WEATHER SUMMARY AND FORECAST DETAILS
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FROM MEDFORD NWS 10/20
KEY POINTS
Low pressure dominates weather pattern this week, maintaining near normal/seasonable temperatures. Tues/Wed warmest days of forecast period.
Wrap around moisture likely brings wetting rainfall and slight chance thunderstorms east of the Cascades Wed-Thurs; 0.25"-0.50" for Modoc/Lake Counties, 0.10"-0.25" for remainder of East Side to the Cascades.
Increasing chances for drier/warmer conditions over the weekend (20% -> now 40%), though a cooler wetter pattern continues to hold the majority of solutions (60% chance) - first chance of rainfall for West Side Valleys since Sept 24th/25.
An upper level low pressure remains offshore this morning, continuing to trek southward through the day today. This system will close off and linger off the California Coast through most of Wednesday, then gradually push inland late Wednesday into Thursday. It`ll get swept eastward by another trough swinging through to the north Thursday into Friday. The forecast models are in fairly good agreement in the overall pattern through Friday. Beyond Friday, model disagreement increases in the pattern evolution for the weekend with the GEFS suite maintaining more of a ridging/dry pattern and the EC suite showing a wetter/cooler scenario.
Deformation band remnants continue on radar this morning, lingering over Curry/Coos and eastern Douglas Counties. This band managed to bring a few hundreths across much of Josephine County/Illinois Valley as well as in the Cascades up near Crater/Diamond Lakes. Amounts were a bit higher in western Siskiyou County where amounts
were closer to 0.10-0.15". Precipitation will continue to diminish this morning with quiet conditions expected across the area. Southerly flow persists today, even turning a bit southeasterly over the region. This will bring another day of breezy winds across northern California/East Side, this time winds will be from the south to southeast and generally weaker than what occurred the previous two days. If winds line up, we could even see some gusty southeast winds here in the Rogue Valley. Temperatures trend warmer by about 5-10 degrees today, most notable west of the Cascades this afternoon, feeling more similar to what occurred this past weekend. Dry conditions are expected for much of the day today, but increasing moisture under south/southeast flow could bring some isolated showers to portions of northern California late this tonight into early Wednesday.
Low pressure pushes inland into California on Wednesday, and wrap around moisture will bring a more widespread potential for precipitation Wednesday afternoon/evening into Thursday. Currently, the highest chances for precipitation (50-80% chance) is focused across eastern Siskiyou/Klamath Counties and much of Modoc/Lake County for Wednesday evening into Thursday. 24-hour rainfall amounts (5 pm Wed - 5 pm Thurs) in these areas could reach between 0.25"- 0.50", with the higher end amounts most likely in favored upslope areas of the Warners. There is some weak instability around Wednesday afternoon, so there is a slight chance of thunderstorms across the Modoc and southern Lake County. Precipitation chances drop to 20-40% for areas westward to the Cascades, then down to 10- 15% for the western slopes of the Cascade Foothills and even less for points farther west. This event/pattern favors precipitation chances for northern California/East Side and drier conditions for the West Side.
Showers linger across the East Side into Thursday evening before this system finally gets swept eastward by a kicker trough from the northwest on Friday, bringing the return of dry conditions. Temperatures trend cooler on Thursday and Friday compared to Tuesday/Wednesday, hovering near to a few degrees below normal Thursday, then 5-10 degrees below normal on Friday. The equates to mid 60s for the West Side, mid-low 50s East.
High pressure over the eastern Pacific nudges eastward Friday, and this is when guidance diverges on the overall pattern progression. There are differences in how fast the trough progresses eastward, which influences if/when an upstream deeper trough arrives over the Pacific Northwest. There`s been an increase in the amount of model
solutions that want to maintain a warmer/drier pattern for the weekend, increasing from 20% of solutions to now 40%. There`s still a respectable amount of the EC members, however, that bring a wetting rain to the valleys west of the Cascades, but the GEFS suite is markedly dry for the weekend. Currently the forecast supports the wetter and somewhat cooler solutions. It should be noted that if the wetter solutions come to fruition, it will be the first opportunity for a more widespread rainfall for valleys west of the Cascades in nearly 4 weeks...the last measurable precipitation recorded in Medford/Roseburg was September 24th/25th. Some guidance brings this potential as early as Saturday morning, while the majority holds off until Sunday. Stay tuned as details become more clear in the coming days.
