Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 261000

Area Forecast Discussion
National Weather Service Medford OR
300 AM PDT Sat May 26 2018


Showers persist this morning east of the Cascades and over
northern California, but the thunderstorms have dissipated. No
precipitation on the west side at this time.

A cutoff low now over central California will move slowly east
into Nevada Saturday. As it does so, the most favored area for
convection will also move east.

By later this morning, the low will be far enough east for the
flow aloft to shift to northerly as a ridge builds in from the
west. This will bring the precipitation to an end west of the
Cascades. Models still show significant activity east of the
Cascades, but lifted indices indicate that lapse rates will be
stable. So, expect the precipitation to be stratiform with no
thunderstorms. The precipitation will dissipate by Saturday

Saturday highs inland will be warmer than the Friday highs but
still 5-10 degrees below normal. Along the coast, highs will be
near normal except a bit above normal near Brookings.

Low level easterly flow will develop Saturday night and this will
clear out the west side Saturday night into Sunday night. Inland high
temperatures will warm back up to around 5-10 degrees above
normal. It will near normal along the coast except near Brookings,
where it will be quite warm with highs in the middle 70s.

The ridge will hold through Monday for continued warm and dry
weather. It will be the warmest day of the stretch for all but the
coast and far east side with highs around 10 degrees above normal.

The next upstream trough will dig around 130W Tuesday, and
southwest flow aloft will increase. This will leave the Pacific
Northwest vulnerable to short waves ejecting from the trough.
Model lifted indices support showers and thunderstorms over
Siskiyou County and east of the Cascades Tuesday afternoon and
evening, but moisture will be limited and coverage will likely be
no better than isolated. Highs will be near normal along the
coast and in the Umpqua, and 5-10 degrees above normal over the
rest of the area.

Long term discussion from the Friday afternoon AFD...Tuesday 29
May through Friday 01 Jun 2018. The extended portion of the
forecast looks pretty quiet compared to the recent stretch of
active weather. Upper troughing will begin to influence Southern
Oregon and Northern California on Tuesday, and given that the
upper trough is coming from the northwest, instability will
generally be on the weak side. Instability will be greatest
Tuesday and Wednesday afternoons, ahead of the trough axis, and we
have a slight chance of thunderstorms east of the Cascades for
those times. Further west, we expect some morning pushes of clouds
into the Umpqua Basin ahead of the trough.

The EC and GFS operational models begin to diverge on Thursday
despite most of the GEFS members showing upper troughing over the
Pacific Northwest. The EC flow is more zonal, indicating a smaller
chance for any precipitation. In any case, both models suggest a
pattern that will yield near to below normal temperatures and
limited instability. Given that the GFS has a higher-amplitude
pattern, warming conditions are expected behind the upper trough on
Saturday, while 500mb heights are substantially lower on the EC, and
this suggests cooler conditions. Our forecast features a compromise
between the two models, with slightly higher temperatures on
Saturday and continued mostly dry conditions.

In short, the long-term can be characterized by near to below normal
daytime temperatures with little to no precipitation or major
thunderstorm outbreaks.


.AVIATION...26/06Z...Along the coast, widespread MVFR and local IFR
cigs are expected to develop tonight and continue into Saturday
morning, with conditions improving to VFR late Saturday morning into
Saturday afternoon. Inland, as light showers persist, widespread
MVFR cigs and local IFR will continue tonight. Showers will move
eastward and gradually diminish late tonight and Saturday morning
and expect a mix of VFR with areas of MVFR and local IFR cigs.
MVFR/IFR will be most likely for areas east of the Cascades and in
the Umpqua basin late tonight and Saturday morning. However, expect
MVFR cigs also at KMFR overnight. Widespread mountain obscurations
tonight will gradually lessen Saturday morning. By Saturday
afternoon, expect VFR areawide. -CC


.MARINE...Updated 200 AM PDT Saturday 26 May 2018...Winds and
seas will trend calmer this morning, but gusty north winds and steep
seas are expected to redevelop south of Cape Blanco this afternoon
into this evening as the thermal trough returns to our south. As the
thermal trough strengthens along the coast and high pressure builds
offshore on Sunday, expect north winds and steep seas to gradually
increase with continuing small craft advisory level winds and seas
south of Cape Blanco.

By Monday, the pattern is expected to strengthen further, spreading
at least small craft advisory winds and seas to all areas. North
gales and very steep seas are possible as soon as Monday afternoon
over the southern waters, and could continue through mid week.
Conditions may not improve significantly until late in the week
into next weekend. -BPN/CC




Pacific Coastal Waters...Gale Watch from Monday morning through late
        Wednesday night for PZZ356-376.
     Small Craft Advisory from 2 PM this afternoon to 5 AM PDT
        Thursday for PZZ350-356-370-376.


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