Area forecast discussion 
National Weather Service San Francisco Bay area 
202 PM PDT Thursday Apr 24 2014 


Synopsis...a storm system will bring cooler temperatures and 
chances for precipitation to the region late tonight through 
Friday. Another weaker system could bring rain chances Saturday 
night and Sunday. Above normal temperatures are expected next week 
as high pressure builds over the region. 


&& 


Discussion...as of 2:00 PM PDT Thursday...active weather through 
the entire forecast period with rain...thunderstorms...poss patchy 
frost Saturday morning and the first real warm up of the season 
next week. 


A mix of sun and clouds over the Bay area this afternoon...but 
just upstream rain is falling. A cold front continues to slide 
south toward the County Warning Area and will impact the region later tonight. In 
the meantime...pleasant temperatures with many locations in the 60s with a 
few 70s in the southern County Warning Area this afternoon. 


Short term(tonight-sunday)... 
change is literally on the horizon. The aforementioned cold front 
is still on track to move through the Bay area tonight and early 
Friday. The evening commute today looks to be dry...but as the 
fronts moves into the North Bay light rain will gradually spread 
southward. There is still some uncertainty as to the southern 
extent of the rainfall...but for now will have a wet commute 
Friday morning for much of the area. Not a total wash out...but 
some light precipitation around the region. Behind the front cold air 
aloft will fill in as a jet maximum takes aim at the Bay area. The 
convective threat still seems plausible for Friday with several 
parameters showing unstable airmass(no cin, decent cape, minus 
lifted indice's and steeper lapse rates). Given the cold air aloft (-28c at 
500mb) storms that develop will be capable of producing some small 
hail. Nothing severe is expected tomorrow...but something to 
monitor on the radar. Storm Prediction Center expanded their 
general mention of thunderstorms to include much California north of San 
Francisco. Total rainfall from this evening through Friday night 
will generally be a a few hundredths up to a tenth or two. 


Precipitation chances and thunderstorm threat diminishes quickly after 
00z Saturday as the best forcing moves east and drier air aloft 
fills in from the west. Dry weather is expected for much of 
Saturday...but below normal temperatures are being forecast. Highs 
on Saturday will be in the upper 50s to middle 60s...high elevations 
in the 40s to 50s. 


Another weak system will move in Saturday night into Sunday 
morning. Low confidence for this potential precipitation event...but 
given recent model output decided to introduce light precipitation late 
Saturday night/Sunday morning. Persons with outdoor activities 
planned Sunday morning...especially along the coast...should at least plan 
for the very low chance of precipitation. Rainfall amounts will be very light. 


Long term(monday-thursday)... 
once the precipitation ends Sunday afternoon...much drier weather is 
expected for the entire long term. Medium range models still 
indicate building high pressure and developing offshore flow by 
Tuesday. The offshore flow will be strongest from Monday night 
through Wednesday night. The daytime will be mild and very dry 
with highs in the 80s to middle 90s inland...70s at the coast. 
Overnight lows will see thermal belts with mild temperatures in the hills 
with moderate to poor humidity recoveries. That being said...fire 
weather may become more of a concern next week. 








&& 


Aviation...as of 10:00 am PDT Thursday...tricky forecast this 
morning with clouds clearing our earlier and then clouds 
returning. Satellite shows plenty of lower clouds to the west 
however loop clearly shows clearing now happening in the Bay. Feel 
that VFR will be at all spots by 19z. Approaching system will 
bring some showers to the area tonight into Friday although latest 
runs have back off on coverage. Therefore, converted all -shra 
just to vcsh. Locally breezy this afternoon into the evening. 
Overall just moderate confidence. 


Vicinity of ksfo...look for VFR to occur shortly and continue 
through at least 02z. Westerly breezes kick up for the afternoon 
with gusts into the middle 20s. MVFR conditions forecast after 03z 
with a chance of showers after 08z. Moderate confidence. 


Ksfo bridge approach...similar to ksfo. 


Monterey Bay area terminals...VFR through at least 02z for both 
kmry and ksns. Breezy at sns with westerly gusts to around 20 knots 
this afternoon. MVFR returns overnight with a chance of showers 
overnight. Confidence is high. 


&& 


Marine...as of 02:00 PM PDT Thursday...west to northwest winds will 
prevail along the central coast into the weekend. A mixed swell will 
enter the southern coastal waters on Saturday featuring a 7 to 9 
foot 14 second westerly swell and a 3 to 4 feet 19 to 21 second 
southerly swell. The southerly swell will produce potentially 
hazardous conditions for south-facing beaches in Monterey and Santa 
Cruz counties through Sunday. 


&& 


Mtr watches/warnings/advisories... 
... Francisco Bay north of the Bay Bridge until 8 PM 
Small Craft Advisory...San Francisco Bay south of the Bay Bridge until 8 PM 
Small Craft Advisory...Monterey Bay until 8 PM 
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm until 8 PM 
Small Craft Advisory...pt pinos to pt Piedras Blancas 10-60 nm until 5 am 
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm 


&& 


$$ 


Public forecast: mm 
aviation: Bell 
marine: Bell 


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