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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 181152

Area Forecast Discussion
National Weather Service San Francisco Bay Area
452 AM PDT Mon Mar 18 2019

.SYNOPSIS...A ridge of high pressure will maintain dry and 
seasonably mild weather conditions over the region today. A more 
progressive pattern will return by Tuesday and persist through late 
week with periods of wet and unsettled weather. Cooler temperatures 
will also return and continue into the upcoming weekend. 

&& of 03:04 AM PDT Monday...An upper level ridge of
high pressure along the West Coast will continue to dominate the 
region's weather today resulting in daytime temperatures above 
seasonal averages. However, as onshore flow increases slightly, 
temperatures near the coast are expected to be a few degrees 
cooler compared to yesterday. Low clouds currently seen on 
satellite imagery will likely remain offshore while few/scattered 
high clouds stream over the region in advance of an approaching 
storm system. 

The latest forecast models are in good agreement with the ridge axis 
shifting inland and to the north as a negatively tilted trough 
approaches the coast on Tuesday. This will cool temperatures region-
wide on Tuesday and bring chance for rain showers to the region by 
Tuesday evening. Rain showers will then continue into Tuesday night 
and much of the day Wednesday as another disturbance pushes inland. 
With the increase in instability aloft, cannot rule out an isolated 
thunderstorm or two. However, given the low confidence for 
convection, will keep thunderstorms out of the official forecast at 
this time. Generally expecting rainfall amounts to range from 0.25" 
to 0.50" for most urban areas with upwards of 1.25" in the Santa 
Cruz and Santa Lucia Mountain Ranges. Overall, these rainfall 
amounts will be beneficial given the recent dry trend over the past 

A weak ridge will build over the region in wake of the exiting 
system and ahead of the next set to arrive on Friday. This will 
bring dry conditions on Thursday with daytime temperatures generally 
in the upper 50s near the coast to lower 60s inland. The next system 
will arrive from the north early Friday before spreading inland and 
to the south through Friday night. Colder air will advect southward 
across the region with snow levels falling as low as 4,000 feet by 
Friday night resulting in light snowfall over the region's highest 
peaks. Lingering showers will be possible into Saturday as well with 
temperatures near to slightly below seasonal averages through the 

While conditions may dry out briefly Saturday night into Sunday, 
unsettled weather looks to return during the first half of next week 
with the arrival of yet another mid/upper level system. The 
operational models do differ in the timing and trajectory, yet the 
ensembles point toward an ongoing cool, unsettled pattern in the 


.AVIATION...As of 4:45 AM PDT Monday...Mainly clear skies will
prevail today with only a few high clouds streaming overhead and
the slight chance of patchy low clouds over the North Bay this
morning. Light winds this morning will increase and veer onshore
through the afternoon. East to southeasterly winds expected this 

Vicinity of KSFO...VFR conditions will persist through the
forecast period. Light winds this morning will increase and veer 
onshore this afternoon. East to southeasterly winds will develop 
this evening.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR conditions will persist through the
forecast period. Light winds this morning will increase and veer 
onshore this afternoon. East to southeasterly winds will develop 
this evening.

&& of 2:23 AM PDT Monday...Light westerly winds will 
become southerly this afternoon ahead of an approaching low 
pressure system moving in from the west. Southerly winds will 
increase and rain chances will be introduced over the coastal 
waters on Tuesday as the cold front moves into the region. A long 
period westerly swell will arrive Tuesday increasing shoaling on 
bars and harbor entrances anticipated.






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