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US Day 3-7 Hazards OutlookNWS Weather Prediction Center College Park MD430 PM EDT Fri Aug 04 2023 Valid Monday August 07 2023 - Friday August 11 2023 Hazards:- Heavy rain across portions of the Lower Great Lakes and Interior Northeast, Mon, Aug 7.- Severe weather across portions of the Lower Great Lakes, Interior Northeast, and Appalachians, Mon, Aug 7.- Flooding possible across portions of the Middle Mississippi Valley and the Ohio Valley.- Hazardous heat across portions of the Southwest, the Southern Plains, the Lower Mississippi Valley, and the Southeast, Mon-Fri, Aug 7-Aug 11.- Hazardous heat across portions of California, Mon, Aug 7.- Hazardous heat across portions of the Southern Plains and Lower Mississippi Valley, Wed-Fri, Aug 9-Aug 11.- Hazardous heat across portions of the Southeast, Mon-Tue, Aug 7-Aug 8.- Hazardous heat across portions of mainland Alaska, Mon-Tue, Aug 7-Aug 8. Detailed Summary:...CONUS...Oppressive heat across much of the southern tier of the country will remain the focus of the medium-range hazards forecast covering next week (Monday, August 7 - Friday, August 11). A stagnant upper-level high anchored over the south-central U.S. will expand once again from the Atlantic to Pacific coasts, shifting a bit west and northward with time, with only some minor areal modifications in the extent of the current heat wave. Upper-level energy dipping south over the eastern U.S. will likely provide some relief for northern portions of the Southeast by Wednesday (August 9th), with relatively lower high temperatures closer to August averages and higher precipitation chances. Meanwhile, as the upper-high shifts a bit westward and upper-level ridging expands overall across the western U.S., hazardous heat will return further northward over portions of the south-central U.S. and Lower Mississippi Valley. After a brief reprieve, hazardous heat will also be returning to the Southwest this weekend and continue through the forecast period. For eastern portions of the outlook area, high temperatures will range between the mid-90s in the Southeast/Florida, the upper-90s to low-100s for the Lower Mississippi Valley into the Southern Plains, and the low to mid-100s for eastern portions of Texas. When combined with high humidity values, this will lead to oppressive daytime heat indices of 105-115, locally higher. To the west, while humidity will not be as high, air temperatures will be hotter, with highs in the upper 100s for west Texas and portions of the Southwest to the mid-110s in the deserts. The heat is expected to be most oppressive over Texas, where daily near-record-tying/breaking high temperatures are forecast through next week. In addition, overnight lows will stay much above average, around or above 80 degrees for many locations, which is at or above record-tying/breaking levels. This will provide little relief from the heat overnight. Portions of central California seeing above average temperatures and hazardous heat this weekend may see one more day of hot temperatures Monday, with highs in the low to mid-100s, before temperatures lower closer to summertime averages. To the north, an energetic upper-level pattern will persist with multiple shortwaves passing through the central-eastern U.S. through the period. One shortwave is forecast to swing through the Midwest/Great Lakes/Northeast during the Monday (Aug 7) - Tuesday (Aug 8) timeframe. Lift ahead of the upper-level wave as well as a well-organized accompanying surface low pressure system pushing eastward is forecast to lead to widespread showers and thunderstorms across portions of the Lower Great Lakes/Interior Northeast southward through the Appalachians on Monday. Notably high surface moisture, with precipitable water (pw) values running around 1.5 standard deviations above the mean, will help promote some locally heavy downpours. In addition, wind speeds with the shortwave aloft will provide sufficient deep-layer shear for some organized, severe storms, with damaging wind gusts the primary threat. Additional heavy rainfall may fall across New England Tuesday as the system pushes east but totals look to remain lighter compared to Monday. The energetic, northwesterly flow setup over the Mississippi Valley into portions of the Southeast, along with seasonable summer moisture, will likely lead to additional storms and heavy rainfall chances. This appears most likely over the Southeast on Tuesday and then further west/north into the Mississippi and Lower Ohio/Tennessee Valleys on Wednesday and Thursday. However, areal rainfall totals will likely be influenced by mesoscale storm organization hard to predict at this timeframe. ...Alaska...The strong upper ridge currently over Southcentral Alaska will move into northwestern Canada over the next few days while an intensifying storm moves into the Bering Sea. The combination of the two will support a highly amplified and blocky pattern next week. Strong southerly flow through the eastern and central parts of the mainland during the weekend into early next week will support much above normal temperatures across much of northern and interior Alaska. Temperatures over the Yukon Flats region will range into the mid 80s to lower 90s. Temperatures will also be above average (well into the 70s) across interior portions of the North Slope. These high temperatures look to cool off by mid-week, but a trend in the guidance for the ridge to persist may lead to a bit longer period of above average temperatures. Moist, onshore flow sourced from the central Pacific ahead of a storm system in the Gulf of Alaska may help to focus precipitation chances along the southern coast into southeastern Alaska next week. However, significant differences in amounts/timing remain in the guidance and the rainfall may ultimately remain moderate and below hazardous levels. The strongest signal for heavy rainfall looks to come towards the end of next week, but will defer to future forecasts to see if this remains a trend before introducing any hazards areas. Putnam