AVIATION
13/00Z TAFS...Cloud cover continues to move across northern California and southern Oregon this evening. In general, ceilings will stay at VFR through the TAF period. Guidance for North Bend and Roseburg suggests inconsistent periods of MVFR through the night and early morning, so timing has been included but levels may fluctuate. Coastal areas will see elevated winds develop near the end of the TAF period. -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.