Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 281211
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
428 AM PDT WED SEP 28 2016

.DISCUSSION...Model agreement remains very good through Saturday,
which covers the approach and arrival from the northwest of a
closed low currently offshore from British Columbia and also the
approach of a subsequent stronger system. Model differences are
more noticeable on Sunday regarding the track and timing of the
arrival of a cold front. There is enough similarity that Sunday
still looks to have the highest probability of any of the next 7
days for a widespread rainfall with amounts in the ballpark of
0.10 to 0.50 inches. Beyond Sunday, uncertainty has increased.
Unlike the 00Z GFS, the 06Z GFS run has trended with the 00Z ECMWF
toward a slower and weaker depiction of a warm/occluding front
around Tuesday.

Presently, a shortwave trough is offshore from Oregon and will
track northeast into Washington. This will serve to weaken the
ridge that lingers over our area. The result will be high temperatures
a few degrees cooler than yesterday and a modest increase in
afternoon and evening wind speeds. Low clouds and patchy fog along
the coast is expected to dissipate late this morning then return
tonight into Thursday morning.

The changes in our weather will trend toward being more noticeable
Thursday into Saturday. The approach of the aforementioned
Alaskan trough will bring another several degrees of cooling for
Thursday and breezy to locally windy afternoon westerly winds
across the east side with gusts of 20 to 30 MPH. A slight chance
of a shower or thunderstorm remains in the forecast for northern
Klamath County during Thursday afternoon and evening with a weak
shortwave in a south to southwest flow aloft.

The parent upper low looks to remain off the Pacific Northwest
coast on Friday but move east toward it. This will bring
additional cooling of about 8 to 12 degrees and stronger winds
with east side gusts of 25 to 40 MPH possible. It will also bring
a chance of mainly coastal light showers. With the steady cooling
trend, morning lows will be back to around normal on Friday
morning while inland high temperatures will be near normal to
several degrees below normal with valley highs mainly in the lower
70s.

After the recent spell of hot temperatures, the much below normal
high temperatures in the 50s and lower 60s that are in store for
the weekend will likely feel especially chilly. The first upper
low is expected to finally track inland with an associated cold front
on Saturday and weaken as it does so. But, it will bring an
increased probability of coastal rain and perhaps a few light
showers inland also.

A stronger front could arrive at the coast as early as Saturday
evening though more likely toward Sunday morning. The GFS digs the
closed low farther south into Central California while the ECMWF
shows a track roughly along the Oregon/California border. This
track will have an effect on the length of precipitation but
there is still decent confidence in a substantial Sunday event
with a light snowfall of up to 3 inches above the snow level of
around 5500 to 6000 feet. The duration is not certain and the
recent data has trended lower with the amounts, but a period of
showers and flurries would normally be expected to follow in the
cold post-frontal air mass on Sunday night...possibly into Monday
morning.

The models have lacked consistency in how to evolve the pattern
early next week. The most recent data shows a much weaker warm
front will be slower and farther north than shown by the previous
model blend. There is still a likelihood of at least light
precipitation at the coast and in the Douglas County Monday night
into Tuesday. The probability of showers diminishes for
Wednesday/day 7 and there should be at least modest warming. The 06Z
GFS shows a stronger ridge compared to a zonal pattern in the
ECMWF.


&&

.AVIATION...28/12Z TAF CYCLE...Sky condition was missing at KOTH
observations again tonight but satellite reading shows widespread IFR
conditions along the coast from Newport south to Cape Blanco with
a clear area from Cape Blanco to Gold Beach where IFR conditions
then develops southward into northern California. Satellite
reading also shows IFR extending into the Coquille River valley
past Myrtle Point to Powers. The IFR conditions should burn off
around 17Z or the same time as yesterday with 20-30kt wind
increasing at KOTH. We could see IFR conditions returning again
tonight.

Patchy IFR conditions are showing up north of Roseburg with
short term model forecasting MVFR cigs around sunrise. Confidence is
not high on this feature and I have trended more toward giving a
scattered layer at KRBG. Elsewhere VFR conditions will continue. /FB

&&

.MARINE...Updated 230 AM PDT Wednesday 28 September 2016...
Satellite derived wind data shows gale force winds continue
overnight just beyond 10 nm from shore and south of Cape Blanco.
Even though the thermal trough is expected to weaken today, it will
still be strong enough to generate strong north winds and Gale will
continue today, moving closer to shore this evening. After the
period of Gale is over, the waters will still see short period fresh
swell continuing into Thursday. /FB

&&

.FIRE WEATHER...Updated 200 PM PDT Tuesday 27 September 2016...
Wednesday will continue the gradual cooling trend as the upper ridge
moves east and loses its influence over the region. As an upper
trough to the west moves closer, temperatures will drop more
noticeably on Thursday. An approaching cold front will bring
stronger winds Wednesday and more so on Thursday, with the front
moving through late Thursday into Friday. Southwest to west winds
will gust to 30 mph in portions of the East Side Thursday and
Friday. Humidity will only increase marginally late this week in
areas of the East Side, so will be monitoring for the potential for
critical fire weather conditions on both of these days, especially
Thursday. That said, right now model consensus suggests Fire Weather
Zones 624 and 285 will not quite meet Red Flag Warning criteria
through the week. It`s worth noting there is a slight chance for
thunderstorms in northern Klamath and northwest Lake counties
Thursday afternoon ahead of the upper trough.

Confidence is increasing for widespread wetting rains Sunday and
possibly Monday/Tuesday as a frontal boundary swings in from the
northwest. The highest confidence for wetting rains is for areas
along and west of the Cascades, but latest model output agrees that
East Side areas should get wet too. Longer-term data suggests that
temperatures will remain near to below normal through much of next
week. SK


&&

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

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 11 AM PDT Thursday
     for PZZ356-370-376.
     Gale Warning from 5 PM this afternoon to 11 PM PDT this evening
     for PZZ356.
     Small Craft Advisory for hazardous seas until 11 AM PDT Thursday
     for PZZ350-356-370.
     Gale Warning until 11 PM PDT this evening for PZZ376.
     Hazardous Seas Warning from 5 PM this afternoon to 11 AM PDT
     Thursday for PZZ376.

$$

DW/FJB


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