FXUS66 KMTR 271917
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1217 PM PDT Wed May 27 2026
...New SHORT TERM, LONG TERM...
.KEY MESSAGES...
Updated at 1215 PM PDT Wed May 27 2026
- Cooler, unsettled weather conditions continue through Thursday
- Warming and drying trend Friday and beyond
&&
.SHORT TERM...
Issued at 1215 PM PDT Wed May 27 2026
(This evening through Thursday)
We have already seen showers and an isolated thunderstorm develop
late this morning across the Eastern Santa Clara Hills and in the
Mountains of San Benito County. As daytime heating continues, we are
expecting convection to fire up in the East Bay Hills, Eastern Santa
Clara Hills, the Santa Cruz Mountains and the Central Coast (County
of Monterey/San Benito) this afternoon and evening. This is as the
atmosphere becomes more unstable with CAPE values between 100-400
J/kg. However, vertical wind profiles don't favor organized
convection, with little to no 0-6km wind shear. Therefore,
probabilities for thunderstorms remain less than 10% through the
afternoon and early evening. Any stronger cell (shower and/or
thunderstorm) that develops over any one given location has the
potential to produce 0.25"-0.50" per hour of rainfall.
The mid/upper level low will begin to retrograde back over the
Pacific tonight into early Thursday morning and begin to pull in
PWAT values of around 1.00". This will increase rain chances
offshore late tonight and then will move onshore along the Central
Coast through Thursday morning. However, with the loss of daytime
heating, the thunderstorm threat will lessen. Forecast rainfall
amounts have increased in the Santa Cruz Mountains and Santa Lucia
Range now having a greater than 60% probability of seeing more than
0.25" through Thursday afternoon (this would include rainfall from
today). These probabilities of seeing greater than 1.00" (40%-75%)
remain confined to the Santa Lucia Range.
Conditions begin to dry out from north to south during the day
Thursday as the mid/upper level low shifts further inland. However,
rain showers look to linger over the Central Coast through the early
evening.
&&
.LONG TERM...
Issued at 1215 PM PDT Wed May 27 2026
(Thursday night through next Tuesday)
Cannot rule out rain showers to linger across the North Bay late
Thursday night into early Friday morning as deeper moisture (PWAT
values approaching 1.00") move across this region. In wake of the
exiting trough, a warming and drying trend will kick off by Friday
afternoon with temperatures gradually returning to near average this
weekend as zonal flow develops over the region. Temperatures are
currently forecast to warm above seasonal averages by Sunday and
into the middle of the upcoming week.
&&
.AVIATION...
(18Z TAFS)
Issued at 1122 AM PDT Wed May 27 2026
The cold core 500 mb low continues to straddle the CA/NV border.
A spoke of 700 mb to 500 mb troughing/instability extending outward
from the low center continues to move southward over the southern
half of our forecast area at the moment. It's cold for late May at
the mandatory pressure levels 925 mb through 500 mb on this morning's
12z Oakland upper air sounding: < 10th percentile for late May. With
solar input and surface heating today, expect a few more showers
along with isolated lightning in the unstable air. KMUX shows a recent
isolated thunderstorm over northeastern Santa Clara county, drifting
to the southwest. Will continue to closely monitor KMUX radar and
satellite through today.
The aforementioned 500 mb low and high precipitable water it has
entrained (near 90th percentile) bring the potential for more wet
weather tonight and Thursday. Will closely monitor radar and
satellite imagery.
Vicinity of SFO...VFR. East to northeast wind 5 knots shifts to
westerly and increases to 15 to 22 knots in the afternoon with
gusts diminishing below 20 knots beginning 03z this evening. Wind
shifts to southeasterly 5 knots Thursday morning then to westerly
12 knots Thursday afternoon.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Lingering MVFR ceilings are expected to
scatter out by the afternoon, if they have not already. Onshore
moderate breezes (~10-14kt) will persist through the afternoon with
the Salinas valley experiencing gusts up to 20kts. MVFR ceilings
will return this evening (00-02Z). Light rain showers begin to
approach the Monterey Bay coastline late Wednesday night with winds
slightly diminishing. Medium confidence in the timing of the rain
showers as they may arrive an hour earlier or later, though they are
expected to stick around for the remainder of the TAF period. Winds
begin to shift SE early Thursday morning. There is low confidence at
this time that visibility will be impacted, however I wouldn't be
surprised if the rain showers cause a slight reduction to visibility
(minimum 5SM).
&&
.MARINE...
(Today through Monday)
Issued at 1005 AM PDT Wed May 27 2026
Northwesterly winds continue to diminish through today and
overnight into widespread gentle to moderate breezes over the
outer and inner waters. Wind gusts also become more moderate, with
the outer northern waters experiencing locally strong gusts
through Thursday morning. Rough seas with heights of 11-16 ft
continue to abate through today and become more moderate (5-9 ft)
by Friday morning. Another round of strong to near-gale force
winds are expected to develop over the weekend with building rough
seas again.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 PM PDT Thursday for Pt Arena to Pt
Reyes 10-60 NM.
Small Craft Advisory until 9 AM PDT Thursday for Pigeon Pt to Pt
Pinos 10-60 NM.
&&
$$
SHORT TERM...RGass
LONG TERM....RGass
AVIATION...Canepa/Navarrete
MARINE...Navarrete/Canepa
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Prepared by Boulder-Creek.com Weather at: Wed May 27 14:30:02 PDT 2026
From the National Weather Service
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