Weather Service Report


683 
FXUS66 KEKA 212354
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
354 PM PST Tue Feb 21 2017

.SYNOPSIS...
Wet and unsettled weather will persist through much of the week. 
Showers and a few thunderstorms may develop through wednesday 
morning, some of which may contain small hail. Additionally, colder 
air filtering into the region will allow snow levels to drop, with 
pass-level snowfall possible.

&&

.DISCUSSION...
.SHORT TERM... 
(Tonight and Wednesday)

Well, things haven't quite played out as we thought with earlier 
forecasts regarding the hail potential or thunderstorm development 
It appears this may be to some drier air aloft, as the latest SPC 
mesoanalysis confirms mid-level lapse rates above 8 deg. C/km, 
MUCAPEs above 500 J/kg, lifted indices of -1 to -3 (offshore), and 0-6km bulk shear values near 25 knots (sufficient for storm organization, but not too strong where any weak updraft would get torn/sheared apart). Thus, while we've received several reports of small hail, not one lightning strike has developed as of yet across the forecast area.

However, this may change later this evening and overnight as another 
strong vort max crosses the region. Mid-level lapse rates will 
increase further to near 9 deg. C/km, with colder air also dropping 
snow levels from their current values of ~4400 feet, to just under 
3000 feet by morning. This may help increase convective activity and 
hail development, with some accumulating small hail possible with 
the stronger showers or thunderstorms.

.LONG TERM...
(Wednesday night through next Monday)

A general showery pattern will continue through the weekend and into 
early next week, as onshore flow is maintained over the next few 
days, followed by a series of systems dropping south to southeast 
across the region in the flow aloft. These disturbances will also 
bring bursts of vorticity/increased ascent to the area, allowing 
periodic increases in convective coverage (and to a lesser extent, 
intensity). The mainly north flow aloft will also help maintain cold 
air advection and lower snow levels, at least through the first part 
of the weekend, before the flow pattern gets modified to a west 
southwest flow. Should this occur as forecast, warmer air with 
increased moisture content would get advected across the forecast 
area. While the long range models agree on this overall numerical 
depiction, subtle differences in time and strength will have a big 
impact on this. These details will become more clear over the next 
few days as they get closer in time to affecting us, with an added 
boost in model confidence likely occurring as they get sampled by the 
RAOB network, which typically improves model continuity. /PD

&&

.AVIATION...
Scattered showers will continue to move across the Redwood Coast 
overnight. High resolution models indicate an uptick in coverage 
between 06Z and 12Z and have included the mention of VCTS. Most of
the showers are forecast to end around KUKI over the next couple 
of hours, with a few more possible Wednesday morning. Winds will 
be light. /SEC

&&

.MARINE...
Winds have decreased to below advisory criteria, but seas continue
to flirt with criteria. The marginal Small Craft Advisory will 
continue in the N waters thru 9 PM and the S waters thru 3 AM. 
Wind directions will gradually veer to more northerly, and 
northerlies are forecast to continue thru Thursday night. Winds 
are progged to become southerly on Friday with speeds increasing a
bit N of Cape Mendocino. /SEC

&&

.HYDROLOGY...
All of the mainstem rivers are forecast to stay below monitor 
stage for the forecast period with the exception being the Eel 
River at Fernbridge. This river is forecast to peak at 17.4 feet 
this afternoon around 4:00PM and to then fall below monitor stage 
around 10:00AM on February 22nd. KAR 

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...None.
NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until 9 PM PST this evening for PZZ450-470.

     Small Craft Advisory until 3 AM PST Wednesday for PZZ455-475.

&&

$$

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Western Regional Climate Center, wrcc@dri.edu