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Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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385 FXUS66 KMFR 112129 AFDMFR Area Forecast Discussion National Weather Service Medford OR 229 PM PDT Sun Aug 11 2024 .DISCUSSION...We`ll be under the influence of an upper trough for the next several days. This will bring increasing onshore flow and a cooling trend. Today could be the last day of 90+F degrees for a while here in Medford as the trough is expected to gradually deepen near or just offshore of the PacNW coast through the week and especially Friday into next weekend. Coastal areas are likely to have nightly marine pushes. Inland locations will be dealing with smoke from area wildfires that will be quite thick at times, with some push east of the thickest smoke. But, weather- wise, it`s pretty benign for the second week of August. There is some weak instability and modest mid-level moisture near the higher terrain in NorCal and northeastward into SE Klamath and southern Lake counties this afternoon and evening, but really nothing to trigger deep convection. Expecting some cumulus or even a buildup or two into this evening, but there`s a less than 10% chance of a thunderstorm. Tonight, the marine layer deepens and expect a more significant push/formation of stratus into the Umpqua Basin, which could bank up against the Rogue-Umpqua Divide and even cover some of the eastern Douglas fires Monday morning. Some guidance is even showing the clouds pushing over the Divide and into portions of the Rogue/Illinois valleys, but probably not quite to here in Medford. Some fog/drizzle are possible along the coast during the early morning. Meanwhile, an upper shortwave out over the ocean this evening will swing through NorCal on Monday. With a bit more forcing, and enough moisture/instability, we think there`s a little better shot at isolated thunderstorms from NorCal northeastward across SE Klamath and into Lake County. The remainder of the area will remain dry and at least a few degrees cooler. There will be more westerly winds Monday afternoon behind this system, so that should push the smoke eastward, but a lot is dependent on fuel type, burn operations and other non-weather factors. The pattern for the smoke should follow a fairly typical ebb and flow with the thickest smoke settling into the valleys at night/early morning and pushing eastward during the midday/afternoon/evening for at least the next few days. This could bring the thicker smoke into the Klamath Basin. Air quality products are out for eastern Douglas, Jackson, Klamath and Lake counties and these will be updated on Monday. Thunder chances could linger into Monday night over the far east side since it will take some time for the short wave to move out to the east. Most areas should have a break Tuesday into Wednesday as the upper trough weakens slightly and another disturbance approaches from offshore. Temps moderate a bit by Wednesday, but remain near to a bit below normal. The next short wave moves in Wednesday evening into Thursday evening and this could bring the next chance at showers/thunderstorms. Since the flow aloft will remain generally from the west-southwest, activity is most likely from the Cascades eastward. Right now, PoPs stand at 20-30% Wednesday evening/night and again Thursday afternoon/evening. Models/ensembles then show the upper trough consolidating into a closed low off the PacNW Friday into this weekend. There are still many details to figure out here with just how deep the trough will be and how far south it will get (and also if it`s closer to the coast or even onshore). This will impact just how much, if any precipitation we get this far south. Right now, since it is still August, precip chances are on the low side. But, daytime maximum temperatures should be about 5-10F below normal. -Spilde && .AVIATION...11/18Z TAFS...IFR/LIFR conditions along/near the coast this morning have cleared to VFR, but are expected to return this evening and tonight, perhaps pushing well inland within the Umpqua Basin and all areas west of the coastal ranges. Inland TAF sites will be under mostly clear skies with breezy afternoon winds, with widespread smoke impacts expected to produce MVFR/IFR visibilities, especially in area valleys where smoke settles in overnight and persists into the morning. -BPN && .MARINE...Updated 230 PM Sunday, August 11, 2024...Wind speeds will peak this afternoon combined with steep seas which will result in conditions hazardous to small craft through this evening. The probability for wind gusts of 34 knots or greater south of Cape Blanco is roughly 40-60% where we have the current Small Craft Advisory. These speeds will remain breezy/gusty until sunset before slowly decreasing overnight. Thereafter, winds and seas will both ease through at least the middle of the week. -Guerrero/Smith && .FIRE WEATHER...Issued 200 PM Sunday August 11, 2024...After another day of above normal temperatures today, the forecast period will trend cooler through next week with increasing onshore flow, improving humidities, and breezy afternoon winds as upper level troughing settles in and remains over the Pacific Northwest. We are expecting a relatively strong marine push tonight into tomorrow, with extensive stratus and fog decks west of the Cascades that may even push into the Rogue Valley by daybreak Monday. We also expect increased winds through the day, especially east of the Cascades. Despite these winds, rising humidities should keep us below any critical thresholds, although it might briefly approach those thresholds over eastern Lake and Modoc counties (FWZs 285 and 625). With the weak upper trough overhead, some instability is expected to develop this afternoon and again Monday afternoon. Instability is marginal at best, with little or no trigger, and mid level moisture is lacking, therefore the threat for thunderstorms are very low. The most likely scenario will be cumulus build ups this afternoon over the Cascades, higher terrain east of the Cascades, and in northern California. A shortwave will slide under the main trough and pass just to the southeast of the area Monday. The potential for isolated thunderstorms will therefore be higher Monday afternoon, mainly east of the Cascades and across northern California, with increased mid level moisture and the shortwave acting as the trigger. Given the overall weak system, marginal instability, and the track of the shortwave, only isolated storms are expected, and even then, confidence is low. With the trough remaining overhead through the week, we can not completely rule out additional afternoon convection, particularly Wednesday and Thursday afternoons as additional shortwaves pass through the region. Again, we only expect isolated storms should any develop, and confidence is pretty low across the board, especially given that wildfire smoke has a tendency to suppress convective development. The main threat from any convection through this week will be outflow winds, which could initialize not just from showers and thunderstorms, but also any of the more robust cumulus fields. Models are showing the potential for a much stronger, broader trough arriving and setting up over or very near the area late this week into this weekend. This will maintain our cooler temperatures and higher humidities, and may also produce more widespread chances for showers and thunderstorms Friday into Saturday. While wetting rains are very unlikely, we will keep a close eye on how the system develops, as cooler temperatures, higher humidities, and even a small amount of rain will be very welcome to fire concerns. -BPN && .MFR WATCHES/WARNINGS/ADVISORIES... OR...CA...None. PACIFIC COASTAL WATERS...Small Craft Advisory until 2 AM PDT Monday for PZZ356-376. && $$ MAS/BPN/CZS