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000
FXUS66 KMTR 100540
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1040 PM PDT Tue Apr 9 2024

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 150 PM PDT Tue Apr 9 2024

We`ll continue our warm spell across the Bay Area and Central
Coast through the middle to latter half of the week. Thereafter,
the weather will turn cooler, windier, and wetter. There is some
uncertainty regarding the timing of the upper storm system...and
thus rain and storm chances, so stay tuned for updates to the
weekend forecast.

&&

.UPDATE...
Issued at 912 PM PDT Tue Apr 9 2024

Clear skies have persisted through sunset, allowing temperatures
to quickly drop back into the 50s for most areas. Enhanced
radiational cooling will continue through the night. A shallow
marine layer will develop under high pressure tonight and persist
for the next few days along coastal areas. While the low level
air is still pretty dry, this marine layer may bring some low
stratus to the SF Peninsula Pacific coast and Monterey Bay area
early Wednesday morning before mixing out when day time heating
kicks in.

In the long term, the incoming storm on Saturday remains the
primary focus. The uncertainty remains high with respect to
timing, however the probability for precipitation is continuing to
trend higher. The Weather Prediction Center has added the coastal
counties to the latest excessive rain outlook for Saturday, with a
marginal chance of exceeding flash flood guidance. With robust
ensemble support and National Center attention, it`s now looking
likely that we will have widespread rain through the day Saturday,
with a chance for scattered showers and a possible thunderstorm or
two on Sunday.

&&

.SHORT TERM...
(This evening through Wednesday)
Issued at 150 PM PDT Tue Apr 9 2024

A picturesque day is in progress across the region, with cloud
cover relegated to the coastal waters. Interior parts of the area
have climbed into the low 70s, with many of the coastal regions in
the 50s and 60s. Tonight should feature another good radiational
cooling night, though 925mb flow around 10 knots may keep the
boundary layer from completely decoupling from the free
atmosphere. This should serve to keep temperatures a few degrees
higher than the previous night and may curb the fog potential. The
exception will be across some of the sheltered spots of the North
Bay.

Wednesday will be warm with high temperatures largely in the
upper 60s to low 80s. As mentioned in previous AFDs, while our
forecast high temperatures are well below any records (10 to 20
degrees below records), it`ll still be the warmest stretch of
weather we`ve experienced for several months. There`s a minor heat
risk, particularly for sensitive groups (elderly and infants). Be
sure to never leave children or pets in unattended vehicles. If
you`re working or playing outdoors, be sure to hydrate with plenty
of water.

&&

.LONG TERM...
(Wednesday night through next Monday)
Issued at 150 PM PDT Tue Apr 9 2024

Mild overnight conditions are forecast Wednesday night into
Thursday with similar MaxT values. However, with the progression
of our next storm system being delayed, the coverage of mid/upper
level clouds that would shave a couple of degrees off of high
temperatures may not transpire, particularly across the South Bay
and across Monterey and San Benito Counties on Thursday. If the
progression of the upper trough slows more, then high temperatures
on Thursday will really soar into the mid 80s which would
translate more into a moderate heat risk for the aforementioned
areas (and thus some heat headlines). Stay tuned for updates for
Thursday`s MaxT values.

Friday`s MaxT values may also need to be adjusted upward if
confidence increases in a slower progression of the upper low. At
this juncture, high temperatures on Friday are forecast to range
in between the 50s across the higher terrain and along the coast
to 60s and 70s elsewhere.

Taking a look at some of the cluster analysis tools, a lot more
of the Canadian ensemble members are coming into alignment with
the multi-model ensemble for a slower progression of the trough.
At least anecdotally, there`s the potential that the overall
multi-model mean may still be a bit too fast and too far east with
the trough. With a slower moving trough more and more of the area
could remain rain-free (though clouds will increase) through at
least Friday afternoon. The exception to this will be parts of the
North Bay (near and north of a Bodega Bay to Cloverdale line).
While the current forecast advertises around a 20-30 PoP late
Friday into Saturday, the more probable area for rainfall (closer
to 50%) will be across the North Bay during the daylight hours. As
the upper level low churns and drops southward through the pre-
dawn hours on Saturday, rain chances will fill in from north to
south.

At this time, Saturday appears to be the wettest time frame of
the outlook period. Taking a look at some of the instability
progs, CAPE values appear quite meager through the day, generally
at or below 25 J/kg. With the region being placed beneath the left
exit region of a 70 knot jet (NBM upper air mean 500 mb flow),
forcing for ascent appears that it`ll be maximized on Saturday.
Depending on the exact evolution of this upper trough, however,
we`ll need to be cognizant that if forcing arrives later in the
day, this may allow instability to build, thereby increasing the
thunderstorm potential. At this point in time, flow above the
surface appears uni-directional which would support training of
rain bands/convective cells. This would equate to an increase
flood risk, especially since many areas are running anywhere from
100-200 percent of normal over the past couple of weeks precip
wise. We`ll keep tabs on this.

Forecast uncertainty continues through Sunday as the range of
solutions widens. If the upper low quickly translates eastward,
then morning rain showers will yield to improving conditions in
the afternoon. However, if the upper trough continues to amplify
(which would be more in line with the current trends), then there
will be a potential that showers and thunderstorms would linger
later in the afternoon. Stay tuned for updates as the forecast
still exhibits a degree of variability for the upcoming weekend.

&&

.AVIATION...
(06Z TAFS)
Issued at 1033 PM PDT Tue Apr 9 2024

Mostly clear through the night across most terminals. Evidence of
a shallow marine influence today leading to the possibility of
IFR stratus for coastal terminals, with a slight potential for
KSTS as well. Any overnight cigs that develop clear by mid-
morning. FEW-SCT high clouds persist through the day Wednesday
with typical diurnal onshore flow.

Vicinity of SFO...VFR through the period. Low confidence in a hint
of FEW-SCT stratus through the San Bruno Gap by morning, but
overall around the Bay and approach should remain VFR. Otherwise
mostly clear Wednesday with some high clouds. Typical diurnal
onshore wind pattern through the TAF period.

Monterey Bay Terminals...Clear going into tonight with some hints
of low clouds beginning to develop near the coast and the Salinas
valley. Moderate confidence in IFR cigs developing around the bay
overnight, but expected to clear rapidly by about 16-17Z.

&&

.MARINE...
(Tonight through next Monday)
Issued at 1033 PM PDT Tue Apr 9 2024

Strong high pressure centered approximately 500 nautical  miles
west of San Francisco is supporting fresh to strong NNW winds
across the outer coastal waters with moderate to rough seas.
Conditions are much more favorable in protected areas along the
coast and in the Bays. This pattern will be fairly stable through
Thursday. By Friday an approaching gale force low pressure system
from the Gulf of Alaska will move into the California offshore
zones. This system will bring unsettled weather, changing wind
directions and building seas through the weekend. The return of
strong NW flow next week will sustain rough seas.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 9 AM PDT Thursday for Pt Arena to Pt
     Reyes 10-60 NM.

     Small Craft Advisory until 3 AM PDT Wednesday for Pigeon Pt to
     Pt Pinos 10-60 NM.

     Small Craft Advisory from 3 PM Wednesday to 9 AM PDT Thursday
     for Pigeon Pt to Pt Pinos 10-60 NM.

&&

$$

SHORT TERM...Bain
LONG TERM....Bain
AVIATION...Behringer
MARINE...Flynn

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