WEATHER SUMMARY AND FORECAST DETAILS
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FOR 12/9/2018 - From Medford NWS
The weather will become increasingly more active with time over the next week, and the 7-14 day period is looking as if it will be wetter than this current week, so expect frequent storm activity and active weather over the next 2 weeks.
The frontal system moving into the area has pushed an initial precipitation band out ahead of it that has remained fairly healthy on radar. Rain is falling across much of the Rogue Valley now, and flakes are flying at Mount Ashland. the Oregon Cascades, and Siskiyous with snow levels between 4500 and 5kft. Total new snow amounts through Monday morning are expected to be generally in the 2 to 4 inch range above 5kft, though locally higher amounts up to about 6 inches are possible. Also, for the elevations between 4000 and 5000 lighter accumulations of 2 inches or less are expected, with about a half inch expected at Klamath Falls and on Siskiyou Summit. These lighter amounts at these lower elevations will be, in part, due to above freezing high temperatures today resulting in a warmer ground, thus limiting accumulations. It should be noted, however, that the latest run of the NAM 12 forecast model does show some higher amounts east of the Cascades tonight, so the current weak wave that appears to be developing along the coast near Crescent City needs to be watched this evening to ensure it behaves as we`re expecting. Elsewhere, we`ll see some beneficial rainfall, generally a tenth of an inch or more, from the Cascades westward, and over an inch in portions of Curry County.
The next frontal system arriving on Tuesday and continuing into Wednesday will come in on a more westerly to northwesterly flow and compared to today`s, which is coming in on a more southwesterly flow. We`ll probably need some wind advisories east of the Cascades mainly for the Summer Lake area. On the front end of the Tuesday frontal system cold air could become trapped, yielding lowish snow levels initially. Model guidance is suggesting a stronger westerly flow in the mid-levels with this frontal system, so we expect a bit more precipitation with this one in the west side valleys. Amounts should be a quarter inch or more from the Cascades westward in Oregon, and a half inch to inch of water is expected in the mountains, Umpqua Basin, and coastal counties. With winds perpendicular to the Cascades at about 50 knots, the highest snow amounts will be in Cascades versus the Siskiyous. We expect 6 to 12 inches in the mountains north of Highway 140, with lesser amounts south of there. We`ll then catch a relative break Wednesday afternoon through Thursday morning.
Weak ridging over the area Thursday morning will quickly shift east with a southwest flow aloft. The models are in pretty good agreement keeping most, if not all precipitation north of our area on Thursday as a warm front stays to our north. Have kept in a slight chance to chance over the northwest part of the forecast area, but it could easily end up flat out dry. Elsewhere, confidence is moderate to high we`ll stay dry on Thursday. In fact we could have some clearing along with a favorable wind flow for mild temperatures in the Rogue Valley.
Confidence is higher we`ll have a fairly active weather pattern in the works from Thursday night until the end of the forecast period. A series of fronts will move through the forecast area bringing valley rain and mountain snow. The main question will be the timing of each system which is not completely clear at this time. The one thing that is common among the models is the pattern will be progressive. This means storms will quickly move in and out, thus limiting the duration of moderate to heavy precipitation. This will be good news in terms of keeping flooding concerns for the burn scars in check. In other words, flooding concern from the burn scars should remain low.
The first front will move into the area either later Thursday night or Friday morning. One of the operational models shows the front coming in sooner while other show a later arrival. Snow levels are expected to be around 4500 feet Thursday night, but could lower to 4000 feet in heavier precipitation, so it looks like the higher passes like highway 140, Diamond Lake and Crater Lake will get accumulating snow. Right now, Siskiyou summit should be mainly rain, but wet snow could mix in at times if precipitation becomes heavy.
The other concern will be wind east of the Cascades as the upper mid level winds are showing sustained wind speeds around 55 to 60 knots which means we could be looking at high winds east of the Cascades near the Summer Lake area and over higher terrain.
Post frontal showers follow Friday with snow levels between 3500 and 4000 feet, depending on the intensity of precipitation. Weak ridging builds in Friday night giving us a relative break in the action. Another strong storm is expected Saturday evening or night. The timing on this one is in question because the models are showing varying solutions. Thus confidence in the forecast for Saturday is low. Because of timing issues, it`s hard to really pin down how high and how low snow levels will be. Sunday remains active with a upper trough over our area with a cooler air mass aloft.
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