Area Forecast Discussion
Issued by NWS Sacramento, CA
FXUS66 KSTO 252312
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
312 PM PST Sun Jan 25 2015
Dry weather with areas of night and morning valley low clouds and
fog through Monday. Temperatures expected to remain well above
normal through Monday in fog-free areas. Light precipitation is
possible Tuesday and Wednesday.
Continued offshore flow, albeit a little weaker than Saturday,
helped to dissipate the fog/stratus out of most of the valley by
late morning/early afternoon. It helped that the fog/stratus layer
was a little more shallow compared to 24 hours ago. The increased
sunshine over the valley along with the very mild airmass over
NorCal resulted in milder temperatures from about the Sacramento
area southward in the valley while the north valley cooled
considerably compared to Saturday with the lack of north winds.
We`ll likely see a repeat of fog in the Central Valley tonight
given the clear skies, relatively light winds and dew points in
the 40s. Expect we`ll see some areas of dense fog once again
developing by late evening with the most widespread dense fog
likely around sunrise on Monday.
The strong upper ridge will shift east into the Great Basin on
Monday, allowing for some synoptic cooling. Prevalent valley fog
in the morning will likely give way to plenty of sunshine once
again as the fog/stratus layer will likely be quite shallow. We
may begin to see increasing high cloud cover late in the day as a
weather system off the Baja California coast begins to approach.
This weather system will skirt by the area on Tuesday. It is weak
and is expected to have little impact on the area besides bringing
showers to the northern Sierra and a chance of showers elsewhere.
The Sierra will likely see some precipitation, with a inch or so
of snow possible above 6000 ft. Parts of the valley may see a
sprinkle or light shower, but odds don`t look great at this point.
Showers may linger over the mountains through Tuesday night, with
dry weather expected to return on Wednesday.
.Extended Discussion (Thursday through Sunday)
Upper level ridging will bring generally dry and mild weather for
the extended. Weak troughing develops over California on Thursday.
This system shifts eastward into Nevada, just brushing the
southeastern portion of the forecast area. Have kept just a slight
chance of some rain and snow showers for higher elevations of
Tuolumne and Alpine counties Thursday into Friday.
A positively tilted Pacific ridge spreads eastward Friday and
Saturday and the trough closes off into a low over southern
Nevada/southern California. This is a Rex block pattern, which
will deflect systems well to the north of the region, keeping the
weather dry. A strong surface pressure gradient develops with this
pattern. Breezy northerly winds are expected in the Valley by
Friday afternoon, with gusty north to easterly winds in the
mountains peaking Friday night. The winds should gradually
diminish Saturday as the low shifts southward.
Dry and seasonably mild weekend is expected. The ridging should
break down early next week as the ridge flattens out. Some
moisture riding over the ridge could potentially spread some
precipitation into far northern California/southern Oregon after
next weekend. EK
VFR is expected late this afternoon and early this evening over
most of the Valley, but MVFR vsibilities are expected to quickly
return by around 04z. VLIFR/LIFR conditions should redevelop in
fog and low ceilings for most of valley through the morning hours
(around 06-09z). An exception to this may be RDD, which could have
enough north winds to maintain VFR. Fog/low ceilings will
gradually erode Monday morning. EK