Area Forecast Discussion
Issued by NWS Medford, OR

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000 FXUS66 KMFR 270352 AFDMFR Area Forecast Discussion National Weather Service Medford OR 852 PM PDT Tue Mar 26 2024 .DISCUSSION...
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Some scattered showers are moving eastwards over the coast and northern Doulas County this evening ahead of a warm front. A quick update was made to the forecast to extend the area where we`re expecting precipitation to better reflect radar imagery. Otherwise, the forecast looks on track. This warm front will continue to bring light precipitation to the area tonight, mostly to the coast into Douglas County. A cold front will then arrive early Wednesday morning, bringing more widespread moderate to heavy precipitation and areas of gusty winds, especially to the Shasta Valley in central Siksiyou County and higher terrain east of the Cascades where wind advisories are in place for tomorrow. Plenty of warm flow out ahead of this front will result in rising snow levels, so snow impacts aren`t expected in the first part of this system below 5,500 feet. For areas 5,500 feet and above in the Cascades, a winter weather advisory begins early Wednesday morning through the evening for heavy snow. Travel over the mountains will be hazardous for much of tomorrow, especially in the late morning into the afternoon, when snowfall rates exceeded an inch an hour are possible (80+% chance for the higher Cascades) and very low visibility conditions are expected. For more details about this system and the rest of the forecast, please see the previous discussion below. -CSP
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&& .AVIATION (27/00Z TAFs)...
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VFR conditions prevail across the region this afternoon and evening with increasing high level clouds ahead of the next front expected to arrive tonight into Wednesday morning. Low level wind shear concerns will increase tonight between 06z-10z, mainly along the coast and into the Umpqua Basin (including North Bend and Roseburg), wind shear concerns will linger in these places through mid Wednesday morning. Otherwise, gusty winds are expected to increase along the coast, east of the Cascades, across the higher terrain and in the Shasta Valley late tonight into Wednesday afternoon. -Schaaf/BR-y
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&& .MARINE...
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Updated 800 PM Tuesday, March 26, 2024..Mixed westerly swell will build into waters today due to a 5 to 6 ft west swell at 14 seconds and 2 to 5 ft west swell at 19 to 21 seconds. Then, a strong front approaches later this evening and moves onshore early Wednesday morning. This will bring increasing southerly winds, reaching gales, and very steep and chaotic seas late this evening and overnight. In addition to the gales, expect very steep chaotic seas that are a mix of 8 ft west swell at 15 to 16 seconds and 10 to 14 ft southerly wind seas. Winds will ease for a brief period early Wednesday morning into the afternoon, then increase again Wednesday evening and overnight. High end advisory southwest winds are expected during this time, but could approach gales Wednesday night. Seas will remain very steep and hazardous through Thursday as high to very high west swell builds behind this front Wednesday and Thursday. Winds diminish late Thursday into Friday and seas will gradually lower on Friday but remain high and steep into the afternoon. Winds will turn northerly Friday afternoon as a thermal trough develops. There will likely be a brief period of sub-advisory conditions on Friday, but it will be short lived as northerly winds strengthen and seas become steep and wind driven through the weekend. /BR-y
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&& .PREV DISCUSSION...
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/Issued 453 PM PDT Tue Mar 26 2024/ SHORT TERM...Through Friday morning (3/29)...Calm conditions will continue this afternoon across northern California and southern Oregon. Upper level clouds are approaching from the Pacific while low level cumulus develop as lower level airflow moves over the terrain. Partial cloudy skies and light winds will persist through tonight. An approaching low pressure system will bring more activity through Wednesday and Thursday. A warm front will arrive from the west early Wednesday morning, followed closely by a more impactful cold front. Precipitation will move eastward across the area, with the Oregon coast forecast to get substantial rainfall through the day Wednesday. The heaviest period will be Wednesday morning, with heaver rainfall continuing south of Cape Blanco into the evening. Through Wednesday and Thursday, areas south of Cape Blanco will total between 2 and 3 inches of rainfall while areas farther north will stay between 1 and 1.5 inches. The Illinois Valley will get between 1 and 2 inches of rainfall and the Umpqua Valley will get between 0.5 and 1 inches. Thunderstorms will also be possible with this pair of fronts, mostly over Coos and Curry counties through the day Wednesday. Chances along the Oregon Coast will remain between 20-20% through Wednesday and Thursday, while slight 15-20% chances will move inland during the day Thursday and reach as far east as Klamath County. Overall thunderstorm chances are expected to decrease through Friday morning. Snow levels will start high behind the warm front, rising to 5500 to 6500 feet on Wednesday morning. The abundant moisture will bring heavy snowfall to higher terrain, especially over Mount Shasta and the Cascades. While the high snow levels will keep heavy snowfall over the remote Mount Shasta peaks, well-traveled areas in parts of the Cascades are facing potentially hazardous snowfall