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000
FXUS66 KMFR 231001
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
301 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

&&

.AVIATION...23/06Z TAFs...Other than some high clouds, conditions
remain VFR area wide late this evening. This will continue overnight
into Tuesday for most areas.

Hi-res models/soundings are showing a southerly surge of
stratus/lower ceilings and also some fog reaching the SW coast,
including Brookings ~12z, then up to around Gold Beach (Port
Orford?) by around 18z Tuesday morning. This could result in coastal
IFR/LIFR and also over the marine waters off Pt. St. George out to
about 30 NM from shore. Soundings also show a low-level moist layer
pushing into the Coquille Basin/North Bend area Tuesday morning
(around 14z), so have maintained a few hours of IFR ceiling in KOTH,
though confidence in this occurring is low to moderate.

Inland, Tuesday remains VFR, though cumulus buildups are expected to
develop in the afternoon/evening roughly south and east of a line
from the Oregon Siskiyou Mountains to Lake of the Woods (probably
southeast of Medford) to Winter Rim. In these areas, there can be
isolated to scattered showers and thunderstorms. Highest thunder
probabilities (25-40%) are in NorCal. And, given a very dry sub-
cloud layer, some stronger cells could produce gusty winds.

IFR/MVFR ceilings may return to the coast Tuesday evening. -Spilde

&&

.MARINE...Updated 200 AM Tuesday, April 23, 2024...Elevated
northerly winds continue under a thermal trough. Early this morning,
the strongest winds remain south of Cape Blanco and beyond 10 nm
from shore. Very steep and hazardous seas will continue in this area
early this morning, with steep seas in all other waters. The thermal
trough will weaken through the day, but steep seas will remain. A
Small Craft Advisory will be in place for all waters from 5 AM
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

&&

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

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

Hazardous Seas Warning until 5 AM PDT early this morning for
     PZZ376.

&&

$$

SBN/SBN/SBN