Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 241124
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
424 AM PDT WED AUG 24 2016

.DISCUSSION...Model agreement is good to excellent through this
weekend then uncertainty in the forecast for beyond Sunday increases
quickly and substantially. The pattern will change today into
Thursday with the change most apparent at the coast. Coastal low
clouds and fog are persistent this morning but developing
northeasterly winds are expected to dry out the marine layer
during the day. This will lead to coastal temperatures today that
are modestly warmer than yesterday then clear skies are expected
to persist tonight into Thursday morning with much warmer and
drier conditions on Thursday. A coastal thermal trough is expected
to move inland on Friday with a southerly surge of marine air
with stratus and fog later Friday through Friday night. Thus,
coastal temperatures will peak on Thursday.

The warming trend will also be apparent inland with hot and dry
conditions becoming hotter and drier into Friday. High temperatures
on both Thursday and Friday will approach and may possibly set
records. West side valley highs on Thursday and Friday will range
from around 95 to 103 while east side highs will be mainly in the
mid to upper 80s. These readings will be around 5 to 15 degrees
above normal with heat likely to reach peak levels on Friday
afternoon. This level of heat should be respected with proper
precautions taken, but a heat advisory is not expected to be
necessary. Readings will be around 5 to 10 degrees lower than the
extremes reached last week. Most notably, overnight valley lows
will be only around 5 degrees above normal.

The evolution of the upper level pattern through Friday shows an
increasing influence of a broad ridge presently over the eastern
Pacific. This weekend..a trough will move southeast across British
Columbia into Alberta. The trough will bring an onshore flow and flatten
the ridge over the Pacific Northwest slightly. The onshore pattern
will bring noticeably cooler temperatures to the coast with night
and morning low clouds and patchy fog. Meantime...the cooling
inland this weekend will be modest. High temperatures on Saturday
are expected to resemble those that are expected today, then
readings on Sunday will resemble those of yesterday.

Beyond the weekend...another shortwave is expected to track south
to southeast into British Columbia and carve out a deeper trough.
The track of this feature and the depth of the resultant trough
are very much in question. For at least the last couple of runs,
the ECMWF solution shows a deeper and more rapidly developing
trough than the GFS. The forecast leans toward the ECMWF idea of a
more pronounced though still largely dry trough. A slight chance
of light showers remains in the forecast for the northern portion
of our coastal waters and northward over the waters Monday night
into Tuesday. By day 7/Wednesday, uncertainty increases further
though the forecast still looks dry with temperatures around
normal.


&&

.AVIATION...24/06Z TAF cycle...Offshore NE winds are developing
over the CWA this evening. This will keep almost the entire area VFR
overnight. Patches of IFR stratus/fog are along the coast north of
Cape Blanco and also south of Gold Beach. Models are showing the NE
flow potentially eroding the stratus north of Cape Blanco toward
sunrise. Confidence in this occurring is low, however, so have
prevailed IFR at KOTH through 14z, with temporary VFR from 10-14z.
Either way, IFR will likely give way to VFR early Wednesday morning.
-Spilde

&&

.MARINE...Updated 200 AM PDT, Wednesday 24 August 2016...North winds
will continue through Thursday evening as a thermal trough remains
along the coast. Winds and seas will be at small craft advisory
levels near and south of Cape Blanco with the highest winds and seas
over the southern outer waters. The thermal trough weakens and moves
out of the waters Friday and winds will weaken as a result.

There is no major change in the way new models handle the weak low
pressure over the waters through the weekend, and we expect winds to
be light and variable during this period with no major swell train
higher than 5 feet. /FB

&&

.FIRE WEATHER...Updated 330 AM PDT, Wednesday 24 August 2016...
Critical Fire Weather situation continues again today and likely
will continue into the end of the week as daytime highs are still
about 5 degrees warmer than normal and widespread minimum humidity
in the lower teens and single digits. Winds are not expected to
reach a warning level, but models indicate winds east of the
Cascades could remain breezy into the night Wednesday night.

Offshore east to northeast flow will develop tonight and continue
through Friday morning as the thermal trough expands and strengthens
along the coast. This means another period of nighttime poor to
moderate humidity recovery over the mid slopes and ridges. The
strongest offshore flow at night looks like Wednesday night and
Thursday morning for the coast, Cascades and Siskiyous. Thursday
night and Friday offshore easterly flow and low humidities will
continue in the Cascades and may reach critical conditions in zone
617 and northern zone 623. Will need to monitor for the potential of
meeting red flag conditions for these areas.

Friday will be the warmest day inland as the thermal trough comes
inland with cooling starting at the coast. Models are coming into
better agreement with another trough moving inland to the north on
the weekend. This is expected to bring gusty west winds late
Saturday afternoon and evening, especially for areas east of the
Cascades. No precipitation is expected at this time for the weekend.
/FB

&&

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

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT Thursday for
     PZZ350-356-370-376.

$$

DW/FJB/MND



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