FXUS66 KMFR 260544 AFDMFR Area Forecast Discussion National Weather Service Medford OR 1045 PM PDT Sat May 25 2019 Updated AVIATION Section .DISCUSSION...An update to the forecast was issued this evening to fine tune the probability of precipitation and expected cloud cover through early next week. This included adding a slight chance of showers and thunderstorms for Klamath Falls on Monday evening. The weather this evening is proceeding as forseen with light to moderate showers over a wide swath of the area. This includes a limited occurrence of thunderstorms (though with a widespread area with a slight risk) with a few strikes reported in Lake County and another cell now strengthening south of Mount Shasta that looks to be of sufficient strength to produce lightning. Many of the showers will now be at peak intensity with the center of a broad closed low now along the Oregon coast. There will also be unseasonably low snow levels overnight at around 5500 feet. The higher passes, including around Diamond Lake/Crater Lake, Lake of the Woods, and Mount Shasta could have a slushy accumulation of snow late tonight with a few inches of accumulation off of the warmer road surfaces. Snowfall is likely to be most significant on Mount Shasta with 6 to 10 inches possible through 8 AM Sunday. Thus, a Winter Weather Advisory is in effect for the Lake of the Woods area and a Winter Storm Warning for the vicinity of Mount Shasta. The majority of showers will taper off during Sunday morning as the low continues its south to southeast track to around San Francisco. As such, the heaviest precipitation will be south of our area on Sunday and there will be a brief minimum of shower activity during late Sunday morning. But, wrap-around showers and isolated thunderstorms on the north side of the low will intensify and increase in coverage in our area during Sunday afternoon and evening. This activity will be most numerous from the Cascades eastward, but the steering flow will be northeasterly which may shift storms off of the higher terrain into valleys between the Casades and the coastal range. Once again, showers will diminish late Sunday night into Monday morning. The upper level pattern will continue to change on Monday with the main low headed toward Las Vegas. But, conditions will be very similar to Sunday. The steering flow will back to northerly while a strong shortwave on the back side of the low swings across the area during the period of maximum heating/late in the day. This will result in increasing coverage of showers and thunderstorms during the afternoon and evening. Instability will be highest east of the Cascades. The pattern will remain active and progressive at least through Thursday evening with day-to-day variation in the extent and coverage of the probability of showers and late day thunderstorms. && AVIATION...For the 26/06Z TAFS... For the 26/06Z TAFS...Expect widespread MVFR overnight into Sunday morning with local IFR, periods of rain and terrain obscured. Isolated thunderstorms will remain possible across Lake and Modoc Counties. The lowest CIG/VIS is expected between from now through 26/1200Z with some improvement thereafter. Freezing levels will be low enough that icing should be expected down to about 5KFT MSL Sunday morning along and near the Cascades. The thunderstorm threat Sunday afternoon/evening will be roughly from the Cascades eastward, but we can't completely rule out that isolated storms drift south-southwestward off the Cascades into eastern Douglas/Jackson Counties. Conditions should improve to VFR for most locations, but areas of MVFR will persist, especially in and near showers/t-storms. -Spilde && MARINE...Updated 830 PM PDT Saturday, 25 May 2019...Steep to very steep seas will be the primary concern across all of the coastal waters through Sunday, although gusty north winds will be an issue south of Cape Blanco. Winds will gradually diminish late tonight through Sunday evening as an upper level disturbance slides by, but will not calm below 10 to 15 knots until Monday morning. Seas will likewise gradually improve, finally dropping below 8 feet by Monday morning. Light winds and calmer seas are then expected through Tuesday as high pressure builds in from the west. The break will be brief, however, as north winds are expected to increase once again Tuesday afternoon due to the re- development of the coastal thermal trough. As a result, gusty north winds and steep seas are likely through the latter half of the week. -BTL/Spilde && .PREV DISCUSSION... /Issued 