003 
fxus66 kmtr 211618 
afdmtr 


Area forecast discussion 
National Weather Service San Francisco Bay area California 
918 am PDT sun Mar 21 2010 


Discussion...as of 9:18 am PDT Sunday...the latest satellite water 
vapour image is showing a cold front sliding in from the north and 
a warm front merging with it from the south. This will result in 
cloudier skies than previously forecast for today. The cold front 
may also result in a slight chance of light rain in the northbay 
area. At the moment the closest station reporting rain is Ukiah 
located in southeastern Mendocino County. Kmux Doppler radar is 
currently unavailable so have been monitoring the situation with a 
combination of neighboring radars. 


As previously mentioned this scenario is resulting in cloudier 
skies than previous forecast so have updated the sky forecast for 
today. In addition the 1200 UTC run of the nam12 and NAM bufr 
solutions indicate that stratus will form tonight with a marine 
layer around a 1000 to 1500 feet deep. Therefore updated the 
forecast to reflect this scenario. Skies should clear out tomorrow 
afternoon as high pressure builds over the area. Models are 
indicating offshore flow tomorrow night into Tuesday afternoon. 
Therefore stratus shouldn't be an issue into at least the middle of 
the week. 


Models are indicating a series of low pressure system pushing into 
the Gulf of Alaska and the Pacific northwest beginning midweek. This 
will result a week cold front clipping northern portions of the County Warning Area 
Wednesday night. A slight chance of rain will be possible Friday... 
however...the 0000 UTC European model (ecmwf) and 0600 UTC GFS are in disagreement on 
the timing and location of this potential weather system. 


Looks as though rain chances will increase late next weekend and 
early into the following week as a more substantial weather system 
approaches the West Coast. Both the GFS and European model (ecmwf) forecast decent 
rainfall across northern California by Monday the 29th. 


&& 


Aviation...as of 10:30 PM PDT Saturday...VFR continues at this hour 
and will likely extend for a few more hours tonight. By daybreak 
Sunday morning a few patches of stratus are possible in a moistening 
boundary layer. VFR is forecast by late Sunday morning. A shortwave 
trough moves through the area Sunday evening which should help keep 
stratus coverage to a minimum due to increased mixing and drying of 
the airmass. 


Vicinity of ksfo...tempo broken ceilings are forecast Sunday morning. 
VFR is forecast by 18z. 


Ksfo bridge approach...same as ksfo. 


Mry Bay area terminals...VFR but broken ceilings are possible by early 
Sunday morning. VFR is forecast by late Sunday morning. 


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. 


&& 


Mtr watches/warnings/advisories... 
.None 


&& 


$$ 


Public forecast: Larry 
aviation/marine: canepa 


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