Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 231105

Area Forecast Discussion
National Weather Service Sacramento CA
305 AM PST Thu Nov 23 2017

Mild temperatures this week with a weak weather system today.
More widespread rain spreads south Saturday into Sunday followed
by a colder system early next week.


Plenty of cloud cover continues to stream up from the southwest
early this morning and some spotty light precipitation has been
occurring over the northern half of the forecast area overnight
along a weak frontal boundary. The cloud cover has inhibited dense
fog development, but surface observations in the valley are
saturated (or nearly so) so some patchy fog and stratus will be
possible thru the morning. Current temperatures are milder
compared to 24 hours ago and range from the mid 30s in the
mountain valleys to the upper 40s and 50s elsewhere.

Deep moisture plume with TPW of 1.25 to 1.5 inches continues to
feed into NorCal from the southwest as the upper ridge retreats
slightly eastward. This moisture will interact with a weak front
that is forecast to slide south to around I-80 by 00Z Friday
resulting in a mostly cloudy Thanksgiving across the region. Some
light rain may make it as far south as the Sacramento region by
mid to late afternoon. Only light amounts of QPF are expected with
less than a quarter inch in the mountains and only a few
hundredths of an inch in the Sacramento Valley.

Precipitation is expected to retreat northward tonight and Friday
as ridging reasserts itself across NorCal ahead of a stronger wave
developing over the eastern Pacific. Most of the region will see
dry weather for Friday into Saturday with mild temperatures.

A stronger frontal system is forecast to spread precipitation
southward across interior NorCal Saturday night and Sunday along
with stronger southerly winds. Snow levels will remain high ahead
of the front limiting potential winter weather impacts to travel
at the end of the holiday weekend.


The 12z GFS is a bit quicker than the ECMWF with the easterly
progression of the Sunday-Monday storm system, with precipitation
ending by Monday evening. The ECMWF holds onto precipitation
across the region into Monday night. By Tuesday into Wednesday,
confidence is high that a strong ridge of high pressure will bring
dry weather to Northern California. Depending on how much
northerly wind develop behind the frontal system, we could also
see fog development again in the valleys. Dry weather is likely to
continue through the rest of the extended period. Dang


Extensive mid and high cloudiness bringing less foggy conditions
than last night. Patchy IFR/LIFR fog still possible in the Central
Valley, mainly from KMYV southward, into the morning. A weak
frontal system will bring light rain showers and local MVFR
conditions mainly north of Interstate 80 today. Light winds
continue. Dang




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