457 PM PDT Sat May 25 2019/ SHORT TERM...Satellite imagery at 2:45 PM is showing an influx of Cirrus clouds filtering in west of the Cascades and reaching the very south reaches of Siskiyou County in our forecast area. Meanwhile, the satellite is showing clouds underneath these cirrus north of the Umpqua Divide and at the coast north of Port Orford. Concurrent RADAR imagery show that rain has already begun at the coast and is moving ever closer to Roseburg where rain is imminent. The rain will further slide southward as a low pressure system slides southward along the Pacific Coast. This low has an upper level jet streak attached to it, so expect this low to strengthen (or deepen as depicted by the models). Have gone ahead and maintained the rainfall amounts tonight which will be rather heavy for this time of year, but the one-after-another (or training) storms seen in Modoc County which prompted the flash flood warning are not expected except in extremely isolated cases. Still, expect rainfall with your evening outdoor activities. Snow levels will come down to between 5000 and 5500 feet, so most roadways will see rain, including Siskiyou Summit. That being said, the pass near Lake of the Woods on Highway 140 will see the potential for some moderate snow overnight. Accumulations of 3 to 4 inches will be possible. Combined with the heat of the roadways, this snow will become slushy and allow for cars to slide more easily on the roadways. Have gone ahead an issued a winter weather advisory for this area for tonight from 8 PM until 8 AM. Although snow may start before this, the heaviest snow will occur between 11 PM tonight and 5 AM Sunday morning. The additional snow headline I want to discuss is for Mt. Shasta and the Mt. Shasta Highlands, including Medicine Lake area and the Mt. Shasta Ski Park. With the inevitable influx of out of area hikers, have decided to issue a Winter Storm warning as Mt. Shasta area could see 6-10 inches of new snow in a 6 to 12 hour period. Overnight camping and hiking are not recommended. Moreover, if you are trekking across any of the mountains in this area, you should be completing your trek within the next 1 to 3 hours (the further south you are, the more time you have), and be off the mountains by 4 or 6 PM. Please see the WSWMFR for more details for the Winter Storm Warning and Winter Weather Advisory. Tomorrow and Memorial Day, the low will push farther south. This will create easterly winds, but there will be the chances for more showers and storms. The HREF ensemble shows thunderstorm possibilities as far west as the Rogue Valley, stretching along a line north to the Cascade Foothills in Douglas County and south in the Shasta Valley. The best chances for Thunderstorms, however, will be along and east of the Cascades on both days. The Boatnik festival in Grants Pass may see a few showers both Sunday and Monday, but the thunderstorm potential is extremely low. Meanwhile, the air should dry out by the time it gets to the coast and conditions could be relatively rain-free. Things begin to dry out on Tuesday west of the Cascades. The low has pushed inland, and some showers and thunderstorms will be possible Tuesday afternoon and evening, mainly east of the Cascades. Temperatures will also have rebounded back to normal as compared to today and tomorrow where they're several degrees below normal. -Schaaf LONG TERM...Wed, May 29th through Sat night, Jun 1st... A slow, gradual warming trend from near normal temperatures to temperatures about 5 degrees above normal is expected during the long term period. This means most valley areas will be 70 to 80 degrees for highs, though the usually warmer valleys away from the coast are expected to reach 80 to 85F by the end of the period. A weak trough of low pressure will linger over the area through the forecast period, with shortwave impulses moving through it. This will result in showers and thunderstorms, primarily in the afternoon and evening hours, every day from Wednesday through the weekend, with the western edge of that threat pushing a bit southeastward each day. Wednesday and Thursday currently look as if they'll be the most convectively active days of the week. BTL && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Winter Weather Advisory until 8 AM PDT Sunday for ORZ028. CA...Winter Storm Warning until 8 AM PDT Sunday for CAZ082-083. Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT Monday for PZZ350-356-370-376. Hazardous Seas Warning until 2 AM PDT Sunday for PZZ350-356-370-376. $$ DW/Spilde