Scientific Forecaster Discussion
fxus66 kmtr 241147
Area forecast discussion
National Weather Service San Francisco Bay area
347 am PST Fri Feb 24 2017
Synopsis...drier and cooler conditions are forecast through
Friday with chilly overnight temperatures. Unsettled weather
conditions return over the weekend with a storm system moving in
from the north. A longer stretch of dry weather is expected
starting the middle of next week.
Discussion...as of 2:24 am PST Friday...skies are generally
clear over the district at this time, except for scattered strato-
cumulus clouds over the coastal waters. Latest observations show
temperatures ranging from the mid 30s to the mid 40s, generally 2
to 6 degrees cooler than at yesterday at this time. Dew point
temperatures are in the 30s, also cooler. Clear skies, light
winds, and drier air will result in cooler morning lows this
morning and Saturday morning. Overnight lows are forecast to be in
the 30s in most locations away from the coast and some of the
coldest inland valleys may see upper 20s. Patchy frost is likely
in most valleys by sunrise.
Dry and cool conditions are expected to persist today into
Saturday before a couple of low pressure systems bring rain
chances back to the district. The first system, now over British
Columbia, will move south of the coast on Saturday, but latest
model runs hold off any rain until late in the afternoon, as the
main system remains offshore most of the day. A second system then
moves south into northern California by late Sunday. Neither of
these are expected to bring much in the way of rain to the area,
up to a half inch at the very most, per the latest GFS and European model (ecmwf).
After these systems move through, drying conditions are expected
as a blocking high forms off the coast. Even the most recent
outlooks from the climate prediction center put California under a
"below normal" probability of precipitation into the first week of
Aviation...as of 3:45 am PST Friday...for 12z tafs. Ridging will
be suppressed today as an upper-level storm system swings
southward from the Pacific northwest towards northern California.
This system will advect mid-level and upper-level moisture over
the area through the day. As such, VFR conditions should prevail
through at least this evening for all terminals. Cigs will lower
tonight as the upper-level system draws closer. There is some
uncertainty on exact timing and as to how low cigs will be.
Current thinking is MVFR cigs will develop sometime around 08-09z
Saturday for sf Bay area terminals. Light-moderate onshore winds
this afternoon. Low to moderate confidence on forecast.
Vicinity of ksfo...VFR this morning and afternoon. MVFR possible
by 08z as a low pressure system approaches. Lighter onshore winds
today than previous couple of days, ranging from 9-12 kt by this
Sfo bridge approach...similar to sfo.
Monterey Bay terminals...VFR today, with a few low clouds possible.
Uncertainty on ceiling development by this evening. Only have few-scattered
low clouds at this time, but will have to be amend in later
updates, if necessary. Generally light onshore winds this
Marine...as of 2:19 am PST Friday...high pressure will continue
to weaken today as a low pressure system drops south along the
West Coast. Winds will briefly turn southerly on Saturday then
Switch Back to northwest by Sunday as the low dissipates. Winds
and seas should remain generally tranquil through the forecast
period, with showers possible Saturday through Monday.
... Watch...Salinas river
Public forecast: Sims
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