Scientific Forecaster Discussion

000 fxus66 kmfr 240413 afdmfr Area forecast discussion National Weather Service Medford or 913 PM PDT Thu may 23 2019 Update...radar imagery this eveing shows a clump of showers moving south along the western edge of the Cascades towards Green Springs and Ashland. Clusters of showers also continue to track south over Modoc County and far southeast Lake County. Have adjusted the current forecats to account for these showers, which should dissipate slowly through the evening. Also, have significantly increased preciptiation chances for much of the area on Saturday afternoon and evening, mainly due to increased confidence provided by the newest model runs. The vast majority of model suites show a significant area of showers moving north to south across the area Saturday afternoon, and although the timing is slightly different across each solution, there is more than enough reason to say that it will rain nearly everywhere on Saturday, which may pose an issue for several Memorial Day weekend festivities and events. In other wors, be prepared for rain this weekend if you have any events scheudled outdoors. For more information on the rest of the forecast, please see the previous discussion below. -Bpn && Aviation...for the 24/00z tafs...along the coast and over the coastal waters...widespread IFR cigs will persist through tonight with patchy drizzle and fog, except south of Cape Blanco and 5-10 miles offshore where VFR conditions will prevail. Coastal terrain will become obscured overnight as clouds move further inland. Showers will develop Saturday morning with increasing coverage of IFR into Friday evening. Inland areas west of the Cascades...VFR conditions will prevail through this evening, except for areas of late night into Friday morning IFR/MVFR cigs, mostly over the Umpqua Basin. Mountain obscuration is also expected tonight, especially over northwest- facing terrain. Showers with increasing coverage of IFR is likely north of the Umpqua Divide late Friday morning into Friday evening. From the Cascades east...mostly VFR conditions are expected through Friday morning, but there will be isolated to scattered showers Friday afternoon, mainly over lake and Modoc counties. Keene/dw && Marine...updated 830 PM PDT Thursday 23 may 2019...the main update this evening was to extend the Small Craft Advisory by 3 hours into Saturday afternoon. There will be 2 periods of peak seas. First, this evening with very steep seas beyond 5 nm from shore south of Gold Beach and steep seas elsewhere. Seas will diminish very slightly early Friday morning, but then build to a higher peak of 8 to 11 feet on Saturday morning. With persistent high pressure offshore and low pressure inland, the steep to very steep seas will be mainly due to the combination of north wind waves and fresh north to northwest swell. Seas will diminish as a stronger low and it's associated cold front move south along the coast late Saturday into Sunday then pushes inland on Monday. Through the long weekend, the strongest winds and highest seas will occur south of Gold Beach beyond 5 nm from shore, especially between 5 nm and 30 nm from shore. Seas are likely to be at a minimum on Tuesday morning then high pressure offshore and a thermal low along the coast are likely to strengthen again. Dw && Previous discussion... /issued 246 PM PDT Thu may 23 2019/ Discussion...we know there are lots of folks planning outdoor activities this Holiday weekend, so we spent a good bit of effort coordinating our forecast ideas today for the Friday through Monday time period. The rest of today will be relatively quiet with a few showers moving through lake and Modoc counties under the continued influence from the upper low over the Great Basin. In the Umpqua basin and towards the coast, light rain is possible again due to some weak energy aloft and continued deep marine layer. That rain chance continues overnight. Weather will be mostly dry Friday with afternoon temperatures similar to Thursday. Low pressure will be moving south towards the area from Washington, but it will be too distant to cause significant weather impacts to our forecast area with the exception of the Umpqua basin and coast where rain chances will continue. On Saturday conditions will begin to change. The low to the north will be closer, and the air mass will cool significantly. Temperatures Saturday will be about 10 degrees cooler than Friday. Clouds will increase as the low approaches and rain will move into the area from north to south. After a mostly dry first part of the day for the Roseburg and the Coos County coast, rain should reach there in the early afternoon. Latest data suggests rain affects the rest of the forecast area between 5pm and 10pm and then continues overnight. Snow levels late Saturday into Sunday morning will dip into The Crater lake level (between 6000 and 7000 feet), so those traveling to the high mountains this weekend should be prepared for some cold if not wintry conditions. On Sunday the low will be over central or northern California (model guidance has some spread), and there will be favorable dynamics and moisture to support more rain over at least the southeastern half of the forecast area. This would include areas from Medford south and east towards lake and Modoc counties. Gfs20 forecast lifted index values of near zero along and east of the Cascades support a slight chance of thunderstorms there Sunday afternoon. If the low hangs a little farther north, like the ec operational model shows, then the thunderstorm chances could extend westward to valleys west of the Cascades. Keene Monday through Thursday...Memorial Day could start out dry for most locations west of the Cascades in the morning. It could actually be perceived as a nice day in the morning hours. However from late morning through the afternoon, we'll see building clouds with a chance for afternoon showers and a slight chance for thunderstorms. Not everyone will get showers, but if you have any outdoor plans, be prepared for changing weather conditions. East of the Cascades, clouds cover could be more extensive and there is a better chance for showers. This is because the upper low is expected to set up southeast of our area and there is concern we could be caught up in some wraparound moisture. It this turns out to be the case, then we'll have a higher chance for showers pretty much all day with the highest chance for showers in the afternoon and evening. The upper should finally move far enough away where we could end up with drier and milder conditions next Tuesday, but weak troughing will remain over the area, so could not rule out isolated showers mainly east of the Cascades Tuesday afternoon. Wednesday and Thursday should be mostly dry and milder. Any isolated showers should be confined to northern California Wednesday afternoon and east of the Cascades Thursday afternoon. -Petrucelli && Mfr watches/warnings/advisories... or...none. California...none. Pacific coastal waters...Small Craft Advisory until 11 am PDT Saturday for

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