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000
FXUS66 KMFR 121801
AFDMFR

Area Forecast Discussion
1101 AM PDT Fri Apr 12 2024

...Updated AVIATION discussion...

.SHORT TERM...An upper low is moving south today off the Oregon
and northern California coast then will remain off the northern
California coast Saturday. This low will bring cooler and showery
weather along with chances for thunderstorms. There is chance for
strong gusty winds and hail with thunderstorms that develop today
or Saturday, especially from the Cascades east, and there is a
marginal risk (5%) for severe thunderstorms today over eastern
Lake County and over northern/eastern Klamath and norther/western
Lake counties on Saturday.

The main concerns today are where the band of showers will set up
and where thunderstorms will develop. Current radar shows a band
of light rain along the coast. Inland, there is band of weak radar
returns over eastern Siskiyou and Klamath counties but little or
no rain at this time. High resolution models show showers
increasing across much of the area late this morning and moreso,
this afternoon. East of the Cascades as well as over the Crater
Lake area, there is a chance for thunderstorms (20-30%) this
afternoon. Further west, this chance is lower (10-15%). Of
concern, there is marginal (2-5%) chance for severe storms with
strong winds and hail this afternoon in far eastern Lake County,
generally east of Lakeview and east of Silver Lake. This focus is
mainly from far eastern Lake county eastward/northeastward.
However, the NAMNest model indicates a potential for strong
storms slightly further west today, into western Lake and far
eastern Klamth Counties. So, we will be monitoring this closely
and updating as needed. The chance for strong thunderstorms for
eastern Lake county is mainly from 1pm through 7pm today.

Tonight, the focus for precipitation shifts to the coast and
northern California areas. However, precipitation will increase
in Saturday morning, mainly from the Cascades east and Siskiyous
south, then spread across most the area by afternoon. On
Saturday, models support a risk for thunderstorms across most
inland areas, 10-20% chance west of the Cascades and 20-35% chance
east of the Cascades. Additionally, across northern/eastern
Klamath and northern/western Lake counties Saturday
afternoon/evening, models show this area under the exit region of
an upper level jet and indicate sufficient CAPE and shear to
support a marginal risk (2-5%) for severe thunderstorms with
strong wind and hail possible.

Widespread precipitation continues Saturday evening into Sunday.
Snow levels will also lower from 5500-7500 feet Saturday down to
around 4000-5500 feet Saturday night and Sunday morning with
light to locally moderate snow expected in the mountains and down
to some valleys across eastern Siskiyou and Modoc counties.


&&

.AVIATION...12/18Z TAFs...Southerly flow aloft around a low pressure
center is bringing widespread cloud cover, although levels are
generally at VFR with occasional localized MVFR ceilings. Showery
activity is developing over elevated terrain and moving to the
north, with radar indicating showers over the Mount Shasta area, the
Cascades, and northern Klamath County. Precipitation chances remain
moderate (50-75%) east of the Cascades through the afternoon and
similar chances developing east of the Cascades this evening.

Elevated chances (15-30%) for thunderstorms remain in the forecast
for areas east of Cascades remain in the forecast, especially over
the Lake, Modoc, and eastern Klamath counties. Thee chances will
decrease quickly after sunset. Remote sensing has picked up some
isolated lightning strikes southeast of Redding, so the potential
does exist. Extra caution around developing activity is encouraged,
as strong winds or lower visibility as well as lightning may be
possible. -TAD


&&

.MARINE...Updated 830 AM Friday, April 12, 2024...Low
pressure will move southward offshore today. North winds will
gradually increase and become stronger, especially in the outer
waters and in the offshore waters beyond 60 nm from shore. This
combined with increasing northwest swell will bring hazardous
conditions over the outer waters, and especially beyond 10-30 NM
from shore tonight into Saturday.

North winds will persist over the waters Sunday through most of next
week, strongest during the afternoons and evenings and especially
south of Cape Blanco. Conditions there may be hazardous to small
craft at times due to the winds and steep seas. -Spilde

&&

.PREV DISCUSSION... /Issued 528 AM PDT Fri Apr 12 2024/

DISCUSSION...

A significant change in our weather is in store for
today through Sunday night. Low pressure offshore will approach
the area today then move into northern California this weekend.
This will result in cooler, breezy, and showery weather with a
slight chance to chance of thunderstorms. The probability of
thunderstorms will be highest during the afternoon and evening
hours, and in eastern Lake County (northeastward toward Burns) today,
northern Klamath County (into Deschutes County/toward Bend) on
Saturday, and Lake County northward on Sunday. Thunderstorms may
contain strong, gusty winds, hail and downpours. A colder air mass
moves in Saturday night with snow levels dropping to around 4000
to 5000 feet. It looks to dry out after the weekend with
temperatures trending back up to around normal.

