Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 210353 CCA
AFDMFR

Area Forecast Discussion...CORRECTED
National Weather Service Medford OR
853 PM PDT Fri Apr 20 2018

.UPDATE...A weak front is slowly approaching the Coos County coast.
Though there haven been some radar returns indicating
precipitation, based on gauge data it doesn`t look as if much (or
any) is reaching the ground. Will probably see some sprinkles
along the coast and possibly into the Umpqua Valley tonight as the
front moves inland... but likely no more than a few hundredths.
High temperatures today were 5 to 10 degrees above normal across
the area. Tomorrow will likely be a few degrees colder than today
due to that front. The only updates made to the forecast were
minor changes to temperatures over the next 24 hours. Otherwise,
current forecast is on track, see previous discussion below for
more details. -M&M

&&

.AVIATION...21/00Z TAF CYCLE...At the coast, VFR conditions will
lower to IFR around 3z as marine stratus develops ahead of an
approaching front. CIGS are expected to improve behind the front
around 15z Saturday morning with VFR to follow into Saturday
evening.

Inland Westside, VFR CIGS will continue into tonight. Cigs will
lower late tonight and could hover close to MVFR towards daybreak
Saturday with partial mountain obscuration mainly along and north of
the Umpqua Divide and at west facing slopes of the Cascades.
Elsewhere, including Medford and Klamath Falls, VFR conditions will
continue through Saturday evening. -Petrucelli/DW

&&

.MARINE...Updated 800 PM PDT Friday 20 April 2018...Calm weather
will continue through tonight. A weak front will dissipate as it
moves onshore early Saturday morning. Offshore high pressure will
build and strengthen west of the waters Saturday morning. At the
same time a thermal trough will develop and strengthen along the
coast. This will result in increasing north winds and steep wind
driven seas developing late Saturday morning then lasting through
Sunday evening. There`s good agreement winds will be strongest
from about Gold Beach south, but low end gales are still expected
just south of Bandon and beyond 10 nm from shore, thus affecting
the southern portion of Zone 370. Elsewhere small craft advisory
conditions are expected. Please see MWWMFR for more details.

Winds and seas will gradually lower Sunday evening, especially over
the northern waters. However, steep wind driven seas will persist in
the southern waters, and it is not until Sunday night that they are
expected to diminish below gale force.

The general consensus is for the thermal trough to build north and
weaken Sunday night through Monday. This will result in diminishing
winds and seas. This pattern is not expected to change much Tuesday
and Wednesday, therefore conditions should be calmer during this
time. -Petrucelli

&&

.PREV DISCUSSION... /Issued 225 PM PDT Fri Apr 20 2018/

SHORT TERM...Rest of today through Monday night...Spring-like
weather is in place as temperatures are running about 5 to 10
degrees warmer than they were this time yesterday. Mid-level
clouds associated with a weak front are pushing inland. For those
away from the coast and south of the Umpqua Divide, this will be
all that is really noticed about the front as it will wash out as
it moves inland. Those along the coast and north of the Umpqua
Divide could see some light precipitation late this evening and
overnight. There are some returns on the radar already, but a look
observation sites and area webcams show that nothing is making it
to the ground. After this weak front moves through tonight, flow
aloft becomes zonal and a thermal trough will develop along the
coast Saturday, leading to gales in the marine waters and
seasonable temperatures.

A shortwave trough will move through on zonal flow Sunday. Models
have trended further south and deeper with this trough which could
lead to possible convection in the far eastern portions of the
forecast area. Instability parameters look marginal at best and
there really isn`t much southerly flow ahead of this trough to bring
in the moist unstable air to "prime the pump". Although moisture is
limited, models are indicating enough instability to warrant a
mention of slight chance of thunderstorms for eastern portions of
Modoc county and southeast Lake county Sunday afternoon. For the
rest of the area, conditions will be similar to Saturday (dry and
mild), but may be a few degrees warmer along the southern coast
thanks to the Chetco Effect.

Upper level ridging builds in Monday and temperatures will begin a
warming trend. Monday will be quite warm for this time of year with
temperatures around 10 to 15 degrees above normal. This translates
to upper 70s west of the Cascades, with some locations reaching the
80 degree mark (low to mid 80s in the Klamath River Valley in
northern California), and mid to upper 60s east of the Cascades.
Temperatures will only get warmer as we head into the extended. /BR-y

LONG TERM...Tuesday morning through Friday night...The focus for
this discussion is how the models are handling the low in the
Pacific and when it will actually arrive inland. A few days ago
the GFS was forecasting that to be around Tuesday and Wednesday,
but the slower ECMWF solution was correct. We went with the ECMWF
forecast today, which is depicting the low hitting us around
Friday. Stayed away from thunderstorms at this time because we
didn`t see any instability in the area, so just some showers
forecasted at this point.

The other topic will be high temperatures across the region Tuesday
to Thursday.  The guidance has warmed up over the last few forecast
cycles.  High temperatures are expected to easily break the 80`s in
the west side valleys and mid 70`s for the east side.  Have moderate
to high confidence in these warmer temperatures. Some records may
fall Tuesday through Thursday, but we`re not expecting records in
the west side valleys to fall.  Right now Thursday is looking like
the warmest day as thats when the ridge is at it`s strongest, but
all three should be quite warm. -Smith

&&

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

CA...None.

Pacific Coastal Waters...Small Craft Advisory from 1 PM Saturday to 11 PM PDT Sunday for
     PZZ350-356-370-376.
     Gale Warning from 1 PM Saturday to 11 PM PDT Sunday for
     PZZ356-370-376.

$$

MSC/MNF/MAP



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