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

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS66 KMTR 202334
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
334 PM PST Sun Jan 20 2019

.SYNOPSIS...A cold front will spread precipitation across the
Bay Area today. Showers and a slight chance of thunderstorms are
expected late this afternoon and evening, diminishing overnight
and ending by Monday morning. Gusty west to northwest winds are
expected from late this afternoon through much of tonight,
especially near the coast. Dry conditions, cool overnight
temperatures, and progressively warmer days are then forecast
through the end of the week and into next weekend as strong high
pressure builds over the West Coast.

&&

.DISCUSSION...as of 01:28 PM PST Sunday...Latest surface analysis
shows a cold front continuing to work its way through the Bay
Area this afternoon. KMUX radar imagery picks on this front and
currently has the front moving through the South Bay. Showers
continue ahead and along the front with radar returns and
automated rain gage tips. Rainfall amounts are still mostly on the
order of a few hundredths to a tenth. The front will continue to
move SE through early tonight before exiting the forecast area.
The main shower activity will also continue to move SE as well.
Latest hi-res models (HRRR/WRF) remain on track showing post
frontal showers associated with increased surface instability and
cold pool aloft. Previous forecast had a mention of thunderstorms
and see no reason to remove them from the forecast. Chances for
thunder still remain low, but upstream convective cu on satellite
and the occasional offshore lightning strike does add some
confidence. Speaking of the cold pool aloft, if thunder does
develop small hail will be possible with lowering freezing levels.

The lower snow levels (5kish ft) will also allow for possible snow
over the higher peaks of the Santa Lucias and southern Galiban
Range. Minor accumulations are possible.

A few lingering showers/snow showers will be possible early Monday
morning (models suggest through about 5/6am) over the coastal
waters and southern coastal mts. After mid-morning Monday any
remaining showers should end quickly from NW to SE.

Winds are still expected to increase behind the front, especially
over the waters, immediate coast and higher terrain. Still looks
like a marginal event for a Wind Advisory, but as others have
noted it may be more about impacts than wide spread wind. Given
the very wet soils trees could be more susceptible to falling
over. One could argue a Wind Advisory for the N and E Bay hills,
but the strongest winds will likely be above 2,500 feet where Wind
Advisories aren`t issued. Gusts of 35 to 45 mph will be possible.

After a rather soggy period the forecast is going to completely
flip. Medium range models build a decent ridge of high pressure
off the West Coast and ultimately over CA next week. The onset of
the ridge will be Monday into Tuesday and peak later in the week.
The ridge will lead to an overall warming trend with warmer than
normal temperates by next weekend. Highs in the 60s and 70s will
be common place. Did up temperatures for much of next week from
previous forecast.

&&

.AVIATION...as of 3:34 PM PST Sunday...for 00Z Monday TAF
package. MVFR conditions are forecast to prevail at most TAF sites
through the evening hours, associated with post-frontal showers
that have been observed throughout the Bay Area. Can`t rule out
the occasional IFR observation coinciding with a heavier rain
shower dropping ceilings and/or visibilities. Winds will likely
veer more west to northwesterly over the next several hours, and
become gusty at times, particularly at the wind-prone terminals.
Showers will gradually diminish in coverage through the night.
Have introduced some lower visibilities at STS with possible
overnight fog development -- such occurrence will hinge on whether
the winds subside and if the skies clear a bit.

Vicinity of KSFO...Generally expect MVFR conditions to prevail
through the evening hours as showers continue to impact the
terminal. Will continue to keep a close eye on winds over the next
several hours as some guidance brings gusts at/above airport
weather warning criteria (>= 35 kt). Gradual improvement around
12Z may allow VFR conditions to return, but still some
uncertainties as to the exact timing.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...MVFR ceilings likely will prevail at STS
and MRY through the evening as rain showers impact the terminals.
Breezy and gusty westerly winds will develop around sunset.
Expect the return to VFR conditions sometime in the morning hours,
but confidence on timing remains rather low.

&&

.MARINE...as of 2:12 PM PST Sunday...Strong and gusty northwest
winds will develop in wake of a frontal passage and persist
through Monday before gradually diminishing by Tuesday. Lingering
showers with the potential for thunderstorms will also continue
through late tonight. West swell will continue to gradually
diminish over the weekend before a northwest swell arrives early
next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...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...SF Bay
             SCA...Mry Bay

&&

$$

PUBLIC FORECAST: MM
AVIATION: Rowe
MARINE: RGass

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/nwsbayarea
www.twitter.com/nwsbayarea
www.youtube.com/nwsbayarea


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.