000 
fxus66 kmtr 242159 
afdmtr 


Area forecast discussion 
National Weather Service San Francisco Bay area 
159 PM PST Sat Feb 24 2018 


Synopsis...partly cloudy skies with scattered showers across the 
North Bay this afternoon. Otherwise, some clearing is expected 
tonight with chilly low temps. Dry weather and slightly warmer 
temperatures are expected through the weekend. Cooler and 
unsettled weather is expected to return by early next week with 
another system bringing rain to the area later next week. 


&& 


Discussion...as of 01:50 PM PST Saturday...a little afternoon 
excitement as a few showers popped up over the North Bay. 
Spotters/general public reported a few showers near Santa Rosa, 
Healdsburg and Windsor. For what it's Worth, local WRF and hrrr 
kept showers off the coast this afternoon. That definitely didn't 
pan out and therefore updated forecast to better reflect reality. 
Do expect this showers to gradually dissipate over the next hour 
or so. 


No frost or freeze headline needed for tonight. A slight increase 
in cloud cover will limited cooling potential. Temps tonight are 
forecast to be a few warmer than last night. That being said, 
overnight lows will still be rather chilly and in the upper 20s to 
mid 30s for most locations. Bay shoreline and coast in the low 40s 
for lows. 


Weak ridging ahead of the next storm system will allow for warmer 
weather on Sunday. In fact, it could be some of the warmest temps 
of the last several days with highs hitting 60 plus across the 
interior. 


By Sunday night the next system approaching from the north will 
begin to impact the Bay area. Showers will move in from north to S and 
likely impact the Monday morning commute. Snow levels will 
initially be greater than 3k feet, but then gradually drop through 
the day. Winter precip will be possible over the higher peaks of 
the forecast area, similar to earlier this week. Precip will end 
from northwest to southeast Monday night into Tuesday. Rainfall amounts are 
still generally low and mainly a few hundredths to a few tenths. 


Dry weather returns briefly on Tuesday with a slight warm up, but 
the next storm is waiting in the wings. For several model runs 
(deterministic/ensemble) now a potent low pressure has been 
forecast to impact the pac northwest Wednesday into Thursday. The 
associated cold front is also forecast to move into norcal by 
Thursday morning. The front pushes through the Bay area Thursday 
with Post frontal showers lingering well into Friday. Not an 
atmospheric river event per se, but a better moisture tap than we 
have seen over the last week. Rainfall amounts could exceed an 
inch across the North Bay and one quarter to one half elsewhere. 
Details will likely be sorted out between now and then, but 
initial thinking is a wetter scenario. It should be noted that 
this set up will be warmer with higher snow levels and initially 
impacting only the Santa lucias. The snow levels will drop behind 
the front. 


Lastly, the mjo has been on track to swing into phase 2/3, albeit 
weak, for some time now. Climo charts for phase 2/3 indicate 
wetter results for California. The shift to phase 2/3 corresponds with Feb 
28/March 01 time frame, which fits the approaching front on the 
medium range models. 


&& 


Aviation...as of 9:47 am PST Saturday for 18z tafs. Skies 
currently VFR across the region but a weak boundary is over 
Mendocino County and about to bring some clouds into the North 
Bay. Wind boundary currently has southeast winds at koak and ksjc 
while west winds have already developed at ksfo. The buoys are 
strong WNW so expect ksjc and koak to begin shifting shortly. 


Vicinity of ksfo...increasing WNW winds this afternoon and 
evening (gusts to around 28kt) with some MVFR cigs possible with 
increasing onshore flow as weak boundary passes the region. 


Sfo bridge approach...similar to ksfo. 


Monterey Bay terminals...VFR conditions expected through mid- 
morning, then VFR/MVFR for the afternoon as increasing clouds 
arrive. Generally light offshore winds in the morning will become 
onshore in the afternoon/evening around 10-20 kt. 


&& 


Climate... 


Here are the record low temperatures and the years they occurred for 
Saturday, February 24. 


Location Saturday 


Sf Bay area 


Healdsburg 29 in 1944 
Santa Rosa 28 in 1920 
Calistoga 29 in 1982 
Kentfield 29 in 1955 
San Rafael 34 in 2017 
Napa 30 in 1919 
San Francisco 40 in 1891 
sfo Airport 35 in 1955 
Half Moon Bay 33 in 2017 
Oakland Airport 36 in 2015 
Richmond 36 in 1955 
Livermore 29 in 1987 
Moffett field 34 in 2017 
San Jose 26 in 1897 
Gilroy 28 in 1960 


Monterey Bay area 


Santa Cruz 29 in 1925 
Salinas 31 in 1982 
Salinas Airport 30 in 1953 
Monterey 37 in 1955 
King City 24 in 1982 


&& 


Marine...as of 9:41 am PST Saturday...a dry cold front moving 
through the waters will produce breezy NW winds through tonight. 
High pressure briefly builds Sunday with easing winds. Early 
Monday an approaching cold front will bring a renewed chance of 
strong winds, fresh swell, and showers. 


&& 


Mtr watches/warnings/advisories... 
... Reyes to Pigeon pt 0-10 nm until 3 am 
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm until 3 am 
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm until 3 am 
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm 
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm 
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm until 9 PM 
Small Craft Advisory...mry Bay until 9 PM 


&& 


$$ 


Public forecast: mm 
aviation: rww 
marine: rww 


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