Technical NOAA Weather Discussion

FXUS66 KMTR 291154
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
454 AM PDT Fri Mar 29 2024

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 230 AM PDT Fri Mar 29 2024

A weather system brings wind, rain, and a few thunderstorms to the
region later today through Saturday. Moderate impacts are
anticipated including minor flooding and potential tree and power
line damage. Stay weather aware and prepare for longer afternoon
and evening commute times today. 

&&

.SHORT TERM...
(Today and tonight)
Issued at 230 AM PDT Fri Mar 29 2024

Key Points:
* Impactful weather system today into Saturday
* Moderate wind and water impacts anticipated
* Strong wind gusts may cause tree and power line damage
* Minor flooding potential from locally heavy rainfall
* Isolated thunderstorms with lightning and small hail
* Peak impacts this afternoon into Saturday evening

Weather Overview:

A cyclonic flow pattern prevails aloft across the northeast Pacific 
early this morning. Two low pressure systems are evident -- one west 
of Washington and another located around 400 nm west of the Redwood 
Coast. A consensus of the forecast models suggest the lower latitude 
system will become the prevailing low as it drops southeast towards 
the northern/central CA coast. The surface low will subsequently 
deepen to around 995 mb as it locates just east of the Bay Area by
this evening. This dynamic system will bring impacts to the 
region in the form of strong gusty winds, periods of moderate to 
heavy rainfall, and thunderstorms through the forecast period.
Below is a timeline of our expectations for today into tonight.

This Morning:

Scattered showers will increase in coverage across the Bay Area 
during the mid to late morning hours as warm advection aloft becomes 
the primary forcing mechanism for ascent. Breezy southerly winds 
will begin to pick up as well, especially along the coast and within 
the coastal ranges of the Bay Area. Showers should be light to 
moderate through most of this period, with heavier showers 
approaching the Bay Area as afternoon approaches. The primary 
impacts during this period should be wet roadways along the with 
the potential for a few branches down due to the breezy winds. 

This Afternoon and Evening:

This will be prime time for the greatest impacts. Look for the 
deepening surface low to wobble towards the coast as a surface warm 
front lifts north early in the period before a cold front moves 
onshore during the late afternoon to early evening. Coverage and 
intensity of showers should increase by early afternoon with 
elevated instability providing for isolated thunderstorm potential 
as well. A 50 kt southerly low-level jet (LLJ) will impinge on 
coastal portions of the region as well with an uptick in strong 
and gusty gradient winds occurring. In addition the higher 
resolution convection allowing models are suggestive of a 
conditional risk for mixing these stronger winds to the surface in
convection particularly as the main frontal band moves onshore 
during the early to mid afternoon hours. As mentioned instability 
is sufficient for thunderstorm development as early as this 
afternoon, but actually peaks within the colder and unstable 
airmass following the cold frontal passage. Regardless, 
thunderstorm hazards will exist in the form of occasional 
lightning, brief heavy rain, gusty to perhaps locally damaging 
winds, and small hail. Given the strong low-level wind fields and 
sufficient low-level directional shear can't rule out the 
potential for a landfalling waterspout as well, especially this 
afternoon. Scattered showers and isolated thunderstorms will 
continue within the post-frontal environment overnight as the 
cold-core low remains in the vicinity. Now that we've outlined 
the weather setup here's a quick breakdown on potential hazards 
for today and tonight:

* Strong gusty winds with tree and power line damage possible
* Locally heavy rainfall leading to urban/street flooding
* Isolated thunderstorms with lightning, wind, and small hail
* Conditional risk for landfalling waterspout

Stay weather aware today and keep up with forecast changes. 

