Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 192114
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
214 PM PDT Tue Sep 19 2017

.SYNOPSIS...
Showers and cooler temperatures will persist through
Thursday due to an unseasonably cold upper level low. High
pressure will rebuild this weekend leading to a warming and drying
trend into the early portion of next week.

&&

.DISCUSSION...
Rain will start to increase again late this afternoon into this
evening as a frontal system moves toward the north coast. We will
see a period of gusty southerly winds in advance of the front this
evening, primarily over the ridges and coastal headlands,
followed by a rapid shift to the northwest early Wednesday. The
southerly downslope flow in the lee of the King range may delay
the arrival of rain for the Eureka area. The high resolution
models capture the lee side drying the best.

The front will move across the area overnight through early
Wednesday morning and provide a period of moderate to heavy rain.
Totals of a quarter to half an inch are expected for Del Norte and
Humboldt counties. The west slopes and higher elevations will no
doubt see greater quantities due to the enhancement from
topography. A few hundredths to tenth or two will be possible for
Mendocino and Trinity counties.

Cold air aloft and greater instability will follow behind the
front on Wednesday. On and off showers will probably continue
through the day on Wednesday for Del Norte and Humboldt counties
as a post frontal trough embedded in NW flow approaches the north
coast. The potential for low topped convection will increase by
Wed evening with 500mb temperatures plummeting to -25C over the
coastal waters. The upper trough will dig SW and away from land
during this time frame and prevent thunderstorms from reaching the
coast.

Colder and drier air will settle over the area on Thu. There will
be a threat for morning frost in the interior valleys. The
greatest threat will be across Trinity county, however some spots
in northern and eastern Mendocino county may also see early
morning frost. The threat for early morning frost in the valleys
will continue on Fri and perhaps into Sat even as the air warms
aloft.

The chance for showers will continue on Thu. The models were still
not in agreement. The NAM12 and GFS dry us out, while the ECMWF
continues to indicate the potential for showers. There will
probably be a fair amount of cumulus with daytime heating thanks
to the cold air aloft. Thus, a few terrain driven showers may
sprout up over the mountains. The cold weather will moderate this
weekend as high pressure builds back over our region. An offshore
flow will result in a warming and drying trend this weekend that
will last into the early portion of next week.

&&

.AVIATION...
Local aviation sites remain under the influence of an Upper Level
Low which has ushered in cloudy and wet conditions. An associated
frontal system tonight, which may be a little more impactful, will
continue to advect a multi-layer blend of clouds across the North
Coast and northern interior areas. Cigs will stay VFR with spotty
MVFR through the afternoon with occasional light sprinkles.  A warm
front will proceed the cold front this evening, so therefore
rain/showers amounts will increase overnight and cigs will lower.
ACV & CEC can expect IFR-LIFR Cigs/Vis overnight...while UKI may see
MVFR cigs in the morning.

&&

.MARINE...
Buoy observations this afternoon show a mix of rising and
falling wave heights as one of the first large swells of the season
moves through the region. Majority of the buoys north of Cape
Mendocino are reporting wave heights of 11 to 13 feet at roughly 14
seconds with buoy 22 being the only site reporting an increase in
wave height. South of Cape Mendocino buoy 14 is reporting building
waves, however; all sites should start to will be seeing throughout
the rest of the week. Small Craft Advisories will remain in effect
for these conditions, but may still need to be adjusted if they fall
below criteria earlier than expected. Winds during this time frame
will remain moderate during this time frame, however; they`re
currently blowing from the south and will turn back to the north-
northwest over the next 24 hours. We will then experience
increasing northerly winds later this week as high pressure builds
offshore. /KR/KML

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through Wednesday evening for
     CAZ101-103-104-109.

NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until 3 AM PDT
     Friday for PZZ450-455-470- 475.

&&

$$

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