089
FXUS66 KMFR 090342
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
842 PM PDT Wed May 8 2024

Updated MARINE Section

.DISCUSSION...Satellite imagery is showing mostly clear skies
across southern Oregon and northern California. This is due to the
ridge of high pressure that is the dominant feature of our
weather. Temperatures will be warmer than last night, so freezes
are still not anticipated. Please see the previous discussion
below for more details on the forecast. -Schaaf

&&

.MARINE...Updated 840 PM Wednesday, May 8, 2024...Northerly gales
south of Cape Blanco along with steep to very steep seas will
persist overnight. The thermal trough will weaken Thursday and
Thursday night, with conditions subsiding somewhat. Even so, steep
to very steep seas and gusty north winds will continue to bring
hazardous conditions. Lighter winds and calmer seas are expected
Friday into the weekend. -Spilde


&&

.PREV DISCUSSION... /Issued 433 PM PDT Wed May 8 2024/

SHORT TERM...through Saturday night...Aside from some fair
weather cumulus over eastern Lake County, skies are clear across
the region. Temperatures are running about 5 to 10 degrees warmer
than this time yesterday, and this is the start of a sharp warming
trend expected through the weekend. Today is a transition day as
the pattern changes from a cool, showery spring pattern to one
that is very common during the summer. High pressure aloft is
strengthening over the eastern Pacific and will gradually nudge
inland over the Pacific Northwest tonight into the weekend.
Meanwhile, at the surface, a thermal trough is strengthening along
the coast, bringing gusty north to northeast winds across the
region. These two features will be the dominant weather drivers
through much of the weekend before the upper level ridge briefly
weakens late weekend into early next week.

After a day of near normal temperatures today, afternoon highs will
jump by another 10 to 15 degrees on Thursday as upper level ridging
extends north and east into the Pacific Northwest. Additionally,
with the thermal trough lingering through the remainder of the week
and into the weekend, expect east to northeast winds to persist. The
upper level trough that passed over the area earlier in the week
will retrograde, moving back to the west and setting up over the
Great Basin, just south of the ridge, creating east winds aloft that
will enhance and align with the east winds at the surface. All of
this will result in very warm temperatures through the end of the
week and into the first part of the weekend. As a result, a strong
Chetco effect is forecast for the southern coast near Brookings.

The Chetco Effect will peak on Thursday, with highs in Brookings
expected to reach the 80s (and a few models even suggest 90 degrees
is possible) Thursday afternoon and perhaps Friday as well. When the
thermal moves inland on Friday into Saturday, the south coast will
begin to cool as the marine layer regains control, while
temperatures for most inland areas will reach their warmest Friday
afternoon and Saturday afternoon. Friday afternoon looks to be the
hottest places like North Bend and Roseburg. The upper level high
will take a west/east orientation and this pattern typically results
in hot temperatures for those locations with slightly cooler
temperatures elsewhere.

Another hot day is expected Saturday as the thermal trough shifts
farther inland, though temperatures along the coast will cool by
several degrees. High temperatures over the next few days will be
more in line with early July than early May, with highs 10 to 20
degrees above normal for this time of year.

Heat Risk values do show some moderate impacts possible for those
sensitive to heat both Friday and Saturday for valleys west of the
Cascades. We aren`t too far from when the typical first 90 degree
day of the year occurs in Medford (May 20th), and we do expect
temperatures to adequately cool during the overnight hours, so any
impacts should be brief. It should be noted though that this is the
first sharp warm up of the year and most of us aren`t acclimated to
these temperatures. So take it easy if working/recreating outdoors
over the next few days. If you plan to seek relief in the area`s
waterways, remember that these water sources are fed by snowmelt
and the water is COLD. Wear a life jacket and take frequent breaks
from the cold water to warm up. Don`t forget about pets...they need
shade and water too, and please please never leave children
unattended in a closed vehicle!! /BR-y

LONG TERM...(Sunday through Wednesday)...Dry and warm
weather is expected to continue through the forecast period. The one
day that may be in question will be Sunday afternoon and early
evening for portions of northern Cal. Sunday, very weak upper
troughing will set up over the area. The forcing is pretty weak. The
operational GFS shows a stronger trigger which could be enough to
warrant a slight chance of thunderstorms in northern California mid
to late Sunday afternoon and early Sunday evening. However, the
majority of the individual GFS ensemble members don`t show anything.
The troughing while weak is a little more pronounced in the
operational ECMWF, but there is no trigger. The ECMWF individual
ensembles show several members hint at something. Therefore we`ll
keep a light chance of storms in for Sunday afternoon and early
Sunday evening.

Monday, a drier stable northwest flow sets up with the mean ridge
west of the forecast area. There could be some building cumulus
around and east of Mount Shasta Monday afternoon and evening, but
mid level moisture is lacking and the pattern is not one which is
favorable for thunderstorms. The pressure gradient will be tighter
resulting in gusty afternoon and early evening breezes east of the
Cascades and Modoc County. The thermal trough will be along the
coast in the morning with breezy east winds at the mid slopes and
ridges for the coastal mountains in southwest Oregon.

Tuesday through Wednesday will be dry, with the ridge centered
offshore. Temperatures will still be above normal, but not as warm
as what we are expecting later this week into this weekend.
-Petrucelli

AVIATION...09/00Z TAFs...Expect VFR to prevail through Thursday.
Gusty north to northeast winds will occur this evening, gusting up
to 20 to 25 kt inland and around 30 kt at North Bend, easing during
the mid-late evening. Expect gusty NNE breezes again Thursday
afternoon, but slightly lower than today, generally in the 15-25 kt
range. -Spilde

MARINE...Updated 200 PM Wednesday, May 8, 2024...A strong thermal
trough will persist through tonight. This will result in moderate
to strong winds, with winds strongest south of Cape Blanco with
gales and very steep seas. Winds will increase north of Cape Blanco
later this afternoon into tonight. Wind speeds should remain on the
high end of Small Craft, however very steep wind driven seas will
result in Hazardous Seas Warning conditions for the all of the
northern waters. The thermal trough will weaken Thursday and
Thursday night, but lingering gusty winds and steep to very steep
seas are expected. Lighter winds and seas expected Friday into the
weekend. -CC

&&

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

PACIFIC COASTAL WATERS...Gale Warning until 5 AM PDT Thursday for
     PZZ356-376.

Small Craft Advisory from 5 AM to 2 PM PDT Thursday for PZZ350-
     356-370.

     Hazardous Seas Warning until 5 AM PDT Thursday for PZZ350-370.

     Hazardous Seas Warning from 5 AM to 2 PM PDT Thursday for
     PZZ376.

&&

$$