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Area Forecast Discussion (AFD)

Issued by Sacramento, CA (STO)

FXUS66 KSTO 211728

Area Forecast Discussion
National Weather Service Sacramento CA
925 AM PST Thu Feb 21 2019

A few showers linger into this evening, mainly across the northern
Sierra, otherwise dry with breezy north winds today and Friday.
Next chance of precipitation will be over the weekend.


Nly gradients have increased to over 9 mbs and Nly winds will be 
increasing for the rest of the day. Deck of low clouds have 
developed on the E side of the Sac Vly from around Sac County Swd 
but these clouds should erode by midday as drier air works over the 
area. Cyclonic flow around deep upper low vcnty of KLAS will keep 
clouds banked up near the Sierra Crest with some spillover W of the 
Crest. Nly barrier jet wind on the W side of the Vly will decrease 
in speed overnite, but should preclude frost W side of the Vly due 
to enough mixing. Winds should diminish on the E side of the Vly but 
looks as if temp and dewpoint spreads will be wide enough for just 
patchy frost in the wind sheltered areas overnite. 

Next chance of precip forecast to move into the CWA late Sat and 
into Sun, mainly over the Nrn mtns and Sierra, as low pressure drops 
Swd from B.C. into WA. The Srn half of the Vly is expected to be 
mostly dry. But a wet pattern re-emerges for the start of next week. 

.Previous Discussion...
Trough continues to carve slowly southward toward SoCal as main vort 
energy digs along the coast. Satellite/radar imagery shows much of 
the cloudiness and showers currently ongoing from about the 
Sacramento area southward with clearing skies over most of the 
Sacramento Valley. Current temperatures are cooler compared to 24 
hours ago across much of the region and range from the teens and 20s 
in the mountains to the mid 30s to lower 40s across the Central 

Snow showers will likely continue into this evening along the
crest of the northern Sierra while precipitation chances will
mostly end elsewhere by mid-morning. Additional snowfall
accumulations of an inch or two will be possible across the higher
mountain passes.

Increasing subsidence in the wake of the low along with tightening
northerly surface pressure gradients will result in breezy
north winds today across the Sacramento Valley. Gusts to around 40
mph will be possible this afternoon. Gradients gradually transition
to more easterly later tonight allowing winds to slacken over the
eastern half of the valley, but some breeziness will likely linger
along the west side. A wind advisory has been issued.

Short-wave ridging expected to shift over NorCal on Friday
continuing cool and dry weather with lighter north winds. Areas of
frost will be possible in the morning for areas of the valley
where the winds subside enough.

Precipitation chances return over the weekend, mainly for the
northern half of the forecast area, as energy begins to undercut
the blocking high over the Gulf of Alaska and make its way into


Active weather pattern looks likely for the extended portion of 
the forecast with Monday and Tuesday looking to be the wettest 
days. Periods of moderate to heavy rain will be possible for the 
start of the work week, as a low pressure system will tap into 
tropical moisture. Snow levels are progged to rise to 4000-5000 
feet for this AR event. Come Wednesday, the precip is forecast to 
move to the north; however, models deviate on how fast it will 
exit the region. 


Showers will be possible for TAF sites south of KSMF which may 
lead to periods of MVRF conditions. However, once the showers come
to an end later this morning, VFR conditions will prevail. 

Brisk N/NWly winds 20G30KT developing in the Vly after 18z 
resulting in light to moderate turbulence during takeoff/landing 
operations at TAF sites. 


Wind Advisory from 10 AM this morning to 6 PM PST this evening 
for Carquinez Strait and Delta-Central Sacramento Valley-Clear 
Lake/Southern Lake County-Northern Sacramento Valley-Southern 
Sacramento Valley.