Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 240219

Area Forecast Discussion
National Weather Service Eureka CA
719 PM PDT MON MAY 23 2016

.SYNOPSIS...An upper level low will bring a chance of showers and
thunderstorms to interior Northwest California on Tuesday. High
pressure will produce a warming and drying trend across the
interior Wednesday through Friday.


.AVIATION...UPDATE...stratus has started to spread across the
coastal areas this evening bringing IFR conditions to some of the
area. Expected this will continue to expand as the evening goes on
and eventually spread across most of the coastal areas. MKK



SYNOPSIS...An upper level low will bring a chance of showers and
thunderstorms to interior Northwest California on Tuesday. High
pressure will produce a warming and drying trend across the
interior Wednesday through Friday.


SHORT-TERM (Tonight through Thursday Night)...

Showers have been developing over the interior mountains of
Northwest California this afternoon. Convective parameters were
marginal at best for thunderstorms. BUFKIT profiles do show lifted
indices near -1C and CAPE values of 500J/KG. An isolated
lightning strike will be possible late this afternoon before the
convective activity ends with the loss of daytime heating.

Instability will increase again on Tuesday across the interior as
an upper level low heads southward toward Central California.
Light mid-level easterly flow is a favorable pattern for storms
in eastern portions of Humboldt and Mendocino counties. The
highest instability will be over Trinity county where BUFKIT
profiles indicate lifted indices around -2C and surface based CAPE
around 800J/KG during peak heating. Main impact will be cloud to
ground lightning strikes...locally heavy rain and small hail.

The storm activity will die off Tuesday night after the loss of
daytime heating. A ridge aloft will start to build closer to the
North Coast Tuesday night and Wednesday. The warming aloft and
mid level drying will limit the threat for more deep convection on
Wednesday. The nam12 continues to indicate weak instability over
eastern Trinity and Mendocino counties during the afternoon hours
on Wednesday. Considering the large scale subsidence assoiated
with the building ridge, the nam12 may be overdone. Thunderstorm
chances look minimal at this point and for now we will just
maintain a chance of showers across the eastern portion of our
forecast area.

Coastal areas will most likely remain mostly dry with only
patches of morning drrizle for the next day or so. A few showers
may occur in the wrap around easterly flow along the Mendocino
on Tuesday as well. Northerly flow over the coastal waters will
most likely keep coastal areas in a stratus regime on Wednesday
and Thursday. The timing of the stratus is not certain and
Tuesday may end being another partly cloudy to mostly sunny day
along the North Coast.

Temperatures in the interior will continue to trend upward on
Thursday after 5 days in a row of below normal temperatures. We
nudged high temperatures into the mid and upper 70s which is very
close to climatological normals. A few inland sites such as Ukiah
may reach the lower 80s. Unfortunately, the North Coast will
probably by under a layer of low overcast with high temperatures
only in the lower 60s. It does not look like a completely gray and
gloomy day though. The brisk northerly flow should gradually mix
out the low clouds by afternoon or evening.

LONG-TERM (Friday through Monday)...

Drier and warmer weather anticipated for the long term forecast
period from Friday through Monday. The long term forecast period
will start with a high anchored over Eastern Pacific into Gulf of
Alaska. This will create generate NW-ly flow across NW California,
and this will bring in drier air across the area. The ridge will
remain in place through Monday. Right now, doesn`t seem like there
are too many disturbances embedded in this general NW flow. With
daytime heating, do expect high temperatures to get into the 70s
inland, and 60s inland.

Forecast confidence is slightly above average. Models are performing
fairly well in this weather pattern. General northwesterly flow over
NW California should persist through the long term forecast period.
However, ECMWF and GFS models have some disagreements in the
intensity and placement of individual short wave troughs dropping in
from the northwest.

AVIATION...VFR Conditions on this Monday. This morning, mostly
sunny skies prevailed over Arcata airport. Mostly clear skies were
common along the Northwest California coast, while convection is
building over the Coast Mountains. These afternoon convections
should spread into the coastal area by this evening. Expect low to
mid- level stratus cloud deck to return to return to Crescent City
and Arcata. Low clouds and fog shouldn`t be a concern tonight. Do
expect VFR continue through the next 24 hours. /RCL

MARINE...A weak pressure gradient will maintain the current
light winds and low to moderate seas across the waters tonight and
Tuesday. High pressure will build over the NW Pacific as warming
inland deepens low pressure over CA from mid-week through this
weekend. the resulting pressure gradients will bring strong winds
and building short period seas over the NW CA waters as the week
progresses. /ST




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