66 KMTR 191753
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1053 AM PDT Thu Mar 19 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 1247 PM PDT Wed Mar 18 2026

 - Early season, long duration heat wave continues to bring
   record- breaking temperatures and Moderate HeatRisk through
   Friday

 - Elevated potential for grass fires through the week due to
   warm and dry conditions with periods of moderate offshore winds

 - Gradual cooling trend begins this weekend

&&

.UPDATE...
Issued at 825 AM PDT Thu Mar 19 2026

The main weather impact message for today continues to be focused
on the ongoing heat wave. Latest probabilistic data shows highest
potential for cracking 100 degs remains over the Santa Cruz Mts
(Boulder Creek/Scotts Valley) and interior Monterey county near
Pinnacles. Heat Advisory remains in effect. However, as noted
below the marine layer is making a return. Satellite imagery and
cams show a very shallow marine layer hugging the immediate
coastline from Point Arena southward to near Pigeon Point. As
such, near the coastline will be a day of micro- climates with
bust potential for max temps being forecast too warm. We`ll need a
offshore push to nudge the marine layer to west to keep the
hotter temps on track. We`ll leave the forecast as is for now,
but watch it closely.

Given the ongoing heat, here are a few safety reminders.

* Stay hydrated and drink plenty of fluids.
* Wear lightweight, light-colored clothing.
* Reduce time spent outdoors or stay in the shade.
* Never leave people or pets unattended in vehicles.
* Use sunscreen if going to the coast or the pool.
* Use caution at the beach, the water is still cold.

MM

&&

.SHORT TERM...
Issued at 1218 AM PDT Thu Mar 19 2026
(Today and tonight)

While the heat wave continues to bring another day of record
breaking temperatures inland, there is some nuance along the
coast. The Half Moon Bay buoy is reporting 51F air temp, 50F dew
point, and 56F water temp. That combination of air temp near dew
point but lower than the SST is a canary in the coal mine for a
cloud filled marine layer. Not only is the air 5 degrees cooler
than this time yesterday and nearly saturated, it`s also now
significantly 5 degrees cooler than the SST. That means there is a
latent heat flux (of moisture) from the warmer ocean to the
cooler boundary layer air. Due to the warmer temperature, the sea
surface-air interface has a higher saturation vapor pressure
(capacity to hold water vapor) than the air at 2 meters. This
drives evaporation from the sea surface to the air, increasing the
dew point until the air is fully saturated. At this point any
further latent heat flux will force the water vapor in the air to
condense into cloud droplets.

And wouldn`t you know it, fog rolled into Half Moon Bay just
prior to 10 PM Wednesday night. The IR satellite image shows low
clouds extend along the entire coast from Bodega Bay to Big Sur.
The Bodega Bay vertical profiler doesn`t quite have the resolution
to capture the shallow depth, other than it`s less than 100
meters (328 ft). ALERT California cameras show the top of the fog
monster is around the Golden Gate Bridge deck, which is around 220
feet. That`s very shallow for a marine layer, which averages
around 1,500 - 2,000 feet in the Summer. If the onshore winds
persist through the day, this marine layer will bring morning
clouds and fog with much cooler and more humid air along the coast
and adjacent low-lying areas today. If offshore winds become
reestablished, we may still get a warm afternoon at the coast.
Since the wind speed is so light, it`s really hard to predict
these direction changes. The most likely outcome is the return of
offshore winds through the day, but the exact timing is unknown.
Either way the shallow nature of the marine layer will
significantly limit it`s inland progression.

&&

.LONG TERM...
Issued at 1218 AM PDT Thu Mar 19 2026
(Friday through Wednesday)

Friday still looks like the last day of the heat wave before a
cold front brings some relief on Saturday. That being said, Friday
may be the hottest day of the week for inland areas as the ridge
reaches it`s most powerful form. The 850 mb temperature is now
expected to reach 22C. That`s 2.8 standard deviations above the
mean. Before this week, we`ve never seen anything over 19.2C in
March. 22C is roughly the 75th percentile for August. The hottest
spots (Ben Lomond, Gilroy, King City) will likely reach the mid
to upper 90s. After the grand finale Friday afternoon, some high
clouds will start to move in, signaling the approaching cold
front. The surface front should move through Saturday morning,
effectively ending the heat wave. Inland temperatures will drop
around 10 degrees Saturday, and a further 5 degrees Sunday. Next
week will still be warmer than normal, but nothing compared to
this week. The next chance for rain is around the first of the
Month, but the forecast trend has been pushing that back. While
the rainy season is winding down, we still normally get 1-2 inches
in April.

