NATIONAL WEATHER SERVICE FORECAST DISCUSSION
Area Forecast Discussion
Issued by The National Weather Service
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000
FXUS66 KSTO 140645
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1040 PM PST Wed Feb 13 2019

.SYNOPSIS...
A strong storm event will bring widespread precipitation with
moderate to heavy rain and mountain snow. Local flooding with
ponding on roads and rises on streams and rivers possible through
Thursday. Periods of wet weather continue into the weekend.

&&

.DISCUSSION...
Evening Update: Vigorous mid-latitude cyclone nearing 130w will
continue to tap a highly anomalous TPW plume (AR) overnite and Thu
as it nears the coast by 18z Thu, and then sweeps across the CWA
during the afternoon. Orientation of energy within the trof and the
fast movement of the trof suggests a NiCFR is possible in the
morning/early afternoon as upper dynamics sweep across the area.
After the morning rain band moves through, a mid-level dry slot
should move over the area and this could transport the higher
momentum air downward for a high-end wind advsry situation, perhaps
even a borderline high wind event. The 925 mbs winds decreased just
slightly in the evening run from the day run, but still have a core
of 54+ kt winds from SAC up to OVE around 12z Thu. The higher 60+ kt
winds were elevated slightly up to around 3 kft. During the
afternoon, the soundings indicate a little deeper mixing than the
last couple of days which could allow for stronger winds aloft to
mix down. Generally though, the 925 mbs are forecast to decrease.
However, the onshore flow should strengthen and we should see a good
band of SW/Wly winds developing with could also ramp up into the
wind advsry area.

Still looks like lowering snow levels as the day wears on tomorrow,
with another yard stick or two of snow forecast for the Sierra. The
colder low center is showing up off the B.C./WA coast now and will
begin to impact Norcal Thu afternoon and into the weekend.  JHM

.Previous Discussion...
A strong and very wet system has brought hazardous weather
conditions to the area today. Cold air entrenched across the far
north end of the Sacramento Valley and northern mountains allowed
heavy snowfall to fall into the northern Sacramento Valley since
yesterday evening, with totals up to 10 to 14 inches for Redding
causing major disruption to travel, power outages, and school
closings. Warmer air has spread in, changing precipitation to rain
over the area, including the Sierra passes. Moderate to heavy
precipitation has brought road flooding and stream rises to portions
of the area. An area Flood Warning has been issued as the concern
changes to flooding. This has been extended until Thursday evening,
and expanded northward over the northern Sacramento Valley, where
low snow melt and snow clogged drains could increase runoff. A Flood
Watch continues through Thursday early evening for much of the area.

The next surface low races northward off the coast up into
western Oregon by midday Thursday. This will also bring another
upswing in precipitation and gusty southerly winds as gradients
tighten to around 15 mbs from SAC to MFR bringing an elevated risk
for power outages and tree damage. A Wind Advisory begins Thursday
morning and continues through early evening. The potential for
flooding issues will increase further as runoff from the ongoing
precipitation is enhanced by low-elevation snow melt.

Snow levels expected to come back down Thursday afternoon and
night as the next cold upper low drops down to off the coast of
Oregon and displaces the milder airmass to the east. At the same
time, snowfall will increase over the northern Sierra Thursday
night as lapse rates steepen and upslope component to the flow
increases. Thunderstorms will be possible in the Central Valley.
Shear and instability are looking increasingly favorable. There is
some potential for debris flows over burn areas due to higher
intensity rainfall over already saturated locations.

Wet and cooler pattern will continue into the weekend as several
disturbances drop down from the northwest bringing showers and
adding to the snowpack in the mountains. EK

&&
.EXTENDED DISCUSSION (Sunday THROUGH Wednesday)

Unsettled weather forecast through the weekend as upper low moves
through. More widespread showers expected Saturday becoming
scattered Sunday. Drier weather, along with some breezy north to
east wind, returns Monday into Tuesday as subsidence increases
over Interior NorCal. Models diverge enough by the middle of next
to lead to forecast uncertainties. Daytime temperatures remain
below normal through the extended forecast period.

&&

.AVIATION...

In Cntrl Vly, wdsprd MVFR with areas IFR conds nxt 24 hrs. Lcl SE
sly wnd gsts to 25 kts fm SAC area S. Wdsprd SE sfc wnd gsts to 35
kts aft 07z thru abt 20z Thu. Isold tstm poss. In fthls and mtns,
wdsprd MVFR/IFR with areas LIFR obscrg trrn. Areas S-SE sfc wnd
gsts up to 50 kts or gtr ovr hyr trrn tngt and Thu. Sn lvls
incrsg abv 075 tngt, lwrg to 040-055 Thu aftn.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Thursday evening for Carquinez Strait and
Delta-Central Sacramento Valley-Clear Lake/Southern Lake County-
Motherlode-Mountains Southwestern Shasta County to Northern Lake
County-Northeast Foothills/Sacramento Valley-Northern Sacramento
Valley-Northern San Joaquin Valley-Shasta Lake Area / Northern
Shasta County-Southern Sacramento Valley-West Slope Northern
Sierra Nevada-Western Plumas County/Lassen Park.

Winter Storm Warning until 4 AM PST Saturday for Burney Basin /
Eastern Shasta County-Shasta Lake Area / Northern Shasta County-
West Slope Northern Sierra Nevada-Western Plumas County/Lassen
Park.

Wind Advisory from 6 AM to 6 PM PST Thursday for Carquinez
Strait and Delta-Central Sacramento Valley-Clear Lake/Southern
Lake County-Motherlode-Mountains Southwestern Shasta County to
Northern Lake County-Northeast Foothills/Sacramento Valley-
Northern Sacramento Valley-Northern San Joaquin Valley-Southern
Sacramento Valley.

&&

$$
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