Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 241633

930 AM PDT Thu Apr 24 2014

Mild temperatures are forecast today. Then another weather system
will bring a chance of widespread precipitation along with cooler
temperatures and lowering snow levels tonight into early Saturday.
Potential for isolated thunderstorms on Friday.


.Short Term Discussion (Today through Sunday)...
WSWly flow aloft over Norcal moistening as .80+" TPW plume moves
onto the Nrn CA coast. Light precip forecast today and for most of
tonite as frontal band moves towards the I-80 corridor by around
midnight. Synoptic scale or larger scale forcing forecast to
increase over Norcal on Fri (per convergence of Q vectors) as short
wave and jet energy on the backside of Ern Pac trof digs the trof
along the coast during the day. Friday night and early Sat this
energy continues to dig rapidly into Socal. Thus...for our CWA the
bulk of the precip is expected on Fri...with QPF decreasing from N
to S during the afternoon and evening.

The digging trof will bring colder/unstable air into Norcal...not
only lowering snow levels...but resulting in showers and
thunderstorms. First...snow levels should lower to around around
4000 to 4500 feet on Fri. Second...the best instability and greatest
thunderstorm potential looks to be over the central and southern
Sacramento valley in deference to the location of the NE quad of the
vort max during the 18z-00z Fri time frame.

Up to a foot of snow is expected over the higher elevations of the
Siernev and around half a foot or so near pass levels...although
melting/settling at this time of year may account for a couple of
inches less accumulation. Greatest snowfall amounts expected to be
from the I-80/Hwy-50 corridor Swd into zone 69 given the track of
the short wave energy within the upper trof.

This rapidly digging trof maintains a neutral tilt over CA. Forecast
hodographs for the valley on Fri are mostly cyclonically curved...
not broadly looping and favoring left moving storms with negative
helicity. This is not the typical TOR set-up for Norcal...and favors
more the hail producing storms given the steep lapse rates forecast
with the cold air.

As this system moves across the Four-Corners Sat nite...another
short wave may give Norcal a shot of light precip mainly over our
mtns into Sun morning. By Sun afternoon...ridging should prevail
over Norcal with warmer/drier wx.  JHM


.Extended Discussion (Monday through Thursday)
Dry and much warmer temperatures arrive next week as ridging
develops. Temperatures will warm up to near to above normal on
Monday with mid to upper 70s in the Valley. Ridging builds
further on Tuesday and Wednesday with well above temperatures,
with some Valley spots potentially reaching into the lower 90s,
upper 50s to low 70s in the mountains.

Ridging now appears more likely to hold firm with little potential
for any precipitation through next week. 06z GFS now shows a low
off the coast Thursday night, which the 00z run did not have. Will
go with the more consistent ECMWF with the ridge remaining, along
with dry and very warm temperatures. EK


Pac fntl sys apchs tda then movs thru Intr NorCal this aftn thru
Fri. Genly VFR tda exc lcl MVFR N of a KUKI-KCIC-KSVE line. Bcmg lcl
MVFR/IFR in Cntrl Vly and areas MVFR/IFR with lcl LIFR omtns tngt
and Fri. Isold TSRA/TSRAGS on Fri. Sn lvls 060-070 tda and tngt lwrg
to 045-055 Fri. Lcl SW sfc wnd gsts to 25 kts poss thru Delta and
lcl S-W in ptns of Srn Sac/Nrn San Joaquin vlys this aftn/eve. Lcl
Swly sfc wnd gsts up to 35 kts poss ovr hyr mtn trrn nxt 24 hrs.


.STO Watches/Warnings/Advisories...
Winter Weather Advisory from 11 pm this evening to 5 am PDT
Saturday above 5500 feet in the west slope Northern Sierra
Nevada...western Plumas county/Lassen Park.


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