Sunrise 5:58 AM   Sunset 8:09 PM Moonrise 2:18 AM   Moonset 12:39 PM

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FXUS66 KMFR 020002 AFDMFR

Area Forecast Discussion National Weather Service Medford OR 502 PM PDT Wed May 1 2024

.Updated Aviation Discussion.

AVIATION
02/00Z TAFs...Conditions will remain VFR through early this evening, with gusty, breezy west to northwest winds east of the Cascades, including at Klamath Falls. An approaching front will result in ceilings lowering to MVFR, then IFR at the coast later this evening into tomorrow morning. Even though the TAF at North Bend shows a prolong period of IFR ceilings, it's possible there could be brief periods of MVFR ceilings after 13z.

Inland west of the Cascades, VFR ceilings will lower to MVFR tonight north of the Umpqua Divide, confidence on the timing of lowering ceilings indicated in the Roseburg TAF could be delayed by an hour or two. Medford is expected to remain VFR through the TAF period, however the higher terrain will be at least partly obscured towards 11z.

East of the Cascades, VFR ceilings will continue into tonight, then MVFR will follow at Klamath Falls as precipitation moves in. Areas of mountain obscuration are expected after 12z until the end of the TAF period. -Petrucelli


DISCUSSION

Short Term
Tonight through Saturday...Warmer temperatures and dry conditions have been the rule today under ridging aloft.
Mostly clear skies today will start to give way to increasing clouds late this afternoon and evening as the next trough approaches from the northwest.

This next system, smaller in scale and weaker than most, will arrive tonight, then pass overhead through Thursday. Due to the angle of the system, there will be considerable westerly onshore flow on the front side, along with relatively little in the way of strong winds out of the south. This type of pattern typically produces a good shot of wetting rain across the region, especially along and west of the Cascades, with little in the way of downslope drying. As a result, most areas in Oregon should see measurable rain, although northern California may not be as lucky, as those areas will remain well south of the main moisture flow and dynamics. Temperatures will trend towards normal for this time of year, which means snow levels with this event will remain at or above 5000 feet, so winter impacts will remain confined to the backcountry and the highest passes, and even then, those impacts will be minimal.

Most precipitation will dissipate or move out of the area by Thursday night as the next ridge briefly builds in overhead, but some light showers are likely to continue into Friday morning west of the Interstate 5 corridor as a weak warm front skirts by just offshore. Then, the next system arrives late Friday into Saturday.

This system, much like the last, will see more of a westerly onshore flow and little in the way of southerly winds, so once again, downsloping will be minimal (except east of the Cascades)
and most areas will see a good shot of rain or snow. There will be cooler air arriving with this front, and snow levels are expected to drop to between 3000 and 4000 feet, lowest Saturday morning just after the passage of the cold front. Some minor winter impacts are expected across many of the area passes, including the Cascade passes and Siskiyou Summit, but due to warm ground temperatures, accumulations on roadways may be as significant as they otherwise would be. This system also appears to have a stronger moisture inflow than the last one, so rainfall amounts Friday into Saturday will be fairly potent. Rain amounts of a half inch or more are almost guaranteed for almost all areas in southern Oregon and far northern California, with up to 2 or even 3 inches of rain possible along the coast. Meanwhile, snowfall amounts of between 6 and 12 inches will be common in the mountains. The cooler, wetter weather pattern with post-frontal showers will continue Saturday afternoon, and although there is only a slight chance (around 15%), we cannot rule out a thunderstorm or two behind the front Saturday afternoon.

LONG TERM DISCUSSION
Saturday night though Wednesday...The cooler and showery pattern will continue Saturday night into Sunday as an upper level low remains over the area. Showers will continue on Sunday but will decrease in coverage as the low shifts eastward. High temperatures on Sunday are expected in the mid 50s in the west side valleys and along the coast, with highs in the mid to upper 40s for valleys east of the Cascades.

Models continue to show an active pattern into early next week. A front moving into the area on Monday will bring high chances (50 to 85 percent) for precipitation for areas from the Southern Oregon Cascades west as well as into western Siskiyou and northern Klamath counties. Expect chances (20 to 50 percent) for precipitation elsewhere east of the Cascades and across Northern California.
Precipitation amounts with this front on Monday will be mainly light. Snow levels will range from 4000 to 5500 feet. Then onshore flow will allow for lingering showers on Tuesday, especially across southwest Oregon zones with lesser chances across Northern California.

We may get a reprieve from the active weather as the Climate Prediction Center 8-14 day outlook continues to favor a return toward more "normal" conditions (temps/precip) for the second week of May (May 9-May 15). -CC


MARINE
Updated 200 PM Wednesday, May 1, 2024...A weak front will move through the waters tonight into Thursday with a modest increase in short period west-northwest swell. A break Thursday night will bring calmer conditions, then the active pattern resumes with rain and hazardous conditions for small craft possible Friday into Saturday morning. Weak winds and a slight increase in short period west-northwest swell dominated seas are expected during the weekend. The next in a series of fronts is likely to arrive on Monday. -DW



MFR WATCHES/WARNINGS/ADVISORIES
OR...None.

CA...None.

PACIFIC COASTAL WATERS...None.

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