&&

.LONG TERM...
(Saturday through Thursday)
Issued at 230 AM PDT Fri Mar 29 2024

Saturday into Sunday morning:

While the weakening surface low will depart to our south the region 
remains under the influence of the cold-core upper low. This means 
we'll see plentiful showers and isolated thunderstorms on Saturday. 
The day won't be a total washout (we'll probably even see some 
sunshine at times), but watch out because when it rains, it pours 
(as they say). So watch out for lightning, brief locally heavy 
rainfall, and small hail as potential hazards. This risk is greatest 
on Saturday afternoon, with coverage continuing overnight. By Sunday 
morning look for precipitation to have largely ended for most areas 
outside of perhaps the Santa Lucias and southern Diablo range. 
Overall amounts should be lighter compared to during Friday/Friday 
night, but locally heavy amounts could cause minor flooding concerns 
if a heavier shower or storm traverses an urban or hydrologically 
sensitive area. Winds should be quite a bit lower as well as the 
pressure gradient relaxes. For temperatures, they'll be a little on 
the cool side with highs in the upper 50s to lower 60s and lows 
mostly in the 40s. 

Late Sunday through Thursday:

High pressure builds into the region with dry conditions and a 
warming trend through mid week. Expect a cooling trend by late week 
as upstream troughing traverses the Pacific Northwest states. A 
little light precipitation may accompany this feature as well but it 
doesn't appear to be anything noteworthy at this point.

&&

.AVIATION...
(12Z TAFS)
Issued at 454 AM PDT Fri Mar 29 2024

Increasingly strong and gusty southeasterly winds aloft resulting
in low level wind shear, otherwise moderate to heavy rain including
periodic gusty southerly surface winds also developing today. Windy
conditions continuing tonight along with moderate to heavy showers
and a slight chance of thunderstorms. Winds easing somewhat by early
Saturday morning. MVFR-IFR conditions during the period.

Vicinity of SFO...Southerly to southeasterly winds increasing today
with gusts 25 to 30 knots, possibly a few higher gusts during the
afternoon. Low level wind shear developing by late morning, continuing
through the afternoon. Rain developing today, showers along with a
slight chance of thunderstorms tonight and Saturday morning.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals...Southerly to southeasterly winds increasing
today, especially gusty in the Salinas Valley. Localized low level
wind shear possible during the afternoon. Otherwise rain developing
today, showers along with a slight chance of thunderstorms tonight
and Saturday morning. 

&&

.MARINE...
(Today through Wednesday)
Issued at 445 AM PDT Fri Mar 29 2024

A strengthening low pressure system over the eastern Pacific will
continue moving toward California resulting in southerly gales and
moderate to heavy rain developing today. Cold, unstable air aloft
with the low will also result in a slight chance to chance of
thunderstorms later today, tonight and Saturday. A high pressure
system will build in behind the low late in the weekend and early
next week bringing drier, milder conditions to the area.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from 11 AM this morning to 5 AM PDT Saturday for 
     CAZ006-504-509-510-512-514>516-518-528>530.

     Wind Advisory from 8 AM this morning to 3 AM PDT Saturday for 
     CAZ502-503-505.

     High Wind Warning from 11 AM this morning to 9 PM PDT this 
     evening for CAZ517.

     Wind Advisory from 9 PM this evening to 5 AM PDT Saturday for 
     CAZ517.

PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this 
     evening for SF Bay N of Bay Bridge.

     Small Craft Advisory from 9 AM this morning to 3 PM PDT this 
     afternoon for Mry Bay.

     Gale Warning from 3 PM this afternoon to 3 AM PDT Saturday for 
     Mry Bay.

     Small Craft Advisory until 9 AM PDT this morning for Pigeon Pt 
     to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena 
     to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Pinos 
     to Pt Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

     Gale Warning from 9 AM this morning to 3 PM PDT this afternoon 
     for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 
     NM-Pt Reyes to Pigeon Pt 0-10 nm.

     Gale Warning from 9 AM this morning to 9 PM PDT this evening for 
     Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 
     NM-Pt Pinos to Pt Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...SPM
LONG TERM....SPM
AVIATION...Canepa
MARINE...Canepa

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Prepared by Boulder-Creek.com Weather at: Fri Mar 29 06:30:02 PDT 2024
From the National Weather Service