FXUS66 KMTR 140642
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1142 PM PDT Mon Jul 13 2026

...New SHORT TERM, LONG TERM, FIRE WEATHER...

.KEY MESSAGES...
Updated at 225 PM PDT Mon Jul 13 2026

 - Moderate HeatRisk across the interior through Wednesday

 - Breezy onshore winds Tuesday through Thursday afternoon
 
 - Minor coastal flooding continues through Thursday

 - Monsoon moisture clearing out today

&&

.SHORT TERM...
Issued at 1116 PM PDT Mon Jul 13 2026
(Tonight through Wednesday)

While the 12Z HRRR showed some interesting thunderstorm potential 
early Tuesday morning, the 18Z backed off, and the 00Z continued 
that trend. The radar picture is also losing steam and it now 
seems unlikely that thunderstorms will develop. By sunrise, the 
clouds will be gone and the threat will basically be over. 
There's another 5% chance Tuesday afternoon during peak daytime 
heating, but the best chance for convection is now behind us.

The big weather story now shifts to heat. According to commercial 
aircraft soundings, the 850mb temperature was around 22C at 00Z. 
That's somewhere between the 75th and 90th percentile. Even with
the cloud cover, temperatures were around 5-10 degrees warmer 
than normal on Monday. The 850 mb temperature will be broadly 
similar Tuesday, but we won't have the overcast mid level clouds 
to take the sting out of the heat. Surface temperatures will 
increase a few degrees, but the HeatRisk will increase more 
substantially for a few reasons; the radiant heat from direct 
sunlight, the cumulative effect of multiple hot days, and very 
warm overnight temperatures. In fact, we may see the warmest 
minimum temperature of the year for many locations thanks to the 
lingering altostratus acting as a blanket for the first half of
the night. All these factors combine to bring widespread moderate
HeatRisk Tuesday. Max temperatures will be in the 90s inland and 
70s along the coast.

On the other hand, the humidity will be a little lower and a decent 
onshore breeze will pick up in the afternoon. While low humidity and 
a breeze help people deal with the heat, they also contribute to 
elevated fire weather conditions. Refer to the fire weather section 
for more information.

&&

.LONG TERM...
Issued at 1116 PM PDT Mon Jul 13 2026
(Wednesday night through next Monday)

The hot weather will continue through Wednesday before a cooling 
trend starts on Thursday. A trough will move in from the Eastern 
Pacific, bringing a weak cold front Thursday morning. Inland 
temperatures will drop by as much as 10 degrees, bringing us back to 
normal for this time of year. The cooling trend will continue, and 
Friday and Saturday will actually be about 5-10 degrees cooler 
than normal while the marine layer expands back to around 1,000 
feet. The low pressure system will generate some gusty winds, 
particularly in the afternoon as the mixing depth increases and 
higher momentum is transfered to the surface.

At 500 mb the high pressure over the Rockies will remain in place as 
the trough approaches the coast. This pattern will keep mid-level 
winds out of the south to southwest through the week. That means the 
tropical moisture conveyer belt will remain open. While dry air will 
dominate the middle of the week, there is an increasing chance that 
one of the many robust tropical waves off the coast of Mexico will 
develop into a tropical cyclone this week aided by the warm El
Nino waters. If that happens, there is a chance that some of the 
associated moisture will be drawn into the SW winds and advect 
over the Bay Area, bringing us similar impacts and considerations 
that we saw with recent monsoon moisture event. Depending on the 
strength of the TC, there could also be impacts from ocean swell 
at the beach. The uncertainty is still high, but it's been 
trending more likely recently. The ECMWF 50 member ensemble has a
mean PW returning above 1.0" by Sunday- Monday. That's around the
90th percentile for this time of year. I also noticed 7 of the 
members have a PW over 1.5", and 2 members are over 2". The 
highest we've ever recorded is 1.79", and that was on 8/16/2020, 
when the remnants of Tropical Storm Fausto brought a major dry 
lightning outbreak to the Bay Area and sparked several wildfires. 
I'm certainly not predicting a repeat of August 2020, but it's 
worth keeping an eye on this next potential moisture push given 
the current warm temperatures and dry fuels.

&&

.AVIATION...
(06Z TAFS)
Issued at 832 PM PDT Mon Jul 13 2026

Radar and satellite continue to show northward moving high based 
showers over the forecast area. Patchy coastal stratus and fog may
develop tonight and Tuesday morning. Overall conditions favor VFR
with the highest probability of LIFR-IFR along the immediate 
coastline.

Vicinity of SFO...VFR. Northwest to west wind 5 to 15 knots except
15 to 25 knots Tuesday afternoon and evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR except patchy stratus and fog /LIFR-
IFR/ nearby late tonight and Tuesday morning. Winds mainly from 
the northwest 5 to 15 knots.

&&

.MARINE...
(Tonight through next Sunday)
Issued at 829 PM PDT Mon Jul 13 2026

Moderate to fresh north-northwest winds across the northern outer
waters continue with hazardous conditions, along with moderate
northwest swell. Northerly winds over the coastal and outer waters
become fresh to strong mid to late week, with near gale force
gusts. Expect building seas in response to the increasing winds
and long period southerly swell late week into next weekend.

&&

.FIRE WEATHER...
Issued at 1116 PM PDT Mon Jul 13 2026

Warming temperatures will result in fuels rapidly drying this 
week with ERC charts expected to exceed the 97th percentile across
the Mid Coast to Mendocino zone and get close to the 97th 
percentile across the Central Coast. Fire weather concerns will 
remain elevated Tuesday afternoon through Thursday due to near 
critically dry conditions, gusty onshore winds, and very dry fuel 
conditions. This may result in additional fire starts particularly
across the interior and higher elevations. Unsettled weather is 
possible next weekend with returning potential for dry 
thunderstorms and gusty, erratic winds.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 4 AM PDT Thursday for CAZ006-506-
     508.

     Heat Advisory from 10 AM to 10 PM PDT Tuesday for CAZ503-504-506-
     510-513>517-528.

     Coastal Flood Advisory until 4 AM PDT Wednesday for CAZ505-509-
     529-530.

     Heat Advisory from 10 AM to 10 PM PDT Wednesday for CAZ516-517.

PZ...Small Craft Advisory from 3 PM Tuesday to 3 PM PDT Wednesday for 
     Pt Arena to Pt Reyes 0-10 nm.

     Small Craft Advisory from 9 PM Tuesday to 9 AM PDT Wednesday for 
     Pt Pinos to Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory until 3 PM PDT Wednesday for Pt Arena to Pt 
     Reyes 10-60 NM.

&&

$$

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

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Prepared by Boulder-Creek.com Weather at: Tue Jul 14 02:30:03 PDT 2026