MARINE
Updated 845 AM Saturday, September 7, 2024...Moderate north winds will continue steep seas in the outer waters, beyond 10 nm, into this evening. Steep seas could also briefly reach the inner waters. Winds will decrease and seas will subside tonight into early Monday. A brief increase in wind dominated seas is likely on Monday, with low end Small Craft conditions possible for the outer southern waters. Weak low pressure will move into the waters Tuesday with light to moderate winds. Some evidence points towards increasing north winds later next week. _petrucelli



FIRE WEATHER
Issued 800 AM Saturday, September 7, 2024...Hot, dry, and unstable conditions will continue into this weekend. Isolated dry thunderstorms remain a concern for today. Additionally, gusty winds and low humidities may result in brief or local critical conditions for areas in the Scott and Shasta Valleys and east of the Cascades.

Current models show the upper level disturbance remaining just off the southwest Oregon coast today, then gradually moving inland tonight and east on Sunday. This slightly slower inland progression is allowing for isolated showers and thunderstorms to develop over eastern portions of the area, including Lake and northern Klamath Counties. This is also a very low (10%) chance for storms into eastern Douglas County this afternoon/evening. We have updated the forecast to reflect this changes and added a headline. Storms are expect to be isolated and have some rain with them. Gusty outflows are possible again near thunderstorms.

Gusty south to southwest winds and dry humidities are expected again this afternoon and early evening, for the Scott and Shasta Valleys as well as for some areas east of the Cascades into southeastern fire weather zone 624, southern 625 and eastern 285. Conditions may near critical RH/wind levels in these areas. A headline is in the forecast for these potential conditions.

Sunday and Monday, temperatures are expected to trend less warm as another upper trough approaches the region. However, humidities will remain dry. On Monday, there is also a potential for some breezy afternoon conditions in Modoc and Lake counties. The trough and associated front will then move through Tuesday and Wednesday, resulting in chances for light rain showers and isolated thunderstorms, cooler temperatures, and a potential for breezy to gusty winds. Confidence is low on the strength of this trough and how much rain will arrive, but there is a chance (10-20%) for wetting rainfall (0.25"+) on Wednesday for areas from the Cascades west. The thunderstorm potential is current low (10-20%) and is focused on Wednesday for areas east of the Cascades, mainly in Lake and Modoc counties.

-CC

PREV DISCUSSION
/Issued 448 AM PDT Sat Sep 7 2024/

Updated Aviation Discussion.

DISCUSSION (Today through Friday)...

Overview:

With this round of thunderstorms in the rearview mirror, we are now focused on the trend towards cooler temperatures next week, and a chance at widepsread light rainfall during the middle of next week (Tue/Wed). That being said, we are still going to see at least elevated/near-critical fire weather candidness through the weekend and into Monday given the hot, dry, and at times breezy conditions.
Please see the fire weather section below for further information.

Further Details:

Upper level shortwave trough will continue to pass through the region today, yet the placement/orientation of the upper level energy should keep most of the convection north and east of our forecast area. However, there is an area of potential development across northern portions of both Klamath and Lake Counties where lingering PVA continues to round the trough. We can see this now on radar with some high based cells over northern Lake County. Very little--if any--rainfall is actually hitting the ground given the dry air near the surface. This leads to the potential for virga to create some gusty winds now through late morning/early afternoon. We could see gusty winds around 25-45 mph through this timeframe. Dry air is anticipated to move in quickly this afternoon, so can't image these chances going too far into the afternoon as showers run out of moisture for development. This chance is <15% given the progression of the disturbance, but if the trough happens to slow down at all we could see those chances increase. Something to watch for later to update the forecast as needed.

We will end the weekend and go into early next week under zonal flow as the aforementioned trough slides east. By Tuesday, we will see the early stages of a developing trough over eastern parts of the Gulf of Alaska. This trough will dig south and eventually a broad area of cyclonic flow will consume the western CONUS. Deterministic models are in generally good agreement through Wednesday evening which does boost confidence for this rainfall event. However, there are some stark differences within the suite of ensemble members, especially the suite of GFS ensemble members versus the EC members.
Of the 30 members from the GFS, only a handful have QPF compared to the EC where nearly every member (out of 50) has QPF. This is really concerning with regards to confidence in the forecast. Interestingly enough, the National Blend of Models (NBM) has increased the probability for 0.10" or more of rainfall over 48 hours ending Wednesday night/Thursday morning. That probability is now 30%-60% for 0.10" or more of rainfall compared to 24 hours ago when it was 10%-40%. The NBM does weigh the EC more in the extended so its not completely a shock, but this is something we should watch going forward because at this time widespread light rainfall does appear to be a possibility. We will continue to monitor this next system as the rainfall would be welcoming to the wildfire situation across the region.

Lastly, we are looking at a significant cool down next week compared to the last couple of days. Wednesday will be the peak of this cooling with high temperatures likely not hitting 80 degrees for nearly the entire area. The probability for 80 degree high temperatures or greater on Wednesday is 0-10%. On Thursday, even our hotter locations (valleys) only have a 20-30 percent chance of hitting 80 degrees. So, we are looking at the potential for highs to be about 25+ degrees cooler than the last couple of days. Its going to actually feel like fall middle of next week with cooler temps, clouds, and light rainfall.

-Guerrero

AVIATION
07/12Z TAFS
Along the coast and over the marine waters, stratus and fog will result in continued IFR/LIFR ceilings for all areas, including North Bend for most of the TAF period. It's possible ceilings could briefly improve to MVFR between 21-23z, but confidence is high enough to include this at the North Bend TAF.

The marine stratus will push into the lower Umpqua and Coquille valleys by daybreak, but will stay north and west of Roseburg, then burn off between 16-18z. Marine stratus will return in similar locations late tonight.

Elsewhere VFR conditions will continue through the TAF period. The exception will be in the vicinity of the Devils Knob Fire and areas to the north where MVFR visibilities are possible. -Petrucelli

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

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 8 PM PDT this evening for PZZ370-376.