676
FXUS66 KMFR 100413
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
913 PM PDT Thu May 9 2024

.DISCUSSION...An update is not necessary this evening. With
easterly downslope winds, Brookings had a high of 85 this
afternoon. As is often the case, the current Chetco Effect
episode is expected to end with onshore westerly winds and a shift
inland of the thermal trough late Friday morning/early Friday
afternoon. Thus, Brookings will be cooler in the afternoon than in
the morning. Inland, the strong warming trend will continue into
Saturday on the west side and into Sunday for the east side.

The ridge will be kicked east by an approaching trough on Sunday.
We will await a full suite of new data to analyze for any possible
changes to make in the probability of late day thunderstorms. The
18Z GFS does continue to indicate weak instability and an increase
of mid-level moisture to accompany the trough with a slight chance
for portions of eastern Siskiyou, Modoc, Lake, and southern
portions of Klamath counties.


Ridging and a stabilizing of the air mass is expected for Monday
and Tuesday, with a cooling trend, but temperatures still above
normal. A change in the pattern is possible Wednesday with a near
even split in model solutions for the remainder of the week between
further warming and drying, or a continuation of a modest cooling
trend and perhaps some slight rain chances, with the best chance
for the coast, Douglas County, and northward.

&&

.AVIATION...10/00Z TAFs...VFR prevails throughout the TAF period.
Expect N-NE breezes along the coast and in the Umpqua Basin again
this afternoon, while broad mainly E-NE flow can be expected
elsewhere. Winds calm overnight, then breezy winds return Friday
afternoon, although winds should be weaker than those of today. -BPN

&&

.MARINE...Updated 830 PM Thursday, May 9, 2024...The thermal
trough is weakening, but gusty north winds and steep wind-driven
seas will continue through tonight. Lighter winds and calmer seas
are expected Friday into the weekend, then the thermal trough
returns next week. -BPN/Spilde

&&

.PREV DISCUSSION... /Issued 216 PM PDT Thu May 9 2024/

DISCUSSION...
Discussion...Satellite imagery shows clear skies over most of the
forecast area. A few cumulus clouds are moving east to west over
eastern Modoc and southeast Lake County, but that`s it. A rather
quiet pattern is in the cards for the next several days with
afternoon temperatures warming op over the next couple of days
followed by a slight cool down Sunday into early next week.

The latest surface analysis shows the thermal trough parked just off
the southwestern oregon coast. This has resulted in gusty east to
northeast winds at the mid slopes and ridges and also in the
Illinois Valley. The east winds will also be favorable for a Chetco
effect to set up with Brookings expected to warm up late this
afternoon. Currently it`s 76 degrees and could hit or get into the
lower 80s later this afternoon. The offshore flow is also resulting
warmer temperatures near North Bend where it`s currently 68 degrees.

Breezy east winds are also occurring east of the Cascades and this
is likely to continue into early this evening. Winds aloft (near
700mb) are also contributing to the east to northeast winds.

Tonight, winds will generally diminish, however it will remain
breezy near and and at the ridges for the coastal mountains in
southwest Oregon and western Siskiyou County. The continued offshore
flow will keep marine stratus at bay, so were expecting skies to
remain clear. However some of the deeper valleys for the coastal
counties could experience a brief period of low clouds towards
daybreak tomorrow. If anything were to develop, it`s only going to
last for a brief period of time.

Friday will be similar to today, except it will be warmer in the
afternoon for the interior westside valleys. The thermal trough will
shift inland over the interior westside valleys and this will lead
to lighter winds in the afternoon. Afternoon temperatures could push
90 degrees in portions of the Rogue and Illinois Valley, and Umpqua
Basin which will be the first time this season many of these areas
could get to 90 or just a hair above that.

Saturday will be dry and warm again for the interior. The thermal
trough will remain inland on Saturday and this will open up the door
for weak onshore flow near and at the coast and there`s enough
evidence to suggest marine stratus will make a return and/or form
along the coast and over the marine waters overnight Friday and
persist into Saturday, although it could peel back just off the
coast Saturday afternoon.

Saturday night will be dry with weak onshore flow bring solid layer
or marine stratus back along the coast and could make it`s way a bit
inland into portions of the Coquille Basin.

Most areas will be dry Sunday with slight cooling Sunday afternoon
for the interior. Some of the data suggest there could be enough
instability and trigger for a isolated storms to pop up late in the
afternoon and early evening in portions of northern California. The
operational GFS continues to be the most bullish with the extent of
the instability, while others not so much. The thermal trough will
shift east Sunday resulting in breezy afternoon winds for the
interior westside valleys and east of the Cascades.

The mean ridge remain offshore early next eek with a continued
northwest flow. However the latest operational ECMWF shows a
stronger upper trough moving into the area Monday which if correct
could bring enough instability and trigger for isolated
thunderstorms along and east of the Cascades Monday afternoon and
evening. However only 11 of 50 members of the ECMWF ensembles hint
at any convection, and the operational GFS and ensemble members show
a dry and stable solution. For now we`ll keep it dry Monday, but
we`ll continue to monitor this.

The upper ridge will remain west of the forecast area Tuesday and
Wednesday with a dry, stable west to northwest flow over our area
and temperatures above normal for most interior locations.

Thursday, there`s some indications the upper ridge will break down
as an upper trough moves towards the area, but it`s pretty much a
50/50 split between the cluster mean solutions and individual ECMWF
ensemble solutions. The individual GFS ensemble means show ridging.
-Petrucelli

&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory until 5 AM PDT Friday
     for PZZ350-356-370-376.

&&

$$