606
FXUS66 KMFR 231558
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
858 AM PDT Tue Oct 23 2018

.DISCUSSION...
No updates are necessary this morning.

Rain is showing up on the radar between about 30 and 80 nautical
miles west of the coast. The forecast looks well on track for
measurable rain from along and near the coastal ranges westward
and east to about Grants Pass and Roseburg this afternoon into
this evening. Most areas east of there from the Oregon Cascades
and Marble Mountains westward, to include the Rogue Valley, will
probably get a few drops of rain, and even an isolated hundredth
or two is possible. Altogether, the rainfall with this front will
fade out as the front moves inland.

Out in the longer term the models continue to look promising for
some wetting rainfall across most of the area toward the end of
the month into the first week of November. We`ll continue to tread
lightly with the precipitation forecast probabilities east of the
coastal ranges and Umpqua Basin in the long term portions of the
forecast though because the guidance has been consistently
indicating these weather systems to be wetter in the 7-14 day
period than what they end up being. -Lutz

&&

.AVIATION...For the 23/12Z TAFs...Along the coast and into
the coastal ranges, IFR/MVFR conditions are expected to persist
through the early half of the morning. Low ceilings will lift to
MVFR with local VFR as a front moves towards the coast. As the front
moves onshore in the afternoon, expect rain along with widespread
MVFR ceilings and mountain obscuration. Rain will end around 00 UTC,
but low clouds and fog are expected to develop in the evening and
overnight, resulting in MVFR/IFR ceilings and visibilities into
Wednesday morning.

Inland, expect mainly VFR conditions to prevail into this afternoon,
except for local areas of MVFR visibilities in patchy fog in the
Umpqua basin. As the front moves inland later today, expect areas of
light rain to develop from the coast into the coastal mountains and
Umpqua Basin with areas of mountain obscurations. Most other areas
should remain dry, with gusty southwest winds likely in the
afternoon and early evening east of the Cascades. VFR should then
prevail through the night, again with the exception of portions of
the Umpqua basin, where MVFR may develop by early Wedensday morning.
-BPN/CC

 &&

.MARINE...Updated 200 AM PDT Tuesday 23 October 2018....South winds
will increase ahead of a weak front that will make its way through
the coastal waters today. Even though the front is expected to wash
out as it moves onshore, some light rain and periods of low
visibility are likely to accompany its passage. Also, gusty winds
and steep seas are expected to develop by mid-morning for the bulk
of the forecast area and persist until after the front moves onshore
this evening.

Conditions will improve tonight, with west swell continuing through
Wednesday. The next front will move into the waters on Thursday, and
is expected to produce another round of gusty south winds and steep
seas. Conditions will improve by Friday morning, as high pressure
builds in overhead through Saturday. Another front is forecast to
pass through the region Sunday. -BPN

&&

.FIRE WEATHER...Updated 330 AM PDT Tuesday, 23 October
2018...South-southeast winds are becoming gusty over the coastal
mountains and through the Shasta Valley this morning, and conditions
remain relatively dry in these locations. While winds will remain
gusty and increase until the front moves onshore this afternoon,
they will gradually shift to more of an onshore (southwesterly)
direction, and this will bring higher humidities to the area. Any
chance for wetting rainfall is expected to be confined mostly to the
coast and adjacent mountains with lighter rain (a few hundredths of
an inch) making it as far east as the I-5/Highway 199 corridor.
Expect little to no rain east of I-5 and none in and east of the
Cascades.

Thursday`s front looks much weaker than previously thought and is
unlikely to produce much, if any, rain inland from the coast.
Another front may brush the area Friday, then guidance generally
agrees on a wetter front, primarily on the west side, Sunday into
Monday. That said, it is hard to get too excited given the recent
tendency of models to over-forecast rain in the extended. -Wright

&&

.PREV DISCUSSION... /Issued 330 AM PDT Tue Oct 23 2018/

SHORT TERM...Many of the short term grids were massaged this
morning, but no major changes were made.

A front is rapidly approaching the coast this morning. Stratus
has pushed well inland over coastal areas as well as the Umpqua
Basin this morning. Elsewhere inland, skies remain mostly clear,
but that will change later this morning as mid and high clouds
increase ahead of the front. We`ll see some rainfall along the
coast with this front, but it falls apart pretty rapidly as it
moves inland today. As a result, we don`t expect much more than a
few hundredths of rain inland from the immediate coast, and little
to none as you get to I-5 and points east.

The bigger impact, and it isn`t much of an impact, is the south
winds ahead of the front. It`s already becoming gusty over the
coastal mountains and through the Shasta Valley. While these
winds will increase until the front moves onshore this afternoon,
we don`t expect anything excessive. It also remains dry in the
locations where the wind is blowing, but humidities are coming up
along the coast, and we expect this to continue as clouds arrive
and the flow turns more onshore.

This first front peters out over the west side this evening, and
then the balance of tonight will be dry. Nothing much happens
Wednesday as a very weak upper ridge slides through. The next
front is scheduled for Thursday, and this one looks weaker with
each model run, and its rainfall is now expected to be light and
confined mainly to the waters and coast north of Cape Blanco. Pops
and rainfall amounts have been lowered given the latest trends in
guidance. Winds are not expected to be much of a concern with
Thursday`s front, but they were bumped up a little in the usual
spots such as the east side. -Wright

LONG TERM...Friday 26 Oct to Monday 29 Oct...The second sacrificial
front brushes the northwestern portion of the forecast area with
some rainfall Friday, but most areas will remain dry as ridging
builds quickly behind the front. To give an idea on how little this
front impacts the area, surface temperatures are expected to rise on
Friday as the upper ridging builds.

Temperatures rise further on Saturday, and there is high confidence
in dry weather for the entire forecast area on Saturday. All GEFS
members are void of precipitation for the forecast area on Saturday,
and we are forecasting high temperatures of 15 degrees above normal
for Saturday afternoon. We won`t be surprised if we manage to hit 80
degrees in a few West Side valleys Saturday afternoon. In contrast,
we will be very surprised if we see 80 degree temperatures after the
weekend given how rare it is to observe 80 degrees in West Side
valleys in late October (and very rare in November).

Operational models show another chance for rain Sunday, but
confidence is low for rainfall at this point, given the recent
"overforecasting" of rainfall by the models. This is especially the
case given the building ridge on Saturday, and the fact that GEFS
median QPF is zero on Sunday even for the coast. Another tool in the
toolbox, the CFSV2 model, suggests dry conditions in week 2 for its
latest run (initializing on 21 Oct). Monday we continue to feature
slight chance of precipitation for most areas under weak upper
troughing per the GFS and EC operational models. Even though we`re
not confidence in rain chances Sunday and Monday, we are more
confident in daytime temperatures lowering to closer to normal for
this time of year.

-Keene

&&

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

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 11 PM PDT this evening for
     PZZ350-356-370-376.

$$

BTL/MAS/MAP

NWS MFR Office Area Forecast Discussion