WEATHER SUMMARY AND FORECAST DETAILS

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FROM MEDFORD NWS 7/23

Key Points:

*A much drier air mass moves into the area today and will persist for at least the next 7 days.

*Overall, temperatures will be very warm, but should be pretty close to or just slightly above normal for late July.

*Other than daily intrusions of marine stratus along the coast (and perhaps a slight chance of drizzle at times), cloud cover will be minimal and precip chances will be near zero for inland
areas.

*Little to no risk for thunderstorms during this time period, but there will be periods of strong, gusty winds and also very low humidity. These two elements will overlap at times during the
afternoons/evenings causing critical fire weather conditions.This is most likely Friday and Saturday for portions of northern California and also areas east of the Cascades.

Summary:

Low pressure offshore this morning will gradually eject toward the northeast over the next 24-48 hours while upper ridging persists near the Rockies. The flow aloft, which had been southerly during the past few days, is turning southwesterly, and this is allowing a much drier air mass to move in. As such, the risk of thunderstorms today is near zero with any convective activity occurring well to the north and east of the Medford NWS Forecast zone.

Temperatures were hot yesterday here in the valley due to strong downward transport (mixing down from 12000 feet AGL!) during the afternoon -- we managed to hit 105F at the airport, which was only one degree shy of the record (106F set in 2006/1928). Other areas didn`t see the degree of mixing that we saw here in the Rogue Valley, so temps didn`t get so hot -- highs of only 87F in Mount Shasta City, 90F in Klamath Falls, 93F in Roseburg, and 94F in both Montague and Alturas. Expect temps to be a bit cooler today compared to yesterday here in Medford (high of 96F), but similar readings compared to yesterday elsewhere. Marine clouds should peel back to the beaches, but may persist along the immediate coast this afternoon, then return to areas just inland tonight.

As the low ejects to the NE, mid-level SW flow will increase across the CWA. So, by Friday afternoon and evening, a well- mixed boundary layer will transport some of those stronger winds
aloft down to the surface, especially east of the Cascades, but also in northern California. Expect widespread SW-W winds of 10-20 mph with peak gusts of 30-40 mph. At the same time, the surface dewpoints will crash resulting in very low humidity, in some cases, as low as 5-10% over the far east side. This will bring critical fire weather conditions and Fire Weather Watches are in effect. This pattern will persist into Saturday with a gradual shift eastward and southward of the main core of overlapping gusty winds/low humidity. A smaller area of critical fire conditions could linger Sunday pm/eve over Modoc and portions of SE Klamath/Lake counties.

A broad upper trough is forecast to persist off the British Columbia coast or in the Gulf of Alaska next week with the upper ridge remaining over the Intermountain West/Four Corners. This pattern should allow winds to relax a bit early next week, but it will remain dry as any monsoonal moisture will remain cut off from the area (shunted to the southeast by prevailing SW flow aloft). Temperatures overall should be within a few degrees either side of normal, a bit lower (cooler) though nearer the coast where daily marine intrusions bring more cloud cover.