FXUS66 KMTR 010408
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
908 PM PDT Sat May 31 2025
...New AVIATION, MARINE...
.SYNOPSIS...
Issued at 825 AM PDT Sat May 31 2025
High pressure remains in place, with hazardous heat expected across
our inland areas once again today. Given the dry conditions, expect
elevated fire weather conditions to continue as well. However,
an upper level trough will bring cooler conditions to the region,
with more seasonal temperatures expected by this coming week.
&&
.UPDATE...
Issued at 810 PM PDT Sat May 31 2025
Sunny skies blanketed the Bay Area as the 00Z KOAK sounding
balloon ascended through the atmosphere. As it climbed it
recorded a variety of weather related parameters. Most notably
for today was the temperature profile. Today's sounding recorded
an 850mb (~5k ft) temperature of 25.35C. Why's that important? It
broke a daily record for max values for this date with a period
of record dating back to 1948. Definitely one of the longer
running histories for weather balloons in the west. I digress.
This rather warm airmass over the region brought the much
discussed heat to the interior portions of the forecast area. For
what it's worth the Heat Advisory was allowed to expire at 8 PM.
So how hot did it actually get? The hottest inland locations
ranged from 100-108 degrees. Much cooler toward the bays
immediate coastline, but even some of those locations were still
above normal for late May. Also was the temperature spread across
the region - coast to inland. Monterey county for instance, throw
a 5k foot high mt range in between cool marine air and inland
heat you end up with a 40 degree spread. Big Sur Coast had a few
readings in the mid 60s, but just to the east at Arroyo Seco it
soared to 105 degrees. I've been forecasting the weather here for
over 20 years and these temperature spreads in a single county
still fascinate me.
So what's on tap to round out the weekend? If you're not a fan of
the heat you're in luck. Much colder air is on our doorstep. The
ridge of high pressure with a very warm airmass will be old news
as a it's replaced by a passing upper trough through NorCal.
Temperatures will drop 10-20 degrees.
No update needed this evening.
MM
&&
.SHORT TERM...
(This evening through Sunday)
Issued at 200 PM PDT Sat May 31 2025
-Moderate HeatRisk for far interior locations and the Santa Clara
Valley, which is where a Heat Advisory will go into effect later
today.
-Elevated fire weather concerns today.
-Non-zero chance for high-based convection Saturday
Water vapor imagery continues to show Northern California
sandwiched between a trough of low pressure that is pushing into
the Pacific Northwest this afternoon and an upper level low off
the Northern Baja Peninsula, with the high pressure over our
region starting to get squashed. That said, warm to hot
conditions are prevailing across the Bay Area and the Central
Coast, with most locations running 2 to 7 degrees warmer than
those at this time yesterday. Therefore, expect our high
temperatures to be similar those of yesterday, with the Heat
Advisory remaining in place through 8 pm this evening for through
interior areas.
One other thing that we are continuing to watch for late this
afternoon and this evening is the non-zero threat of some
convection over Southern Monterey County. At this time though,
confidence is relatively high that it will not occur, as the best
areas of instability and moisture are to our south and east.
That said, showers and isolated thunderstorms have start to fire
along the Southern Sierra, as far north as Yosemite and Hetch
Hetchy and some midlevel moisture is starting to spread across
the southern portion of the Central San Joaquin Valley. Therefore,
cannot fully rule out something trying to develop. Just think it
is highly unlikely, with the threat being minimal at best.
As for the upper level trough moving into the Pacific Northwest,
expect it to deepen along the West Coast over the next 24 hours,
with a bit of energy expected to cut off from the main flow on
Sunday over Northwest California Coast. As a result, expect the
marine layer to reform and deepen tonight to around 2000 feet deep
in response to this trough, with a more prominent stratus deck
expected by Sunday morning. 850 mb temperatures will also fall
between 7 or 8 degrees C by tomorrow, so expect cooler conditions
to develop region wide for Sunday. Palmer
&&
.LONG TERM...
(Sunday night through next Friday)
Issued at 200 PM PDT Sat May 31 2025
The energy that cuts off from the main flow will form an upper
level low over the Northwest Coast late in the day on Sunday,
which will slowly drift south along the coast through Tuesday
night. Given this troughy pattern, expect temperatures to continue
their downward trend into Monday and Tuesday, and then remain
near or below normal through at least Wednesday and potentially
into Thursday.
