Holy City, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

467
FXUS66 KMTR 290447
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
847 PM PST Sat Dec 28 2024

...New UPDATE...

.SYNOPSIS...
Issued at 153 PM PST Sat Dec 28 2024

Another round of rain is anticipated through Sunday morning
across the Bay Area and Central Coast. A respite from the
widespread rainfall is on tap Sunday evening and into early
Wednesday. With light offshore flow, a dry airmass will translate
to cold overnight conditions through at least mid-week. The
chances for more widespread rainfall returns just after the start
of 2025.

&&

.UPDATE...
Issued at 816 PM PST Sat Dec 28 2024

Key Messages for the Short Term:
-Moderate to heavy rainfall across the North Bay on Sunday
-Largely light to moderate rain elsewhere on Sunday
-Elevated wind gusts of 30 to 40 mph on Sunday, isolated to 50 in
 North Bay

Let`s start with rain. WPC, back east, continues to keep Sonoma
County in an Excessive Rainfall Outlook. This simply means that
rain rates could exceed flash flood guidance. For the layperson,
we may have the need to issue flood advisories and a possible
flash flood warning in North Bay as this front slices across the
region. Projections remain on track for timing of the rain. Rain
will start to spread across North Bay just after midnight then
jump in intensity in the 4-6 AM window. This band of rain is
slated to slide from NW to the SE through the AM hours of Sunday.
across the Bay Area. Central coast will be late AM hours into the
PM hours. Storm total rainfall will likely be in the 2-3" for
Sonoma Coastal range and the Mayacamas. Totals will fall off as
the rain moves south, with the Santa Cruz mountains picking up
1-2". San Jose, on the other hand, may end up so rain shadowed
that they only pick up a tenth of an inch. All told this front
looks progressive and should clear our entire service area by
Sunday night. The possible impacts with this front will be
localized flooding, especially in North Bay, and wind along the
frontal boundary. Some of the higher peaks of North Bay and North
Bay coastal areas may see a few gusts in excess of 45 mph. This
should be short lived and associated with frontal passage.
However, given the saturated soils and rain, trees falling is
likely. Given that, expect a few isolated power outages. Winds
will be gusty as the front slides south, but lower than what is
expect in North Bay. Still, this may bring down a few trees.

Overall the forecast remains on track. Satellite and radar
support the model guidance and the ongoing forecast.

&&

.SHORT TERM...
Issued at 153 PM PST Sat Dec 28 2024
(This evening through Sunday)

Key Messages for the Short Term:
-Moderate rainfall across the North Bay on Sunday
-Largely light to moderate rain elsewhere on Sunday
-Elevated wind gusts of 30 to 40 mph on Sunday

After morning rainfall, shortwave ridging will dominate our
weather over the next 6 or so hours. There may be a repeat of
pockets of dense fog, across the southern Salinas Valley, however,
925mb winds are forecast to increase some ahead of our next upper
shortwave trough. Before the moisture deepens ahead of the
stronger energy, pockets of fog and drizzle will likely
intermingle, especially across the higher terrain of the Bay Area
and Central Coast.

Our next shortwave trough is already taking shape just offshore
(around 50 N 140 W) and will be the primary culprit for our next
round of potentially hazardous conditions. The main trough,
characterized by 12 hour 500mb 150 meter height falls, will drag a
cold front southward through the Bay Area and portions of the
Central Coast through the day on Sunday. Model agreement with the
placement of the greatest rain amounts is high with areas across
the North Bay slated to receive anywhere between 1/2 inch to
around 1 1/2 inch, largely across Sonoma and Marin counties. Rain
amounts may overachieve in regions of higher terrain and there`s
around 20% chance that rain amounts could climb as high as 2
inches across western portions of the Sonoma Coastal Range. Recent
intel from soil experts across the North Bay indicate that the
probability of rapid runoff (and thus flooding) is close to 100%.
With some area creeks and streams still recovering from our recent
rainfall, there`s a high likelihood that they`ll return to minor
flood stage. Additional, low water crossings may become impassable
and regions of poor drainage (e.g., highly urbanized areas) may
experience largely nuisance flooding. As a result of the high
probability of runoff, we`ve hoisted a small/short fused Flood
Watch for Marin and Sonoma counties. Avoid flood prone areas and
never let children play near drainages or culverts. In addition,
saturated soils will equate to an additional risk for landslides.
As the main upper trough slides eastward, the trailing cold front
will weaken or undergo frontolysis. This will diminish low level
convergence, thereby diminishing forced ascent and as a result
rain chances generally taper downward with southward extent. Still
most areas will see measurable rainfall, with the exception being
across the southern Salinas Valley. HREF calibrated thunder
probabilities are not impressive and while many HREF members
(about 80% of them) indicate CAPE above 100 J/kg, a lot of this
instability is confined to the warm cloud layer which suggests
more in the way of efficient rainfall processes and less in the
way of a thunder threat. Trends will be monitored, however.

Finally, as low level cyclogenesis transpires across the WA/OR
coastline, the surface pressure gradient will tighten. As such the
wind field will respond with 925mb flow increasing to around 40
knots, mostly across the North Bay. At this time, forecast
soundings don`t indicate a high potential for momentum transfer,
outside of precipitation loading (where rain will help to "drag"
higher momentum toward the surface). With the probability of wind
gusts over 45 mph being less than 20%, we`ll forgo the issuance
of a Wind Advisory. Some of the high-res guidance is a little more
bullish with widespread wind gusts of 45 to 50 mph. At this time,
will rely on forecast soundings and largely hold serve with a mix
of the inherited forecast, our local WRF and the 50th percentile
NBM (which is higher than the deterministic NBM). That being
said, wet soils may translate to a greater risk for treefall, so
we`ll need to be cognizant of this threat going through the day on
Sunday.

