Weather Service Report


110 
FXUS66 KEKA 192208
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
208 PM PST Sun Nov 19 2017

.SYNOPSIS...Rain will spread inland tonight, and then increase in
intensity during Monday. Rain will become light by Tuesday. 
However, the potential for wet and unsettled weather will likely 
continue through late week.

&&

.DISCUSSION...Latest satellite imagery and model guidance shows a
longwave trough extending southwest from NWRN Canada toward
Hawaii. An atmospheric river, characterized by PWAT values from
1.5 to 2.5 inches, and very high freezing levels (at or above
10000 feet), was observed spreading northeast from the tropics 
toward the Pacific Northwest region. Short term model trends 
indicate the anomalously moist airmass will become collocated with
a zone of increasing WAA/isentropic upglide over NWRN CA tonight,
resulting in the development of rain. By midday Monday, rainfall 
rates are forecast to rapidly increase as intense westerly 
moisture flux encounters the coast mountains. The zone of strong 
moisture flux is forecast to shift northward with time, eventually
exiting across Oregon by late Monday night. Once that happens, 
rain will become light over NW CA.

After Monday night, the atmospheric river (AR) will take aim on 
Oregon and Washington, leaving NRN CA mainly dry Tuesday.
Thereafter, remnants of the AR may impact the EKA CWA during 
Wednesday and Thursday, resulting in another period of rain. By
late week (Saturday/Sunday), model guidance shows a surface
cyclone ejecting northeast toward the west coast, which would
increase the potential for rainfall once again.

&&

.AVIATION...High clouds in advance of the next system have moved 
over all terminals and these ceilings will continue to lower 
through the afternoon and evening. Strong winds aloft will also 
lead to low level wind shear concerns later this afternoon and 
persist through tomorrow for ACV and CEC. Light rain will begin 
for all terminals tonight and gradually pick up in intense through
the early morning hours. Periods of heavy rain tomorrow will lead
to reduced visibilities at all three terminals. However, these 
conditions will be more prevalent for ACV and CEC. With the clouds
and rain ground fog will not be able to form tonight as has been 
the case the past few days. /WCI

&&

.MARINE...Southerly winds gusting to near gale force are expected
over the northern outer waters tonight into Monday, with solid
small craft southerlies expected over the remainder of the coastal
waters. The increase in wind speeds will generate steep seas, and
when combined with a west-northwesterly swell, will yield a 
confused sea state. Southerly winds and steep seas will continue
through mid week, followed by weaker winds and lower seas during
late week.

&&

.HYDROLOGY...Heavy rainfall appears probable across much of
Humboldt, Del Norte, and possibly Trinity county during Monday. 
Light rain is forecast to spread across northwest California 
Sunday night, and then dramatically increase in intensity by late 
Monday morning. Average rainfall totals are forecast to range from
1-2 inches over coastal plains and interior valleys...with higher
totals upwards of 2-5 inches probable over the windward side of 
mountains and ridges. However, latest high resolution model 
guidance shows localized extreme rainfall totals of 6-10 inches 
Sunday night through Monday night over west facing terrain. Given
moderate rainfall totals are very probable, and extreme rainfall 
totals showing up in the tail of potentiality, a flood watch has 
been issued for all of Humboldt, Del Norte, and Trinity counties 
(excluding coastal plains). Small stream/localized urban flooding
and rock/mud slides will be the primary impacts associated with 
areas of heavy rain.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch from 10 PM PST this evening through Monday evening 
     for CAZ102-104>108.

NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory from 4
     PM this afternoon to 4 PM PST Wednesday for PZZ470.

     Small Craft Advisory from 4 AM to 4 PM PST Monday for PZZ450-455.

     Small Craft Advisory from 11 PM this evening to 4 AM PST 
     Wednesday for PZZ475.

&&

$$

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Western Regional Climate Center, wrcc@dri.edu