Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 230413
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
913 PM PDT Mon May 22 2017

.DISCUSSION...An update to the forecast is not necessary.
The weather on Tuesday will resemble that of today in many
respects. Low clouds and patchy morning fog are expected along
much of the coast into the Coquille Valley. Otherwise, there will
be a few high clouds in advance of an upper trough. High
temperatures were near record levels today and will be again on
Tuesday. Afternoon winds on Tuesday will once again be weaker than
normal.

The upper trough will pass by to the north on Wednesday with
high temperatures returning to near normal...generally about 15
degrees cooler inland than the day before. The very recently
arrived 00Z GFS continues to indicate weak instability over the
southern portions of Siskiyou and Modoc Counties Wednesday
afternoon and evening. But, the atmosphere will be quite dry above
about 650 MB. Thus, cumulus buildups are more likely than
thunderstorms but will maintain the mention of a slight chance.
Available moisture will be diminished Thursday afternoon and
Friday afternoon with weak instability shifting southeast out of
our area.

A weak disturbance arriving from the southwest will usher in a few
days of weak instability Saturday into next week with the best
chance of afternoon and evening thunderstorms currently indicated
for the Siskiyou and Cascade Mountains.

&&

.AVIATION...23/00Z TAF CYCLE...Low stratus and patchy fog is
expected to spread along the coast north of Brookings and into the
Coquille Valley after 05Z this evening then persist through
Tuesday morning. Coastal stratus will thicken again Tuesday
evening. Otherwise, VFR with mostly clear skies is expected across
the area through Tuesday evening. -DW

&&

.MARINE...Updated 800 PM PDT Monday, 22 May 2017...The thermal
trough pattern will strengthen with steep seas becoming very steep
and gales developing south of Cape Blanco on Tuesday morning.
Fog will continue to be an intermittent concern...mainly beyond a
few miles from shore during the night and morning hours. Gales
are expected to subside Thursday morning as the thermal trough
pattern weakens. But a steep fresh swell will then likely persist
into Thursday night. -Sven/DW

&&

.PREV DISCUSSION... /Issued 256 PM PDT Mon May 22 2017/

SHORT TERM...Today through Thursday...The ridge aloft has
strengthened and progressed eastward slightly. Temperatures in
many valleys west of the Cascades have already reached the
90s...including Medford...Merlin...Somes Bar...and Dunsmuir.
Temperatures will continue to warm over the next few hours.
Offshore winds along the coast will persist until late
tonight...then expect patchy fog in onshore flow along the coast
early tomorrow morning. Mostly clear skies will persist in areas
east of the Coastal Range tonight. Tomorrow will start out similar
to today...with patchy fog and low stratus along the coast
clearing in offshore flow mid to late morning...and highs across
the area again 10 to 20 degrees above normal with mostly clear
skies.

The ridge aloft will weaken Tuesday night into Wednesday morning as
a low passes over British Columbia and northern Washington. This
will bring onshore flow Wednesday...and highs Wednesday afternoon
should be 5 to 10 degrees above normal. As that low moves inland
over the northern Rockies, it will spin a few waves over the
PacNW, bringing increased cloud cover and gusty winds over the
east side Wednesday afternoon. Cool low level air should prevent
most thunderstorm development...however could not completely rule
out thunderstorms in Modoc County and eastern Siskiyou County.

Temperatures Thursday will be several degrees cooler than
Wednesday, as pressure aloft drops and onshore flow continues.
-MSC

Long Term...Friday through Monday...The ridge will regain control
of the area by Friday night, and this will produce another period of
warm and dry weather through the holiday weekend. There will be a
slight chance for daily afternoon thunderstorms, mainly along the
Cascades and in the mountains of Northern California through Monday,
but these will depend greatly on the presence of shortwaves within
the flow aloft. Any shortwave will be extremely hard to predict at
this time range, but the models suggest there could be some during
the weekend. With this in mind, have changed the timing and
placement of convection to more general terms, and only in those
locations where we typically see development. For most areas,
Memorial Day and the weekend should be warm and mostly clear with no
significant threat for rain. -BPN

AVIATION...22/18Z TAF CYCLE...VFR conditions across the area
will continue for the duration of the TAF period. A return of IFR
conditions is possible this evening and overnight near KOTH, but
is not expected. -BPN

MARINE....Updated 210 PM PDT Monday, 22 May 2017...The thermal
trough pattern will strengthen today with gales expected to begin
south of Cape Blanco Tuesday afternoon. Gales are expected to begin
for portions of the area north of the cape Tuesday night into
Wednesday. Fog will continue to be an intermittent concern...mainly
beyond a few miles from shore. Gales are currently expected to
subside Thursday morning as the thermal trough pattern weakens.
Sven

&&

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

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 11 AM PDT Thursday for
     PZZ350-356-370.
     Gale Warning from 5 AM Tuesday to 11 AM PDT Thursday for
     PZZ356-376.
     Hazardous Seas Warning from 5 AM Tuesday to 11 AM PDT Thursday
     for PZZ350-356-370-376.
     Small Craft Advisory until 5 AM PDT Tuesday for PZZ376.

$$

DW/MSC/SBN



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