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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 180448

Area Forecast Discussion
National Weather Service San Francisco Bay Area
848 PM PST Sun Feb 17 2019

.SYNOPSIS...Isolated showers will continue through this evening. 
Clearing skies after midnight will allow for cold minimum 
temperatures tonight and again Monday night. Dry weather is 
expected for Monday and Tuesday with a slight chance of showers 
returning from Wednesday through early Thursday. Temperatures will
remain below normal through the week ahead.


.DISCUSSION...As of 8:45 PM PST Sunday...A line of intense 
showers and isolated thunderstorms moved through the East Bay late
this afternoon, producing several lightning strikes near 
Livermore and small hail at several East Bay locations. That 
convective activity has since dissipated, but radar shows isolated
showers continuing across the southern half of our forecast area.
The latest NAM and HRRR models agree that shower activity will 
end in all areas by midnight. 

Brisk northwest winds earlier today have been decreasing since 
sunset and models indicate winds will continue to decrease 
overnight. Skies are forecast to clear overnight as the upper low 
over Nevada continues to track to the southeast and drier air 
moves in from the north. Clearing skies and light winds will allow
temperatures to drop quickly after midnight tonight. Overnight 
lows are forecast to be in the 30s in most locations, except lower
40s along the immediate coast. Some upper 20s are possible, 
especially in the North Bay Valleys if winds go calm late tonight.
Frost is likely for many inland valley locations late tonight and
early Monday morning.

Monday is forecast to be the first completely dry day that some
portions of our area have seen in 10 days. High temperatures on
Monday are forecast to be 5 to 10 degrees below normal. However,
with plenty of sunshine and lighter winds, tomorrow afternoon 
will likely feel quite a bit warmer than today.

Another cold night is on tap for Monday night when dewpoints will
likely be lower and winds lighter. Areas of frost are once again
expected in the interior valleys late Monday night and early
Tuesday. Our southern inland valleys will probably experience
their coldest night on Monday night, with early morning lows on 
Tuesday forecast to be as cool as the mid and upper 20s in 
southern Monterey County.

Dry weather is forecast through at least Tuesday night, and likely
into Wednesday morning, before the next cold system drops in from
the north and brings renewed shower chances by Wednesday
afternoon. This midweek system is forecast to have much less 
over-water trajectory compared to recent systems, and therefore 
will be lacking moisture. Models indicate only scattered light 
precipitation over our area from about midday Wednesday through 
early Thursday. Rainfall totals with the midweek system will
likely to be on the order of a quarter inch or less and many 
locations may not see rain at all. Snow levels will be low once 
again, but very little accumulation is expected in the hills due 
to the lack of moisture.

Forecast confidence remains rather low for the longer range 
forecast from Friday into next weekend. The operational GFS has 
been alternating between dry weather and another cold system 
from the north bringing more precipitation. Meanwhile, the ECMWF 
seems to be settling on a dry solution.


.AVIATION...As of 03:29 PM PST Sunday...For 00Z TAFs. Scattered 
showers to remain in the vicinity until this evening. After that, 
dry conditions expected through the rest of the forecast period. 
VFR prevailing with the exception of possible patchy fog in the 
morning in the North Bay. SCT to BKN cigs will continue into this 
evening between 3500-5000 ft AGL. Skies expected to gradually 
clear overnight and through tomorrow morning. Gusty onshore winds 
continue this afternoon and into the early evening with gusts 
generally around 20-25 kt with isolated gusts up to 30 kt. Winds 
forecast to subside overnight. 

Vicinity of KSFO...VFR prevailing with SCT to BKN cigs 3500-5000
ft into this evening before conditions are expected to gradually
clear through the morning. Showers to diminish this evening. 
Breezy westerly winds into the early evening with gusts 20-25 kt 
and isolated gusts up to 30 kt. Winds forecast to ease overnight.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR with scattered showers into this
evening. SCT-BKN cogs 3,500-5,000 ft AGL this afternoon and
evening. Onshore winds remain breezy with gusts 20-25 kt. Winds
forecast to ease overnight and turn more SE by the early morning.


.MARINE...As of 8:44 PM PST Sunday...Gusty northwesterly winds 
will persist across the coastal waters overnight and through early
this week. The northwest swell that arrived late Friday will 
continue to subside overnight. A second long period northwest 
swell will begin to arrive tonight, but will bring more modest 
swell heights than the previous one.


     .Tngt...SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm



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