amounts. Snowfall will start fast on Wednesday morning, with moderate to high chances (50-90%) of accumulation rates reaching an inch per hour along Cascades peaks. Slight chances (20-40%) of rates reaching 2 inches per hour are briefly possible Wednesday evening. Given this extended period of possible heavy snowfall rates, a Winter Weather Advisory is in place for areas of the Cascades above 5500 feet and north of Highway 140. The Advisory will start at Wednesday at 5 AM and continue through 11 PM. The cold front trailing behind the warm front will bring snow levels down to 3000 to 4000 feet by Thursday morning. This will allow for snowfall over higher terrain west of the Cascades as well as across wide areas east of the Cascades. However, with the bulk of the moisture past the area, amounts over low-lying areas will be fractions of an inch. Higher elevation areas may see 1 to 3 inches and remote parts of westernmost Siskiyou County may see up to 6 inches. Hazardous winds are also expected during the day Wednesday. Gusty southerly winds are expected to funnel into the Shasta Valley and reach speeds of up to 50 mph. A Wind Advisory is in place from Wednesday from 8 AM until 2 PM to cover the period of strongest winds. Advisory winds don`t quite reach Grenada and Montague, but gusts of 30 to 40 mph could reach those cities. An additional Wind Advisory is in place from Wednesday at 11 AM through 11 PM for areas across Lake County and over the Warner Mountains in Modoc County, where gusts of 50 mph are also possible. Elevated winds are also expected across the area Thursday afternoon and evening, but currently those winds are not expected to reach hazardous speeds. -TAD Extended Discussion...(Friday through Tuesday)...The upper low will move southeast towards northwest Cal Friday, taking most of the energy with it into that area. A cool air mass along with weak dynamics will still result in convective showers and cool weather over portions of the area. Precip amounts Friday will be light. The upper low will dig south to southeast towards the Bay Area Friday night and south of there Saturday. However there`s some evidence we`ll get some return flow into northern Cal and southern Oregon during this time. Northern Cal has the best chance of getting measurable precipitation while southern Oregon should be far enough north where precip amounts will be light. Showers will be far and few in between Saturday morning, then we could see an uptick in shower coverage Saturday afternoon due to daytime heating and increasing instability. However, were still expecting light precipitation amounts. Showers will diminish Saturday night into Sunday as a northerly flow begins to set up. Still could not rule out some showers in northern Cal and portions of the East Side due to the proximity of the upper low still within ear shot during this time. The general consensus is for the upper trough to move southeast of our area Monday with a continued dry north to northeast flow as an upper level ridge builds in which typically results in dry weather. The upper ridge remains a fixture Tuesday with continued dry and milder weather. It`s worth noting the ensemble clusters are pretty much lock in step with the operational models for the start of next week, thus the higher confidence of dry and mild weather. -Petrucelli AVIATION (27/00Z TAFs)...VFR conditions prevail across the region this afternoon and evening with increasing high level clouds ahead of the next front expected to arrive tonight into Wednesday morning. Low level wind shear concerns will increase tonight between 06z-10z, mainly along the coast and into the Umpqua Basin (including North Bend and Roseburg), wind shear concerns will linger in these places through mid Wednesday morning. Otherwise, gusty winds are expected to increase along the coast, east of the Cascades, across the higher terrain and in the Shasta Valley late tonight into Wednesday afternoon. -Schaaf/BR-y MARINE...Updated 200 PM Tuesday, March 26, 2024..Mixed westerly swell will build into waters today due to a 5 to 6 ft west swell at 14 seconds and 2 to 5 ft west swell at 19 to 21 seconds. Then, a strong front approaches later this evening and moves onshore early Wednesday morning. This will bring increasing southerly winds, reaching gales, and very steep and chaotic seas late this evening and overnight. In addition to the gales, expect very steep chaotic seas that are a mix of 8 ft west swell at 15 to 16 seconds and 10 to 14 ft southerly wind seas. Winds will ease for a brief period early Wednesday morning into the afternoon, then increase again Wednesday evening and overnight. High end advisory southwest winds are expected during this time, but could approach gales Wednesday night. Seas will remain very steep and hazardous through Thursday as high to very high west swell builds behind this front Wednesday and Thursday. Winds diminish late Thursday into Friday and seas will gradually lower on Friday but remain high and steep into the afternoon. Winds will turn northerly Friday afternoon as a thermal trough develops. There will likely be a brief period of sub-advisory conditions on Friday, but it will be short lived as northerly winds strengthen and seas become steep and wind driven through the weekend. /BR-y
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&& .MFR WATCHES/WARNINGS/ADVISORIES...
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OR...Wind Advisory from 8 AM to 2 PM PDT Wednesday for ORZ031. Winter Weather Advisory from 5 AM to 11 PM PDT Wednesday above 5500 feet for ORZ027-028. CA...Wind Advisory from 8 AM to 2 PM PDT Wednesday for CAZ081-085. PACIFIC COASTAL WATERS...Gale Warning until 11 AM PDT Wednesday for PZZ350-356-370-376. Hazardous Seas Warning from 11 AM Wednesday to 11 PM PDT Thursday for PZZ350-356-370-376.
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