679 
FXUS66 KSTO 061631
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
830 AM PST Wed Mar 6 2019

.SYNOPSIS...
Occasional showers and thunderstorms with mountain snow today. 
Mountain travel will be impacted and additional rain may increase
flood potential. Showers continue Thursday into the weekend.

&& 

.DISCUSSION...
Morning Update: Front has progressed into the Ern portion of our CWA 
this morning, over the W Slope Sierra, and we should begin to see 
the surface winds turn from SE to S/SW over the Srn portion of the 
CWA. BUFKIT indicates this will result in more straight-line 
hodographs over the Srn portion of the CWA, but with 
onshore/upvalley flow and topographic forcing of the wind in the 
Central/Nrn Sac Valley, the wind profiles are still favorable for 
anticyclonic curving hodographs up to 1 km and favorable CAPE values 
for thunderstorms, and the potential for rotating storms, say N of 
KMYV this afternoon. 

Another concern and active monitoring is the potential for a 
convective precip band that could set-up over Shasta Co this 
afternoon and evening. The higher resolution QPF/REF progs indicate 
a heavy rain band developing this afternoon and lasting well into 
the evening over mainly Shasta Co. This heavy precip band sets up 
along a nearly stationary/quasi-stationary front developing mainly 
due to topographic forcing which often persists until the synoptic 
forcing relaxes. The remnants of the closed upper low is just off 
the Nrn CA coast and is forecast to move inland this afternoon over 
that portion of the CWA, while other subtle and weaker waves move 
inland over the rest of the CWA which could trigger other convective 
activity over the rest of the CWA. 

Snow profilers this morning indicate the snow level around 6000 ft. 
   JHM 

.Previous Discussion...
Front moving inland early this morning accompanied by a line of 
showers with mainly light to moderate rain. Gusty south to southeast 
winds have increased ahead of the front and are currently gusting 
around 25-35 mph across much of the region. Snow levels remain 
fairly high (around 6000-7000 ft per profiler data) and KBLU precip 
remains rain.

Front and widespread precipitation moves through early this 
morning followed by scattered showers and thunderstorms from late 
morning through the afternoon as weaker upstream short-wave
approaches. Forecast soundings in the post-front environment this
afternoon indicate the potential for a few longer-lived storms 
with their attendant risks, heavy rain, hail and gusty winds.

Higher res models also continue to indicate the potential for a 
persistent line of showers and thunderstorms over Shasta County 
this afternoon into this evening with the setup of the north 
valley convergence zone.

12 to 18 inches of additional snow can be expected across the
passes today, with 2 feet or more over the peaks, before snow
tapers a bit tonight. Showers may bring another foot or more of
accumulation through Thursday morning. Additional valley rainfall
of 1/4 to 1/2 inch is expected today with much lighter amounts
expected tonight and Thursday.

With saturated soils, and streams, creeks and main stem rivers 
running high, additional rain may increase the potential for 
flooding, especially near thunderstorms which are capable of
bringing higher amounts in a short period of time.

Showers will persist Thursday and Friday as a longer wave trough 
moves through the West. Lowering snow levels during this time 
will result in some snow below the BLU level which could lead to a
downgrade of the winter storm warning to an advisory.

&&

.EXTENDED DISCUSSION (Sunday THROUGH Wednesday)
A broad positively-tilted upper trough will settle offshore of 
the state on Sunday. Forecast guidance has been fairly consistent 
in carrying the parent upper low toward northern Baja California 
by early next week. Some snow showers are possible over the 
mountains (primarily from Highway 50 southward) to conclude the 
weekend. Given the general lack of moisture, perhaps an inch of 
snow could be squeezed out over regions which see such a shower. 

As the axis of lower heights exits toward northern Mexico, dry
northerly winds are anticipated to commence next week. The next
system to keep an eye on would be Tuesday as a longwave trough
advances through the Pacific Northwest. It remains to be seen
where the southern extension of this storm will reside. Currently
the 00Z ECMWF is flatter while the 06Z/00Z GFS shows a more
amplified solution. While the latter does have ensemble support,
would like to see the ECMWF join this wetter scenario. Thus, have
kept the forecast mainly dry for the early/middle part of next
week for now.

The temperature forecast supports slightly below average
temperatures for early to mid March. Valley high temperatures
should sit anywhere from the mid 50s to low 60s while mountain
locales remain in the 30s and 40s. ~BRO

&&

.AVIATION...
TAF sites should generally remain in MVFR conditions throughout 
the forecast given passing showers reducing visibilities. KRDD and
KRBL may see conditions deteriorate to IFR due to low ceilings. 
Between 21Z-00Z, scattered thunderstorms could affect Sacramento 
airports down to KSCK and KMOD. Forecast winds will remain out of 
the south to southeasterly direction with gusts possible up to 25 
knots. After 06Z, wind speeds are expected to decrease a bit, but 
will stay in the 10 to 15 knot range. ~BRO

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 10 AM PST Thursday for Western Plumas 
County/Lassen Park.

Winter Storm Warning until 10 AM PST Thursday for West Slope 
Northern Sierra Nevada.

Flood Watch through Thursday morning 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.

&&

$$