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000
FXUS66 KMFR 121148
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
448 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...12/06Z TAFs...A weak cold front has started to move
onshore, bringing light rain/drizzle and lower ceilings to coastal
areas. These lower ceilings/light rain will spread into the coast
ranges and into the western Umpqua River Valley through the
overnight, but will stop short of the Rogue Valley/Medford and areas
eastwards. VFR is expected to continue in these areas.

The character of precipitation changes Friday afternoon as the low
pressure follows the front and the atmosphere becomes more
convective. Precipitation will move into the area in waves as the
low spins southeast-wards. Scattered showers are most likely near
and west of the Cascades, but also over portions of the east side
(especially from the Warner Mtns in eastern Modoc County northward
into Lake County). There is also a slight chance (~20%) of
thunderstorms. In between those areas, there will be a relative
minimum in shower potential (though not zero). More gusty winds out
of the south are expected over and eastwards of the Cascades late
Friday afternoon into the evening. -Spilde/CSP

&&

.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.

&&

$$