National Weather Service Raw Text Product

Displaying AFOS PIL: AFDMTR Received: 2018-04-16 10:21 UTC


308 
FXUS66 KMTR 161021
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
321 AM PDT Mon Apr 16 2018

.SYNOPSIS...Scattered showers and isolated thunderstorms will 
remain possible over much of the region through this afternoon. 
Dry and cool conditions are likely for Tuesday and into most of 
Wednesday before a weak, fast-moving system pushes through the 
region late Wednesday into early Thursday. A drying and warming 
trend is then likely by late week. 

&&

.DISCUSSION...as of 03:21 AM PDT Monday...An unseasonably cold 
mid/upper level trough will to advect a much colder air mass in 
over the region today. As a result, showers will likely increase 
in coverage and intensity across much of the San Francisco Bay 
Area and Central Coast through the morning and into the early 
afternoon. With 500 MB temperatures forecast to drop as low as -33
deg C today, the atmosphere aloft will become increasingly 
unstable. With this and increased surface CAPE by this afternoon, 
isolated thunderstorms will also be possible over much of the 
region. A few thunderstorms have already been detected offshore 
and over the North Bay early this morning. Any thunderstorms that 
do develop will likely produce brief heavy downpours, small hail, 
cloud to surface lightning and locally gusty winds. 

Snow levels are also forecast to drop to as low as 3,000 feet 
through the day which would support some snow showers in the higher 
elevations. Thus, a dusting of snow will be possible in the Bay Area 
peaks with light accumulations possible in the Santa Lucia Mountains 
of Monterey County (especially above 4,000 feet). 

Additional rainfall amounts are likely to be around 0.10" to 0.25" 
for most areas with locally higher amounts within any heavier 
showers/thunderstorms that do develop. Shower activity is then 
forecast to diminish by late this evening as the main trough axis 
shifts inland to our east. As winds also diminish, look for colder 
conditions region-wide tonight into Tuesday morning with lows in the 
30s to middle 40s. 

Dry, cool weather conditions are forecast for Tuesday and into most 
of Wednesday ahead of another approaching system. This system is 
forecast to move in from the northwest and bring light precipitation 
to portions of the region from Wednesday night into early Thursday. 
The quick moving system will only produce light rainfall amounts, 
generally 0.10" or less with isolated amounts upwards of 0.25" along 
the coastal ranges. 

A ridge of high pressure is then likely to build back over the 
region and along much of the West Coast by late in the week. This 
will result in a warming and drying trend for the region from Friday 
into the upcoming weekend. Look for temperatures to warm back to or 
above seasonal averages by Saturday with widespread 70s to lower 80s 
expected for inland areas. Dry weather conditions also appear likely 
into the extended forecast period. 

&&

.AVIATION...As of 10:30 PM PDT Sunday...A frontal system is 
just past the MRY Bay Area. Clouds have scattered out behind the
front but expect cigs to reform in areas as the low levels remain
quite moist. A few showers will move through through 12Z then 
shower activity increases as the upper trough moves through. 
Showers should last until the afternoon as models indicate drying 
conditions by late afternoon. There is an outside threat of a 
thunderstorm due to the instability of the airmass on Monday. 

Vicinity of KSFO...Becoming MVFR after 14Z with showers
increasing. West winds to 10 kt increasing to 15 kt after 14Z. 

SFO Bridge Approach...Areas of MVFR cigs will persist mainly 
south and east of SFO. Showers increasing after 14Z. 

Monterey Bay Terminals...IFR cigs locally in the SNS area through
08Z. Showers with MVFR cigs expected to arrive after 14Z. 

&&

.MARINE...as of 03:21 AM PDT Monday...Chilly, showery weather with
a slight chance of thunderstorms will continue as an upper level
trough passes over northern California today. Northwest winds will
increase today. Winds will decrease  Tuesday but another system
will arrive late Wednesday increasing  winds again.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Pt Arena to Pt Reyes 0-10 nm from 11 AM
             SCA...Pt Reyes to Pigeon Pt 0-10 nm from 11 AM
             SCA...Pigeon Pt to Pt Pinos 0-10 nm from 11 AM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 11 AM
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Mry Bay from 11 AM
             SCA...SF Bay from 3 PM

&&

$$

PUBLIC FORECAST: RGass
AVIATION: W Pi
MARINE: Canepa

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