Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 102320
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
320 PM PST Sat Dec 10 2016


.SYNOPSIS...
Wet weather continues into this evening. Generally dry Sunday and
Monday followed by potentially significant rain and mountain snow
Tuesday through Thursday.

&&

.Short Term Discussion (Tonight through Wednesday)...
Zonal flow is stretching a west to east frontal system across
NorCal with our forecast area within the warmer air, as the
jetstream is still in southern Oregon. Hence, snow levels are
around 9000ft or above. Moderate to heavy precipitation has fallen
today over the mountains with 3 to 6 inches over the past 12
hours. We have had several reports of some street flooding and
streams running high. As a result, we issued an Areal Flood
Advisory for the Sierra and foothills through around 1100 pm PST.
As of 300pm PST, the mountains 4-7 inches of rain over the past
24 hours with the heaviest amounts from Placer county up through
eastern Butte and western Plumas counties. More is expected into
this evening over the Sierra and southward of I-80 in the Valley.

Drier air comes in Sunday and Monday followed by Tuesday through
Thursday shaping up to be a very wet period with moderate snow
levels (4000 to 6000 ft from north to south).  JClapp

&&
.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)
The subtropical moisture tap will continue into Wednesday with
high snow levels for the Sierra (likely around 7000 ft). All major
global models (GFS/ECMWF/GEM) show this moisture plume directed
at the Sierra although there are differences on the exact
location. Given the large amount of rainfall forecast on Tuesday &
Wednesday, combined with the relatively high snow levels, we
could be looking at another period of minor street and small
stream flooding, especially for the Sierra. By Thursday, a short
wave rotating through will continue the precipitation for our CWA.
At this point, models are coming into agreement of a frontal band
moving through sometime on Thursday with colder air ushering in
behind.

By Friday, the flow aloft turns northerly and colder air continues
to filter into are area. Both the GFS and ECMWF hint at a weak
wave rotating through which could provide some minimal
precipitation. Additionally, 850 mb temperature are expected to
be around -3C to -4C which would support relatively low snow
levels. Beyond this, cold temperatures will continue for Saturday
with daytime highs 5-10 degrees below average for the Valley.
Wilson


&&

.AVIATION...
IFR/MVFR conditions will improve to VFR for the valley tonight as
the frontal band slowly moves southeast across our area. Models
indicate skies may clear enough early tomorrow morning for some BR
around the Sacramento sites and KSCK. Beyond this, VFR conditions
expected for Sunday with light and sometimes variable surface
flow. Wilson

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$



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