fxus66 kmtr 190549 

Area forecast discussion 
National Weather Service San Francisco Bay area 
1049 PM PDT Thu Oct 18 2018 

Synopsis...a slight warming trend is forecast through the upcoming 
weekend as high pressure builds over the region. Dry weather 
conditions are also likely to prevail through the weekend. A pattern 
change will result in cooling conditions early next week that will 
persist through late week with a slight chance of precipitation 
developing over the North Bay. 


Discussion...as of 08:48 PM PDT Thursday...the marine layer 
remains at around 1000 ft per The Fort Ord profiler. Satellite 
imagery shows stratus offshore as well as patches of low clouds 
developing around Point Reyes, along the San Mateo coast, and 
around the Monterey peninsula. Expecting similar, if not less, 
cloud coverage overnight tonight than was seen this morning. 
Temperatures this evening are a few degrees warmer than this time 
yesterday as high pressure builds across the region and onshore 
flow has slightly lessened. 

No changes made to the forecast this evening. A warming trend is 
expected tomorrow and Saturday as onshore flow weakens and a ridge 
of high pressure builds over the region. Lingering offshore winds 
aloft will allow for warming to reach the coast as well. Expect 
highs tomorrow in the 60s to 70s at the coast with some 70s and 
more widespread 80s inland. Isolated interior locations may 
approach 90 deg f. As high pressure builds over the region and 
weak offshore flow aloft remains, the marine layer is forecast to 
compress into the weekend. Therefore, expect less overnight and 
morning low cloud coverage. Some low clouds may still form along 
the coast and around San Francisco. 

The upper ridge will then move further inland late this weekend 
and into next week allowing for some cooling. Models still show an 
upper trough approaching the region early next week. This would 
bring widespread cooling and increasing cloud cover as the marine 
layer expands. Many locations could see afternoon high 
temperatures at or even a few degrees below seasonal normals by 
Monday. Disagreement remains among forecast models as to the 
possibility of precipitation Tuesday through Friday. The GFS 
shows rainfall chances further south into the North Bay on 
Wednesday with a moist flow into northern California. The European model (ecmwf) 
has been trending drier, keeping precipitation well to the north 
of our area. Will need to see if there is more consistency with 
upcoming model runs. Whether or not we see any precipitation, 
temperatures are forecast to cool next week to near or below 
seasonal averages. Chances of precipitation will continue to be 
monitored as the event nears. 


Aviation...as of 10:30 PM PDT Thursday...marine layer has 
compressed down to around 1000 feet this evening. Northerly 
gradient has increased which will delay the stratus from 
spreading inland and may keep it out completely if the latest 
model guidance verifies. For now will delay the timing of cigs and 
see how much the stratus spreads inland. 

Vicinity of ksfo...VFR is expected through 13z. Becoming MVFR from 
13z-17z but confidence is low as latest model guidance has backed 
off on the amount of stratus. 

Sfo bridge approach...similar to ksfo. 

Monterey Bay terminals...stratus over southern mry Bay extends 
into sns. Stratus has stopped just north of kmry but should be in 
after 08z. IFR cigs clearing after 17z. 


Marine...as of 10:34 PM PDT Thursday...a 1024 mb high centered 
350 miles west of Point Arena will slowly weaken over the weekend. 
This will keep light northwest winds over the coastal waters. 


Mtr watches/warnings/advisories... 


Public forecast: as 
aviation: west pi 
marine: west pi 

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