Rheem Valley, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

790
FXUS66 KMTR 151735
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1035 AM PDT Tue Apr 15 2025

...New AVIATION...

.SYNOPSIS...
Issued at 349 AM PDT Tue Apr 15 2025

Cooler temperatures are forecast through Thursday and warmer weather
returning for the weekend. Slight chance for thunderstorms on
Wednesday, primarily for the Central Coast and Southern Coastal
Range.

&&

.UPDATE...
Issued at 859 AM PDT Tue Apr 15 2025

The inherited short term forecast is in good shape, with just a
few alterations to sensible weather elements for this morning.
Our 12 UTC weather balloon from the Oakland Airport revealed a
gradual moistening of the boundary layer (thanks to an intrusion
of the marine layer) and an increase in mid to upper level
moisture. In addition, 700-500mb lapse rates continue to steepen
with values of around 8.5 C/km. More on this later. With modest
ascent ahead of our quasi-cutoff low to the southwest, pockets of
drizzle have developed. Ascent assisted by terrain (orographic
lift) across areas such as the Santa Cruz Mountains has allowed
for measurable precipitation. As such, I`ve added in patchy
drizzle along the coast and across some of the higher terrain. I
anticipate that as we progress through the morning, the coverage
of drizzle will dwindle.

Otherwise, we will continue to monitor the 5-10% chance for very
isolated showers and storms today. While mid-level lapse rates
are steep, the overall prospects for elevated convection are not
great today as the more "moist" areas of the column don`t coincide
with the regions of greatest potential energy. As we progress
into tomorrow and tomorrow evening, however, a signal still
remains such that isolated thunderstorm wording is appropriate in
the forecast (20% chance). We`ll have more insight on this later
today.

The remainder of the forecast remains unchanged and updated
products have already been transmitted.

&&

.SHORT TERM...
(Today and tonight)
Issued at 349 AM PDT Tue Apr 15 2025

Satellite imagery shows the upper level low spinning west of of
southern CA this morning. Water vapor imagery shows rather dry air
across much of the lower levels with moisture increasing as you go
up in the atmosphere. Convective ingredients for today, and in
particular this morning, look to be slightly healthier than
tomorrow; however, based on soundings across the area we`ll need to
overcome the dry air and CIN to really get anything going. Should it
happen, we might be able to get a few showers or thunderstorms out
of it with lightning and perhaps a few bouts of gusty winds. A note
about the drier air, that increases the DCAPE values putting us
close to 800 J/kg supporting stronger downdrafts should showers or
storms form. Confidence is low on this happening, thus I opted to
keep PoP and the mention of thunder out of the forecast for today.

&&

.LONG TERM...
(Wednesday through Monday)
Issued at 349 AM PDT Tue Apr 15 2025

The forecast looks to be on track for the long term, with the main
feature being the possibility for elevated thunderstorms on
Wednesday. Low pressure is expected to move onshore into southern CA
sending a slug of moisture to the north. This should help kick up
showers and perhaps thunderstorm or two over the Central Coast and
our portion of the southern Coastal Range. Looking at hi-res
guidance and soundings, CAPE has quite the range of possibilities.
The NAM and the HRRR are the most aggressive with up to 500 J/kg of
MUCAPE. But when you look at the soundings, there is a lot of CIN to
overcome. Kept the mention of thunder in the forecast over Central
Coast and up into the Diablo Range, though confidence remains on the
lower end.

Heading into Thursday, a secondary system slides into northern CA
from the north while the upper low over southern CA meanders east.
Dry weather is expected, which may be accompanied accompanied with
some breezier winds. An upper level high builds over the eastern
Pacific during this time, which will eventually nose in for Friday
and Saturday. More zonal to weak troughing is expected by Sunday.
Cooler temperatures prevail through Thursday, with a warming trend
expected for the weekend.

&&

.AVIATION...
(18Z TAFS)
Issued at 1021 AM PDT Tue Apr 15 2025

Tricky forecast this morning as ample low level moisture remains
(deep marine layer) with mid-high level clouds streaming
overhead. Some thinning of the stratus deck is occuring, but
slow, especially with high clouds overhead. Do expect mainly VFR
this afternoon into this evening. Cigs/marine layer do return
tonight with impacts for the Wed AM rush again. Overall conf is
low to moderate.

Vicinity of SFO...ACARs profiles continue to show deep moisture
from SFC to 1500-2000 feet. Satellite/cams do show some blue
poking through, but will leave cigs through 19Z. VFR this
afternoon. Cigs will return tonight.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Cigs linger 19Z and lower conf through
20Z. VFR this afternoon. Cigs early return tonight.

&&

.MARINE...
(Today through Sunday)
Issued at 349 AM PDT Tue Apr 15 2025

Light to moderate winds last through much of the week. Moderate
seas hold through midweek or so, and then build into the latter
portion of the work week. Northwesterly winds look to become fresh
for the weekend leading to concerns for smaller craft.

&&

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

$$

SHORT TERM...KR
LONG TERM....KR
AVIATION...MM
MARINE...KR

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