FXUS66 KMFR 231056

Area Forecast Discussion
National Weather Service Medford OR
356 AM PDT Thu May 23 2019

.SHORT TERM...Morning satellite imagery reveals plenty of low
cloudiness over the coastal waters and adjacent inland areas of
Coos and Douglas Counties where there could be some drizzle early
on, but an area of clear extends southward from Port Orford to
Brookings. Skies are partly to mostly cloudy across the remainder
of the forecast area with isolated showers out in portions of
Lake/Modoc Counties. We'll remain in between upper level low
pressure located over the Desert SW/Great Basin and a ridge
offshore. This will maintain broad north-northeast flow, but with
a general warming of the air mass aloft. Clouds pull back to near
the coast this afternoon, but it should at least be partly sunny
elsewhere. Some moisture will continue to wrap around the low
resulting in isolated to scattered showers, primarily near the
Cascades and also over portions of SE Lake and Modoc Counties this
afternoon and evening. There is some instability over the
Cascades, and latest convection allowing models (CAMS) still show
isolated cells that could produce lightning, so we'll maintain the
going forecast for thunder there. Overall, high temperatures
should be right around normal for this time of year (low to mid
70s west side valleys and mid 60s east side).

Tonight into Friday morning, clouds return to coastal areas and
inland into the Umpqua Basin. Some of these could spill over into
the Rogue/Illinois Valleys. With the deeper marine push, it will
be cooler north of the Umpqua Divide Friday afternoon. But,
temperatures south and east of there should be similar to where
they end up today. The next disturbance dropping southward from BC
will develop into a closed low by Friday evening near the WA/OR
border. Instability will increase Friday afternoon/evening in
advance of this system with showers and isolated thunderstorms
from southern Siskiyou County northeastward across Modoc/Lake
Counties. Most everywhere else will remain dry, but isolated
showers may also develop near or just north of Roseburg.

Additional energy will dive southward along the BC coast Friday
night, then along the PacNW Saturday and eventually into
California on Sunday. This will bring an increasing likelihood of
showers focused across much of our area Saturday night, then
especially from the Cascades/Siskiyous eastward on Sunday. -Spilde

.LONG TERM...From Wednesday afternoon's discussion...Sunday
through Wednesday...Not much has changed with the overall pattern
through the holiday weekend. General troughing will remain over
the area which means we could be dealing with a chance of showers
and afternoon and early evening thunderstorms Sunday through
Memorial Day for most inland locations.

There's been fairly good agreement among the models the past couple
of runs. However the latest ECMWF now shows a stronger upper low
moving south along the Oregon Coast and has enough over water
trajectory to produce a significant amount of moisture for this time
of the year on Sunday. The GFS and Canadian have stayed the course
and show a weaker upper low near or over the area which would result
in a fair amount of dry time in the morning, especially west of the
Cascades followed by increasing showers in the afternoon with
isolated thunderstorms possible. It remains to be seen if the latest
ECMWF solution is a one hit wonder or will it revert back to a
solution that's more in line with the GFS/Canadian. For this reason
and high spread among some of the ensemble members, have decided not
to increase pops much on Sunday, but watch for updates on this
should future runs continue to show the wetter solution.

The upper low is expected to set up southeast of our area Monday and
there is concern we could be caught up in some wraparound moisture.
it this turns out to be the case, then we'll have a higher chance
for showers pretty much all day with the highest chance for showers
in the afternoon and evening. The individual ensemble members show a
pretty good spread with the location of the upper low. Confidence is
higher we'll have frequent showers east of the Cascades, but lower
for shower coverage west of the Cascades, especially Monday morning.

The upper should finally move far enough away where we could end up
with drier and milder conditions next Tuesday. Wednesday also looks
mostly dry and milder, although isolated showers are possible in the
afternoon east of the Cascades. -Petrucelli


.AVIATION...For the 23/06Z TAFS...Along the coast and over the
coastal waters...Widespread IFR cigs will persist through Thursday
evening with patchy drizzle and fog, except south of Cape Blanco and
5-10 miles offshore where VFR conditions will prevail. Inland areas
west of the Cascades...VFR conditions will prevail through Thursday
evening, except for areas of late night into morning IFR/MVFR cigs,
mostly over the Umpqua Basin. Isolated rain showers will end
Wednesday night. From the Cascades east...VFR conditions will
prevail through Thursday evening, but there will be scattered
showers and isolated afternoon/evening thunderstorms with some
obscuration of higher terrain.


.MARINE...Updated 300 AM PDT Thursday 23 May 2019...Offshore high
pressure/coastal thermal trough pattern will continue into Friday
afternoon and evening. Look for strong north winds south of Gold
Beach and roughly 3 to 5 nm away from shore Thursday. As a result,
seas will likely be hazardous for most of Thursday. The thermal
trough will still persist into Friday, but winds will be about 3
to 5 knots weaker and seas should be lower as a result. Therefore,
we felt like a small craft advisory was more appropriate for all
the waters on Friday.

A cold front will move into the waters Friday night bringing a steep
fresh swell into the region. Wave heights will be around 10 feet at
10 seconds when this front moves through. Another quick moving
system will keep seas high and steep into Saturday. Eventually,
low seas will develop Monday and Tuesday as high pressure builds.





Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT Saturday
for PZZ350-356-370-376.
Hazardous Seas Warning until 5 AM PDT Friday for PZZ356-370-376.


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