Discussion
The upper trough that has been guiding conditions over the weekend has moved on to the northeast, leaving southwest flow aloft under the western side of a continental ridge. This pattern will bring some warming to most areas today, with easternmost Lake and Modoc County seeing similar temperatures as on Saturday.
Monday will be the warmest day of the forecast period for most areas. Temperatures west of the Cascades may reach up to 10 degrees above normal, while to the east highs look to be about 5 degrees above normal. A passing shortwave will bring elevated winds into the Shasta Valley, the Klamath Basin, Christmas Valley, and parts of the Rogue Valley. For western Siskiyou County, Jackson County, and western Cascades foothills, these winds align with ongoing dry conditions to possibly reach critical fire weather conditions. A Red Flag Warning has been issued for Monday afternoon and evening to highlight these concerns. This shortwave is also support slight (15- 20%) thunderstorm chances over eastern Modoc and Lake counties, given its interactions with monsoonal moisture moving over those areas. While the chances for thunderstorms are not high enough to meet Red Flag criteria, any thunderstorms that do develop can still be locally hazardous by bringing lightning strikes or erratic and gusty winds.
On Tuesday, an approaching trough around a low pressure system over the Pacific will shift flow to be more southerly. With dry air aloft precipitation is not expected. Temperatures west of the Cascades will drop a bit, but highs across the area look to stay about 5 degrees above normal. A weak front swinging around that trough may bring marine drizzle and some inland cloud cover On Tuesday morning, but significant impacts are not expected.
For midweek and into the weekend, the upper trough starts to work against high pressure centered around the Four Corners area. The first low will weaken and move off to the northeast but another low follows to keep the trough in place possibly through Saturday. With this pattern, slow and steady cooling would bring generally seasonable warmth across the area by Friday or Saturday. Upper disturbances may bring elevated breezes on Friday, but details that far out are hard to forecast with high confidence. Overall, the forecast through the rest of August looks to be unimpactful. -TAD