WEATHER SUMMARY AND FORECAST DETAILS
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FROM MEDFORD NWS 9/19
KEY POINTS
* Low impact weather expected this weekend and through at least Thursday. Inland temperatures will generally be a few to several degrees above normal (though as much as a dozen degrees), with late day breezes at or slightly below typical strength.
* Also, coastal stratus and patchy fog mainly during the night and morning hours, extending into the central portion of the Umpqua Valley in the early mornings.
* A frontal passage is possible late in the week. It would at least bring stronger breezes to the east side, but could be strong enough to bring shower and thunderstorm chances to southern Oregon and northern California.
A ridge will build across the area this weekend.This is producing night and morning valley inversions with marine low clouds extending into coastal valleys. These low clouds will be stubborn to clear at the coast, especially during Sunday. But, will gradually dissipate in the Umpqua Valley by the afternoon, and also be slowest to develop in the overnight hours in the Roseburg area. Besides the low clouds, there will be variable amounts of mainly thin high clouds over the area. This is the result of a change to a
seasonable pattern of westerly flow aloft while a series of disturbances track into western Canada. The main characteristic through much of next week will be dry and warm to very warm weather.
There will be a bit of a change on Wednesday as a slightly stronger front brings rain chances into western Washington. For our area, that is expected to result in a thicker band of high clouds, a few degrees of cooling, and a modest uptick in the strength of afternoon east side breezes. East side winds will see a more noticeable uptick, though likely still just breezy, on Thursday and/or Friday as a broader trough over the eastern Pacific Ocean swings southeastward.
Forecast uncertainty increases substantially beginning Friday. For late in the week, the 00Z operational versions of the ECMWF and GFS are both on the stronger side of their respective suites of ensemble data. This situation is well represented by the NBM with its probabilities of precipitation forecast at less than 10%. With that said, around 20% of GEFS members and around 30% of ECMWF members indicate a frontal passage either on Friday or during next weekend that would be strong enough to warrant mentionable shower chances in our area, stronger breezes, and cooling of temperatures to at least near normal levels. Lastly, of that cohort of active solutions, a few also depict an environment that would support a modest level of thunderstorm development.
