Blackhawk, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

436
FXUS66 KMTR 160455
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
955 PM PDT Tue Apr 15 2025

...New AVIATION...

.SYNOPSIS...
Issued at 146 PM PDT Tue Apr 15 2025

Cooler conditions will continue through Wednesday, with a 20%
chance for isolated showers and a thunderstorm or two. Thereafter,
a warming trend is anticipated through the weekend.

&&

.UPDATE...
Issued at 821 PM PDT Tue Apr 15 2025

Isolated thunderstorms continue to be the biggest forecast concern
over the next 24 hours. The 00Z OAK sounding reveals a
precipitable water value of 0.67 inches, conditionally unstable
lapse rates in the mid-levels, and an MUCAPE (713 mb) value of 2
J/kg with a CIN value of -101 J/kg. So overall, nothing impressive
with ingredients remaining displaced from one another and a dry
looking sounding below 400 mb. I think the key is going to be
whether or not sufficient moisture will be ingested into the mid-
levels where the relatively steep lapse rates are. As a reminder,
what we are expecting is elevated convection. Because of this
nature, dry lightning (lightning occurring with less than 0.10
inches of rain) remains the primary hazard with erratic/gusty
winds being the secondary hazard.

Sarment

&&

.SHORT TERM...
Issued at 146 PM PDT Tue Apr 15 2025
(This evening through Wednesday Night)

Short Term Key Messages
*Cool conditions continue
*10 to 15% chance for very isolated dry storms
*Patchy Coastal Drizzle

A stubborn marine layer today continues to gradually erode as
southerly flow envelops the region. A veil of mid to upper level
clouds continues to lift northward ahead of a cutoff upper low
parked to our southwest. These intermittent clouds will translate
to partly sunny skies across most areas this afternoon, with
little in the way of fanfare anticipated this afternoon. Afternoon
ACARs data (soundings from aircraft) from across the Bay Area
indicate that moisture is bifurcated vertically and this pairs
well with the aforementioned satellite discussion. This is
important because moisture is currently not aligned with the
location of the steepest lapse rates (at least not yet), which is
needed for convection. I don`t anticipate this to change this
afternoon or tonight across our region and as a result, the worded
forecast for this time period remain void of any rain or storms.

It`s highly probable that we`ll contend with another round of
marine stratus late tonight and into Wednesday morning as 925mb
flow remains largely onshore. Similar to this morning, the very
gentle ascent through the column, thanks to the upper low to the
south, will promote the development of drizzle where the marine
layer is deepest/most moist and across areas of terrain. The
largely onshore flow will promote cool conditions across the area.

As it pertains to the potential for high based convection, the
opportunity remains around 20%. Most model guidance remains in
agreement that a plume of moisture, characterized by precipitable
water values of at or above 0.75" will lift northward. In
addition, 700-500mb lapse rates of 8 C/km are also advertised. The
combination of the moisture and cooler air aloft will support
MUCAPE values of a few hundred J/kg. While this matches conceptual
models of infamous lightning events across the region, it appears
unlikely (though not zero) that there will be alignment of
sufficient moisture and steeper lapse rates in the vertical to
warrant anything more than a 20 PoP. Furthermore, a consensus of
higher resolution NWP and other tools don`t appear to necessitate
the messaging of a higher end threat. For now, we`ll continue to
monitor trends in satellite, radar, and supplemental upper air
observations.

The most probable area for convection (high based showers and/or
dry thunderstorms) will be across extreme southern portions of the
South Bay and into the Central Coast through the day on Wednesday.
The primary hazards, as is typically the case with high based
convection, will be for isolated lightning strikes and
gusty/erratic outflow winds over a confined area. The good news is
that proxies for fuel/vegetation volatility suggest that while
lightning-initiated fire starts will be possible, they should not
exhibit much resistance to control. Furthermore, the extended
forecast does not offer much in the way of any *big* wind events
should the coverage of dry thunderstorms exceed expectations.

&&

.LONG TERM...
Issued at 146 PM PDT Tue Apr 15 2025
(Thursday through next Monday)

Longer Term Key Messages
*Warming trend ensues
*Little to no precipitation forecast

The long term forecast appears very tranquil, with really the
primary item to note being a warming trend. Medium to long range
ensemble cluster guidance indicates that the long term pattern
will be largely governed by slight ridging over the Gulf of
Alaska. Downstream from this feature, zonal to slight troughing is
anticipated.

Ahead of this ridging across the Gulf of AK will be a longwave
trough that will slide southward through the Great Basin on
Saturday. As this feature slides southward, it`ll tighten the
surface pressure gradient between building surface high pressure
across Nevada and remnant troughing along the coast. These
offshore winds don`t appear terribly strong, but the 925mb winds
average between 20 and 25 knots and the tail end of our local WRF
does support some of this momentum mixing down toward the surface.
We`ll need to be mindful of any changes to the winds here. Otherwise,
it appears rain-free for the foreseeable future and as such, the
current extended forecast offers no meaningful PoPs.

&&

.AVIATION...
(06Z TAFS)
Issued at 955 PM PDT Tue Apr 15 2025

Generally VFR with mid- to high level clouds across the Bay Area and
central coast. MVFR stratus is thought to persist across parts of
the North Bay, although high cloud cover is making it difficult to
determine accurate extent. Moderate confidence in MVFR-IFR stratus
expanding back into the coastal valleys overnight into Wednesday
morning, when the time of clearing remains uncertain, although all
terminals should be VFR by 20Z. Breezy onshore winds with a
continues southerly component will develop Wednesday afternoon, with
stratus building back into the region as the winds diminish in the
evening. There is some convective activity possible Wednesday
afternoon and evening in the South Bay south of SJC and the Central
Coast, but probabilities are low and have opted to keep VCTS out of
the TAFs at this point.

Vicinity of SFO... VFR with mid- to high level clouds at the moment
with MVFR stratus returning within a couple of hours. Moderate
confidence on the clearing time on Wednesday morning, but VFR
conditions should return by 20Z. Breezy west-southwest winds
continue to diminish through the next few hours before resuming
Wednesday afternoon.

SFO Bridge Approach... Somewhat lower confidence of MVFR
stratus over the approach path. Otherwise similar to SFO.

Monterey Bay Terminals... VFR with mid- to high level clouds will
give way to returning stratus within a couple of hours. Moderate
confidence in clearing by late Wednesday morning. Light drainage
winds overnight before breezy onshore flow (southwesterly at MRY,
northwesterly at SNS) resumes Wednesday afternoon. There is a low
confidence (10-20% probability) of thunderstorms Wednesday afternoon
and evening, but have opted to keep VCTS out of the TAFs.

&&

.MARINE...
(Tonight through next Monday)
Issued at 821 PM PDT Tue Apr 15 2025

Southerly flow with light to moderate winds continues through
early Wednesday. Northerly winds will develop north of Point Reyes
Wednesday, but southerly winds persist elsewhere. Northerly winds
will spread through the rest of the waters through Thursday and
gradually build into the weekend. Small to moderate seas persist
into the weekend.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...Bain
LONG TERM....Bain
AVIATION...DialH
MARINE...DialH

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