Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 291021
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
321 AM PDT Wed Mar 29 2017

.DISCUSSION...A warm front to our north is producing some showers
across the area early this morning. These will continue through
roughly noon, then the associated cold front will arrive this
afternoon and evening. Models have backed off a bit on the
moisture associated with this system, so currently it does not
appear that rainfall amounts will be excessive. On the other
hand, the front will be progressing a bit on the slower side, so
while rainfall rates may not be high, just about every location
within the forecast area has a good chance of getting a healthy
dose of rain. Meanwhile, snow levels of about 8000 feet will keep
snow from falling over all but the highest terrain. Rain will
transition to showers late this evening, and snow levels will
drop behind the front to about 3500 feet, but by that time, the
bulk of the precipitation will have passed, and any snow or rain
amounts will be light.

The front itself will not be a major wind producer, but as high
pressure builds in to our north and west on Thursday, cold air
will spill into the region, and the difference between the cooler
higher pressure and the warmer low pressure to the south and east
will produce a tight pressure gradient, and strong winds will
result. Breezy northwest winds are expected over much of the
region, especially for higher terrain, gaps and passes, and any
northwest to southeast oriented valleys, but the strongest winds
are likely to develop over the East Side. A Wind Advisory has been
issued for portions of Lake and Modoc Counties, and details can
be found in the Weather Message PDXNPWMFR.

Light showers will continue through Thursday afternoon as the
upper level trough passes overhead, then the area should clear
Thursday night as ridging builds in. Clearer skies and a cooler
air mass are expected to produce cold morning lows Friday, and
frost is possible in the West Side valleys.

Ridging and high pressure will keep the area dry through Friday
and into Saturday, until the trailing edge of a dissipating front
to our north glances Southern Oregon on Saturday afternoon. The
models diverge on what happens as the upper level wave approaches
the region Saturday night into Sunday. There is agreement that an
upper level trough will pass in the vicinity, but much will
depend on the strength of the trough and its track. The ECWMF
solution is drier, producing only light showers as a broader
trough traverse quickly overhead, but the GFS depicts a much
wetter solution, with a sharper trough and some form of frontal
development almost directly over Southern Oregon and far Northern
California. Have kept at least a chance of showers in the forecast
during this time, but some changes are likely forthcoming as
models attempt to come to some consensus during the next several
forecast cycles.

The on-again, off-again pattern is expected to continue for the
remainder of the forecast term, with high pressure and dry
conditions returning Monday and Tuesday, then another wet front
arriving by midweek. Due to the wide range of solutions during the
long term, there is little confidence in the details, so will wait
to refine these as focus sharpens in the coming days. -BPN

&&

.AVIATION...28/06Z TAF CYCLE...A warm front will lift north of
the region overnight. Expect VFR to prevail despite light
rain at times along the coast north of Cape Blanco. Ceilings will
gradually lower to MVFR and local IFR with terrain obscured
Wednesday into Wednesday evening as a cold front moves through.
Light to moderate rainfall will accompany the front, heaviest
along the coast and north of the Umpqua Divide and in the Cascades.
Precipitation will become showery behind the front Wednesday evening
west of the Cascades. -Spilde

&&

.MARINE...Updated 300 AM PDT Wednesday 29 March 2017...Long period
west swell will make bar crossings hazardous today. Seas will remain
high and steep through Wednesday night. A front which will bring
increasing southerly winds this morning and this afternoon. Wind
speeds are expected to reach advisory strength for areas from Gold
Beach northward. Steep seas will become a mix of west swell and
short period southerly wind waves.  Winds will decrease this evening
and then veer to the north tonight into Thursday. Winds may reach
advisory strength in the waters south of Gold Beach Thursday evening
into Saturday. A weakening front moves into the area late Saturday
followed by an upper level disturbance with showers Sunday. High and
very long period west swell is expected to arrive late Saturday into
Sunday. This may bring dangerous seas to the waters. -CC

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 5 AM to 11 PM PDT Thursday for ORZ031.

CA...Wind Advisory from 5 AM to 11 PM PDT Thursday for CAZ085.

Pacific Coastal Waters...Small Craft Advisory until 5 PM PDT this
     afternoon for PZZ350-356-370-376. Small Craft Advisory for
     hazardous seas until 11 AM PDT Thursday for
     PZZ350-356-370-376.

$$

BPN/CC/MAS



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