fxus66 kmtr 210028 

Area forecast discussion 
National Weather Service San Francisco Bay area 
428 PM PST Tue Feb 20 2018 

Synopsis...the storm door is back open with cool unsettled 
weather through the duration of the forecast. A pair of dry 
systems are expected this week, both with the potential for a 
dusting of snow down to around 2000 feet. Another round of gusty 
winds on Thursday. A trio of wetter, more organized storm systems 
possible throughout next workweek. 


Discussion...as of 02:30 PM PST Tuesday... a very cold 
Continental airmass from western Canada surged into the region 
earlier this week, bringing the coldest temperatures all winter, 
and in some locations, years. Widespread upper 20s to mid 30s were 
the norm across the area with some select locations dropping into 
the 10s, while other areas moderated by the relatively warmer San 
Francisco Bay hovered around 40 at the higher end of the 
spectrum. Morning temperatures were generally 10 to 15 degrees 
below normal low temperatures. Record temperatures were broken or 
matched at Oakland Airport (30f vs 34/2006), San Francisco Airport 
(36f vs 37/2011), Salinas Airport (28f vs 28/1953), San Rafael 
(32f vs 32/2006), Livermore (27f vs 28/1942), among others. 
Most official climatology sites do not report their temperatures 
until after 4pm, so we will very likely have more official records 
to report later today. So far this afternoon, temperatures are 
generally similar to this same time yesterday, with slightly 
cooler temperatures in the San Francisco Bay and slightly warmer 
temperatures in the Monterey Bay area. This difference is 
primarily the result of some mostly cloudy to overcast conditions 
seen over the San Francisco Bay area earlier this morning. 

This last storm system essentially paved the way for a series of 
weaker storm systems to follow in its footsteps, essentially 
opening the storm door for more storm systems to enter the region. 

The first of these weaker systems is already on our doorstep and 
is set to pass over the area later today through early tomorrow. 
Latest satellite imagery is already showing high clouds advancing 
from the northwest over the North Bay on the Vanguard of this 
storm system. The main impacts will be somewhat increased cloud 
cover (which will help warm the overnight lows tonight), a slight 
chance to chance of very light rain, perhaps even a dusting of 
snow over 2000 feet, and a continuation of the below average 
temperatures. That said, temperatures overall are forecast to 
remain below normal through the coming days, increasing about a 
degree or two each day from now through the weekend. Temperatures 
will rebound to be just around 3 to 6 degrees shy of normal by 
this weekend. 

After that, another storm system will follow quickly in the 
footsteps of tonights storm system -- bringing windy conditions 
and a minor shot of light precipitation (both in the form of rain 
and snow showers -- again down to around 2000 ft) late Wednesday 
through late Thursday. Minor snow accumulations are possible over 
the highest peaks. The strongest winds will be along the coast 
and over the higher elevations and a Wind Advisory may be 
necessary in those areas. Peak sustained wind speeds of 20 to 30 
mph with gusts 40 to 55 mph are possible Thursday PM. 

Neither of these two upcoming storm systems look particularly wet, 
so look for the precipitation deficient to grow through the end of 
the month. Percent of normal seasonal precipitation, as of 
midnight, is currently ranging from around 40% to 55%, with 
Monterey Airport the relative "wet" spot, at 64% of normal 
seasonal precipitation. 

That may change next week as a trio of wetter, more organized 
storm systems are set to move across the area, the first Mon-Tue, 
and the second Wed-Thu, and the third into the end of next week. 
Needless to say, the weather pattern has definitely shifted from 
warm and dry towards cool and unsettled. Stay tuned for updates on 
this weeks wind and low elevation snow and any potential news 
about next weeks trio of storm systems. 


Aviation...as of 4:30 PM PST Tuesday...VFR this evening with 
increasing clouds after 12z as an upper level shortwave 
approaches. The challenge for Wednesday morning is how low the 
cigs will be. Models indicate a few showers over the sfo Bay area 
Wednesday morning which is usually associated with cumulus clouds. 
So forecast is for cigs to remain in the 4000-5000 foot level but 
cannot rule out lower cigs. 

Vicinity of ksfo...VFR through the Airport evening rush. 
Cigs down to 5000 ft after 12z with a few showers. There is the 
possibility cigs could be lower, even into marginal MVFR range. 

Sfo bridge approach...similar to ksfo. 

Monterey Bay terminals...VFR with increasing mid and high clouds 
after 04z. 



Here are record low temperatures and the years they occurred for 
Tuesday and Wednesday. 

Location Tuesday Wednesday 

Sf Bay area 

Healdsburg 22 in 1922 28 in 1929 
Santa Rosa 26 in 1913 26 in 1913 
Calistoga 25 in 2006 25 in 2006 
Kentfield 27 in 1913 29 in 1953 
San Rafael 32 in 2006 33 in 1955 
Napa 28 in 1920 29 in 1955 
San Francisco 38 in 1897 36 in 1890 
sfo Airport 37 in 2011 34 in 1955 
Half Moon Bay 32 in 2013 31 in 2006 
Oakland Airport 34 in 2006 33 in 1955 
Richmond 35 in 1990 35 in 1981 
Livermore 28 in 1942 27 in 1955 
Moffett field 34 in 2006 32 in 1955 
San Jose 30 in 1897 25 in 1897 
Gilroy 30 in 1990 31 in 1976 

Monterey Bay area 

Santa Cruz 29 in 1913 30 in 1955 
Salinas 31 in 2006 31 in 1970 
Salinas Airport 28 in 1953 30 in 1953 
Monterey 35 in 2006 36 in 1952 
King City 22 in 1953 23 in 1953 


Marine...as of 04:09 PM PST Tuesday...light to moderate winds 
with an improving sea state will continue through early Wednesday. 
Northerly increase Wednesday and Thursday as another storm system 
moves through through region. The gusty winds will produce 
hazardous conditions with steep wind waves and fresh swell. 


Mtr watches/warnings/advisories... 



Public forecast: drp 
aviation: west pi 
marine: mm 

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