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000
FXUS66 KMFR 231640
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
940 AM PDT Tue Apr 23 2024

.DISCUSSION...An update is not necessary. Instability will develop
this afternoon with the highest probability for thunderstorms
between 2 pm and 6 pm in Siskiyou and Modoc counties, extending
into southern portions of Klamath and Lake counties. The
northernmost extent of storms could extend to the Siskiyou
Mountains, and the Winter Rim area into northern Lake county.
This includes Fort Jones, Yreka, Weed, Mt. Shasta, Tennant, Lava
Beds, Alturas, and Lakeview.

There is some similarity in the scenario for tomorrow, with a
slight southeastward shift, with the highest probability for
afternoon thunderstorms in southeast Siskiyou into Modoc and
southeast Lake counties, including Alturas and Lakeview.

A change to a wet, cool/cold pattern occurs Thursday through
Friday night with a cold frontal passage on Thursday. The pattern
looks to remain active with additional episodes of wet weather
during the weekend through early next week.

&&

.AVIATION...23/12Z TAFs...VFR levels continue across much of
northern California and southern Oregon this morning. Marine stratus
is moving north along the Oregon coast, bringing IFR levels to Gold
Beach. Additionally, stratus may develop near North Bend, but will
only linger briefly this morning if it does. Marine stratus could
return on Wednesday morning.

Chances for showers (30-60%) and thunderstorms (20-40%) remain in
the forecast for Siskiyou and Modoc counties as well as southern
Klamath and Lake counties for this afternoon. The highest chances
for activity are over the California counties, and these chances
decrease quickly near the end of the TAF period. Isolated
thunderstorms may bring lightning and strong winds as well as
locally lower ceilings and visibilities. -TAD

&&

.MARINE...Updated 845 AM Tuesday, April 23, 2024...Elevated
northerly winds continue under a thermal trough. The strongest winds
remain south of Cape Blanco and beyond 10 nm from shore this
morning. Steep seas continue in all waters. The thermal trough will
weaken through the day, but a Small Craft Advisory will be in place
for all waters through 5 PM today, then will continue for waters
south of Cape Blanco until 8 PM.

Seas will remain calm through Wednesday and into Thursday morning
before active weather returns to the area. Westerly fresh swell and
gusty southerly winds could rebuild steep seas by late Thursday or
early Friday, especially in outer waters. However, current guidance
suggests that waves only have a 10-20% of exceeding 9 feet through
the weekend. So while steep seas are possible, more hazardous
conditions are not expected. -TAD/Hermansen

&&

.PREV DISCUSSION... /Issued 457 AM PDT Tue Apr 23 2024/

DISCUSSION...The upper level pattern will transition with low
pressure developing off the California coast and low pressure
pushing toward the British Columbia Coast. This will put our
region in southwest flow and some mid level moisture will move
into the area. This combined with some model indicated instability
(-2 to -4 LIs, 300-500 J/kg CAPE) is boosting confidence in
thunderstorm potential for today and Wednesday. Right now, today
looks to be the bigger day in terms of thunderstorm coverage. The
best chances (40%-70%) look to be over western Siskiyou County and
Modoc County with some potential (20%-40%) extending into the
southern portions of Jackson/Klamath/Lake Counties. Storm motion
will be from the southwest, but current thinking is that any
storms that develop over the Siskiyous would likely stay stuck on
the terrain and not really drift into the Rogue Valley...though
it`s not out of the question (10% chance) a storm skates by
Ashland Tuesday afternoon. The focus for storms on Wednesday
shifts farther east on Wednesday over eastern Siskiyou, Modoc and
southern Lake Counties and the trigger looks weaker for Wednesday,
so thunderstorm coverage looks less overall. For the remainder of
the area, conditions will remain dry, though expect an uptick in
afternoon winds and cloud cover with temperatures trending cooler.

The pattern turns cooler and wetter as we head into the extended
period.

Previous Extended Discussion (Thursday through Monday)...Generally
it will be cool and unsettled during the forecast period. A
stronger front will approach the coast Thursday morning, then
moving inland during the day. The bulk of the precipitation will
be along the coast, coastal mountains, Cascades and north of the
Umpqua Divide. The front will move east of the Cascades Thursday
afternoon with precipitation becoming scattered. Snow levels will
also lower to around 5500 feet along the Cascades late Thursday
afternoon and hover around that elevation Thursday night. This in
combination with a higher mid-late April sun angle, will put a cap
on snow concerns due to warm road surface temperatures, and
should be mainly confined to Crater Lake and Diamond Lake areas
Thursday night.

Upper troughing remain over the area Friday, although the upper
trough axis will shift east late Friday afternoon and we could see
showers gradually diminish in coverage.

The operational ECMWF and GFs show different solutions Saturday
with the GFS showing more ridging and a relative break in the
action. The ECMWF brings another upper trough and front into the
area Saturday morning. No surprise the majority of the respective
ensemble members also show varying solutions. Even taking the
operational GFS at face value the ridding is weak and with a weak
upper trough just offshore, but still hints at a progressive
pattern. Therefore we`ll keep showers and cool afternoon
temperatures in the forecast.

Upper troughiness remains over our area Sunday through Monday, and
possibly through the middle of next week which will result in cooler
temperatures and high chance for showers over a good portion of the
forecast area. -Petrucelli

&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory until 8 PM PDT this
     evening for PZZ350-356-370-376.

&&

$$