WEATHER SUMMARY AND FORECAST DETAILS
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FROM MEDFORD NWS 6/11
Currently, southern Oregon and far northern California lie under cloud-free skies as high pressure builds in overhead. This may be the last time we speak of cool temperatures for some time, however.
A broad trough over the Rockies and Central Plains will shift east over the coming days, allowing the upper level ridge over the eastern Pacific to amplify and build into the western US through this weekend. Meanwhile, with high pressure in control, a thermal trough will strengthen along the coast, with temperatures in and around Brookings expected to rise well into the 80s each day. Inland, temperatures will rise by 2 to 5 degrees over the previous day each afternoon into this weekend.
The upper level ridge will weaken slightly Saturday night into Sunday as a trough interrupts the flow briefly, then the ridge rebuilds quickly and remains overhead through the first part of next week. This interruption will also push the thermal trough inland, and this will result in very warm temperatures Sunday through Tuesday/Wednesday. Daytime highs across the area will be 20 to 25 degrees above normal for early to mid June, with widespread triple digit, or upper 90s, highs west of the Cascades, and upper 80s to low 90s to the east.
Model forecast 850 temperatures (a very reliable signal for daily highs) are forecast to reach 26 to 28 degrees C, which when mixed to the surface (especially now during our longest daylight hours of the year), suggest highs could reach 105 degrees F in Medford and Grants Pass, and as high as 110 in the lower Klamath and Salmon valleys in western Siskiyou County. These will be the highest temperatures we have seen so far this year, and chances are very good that we will see record daily highs for many locations across the region.
The ridge is expected to flatten a bit by Wednesday. This could be delayed by as much as a day, as these pattern typically are, which will let temperatures cool slightly through the rest of the week. However, temperatures are still expected to remain above normal. Of note, we tend to see an increased risk for thunderstorms on the back side of heat waves. Currently, model suites keep the area dry at the end of this one, but there are some hints of instability starting to appear in some runs on Wednesday or Thursday afternoon, mainly over Modoc and Siskiyou county. The limiting factor will be atmospheric moisture, which appears lacking as of now, and a clear trigger to set off convection. So while chances are very low now, we can not rule out some lightning around the middle of next week. Confidence should improve as we get closer to the time period in question, and model better resolve the situation.
