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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

                            
000
FXUS66 KMTR 142340
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
340 PM PST Thu Feb 14 2019

.SYNOPSIS...Lingering rain showers are forecast to continue in 
wake of a frontal passage tonight. Snow levels will also lower 
Friday into Saturday with the potential for accumulating snowfall 
in the region's highest peaks through the weekend with cool, 
showery conditions region-wide. Overnight temperatures will turn 
much colder early next week as dry weather develops and sky 
conditions clear. Unsettled conditions potentially return for the 
latter half of next week.

&&

.DISCUSSION...as of 01:08 PM PST Thursday...A weak mid/upper 
level disturbance moving across the region this afternoon has 
brought another round of widespread rain showers with moderate to 
locally heavy rainfall at times. This system is in wake of the 
exiting atmospheric river and approaching cold front that will 
sweep across the region late tonight into early Friday morning. An
additional round of rain showers will be possible as the main 
cold front pushes inland and to the south. While widespread 
thunderstorms are unlikely, we cannot rule out an isolated 
lightning strike or two through this afternoon. 

Rain showers are then likely to linger in wake of the passing cold 
front into Friday with cooler temperatures and lowering snow levels. 
Given the cold air mass aloft, we cannot rule out convective showers 
with small hail. While thunderstorms have been added to the forecast 
for Friday, the primary threat will be for periods of small hail and 
not so much lightning itself. As mentioned above, snow levels are 
forecast to drop to between 2,500 and 3,500 feet which would result 
in the potential for accumulating snow fall in the region's highest 
elevations, mainly in the Santa Lucia Mountains and Diablo Range.

A secondary mid/upper level trough is forecast to drop southward 
along the West Coast and result in further lowering of snow levels 
and additional chances for rain/snow showers late Saturday night 
into Sunday. At this point snow levels are forecast to lower to 
around 1,800 feet in the North Bay to around 2,500 feet along the 
Central Coast. Thus, light snowfall accumulations will be possible 
in the Santa Cruz Mountains, Sierra de Salinas and the Gablin 
Range. Given this, a Winter Weather Advisory may be needed for the 
Santa Lucia Mountains and Diablo Range as forecast confidence 
increases. In lower elevations, cool conditions will continue with 
periods of rain showers. All in all, additional rainfall amounts 
from Friday afternoon into the weekend will range from around 0.25" 
to 0.75" with locally higher amounts in the coastal ranges and 
within areas of stronger rain showers. The forecast models generally 
agree that precipitation will tapper off from north to south 
sometime Sunday afternoon and evening. This will result in clearing 
skies and much cooler overnight conditions with more widespread 30s 
inland to upper 30s or lower 40s near the immediate coastline. 
Expecting these colder conditions to persist into at least the first 
half of next week with daytime temperatures only warming into the 
50s for most urban areas (similar pattern to before the arrival of 
our atmospheric river event). 

Forecast confidence greatly diminishes for the middle of next week 
as the models diverge from one another. The general thinking is that 
the region will remain under a cool, unsettled trough through late 
next week. However, the ECMWF shows chances for rain/snow showers 
while the GFS holds off precipitation until the following weekend. 

&&

.AVIATION...As of 3:40 PM PST Thursday...for 00Z TAFs. VFR/MVFR 
conditions through the period with SCT to BKN cigs 3,000 to 5,000 
ft. A cold front remains off the coast and is expected to pass 
through the region overnight. This may bring another round of 
steady showers and lower cig/vis to MVFR. Additionally, isolated 
thunderstorms will be possible tomorrow behind the front. 
Scattered showers to remain in the vicinity through the period. SW
winds this evening and overnight to remain gusty (generally gusts
20-25 kt with isolated spots seeing gusts to 30 kt). Winds 
forecast to ease tomorrow morning for most locations before 
increasing again in the afternoon.

Vicinity of KSFO...Scattered showers to remain in the vicinity
through the period. Cold front forecast to move through the region overnight
and bring another round of steady showers. After such time 
showers will become more scattered. Isolated thunderstorms 
possible tomorrow behind the front. Cigs to remain borderline 
VFR/MVFR into late tomorrow morning. SCT-BKN cigs 3,000 to 5,000 
feet are expected through the period. Winds have eased some this 
afternoon but gusts remain possible up to 30 kt into the evening 
with gusts 20 to 25 kt forecast to continue tomorrow as well.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...MVFR/VFR conditions are forecast to
prevail with scattered rain showers at both SNS and MRY. SW/W
winds overnight with gusts 20 to 25 kt. Winds forecast to turn
more southerly in the morning before shifting back out of the W/SW
in the afternoon.

 &&

.MARINE...as of 03:29 PM PST Thursday...Strong and gusty winds
will continue overnight in the wake of a cold frontal passage. In
addition to these winds, scattered showers and even an isolated
thunderstorm or two are possible through the evening hours. A
large northwest swell will arrive to the waters on Friday and
continue into the weekend.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...SF Bay
             SCA...Mry Bay
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pigeon Pt to Pt Pinos 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
             SCA...Rough Bar Advisory for SF Bar until 6 PM

&&

$$

PUBLIC FORECAST: RGass
AVIATION: AS
MARINE: Rowe

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