June 16, 2019 – A heating trend is expected early this week, peaking on Tuesday, followed by less hot weather. Isolated mountain thunderstorms are possible afternoon and evenings through Monday, mainly over the higher elevations of the Sierra Nevada.
An upper level shortwave trough is bringing onshore flow and cooler temperatures to the area. The Delta breeze is blowing with even cooler temperatures than yesterday for much of the area, about 2 to 4 degrees cooler than the same time yesterday. Downtown Sacramento was down to 55 at 3 am, and most locations in the Delta and Sacramento area were in the 53 to 55 degree range. Marine stratus is expanding across Sacramento County and is expected to spread into neighboring counties over the next few hours. May need to update forecast to increase extent of morning cloud cover and adjust temperatures down slightly. The Delta breeze will not be as strong later today as it was yesterday, though, with sunny skies and warmer temperatures developing by afternoon.
Isolated afternoon and evening thunderstorms will once again be possible over the higher mountain elevations this afternoon and evening, especially over the northern Sierra. Also have the potential over the northern Coastal Range, northern Shasta County and the Lassen National Park area. Some thunderstorms are possible Monday over the Sierra south of I80. Dry weather is expected for the rest of the week.
On Monday, eastern Pacific ridging will expand eastward over the region continuing a warming trend and bringing back some hot afternoon temperatures. Currently, the peak of the heat looks to occur on Tuesday but the northern part of the valley looks like heat will linger a bit longer before cooler temperatures arrive, probably on Thursday. On Tuesday, valley temperatures will range from 98 to 108 degrees with the hottest temperatures over the north end of the valley. Heat related concerns look likely for central and north end of the Sacramento Valley on Tuesday so the potential continues for a Heat Advisory for those areas.
Northerly winds and low afternoon humidity Monday and Tuesday over the northern half of the Sacramento Valley will bring elevated fire weather concerns for that area. Decent humidity recovery may limit concerns overnight, though.
Extended Discussion (Thursday through Sunday)
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Warm and dry conditions will dominate the extended forecast. Ensemble models continue to show high pressure centered over the eastern Pacific with low pressure deepening over the intermountain west Thursday through the weekend. Temperatures fall slowly each day toward near normal by Sunday.
Winds expected to increase Friday into the weekend, though confidence is low at this time on wind strength. Model agreement is low between the GEFS and European ensemble on the depth of the trough. Current Euro ensemble shows the trough deepening significantly east of California, which could bring stronger northerly Valley winds, while current GEFS only shows a slight deepening of the trough, which could bring mainly a slightly increased onshore flow.
Kept forecast persistence of a slighter increase in winds, which is influenced mainly by the NBM forecast. Either way, with the drier weather in place and poor RH recoveries in some areas, there is the potential for fire weather concerns with any increase in winds.