Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 222136 CCA
AFDMFR

Area Forecast Discussion...CORRECTED
National Weather Service Medford OR
236 PM PDT Sun Apr 22 2018

.Corrected Long term Discussion.

.DISCUSSION...Skies will remain clear through this evening over most
of not the entire forecast area. Could not rule out low topped
cumulus in eastern Lake and Modoc County late this afternoon as a
weak upper trough moves east of the Cascades, but that`s it.

The story over the next few days will be a rapid warm up starting
tomorrow and lasting through Wednesday with the warmest max
temperatures so far this season. In fact we could see max
temperatures ranging between 15-20 degrees above normal Tuesday and
Wednesday!

The thermal through will remain along or just off the coast tonight
with moderate east to northeast winds over the higher terrain in
Curry and portions of Josephine County. The thermal trough is then
expected to build north during the day Monday with offshore starting
to weaken and switch onshore over the south coast, including
Brookings, but it may not happen until late in the afternoon, so we
could still see temperatures there flirt with 80 degrees.

There`s good agreement we`ll have a coastal reversal Monday night
through Tuesday and we could see a surge of marine stratus moving
from south to north along the coast. The exact timing of when this
will happen varies, but it`s possible it could get all the way up to
Port Orford by daybreak Tuesday.

Meanwhile dry and very warm weather will continue for many inland
locations as the thermal trough shifts inland over the west side
valleys. Similar weather is likely to continue Wednesday with
slightly higher 850 mb temperatures. Wednesday should be the warmest
day of the forecast period with a few of the typical spots getting
close to 90 in the Rogue Valley, mid 80s in the Umpqua Basin, and
upper 70s to near 80 degrees east of the Cascades.

The other item of note is the location of the upper low that will be
lurking offshore Tuesday through Wednesday. The models still show
different solutions with the position of the low. The ECMWF is
further offshore compared to the GFS and Canadian. However none show
any obvious signs of instability ahead of the upper low, so we`ll
keep it dry through Wednesday afternoon. The GFS suggest a few
showers could develop and move through Curry and western Josephine
County Wednesday night, but it also has the upper low closer to the
coast. So left in the slight chance of showers for Curry and western
Josephine county. -Petrucelli

.LONG TERM...Thursday through Sunday...An upper low approaching from
the west will probably begin to cool us down and bring a chance for
precipitation Thursday. I say probably, because while the models all
agree on the existence of this low, there is a lot of difference in
the position and movement the low in the deterministic models. For
example, by Thursday afternoon, the GFS has the center of the low
approximately 300 miles closer to us than the European model.

While there are also differences between the various model
ensembles, they are not as extreme. That said, ensembles from both
the GFS and European do show a fair amount of spread, and most of
this spread is on the continental side of the low, and this seems to
indicate that the deviant members tend to be closer to us than the
mean (although this is very hard to see in the spaghetti plot). In
other words, there is some support for the closer operational GFS
solution. Needless to say, confidence in the evolution of this low
is not high. As a result, I haven`t made any extreme changes to the
extended forecast, but rather just simply nudged everything toward
the general model consensus.

While confidence in the details isn`t very high early on in the
extended, I think we can say with high confidence that the low will
move in Friday and over the weekend, and that this will result in
much lower temperatures than in the short term as well as lower snow
levels and a good chance for showers. We may also see some
thunderstorm activity, although this is complicated by snow cover in
the mountains (which dramatically lowers surface-based instability).
The most promising day for thunderstorms looks like Friday, since
upper dynamics are the greatest. For the remainder of the weekend,
thunderstorm chances are focused on the east side where there is
little to no snow cover remaining. -Wright


&&

.AVIATION...22/18Z TAF CYCLE...VFR conditions under clear skies
will prevail through Monday. The only exception may be the Coquille
Valley, where there may be an area of IFR cigs/vsbys in low clouds
and fog late Sunday night into Monday morning.


&&

.MARINE...Updated 200 PM PDT Sunday 22 April 2018...Offshore high
pressure and a thermal trough along the coast will bring gusty north
winds over most of the area into tonight. Winds will be strongest
over the southern waters with gales and very steep seas from Bandon
south. Gale force winds could get within 2 nm from shore from Port
Orford south. Small craft advisory winds and seas will persist into
tonight from Bandon north.

Winds and seas will gradually lower late tonight into Monday as
the thermal trough weakens. However, steep to very steep wind driven
seas will linger tonight. Winds and seas will drop below
advisory level by sunrise Monday.

Seas will increase Tuesday morning and afternoon as west swell
moves in. Seas will near small craft advisory levels during this
period but will likely remain below it. Seas will then subside
Tuesday evening through Wednesday. Meanwhile winds will be light to
moderate during the same time frame with weak low pressure over the
waters.

Winds and seas will remain relatively light Thursday and Thursday
night. Northwest swell will move in Friday, raising seas a bit.


&&

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

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT Monday for
     PZZ350-356-370-376.
     Gale Warning until 11 PM PDT this evening for
     PZZ350-356-370-376.
     Hazardous Seas Warning from 11 PM this evening to 5 AM PDT
     Monday for PZZ356-376.

$$



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