This upper level low will be an interesting one. Given the time of
year and the forecasted track, would not expect to see much if any
rain with it, other than some marine layer drizzle, especially
Sunday night and Monday. However, as this low drops south it
starts to interact with the current upper level low to our south
that is kicking inland. As such, the ensembles are hinting at some
midlevel moisture wrapping back Monday night and into Tuesday for
Monterey and San Benito. At this point in time, confidence is low
as to whether or not this will happen, so have left out the
mention of showers for these areas. However, this is something
that we will need to watch.
High pressure starts to rebuild for Friday and Saturday, so expect
dry and warmer conditions developing once again. Palmer
&&
.AVIATION...
(06Z TAFS)
Issued at 859 PM PDT Sat May 31 2025
Widespread VFR continues into the night. Winds reamin moderate to
breezy through the late afternoon and into the evening before
reducing. IFR CIGS reform along the coast and fill over the
terminals around the Monterey Bay in the late evening and into the
night. CIGS will fill at HAF and filter into the SF BAY,
affecting OAK into early Sunday. Pockets of mist and fog look to
build overnight long the coast, and Monterey Bay, with moments of
mist and inconsistent CIGs for the North Bay terminals. Widespread
VFR returns for Sunday afternoon as moderate to breezy winds
build. MVFR and IFR CIGs build along the coast and around the
Monterey Bay as winds ease into Sunday night. As winds reduce,
they look to turn southerly at SJC into Sunday night.
Vicinity of SFO...VFR through the TAF period. Breezes and gusts cut
off in the late evening with light to moderate winds expected
through the night. Spotty low clouds look to affect SFO, but do not
look to fill like at OAK into early Sunday. These clouds erode into
the late morning, with breezy to gusty winds arriving shortly after
into the mid afternoon. Winds are expected to become light again
into that evening.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...VFR lingers into the late evening, but LIFR
to LIFR CIGs will fill around the Monterey Bay into the night as
winds become lighter. Visibilities look to be affected by mist and
fog overnight around the Monterey Bay as CIGs continue to lower. VFR
returns in for SNS the mid morning while CIGs light to MVFR levels
for MRY, as visibilities improve. CIGs scatter at MRY into the
afternoon as winds begin to build around the Monterey Bay. MVFR
CIGs return into Sunday evening as winds begin to reduce.
&&
.MARINE...
(Tonight through next Friday)
Issued at 859 PM PDT Sat May 31 2025
Breezy to gusty winds continue across the waters, resulting in
steep wind waves and hazardous conditions for small crafts.
Expect rough seas over the outer waters with significant wave
heights of 10 to 15 feet across the southern outer waters and up
to 22 feet across the northern outer waters Sunday evening into
Monday morning. Winds begin to gradually ease by Tuesday with
significant wave heights remaining elevated through late next
week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Sunday for SF Bay N of Bay
Bridge.
Small Craft Advisory from 3 PM Sunday to 3 AM PDT Monday for SF
Bay N of Bay Bridge.
Small Craft Advisory until 3 PM PDT Sunday for Pt Arena to Pt
Reyes 0-10 nm.
Gale Warning from 3 PM Sunday to 3 AM PDT Monday for Pt Arena to
Pt Reyes 0-10 nm.
Small Craft Advisory until 3 AM PDT Sunday for Pt Reyes to
Pigeon Pt 0-10 nm.
Gale Warning until 3 AM PDT Monday for Pt Arena to Pt Reyes 10-
60 NM.
Small Craft Advisory until 3 AM PDT Monday for Pigeon Pt to Pt
Pinos 10-60 NM.
&&
$$
SHORT TERM...Palmer
LONG TERM....Palmer
AVIATION...Murdock
MARINE...Murdock
Visit us at www.weather.gov/sanfrancisco
Follow us on Facebook, X, and YouTube at:
www.facebook.com/nwsbayarea
x.com/nwsbayarea
www.youtube.com/nwsbayarea
Prepared by Boulder-Creek.com Weather at: Sat May 31 22:30:02 PDT 2025
From the National Weather Service
|