fxus66 kmtr 240023 

Area forecast discussion 
National Weather Service San Francisco Bay area 
423 PM PST Sat Feb 23 2019 

Synopsis...dry and seasonably cool conditions will prevail across 
most of the region through the remainder of this weekend. The 
exception may be the North Bay where there is a chance of light 
rain late tonight and on Sunday. A plume of moisture will bring 
periods of moderate to heavy rain to the majority of the region 
for the first half of next week, though the exact positioning of 
the heaviest rains continues to vary. Another potentially wet 
system may bring more rain to the region late next week and into 
the following weekend. 


Discussion...as of 2:00 PM PST Saturday...water vapor imagery 
continues to show northwesterly flow aloft prevailing across 
California this afternoon. There is plenty of moisture streaming 
through this flow in the form of high clouds ahead of the next 
system. As a result, skies are mostly cloudy this afternoon, with 
temperatures running similar to this time yesterday. Temperatures 
will still be cool tonight, but not quite as cold as things start 
to moderate with the high clouds in place. 

The upper level ridge of the Pacific will keep restrict how 
quickly the next Pacific storm digs south over the next 24 to 36 
hours. As a result, the front will stall tonight and during the 
day on Sunday, focusing the main moisture plume along the Oregon 
and California border and the far northern California coast. 
Current composite radar is already showing some light showers 
mainly from Cape Mendocino northward. This trend will likely 
continue tonight and into Sunday, with the heaviest rain 
developing and remaining well to our north. That being said, a 
few light rain showers sag south of point area later tonight or 
during the day on Sunday. 

Monday through Wednesday is the time period to watch for US, as 
things will likely start to get interesting for the central coast 
sometime Monday afternoon or evening. At this time, the 12z GFS is 
still the fastest with moving the rain into and south of the Bay 
area proper during the Monday morning commute. Meanwhile, the 12z 
NAM, ECMWF, and Canadian hold off rain any rain until at least the 
midafternoon and more likely the evening commute. 

That being said, our North Bay counties and mountains will likely 
see periods of moderate to heavy rain develop during the day on 
Monday and continue through Wednesday. The models are still 
disagreeing with where the heaviest rainfall will occur. Most are 
focusing on areas north of the Golden Gate bridge up to the 
Mendocino coast. However, the GFS shows the North Bay and Bay area 
getting hit rather harder. This is leading to low confidence in 
the exact placement of the heaviest rainfall. However, believe 
the North Bay will likely see quite a bit of rainfall regardless. 
For now, it is not out of the question that 3 to 5 inches of rain 
with locally amounts upward of 7 inches will be possible, leading 
to flooding and more landslides or debris flows. 

The main take away though is a series of disturbances will move 
along the stalled front between Monday and Wednesday, bringing 
relatively persistent rains, with periods of moderate to heavy 
rain possible. Areas from Santa Cruz County northward will likely 
see a decent amount of rain, with the North Bay seeing the most at 
this time, if models continue to trend this way. These various 
disturbances will also bring periods of gusty winds. Therefore, 
expect rapid rises along area rivers, streams, and creeks to be 
possible the first part of the work week. Trees and powerlines 
will also likely fall, as the grounds remain saturated. 

Although some residual passing showers will be possible on 
Thursday and Friday, they will be our in between days, before 
another potentially more potent system takes aim at the region for 
the weekend. For now, this latter system looks like it could be 
wetter than the first as it has a better tap to the tropics. 
However, the models are moving it through the region much faster. 
Therefore, if comparing to the current system, they might actually 
have similar impacts. Regardless, this week of weather bears 
watching, and we encourage everyone to prepare early and stay 
weather aware. Palmer 


Aviation...as of 4:23 PM PST Saturday...VFR, mid and high clouds 
continue to advance in over the cwa from the west. MVFR cloud 
ceilings are likely over the North Bay Sunday morning as a nearly 
stationary east to west 850 mb elevated frontal boundary develops, 
850 mb warm air advection could result in spotty briefly very 
light precip vicinity ksts per recent NAM/hrrr output. 

A separate, nearly stationary 925 mb frontal boundary develops 
nearby the Monterey Bay terminals Sunday morning which may be the 
focus for MVFR ceilings possibly lowering to ifr; not advertised 
in the Monterey Bay 00z taf cycle as of yet, but will look into it 
a bit more this evening and amend tafs as needed. 

Vicinity of ksfo...VFR, westerly wind 10 to 15 knots until 04z 
this evening, light wind tonight becoming southeast Sunday morning. An 
onshore wind near 10 knots resumes later Sunday. 

Sfo bridge approach...similar to sfo. 

Monterey Bay terminals...VFR, west-northwest winds near 10 knots diminishing 
and becoming light southeast wind by mid evening. Southeast wind Sunday morning 
shifting back to onshore near 10 knots Sunday afternoon. VFR is 
near high confidence through the evening, but confidence level in 
cigs lowers late tonight and Sunday morning, as mentioned if a 
lower level (925 mb level) front develops it may be the focus for 
ceilings lowering from MVFR to IFR, will look into it a bit more 
by 06z taf cycle and of course amend tafs prior to this time as 


a Pacific storm may bring moderate to heavy rain to areas from 
Santa Cruz County northward for Monday through Wednesday, that 
will likely cause rapid rises along area streams, creeks, and 
rivers, especially the Russian River. An esf has been issued. 


Marine...as of 3:34 PM PST Saturday...generally light west winds 
will continue tonight. Winds will turn southerly on Sunday and 
ramp up early in the week. Light to moderate northwest swell will 
persist through the week. 


Mtr watches/warnings/advisories... 


Public forecast: Palmer 
aviation: canepa 
marine: Sims 

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