Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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FXUS66 KMTR 170528

Area Forecast Discussion
National Weather Service San Francisco Bay Area
928 PM PST Sat Feb 16 2019

.SYNOPSIS...Cool weather conditions will persist along with
continued shower activity through Sunday evening. The most
widespread shower activity is expected late tonight. Accumulating
snow is likely above 3,000 feet, with snow levels lowering to
around 2000 by Sunday morning. Overnight temperatures turn colder
early in the upcoming work week as precipitation ends and sky
conditions clear. A chance of showers will return by the middle of
next week, with below normal temperatures expected to persist
through the period.


.DISCUSSION...As of 9:05 PM PST Saturday...Only isolated showers
are currently being observed across our region this evening.
Showers are expected to become more widespread later tonight as a
cold upper low currently centered near Portland, Oregon drops
southward. Satellite and radar currently show a band of widespread
showers associated with the leading edge of a colder airmass
pushing southward through Mendocino County. Based on the lastest
HRRR model, shower activity will increase in the North Bay
shortly after midnight, spread south across the rest of the SF
Bay Area by late tonight, and reach the Monterey Bay Area shortly
before sunrise Sunday. Expect scattered brief heavy downpours and
small hail late tonight, along with gusty winds, as this area of
enhanced shower activity slides south. According to coastal
profilers in the North Bay, snow levels are currently between 2500
and 3000 feet. The 00Z NAM forecasts snow levels to briefly
increase a bit as the band of widespread showers arrives but then
drop as low as 2000 feet by Sunday morning, and perhaps slightly
lower in the North Bay. However, most precipitation is forecast to
mostly end by the time the coldest air arrives. Thus, expect most
of the accumulating snow to occur above 3000 feet late tonight
and into Sunday. A dusting of snow is likely as low as 2500 feet.

Showers will taper off in the North Bay around sunrise Sunday, and
decrease from north to south across the rest of our area through
the day. Both the 00Z NAM and latest HRRR show showers continuing
across the eastern edge of our forecast area into Sunday evening
before all shower activity ends by midnight Sunday night.
Additional rainfall through late Sunday is forecast to generally
range from a tenth to a half inch, with heavier amounts across the
southern two-thirds of our area. The HRRR, and especially the
local WRF, forecast up to an inch or more of additional
precipitation across the Santa Lucias of Monterey County. Most of
the precip above 3000 feet in Monterey County will fall as snow
and the higher peaks of the Santa Lucias could see an additional
10 inches of snow by late Sunday.

Gusty winds occurred for a few hours late this afternoon and
early evening across portions of the San Francisco Bay Area, but
winds have since subsided. Northwest winds are forecast to
increase around sunrise Sunday after the band of enhanced shower
activity moves through, and winds are expected to remain gusty
through much of Sunday, especially in coastal areas. The latest
WRF has trended stronger with winds on Sunday and gusts as high
as 40 mph are possible near the ocean and bays. These winds,
combined with temperatures that will be as much as ten degrees
below normal, will make for a chilly day.

Drier air is forecast to arrive by late Sunday night as the upper
trough shifts to our east. Expect clearing skies after midnight.
The cold airmass that will be in place, combined with clearing
skies, will mean cold overnight lows late Sunday night, but only
if winds subside as quickly as forecast. Latest guidance indicates
early morning lows on Monday morning in the 30s across most of our
area, except for the city of San Francisco which will likely
be in the lower 40s. Some of the colder inland valleys may cool
into the upper 20s and widespread frost is likely in the inland
valleys early Monday morning. Monday is forecast to be a mostly
sunny and cool day. Although the airmass will begin to moderate
over our area by Monday night, drier air and lighter winds will
man another cold night Monday night with overnight lows close to
what they are expected to be on Sunday night. For our southern
inland valleys, particularly in southern Monterey County, Monday
night will likely be the coldest night with lows in the mid to
upper 20s in the coldest spots.

Dry and cool conditions will persist through Tuesday and into
early Wednesday before the next cold upper trough is forecast to
bring renewed shower chances to our area by Wednesday afternoon
and continuing into Thursday. The midweek system is forecast to
have a more inland trajectory which will mean lighter
precipitation amounts. Snow levels are once again expected to be
low, but since the system will be lacking moisture, not much
accumulation is expected.

Yesterday`s model runs indicated that another system would bring
more showery weather to our area next weekend. However, latest
models forecast dry conditions from Friday through next weekend.


.AVIATION...As of 09:28 PM PST Saturday...For 06z tafs. Scattered
showers continue to move through the area with SCT to BKN cigs.
Expecting prevailing VFR conditions with SCT to BKN cigs generally
at or above 4000 ft with lower cigs/vis possible during passing
showers. Scattered showers to remain in the vicinity through
tomorrow evening with a lull in precip this evening before latest
high res models show more widespread showers late tonight into
tomorrow morning. Winds are forecast to ease overnight. Latest WRF
shows gusty onshore winds late tomorrow morning/early tomorrow

Vicinity of KSFO...VFR with cigs remaining at or above 4000 ft.
Showers remain in the vicinity but are mainly away from KSFO.
After a brief lull this evening more widespread showers are
forecast to arrive late tonight into tomorrow morning. Gusty
westerly winds (20-25 kt) will linger over the next couple of
hours before winds ease overnight. Gusty onshore winds to return
tomorrow afternoon.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR with scattered showers coming off the
bay through tomorrow morning. Winds forecast to subside overnight.
A round of more steady showers is forecast by high res models to
move through early tomorrow morning. Latest WRF also shows gusty
winds by late tomorrow morning.


.MARINE...As of 8:15 PM PST Saturday...High pressure west of Cape
Mendocino interacting with low pressure over the Pacific
Northwest is keeping moderate northwest winds along with large
northwest swells across the coastal waters. Gusty winds will
continue through early next week as the low slides into the Great
Basin. The large northwest swell that has been effecting the coast
will subside overnight tonight and tomorrow. A second long period
northwest swell is set to arrive late this weekend, but will have
more modest swell heights.


     .Tngt...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 3 AM
             SCA...SF Bay
             SCA...Mry Bay




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