Winter Weather and Heavy Rain in California, March 24 to 27, 2017

Area Forecast Discussion
National Weather Service Sacramento CA
308 AM PDT Fri Mar 24 2017

.Synopsis...
Rain and mountain snow today into Saturday with mountain travel
impacts likely. Gusty winds today as well.  Brief break in
weather mid weekend. Another system possible Sunday and Monday
with another round of mountain travel impacts. Next storm clips
Norcal and Sierra Wednesday and Thursday.

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.Discussion...
Pacific frontal band currently pushing into northwest California
bringing precipitation as far southeast as a Red Bluff to Santa
Rosa line. Southerly winds starting to pick up in the northern
Sacramento valley with MFR to SAC surface gradient up to 10 mb.
Some discrepancy between models as to max wind speeds this
morning but depending on model, can find wind criteria throughout
the Sacramento valley so have left current advisory through early
this evening as is for now. Significant snowfall over the
mountains still on tap at pass levels so keeping winter storm
warning as is for now as well. Main frontal clouds and precip
looks to be over Norcal during maximum heating today and with lack
of significant instability forecast by models, have removed
threat of thunderstorms northern Sacramento valley for this
afternoon. Cloud cover this morning will preclude valley fog and
combined with cooler airmass will bring cooler daytime highs
today. Post frontal showers tonight will diminish on Saturday with
upper ridging bringing brief drying period Saturday night. Cloud
cover in advance of next upstream system should minimize valley
fog threat. Next upstream Pacific system quickly displaces upper
ridge eastward into the Great Basin on Sunday with precipitation
spreading across the north state as early as mid day with frontal
passage through norcal around Sunday evening. Snow levels with
this system will create mountain travel impacts again Sunday into
early Monday but this system should be a bit drier so snowfall
totals should be a bit lower. Upper ridging begins amplifying
over the eastern Pacific on Monday pushing shower threat north and
east to the northern mountains and Sierra Cascade range by Monday
evening while the valley gets another break in the precipitation.
Stabilization under the ridge along with northerly flow at all
levels should preclude thunderstorm development Monday afternoon
or evening.

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.EXTENDED DISCUSSION (Tuesday THROUGH Friday)

Drier weather Tuesday as NorCal comes under the influence of
upper ridging. Surface high pressure from the EPAC building
through Oregon into the Great Basin will increase N-S surface
pressure gradient over Interior NorCal leading to some breezy
northerly wind Tuesday. Short wave trough moves through Wednesday
into Thursday bringing a threat of showers mainly over northern
and eastern portions of the forecast area.
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.AVIATION...

Pac fnt movs thru Intr NorCal tda with wdsprd MVFR and areas
IFR with lcl LIFR. Areas Sly sfc wnd gsts to 30 kts or gtr in
Cntrl Vly tda with SWly gsts to 40 kts or gtr ovr hyr trrn.

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.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 5 AM PDT Saturday for West Slope
Northern Sierra Nevada-Western Plumas County/Lassen Park.

Wind Advisory from 9 AM this morning to 7 PM PDT this evening
for Carquinez Strait and Delta-Central Sacramento Valley-
Motherlode-Northeast Foothills/Sacramento Valley-Northern
Sacramento Valley-Northern San Joaquin Valley-Southern
Sacramento Valley.

Winter Storm Warning until 5 AM PDT Saturday for Shasta Lake
Area / Northern Shasta County.

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