High Wind in Oregon, May 2, 2020

Area Forecast Discussion
National Weather Service Medford OR
819 AM PDT Sat May 2 2020

.DISCUSSION...8:00 AM RADAR is showing showers across most of
the west side (excluding the Rogue Valley). These showers are
associated with a front that is moving through the area today.
Some of these showers are producing brief periods of heavy rain,
as noted by a spotter near Gold Beach who had a half an inch of
rain fall overnight. These showers and storms will move through
too quickly to pose any real threat for flooding, but will
continue to monitor in case of any showers or storms going over
areas again and again.

The main change to this forecast package was to add a slight
chance for thunderstorms back to the forecast across the west
side this morning and early afternoon. Early morning satellite
imagery already shows almost all of the heavier showers starting
to glaciate (begin to have ice crystal form--a precursor to
lightning)as they tap into some modest energy in the atmosphere.
With the cold pool coming in later, it is not inconceivable that
there may be a few rumbles of thunder across the entirety of our
forecast area (southern Oregon and northern California).

Have kept the small hail/gusty wind threat largely along and east
of the Cascades. The Storm Prediction Center has moved their
location with the highest possibility of severe storms just to the
northeast of Lake County. Thus a couple of storms may become
strong or even severe producing strong, gusty winds; large hail;
and occasional lighting. The main threat will be the winds, as
they'll already be gusty ahead of the front anyway.

To recap: Most of the precipitation that falls today will be
showers. Some showers will produce lightning strikes. A few of
those thunderstorms along and east of the Cascades will become
strong and one or two may even become severe.

More information about the remainder of the forecast is available
in the previous discussion included below. -Schaaf

&&

.MARINE...Updated 800 AM PDT Saturday 2 May 2020...A cold front is
now moving through the waters with south winds gusting almost to
gale force. Steep to very steep seas of 8 to 11 ft will last into
this evening.

Weaker fronts will follow through Tuesday as the pattern will remain
active. West swell dominated seas may become high and steep late
Sunday and Tuesday. A change will occur Wednesday, when a more
summer-like pattern will develop with high pressure offshore and a
thermal trough near the coast. This will bring gusty north winds to
the waters with the strongest winds and highest seas south of Cape
Blanco. This pattern will persist into Thursday before weakening
into the weekend.

&&

.PREV DISCUSSION... /Issued 436 AM PDT Sat May 2 2020/

DISCUSSION...Showers are approaching the coast on the radar
this morning, with rain being reported at Coos Bay, and the rest
of the coast should be seeing rain very shortly. These showers
should turn into more steady rain quickly and move inland to the
Cascades by late morning. Although the PW values have decreased
with this system, down to .6 to .8" from the near an inch
indicated yesterday at this time, there is now indicated very good
upper level divergence aloft in a more "splitting" jet pattern,
and this system still looks to be fairly wet. Winds ahead of the
front also are looking weaker, with 700 mb winds lower at 30-35
kt, compared to yesterday's indication of 40-45 kt winds. Stronger
700 mb winds of 40-45 kt move over the east side overnight, but
there will be de-coupling, and the stronger winds will be at the
ridges, and remain below advisory level for the vast majority of
the area. As we head into the afternoon and max heating, a cold
pool begins to move into the area with 500 mb temperatures of
<-25 C. This will help to develop instability with a slight
chance of thunderstorms from the Cascades across the east side,
and possibly a little west of the Cascades, but as we head into
the evening a dry mid layer moves in with an inversion indicated
above 700 mb, and computed LI's over the west side above 6. lapse
rates below 700 mb will still be high into early evening and some
strong, low topped showers are possible in this area into mid
evening.

Showers taper off overnight into Sunday morning, and the 06Z runs
now showing Sunday to be much less of a front with instability
still indicated in eastern Siskiyou, southern Lake, and Modoc
county in the afternoon, but more stable on the central coast,
This is a major change from the previous run, and hopefully the
upper sounding input into the 12Z runs will settle things down a
bit.

A ridge build in behind this front Sunday night into Monday
morning, with a weak front washing out at the coast as it slams
into the ridge Monday evening into Tuesday morning. The ridge is
still indicating to remain into the end of the week, by ensemble
member are showing great differences as we head into the end of
the week, and although operational runs are showing a decent
front bringing a round of moderate precipitation in on Saturday,
confidence is very low at this time. Sven

AVIATION...For the 02/12Z TAF Cycle...West of the Cascades...MVFR
cigs/vsbys in low clouds and rain at the coast will spread inland
through the day with higher terrain becoming obscured. The lower
conditions will prevail into Saturday evening. Low-level wind shear
will also be a concern at KOTH and at KRBG this morning into the
early afternoon. Lighter, less frequent showers will linger this
evening into early Sunday morning with mainly VFR expected.

From the Cascades east...VFR conditions will persist early this
morning, then valleys will remain mainly VFR but areas of higher
terrain will become obscured and gusty southwest winds will develop.
Isolated to scattered thunderstorms will accompany showers this
afternoon into the evening. These could produce strong wind gusts,
small hail and reductions to MVFR cigs/vsbys. Wind speeds and the
coverage of showers will diminish this evening. -Spilde/DW

MARINE...Updated 300 AM PDT Saturday 2 May 2020...A cold front
will move through the waters this morning with south winds gusting
almost to gale force. It will also produce steep to very steep seas
of 8 to 11 ft that will last into this evening.

More weaker fronts will follow through Tuesday as the pattern will
remain active. West swell dominated seas may become high and steep
late Sunday and Tuesday. A change will occur Wednesday, when a more
summer-like pattern will develop with high pressure offshore and a
thermal trough near the coast. This will bring gusty north winds to
the waters with the strongest winds and highest seas south of Cape
Blanco. This pattern will be strongest late Wednesday through
Thursday evening, but likely persist into next weekend. -Spilde/DW

&&

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

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 8 PM PDT this evening for
     PZZ350-356-376.
     Hazardous Seas Warning until 8 PM PDT this evening for
     PZZ350-356-370-376.