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Area forecast discussion 
National Weather Service Sacramento California
1020 PM PDT Fri Oct 24 2014

Synopsis...
wet and windy weather moves in later tonight into Saturday as an
upper level trough and associated front move into the area.
Thunderstorms with heavy rain, accumulating small hail and gusty
winds and maybe even a weak tornado are possible on Saturday. Snow
levels will lower below Sierra passes Saturday night. Decreasing
winds are expected Saturday evening and precipitation will taper off
Sunday. A brief break Monday will be followed by a chance of rain
over areas north of Sacramento Tuesday and Wednesday. This
precipitation threat will drop southward bringing rain or mountain
snow over much of norcal for the end of the next week.

&&

Discussion...

Occluded front looking very ominous offshore with definite/sharp
backedge of front and area of enhanced clouds indicating band of
convective precip along the front which is along 127w. Warm air advection clouds
precede the front and will be overspreading interior norcal
overnite...but precip associated with the front not forecast to move
into the coastal range until around 12z (5 am). Frontal precip moves
into the siernev late morning and afternoon with break in the valley
until upper air dynamics and colder/unstable move into the area
later in the afternoon and evening.

925 mbs winds indicate 40-45 kts sly winds developing in the valley
by and after 12z with mfr-SAC gradient at least topping 12 mbs. This
is sufficient for wind advsry and aww for krdd as sly gusts top out
at 40+ miles per hour as front moves across the area and for a few hours behind
the front. Strongly sheared environment expected to lead to isolated
to scattered cbs late morning and afternoon.

Locally heavy showers expected with deep convection as precipitable water over +2
Standard deviations Sat morning and at least one Standard deviation
behind the front Sat afternoon. Qpfs will vary widely due to the
convection but the Shasta/siernev mtns with strong upslope flow
should have significant quantitative precipitation forecast. Jhm



Previous discussion...

Upper level trough offshore of the West Coast will move into
northern California tonight into Saturday bringing a change to wet
and windy weather. Increasing clouds and precipitation moving into
the coastal range and Shasta County around midnight and spread
southeast across interior northern California Saturday. Southerly
winds will increase late tonight into Saturday as the cold front and
trough move inland. This will bring breezy and gust winds with
southerly winds 15 to 30 mph with gusts to around 40 mph in the
valley...strongest in the nrn Sacramento Valley and up to 70 mph
over the ridges. Holiday decorations should be secured with the gusty
winds and high profile vehicles should use caution. Winds should be
decreasing Saturday evening. Shasta County mountains could see up to
2 inches of precipitation by Sunday morning with good orographics
with the southerly winds. Snow levels will be around 8000 ft
Saturday morning and drop down to around 5000 to 6000 ft on Sunday
morning. Snow accumulations up to 10 inches are possible on Mt
Lassen and up to 4 inches possible over the higher Sierra passes.
Motorists should be prepared for possible winter driving conditions
in the mountains this weekend. Good instability and shear on
Saturday will bring a threat of thunderstorms and possibly weak
tornadoes. Precipitation will taper off on Sunday with showers
mainly lingering over the Shasta County and down the Sierra. High
temperatures this weekend will be in the mid 60s to low 70s in the
valley and mid 30s to low 50s in the mountains. Monday will be a
drier and warmer day with ridge building into the area as trough
shifts east.



Extended discussion (tuesday through friday)

Flat high pressure over the southwest U.S will keep at least the
southern half of the forecast area dry Tuesday. The northern
portions of the forecast area will see a continued threat of light
rain. Daytime high temperatures under mainly cloudy skies are
expected to come in a few to several degrees below normal. Another
cool low pressure system dropping out of the Gulf of Alaska will
bring precipitation chances southward Wednesday through Friday.
Significant model differences exist in the Wednesday-Friday time
frame. The European model is much deeper and brings deeper
moisture into norcal versus the drier GFS. Have opted for a blend
of solutions but forecast confidence not high during this time
frame.

&&

Aviation...

Pacific cold front moves across the area on Sat bringing chances of
rain and increasing winds. Wind gusts to 45 mph will be possible
after 12z especially over the northern valley.



&&

Sto watches/warnings/advisories...
Wind Advisory from 5 am to 8 PM PDT Saturday central Sacramento
Valley...northern Sacramento Valley...southern Sacramento Valley.

&&

$$

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