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Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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233 FXUS66 KMFR 131136 AFDMFR Area Forecast Discussion National Weather Service Medford OR 436 AM PDT Tue Aug 13 2024 ...Updated AVIATION discussion... .DISCUSSION...An upper short wave trough is swinging through eastern Oregon early this morning. This system was able to trigger some convection over portions of our forecast area last evening, but all of the shower/t-storm activity has shifted to the north and east. We are moving into a stable pattern this morning and today should be quiet weather-wise. Morning satellite imagery is showing most of the area devoid of cloud-cover, though some stratus is over the marine waters and portions of Coos/northern Douglas counties. These should erode later this morning and this afternoon with mostly sunny skies just about everywhere. High temperatures will largely range from 75-85F, slightly cooler at the beaches and in the mountains, and slightly higher in the lower Klamath River Valley of western Siskiyou County. Not bad for mid- August. Just about the only thing keeping this from being a banner mid-late summer day will be the smoke/haze from area wildfires. This will be most prevalent from eastern Douglas, northern Jackson into northern Klamath and Lake counties, but also portions of Siskiyou County (due to the Boise fire). Oregon DEQ has some air quality advisories out and we have relayed those via AQAMFR. We`ll remain under the influence of an upper trough for the foreseeable future. As such, we are very confident that the pattern of cooler (than normal) temperatures will continue. Another short wave disturbance will move in on WSW flow aloft on Wednesday. Models are showing modest instability and best moisture from the Cascades over to the east side, but also extending down into portions of NorCal, where we expect a chance of showers (25-40%) and isolated thunderstorms (<25% chance). This system will slow down as it moves through Oregon Wednesday night into Thursday, so this will keep the risk of showers and thunderstorms going. SPC SREF guidance is showing a higher likelihood of thunderstorms Thursday afternoon as the low pivots east of the Cascades by evening. Highest probabilities (25-35%) are in northern Klamath/northern Lake counties centered on the Christmas Valley. West side areas mostly miss out on shower/thunder potential, but there is a slight chance (~15%) especially for areas east/south of Medford. Expect nightly marine intrusions on the coast through Thursday night. On Friday, NBM is still showing some shower potential (20-30%) from the Cascades eastward and mainly in Oregon, but we should be on the back side of the Thursday trough and also still awaiting the next trough/low taking shape offshore. With a lack of forcing, I wouldn`t be surprised to see those chances drop out of the forecast over the next few shifts. An upper low is forecast to develop off the PacNW coast and remain nearly stationary (wobbling around 130W) this weekend into early next week. This should keep upper ridging locked in over the Four Corners/Texas, while also keeping our area in a cooler than normal pattern. Subtle changes in position/strength of this upper low can and will play a role in if, when and where additional showers/thunderstorms set up, so be on the lookout for daily forecast changes. But, it doesn`t look overly wet or hot any time soon. -Spilde && .AVIATION...13/12Z TAFS...Marine stratus remains offshore tonight, with only brief moments of higher clouds observed over North Bend. Guidance suggests that periods of MVFR are possible but unlikely through the rest of the morning. There`s also some agreement that a marine layer is more likely towards the end of the TAF period. Inland areas will mostly be VFR through the TAF period. Smoke from the eastern Douglas county area may blow moderate to heavy smoke west over northern Lake and Klamath counties, and light to moderate smoke will drift to the south. Some of this smoke may reach Klamath Falls early Wednesday morning and could impact airport visibilities, but smoke models suggest only light amounts of smoke will reach that far south. -TAD && .MARINE...Updated 200 AM Tuesday, August 13, 2024...Light winds and gentle north-northwest swell will keep seas below advisory levels through the week. Swell may increase by 1 to 2 feet near the end of the week, with long-term guidance showing a 20-30% chance of seas exceeding 6 feet on Saturday. Those chances disappear on Sunday, reinforcing that the sea state will be uneventful through the beginning of next week. -TAD && .FIRE WEATHER...We`re in a period of low fire weather risk due to the influence of upper troughing near and just offshore of the PacNW. That isn`t to say there won`t be any fire weather concerns the next several days, but since it will be cooler with higher humidities (at least compared to normal), there is less risk than there typically would be for this time of year. Today we don`t have any significant fire weather concerns, except for fairly typical afternoon/evening diurnal breezes that will allow existing fires to awaken after laying down during the night and early morning. A short wave trough is expected to push onshore Wednesday evening through Thursday evening and this will bring a decent chance of showers and thunderstorms, mainly from the Cascades eastward. Models are pegging Thursday as the most active day, especially in northern Klamath/Lake counties, where instability is greatest as the upper trough pivots east of the Cascades. Aside from gusty outflow winds near thunderstorms, we aren`t anticipating any unusually strong winds through the end of the week. Friday there should be a break as another low develops offshore and the Wed-Thu trough exits to the east. With the high likelihood of the low remaining near and just off the PacNW coast through the weekend, we should remain near to below normal temperature-wise with above normal humidity, though there is some potential for the low to be just far enough offshore for temps to moderate a bit Sat. Since there is still some uncertainty with just where the low will set up, some details are likely to change, so stay tuned. -Spilde && .MFR WATCHES/WARNINGS/ADVISORIES... OR...None. CA...None. PACIFIC COASTAL WATERS...None. && $$ MAS/TAD