FXUS66 KMFR 192142 AFDMFR Area Forecast Discussion National Weather Service Medford OR 242 PM PDT Fri Jul 19 2024 .DISCUSSION...A high amplitude ridge remains in control of the western third of the country, and with the trough to the northwest over the Gulf of Alaska, this places southern Oregon and far northern California under relatively dry and stable southwest flow aloft. Meanwhile, a thermal trough has developed over central California. A shortwave impulse now lies along the southern periphery of the trough to our southwest, and this feature will approach the area through the day Saturday. The southerly flow ahead of the wave will push this hot air into our area Saturday, resulting in very warm temperatures across much of the inland areas. Most inland valleys both east and west of the Cascades will easily reach upper 90s to low 100s for the daily high. This will be just enough above normal to trigger Heat Risk for northern California and the East Side, so Heat Advisories have been issued for those areas for Saturday. The shortwave will also provide instability and additional moisture, while also acting is a sufficient lift mechanism to produce a widespread slight chance to chance (generally 10-30%) for thunderstorms Saturday into Sunday, including during the overnight hours as the wave tracks through overhead. This event looks very similar to the one from earlier this week, both in overall pattern and in the dry lower layers of the atmosphere, so we are concerned about lighting and gusty outflow winds once again, especially given that any storms that develop will produce very little, if any, precipitation. The focus of convection concerns will shift to the East Side on Sunday as the wave exits the region. For the remainder of the week, the pattern will very slowly progress to the east, with the Gulf of Alaska trough gradually moving inland into Canada and Washington. As a result, we are expecting temperatures to "cool" slightly, returning to near normal values for this time of year, with relatively dry west to southwest flow continuing through the week. -BPN && .AVIATION...19/18Z TAFS...Along the coast VFR conditions are expected the rest of the day, with marine stratus re-forming again this evening resulting in IFR conditions. Inland, VFR conditions will prevail through the TAF period. The exception will be in the vicinity of the Trail fire and various other fires in the vicinity of the Trail Fire in eastern Douglas County where visibility could end up between 3-5 miles through 20z. This afternoon and tonight, visibility could be reduced southeast of the fires in eastern Douglas County, including northern Klamath County, then possibly down into Klamath Falls later tonight resulting in MVFR visibility. -Petrucelli/Spilde && .MARINE...Updated 230 PM Friday, July 19, 2024...Relatively calm conditions are expected through this evening. A thermal trough will return tonight into Saturday, eventually strengthening early next week. Moderate north winds and steep seas are expected south of Port Orford beginning tonight and lasting through Saturday. Expect conditions hazardous to small craft to expand across a larger area on Sunday, then stronger, gale force winds are possible Monday afternoon through Tuesday. -Spilde && .FIRE WEATHER...Issued 200 PM Friday July 19, 2024... A dry and stable southwest flow continues into this evening with no concerns for thunderstorms. However, afternoon relative humidities will trend lower for most interior locations with values in the single digits for portions of the East Side along with the typical gusty afternoon and early evening breezes. This will result in near critical conditions for portions of Fire zones 624, 625 and 285, but were not expecting the combination of wind and RH to result in Red Flag conditions. The other concern for those involved in air attack on the various fires in our area will be visibilities lowering to 3-4sm in the vicinity of the Trail Fire and surrounding complexes near the Trail Fire in eastern Douglas County. The latest run of the HRRR smoke fields show the smoke being transported east to southeast late this afternoon and evening. However there are fires up in Lane County that will get transported into eastern Douglas County, so we may not see any improvement through tonight. Meanwhile, smoke from the Trail and other fires in eastern Douglas County will push southeast into Klamath County late this afternoon, then into Klamath Falls proper tonight, and visibility could be reduced to 4-6sm. Tonight, as the mixing height decreases, the smoke will settle and be confined to around the perimeter of the fires resulting in MVFR visibility between 3-5sm. However, a northeast drainage winds could bring smoke towards Medford resulting in visibility lowering to 5sm northeast of the Medford Airport late this evening and tonight. There is now an increased concern for thunderstorm this weekend. Saturday, an upper trough will move up from the south just off the California coast and could tap into some monsoonal moisture with a southeast flow aloft. At the same time, there's good agreement, the upper trough will become negatively tilted Saturday afternoon into Saturday night. Based in part on pattern recognition, this could be problematic in that we could see storms break out mid to late Saturday afternoon in portions of northern California, east of the Cascades, and some could slip into the southern portions of Fire zones 619, 620 and 621 late Saturday afternoon due to a stronger flow aloft which could allow storms to come off the mountains and move north into the lower elevations. Saturday night, the axis of the upper trough is still south of our area which heightens the concern for nocturnal storms west of the Cascades, and portions of the eastside in Oregon Saturday night. Many times the models will not show signs of unstable conditions with this type of pattern, then the next thing you know something breaks out of nowhere. The pattern that is setting up is one where the instability is elevated, and thus the convection will be elevated as well. The most recent data points to a heighten concern for nocturnal storms along and west of the Cascades Saturday night into Sunday morning. This has lead to a higher confidence for a Fire Weather Watch for the Cascades west for abundant lightning on dry fuels and a Fire Weather Watch has been issued. Keep in mind given how dry and hot it has been for the interior and near the coast, that lightning efficiency is high to very high for fire starts. Also gusty and erratic winds are a concern which could further increase fire activity on existing fires. Some of the high res guidance are showing some reflectivity, and PWATS are higher, therefore there we could see some rain out of these storms that could reach the ground, but it will not provide much help in preventing new starts given how dry and hot it's been. Even though the Fire Weather Watch is for the Cascades west, that does not mean the eastside will be in the free and clear. There is concern for nocturnal storms in portions of Fire zone 624 Saturday night, however the confidence is not as high for isolated to scattered storms, so they were left out of the watch for now, but this could change should future data shows evidence to the contrary. With all that said, this is not a slam dunk, but at the same time it cannot be discounted. The upper trough axis shifts north during the day Sunday. Any threat for storms could be confined to the early morning hours over the northwest part of our area, then shifting north late Sunday morning through Sunday afternoon with a drier and stable southwest flow moving into the area. The exception could be in portions of Fire zone 623, 624, 625 and along the Warners in Fire Zone 285 where isolated storms are possible late Sunday afternoon. Monday, a dry and stable southwest flow will set up with any chance for storms shifting east and northeast of our area. It will be cooler with gusty afternoon and early evening breezes for the interior westside valleys and east of the Cascades. The rest of next week is pointing towards dry weather, with ridging nudging back into the area. This will result in afternoon temperatures trending upwards from Tuesday and beyond. Also the concern will shift towards moderate to locally poor overnight recoveries for the mid slopes and ridges in southwest Oregon and western Fire zone 280, and the typical gusty afternoon and early evening breezes for the interior westside valleys and east of the Cascades with low afternoon RH's. -Petrucelli && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Heat Advisory from 11 AM to 11 PM PDT Saturday for ORZ029>031. Fire Weather Watch from Saturday afternoon through Sunday morning for ORZ615>620-622-623. CA...Heat Advisory from 11 AM to 11 PM PDT Saturday for CAZ081>085. PACIFIC COASTAL WATERS...Small Craft Advisory from 2 AM to 11 PM PDT Saturday for PZZ356- 376. && $$