Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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273 FXUS66 KMFR 242119 AFDMFR Area Forecast Discussion National Weather Service Medford OR 219 PM PDT Tue Sep 24 2024 .DISCUSSION... Overview: Well above normal temperatures are still expected today. In fact, a few westside valley areas could flirt with triple digits. We are still expecting rain showers through the day tomorrow, and we could start to see these chances increasing along the coast by late morning (~10am-11am). We are not expecting these showers to go past 8p-9p tomorrow night. Generally light rainfall amounts expected for areas on the westside, with areas along and near the coast having the best chance to accumulate precipitation. That said, still not expecting a lot of rainfall with this system, but some westside areas could see amounts approaching 0.10" of rainfall. Relatively quiet weather expected through the rest of the week. Further Details: A Rex Block pattern is evident over the western CONUS today. An area of high pressure (closed contour) on the poleward side of a closed low pressure system off the southern California coast is expected to continuing sliding east through tonight. This high will eventually be centered over the Four Corners region, and by Wednesday an Omega Block pattern will be evident over the entire CONUS. The location of the H5 high will allow for the trough over the Pacific to ride the western periphery of the high into the PacNW. At this time, the once closed low will now be an open wave as it passes through the region, so it is expected to be a progressive system with rain showers moving west to east through the day relatively quickly. Given the quickness of the system, we likely wont have an opportunity for high rainfall amounts given both the speed and lack of convective elements (CAPE < 75 J/kg). If you draw a line from roughly Brookings to Diamond Lake Oregon, areas to the north and west of this line will have the greatest chance for rainfall accumulation. Elsewhere, very little rainfall (trace to a couple hundreths) is expected. For those areas west and north of that line, there is about a 10%-50% probability for rainfall amounts >= 0.10" over 12 hours ending Wednesday evening. This is one of those high PoP but low QPF scenarios where rainfall in very likely along and near the coast, but the amounts are just not going to be very high. Thereafter, the forecast is relatively quiet with another system likely going north of our area Thursday evening/night, but it might clip parts of far northern Coos County and NW Douglas County with rainfall chances. The biggest change for this forecast was the increase in high temperatures later this week/weekend. Saturday, for example, went up almost 10 degrees in some locations. The Omega Block that sets up across the CONUS could make the long term forecast difficult, especially once Tropical Storm Helene gets absorbed into the mean flow. It will be interesting to see how the Omega Block responds to tropical storm. In other words, we could see some fluctuations in the extended if models don`t handle the blocking pattern well with the addition of Helene. && .AVIATION...24/18Z TAFS...VFR prevails over the area late this morning. This will continue through early this evening, then marine stratus/fog offshore will move into North Bend around sunset with conditions deteriorating to IFR/LIFR. Most immediate coastal areas will have some form of restricted visibility or lower ceilings overnight into Wednesday morning. Inland, VFR continues through most of the overnight, but a deepening marine layer could bring MVFR ceilings into Roseburg toward morning. A frontal system then could bring some light rain to coastal areas and other areas north of the Rogue-Umpqua Divide Wednesday afternoon. This front will cause gusty W-SW winds (25-35kt) Wednesday afternoon and evening east of the Cascades and in NE California. -Spilde && .MARINE...Updated 230 PM ,September 24, 2024... A west-northwesterly swell has arrived in the waters and that swell will persist through the week. A cold front will push through the waters on Wednesday, bringing rain and some weak southerly winds before winds shift back to northerly yet again. The big change will be towards Friday when another cold front shoots down the coast and a strong thermal trough will like develop around Friday night and Saturday. The latest forecast has winds reaching gale force in the southern outer waters. A more probabilistic approaching shows these winds have a 50% chance of reaching gale force. Even if they don`t reach gale force, the winds will still likely be strong. We waited to issue a gale watch to gain a little more confidence on the evolving pattern. Otherwise, plan for more chaotic seas and strong winds towards the weekend. -Smith && .FIRE WEATHER...Issued 200 PM Tuesday, September 24, 2024... Onshore flow at the coast is bringing cooler air to the beaches compared to just 24 hours ago when the thermal trough brought ENE winds that sent temps into the 90s in Brookings. The thermal trough is weakening as it moves inland today, but this is leading to a very hot day for the valleys west of the Cascades. By late this afternoon, most areas will be in the mid to upper 90s, even a few triple digit readings are expected in the lower Klamath Valley of western Siskiyou County. The good news is there isn`t much wind to speak of this afternoon, other than the typical slope winds that usually occur in the afternoons. This will change Wednesday as an offshore upper trough moves inland into the PacNW. Pressure gradients tighten and gusty W-SW winds are expected from the Cascades eastward and in NE CA during the afternoon and early evening. Still looking at sustained winds of 15-20 mph with frequent gusts around 35 mph. And, local RAWS guidance still indicates potential for peak gusts at the more exposed sites (Coffee Pot, Summit, Summer Lake, Timber Mtn) in the 40-45 mph range. Humidity is also still the limiting factor precluding the issuance of a Red Flag Warning (minimum RH values are expected down around 15-20%). So, we`ll maintain the headline in the Fire Weather Forecast. The front itself could bring a little light rain to areas nearest the coast and also for areas north of the Rogue-Umpqua Divide, but expected amounts will be generally 0.10 of an inch or less. Probability of wetting rainfall is low (generally 20% or less) in those areas (including the Bottom Creek fire). Thursday will be a transition day with fairly typical fall weather and little or no fire weather concerns. Another weaker front will skim by to the north of the area Thu night through Friday, but also should have minimal fire weather impacts, though it will turn warmer inland. There is potential for a stronger upper trough to move through the area on Saturday. Recent guidance has shown this trough to be weaker than earlier runs, but there should be an uptick in winds and lowering of humidity again preceding it. We`ll monitor this. After that, models are showing another upper ridge building offshore and allowing another thermal trough to develop along the coast. This may lead to a period of offshore E-NE winds by early next week. Overall, a dry fall pattern with some wind/rh concerns for the next 7 days. -Spilde && .MFR WATCHES/WARNINGS/ADVISORIES... OR...None. CA...None. PACIFIC COASTAL WATERS...None. && $$ JWG/MAS/CZS