Area Forecast Discussion
Issued by NWS Medford, OR

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035
FXUS66 KMFR 302005
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
105 PM PDT Sun Apr 30 2017

.DISCUSSION...30/12Z NAM/GFS/EC in.

A short wave riding over the offshore long wave ridge pushed a
weak front onshore earlier today. That front is now washing out as
the upper level support exits the area. In terms of precipitation
this front is not amounting to much. Precipitation totals thus
far are less than 0.25 inches along the north coast and in the
Umpqua Basin. Amounts are around 0.05 inches or less along the
south coast and in the adjacent Coast Range. Other than that...
just a hundredth or two here and there from the Cascades west.

High temperatures will be around 5 degrees below normal along the
north coast and in the Umpqua Basin...near normal over the south
coast...Oregon west side and the Oregon/California east side...and
around 5 degrees above normal over Western/Central Siskiyou
County.

Another short wave riding over the ridge will push a front onshore
Monday afternoon and evening. This front will look a lot like the
current system with the bulk of the associated precipitation
falling along the coast and in the Umpqua Basin. High temperatures
will be near normal along the coast and in the Umpqua Basin...
around 5 degrees above normal over most of the rest of the area...
and 5 to 10 degrees above normal over Western/Central Siskiyou
County.

After that system...the ridge will strengthen as it approaches the
coast and moves onshore Wednesday. This will make for dry and
warmer weather Tuesday. High temperatures will be around 5 degrees
above normal along the coast and in the Umpqua Basin...and 5 to 10
degrees above normal over the rest of the area.

As the ridge moves onshore Wednesday...the thermal trough will be
forced inland over the west side. This will make that day the
warmest of the coming week over the west side. High temperatures
will be 5 to 10 degrees above normal along the coast and 15 to 20
degrees above normal over the rest of the area. The Medford high
may hit 90 degrees Wednesday.

EXTENDED DISCUSSION...Thursday through Sunday...The models are
coming into better agreement with the evolution of the upper trough
and overall pattern for the forecast period. The upper trough will
approach the forecast area Thursday and the models are in pretty
good agreement convective precipitation will break out Thursday
afternoon into Thursday night. At this time, thunderstorms should
initiate along the Cascades and Siskiyous, then migrate north to
northeast in the afternoon and early evening Thursday with the 700mb
flow from the south to southwest. Keep in mind it`s still a ways
out, so the details on the exact location could change. Therefore
watch for updates. For now kept in a slight chance mention and if
confidence increases, then they could be upgraded to chance.

Temperatures Thursday will be cooler then Wednesday west of the
Cascades. Meanwhile they will be very similar to Thursday east of
the Cascades, but mush of that will depend on the amount of cloud
cover.

An upper trough will replace the ridge Friday through Sunday with
cooler temperatures, lower snow levels and a chance of showers. The
trough axis will still be offshore Friday with a southerly flow
aloft, but instability is marginal at best, so for now kept any
mention of thunderstorms out, but this could change.

The upper trough will move over the area Saturday, then split with a
cutoff low developing to our south which could bring drier
conditions a week from Sunday. However, the details on exactly where
the cutoff low will reside at is not clear. For example the ECMWF
has the cutoff low in central Cal and the GFS in southern Nevada.
The Canadian shows a cutoff low developing sooner in southern Cal.
-Petrucelli

&&

.AVIATION...30/18Z TAF CYCLE...MVFR Cigs along the coast, including
North Bend and Umpqua Basin including Roseburg should improve to VFR
around 20z and remain there for the rest of the TAF period. Current
TAF for both North Bend and Roseburg show Cigs improving to VFR at
20z, but confidence is low to medium for the timing at North Bend.
Elsewhere, VFR Cigs will continue for through the TAF period.
However could not rule out partial mountain obscurations until 19z.
-Petrucelli

&&

.MARINE...Updated 200 PM PDT Sunday, 30 April 2017...A thermal
trough will develop this afternoon resulting in stronger north winds
and steeper seas through late this evening...affecting areas from
about 3 to 40 nm from shore, but with the highest winds and steepest
seas south of Gold Beach.  A weak system will disrupt the thermal
trough Monday and Monday night, but the thermal trough will
redevelop Tuesday into Wednesday.

A cold front will move through the coastal waters on Thursday with
NW flow developing over the coastal waters into the weekend. This is
a change from previous thinking which called for the thermal trough
and NE flow to develop.  While we expect winds to increase toward
next weekend, it does not appear as strong as we previously thought.
/FB

&&

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

CA...None.

Pacific Coastal Waters...Small Craft Advisory from 2 PM this
        afternoon to 2 AM PDT Monday for PZZ356-376.

$$

25/10/08



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