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FXUS66 KMFR 041537 AFDMFR

Area Forecast Discussion National Weather Service Medford OR 837 AM PDT Sat May 4 2024

DISCUSSION
Widespread rainfall continues across northern California and southern Oregon as a low pressure system moves over the area. Oregon highway webcams are showing snowfall and low visibilities at higher elevations. Extra caution is advised for anyone traveling through the Cascades and western Siskiyou County today. Additional details can be found in a continuing Winter Weather Advisory.

Please see the previous discussion for more details about the short- and long-term forecasts. -TAD



AVIATION
04/12Z TAFs...Unfavorable flying conditions are expected through at least 19Z as a potent frontal system moves through. Widespread MVFR ceilings, terrain obscurations and periods of moderate rain and mountain snow can be expected. Local IFR/LIFR can occur as well, especially in times of heavier precip. Some wet snow could even mix in with the rain briefly later this morning in Klamath Falls. Precipitation behind the front will become more showery this afternoon, but we still expect plenty of MVFR along with areas of higher terrain obscured through this evening. Some improvement to VFR tonight, though areas of MVFR will remain.
-Spilde

MARINE
Updated 820 AM Saturday, May 4, 2024...Moderate west winds and fresh short period west swell will continue today. Rain showers and a low chance of isolated thunderstorms are expected today. Southwest winds increase Sunday ahead of another front that will move through late Sunday night into Monday. This could bring conditions hazardous to small craft. Seas are likely to remain elevated Monday night into Tuesday with building west-northwest swell. After that, we expect high pressure to build in mid-late next week with a thermal trough strengthening along the coast. This will bring a return of stronger north winds and steep seas, highest south of Cape Blanco. -Spilde/Miles



PREV DISCUSSION
/Issued 401 AM PDT Sat May 4 2024/

DISCUSSION...RADAR is showing rainfall across most of southern Oregon and northern California -- the dry areas include much of Lake and Modoc Counties, but even those areas will begin to see precipitation in the next few hours. This is part of a low pressure system that is moving across our area. Precipitation will remain somewhat steady into the late morning hours before turning more showery in nature in the afternoon with thunderstorms possible over a relatively large portion of our area.

The bigger issue at the moment is snow levels. While snow levels are remaining somewhat high at the moment, they are expected to crash relatively soon as the front continues to move inland. With the heavier precipitation bands occurring as this happens, there could be some sloppy conditions, especially in the Cascades and in Western Siskiyou County, especially above 4000 feet. Will continue the Winter Weather Advisories at this time.

In addition, winds are expected to pick up later this morning for the higher terrain of Lake County to include the Winter Rim and highway 31 between Summer Lake and Paisley. Will continue the wind advisory for those locations as well.

Showers will continue overnight tonight as colder air filters in behind a frontal boundary. This will lead to some freezing temperatures for portions of western and central Siskiyou County where confidence is high with a 90 percent of reaching freezing temperatures in the Scott and Shasta Valleys. Have issued a freeze warning for these areas for tomorrow night. In addition, portions of the Applegate and the southern Illinois Valley might also reach freezing, with a 40% chance. Statistical guidance is showing temperatures a little warmer than freezing. Would like to see one last model run before making a decision either way for these areas.

Temperatures will begin to warm up over the next several days as the low progresses eastward. Showers, however, will remain as additional weak disturbances pass over the area with zonal (west to east) flow. Widespread impacts from these showers are generally not expected. Then, by midweek the pattern changes and a ridge of high pressure returns. This ridge will help us warm up and dry out into the weekend.

MFR WATCHES/WARNINGS/ADVISORIES
OR...Winter Weather Advisory until 11 PM PDT this evening above 4000 feet for ORZ027-028.

Wind Advisory until 5 PM PDT this afternoon for ORZ030-031.

CA...Winter Weather Advisory until 11 AM PDT this morning above 4000 feet for CAZ080.

Freeze Warning from 2 AM to 8 AM PDT Sunday for CAZ080-081.

PACIFIC COASTAL WATERS...None.

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