FXUS66 KMFR 152138
Area Forecast Discussion
National Weather Service Medford OR
238 PM PDT Mon Oct 15 2018
.DISCUSSION...15/12Z NAM/GFS/EC in.
Clear skies prevail across the Medford CWA this afternoon, except
for areas of marine stratus over the coastal waters and smoke from
the Klondike fire. 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 is moving inland in a weakened state this
afternoon. It will move back to the coast tonight, but it will be
weaker than it was Sunday night, so the associated winds will be
lighter. This pattern will repeat through at least Thursday night,
with the trough becoming 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 is making for a cooler day along the
coast. However, the inland migration of the thermal trough is
bringing warmer temperatures to the inland areas. 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 will still be areas of frost and some sub-freezing lows over
the west side valleys 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 15/18Z TAFs...VFR is expected to prevail across
southern Oregon and northern California today. A couple areas
downwind of wildfires could see some visibility reductions, but
these area will be relatively small. The winds today will be much
weaker than they were yesterday. -Schaaf
.MARINE...Updated 200 PM PDT Monday 15 October 2018...Winds will
generally remain below 15 kts through the week. Persistent long
period southerly swell of around 3 feet may produce rough bar
conditions at Brookings and elevated surf at Port Orford through
tomorrow. 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. As a result, have issued a beach hazards
statement. Swell will diminish Thursday night as the period
shortens, and seas will subside again by the weekend. -Schaaf/BR-y
.FIRE WEATHER...Updated 230 PM PDT Monday, 15 October 2018...
A very dry air mass remains in place this afternoon as east winds
gradually diminish this afternoon. The 15Z SREF indicates the
pressure gradient this morning was about 14MB across the forecast
area, and it's forecasting it to be about 10MB tomorrow morning.
Thus, tonight through Tuesday winds are still expected to remain
high enough for red flag warning conditions to continue for portions
of western Siskiyou County and the Siskiyous, but they will be
lighter than they have been the last two mornings. RHs are expected
to reach their lowest values for the week today. Winds will diminish
below critical levels by Tuesday night, if not sooner, but RHs are
likely to remain low as a light easterly flow continues into the
weekend. The current very low RHs are expected to nudge upward
through Thursday, however. Lighter east winds could increase some
again this weekend, though they are likely to be much lighter than
has been observed the last two days. Current indications from the
GFS is for a pressure gradient around 6MB Saturday morning versus
the 16MB analyzed by the GFS for Sunday morning and 12MB analyzed
this morning. A pattern change is expected to bring higher RHs and,
possibly, some rain early next week. -Lutz
OR...Beach Hazards Statement from late Tuesday night through
Wednesday evening for ORZ021-022.
Frost Advisory from 2 AM to 9 AM PDT Tuesday for ORZ023-024-026.
Red Flag Warning until 8 PM PDT Tuesday for ORZ621.
Freeze Warning from 2 AM to 9 AM PDT Tuesday for ORZ024-026.
CA...Frost Advisory from 2 AM to 9 AM PDT Tuesday for CAZ080.
Red Flag Warning until 8 PM PDT Tuesday for CAZ280.
Freeze Warning from 2 AM to 9 AM PDT Tuesday for CAZ081-082.
Pacific Coastal Waters...Beach Hazards Statement from late Tuesday
night through Wednesday evening for PZZ350-356.
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