Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 011623
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
923 AM PDT Wed Apr 1 2020

.DISCUSSION...No changes were needed to the forecast. Showers this
morning are far and few in between, but they are expected to
increase in coverage this afternoon due to a combination of
daytime heating, colder air aloft moving overhead and a shortwave
(trigger) moving into the area. Guidance continues to show
instability may be sufficient enough for a few lightning strikes
in eastern Douglas and portions of Klamath and Lake county this
afternoon and no changes were made to the slight chance of
thunderstorm coverage.

The main focus will be the potential for near or below freezing
temperatures for several westside locations tonight into Thursday
morning. The freeze watch could end up being upgraded to a warning
and could also include portions of Josephine county by the
afternoon issuance. Also we could be looking at frost/freeze
concerns again Thursday night into Friday morning for many of the
same locations. -Petrucelli


&&

.AVIATION...


&&

.MARINE...


&&

.PREV DISCUSSION... /Issued 523 AM PDT Wed Apr 1 2020/

DISCUSSION...
Partial clearing has resulted in cooler temperatures this morning
with most areas from the Oregon Cascades and Shasta Valley
eastward now reporting below freezing temperatures. West of there
it`s in the 30s and some patchy frost is probably going to form
not too far from the coast and into Douglas County. There are
still a few showers traversing the forecast area, bringing rain
below 2000 foot elevations, snow above 2500 foot elevations, and a
mix in between.

With today being April 1st, the frost and freeze headline area
has expanded due to climatological normals. With a couple of
colder nights-mornings expected tonight through Friday morning,
frost advisories have been issued for portions of Coos, Curry, and
Douglas counties and freeze watches have been issued for portions
of southwestern Douglas County and most of the valley areas of
Jackson County.

There will still be some showers around today, mainly over
northwestern portions of the forecast area, and primarily in the
afternoon and evening hours. Snow levels are likely to be 2500 to
3500 feet. There is a possibility of thunder this afternoon
through early this evening from eastern Douglas County across
northern Klamath County and much of Lake County where a -30C to
-36C 500MB trough is moving overhead leading to <0C 850MB LI`s.

While thunder is possible, what`s more likely to occur is brief
hail and/or graupel in showers. SPC Hi-Res model guidance suggests
the highest radar reflectivities today will be southwest of the
areas of below zero 850MB LI`s, more across the west side from
about Jackson County north and westward. Therefore, expect some
showers to be around and, while they will be brief and will
generally result in a tenth of an inch of water or less, they
could be briefly moderate to even locally heavy.

Aside from some light sprinkles of rain and possibly some flurries
in the Oregon Cascades Thursday night into Friday, it should be
partly cloudy and a little warmer Friday.

The low pressure system is expected to arrive Friday night into
Saturday morning with models varying greatly on the spatial extent
of the precipitation field through the morning. The GFS is much
more robust in bringing precipitation inland, whereas the ECMWF
keeps it over SW portions of the area until Saturday afternoon.
Both solutions are plausible, as the low level wind field is
pretty weak ahead of the occluded low coming in and the situation
is ripe for some light overrunning precipitation. We`ll need to be
on the lookout for some light snowfall during this time period
for elevations between 3kft and 4kft, to include Siskiyou Summit.

Models continue to suggest more precipitation and lowering snow
levels Saturday night into Sunday morning. Right now it appears
snow levels will bottom out in the the 2500-3500 foot range, so
expect some slick spots during that time period on Interstate 5
over Siskiyou Summit, in the mountains, and across the east side.
This precipitation is surely good news for our drier than normal
area, as it will help add to the below average snowpack and help
to prolong spring run-off in area reservoirs from what it would
be otherwise.

After a transition day Monday, models are generally suggesting a
ridge of high pressure pushing in from the northeast. This is
looking to set us up again for increased diurnal temperature
ranges and milder afternoon high temperatures. -BTL

AVIATION...For the 01/06Z TAF Cycle...From the Cascades
west...Areas of MVFR cigs in low clouds and showers with higher
terrain obscured will persist through Wednesday evening.
East of the Cascades...VFR conditions will prevail through Wednesday
evening with isolated showers and some obscuration of higher
terrain. Winds will be gusty, especially in the afternoon and
evening.

MARINE...Updated 200 AM PDT Wednesday 1 April 2020...Northwest
swell is now subsiding, but steep seas will persist through tonight.
A weak front will move onshore Wednesday, then high pressure will
build Thursday and weaken Friday. Seas will continue to subside
through Friday night, but winds may be gusty in the afternoons and
evening Wednesday and Thursday, especially south of Cape Blanco. The
next front will move onshore Friday night into Saturday, and it will
be followed by several weak systems through the weekend. Winds and
seas will increase during this time, but will likely remain below
Small Craft Advisory criteria.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Frost Advisory from 10 PM this evening to 9 AM PDT Thursday for
     ORZ021-022.
     Frost Advisory from 10 PM this evening to 9 AM PDT Thursday for
     ORZ023.
     Freeze Watch from this evening through Thursday morning for
     ORZ023.
     Freeze Watch from this evening through Thursday morning for
     ORZ026.

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 11 PM PDT this evening for
     PZZ350-370-376.

$$


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