WEATHER SUMMARY AND FORECAST DETAILS
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FROM MEDFORD NWS 7/9
Key Points:
Typical summer weather for the remainder of the week: seasonable temperatures and humidities, gusty afternoon winds.
Pattern amplifies Friday into the weekend resulting in tightening pressure gradients and gusty southwest winds (25-35 mph) Friday- Sunday. Gusty winds combined with low RHs bring heightened fire weather concerns (winds strongest/RHs lowest on Saturday).
Thunderstorm pattern early next week. Best chances east of Cascades and across northern California with lesser, but not negligible chances for the West Side.
Another quiet summer morning underway today. The marine layer is far less extensive this morning and only blankets the coast from Brookings southward. Skies are clear everywhere else.
Westerly flow will prevail today under a mostly zonal flow pattern with flat high pressure to the south and a broad trough extending south over the northeastern Pacific from the Gulf of Alaska. This will result in a more stable air mass with thunderstorm potential remaining well east of the area. There will likely be some cumulus buildups today east of the Cascades and across northern California, but no showers are expected today. Generally cooler temperatures are expected into the weekend, so instead of temperatures being 8 to 10 degrees above normal like recent days, high temperatures through the weekend will hover within a few degrees of normal, equating to low 90s West/upper 80s East.
The pattern transitions on Friday with high pressure to the south moving eastward into the Great Basin region, then amplifying on Saturday. Meanwhile, relatively strong low pressure off the northern British Columbia Coast digs southward Friday into Saturday, lingering offshore near Seattle through the weekend. This will turn the flow southwesterly again and southwest OR/northern CA will be wedged between these two systems, resulting in tighter pressure gradients. This pattern will bring multiple days of strong, gusty winds to the region Friday through Sunday when gusts of 25 to 35 mph are expected east of the Cascades and across northern California. The air mass in those areas will be more under the ridge influence, while areas west of the Cascades will be more under the trough influence. This will result in much drier air for areas to the east (daytime humidities in the low teens, possibly single digits), and when combined with those 25 to 35 mph gusts, critical fire weather conditions could be possible east of the Cascades Friday through Sunday, most widespread on Saturday.
The parent low pressure to the north pushes northeastward on Sunday, but a frontal boundary/energy gets left behind, maintaining tight pressure gradients. Guidance maintains another day of gusty winds (25-30 mph), and although humidities do tick upward some, it could still be another day of elevated to critical fire weather conditions. Meanwhile, strong ridging gets nudged eastward with that trough and the flow will turn more south to southwest heading into the early part of next week. This pattern will bear watching for thunderstorm potential as south to southwesterly flow could push some monsoonal moisture into the region. Much will depend on when/where shortwaves develop and at this juncture, it`s too soon to try to pinpoint details. It`s also challenging because our region will remain wedged between strong high pressure to the east and incoming troughs from the northwest. The proximity of those troughs could be enough to keep the flow more southwest or even westerly, and the more westerly the flow, the lower the chances for thunder, especially west of the Cascades. Until further details can be sussed out, it currently looks like the best chances for thunderstorms would be across eastern areas on Monday/Tuesday. We`ll continue to monitor model trends to see if the eastward shift in the upper level pattern persists, or if thunderstorm chances shift westward. Stay tuned for updates as models hone in on additional details.
