Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 221832
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1130 AM PDT Mon Apr 22 2019

The Aviation and Marine sections have been updated...

.DISCUSSION...Current satellite imagery are showing some clouds in
the valleys north of the Umpqua Divide and in the Coquille Basin
with some higher clouds moving overhead. This matches pretty well
the current forecast so no short-term changes are anticipated.
Will be taking a closer look at the thunderstorm chances for
tomorrow, as there are a lot of competing factors coming into
play. -Schaaf

&&

.AVIATION...For the 22/18Z TAFS...
After some morning low clouds and fog along and near the coast and
in the Umpqua Basin, skies have become mostly clear. Model guidance
is suggesting increasing mid-level cloudiness today lowering into
the lower levels over northwestern portions of the forecast area
this afternoon through Tuesday morning. However, satellite trends
indicate this increase in and lowering of cloudiness is likely
overdone. Therefore, TAFs have been written to reflect this lesser
than the model guidance cloud trend, especially for the daylight
hours today. We do expect cloud conditions to thicken and lower to
MVFR to IFR conditions along and near the coast later tonight into
Tuesday morning. BTL

&&

.MARINE...Updated 915 AM PDT Monday 22 April 2019...
Unfortunately, Buoy 27 went adrift this weekend, so it is no longer
available for observations. We are awaiting information about when
it will be redeployed. According to NDBC, Buoy 15 is expected to be
redeployed this August.

The thermal trough has weakened this morning resulting in less wind
and subsiding seas, according to our limited observation platforms
available, as well as model guidance. While winds and seas are
likely to nudge up again this afternoon and evening south of Cape
Blanco, conditions are expected to remain below advisory thresholds.
Based on this morning`s model guidance, the thermal trough is now
expected to re-strengthen Tuesday afternoon and evening bringing
moderate to strong north winds and steep to very steep Tuesday
evening all the way through this next weekend. BTL

&&

.PREV DISCUSSION... /Issued 444 AM PDT Mon Apr 22 2019/

SHORT TERM...

High pressure will build to it`s peak strength on Monday
afternoon. Latest satellite data shows it is already building this
morning as mid layer clouds are evaporating as the air sinks. It
should be a pretty nice day all things considered as temperatures
are about 10 to 15 degrees above average for this time of year.

On Tuesday, the forecast is pretty much the same with the
exception for a slight chance of thunderstorms mainly in northern
California and perhaps east of the Cascades as well. Some of the
deterministic model guidances such as the NAM and GFS show
potential instability in the aforementioned regions. If storms do
form it will be because of warm surface temperatures reaching the
convective temperature. There is really weak forcing in this type
of scenario with broad synoptic descent and perhaps some cold air
advection. In any case, we are really emphasizing the slight
chance for storms on Tuesday afternoon.

As for Wednesday, it`s essentially the same scenario as Tuesday
with a broad area of high pressure, but enough surface moisture
for a slight chance for storms in northern California. The latest
model run cycle appears to be targeting Siskiyou county, but this
could change with the 12z runs. Overall, pretty nice weather for
the next few days with this broad area of high pressure dominating
the weather pattern.

-Smith

LONG TERM.../Issued 229 PM PDT Sun Apr 21 2019/
Thursday through Sunday Night...

As we head into the extended term, the operational runs of the
ECMWF and GFS depict a large closed low to the south, just
offshore of southern California, and another large scale trough to
the north, over or just offshore of British Columbia. The
differences lie in where these lows go and how much influence one
or the other has on the local weather. The consensus of the
ensemble suites, if it can be said to have one, is that showers
and an isolated thunderstorm could kick off over northern
California or southern Lake and Klamath COunties Thursday and
Friday afternoons, and that some areas of precipitation could also
be possible late in the weekend along the Cascades and Warners.
Given our location stuck in between the two features as they
slowly make their way east (the driving flow should be weak due to
upstream blocking over the north central Pacific), and the
disconnect of the region from any significant moisture source, we
are otherwise very likely to stay dry through much of the term.
Meanwhile, temperatures will trend from above normal to very near
normal as the forecast term progresses.

-Nieuwenhuis

AVIATION...For the 22/12Z TAFS...At the coast and just
offshore...LIFR ceilings are being reported at Brookings and North
Bend. This is expected to continue for most of the morning. North
Bend could see saw back and forth from LIFR to VFR over the next
hour or two so added a tempo group in the TAF. The TAF at North Bend
shows improving ceilings at 18z, but improvement could an hour or so
on either side of 18z. Stratus is expected to develop again this
evening into Tuesday morning with IFR and local LIFR ceilings.

Stratus is also developing in the Coquille and portions of the
Umpqua basin. However Roseburg should remain VFR through the TAF
period.

Elsewhere...VFR conditions will persist through the TAF period.
-Petrucelli

MARINE...Updated 200 AM PDT Monday 22 April 2019...Offshore high
pressure and a thermal trough along the coast will continue to bring
gusty north winds and steep seas mainly south of Gold Beach this
morning. The thermal trough will weaken later this morning with
calmer conditions expected Monday afternoon through Tuesday
afternoon. The thermal trough will redevelop Tuesday evening
bringing another round of moderate to strong north winds with
possible gale force gusts and steep to very steep wind-driven seas
Wednesday into Wednesday evening. The trough will weaken once again
Wednesday night, and lighter winds and seas will prevail Thursday
into Friday. Increasing north winds will return again Friday night
into Saturday with gale force winds possible over the southern
waters.

-Petrucelli

&&

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

CA...None.

Pacific Coastal Waters...None.

$$



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