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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

                            
000
FXUS66 KMTR 151717
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
917 AM PST Fri Feb 15 2019

.SYNOPSIS...Cool and showery conditions are expected today  
through the weekend as a cold upper trough digs south along the 
West Coast. Snow levels will lower Friday into Saturday with the 
potential for accumulating snowfall in the region's highest peaks.
Overnight temperatures will turn much colder by early next week 
as dry weather develops and skies clear. Unsettled conditions
could return for the latter half of next week.

&&

.DISCUSSION...as of 09:11 AM PST Friday...No major changes to the
forecast this morning as isolated to scattered showers continue to
move inland across the region. As expected, numerous reports of
very small hail are being reported region-wide as cold air
advection continues aloft. This too has resulted in lowering snow
levels with air temperature below freezing in the region's highest
peaks. Thus, cannot rule out snow showers in those higher
elevations. 

Showers will persist as a reinforcing colder mid/upper level
trough descends southward along the West Coast through the 
weekend. This too will lower snow levels with increasing chances 
for accumulating snowfall in elevations above 2,500-3,000 feet 
while rain showers persist off and on across the region. Will have
additional updates and details with respect the forecast for the 
remainder of the weekend this afternoon. Until then, please see 
the previous forecast discussion below.

&&

.PREV DISCUSSION...As of 2:53 AM PST Friday...A line of showers 
moved through the district earlier producing brief, heavy rain as 
it passed. This line was associated with a cold front that has 
moved through. Scattered showers are expected to persist today 
through the weekend as the area remains in a cold, unstable 
airmass. 

Temperatures have dropped considerably with the passage of the 
cold front. Current readings at area airports are generally 15 
degrees colder than they were 24 hours ago with mid to upper 40s 
being reported. At higher elevations, automated weather stations 
are picking up current temperatures in the 30s and lower 40s. Snow
levels are forecast to drop as low as 2500 feet today and perhaps
below 2000 feet by late Saturday night. Thus, snowfall is likely 
on Bay Area peaks and accumulating snowfall is likely above 3000 
feet. Also, small hail is likely at times with heavier showers.

Flood waters continue to recede in most areas. The Flood Warning
for the Carmel River was cancelled last night, however, water 
levels on the lower Russian River continue to rise and is forecast 
to crest within the next hour or two. A Flood Warning remains in 
effect for the Russian River near Guerneville. 

Drier weather is forecast to return by the beginning of the week.
Clearing skies will result in cold overnight temperatures.
Unsettled weather is possible by midweek. 

&&

.AVIATION...As of 4:43 AM PST Friday...Showers continue to form 
as colder air aloft moves in from the west and northwest. VFR 
except MVFR in heavy showers, steadily lowering freezing levels 
with snow at highest elevations through the weekend. Deeper layer 
cooling arrives from the north later today, 500 mb temperatures 
exceeding -30 Celsius into tonight. Steepening temperature lapse 
rates initiating isolated thunderstorms favoring the Bay Area by 
late afternoon and evening, convective potential up to several 
hundred j/kg; will amend to add thunderstorms in tafs as needed. 
Generally much less wind today, though occasionally gusts to 20-25
knots nearest showers or isolated thunderstorms are possible.

Vicinity of KSFO...VFR, gusty wind to 20-25 knots today. Showers
today tempo MVFR in showers mid to late evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR except MVFR in showers particularly
this morning. SE wind becoming onshore and locally gusty to 20
knots by late morning. More showers arriving tonight and Saturday
morning.

 &&

.BEACHES...25 feet swell with moderate period 16 seconds reported
from buoy 59 located 400 miles northwest of the Bay Area. Large, 
dangerous surf will reach the coastal waters today, a high surf 
advisory begins 10 am today continuing to 9 pm Saturday. Northwest
swell 14 to 17 feet will produce breakers as high as 18 to 25 feet
along west and northwest facing beaches. High surf will also bring
coastal flooding impacts during high tide today. A coastal flood 
advisory is in effect 5 am to 10 am this morning.

&&

.MARINE...as of 09:11 AM PST Friday...Cooler temperatures, gusty 
west to northwest winds, scattered showers and possibly a few 
thunderstorms will continue into the weekend. A large northwest 
swell will arrive across the waters today and continue into the 
weekend.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...High Surf Advisory...CAZ006-505-509-529-530
             Coastal Flood Advisory...CAZ006-505-506-508-509-529-530
             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
             SCA...SF Bay
             SCA...Mry Bay

&&

$$

PUBLIC FORECAST: RGass/Sims
AVIATION: Canepa
MARINE: CW

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