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Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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269 FXUS66 KMFR 161207 AFDMFR Area Forecast Discussion National Weather Service Medford OR 507 AM PDT Fri Aug 16 2024 .DISCUSSION...Satellite imagery this morning shows the marine layer blanketing the Coast and waters north of Cape Blanco and has filled the Umpqua Basin. This should be extent of the inland intrusion of the marine layer tonight as it doesn`t look deep enough to "spill over" the Rogue-Umpqua Divide. Skies are clear for much of the remainder of the region, though there is some fog/low clouds in portions of northern Klamath County north of Chiloquin. Rather quiet conditions are expected today ahead of a more eventful Saturday. There will be moisture and weak instability present today, but with a lack of a defined trigger coming through the region, thunderstorm chances are at a minimum today. It`s likely there will be some cumulus buildups east of the Cascades and over the higher terrain and there`s a small chance (5-10%) a few of those buildups could result in a brief shower. Otherwise, dry conditions are expected today along with continued below normal temperatures (afternoon highs in the mid to upper 80s for West Side Valleys and upper 70s to low 80s for areas east of the Cascades). Despite the reprieve from the summer heat, smoke will be a continued nuisance through the forecast period, and probably longer. An Air Quality Alert (issued by partnering agencies) is in effect for Klamath and Lake counties, and we have relayed those via AQAMFR. The cooler than normal pattern will continue as a deep, large scale trough develops off the PacNW Coast late tonight into Saturday and lingers there well into next week. The center of the low will be at it`s southern most location on Saturday before it drifts northward Sunday into early next week. As such, Saturday will be the day with the highest precipitation potential through at least mid-week. Confidence is fairly high that much of the area along and west of the Cascades will see measurable precipitation (80-90% chance of at least 0.01"), with wetting rains possible (25-50% chance of >=0.25") over portions of western Siskiyou, Jackson and eastern Douglas Counties. Models indicate ample instability to go with this moisture so there is high confidence in thunderstorms occurring west of the Cascades with this precipitation on Saturday. Strong storms are possible on Saturday and the Storm Prediction Center (SPC) has a portion of our region in a Marginal Risk (5-14% chance) of an isolated severe thunderstorm over Jackson and eastern Douglas Counties on Saturday. The main threat would be large hail and damaging winds. If you have outdoor plans on Saturday, be prepared for wet and windy conditions with widespread showers and scattered thunderstorms. There is a good chance (50-70%) that the wildfires burning in eastern Douglas County receive some beneficial precipitation from this event, though there is some uncertainty regarding amounts. Regardless, this event should help to reduce fire activity and (hopefully) reduce smoke output, providing some relief from the persistent smoky conditions. Meanwhile, areas east of the Cascades are likely to remain dry and deal with strong gusty winds. There will be a sharp gradient between where precipitation chances drop off and the concern for strong winds combines with low humidities and results in critical fire weather conditions (see fire weather discussion for more details). Current guidance suggests this gradient will be along and near the Warners, extending northward to Winter Ridge/Summer Lake area. West of that area, the chance for 0.01" of precipitation is about 50%, while the chance for 0.10" drops to 10%. Farther east towards Lakeview and Alturas, the chance for 0.01" of precipitation is only 10% with no solutions indicating a chance for higher amounts. The bigger concern east of the Cascades will be strong winds where south to southwest winds 20 to 25 mph with gusts 30 to 35 mph will be common and gusts of 40 to 45 mph are not out of the question across the higher terrain. The East Side won`t be the only place with strong winds. The remainder of the region will see gusty winds too, especially in the Shasta Valley, but winds will be strongest east of the Cascades. From Sunday onward, low pressure will drift northward and precipitation chances will come to an end. We`ll remain under a cooler than normal pattern with gusty afternoon breezes. Shortwaves will rotate around this low pressure and into the region through the forecast period, though the timing of these are difficult to pinpoint at this time range. Stay tuned and monitor for updates as these shortwaves could result in either enhanced afternoon winds (possible fire weather concerns) or additional thunderstorm chances at some point during the week. /BR-y && .AVIATION...16/12Z TAFS...MVFR marine stratus is present over the near shore waters from Cape Blanco northward, and inland into the Coquille, Camas, and Umpqua valleys. This includes North Bend (KOTH). This marine stratus will burn off during the morning with ceilings gradually transitioning to clear skies late this morning into early afternoon. A southerly surge of coastal IFR is expected to reach Curry County, including Brookings and