Monsoonal moisture along with tropical moisture associated with Hurricane Hillary will begin to increase thunderstorm coverage across portions of the Southwest today, with heavy rainfall and flash flooding possible.
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As Hillary continues to track north in the eastern Pacific near Baja California, the threat for heavy rainfall and flash flooding is likely to increase on Saturday, especially for portions of Southern California, western Arizona, and southern Nevada.
With the increase in cloud cover, temperatures will return to more seasonal values today before dropping below normal across much of Southern California, western Arizona, and the Great Basin over the weekend.
Farther to the north, an area of low pressure is forecast to strengthen over the Canadian Prairie.
Windy and mostly dry conditions to its south and southwest will lead to critical fire conditions extending from the Inland Northwest to northeastern Montana today.
Over the central U.S., dangerous heat will continue to intensify with well-above normal to record-breaking temperatures expected from the central Gulf Coast and lower Mississippi Valley to the northern High Plains today.
This heat will persist from the southern Plains to the central Gulf Coast into the weekend while building across the central Plains and shifting east across the northern Plains into the upper Midwest.
However, a cold front trailing the previously noted low over Canada will bring relief to the northern High Plains over the weekend.
In the eastern U.S., showers and thunderstorms with areas of heavy rainfall will accompany an area of low pressure and its cold front as they move across the Northeast today.
Behind the front, high pressure with seasonal to below-average temperatures will move from the Great Lakes and Ohio Valley into the Northeast and Mid-Atlantic states today and Saturday.
The front is forecast to stall across the Southeast, where seasonal to above-normal temperatures are forecast into the weekend. ■