231 
fxus66 kmtr 200513 
afdmtr 


Area forecast discussion 
National Weather Service San Francisco Bay area California 
1015 PM PDT Friday Mar 19 2010 


Discussion...as of 8:05 PM PDT Friday...subsidence under a high 
amplitude ridge centered along the West Coast of North America warmed 
the airmass to well above normal levels across our area today. High 
temperatures were generally about 15 degrees above normal. And... 
light offshore flow brought warm air all the way to the ocean 
beaches today. As a result...high temperatures were isothermal 
today...mostly within a few degrees of 80 in all areas. Three daily 
high temperature records were either broken or tied in the sf Bay 
area (see record event report...sforermtr sxus76 kmtr). 


The upper ridge axis is beginning to shift to our east this evening 
and a tentative onshore flow has developed. A few patches of low 
clouds and fog may form near the ocean later tonight. However...the 
boundary layer remains very dry and onshore flow is still quite 
weak...so any low clouds that do form will almost certainly remain 
confined to the immediate coast. Temperatures will cool some on 
Saturday as the light onshore flow advects marine air inland. Most 
significant cooling on Saturday will be near the coast where 
high temperatures will likely drop by 10-15 degrees. More modest 
cooling of only about 5 to 10 degrees is expected inland. The 
warmest inland valleys of Monterey and San Benito counties may see 
no cooling at all. A shortwave trough moving into the Pacific northwest and far 
northern California on Sunday will enhance onshore flow and contribute to 
more widespread inland cooling that day. Also...bot the GFS and 
European model (ecmwf) indicate that the tail end of a cold front may brush the far 
northern fringes of our forecast area on Sunday. Thus...will maintain 
slight chance probability of precipitation in our North Bay counties for Sunday. Coastal low 
clouds are more likely by Sunday...and those clouds may surge inland 
by late Sunday or Sunday evening as the front sweeps inland to our 
north. Moderate northwest winds will develop behind the cold front on 
Monday and any low cloud cover should mix out by midday. 


Somewhat warmer conditions are expected by the middle of next week as 
an upper ridge re-develops over California. The Tuesday/Wednesday warm-up 
is not expected to be as robust as warming we've experienced the past 
few days. 


A cooling trend is then expected late next week as a series of weak 
disturbances move inland to our north. Most of the precipitation 
associated with these disturbances should remain to our north. 
However...the 12z European model (ecmwf) and 18z GFS both drop some light precipitation 
across the far northern part of our area late Thursday into 
Thursday night. Will need to add at least slight chance probability of precipitation in the 
north for these time periods if the 00z model runs show something 
similar. 


&& 


Aviation...as of 10:15 PM PDT Friday...aside from a few wisps of 
high clouds drifting across the area tonight conditions continue 
clear with light winds at area airports. The wmc to sfo pressure 
gradient is climbing a bit in recent hours and is forecast to peak at 
7 mb overnight. Overall this will keep the airmass dry and free from 
low clouds tonight and Saturday. The boundary layer moistens late 
Saturday and as a result a few patches of stratus could develop on 
the immediate coastline by late Saturday night and/or Sunday 
morning. 


Vicinity of ksfo...VFR. 


Ksfo bridge approach...VFR. 


Mry Bay area terminals...VFR. 


Proposed policy change...effective 15z Tuesday April 6th 2010 the San 
Francisco Bay area office at Monterey will begin 3-hourly taf 
issuances for ksfo. These intermediate tafs at 03z...09z...15z...and 
21z will be issued as amendments to the tafs issued at 00z...06z... 
12z...and 18z. The intermediate tafs will be issued during a 20- 
minute window between 10 minutes before the designated issuance hour 
and 10 minutes after the hour. Comments on this proposed rule-making 
will be accepted to March 19th. Comments can be addressed to the 
webmaster at the National Weather Service at Monterey at www.Weather.Gov/sanfrancisco. 


&& 


Mtr watches/warnings/advisories... 
.None 


&& 


$$ 


Public forecast: dykema 
aviation/marine: canepa 


National Weather Service on the web at weather.Gov/sanfrancisco