WEATHER SUMMARY AND FORECAST DETAILS
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FROM MEDFORD NWS 9/4
A broad, very slow moving upper level trough will continue to be the main driver of our weather through Sunday. This is the western lobe of a strong omega blocking pattern aloft over the contiguous United States, with a strong ridge centered over the Midwest. A shortwave rotating through the trough, and the aid of day-time heating will enhance shower activity today through this evening, with thunderstorms expected to be embedded. The highest probability will be in northern and eastern Douglas County, with activity possible across our area, but the probability of showers and storms tapering off to the south and east.
The main uncertainty for Saturday is the extent to which the trough will shift/wobble north-northeastward. The NBM and GFS are on the progressive side of solutions, with activity expected to be focused upon Washingtion and northern Oregon. But, the ECMWF and its ensemble members do support a few light, stray showers making it into Coos and Douglas counties. A decrease in cloud cover is expected to help bring warmer temperatures.The trough is expected to wobble back southeastward on Sunday with a shortwave bringing an enhanced, increasing probability of showers and also isolated thunderstorms...with the highest probability near and in the Cascades. Another effect will be several degrees of cooling of high temperatures.
The trough is expected to finally kick eastward Sunday night into Labor Day with a break between systems, before the next trough tracks southward, offshore from California. This is expected to bring a few days of dry and warmer weather to our area, at least into Wednesday and likely through Thursday. Late in the week, into next weekend, the interaction/track of the existing trough offshore of California, and another trough in the northern branch of the jet stream is highly uncertain. But, the probability is that a trough influenced or dominated pattern will bring at least modest cooling and at least sporadic shower chances.
