Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Sacramento California
230 PM PDT Wed Mar 22 2017
unsettled weather will continue into next week as a series of
weather systems move through the region. Chance of thunderstorms
through the evening.
upper trough is positioned over California this afternoon with
disturbance dropping south through it across norcal. Morning's
precip band has shifted east and weakened over the Sierra...but
not before producing a 4 to 6 hour burst of heavy snow. Afternoon
and evenings concerns shift to thunderstorm development with hail
being the main concern due to cold air aloft/steep lapse rates.
Shear is less than yesterday...but stronger than 12z model
forecast as southeast low winds of 10-20 mph continue Red Bluff
to Sacramento. Activity will shift over Sierra late this
afternoon/evening with another burst of heavy snow possible. Snow
levels will drop to 4000 feet at times in heavier activity.
Brief break between storms during the day Thursday before the next
system moves in during the night into Saturday. Valley rainfall
amounts will range from 1-2 inches Redding area to 0.25-0.50
Stockton/Modesto. Mountain precip amounts will be 1-2 inches
liquid. Snowfall amounts 6-12 inches could fall with rather low
snow levels down to 4500 feet.
Extended discussion (sunday through wednesday)
Next in a series of Pacific frontal systems pushes into norcal
on Sunday. All areas of the County Warning Area should see at least a chance
of precipitation by afternoon. Precipitation amounts with this
week system are expected to be fairly light so even with moderate
snow levels, impacts are expected to be minimal. Models diverge
as to how fast this system will exit the region. European model (ecmwf) and Gem
models quickly shift the upper trough axis eastward into the
Great Basin by Monday while the slower GFS keeps cyclonic flow
and shower threat over the forecast area Monday. Models diverge
even more Tuesday and Wednesday. Have kept slight threat of
precipitation over the northern mountains Tuesday with European model (ecmwf)
and Gem showing some sort of trough over Pacific northwest but
GFS puts a fairly strong ridge over norcal Tuesday so confidence
in the forecast for this time period is low. Models seem to be
settling in on idea of West Coast ridging around the middle of
next week for at least a brief drying period but considering poor
model consistency, confidence remains low.
MVFR ceilings Central Valley and IFR over mountains as upper
level trough moves through norcal today. Isolated thunderstorms
valley and foothills through 05z. Snow level 3500 to 4500 feet.
Improving conditions after 05z Thursday becoming VFR over Central
Valley. Southerly winds 5 to 15 mph becoming variable to 10 mph
Winter Weather Advisory until 10 PM PDT this evening for West
Slope northern Sierra Nevada-western Plumas County/Lassen park.