&&

.LONG TERM...
Issued at 153 PM PST Sat Dec 28 2024
(Sunday night through next Friday)

Key Messages for the Long Term:
-Frost and freeze conditions expected Tue and Wed mornings
-20% chance for light rain across the North Bay on late Wed
-20% to 50% rain chances North Bay, Bay Area, northern Central
 Coast Wed - Sat

We`ll finally get a bit of a break from the rain for more than 24
hours across a good portion of the Bay Area and Central Coast.
While the front discussed in the short term section will weaken,
building surface high pressure will actually encourage north to
even northeasterly flow through the day on Monday. Monday morning
could be quite chilly, but the fly-in-the-ointment could be 925mb
winds staying elevated around 15-20 knots. If the PBL is able to
decouple, then Monday morning will be quite chilly to cold. The
offshore flow continues through the day on Monday and this will
help to dry the lower troposphere even more. While typically any
sort of wind will likely keep the mercury from plummeting, ideal
radiational cooling is expected, especially Monday night into
Tuesday morning. The deterministic NBM actually paints widespread
30 and 40 degree MinTs for Tuesday morning. However, with the dry
airmass in place, it`s conceivable that temperatures are a few
degrees lower than currently advertised. This translates to the
potential that more widespread freezing could grip the area. For
now, we`ll start to message the potential for a widespread frost
and freeze event, with the chance of MinT`s falling below 36
degrees (largely away from the coast) being above 80%.

Tuesday night and into Wednesday morning will feature another
opportunity for widespread frost and freeze, however, cloud cover
will invade from the northwest, potentially keeping the area from
radiating too rapidly. Regardless, those with outdoor evening
festivities will need to bundle up as the probability of
temperatures below 45 degrees will be around 80% or higher for
many locations (except along the coast where temperatures will be
around 50 degrees or less). Additional frost/freeze headlines may
be needed, but we`ll get a better handle on the cloud cover
forecast before additional messaging for that time period.

Our largely precipitation-free stretch of weather comes to an end
as we head into 2025. Extreme northwestern portions of Sonoma
County will have the best chances, albeit around 20%, for some
measurable rainfall late Wednesday into Thursday. Most areas will
remain rain-free on Thursday with rain chances increases on
Friday, but mostly across the North Bay and portions of the Bay
Area. There does remain some uncertainty with the exact placement
of measurable rainfall. Diving into some of the model groupings or
clusters reveals that the multi-model ensemble is dominated by
the GEFS and EPS which has a slightly flatter downstream mid-level
ridge. This would translate to the next upper trough having more
of an impact on our sensible weather. If the mid-level ridge holds
stronger, then rain chances will need to be cut down a bit
spatially.

&&

.AVIATION...
(00Z TAFS)
Issued at 350 PM PST Sat Dec 28 2024

Light to moderate winds tonight will increase Sunday morning as
a cold front pushes south and east through our area. The strongest
winds will occur just out ahead of and along the front as the main
area of precipitation pushes through. Along with increased
southerly gusts, and lower ceilings, expect reduced visibility
with the strongest rainfall. Light rain and lower ceilings persist
behind the cold front through the afternoon and early evening with
partial to full clearing expected through Sunday evening,
especially inland terminals.

Vicinity of SFO...MVFR ceilings will persist through with mostly
light winds. Expect southerly winds to increase out ahead of the
front as showers develop. Gusty south winds out ahead of the front
remain elevated behind the front out of the northwest, eventually
beginning to ease late in the day to early evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...MVFR ceilings are expected to persists
for the remainder of today until later tonight, eventually
becoming IFR with light and variable winds. Showers are expected
to be in the vicinity of Monterey Bay by late morning. MVFR
ceilings are expected to develop behind the front and remain MVFR
into the early evening, with clearing skies by late Sunday night.
Fog may be an issue, especially in the Salinas Valley late tonight
into early Sunday morning.

&&

.MARINE...
(Tonight through next Friday)
Issued at 415 PM PST Sat Dec 28 2024

Increasing shower is expected into the night with gusty winds and
choppy seas developing into Sunday. Expect the strongest wind and
moderate rainfall Sunday morning, but rains will exit into that
afternoon. Long to moderate period swell will continue to run
through the waters for the next several days.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory until 4 AM PST Sunday for CAZ006-505-509-529-
     530.

     Flood Watch from 4 AM PST Sunday through Sunday morning for
     CAZ502>506.

PZ...Small Craft Advisory from 3 AM to 3 PM PST Sunday for SF Bay N
     of Bay Bridge.

     Small Craft Advisory from 9 AM to 3 PM PST Sunday for Mry Bay.

     Small Craft Advisory until 9 PM PST Sunday for Pigeon Pt to Pt
     Pinos 0-10 nm-Pt Arena to Pt Reyes 0-10 nm-Pt Pinos to Pt
     Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

     Small Craft Advisory until 9 AM PST Monday for Pigeon Pt to Pt
     Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 NM.

&&

$$

Update...BFG
SHORT TERM...Bain
LONG TERM....Bain
AVIATION...JM
MARINE...Murdock

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