Gold Beach, after 03Z this evening, with a mix of IFR and MVFR returning north of Cape Blanco after 06Z. This will include the Coquille and lower Umpqua valleys, and North Bend (KOTH). By early Saturday morning, showers will become likely over the near shore waters and coastal area with a slight chance of thunderstorms. Farther inland, smoke will be thickest in the vicinity of wildfires in central and eastern Douglas and southern Lane counties, where MVFR visibility between 3-5 miles will be the predominate condition. Smoke from these fires are likely to move into northern and central Klamath County early this morning, and could drift south towards Klamath Falls. Otherwise, conditions will remain VFR. A chance of showers will develop west of Interstate 5 early Saturday morning, increasing to a showers likely with a slight chance to chance of thunderstorms during Saturday, focused from the Coast Range to the Cascades, but extending into Klamath and eastern Siskiyou counties. -DW && .MARINE...Updated 200 AM Friday, August 16, 2024...Relatively calm conditions are expected for the next several days with light to moderate winds and seas remaining 5 feet or less. A rather strong upper low for this time of the year will move into the waters Saturday and will likely bring showers with a slight chance of thunderstorms into early Sunday morning. -DW && .FIRE WEATHER...Issued 400 AM Friday August 16, 2024...Rather quiet conditions are expected today ahead of a more eventful Saturday. There will be moisture and weak instability present today, but with a lack of a defined trigger coming through the region, thunderstorm chances are at a minimum today. It`s likely there will be some cumulus buildups east of the Cascades and over the higher terrain and there`s a small chance (5-10%) a few of those buildups could result in a brief shower. Otherwise, dry conditions are expected today along with continued below normal temperatures and moderated humidities. There are two main fire weather concerns in the short term with the development of an unseasonably strong low pressure off the Pacific Northwest late tonight into Saturday: scattered thunderstorms with potential of wetting rains along and west of the Cascades and gusty winds combined with low RHs east of the Cascades. Thunderstorms...there is fairly high confidence that much of the area along and west of the Cascades will see measurable precipitation (80-90% chance of at least 0.01"), with wetting rains possible (25-50% chance of >=0.25") over portions of western Siskiyou, Jackson and eastern Douglas Counties. Models indicate ample instability to go with this moisture so there is high confidence in thunderstorms occurring west of the Cascades with this precipitation on Saturday. The uncertainty lies in how much lightning there will be...will it be a convective event with abundant lightning or will it be a broad area of showers with embedded thunderstorms. High resolution models indicate a bit of both with widespread showers and scattered thunderstorms. Scattered coverage looks most favorable over Fire Weather Zones 280/621/622/617/623, but a subtle shift westward in the low position could also include zones 620 and 616. Would like to let the dayshift today coordinate with area IMETs regarding any fire weather watches for abundant lightning west of the Cascades. There will be a sharp gradient between where precipitation chances drop off and the concern for strong winds combines with low humidities and results in critical fire weather conditions. Current guidance suggests this gradient will be along and near the Warners, extending northward to Winter Rim/Summer Lake area. West of this area, there is about a 50% chance for measurable precipitation (at least 0.01"). Chances really drop off for amounts greater than that, so mainly dry conditions are expected east of the Cascades in general. Father eastward, a Fire Weather Watch has been expanded for the combination of strong gusty winds and low RHs. The watch now includes much of FWZ 625, the eastern half of the Modoc (FWZ 285) and the far southeastern corner of FWZ 624. Gusty south to southwest winds of 20 to 30 mph with gusts of 35 to 40 mph will be common where we have the watch in place and daytime humidities are expected to reach into the low teens in this area. Gusty winds are also expected in the Shasta Valley and across the Klamath Basin, but RHs should remain high enough to preclude critical conditions there. Beyond Saturday, the upper level low will drift northward but continue to influence the region`s weather. Precipitation chances drop out of the forecast for Sunday onward but gusty afternoon winds will continue through the week. Temperatures will remain cooler than normal through the forecast period. Shortwaves will rotate around this low pressure and into the region through the forecast period, though the timing of these are difficult to pinpoint at this time range. Stay tuned and monitor for updates as these shortwaves could result in either enhanced afternoon winds or additional thunderstorm chances at some point during the week. /BR-y && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Fire Weather Watch from Saturday afternoon through Saturday evening for ORZ624-625. CA...Fire Weather Watch from Saturday afternoon through Saturday evening for CAZ285. PACIFIC COASTAL WATERS...None. && $$ MNF/DW