Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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923 FXUS66 KMFR 261137 AAA AFDMFR Area Forecast Discussion National Weather Service Medford OR 435 AM PDT Wed Jun 26 2024 Updated Avaition Discussion .AVIATION (12Z TAFs)... IFR conditions have spread along the coast. Light drizzle this morning may result in local LIFR and there is a small chance (<20%) for some light precipitation tonight into Thursday morning along the coast as well. Inland of the coastal mountains, expect mainly VFR conditions. Some areas of MVFR/IFR may develop this morning and again this evening in the Umpqua Basin, mainly northwest of Roseburg. Another breezy/gusty day is expected this afternoon and evening ahead of an incoming front. -CC .DISCUSSION...Satellite imagery early this morning shows a plume of mid-level moisture streaming northeastward across norCal and into portions of southern Oregon. There is just enough elevated instability to touch off some showers with very high cloud bases. Precipitation falling from these clouds is mostly aloft (virga) due to a very dry sub-cloud layer. While a few drops have managed to reach the ground here and there, we`ve been hard-pressed to find any reporting stations with more than a trace. Lightning has been sparse beneath this moisture plume, but in the last hour or so, one stronger cell developed near Newell in NW Modoc County and was able to generate a few CG lightning flashes. This has some implications with respect to fire weather given expected strong winds and low RH this afternoon/evening. More on that below. The good news is that this will be pushing out of the area with most activity and the risk of lightning ending by 8 or 9 am. Meanwhile, off to the west, a deeper push of marine stratus is impacting all of the coast and has overspread much of interior Coos County. It`ll continue to advance inland through the early morning hours reaching portions of the Umpqua Basin (maybe Roseburg) and the Camas Valley. This marine layer is resulting in some mist/drizzle in places along the coast and will continue to do so through about 8 or 9 am. The clouds should break up some late this morning and this afternoon as a strong upper trough offshore heads toward western Washington. This will send a mostly dry cold front onshore that will move rapidly south and east of the area by this evening. Overall, today will be cooler for all but the far SE part of the CWA. Inland areas will average 5-15F lower than yesterday, with highs only in the mid 80s here in Medford. The main impact today will be the winds, which will be gusty this afternoon and evening, especially east of the Cascades and in portions of northern California. SW winds in those areas shift to WNW during the evening, but will be generally from a NW direction for areas west of the Cascades. Gusts of 30-35 mph will be common, but could reach 40 mph at some of the more exposed RAWS locations. This will result in fire weather concerns as any new or existing fires will spread rapidly due to the strong winds. Winds subside this evening as the pressure gradient weakens and the core of the upper troughs pushes into northern Idaho by Thursday morning. We expect another strong marine push tonight into Thursday morning west of the Cascades with some cloud-cover likely spilling over the Rogue-Umpqua Divide and into the Rogue and Illinois Valleys. Some light rain and/or drizzle/mist are possible along the coast and into portions of Douglas County again during this time frame. The clouds likely bank up against the Siskiyou Mountains Thursday morning, then break up during the day. Thursday likely will be the coolest day of the forecast period with highs in the upper 70s and low 80s for the valleys west of the Cascades and in the 70s over the east side. Most mountain locations and the coast will have highs in the 60s. Short wave ridging will arrive on Friday providing mainly sunny skies and a warmer afternoon inland. Still could be some marine stratus at the coast in the morning, but these should break up as northerly winds turn gusty again there. Winds will be slightly more offshore (northeasterly) though around Brookings, so we`re looking at highs in the low 70s down there. The next upper trough will move toward the PacNW Friday night and onshore Saturday into Sunday. Another mostly dry frontal passage. Wash, rinse and repeat, it seems. So, expect another period of increased afternoon/evening breezes, highest east of the Cascades. But, this should keep temperatures from deviating too much from normal levels. Any precip would be associated with the deepening marine layer and primarily focused across NW sections of the CWA. Heading into the 1st week of July, nothing stands out as earth- shattering weather-wise. We`ll maintain the pattern that we`ve been in for a while now with some potential for upper ridging in NorCal around Wed/Thu, which would allow things to warm up. Even so, model guidance wants to continue bringing troughs into the NE Pacific and even the PacNW at times, which will keep the real hot stuff to the south and east (where it should be!) and a generally unfavorable pattern for thunderstorms. -Spilde && .MARINE...Updated 230 AM Wednesday, June 26, 2024...Relatively calm conditions are expected through at least Thursday morning. A weak front will push through the region today, bringing a deep layer of low clouds along a chance of showers or drizzle. A return of gusty northerly winds is expected late Thursday into Friday night, with steep seas likely south of Port Orford. Gusty northerly winds and steep seas may begin late Thursday afternoon into Thursday evening, then increase on Friday. Models indicate small craft advisory level conditions are likely during this period. Another front and deep marine layer are likely to disrupt the pattern, with improved conditions Saturday afternoon through Sunday. -CC && .FIRE WEATHER...Mid-level moisture will continue to advance northeastward early this morning, but most of this should shift to the north and east of the area by around 8 or 9 am. While there have been isolated showers/virga with some of this moisture, most precip has had a tough time reaching the ground. In addition, and mostly as expected, thunderstorms have been very sparse beneath this moisture plume, but in the last hour or so (around 2 am) one cell materialized over NW Modoc County near Newell. It managed a few CG lightning flashes and there was one in extreme SE Lake County as well. A slight chance of thunder still exists until just after sunrise, but then that risk ends. Our biggest fire weather concern today will be the ramp up in SW winds expected east of the Cascades and portions of northern California this afternoon in combination with low humidity. The strong upper trough heading into Washington will induce a strong pressure gradient across the area and good vertical mixing will tap into the increased mid-level flow. SW winds over the east side and in NorCal will be 20 to 30 mph this afternoon with gusts to 40 mph. There is a low probability of winds exceeding 40 mph at some of the more exposed RAWS locations. Overall, expect minRH values this afternoon in the 10-15% range for far east side areas. A Red Flag warning is in effect from noon until 8 pm PDT for strong winds/low RH for FWZs 624/625 in Oregon and 285 in California. Any new fire starts or existing fires will have the ability to spread rapidly. Breezy winds are likely most everywhere else, but should also be accompanied by slightly higher RH (at least compared to yesterday). Much better humidity recoveries are expected tonight for all areas with another deep marine push to bank up against the Cascades/Siskiyous. We`ll get a break on Thursday without much wind and higher humidity, though expect fairly typical breezes to develop in the afternoon. It will warm up again Friday with gustier winds expected again over the weekend, especially east of the Cascades. -Spilde && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Red Flag Warning from noon today to 8 PM PDT this evening for ORZ624-625. CA...Red Flag Warning from noon today to 8 PM PDT this evening for CAZ285. PACIFIC COASTAL WATERS...None. && $$ MAS/CC/JWG