FXUS66 KMTR 051756
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1056 AM PDT Wed Aug 5 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 1148 PM PDT Tue Aug 4 2026

 - Elevated fire weather threat across the interior North and East 
   Bays, and the Diablo and Santa Lucia ranges through midweek.

 - Widespread Moderate HeatRisk returns for the end of the work 
   week. 

 - Critical fire weather conditions develop Friday and Saturday.

&&

.UPDATE...
Issued at 950 AM PDT Wed Aug 5 2026

Solid marine layer this morning impacting the Bay Area and 
Central Coast. As another forecaster in the office pointed out 
this morning pretty impressive to see an over performing marine 
layer deepen to nearly 1800 feet with anomalously high 500mb 
heights. Not as much drizzle being reported this morning, but the 
ample moisture in the low levels has led to mist. Above the marine
layer is a completely different story. High elevation sensors 
showed another classic nocturnal drying event this morning. 
Sensors showed humidity "recovery" to around 30 percent yesterday 
evening then humidity values plummeted through sunrise as the 
marine layer moved inland. This would definitely be a fire weather
concern, but fortunately winds are relatively light. Other item 
of note this morning is some high level smoke being picked up by 
satellite lurking over the coastal waters and potentially the 
North Bay. Surface sensors are not showing it reaching the ground
as of now therefore it's likely high level drift smoke. 

For today - the over performing marine layer is bringing much
needed relief to the interior. No Heat Advisories are needed as
temperatures cool and HeatRisk concerns decreases. The marine
layer will slowly ease back to the coast, but linger for the day. 

No update needed this morning.

Will be focusing on another round of heat later in the week and
developing near critical fire weather conditions.

MM

&&

.SHORT TERM...
Issued at 1148 PM PDT Tue Aug 4 2026
(Tonight through Thursday)

The picture from space this evening shows stratus snaking through 
the the region. Earlier model guidance struggled with the onset of 
its arrival and to some extent the depth as well. It's currently 
around 1000ft and has the potential to get to 1200ft, with coastal 
drizzle and patchy fog possible tonight and into Wednesday morning. 
The good news is that this will cool temperatures overnight and 
perhaps take a bit longer to retreat to the coast Wednesday morning. 
With ridging not as strong and those factors in place, the threat 
for Moderate HeatRisk has been pulled back with only a few pockets 
found across the interior Central Coast and interior E and S Bay 
regions. Some of those pockets include areas above the marine layer, 
where temperature recovery won't be as great. Like the prior shift, 
will not be issuing a Heat Advisory for Wednesday.

Wednesday night into Thursday morning, the forecast will be on 
repeat. Look for the marine layer and associated stratus to seep 
into the region leading to another cloudy night.

&&

.LONG TERM...
Issued at 1148 PM PDT Tue Aug 4 2026
(Thursday night through next Tuesday)

The ridge starts to build back into the region on Thursday, which 
will compress the marine layer to perhaps 500ft for the next few 
days. At the surface, winds will have shifted from the south to a 
more north/northwesterly flow; however, aloft, guidance shows the 
southerly flow holding. Deterministic models and ensembles show a 
slug on moisture pushing into our region Thurday-Saturday giving us 
PWATs ranging from 0.75-1.0, which could lead to things feeling 
humid. In terms of the heat portion of the forecast, it looks to be 
on track. Data continues to signal 850mb temps in the 28-30C range, 
leading to toastier daytime and overnight temperatures. Highs, 
especially for interior areas and those not affected by the marine 
layer, will be in the 90s to low 100s while low temperatures there 
fall into the upper 60s-70s. Widespread Moderate HeatRisk is 
expected, with some pockets of Major HeatRisk on Saturday. 

Sunday and Monday, the upper level pattern shows the ridge 
flattening some. The latest NBM seems to keep temperatures a tad 
warmer on Sunday, with the more notable interior cooling trend 
occuring on Monday and Tuesday. 

&&

.AVIATION...
(18Z TAFS)
Issued at 1055 AM PDT Wed Aug 5 2026

Seeing most inland terminals returning to VFR conditions late this 
morning with the remaining soon to follow by 20Z. The exception 
being KHAF where at least MVFR conditions are expected throughout 
much of the day. Onshore winds will increase by this afternoon and 
persist through the early evening before diminishing after sunset. 
As such, expecting MVFR ceilings to return to the coast and lower to 
IFR (potentially LIFR) as stratus pushes inland into the interior 
valleys early Thursday morning. Any stratus and/or fog that does 
develop will mix out by mid-to-late morning on Thursday.

Vicinity of SFO...VFR. VFR conditions have returned to KSFO at this 
hour and is likely to prevail through much of the daytime hours with 
an increase of west to northwest winds through this afternoon and 
early evening. Expecting an earlier return late this evening around 
05Z and linger through at least 18Z Thursday. There is a low-to-
moderate confidence for IFR conditions early Thursday morning, yet 
confidence is not high enough to include in this TAF package, yet 
have mentioned SCT for the timeframe it has the greatest
potential.

SFO Bridge Approach...Later return of stratus Thursday morning, 
otherwise similar to SFO. 

Monterey Bay Terminals...VFR conditions are forecast to return by 
around 1930Z, KSNS has already scattered out. Onshore winds increase 
this afternoon before MVFR ceilings return late this evening and 
lower to IFR a bit later in the evening. There is the potential for 
LIFR conditions late in the night into Thursday morning, yet again 
confidence is not high enough to include in this TAF package.  

&&

.MARINE...
(Today through Monday)
Issued at 950 AM PDT Wed Aug 5 2026

Light to gentle south to southwesterly breezes will persist
through Thursday along with seas between 2-6 feet. Winds will
begin to increase again out of the northwest going into Friday
with building seas and hazardous conditions for small craft
returning for the upcoming weekend.

&&

.FIRE WEATHER...
Issued at 1000 AM PDT Wed Aug 5 2026

Marine layer brought relief to lower elevations this morning, but
above the marine layer another nocturnal drying event bringing
single digit RH. Simply put, little to no recovery last night.

Cooler and slightly more humid conditions are expected across the
interior today and Thursday. Despite the "cooldown" temperatures
across the interior will still be in the 90s to low 100s Wed/Thu
with min RH teens. Still expecting an onshore push each
afternoon/evening with breezy to gusty winds leading to a few
hours of elevated fire weather conditions.

High pressure will build back over the district late Thursday into
Friday. As such, the marine layer will become more compressed and
interior heat increasing and humidity decreasing. Peak times of
greatest concern will be each afternoon/evening Sat/Sun. This will
push Energy Release Component (ERC) back up to critical levels. 
ERC values have climbed above the 97th percentile within the 
Interior Central Coast and Diablo-Santa Cruz (Diablo Mountains and
Santa Cruz Mountains) zones with the Mid Coast to Mendocino Zone 
(North Bay) to reach the 97th percentile this week. Large fires 
become more frequent after ERC values cross the 90th percentile 
with extreme burning conditions expected with ERC values above the
97th percentile. 100 hr fuels continue to respond to the hot and 
dry conditions with values reaching critical levels across the 
region. Latest intel also shows Live Fuel samplings are also 
heading toward critical levels.

Lastly, we're tracking some high level moisture streaming in from
the south Friday and over the weekend. As of right now, upper
level instability seems limited so high based thunderstorms are 
not likely. If anything, some high cirrus is possible with some 
higher dew points.

MM

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...KR
LONG TERM....KR
AVIATION...RGass
MARINE...RGass

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Prepared by Boulder-Creek.com Weather at: Wed Aug 5 14:30:02 PDT 2026