Scientific Forecaster Discussion
Area forecast discussion...corrected aviation
National Weather Service San Francisco Bay area
503 am PDT sun Apr 19 2015
Synopsis...cool conditions expected today along the coast with a
persistent marine layer in place while inland areas warm to above
average values. A region-wide cooling trend will take place early
in the workweek as a series of weak upper level disturbances
impact the state. As a result...unsettled weather will be possible
with a slight chance of showers through the latter half of the
Discussion...as of 04:05 am PDT Sunday...deepening marine layer
across the region this morning has resulted in decent inland
penetration of low level clouds...now spreading into most valley
locations. Meanwhile...a weak middle/upper level low can be seen on
satellite imagery spinning off of the northern California coast.
This feature will drop southward today and advect middle-level
moisture into the interior portions of the state over the next 12
to 24 hours. Across our region...moisture above the marine layer
will be limited and dry conditions will likely prevail.
Temperatures this afternoon will once again be cool along coastal
locations while inland areas away from the marine influence will
warm into the upper 70s to middle 80s.
Slight cooling will take place Monday into Tuesday as 850mb
temperatures cool and onshore flow increases in response to
troughing off of the West Coast. Will maintain a dry forecast on
Monday with model guidance now mostly keeping precipitation over
the higher mountains of northern and central California. With
that said...cannot rule out an isolated shower/thunderstorm over
the higher terrain of southern San Benito County late
Monday...yet confidence remains low. With the marine layer
expected to deepen further Monday night into Tuesday...have added
the mention of patchy drizzle along coastal areas. By Tuesday
afternoon/evening...the models show slightly better instability
and middle-level moisture over the region to maintain a mention a
slight chance of showers and thunderstorms over the
hills/mountains. However...most locations will remain dry.
A slight chance of showers will continue Wednesday and Thursday
over the hills/mountains as another middle/upper level low is
forecast to drop southward just off of the California coast.
Again...with limited moisture and lack of strong middle/upper level
support...do not expect widespread rainfall and measurable
precipitation will be isolated to scattered at best. An unsettled
pattern will persist through late week and likely into next
weekend with a series of weak disturbances moving through the
broad middle/upper level trough over much of the West Coast.
However...the model guidance has once again backed off on the
potential for widespread precipitation through next weekend.
Aviation...as of 4:53 am PDT Sunday...a closed and dry middle level
low 150 miles west of Point Arena this morning will drift south
during the period. Plenty of stratus and fog have moved inland
already at this hour. Little change in the lower level temperatures
..light surface winds and specifically a lack of northerly winds
through Monday evening favor a continuation of the marine layer. A
few pockets of mostly light drizzle along the immediate coast and
near the Bay waters can be expected due to a deepening marine layer.
Vicinity of ksfo...IFR ceiling until 18z then VFR for the afternoon and
evening. Mostly light winds today. Stratus returns tonight. Low to
Sfo bridge approach...similar to ksfo.
Monterey Bay area terminals...IFR until 17z-18z today then VFR. Low
confidence on clearing times today. Stratus likely returning early
Marine...as of 4:05 am PDT Sunday...a moderately deep marine
layer will continue over the coastal waters through early week.
Light northwest winds and gentle sea conditions will continue
through Monday night. Northwest winds are forecast to increase on
Tuesday and Wednesday as low pressure develops over the Great
Basin and high pressure strengthens offshore.
Public forecast: rgass
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