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Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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668 FXUS66 KMFR 142153 AFDMFR Area Forecast Discussion National Weather Service Medford OR 253 PM PDT Wed Aug 14 2024 .DISCUSSION...Cumulus clouds are starting to build generally in southern Jackson county...south central Siskiyou county...and much of Klamath and Lake counties...where thunderstorms are forecast. There is quite a bit of uncertainty with the westward extension of thunderstorms...especially for the rogue valley...where smoke may keep us from getting to the convective temperature. Either way...the short term models have been very consistent in thunderstorms initiating generally along a line from Yreka into Klamath Falls between 3 and 5 pm. Showers and thunderstorms will move northeast...impacting the northern half of Klamath and Lake counties around 10 pm. The activity will move out of the area around 5 am Thursday before a very short break in the action. The second round of thunderstorms is expected develop in Klamath and Lake counties early Thursday afternoon. The best chance for thunderstorms (25% to 35% chance) will be mid Thursday afternoon into the early evening hours over northern Lake county. Please see below for more information regarding fire weather concerns. Otherwise...our focus shifts to this weekend as an upper low drops south along the PacNW coast Friday into Saturday. There is a lot of uncertainty with the position of the low and how it impacts the precipitation forecast over the weekend. For instance, about a third of the clusters indicate precipitation across much of the area Saturday with the upper low a bit more to the east...compared to two thirds to the clusters indicating the low position more to the west...leading to a lesser chance of precipitation. About a third of ensemble members show absolutely no precipitation for Medford...where some show upwards of a half inch of rain. Additionally...depending on the position of the low...there will be the possibility of thunderstorms. Again...still a lot of uncertainty with the weekend storm...but we will continue to monitor closely and hone in on details over the next few days. -Riley && .FIRE WEATHER...Issued 245 PM Wednesday August 14, 2024...Upper level troughing will remain the dominant weather pattern through the forecast period. This will continue the trend of cooler than normal temperatures, moderated humidities and breezy afternoon winds. The two main fire weather concerns on the horizon are thunderstorm potential today through Thursday and the development of a deep upper low offshore over the weekend which could bring some strong winds to the area. First the thunderstorm potential...a shortwave trough will be moving into the region today and linger over the area through Thursday. With ample moisture and modest instability, isolated to scattered thunderstorms are expected. Initially, isolated thunderstorms are expected over portions of northern California, then spreading north- northeastward into Oregon after sunset and into the overnight hours. Isolated thunderstorm coverage is the most likely scenario today mainly along and east of the Cascades (possibly as far west as the Rogue Valley/Medford), but scattered coverage is possible as storms move into Oregon across Fire Weather Zones (FWZ) 624/625. There will be a break in thunderstorm activity early Thursday morning. The trough will linger over the region Thursday afternoon, however, and this will provide a better opportunity for scattered thunderstorms over FWZ 624/625 due to daytime heating effects. Due to these factors, a Red Flag Warning for abundant lightning on dry fuels will be in effect starting this evening, and details can be found at RFWMFR. Storms are expected to have some precipitation with them, but lightning strikes outside of precipitation cores are possible and cause for concern. Additionally, expect gusty and erratic winds near thunderstorms with strong outflows that can travel a good distance from the originating storm. There has been a concern for the smoke moving to areas east of the Cascades in the coming days with westerly flow. The HRRR smoke model is matching well with the current satellite picture. With this in mind, the westerly winds are on track to move the smoke to areas east of the Cascades with the highest concentrations in Klamath County. The smoke may be heavy enough to hinder thunderstorm development, but convective temperatures are in a reasonable range to reach, even if smoke does stay in the area of the Red Flag Warning. The atmosphere will stabilize some on Friday. There will be lingering moisture and instability, but without a sufficient trigger/forcing mechanism, it`s likely there will be some cumulus buildups east of the Cascades and over the higher terrain. The next concern turns to a deep, large scale trough that develops off the PacNW Coast late Friday into Saturday and lingers there well into next week. This will bring some precipitation chances to the region, though confidence is low on the details regarding where and amounts. Ensembles suggest the best chances are along and west of the Cascades, but there could be thunderstorms to accompany these precipitation chances. The other element of concern with this low pressure (and where the higher confidence lies) is the potential for strong south to southwest winds. Guidance suggests gusts of 30-40 mph for areas east of the Cascades and in the Shasta Valley on Saturday and Sunday afternoons. These strong winds could combine with low humidities (which ultimately depends on where precipitation chances occur) and result in critical fire weather conditions. Stay tuned for updates as subtle shifts in the position of this low could have big changes on the forecast. /BR-y/Hermansen && .AVIATION...14/18Z TAFS...Generally VFR through the TAF period. An upper trough remains in place over the Pacific northwest, bringing more westerly winds that help to limit smoke accumulation west of the Cascades. However, that does also mean that smoke may impact visibilities east of active fires. For this area, that includes possible periods of moderate to heavy smoke over Klamath, Lake, eastern Douglas, and western Siskiyou counties. Upper level instability could bring some thunderstorm chances later today. 15-30% thunderstorm chances are present over Lake, Klamath, and eastern Siskiyou and Jackson counties this afternoon and evening. These chances will decrease early Thursday morning, with 15- 20% thunderstorm chances lingering over Klamath and Lake counties through the end of the TAF period. Lightning, locally heavy rain showers, and gusty erratic winds are possible hazards around any storms that do develop. -TAD && .MARINE...Updated 230 PM Wednesday, August 14, 2024...Relatively calm conditions are expected for the next several days with light to moderate winds and seas remaining 6 foot or less. There will be a slight uptick in winds Thursday into Friday south west of Gold Beach, but they will remain below advisory levels. A rather strong upper low for this time of the year will move into the waters Saturday and will likely bring showers over the waters. -Petrucelli && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Red Flag Warning from 8 PM this evening to 11 PM PDT Thursday for ORZ624-625. CA...None. PACIFIC COASTAL WATERS...None. && $$