Scientific Forecaster Discussion
fxus66 kmtr 222055
Area forecast discussion
National Weather Service San Francisco Bay area
155 PM PDT Mon Jul 22 2019
Synopsis...a gradual warming trend will continue through midweek,
especially across the interior. This will lead to seasonably warm
temperatures inland while coastal areas remain mild under the
influence of the marine layer as onshore flow persists.
Discussion...as of 01:55 PM PDT Monday...satellite imagery shows
low clouds along much of the coast with the marine layer situated
at around 1000-1200 ft above ground level. Temperatures across the region this
afternoon are about 5 to 10 degrees warmer than this time
yesterday as high pressure builds over The Four Corners. Coastal
areas are currently in the upper 60s to low 70s while inland areas
are in the mid 80s to low 90s. Expect a few additional degrees of
warming this afternoon before temperatures begin to cool off for
the evening. The latest run of the 12z NAM remains consistent in
showing an increase in mid/upper level moisture over eastern and
Southern California as well as increased mid/upper level
instability this afternoon/evening. Any resulting high based
convection that develops is still expected to remain outside of
our forecast area with only an increase in mid/upper level clouds
over the southeastern portion of the region. Stratus offshore will
move inland once again tonight with patchy fog along the coast
possible late tonight and into tomorrow morning.
This week's warming trend will stall tomorrow as a mid/upper low
currently over the eastern Pacific shifts northeastward while its
associated trough moves into the Pacific northwest. Warming will
then continue over the interior on Wednesday as high pressure over
The Four Corners strengthens and builds westward into California.
Inland locations will see more widespread 90s mid-week with
isolated locations reaching 100 degrees. Persistent onshore flow
will likely keep a shallow marine layer in place resulting in
continued night/morning low clouds and patchy fog along the coast.
This will also act to keep highs for coastal areas in the mid 60s
to mid 70s. High pressure to our east will continue to be the
main driver of our weather through the end of the week and into
the upcoming weekend. This will keep seasonably warm conditions
across the interior with temperatures at or just above seasonal
averages while coastal areas remain relatively mild thanks to the
influence of the marine layer.
Aviation...as of 10:58 am PDT Monday...a shallow marine layer
with a depth of around 1200-1500 feet and building high pressure
has allowed clouds to Peel back to the coastline this morning. VFR
conditions will prevail this afternoon at the taf sites. Onshore
winds will increase this afternoon to around 10-15 kt most sites.
The marine layer will remain compressed through tonight as high
pressure continues to build overhead. For tonight and Tuesday
morning, expect stratus coverage similar to this morning with
mainly LIFR/IFR where clouds develop. Shallow depth should once
again prevent clouds from intruding too far into inland valleys.
Somewhat lower confidence on development around sf Bay, but some
cigs in the vicinity are likely to develop overnight.
Vicinity of ksfo...VFR this afternoon and evening. West-northwest winds
increasing this afternoon and early evening to 15-20 kt. For
tonight and Tuesday morning, moderate confidence on timing and
extent of stratus formation. May see a similar scenario to this
morning where the terminal remained VFR and some cigs developed
over the approach. Will continue to monitor and update as details
become more clear.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...VFR conditions this afternoon. Onshore
winds increasing this afternoon to around 10-15 kt. IFR cigs
likely to return around 03-04z this evening with conditions
deteriorating to LIFR overnight.
Marine...as of 08:42 am PDT Monday...gusty northwest winds will
continue over the northern coastal waters as high pressure builds
into the Pacific northwest and northern California. Light
southerly swell coupled with short period wind waves will continue
through the week.
... Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm
Small Craft Advisory...sf Bay until 9 PM
Public forecast: as
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