Area Forecast Discussion
Issued by NWS Medford, OR

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911
FXUS66 KMFR 151500
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
800 AM PDT Mon Oct 15 2018

.DISCUSSION...15/12Z NAM in.

Clear skies prevail across the Medford CWA this morning, except
for areas of marine stratus over the coastal waters from around
Cape Blanco south. The 15/12Z Medford sounding was remarkably
dry, with a precipitable water value of 0.13 inches. Even lower
than the 0.15 inches reported on the 14/12Z sounding.

An omega block remains over the northeast Pacific, drifting very
slowly east. The anchor lows are now near Las Vegas and 33N 145W.
The high portion is centered near 42N 130W.

The block will continue drifting east, and it will start to break
up just as the ridge axis moves onshore Tuesday afternoon over the
Pacific Northwest. The ridge will remain over the area, but it
will weaken with time through Thursday.

A thermal trough remains along the coast, bringing breezy east to
northeast winds along the coastal mountains in southwest Oregon
and mid slopes and ridges in western Siskiyou county. This trough
will move onshore in a weakened state this afternoon, then move
back to the coast tonight. It will be quite a bit weaker tonight,
as compared to Sunday night, so the associated winds will be
lighter. This pattern will repeat through at least Thursday night,
but the trough will become weaker with time.

It will remain dry over the Medford CWA through Thursday with
mostly clear skies inland, except for possible late night into
morning low clouds and fog in the Coquille and Umpqua valleys and
marine stratus over the coastal waters.

The return of onshore flow will make for a cooler day Monday along
the coast. However, the inland migration of the thermal trough
will heat up inland areas today. Most of that area will see a slow
warming trend into Thursday, but temperatures may bounce around a
few degrees from day to day. By Thursday inland highs will be
10-15 degrees above normal and coastal highs will be 5-10 degrees
above normal.

After a cold Sunday night, the lows will trend warmer as well.
There is still the possibility of frost and freezes over the west
side valleys at least through tonight.

The next long wave ridge will move onshore Thursday, building as
it does so. This will reinforce the dry regime already in place.
Most areas will see warmer temperatures Friday and Saturday, and
Saturday will be the hottest day of this week for many locations.

The ridge will break to the east of the area Saturday. After that
the forecast becomes more uncertain as the medium range models
differ on the strength and timing of the upstream trough and any
fronts associated with it. If the EC solution verifies, the next
front and associated precipitation will move onshore next Monday.

&&

.AVIATION...For the 15/12Z TAFs...VFR will prevail through tonight.
The exception is a band of LIFR now near shore from Brookings to
Bandon that is pushing north very slowly. Not expecting it to make
it much further north than Cape Arago before sunrise, and the marine
layer is expected to burn back offshore later this morning.

Otherwise, gusty east to southeast low level winds from the Cascades
eastward and in the southern portion of the Rogue Valley will remain
breezy through this morning, diminishing as the afternoon
progresses. -DW/BR-y

&&

.MARINE...Updated 800 AM PDT Monday 15 October 2018...Winds have
weakened and will generally remain below 15 kts through the week.
Residual fresh swell will continue through early this morning and
seas will subside to around 5 feet later this morning. Meanwhile,
persistent long period southerly swell of around 3 feet may
produce rough bar conditions at Brookings and elevated surf at
Port Orford. Aside from this persistent southerly swell,
conditions will remain relatively calm today and Tuesday.

Wednesday into Thursday, a longer period west to northwest swell at
16 to 18 seconds will build into the coastal waters. This will
combine with the aforementioned smaller long period southerly swell
and could make for hazardous bar conditions Wednesday into Thursday.
Overall, wave heights will remain below 10 feet as this is only a 7-
8 foot swell, but given the longer period swell, surf conditions
could be a concern as well. Breaker heights of 10 to 12 feet are
possible Wednesday into Thursday and this could catch some beach-
goers off guard as this is a bit higher than what has been typical
for the past few weeks. Swell will diminish Thursday night as the
period shortens, and seas will subside again by the weekend. /BR-y

&&

.FIRE WEATHER...Updated 300 AM PDT Monday, 15 October 2018...
Dry to very dry air continues to spread and dry further today as
easterly winds continue. Wind gusts in the 25 to 40 mph range have
been observed in the Curry County coastal mountains, across the
higher terrain of western Siskiyou County, in the Cascades and
Siskiyous, and in the Ashland area of the Rogue Valley. The latest
fog image shows the a hot spot on the infamous Klondike Fire out of
the northwestern portion of the perimeter.

Later this morning we`ll see the pressure gradient and resultant
winds lessen substantially across the coastal mountains as the
thermal trough shifts inland. For all areas, except for elevations
below 500 feet along and near the the immediate coast, RHs will
remain low today.

We`ll need to keep an eye on at least a couple more items:

The first is that wind and RH could go back into RFW criteria for
portions of FWZ 280 and 621 tonight into Tuesday morning. High
resolution guidance and some MOS guidance are indicating wind and RH
hovering close to the lower end of criteria. However, conditions are
not going to be as widespread or critical as they will be through
Monday morning, so plan to cover this with a headline once the RFW
expires later this morning. If guidance trends up or obs are slower
than expected in moving out of criteria, then we would need to
extend the current warning out in time.

The second item of concern is the drying that has occurred this
weekend and it`s resultant effect on the `real deal` fire danger.
WFAS.net indicates that some areas have moved beyond moderate fire
danger, so we`re going to send out predicted #s today to get better
forecast fire danger #s for tomorrow. Additionally, the Haines Index
across much of the interior west side Tuesday through Thursday (a
mix between the mid and high calculation) is forecast to 5-6.

While winds do fade this week and RHs come up some, the trend will
be very slow and may hit a drier bump again next weekend per the
latest operational GFS. The general east flow at night/into the
morning hours does not go away until Sunday night, so the pattern is
not changing much, rather the winds are becoming lighter. As far as
moisture goes, the ECMWF and GFS hint at the first chance of rain by
Monday evening at the coast. -Lutz/Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Frost Advisory until 9 AM PDT this morning for ORZ023-024-026.
     Red Flag Warning until 11 AM PDT this morning for ORZ621.
     Freeze Warning until 9 AM PDT this morning for ORZ024-026.
     Freeze Watch from late tonight through Tuesday morning for
        ORZ024.

CA...Frost Advisory until 9 AM PDT this morning for CAZ080.
     Red Flag Warning until 11 AM PDT this morning for CAZ280.
     Freeze Warning until 9 AM PDT this morning for CAZ080>082.
     Freeze Watch from late tonight through Tuesday morning for
        CAZ081-082.

Pacific Coastal Waters...None.

$$

15/15/13



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