FXUS66 KMFR 110931 AFDMFR

Area Forecast Discussion National Weather Service Medford OR 231 AM PDT Wed Sep 11 2024

DISCUSSION
A more active pattern begins today. The leading edge of the rain associated with an approaching cold front is now evident at the coast north of Cape Blanco, and will spread across southwest Oregon, most of Klamath County, far northwest Lake County, and far western Siskiyou County this morning. More specifically, reaching most areas north and west of the Rogue- Umpqua Divide by 5 AM, then to the Grants Pass area around 6 AM, Medford/Ashland area around 8 AM, then to the Cascades by 9-10 AM, and east side by noon. Some of the stronger cells within the rain bands could bring thunderstorms with brief downpours and gusty winds.

Widespread wetting rainfall is expected, with the most rain occurring along the coast (in the coast ranges) and also across the Umpqua Valley to the Oregon Cascades/Foothills. These areas will see widespread amounts of 0.40-1.00 inch. Lesser amounts are expected south of the Umpqua Divide and east of the Cascades in Oregon with 0.10-0.40", including around a quarter of an inch for the Rogue Valley. This will be welcome news to those fighting the wildfires burning in the region. It should be noted that rainfall rates could be significant within the strongest convective cells, but these cells will be moving very quickly and sustained heavy rates shouldn't last too long in any given location. As such, we aren't too concerned about flash flood/debris flow risk. Latest CAM guidance is showing potential for rates in the 0.20-0.30"/hr range. This is mainly across Douglas County for a few hours Wednesday morning.

It will be much cooler today, with highs around 25 degrees lower than they were yesterday...mainly 60s for the west side with 50s and 60s for the east side.

Showers will continue this afternoon and evening, though not everyone will get measureable rain. Portions of the Shasta Valley or portions of the Mt Shasta region might get missed all together since the best forcing for precipitation is focused to the north in Oregon. After 8 PM this evening, the upper trough axis will shift to the east and coverage of showers should diminish rapidly.
Onshore flow, however, will keep the probability of lingering light showers higher along the coast and over the Cascades into sunrise Thursday morning.

Things dry out on Thursday as heights rise and precip chances gradually diminish to nil across the Douglas and Coos coast.
Expect increasing sunshine and a comfortable afternoon with inland highs largely in the range of 65-75 degrees. Low temperatures will have a decreasing trend into Friday morning, with freezing temperatures possible for much of the east side on Friday morning.

It will warm up a bit Friday and (and slightly less so) Saturday with temperatures around normal as weak high pressure builds into the area. A marine layer of low clouds is expected to surge into the coastal valleys late Friday evening into Saturday morning.

Another couple of Pacific troughs are expected to be the drivers of our weather around Sunday into early Monday, and around late Tuesday into Wednesday. The NBM solution was utilized with a high degree of model-to-model and run-to-run variability in the timing, track, and strength of these features. The general trend has been toward a weaker solution with less rain produced from the combination of these next two systems than from today's system.
But, this should continue seasonable temperatures, and at least generate surges of mainly night and morning low clouds from the coast into southwest Oregon valleys.

-Spilde/DW
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