Scientific Forecaster Discussion
fxus66 khnx 201052
Area forecast discussion
National Weather Service San Joaquin Valley - Hanford California
252 am PST Mon Feb 20 2017
Synopsis...a significant storm system will impact central
California today bringing abundant precipitation and strong winds
to the area through at least Tuesday. Otherwise...unsettled
weather through Wednesday...with a return to wet weather this
Discussion...a broad upper trough dominates the eastern Pacific
with an embedded upper level shortwave moving quickly east toward
the northern California coastline. This trough is tapping into
abundant atmospheric moisture...with the blended total
precipitable water currently indicating 1.5 inches just off the
central California coastline. Precipitation is impacting much of
central California...especially the west side of the valley and
The high res and medium range models are all in agreement that
steady moderate to heavy precipitation will be present over the
Sierra Nevada and surrounding foothills through at least 00z
Tuesday. This precipitation is being fueled by a 70 to 80 kt 600
mb jet...assisting in significant orographic lifting of this very
moist airmass. Expect precipitation rates of a half inch to three
quarters of an inch over the Sierra Nevada and surrounding
foothills from around 15z to 21z today. This will result in the
possibility of flooding across parts of central
California below the snow line...especially those who have
experienced flooding in the past few months. Additionally in the
higher elevations...rock and mud slides will be possible with
these precipitation rates.
The Sierra Nevada and foothills below the snow line are forecast
to receive between 1.5 and 3.5 inches of rain between this morning
and Tuesday morning. The San Joaquin Valley will see between a
tenth of an inch in the South Valley to three quarter of an inch
in the North Valley.
Snow levels are generally around 8000 feet this morning and are
forecast to drop to around 7500 feet later this
afternoon...falling to 7000 feet tonight. Expect 20 to 40 inches
of new snow above 8000 feet through Tuesday morning from Kings
Canyon National Park north to Yosemite with 10 to 20 inches in
Tulare County above 8000 feet. Between 7000 and 8000 feet...the
Sierra Nevada could see between 8 and 18 inches of snow north of
Kings Canyon with lighter amounts to the south.
Otherwise...strong winds will accompany this storms...especially
along the north and west side of the San Joaquin Valley as well as
the foothills from Fresno County northward. The strongest winds
will occur this evening into early Tuesday morning...with wind
gusts near 50 mph possible. These winds may bring down trees and
power lines. The Wind Advisory was extended in time to account for
these strong winds lasting a bit longer than originally
The upper trough will continue to dominate the area with generally
zonal flow over central California through Wednesday afternoon.
Unsettled weather remains in the area through this time
frame...with steady precipitation over the Sierra Nevada becoming
showery in nature by Tuesday night. Snow levels will plummet from
around 7000 feet on Tuesday to around 3500 feet on Wednesday
evening. Expect light accumulations at this time...but the
foothills may receive a dusting of snow mid week. We will fine
tune these details over the next few days.
A slight chance of thunderstorms was added to the forecast for the
valley and foothills both Tuesday afternoon and Wednesday
afternoon as the convective parameters are indicating an unstable
A period of dry weather will be present across the area Thursday
into Friday with another possibility of unsettled weather
returning to the area over the weekend. Please continue to monitor
the forecast for the latest information.
Aviation...IFR conditions can be expected over the southern
Sierra through at least 12z Tuesday with mountain obscurations.
MVFR conditions will prevail over the Kern County mountains with
local IFR ceilngs through 19z today. Local MVFR ceilings are
possible in the San Joaquin Valley and adjacent foothills through
12z Tuesday. Additionally, strong southeasterly winds gusting
over 35 knots are likely in the San Joaquin Valley and adjacent
foothills from Fresno County northward through 08z Tuesday. VFR
conditions will prevail elsewhere across the central California
interior during the next 24 hours.
Air quality issues...
The level of certainty for days 1 and 2 is high.
The level of certainty for days 3 through 7 is medium.
Certainty levels include low...medium...and high. Please visit
www.Weather.Gov/hnx/certainty.Php for additional information
an/or to provide feedback.
Flood Watch through Tuesday morning caz089-090-093-094-096-097.
Winter Storm Warning until 10 am PST Tuesday above 7000 feet for
Wind Advisory until 7 am PST Tuesday caz089-090-093.