Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
855 PM PDT Monday Jun 29 2015
Synopsis...a significant warming trend will continue across inland
portions of the region through Wednesday as high pressure builds
over the western United States. A slight cooling trend is then
expected for the latter half of the week as the high pressure
weakens and retreats inland.
Discussion...as of 8:55 PM PDT Monday...forecast is looking on
track this evening. Main theme will be for some hot inland weather
on Tuesday and Wednesday. In the short term...as the sun is setting
theres a few marine clouds along the San Mateo coast with Half
Moon Bay reporting a cloud deck at 700 feet. Elsehwhere some
clouds are starting to pile up on the Monterey peninsula while the
rest of the district enjoys a pleasant and warm Summer evening.
The hills will stay balmy tonight with temperatures above 2000 feet
staying steady around 75-80 degrees.
As high pressure builds on Tuesday and the gradients ease with a
thermal trough near the coast...the stage will be set for a hot
day in the inland valleys. Expect widedspread readings from 95-105
degrees. One element keeping US out of heat advisory criteria is
the places that will get the truly hot weather are the typical hot
spots while the heavily populated areas around Oakland/San Jose
and the peninsula will stay seasonably warm but not hot.
For all intents and purposes dont expect much change on Wednesday with
another hot day for the inland valleys.
00z NAM is in and does show some possible convective precipitation on
Thursday which the GFS has been showing for a while...then another
round Thursday night into early Friday. As always confidence
remains low with these southeasterly moisture slugs but the model
output is much more bullish then previous events and will need to
be monitored on the heels of this midweek heat event.
Previous discussion...as of 02:54 PM PDT Monday...many inland locations
are reporting temperatures in the 90s this afternoon as high
pressure over the western Continental U.S. Continues to build toward the West
Coast. In addition...the low level clouds have pushed well off of
the coast this afternoon despite a marine layer at around 1200
feet deep. However...the marine influence and weak onshore flow
has held coastal temperatures generally in the 60s to lower 70s.
The inland warming trend is forecast to continue through midweek
before reaching a peak on Wednesday afternoon. Most inland areas
away from the coast and bays will see afternoon temperatures
warming into the 90s to as high as 108 in the warmest inland
valleys and higher elevations both Tuesday and Wednesday. Coastal
locations will likely warm into the upper 60s to 70s with a
persistent light onshore flow. Meanwhile...the forecast models
continue to show middle- level moisture advection over the state
through late week as monsoonal moisture is pulled northward on the
west side of the middle/upper level high. At this time...the best
chances for convection will be east of our region where greater
instability and moisture is expected. However...the latest GFS
model indicates increased potential for convection over our region
Thursday and Friday. Will closely monitor the forecast models and
look for run-to-run consistency before adding a mention of
thunderstorms in the forecast.
Otherwise...much of the region is forecast to experience dry
weather conditions through the upcoming weekend with high pressure
aloft. Temperatures will begin to cool region-wide late in the
week as the middle/upper level ridge slowly weakens and retreats
inland away from the coast. With the aforementioned middle-level
moisture advection through late week...do expect an increase of
middle/high level clouds over much of the region. This too will aid
in the cooling trend...especially over the interior.
Aviation...as of 5:00 PM PDT Monday...stratus has cleared out
20-30 miles offshore today. Marine layer becoming shallower but
becoming better defined as the airmass above the marine layer
warms up. Stratus expected to spread back into the sfo and mry Bay
areas tonight but after the Airport evening rush.
Vicinity of ksfo...MVFR after 05z possibly later. West winds
to 20 knots gusting to 25 knots until 03z.
Ksfo bridge approach...same as sfo.
Monterey Bay area terminals...clouds have cleared well away from
the Bay today and IFR ceilings should stay out until at least 04z.
Marine...as of 08:38 PM PDT Monday...high pressure will continue
to bring moderate gusty northwest winds over the coastal waters
this afternoon and through tonight. Winds decrease after Tuesday
as a thermal trough over the interior shifts to the coast.
... Bay until 9 PM
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm until 9 PM
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm until 3 am
Public forecast: rww
aviation: west pi
marine: west pi
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