Mad River, California Weather Forecast Discussion

510
FXUS66 KEKA 090834
AFDEKA
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
134 AM PDT Tue Sep 9 2025
.SYNOPSIS...Periods of rain and thunderstorms are forecast to
continue today through Wednesday. Locally heavy rain will be
possible with storms in the interior each day. Drier weather will
be possible toward the end of the week, followed by another
chance of rain during the weekend.
&&
.DISCUSSION...
A cool mid-level cyclonic circulation offshore will continue to
generate widespread periodic light to moderate rain today through
Wednesday. Cool air aloft around -16C at 500mb, steep mid level
lapse rates and PWATS in excess of 200% of normal will be
sufficient for development of deep moist convection and locally
heavy rain in the interior with daytime heating today. HREF
guidance indicates 30-50% probabilities for rain rates over
0.50in/hr with isolated convective cells. A few of the CAMS
indicate hourly rain rates near 1 inch an hour. There is very low
risk (5% chance) for debris flow on recent burn scars with high
severity.
The cool mid level low will slowly move across the forecast area
on Wednesday. Once again more deep moist convection and locally
heavy downpours are probable over the interior. The main threat,
other than cloud-to-ground lightning strikes, will once again be
heavy rain rates and possible localized flooding of low lying
areas and ponding of water on roads. A shortwave trough rotating
around the weeble-wobble low will lend support for perhaps
stronger convection and heavy rain rates over 0.50in/hr.
This upper trough/closed low complex will finally begin to edge
eastward into the northern Great Basin on Thu. GFS and ECMWF models
continue to indicate wrap around precip and sufficient instability
for a low threat (10-20% chance) for thunderstorms across Trinity,
NE Mendocino and northern Lake.
Drier and warmer weather conditions are anticipated for Friday as
a 500mb ridge axis builds over the area and the mid level low
departs into the northern Great Basin. ECMWF does show another
perturbation pin-wheeling around on the backside of the low on
Friday with low shower potential for Trinity County. Otherwise,
the rest of the area should enjoy dry weather. After multiple
days of rain in the interior, expect a fair amount of valley
fog and low clouds on Friday.
The dry weather may not last long as another splitting trough
approaches the Northern California coast by Saturday. Rain chances
will increase Sat into Sun, however the timing, duration and
amounts of rain remain highly uncertain. Models continue indicate
rising 500mb heights and warming/drying early next week, Mon and
Tue. There are subtle signs of another trough coming down the pike
and perhaps more rain early next week.
&&
.AVIATION...
(06Z TAFs)...MVFR ceilings are expected along the coast early
Tuesday morning as showers begin to diminish. Southerly flow will
slowly transition to more northwesterly flow into Tuesday afternoon.
There is a probability that ceilings could drop to IFR/LIFR for
coastal terminals by late Tuesday evening. Showers will continue
for interior Mendocino and Trinity counties into very early
Tuesday with MVFR ceilings continuing until mid to late morning
with ceilings lifting to VFR conditions by the afternoon.
&&
.MARINE...
Into Tuesday, southerly winds will become variable as the low
pressure crosses the coastal waters. Winds are expected to remain
fairly light, with up to 10 to 15 kt winds as it moves through.
Through Tuesday morning, isolated to scattered showers and
thunderstorms are expected to move through. Some of these could
produce wind gusts of over 30 kt. The wind driven waves have
picked up with the southerly winds and are around 4 feet. The
swell currently is fairly small. There is a 1 to 2 foot southerly
wave at around 14 seconds and a 1 to 2 foot northwesterly wave.
The wind driven waves are expected to diminish into Tuesday
morning following the winds.
Wednesday, the low starts to move onto the coast and at some point
during the day northerly winds are forecast to pick up. The models
are not in great agreement on how quickly this will happen but once
they do, the 10 to 20 kt northerly winds are expected to continue
through the work week. The strongest winds are expected to be in the
southerly waters. Another weather system is expected to approach the
area on Saturday and bring a return to southerly winds. Again there
is still quite a bit of uncertainty on the strength and timing of
this. Also, early on Wednesday a northwest wave around 13 seconds
will build into the waters at around 2 to 3 feet and continue
through Thursday. A 16 second southerly wave is also expected to
build into the waters on Wednesday to around 2 feet. This is
forecast to continue several days with the period gradually
diminishing. MKK
&&
.FIRE WEATHER...
Cooler temperatures, higher relative humidity, and a chance for
wetting rain (0.10 inches) are expected to continue today through
Wednesday. Locally heavy rain with thunderstorms is expected this
afternoon and evening and again on Wednesday. Thus, there is a
a low threat for debris flow on recent burn scars. This threat
will decrease on Thursday. Warming and drying is expected on
Friday, however there will likely be considerable low level
moisture, fog and low clouds, trapped in the valleys during the
morning hours. Another trough or cut-off low will likely bring
cooling and more showers next weekend. Gusty northwest and
westerly breezes are expected just about every day this week in
the valleys of southern Mendocino and southern Lake. Southern
Mendo and Lake are on average the driest this time of year and may
not get any rain at all this week.
&&
.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
None.
&&
$$
NOTE: The full forecast discussion is now regularly issued between
10 am/pm and 1 pm/am. Additional updates will be issued as needed.
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NWS EKA Office Area Forecast Discussion