Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Sacramento California
955 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.
leading edge of high cloudiness spreading nwd into the srn portion
of norcal ahead of low pressure system off baja. High clouds are
masking the St/fog developing over the nrn San Joaquin Vly and may
have to rely on metars/web cams the rest of the nite to monitor
extent of St/fog.
Light fog (br) forming over srn SAC Vly but extent of St is much
less than the last couple of nites so dense fog likely to form a
little later. Don't think the cirrus will be dense enough to limit
radiational cooling so dense fog likely to form late tonight and
become widespread around sunrise on Mon. Higher resolution progs
indicate the St/fog may advect/form all the way up into the rbl
possibly the rdd area again by Mon morning as low level sely
increases from <5 kts to as much as 15 kts by morning. Jhm
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
MVFR visibilities returning this evening with LIFR conditions in fog
spreading nwd from the nrn San Joaquin Vly into the SAC Vly through
the morning hours (after 09z-18z). An exception to this may be rdd,
which could have enough north winds to maintain VFR or brief periods
of MVFR/IFR Mon morning. LIFR conditions eroding Mon afternoon. High
cirrus spreading nwd into norcal ahead of low pressure system moving
newd into socal on Mon.