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Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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533 FXUS66 KMFR 152134 AFDMFR Area Forecast Discussion National Weather Service Medford OR 234 PM PDT Thu Aug 15 2024 .DISCUSSION...Cumulus continues to build and develop over north central Klamath county this afternoon...with thunderstorm development to begin within the next few hours. The short term models are struggling with the initiation of thunderstorms in Klamath and Lake counties this afternoon...as some indicate the activity should have started by now...and some indicate that it should start in the next few hours. Either way...confidence has diminished a bit for this event. Once any chance of thunderstorms ends this evening...we are expecting a break in the activity on Friday ahead of an unseasonably strong low impacting the region on Saturday. An upper low will move south from the British Columbia coastline toward the Pacific northwest coastline Friday morning into Saturday. The upper low is forecast to be right off the southern OR coastline Saturday afternoon into early Sunday morning...before lifting north...but still keeping us in a trough pattern. The main concern with this storm will be thunderstorms generally along and west of the Cascades with strong gusty downdraft winds Saturday afternoon and evening. In fact...the Storm Prediction Center has this same area in a Marginal Risk for severe weather (with the severe wind threat) on Saturday afternoon and evening. Additionally...areas along and west of the Cascades are expected to receive between a quarter and a half inch of rain. The east side is not expected to receive much if any rain or thunderstorms...however there will be gusty southwest winds...with wind gusts upwards of 35 kts. Please see the fire weather discussion below for more information on thunderstorm/wind threats and our fire weather concerns. Precipitation will move out of the area on Sunday morning...with dry conditions through the rest of the forecast period. The meteograms are in good agreement that we will remain dry after this weekend...with the exception of a few members showing very light precipitation possible mid week...however confidence is low. There is quite a bit of uncertainty in the upper level pattern mid next week as 20% of the clusters show the upper low off the coast shifting north...keeping us dry with warmer temperatures...where a little over 50% of the clusters showing broad troughing over the Pacific Northwest with cooler temps and the possibility of precipitation. Either way...continue to monitor the forecast for the latest information. -Riley && .AVIATION...15/18Z TAFS...Ceilings at the coast and across coos and coastal Douglas Counties will be VFR for much of the day before returning to to MVFR late evening and overnight. Guidance is suggesting around a 30 percent chance for IFR stratus, but left it out of the TAF due to the unsettled nature of the pattern. Thunderstorm chances this afternoon and evening are generally limited to Lake and Klamath counties, with 20% chances at the southern end and 40% chances along the northern edge of these counties. Extra caution is advised around any storms that do develop, as thunderstorms can generate lightning, gusty erratic winds, and locally lower ceilings and visibilities. Chances for activity drop to single digits late tonight. Wildfire smoke also continues to complicate conditions. Winds will generally come from the west and brief periodic moderate to heavy smoke over western Siskiyou, northern Lake, northern Klamath, and eastern Douglas counties with MVFR conditions in their vicinity and downwind. Light to moderate smoke is possible over most inland counties through the TAF period. -Schaaf/TAD && .MARINE...Updated 130 PM Thursday, August 15, 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 of Cape Blanco, 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 through early Sunday morning. -Petrucelli/TAD && .FIRE WEATHER...Issued 215 PM Thursday August 15, 2024...Upper level troughing will remain the dominant weather pattern through the forecast period. This will continue the trend of cooler than normal temperatures and breezy afternoon winds. The two main fire weather concerns on the horizon are thunderstorm potential today and the development of a deep upper low offshore over the weekend which could bring some strong winds and storms to the area. First the thunderstorm potential...a shortwave trough is lingering over the area today. With ample moisture and modest instability, isolated to scattered thunderstorms are expected. The trough will linger over the region this afternoon, however, and this will provide a better opportunity for scattered thunderstorms over FWZ 624/625 due to daytime heating effects. Thunderstorms will once again move north-northeastward into Oregon this afternoon and evening. Although there has been a concern for smoke to be a limiting factor on thunderstorm development, temperatures are warming to near the convective temperature needed, so a Red Flag Warning for abundant lightning on dry fuels remains in effect through this evening. The only change to the Red Flag Warning is that it was trimmed to end a few hours earlier because guidance has showed the main concern of thunderstorms being north and east of our area by then. 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. 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. A closed low moves near the southern Oregon coast late Friday into Saturday, and the next thunderstorm concern will be on Saturday. New guidance brings more confidence on measurable rainfall for west side valleys. Between 5 PM Friday to 5 PM Saturday, there is now a 70% probability to see 0.10" in Medford compared to last night`s forecast of 50%. Roseburg increased slightly from 65% to 70% in the same time period. Klamath Falls almost saw their probability for 0.10" more than double, going from 15% to 37%. Forecast soundings support fast moving storms with 0-6 bulk shear in the 25-50 knot range. The factor of these storms being fast movers suggests the flash flooding threat is moderate if storms don`t over run the same location quickly. Winds and RH... The other element of concern with this low pressure 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. There is confidence that portions of 625 (including the Warner Peak Fire) will meet critical thresholds for a Red Flag Warning, so have gone for a Fire Weather Watch in this area from 21Z Saturday - 03Z Sunday, and more details can be found in RFWMFR. Stay tuned for updates as subtle shifts in the position of this low could have big changes on the forecast. /BR-y/Hermansen && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Red Flag Warning until 8 PM PDT this evening for ORZ624-625. Fire Weather Watch from Saturday afternoon through Saturday evening for ORZ625. CA...None. PACIFIC COASTAL WATERS...None. && $$