Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 251607

Area Forecast Discussion
National Weather Service Medford OR
907 AM PDT Thu May 25 2017

.DISCUSSION...The latest visible image shows marine stratus
confined to parts of the Umpqua Basin, just south of Roseburg and
portions of the Coquille Basin. This will burn off fairly quickly
with clear to mostly clear skies the rest of the day. Meanwhile a
shortwave located in central Washington will move south during the
day and could bring enough instability for isolated showers north
of Crater Lake and thunderstorms in northeast Lake County later
this afternoon. Made a few adjustments to the sky cover this
morning and coverage for slight chance of thunderstorms this
afternoon for northeast Lake County. See previous discussion for
more details for Friday through the holiday weekend. -Petrucelli


.AVIATION...25/12Z TAF CYCLE...Along the coast and over the
coastal waters...MVFR cigs in marine stratus will affect
areas primarily from Cape Blanco northward. The coast will clear by
late this morning but the lower conditions will persist offshore
before moving back onshore Thursday evening. In the Umpqua
Valley...areas of MVFR cigs will clear to VFR by mid-morning
Thursday...then VFR conditions will prevail through Thursday night.
Over the rest of the area...VFR conditions will prevail through
Thursday night...but there may be some afternoon and evening showers
over the northern Cascades and afternoon and evening isolated
thunderstorms with gusty winds over Lake County.


.MARINE...Updated 800 AM Thursday 25 May 2017...North winds reached
a peak last evening but seas will remain steep to very steep through
tonight with the strongest winds south of Gold Beach and beyond 5 NM
from shore. Winds will drop below small craft advisory criteria by
Friday morning. Seas will be slower to subside...dropping below
small craft criteria by Friday afternoon. Light south winds will
develop along the Curry County coast Friday...spreading north of
Cape Blanco Friday night. This will bring low clouds and fog to the
waters. The thermal trough will redevelop Sunday into Monday with
moderate north winds returning.


.PREV DISCUSSION... /Issued 237 AM PDT Thu May 25 2017/

DISCUSSION...An upper level trough will be the main driver of
the weather across the area today. A short wave will dig south-
southeastward from western Washington this morning and move
through areas east of the Cascades in Oregon late this afternoon
and evening. Mid-level moisture is limited, however, model
guidance is now showing some instability near the Cascade Crest
north of Crater Lake and also over portions of northern/eastern
Lake County this afternoon into this evening. We should see at
least some cumulus buildups in these areas during this time frame.
Models also spit out some light precipitation beneath the upper
short wave between 2 pm and 11 pm. For these reasons, we have
added a slight chance of showers to the Cascades north of Crater
Lake and a slight chance of showers/thunderstorms from Fort Rock
southward to near Hart Mountain wildlife refuge. Guidance keeps
most of the moisture to the north and east of Lakeview. The rest
of the area will have another dry day. Low stratus in some areas
from the Umpqua Divide north and west through 8 or 9 am this
morning will burn off yielding sunshine. High temperatures today
will be very similar to what they were yesterday, but still about
5 degrees above normal. The thermal trough along the coast will
weaken, so winds at the beaches won`t be quite as strong as they
were yesterday. Still expect some gusty northwest breezes over the
East Side this afternoon.

Skies will become mainly clear across most of the CWA tonight,
but low clouds/fog will return to the coast north of Cape Blanco
and also near Brookings. The marine layer will be a bit shallower,
so it may have a bit tougher time reaching Roseburg.

The upper trough will shift to the east Friday with one last short
wave moving southward on the back side through south-central
Oregon. Once again, expect some buildups over the East Side, but
have kept the forecast dry for now. An upper ridge offshore will
strengthen and this will result in warmer weather, especially over
the west side. Expect highs (inland from the coast) to be about
5-10 degrees higher than today. East side areas will have highs
similar to or just a touch higher than today due to the influence
of the trough. A southerly surge of stratus is expected up the
coast as a coastally trapped wind reversal occurs. Stratus may
reach north of Cape Blanco by Friday evening.

By this weekend, the upper ridge will move into the West Coast and
set up over the Great Basin. This is a good set up for well above
average warmth over the CWA (high temps 15-20 degrees above
normal) and also gradually increasing moisture and instability.
We are carrying a slight chance of thunderstorms Sunday afternoon
in the mountains of northern California and up along the Cascades
with perhaps a bit better chance in those areas on Memorial Day
afternoon. Right now, though, it appears convective activity will
be isolated.

The very warm weather could last into Tuesday, then models are
showing a trough advancing toward the coast Wednesday into
Thursday with the potential for a cooling trend. -Spilde




Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT Friday for PZZ356-376.
     Small Craft Advisory for hazardous seas until 11 AM PDT Friday
     for PZZ350-356-370-376.
     Hazardous Seas Warning until 5 AM PDT Friday for PZZ356-376.

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