Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1100 am PDT Tuesday Jul 22 2014
Synopsis...a weak system will bring a slight chance of showers
and thunderstorms to a portion of our area through this afternoon.
Building high pressure to our east will bring a warming trend
Thursday and Friday especially to inland areas...and warm
conditions will continue into the weekend.
Discussion...as of 09:00 am PDT Tuesday...made a few adjustments
to the forecast this morning based on current trends. Per kmux
88-d radar...already seeing the elevated convection tapering off
at this hour as the middle/upper level shortwave approaches the San
Francisco Bay area. This feature...clearly seen on water vapor
satellite imagery at this hour...is forecast to move across the
North Bay this afternoon and eject out of the region by tonight.
With this...expecting chances for convection to drop off shortly
Expecting the marine layer to mix out late this morning or early
afternoon with middle/high level clouds exiting as the aforementioned
disturbance passes. This will result in mostly sunny conditions
by late afternoon/early evening. Temperatures this afternoon will
be near...or slightly warmer than yesterday depending on when the
clouds break out.
Previous discussion...as of 3:00 am PDT Tuesday...kmux radar at this
hour shows a few cells located about 50 miles west of Big Sur
heading to the NE. These cells are associated with subtropical
moisture and a weak area of instability that is heading into our
area. Radar shows cell tops to 35k feet and dbz numbers up to 55 --
not too bad for our area during overnight hours. Currently no
lightning strikes, however would not br surprised if we get a few
out of it. As the day progresses, the most unstable air will
continue to the north and east bringing a slight chance of
showers or thunderstorms for spots from Santa Cruz up to the
Sonoma coast. Worth noting that the latest NAM/GFS runs have
backed off a bit with the different convective parameters such as
cape and modified total totals.
Outside of the possible convection today, look for another mild
day across our area as water temperatures will remain well above normal
along with higher than normal precipitable water values. Highs will be in the middle
60s to upper 70s at the coast with upper 70s to lower 90s inland.
Warmer and drier weather will return for the second half of the
week as a ridge of high pressure over The Four Corners region
will push back into our County Warning Area. 500 mb heights around 582 dm will
jump to 590 by Thursday while increase 6c back to the 21-22c
range. This will help to boost temperatures around 10 degrees inland
with only 3-6 degrees of warming at the coast. Highs should fall
well short of heat advisory/watch/warning levels. The warm
weather should continue into next week.
Aviation...as of 11:00 am PDT Tuesday...precipitation and lightning
activity are winding down as the shortwave moves in. Clouds are
rather mixed this morning with periodic low ceilings and numerous middle
and high level clouds. Areas of clearing are evident just offshore
however and conditions will quickly improve over the next couple
of hours. Stratus to return to the terminals tonight.
Vicinity of ksfo...MVFR through 18-19z. Ceilings are rapidly improving
though could see lingering issues through 19z. Winds turn west in
the afternoon. Stratus to return late.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...scattered low clouds to become VFR
this afternoon. Ceilings return this evening.
Marine...as of 09:00 am PDT Tuesday...a weak disturbance moving
across the district today will generate scattered showers and a
slight chance of isolated thunderstorms across the coastal waters
this morning. A weak surface pressure gradient across the region
will maintain light winds and gentle seas through first half of
this week. By midweek...northwesterly winds will increase as a
thermal trough develops inland.
Public forecast: rgass
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