The change in conditions will become more apparent this
afternoon, and especially Saturday afternoon with increases in
shower coverage, precipitation amounts, and the probability of
thunderstorms. For now, a front is skirting the coast with light
rain to continue there this morning. Conditions this afternoon
through tonight into Saturday morning will be generally be more
unsettled than wet for much of our area with showers likely to be
mostly light and focused upon the higher terrain.

With the upper low in closer proximity to northern California by
noon Saturday, showers and thunderstorms into Sunday are more
likely to produce a drenching rainfall. Snow levels will also drop
Saturday night, with the lowest snow levels around 4000 to 5000 feet
in northern California. The higher elevations will have the best
chance of accumulating snow, including Mt. Shasta and Cedar Pass
over the Warner Mountains in eastern Modoc County.

The previous long term discussion with additional details follows:

LONG TERM...Sunday through Thursday, April 14-18, 2024...The
cooler, active weather pattern will continue into Sunday across
southern Oregon and northern California. The upper level low
spinning near or just offshore of the San Francisco Bay area will
pivot inland by Sunday morning, eventually shifting into the Great
Basin during the late afternoon/evening. A colder air mass will
arrive and be in place Sunday morning across NorCal such that snow
levels will drop to 4000-4500 feet. This will allow remaining
precipitation to change to snow in some areas, especially SE
Siskiyou and Modoc counties. Given preceding mild weather, winter
impacts are expected to be mostly minor. Right now, most likely/
preliminary snow amounts by Sunday morning (11 am) look to be in the
1-3 inch range above 4500 feet in Siskiyou/Modoc, with some of the
higher passes, like Cedar Pass on Highway 299 east of Alturas
getting up to 6 inches. Other passes that may be impacted by wet
snow Sunday morning -- Highway 97 near Grass Lake, Highway 89 near
Snowman Summit/Pondosa and Highway 139 south of Tionesta to Adin.
The higher pass on Sawyers Bar road west of Etna could also see a
little snow accumulation, but I-5 should be OK.

Shower chances diminish (to 10-30%) during Sunday afternoon west
of the Cascades as heights begin to rise, but fairly high PoPs
(40-70%) linger over the East Side, where there is still a slight
chance (20%) of thunderstorms. Isolated showers probably linger
into Sunday evening over the far East Side due to the proximity of
the low. High temperatures Sunday will be at least a few degrees
below normal in most cases, but 10-15F below normal in NorCal.

There should be a break Sunday night through Monday night for most
areas, though onshore flow may bring just enough moisture in the 925-
850mb layer to squeeze out some sprinkles near the coast/western
Douglas County or sprinkles/flurries in eastern portions of Douglas
County. Other areas remain dry with temperatures moderating but
still remaining at least a few degrees below the seasonal norms
Monday afternoon. If skies remain mostly clear Monday night, low
temperatures could be in the low to mid 30s in the valleys west of
the Cascades.

The next upper trough will drop southward from western Canada into
the PacNW Tuesday resulting in a bout of gusty NW winds (not too
unusual though). While we expect an increase in PoPs, shower chances
are highest across the north (in Oregon) and near the Cascades (30-
50%). Snow levels near or even a bit below 2500 feet Tuesday morning
will rise to 3500 feet or higher Tuesday afternoon. This will bring
a reinforcing shot of cooler air with another cold night expected
Tuesday night.

Broad upper troughing will linger over the area Wednesday into
Thursday. While there is a chance (15-30%) of showers each
afternoon/evening due to instability, moisture is lacking so much of
the time/area will be dry. Best chance of showers will be in the
mountains. Temperatures should return closer to normal. -Spilde

AVIATION...12/12Z TAFs...MVFR ceilings are likely closer to the
coast this morning as a weak front moves in.  Light rain is likely,
and it is currently being observed on radar right now.

By the afternoon hours, scattered to widespread showers are likely
across the forecast region with some thunderstorms east of the
Cascades. These showers will have VFR ceilings given the depth of
mixing in the afternoon hours.  Some of the thunderstorms that form
could be strong with gusty winds and small hail as a threat.  By the
late evening and overnight hours, the storm threat will diminish and
some MVFR ceilings are possible over a few of the TAF sites with
LIFR ceilings closer to the coast.

-Smith

MARINE...Updated 330 AM Friday, April 12, 2024...Relatively calm
seas and winds will continue through Friday morning. Eventually,
winds will increase by Friday evening, with stronger, gusty
northerly winds in the offshore waters, beyond 60 nm from shore.

As a low moves inland into central California, these stronger north
winds are likely to move into the coastal waters late tonight, with
the strongest in the outer waters, and persist through the weekend.
Hazardous conditions are likely to return later tonight as gusty
north winds build steep wind-driven seas through the weekend, with
areas of very steep seas beyond 40-50 NM from shore or so. A small
craft advisory for these conditions begins late Friday afternoon.

These pesky north winds will remain in place for most of next week.
Seas could be high and steep at times, especially in the southern
waters around Brookings.

-Smith/CSP

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory from 5 PM this
     afternoon to 5 PM PDT Saturday for PZZ370-376.

&&

$$

CC/CC/CC