Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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737 FXUS66 KMFR 151535 AFDMFR Area Forecast Discussion National Weather Service Medford OR 835 AM PDT Sun Sep 15 2024 .DISCUSSION...Low pressure has moved into the region and this will bring a much cooler and cloudy day compared to the last two days. Isolated to scattered showers are on the radar this morning over the marine waters, along the coast and into the Cascade Foothills. A few hundreths have been reported out of these showers and this is likely to continue through the day. Some heavier returns are observed moving across Lake County this morning associated with a frontal band pushing across Klamath/Lake/Modoc Counties. This will be the area of focus for this afternoon regarding showers/thunderstorms along with much of Siskiyou County. High temperatures will be about 10 degrees cooler than yesterday, feeling more like late October. All of this is covered well in the going forecast, and no updates are needed this morning. Please see the previous discussion below regarding shower/thunder activity today and the next trough expected Tuesday into Wednesday. /BR-y && .MARINE...Updated 830 AM Sunday, September 15, 2024...North winds will increase today as an upper level trough slides over the region. This will bring steep wind-driven seas to areas south of Port Orford this morning. Northerly winds strengthen today as the day progresses, resulting in steep seas spreading north of Cape Blanco to all areas. Additionally, very steep and hazardous seas will develop late this afternoon for areas south of Gold Beach. These conditions will persist through Monday night, then winds will ease and seas will briefly lower into Tuesday. A front will move into the region on Tuesday bringing widespread precipitation and lowering visibility. Moderate to occasionally strong north winds and steep seas return late Tuesday into Wednesday, likely bringing the return of conditions hazardous to small craft. -Guerrero/Petrucelli && .PREV DISCUSSION... /Issued 450 AM PDT Sun Sep 15 2024/ ..New Aviation Section... AVIATION (12Z TAFs)... A complicated TAF cycle is underway as an upper level disturbance continues to pass through the region. We will see low clouds (MVFR) and showers increase across the region today. There is also a low (10-15%) potential for a thunderstorm today, but through this cycle Klamath Falls would be the main terminal for these thunder chances and overall best chance for rain showers. Otherwise, isolated to scattered showers today could impact the other terminals, but confidence was too low to include in this cycle. Guerrero PREV DISCUSSION... /Issued 251 AM PDT Sun Sep 15 2024/ SYNOPSIS...It`ll feel more like mid-October than mid-September the next several days as two upper troughs swing through the area. This will bring a cooler than normal weather pattern with some showers, isolated to scattered thunderstorms and occasionally breezy afternoon winds. We`ll maintain this pattern through Wednesday. However, signs are pointing toward a drier, warmer pattern moving in late this week (beginning Thursday) and continuing into next weekend. We will have to watch a system coming over the top that could graze the area later Saturday into Sunday. DISCUSSION...An elongated upper trough, closing off into an upper low near Vancouver Island this morning, will usher in a cooler air mass across SW Oregon and northern California today along with some showers and isolated/scattered thunderstorms. This will be the first of two upper troughs/lows that traverse the area today through the middle part of the upcoming week resulting in a pattern more resembling mid-October than mid-September. Highs today will be down about 8-12 degrees compared to yesterday for the west side valleys (low 70s) and 10 to as much as 20 degrees lower than yesterday over the East Side and in NorCal (60-70F). The best forcing for showers and thunderstorms will extend from NorCal northeastward across SE Klamath and into Lake County. This will be the focus area for wetting rainfall today. Satellite shows a corridor of moisture in this area right now and KMAX is picking up some light returns at this early hour. Meanwhile, as the low moves southward today, there will be an area of subsidence and mid-level drying on the NW periphery of the low and this will result in a relative minimum in shower activity, which will be for areas on the west side of the Cascades. That`s not to say there isn`t a chance of showers over here (including the Rogue Valley), but they`ll be much more hit-or-miss than they are over Siskiyou/Modoc up into southern Klamath/Lake counties. Coverage of thunderstorms over/down in those areas could reach scattered this afternoon/evening affecting locations like Mt. Shasta City, Alturas and Lakeview. We aren`t too concerned about the thunderstorm activity today since they`ll largely be wet storms, but they could produce cloud to ground lightning, and some gusty winds. Tonight into Monday morning, the closed low will pivot across northern California and then move into the Great Basin Monday afternoon. This will turn the mid-level flow to easterly across our area. Showers and isolated thunderstorms will continue over the East Side, while shower chances diminish west of the Cascades. Overall, rain amounts with this first system will be light west of the Cascades. Some locations will miss out on rain completely while others could get up to a tenth of an inch. Widespread wetting rain is likely though east of the Cascades where amounts of 0.10-0.25 of an inch will be common, with up to 0.50 of an inch in the mountains where showers tend to focus. There will be a break between systems late Monday night or first thing Tuesday morning, but as one upper low departs to the east, another will dig southward along the PacNW coast. Showers likely reach coastal areas again Tuesday morning, then spread inland over to the Cascades by late Tuesday afternoon. Highest rainfall probabilities will be along the coast (near 90%) Tuesday, but most areas east of the Cascades and in NE CA should be dry. This low will move into NorCal Tuesday night and showers will overspread the remainder of the region, then settle south and eastward Wednesday into Thursday. We`ll see showers gradually diminish across the area from NW to SE during this time frame. Rain amounts this time will likely be highest along the coast over to the Cascades, but near/north of the Rogue-Umpqua divide. Overall 0.50-0.75 of an inch is likely, perhaps around an inch in the coast ranges. A tenth to 0.25 of an inch appear to be the most likely amounts across the remainder of the area, though with a showery regime, some areas could have more or less. Heights are shown to rise Thursday into next weekend with a drying trend and temperatures rising back closer to normal. However, guidance does show another system moving over the top to our north during the weekend. Right now, it looks like mainly a dry trough/frontal passage Saturday or Saturday night. Rain chances at this time are less than 10%. While this could change, as of now, it appears this system is much more likely to cause an increase in afternoon/evening breezes over the east side than anything else. -Spilde FIRE WEATHER...Updated 245 AM Sunday, September 15, 2024...The main fire weather risk today will be isolated to scattered thunderstorms this afternoon/evening for portions of the Shasta, the Klamath/Modoc and Fremont National Forests. While cloud to ground lightning and outflow wind gusts are the main threats, thunderstorms will be wet and humidity will be much higher than recent days. As such, significant fire risk is low. It will remain that way through at least the middle of this week. We are expecting a drying, warming trend late this week into next weekend, but only back closer to what would be considered "normal" for this time of year. -Spilde && .MFR WATCHES/WARNINGS/ADVISORIES... OR...CA...None. PACIFIC COASTAL WATERS...Small Craft Advisory from 5 PM this afternoon to 5 AM PDT Tuesday for PZZ350-356-370-376. Hazardous Seas Warning from 5 PM this afternoon to 5 AM PDT Tuesday for PZZ356-376. && $$ MAS/JWG/MNF