&&

.AVIATION...
(18Z TAFS)
Issued at 1052 AM PDT Thu Mar 19 2026

A marine layer formed this morning, around 250ft, which brought
stratus and reduced visibilities along portions of our coastline.
KHAF and KMRY were the only TAF sites to really deal with this, with
other areas remaining VFR. Now that the stratus as eroded, all
sites are VFR this afternoon, with these conditions continuing
through the evening. There is some uncertainty as to whether or not
we`ll see round two of stratus or a marine layer returning tonight.
Opted to keep what the prior TAFs had, which is reduced cig and VIS
at KHAF, while the rest of the TAF sites remain VFR. High confidence
for interior sites, moderate to low confidence for KHAF and areas
along the immediate coast.

Vicinity of SFO...Offshore winds are expected for a few hours this
afternoon, before onshore winds return and then continue into the
evening. Winds may peak around 10-15kt around KSFO from 22Z-6Z or
so. Winds decrease to less than 10kt overnight.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR conditions prevail around the region
with mainly offshore flow occuring. Expect winds to gradually become
onshore over the next few hours and continuing through the
afternoon. Offshore flow is expected to return late this evening and
continue into the overnight hours. Low to moderate confidence in the
marine layer returning, opted to keep the hint of it in the KMRY TAF
rather than fully locking in.

&&

.MARINE...
(Today through Tuesday)
Issued at 412 AM PDT Thu Mar 19 2026

Gentle breezes continue across the inner waters with moderate
north to northwest breezes over the outer waters. Northwest winds
will begin to increase tonight and Friday and persist through the
weekend, with hazardous seas developing by Friday night in
response to the strengthening winds.

&&

.CLIMATE...
Issued at 421 AM PDT Wed Mar 18 2026

The following are the record high temperatures at the long term
sites for March 18th, 19th and 20th.

Location             Mar 19      Mar 20

Santa Rosa         83 in 2004  84 in 2004
San Rafael         81 in 1964  82 in 1960
Kentfield          83 in 1996  82 in 2001
Napa               86 in 1914  86 in 2004
Richmond           80 in 1996  81 in 2004
Livermore          82 in 2015  87 in 1915
San Francisco      80 in 2010  78 in 2004
SFO Airport        78 in 2010  78 in 2004
Redwood City       81 in 2010  82 in 2004
Half Moon Bay      79 in 2010  75 in 2010
Oakland Museum     81 in 1984  78 in 2001
San Jose           82 in 1988  78 in 2004
Salinas Airport    87 in 1997  80 in 1934

The following are the record high temperatures at the long term
sites for the entire month of March.

Location

Santa Rosa       91 on March 16, 2004
San Rafael       88 on March 25, 1952
Kentfield        91 on March 28, 1923
Napa             92 on March 17, 1914
Richmond         88 on March 18, 2026
Livermore        90 on March 25 and 26, 2025
San Francisco    87 on March 11, 2005
SFO Airport      85 on March 25, 1952 and March 17, 2026
Redwood City     93 on March 17, 2026
Half Moon Bay    83 on March 31, 2000 and March 17, 2004
Oakland Museum   89 on March 17, 2026
San Jose         89 on March 14, 2015
Salinas Airport  93 on March 18, 2026

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 8 PM PDT Friday for CAZ006-502>506-508>510-
     512>518-528>530.

PZ...Small Craft Advisory from 3 PM Friday to 9 AM PDT Saturday for
     Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm.

     Small Craft Advisory from 9 PM this evening to 9 AM PDT Saturday
     for Pt Arena to Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...KR
MARINE...Canepa

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