Weather Service Report


585 
FXUS66 KMFR 230554
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1054 PM PDT Wed Sep 22 2021

.DISCUSSION...Updated AVIATION and MARINE sections below. -Spilde 

&&

.AVIATION...23/06Z TAFs...Areas of IFR/LIFR fog/stratus will 
affect the coast overnight into Thursday morning. There can also be 
patches of fog and/or stratus in the coastal valleys as well as the 
Umpqua Basin around daybreak; otherwise, expect largely VFR across 
the area over the next 24 hours. Gusty north winds are expected 
Thursday afternoon/evening at North Bend. -Spilde


&&

.MARINE...Updated 830 PM PDT Wednesday 22 September 2021...
A thermal trough will strengthen along the coast and result in 
another round of gusty north winds and steep to very steep seas 
tonight through Thursday. The strongest winds and steepest seas will 
be south of Cape Blanco. Steep seas are expected to persist into 
Friday, but will ease Friday afternoon through Saturday. Then a 
significant west swell may build into the waters early next week. 
Early indications are showing the swell arriving Monday night and 
peaking in the 12-16 foot range on Tuesday. -Spilde

&&

.PREV DISCUSSION... /Issued 907 PM PDT Wed Sep 22 2021/ 

UPDATE...With the dry cold front already moved through the
region, skies are already clearing across the inland areas.
However, with current dew points in the Umpqua basin at or a 
little bit higher than expected low temperatures in that area, am
expecting stratus to form in that area by the morning. Have
adjusted the sky cover in that area to reflect this, otherwise 
the forecast looks on track.

PREV DISCUSSION... /Issued 237 PM PDT Wed Sep 22 2021/ 

DISCUSSION...Happy fall, everyone. The autumnal equinox happened
at 12:20 pm today, but the short-term forecast will remind you
more of summer. Despite a frontal passage early this morning, a
ridge will build back into the area generating a thermal trough
and some warmer weather. Ensembles suggest that temperatures will
likely reach into the 90s by Friday for the west side valleys with
highs reaching back into the 80s for the East Side and 70s for the
coast. However, the ridge will begin to break down as flow become
more zonal over the weekend, bringing some somewhat breezier winds
with cooler temperatures over the weekend, which will begin to
feel like early fall. 

The main story of the forecast will be at the start of next week
when a frontal system comes through the area. Models agree that
there will be a front, but they disagree with the timing, the
strength and the speed of said front. Taking a look at the
ensembles and their members, it appears as if the ECMWF ensemble 
has a more favorable solution for rainfall in southern Oregon and 
northern California with a low that deepens as it approaches the 
Pacific Northwest. The GEFS, however, keeps the front pointed
farther to the north with southern Oregon getting some rainfall,
but not as much, and not for the duration. Looking at the
clusters, it appears as if the ensembles are favoring the more wet
solution of the EC ensemble mean, as does the National Blend of
Models in which this forecast has trended toward. That being said,
it is important to be circumspect with regard to this solution
since this pattern will rely on the ridge breaking down over the
weekend antecedent to the front's arrival on Monday.

The impacts of this front will be mainly felt in the form of
wetting rain, however it is important to note that the amount of
rainfall from this system will not be as much as the previous
system front. Winds may be breezy ahead of the front as well.

After the frontal boundary passes through, showers will linger for
a short while before drying out. Forecast confidence decreases as
ensemble spread becomes diffuse, but chances remain that we'll 
remain cooler and another front could approach by the end of next 
week as well. -Schaaf

AVIATION...22/18Z TAFs...VFR conditions will prevail through this 
evening aside from some haze over N. Cal. Breezy to gusty winds are 
expected in the late afternoon and early evening for most locations. 
Then, this evening and overnight, areas of IFR/LIFR cigs/vis will 
develop along the coast. There is an 80% chance that marine moisture 
will spill into the Umpqua Basin tonight with a 40% chance of an 
MVFR ceiling forming after 12z. -Miles

MARINE...Updated 200 PM PDT Wednesday 22 September 2021...
West swell will build across the waters this morning and persist 
into this evening, then gradually lower. A thermal trough will 
develop along the coast late this afternoon through Thursday. Expect 
another round of gusty north winds and steep to very steep seas to 
develop late this afternoon into this evening, then continue through 
Thursday, with the strongest winds and steepest seas south of Cape 
Blanco.  Gusty winds and steep seas are expected to linger on 
Friday, mainly across the outer waters beyond 10 nm from shore. 
Winds and seas lower on the weekend. Then a significant west swell 
may build into the waters early next week. -CC

FIRE WEATHER...Updated 200 PM PDT Tuesday 21 September 2021...
Overall, relatively quiet weather is expected through the weekend. 
The only concerns in the short term, if there is any will be gusty 
winds later this afternoon into this evening in the wake of an upper 
trough passage. However relative humidities will be higher and were 
not expecting any headlines. Also we can expect moderate to locally 
poor overnight overnight recoveries in fire zones 618, 619 and 
western 280 Thursday night and Friday night. 

Dry weather will continue through the weekend with temperatures 
heating up Thursday and Friday for most inland locations. 
Temperatures will be highest in the Rogue and Illinois Valleys where 
max values could end up in the lower to mid 90s. East of the 
Cascades will not be as hot, but still we an expect values in the 
lower to mid 80s. Slight cooling is expected Saturday and Sunday as 
the upper ridge flattens out with increasing onshore flow.

Winds after today are not expected to be much of a concern. Yes. 
we'll get our typical afternoon breezes east of the Cascades, but 
nothing that is considered noteworthy. 

Next week, the operational ECMWF and GFS are in pretty good 
agreement showing an increased chance for wetting rain along and 
west of the Cascades as an upper trough deepens offshore and a cold 
front approaches southwest Oregon. Unlike the last one, this front 
does not have a deep moisture fetch, therefore rainfall amounts are 
not going to be significant. There are timing differences with the 
front with the ECMWF bringing the front and precipitation sooner. 
However typically when an upper trough digs (deepens) offshore, it 
typically results in a later arrival of the front and precipitation. 

Of note: The individual ECMWF ensemble members show mixed results of 
the onset of precipitation Monday, but it looks like we'll 
see increasing chance of precipitation by the start of next week.  

The general consensus in the long term (beyond next Tuesday) points 
to a strong upper ridge in the eastern third of the U.S. with a 
general troughiness in the Pac NW which could be a bit of good news 
in that the chance for temperatures heating up is pretty low and we 
could see an increased chance of precipitation. -Petrucelli 

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Small Craft Advisory from 8 AM Thursday to 5 AM PDT Friday for 
     ORZ021-022. 

CA...None.

Pacific Coastal Waters...
     Small Craft Advisory from 8 AM Thursday to 5 AM PDT Friday for 
     PZZ350-356-370-376. 
     Hazardous Seas Warning from 8 AM Thursday to 5 AM PDT Friday for 
     PZZ376. 

$$

MAS/MAS/MAS

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Western Regional Climate Center, wrcc@dri.edu