July 9, 2018 – Hot temperatures continue through the week. Monsoonal moisture will bring chances for showers and thunderstorms to the higher elevations late week into the weekend.
DISCUSSION (Today through Thursday)
Upper level trough moves through the PacNW Monday allowing an enhanced Delta Breeze through early Tuesday. Ridging begins to dominate Tuesday through the rest of the week, with the ridge axis remaining east of the area early in the week. Temperatures will slowly increase over the northern Sacramento valley, which could see daytime temperatures near 105-110 degrees by Wednesday. Temperatures over the rest of the valley will remain in the mid to high 90s through the week. The ridge axis begins to retrograde Wednesday and Thursday. This will allow monsoonal moisture to push north and begin impacting the Sierra by Thursday, though models are still uncertain on how widespread thunderstorms could become over the Sierra.
EXTENDED DISCUSSION (Friday THROUGH Monday)
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Upper level high pressure will be the dominant feature driving the forecast for the late week into next weekend. Monsoonal moisture could drift eastward and bring some chances for afternoon showers and thunderstorms, mainly for the Sierra. Differences exist between the latest runs of the GFS and ECMWF. GFS has more of a weaker upper flow pattern and greater chances for precipitation in the long term forecast, whereas the ECMWF has more of a westerly flow aloft to keep moisture to the east of the Sierra. Verification skill scores tend to favor the ECMWF at longer forecast hours, so nudged the forecast towards the ECMWF and a more dry QPF solution. Showers and thunderstorms for the Sierra cannot be ruled out however, so kept some chances each afternoon through the weekend.