Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 291559

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

.DISCUSSION...The going forecast looks pretty good, so no updates
are planned this morning. A front is approaching the coast this
morning, and light rain has already started in many coastal
locations. Some pre-frontal showers have developed over the inland
west side, and rain should gradually increase from west to east
across the area today. This isn`t a particularly dynamic system,
and wind isn`t a huge factor. The net result of this is less
downsloping to inhibit rain than usual, so all locations are
expected to get wet with this front. High snow levels (around 8000
feet this morning) will keep snow from being an impact today. The
front itself move through the west side later today and the east
side tonight. Rain will change to snow in the mountains as snow
levels lower to around 3500 feet behind the front tonight.
However, there won`t be much precipitation left by that point, so
we don`t expect much more than nuisance snow accumulations (a few
inches) in the mountains with this front. -Wright


.AVIATION...28/12Z TAF CYCLE...A cold front will move inland this
afternoon and evening.  Ceilings will gradually lower to MVFR and
local IFR with terrain obscured today through this evening as the
cold front moves across the area. Widespread MVFR is expected to
develop across the area in the afternoon and continue into the
evening. 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 tonight
with widespread MVFR and local IFR continuing across the area. -CC


.PREV DISCUSSION... /Issued 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

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


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
     Small Craft Advisory for hazardous seas until 11 AM PDT Thursday
     for PZZ350-356-370-376.

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