774
FXUS66 KMFR 130523
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1023 PM PDT Thu Sep 12 2024

...Updated AVIATION discussion...

.DISCUSSION...

Cold overnight lows with some widespread frost and potential
freezing temperatures are the main concern tonight. Northern
Klamath County in addition to the Christmas Valley are the
locations we`re most concerned for as lows are expected to drop
below freezing in these locations tonight. Satellite indeed looks
clear with daytime cumulus field clearing out. With the current
temperature forecast on track, we are feeling pretty confident in
the current freeze headlines.

Aside from the frost and freeze warnings, satellite does indeed show
the Flat Top and Firestone fires between Lake County and Deschutes
County cooking tonight based on the GOES West 3.9um channel.
Smoke should still impact air quality around northern Lake and
Klamath Counties later tonight into Friday morning.

-Smith

&&

.AVIATION...13/06Z TAFS...While areas terminals are at VFR levels,
satellite imagery shows clouds developing over the Umpqua Valley and
Coos County. Guidance suggests these clouds may bring periods of
MVFR visibilities over North Bend and Roseburg. The timing for
possible MVFR will remain in the TAFs, but only with moderate
confidence in the possibility.

VFR levels are expected through the day Friday, with elevated and
possibly gusty winds along the Oregon coast in the afternoon. -TAD


&&


.MARINE...Updated 830 PM Thursday, September 12, 2024...A thermal
trough is bringing gusty north winds and steep wind-driven seas,
especially south of Cape Blanco. A brief period of very steep seas
is possible south of Cape Ferrelo Friday afternoon. Conditions
improve on Saturday morning, then showers and wind-driven steep seas
are possible on Sunday and Monday. /BR-y/TAD

&&

.FIRE WEATHER...Issued 300 PM Thursday, September 12, 2024...A
weak upper ridge will build into the area tonight and Friday.
Temperatures will trend warmer, closer to seasonal averages, and
humidities drier on Friday and Saturday. A weak front and upper
trough arrive Saturday night into Sunday. Ahead of this system,
breezy to gusty west winds are expected to develop Saturday
afternoon, especially east of the Cascades. Then as this system
moves into the area, expected cooler temperatures, chances for
showers (40-60%), along with a slight chance (15%) for
thunderstorms (for eastern and southeast portions of the area).
The slight chance for thunderstorms is highest in southeast
Klamath, southern Lake, eastern and southern Siskiyou and Modoc
counties. Then, on Monday, the upper low will move southward but
expect moisture to wrap around into the area and bring additional
showers, with best chances from the Cascades east and Siskiyous
south. This system moves eastward Monday night but another trough
is expected Tuesday into Wednesday, continuing to bring cool and
wet weather.

&&

.PREV DISCUSSION... /Issued 413 PM PDT Thu Sep 12 2024/


DISCUSSION...A moist northwest flow on the backside of the
departing upper trough is helping to keep the cloud cover around a
little longer than anticipated in Oregon. In northern Cal, clouds
are much less extensive. Cloud cover should dissipate early this
evening and moreso late this evening and tonight, especially east of
the Cascades. West of the Cascades, we could see stratus develop in
the Umpqua and Coquille Basin late tonight and lasting into at least
the mid morning hours Friday.

As mentioned mostly clear skies are expected east ofthe Cascades
tonight, and this will allow temperatures to drop off fairly quickly
after dark with near or below freezing temperatures late tonight
into tomorrow morning. Given this will be the first freeze of the
season and the fact the typical first freeze of the season in these
areas take place right around this time, a Freeze Warning and Frost
advisory has been issued in the event folks have any outdoor plants
will take the necessary steps to protect them.

Dry weather will continue Friday into Saturday with warmer
afternoon temperatures for the interior Friday. Saturday will be
cooler as an upper trough approaches the area along with increasing
cloud cover.

Another upper trough will drop in from the northwest later Saturday
night into Sunday bringing another round of showers for most of the
area. Showers will tend to develop sooner west of the Cascades
Sunday morning, then showers will pop up in most areas, including
east of the Cascades late Sunday morning and afternoon. Instability
will be marginal east of the Cascades and this in combination with
some PVA moving in from the west to southwest could be enough to
trigger isolated thunderstorms in southeast Klamath and Siskiyou
County, all of Modoc county and most of Lake County from mid
afternoon Sunday into early Sunday evening.

The upper trough will dig south of the area Sunday night into Monday
morning with weak ridging nudging in from the west. Meanwhile,
there`es pretty good agreement for wraparound moisture to impact
areas from the Cascades east and in northern California. These areas
could experience persistent rainfall for most of the day Monday with
showers more isolated the farther northwest we go, So for example
showers could end up being more isolated west of the Cascades and in
the northwest part of the forecast area.

A brief break in the action is expected Monday Monday night, then
another upper trough will drop south into the area Tuesday bringing
another round of precipitation, first impacting the westside
Tuesday morning, then east of the Cascades and northern Cal Tuesday
afternoon and Tuesday night.

Cool and unsettled weather is likely Tuesday night into Wednesday
morning with scattered showers likely. Showers will gradually
diminish Wednesday afternoon as the upper trough/upper low digs
south of the forecast area.

After Wednesday, there`s increasing evidence for upper ridging to
build back into the area with dry and warmer weather that could set
up by next Thursday and last into the following weekend. Stay tuned.
-Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Frost Advisory from 2 AM to 9 AM PDT Friday for ORZ029>031.

     Freeze Warning from 2 AM to 9 AM PDT Friday for ORZ029>031.

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 5 AM PDT Saturday
     for PZZ350-356-370-376.

&&

$$