Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 255 PM EDT Fri Jun 21 2024 Valid 00Z Sat Jun 22 2024 - 00Z Mon Jun 24 2024 ...Record hot temperatures over portions of the Midwest/Ohio Valley & the Mid-Atlantic states this weekend... ...Heavy rain and flash flooding concerns across the Upper Midwest Friday night and Great Lakes Saturday... ...Monsoon-like conditions for this Southwest this weekend into Monday...Heat building across the West... A heat wave should continue for portions of the Midwest/Ohio Valley and the Mid-Atlantic States, to the south of a stationary front. Forecast high temperatures will rise into the upper 90s/near 100 Saturday in the Mid-Atlantic, with record-tying/breaking temperatures possible. Heat-related Advisories and Warnings are in place as these temperatures, when combined with the humidity, will bring heat index values into the 100-105 degree range, with values as high as 110 possible through the southern Mid-Atlantic on Saturday. Additionally, overnight low temperatures will remain in the mid-70s for many locations, at potential record-tying/breaking levels, providing little relief from the heat. The early arrival of this heat in the Summer season, persistence over multiple days, and abundant sunshine will aggravate heat stress on those without reliable air conditioning. Temperatures more broadly from the East Coast to the central/southern Plains will be in the mid-90s this weekend. Meanwhile, relief continues to the north of a frontal boundary draped though southern New England, with highs now mostly in the 70s and low 80s. Isolated to scattered excessive rainfall/flash flooding is possible near the stalled frontal boundary. The greatest threat for significant heavy rainfall will be ahead of a surface wave over portions of the Upper Midwest as thunderstorm complexes late on Friday unleash their potential. A Moderate Risk of Excessive rainfall (level 3/4) is in effect, from southeast South Dakota to in and near the Minnesota/Iowa border, where the highest potential for heavy rainfall/significant flash flooding exists. Moderate to major river flooding is also forecast to worsen. Additional scattered instances of flash flooding will be possible more broadly across the Upper Midwest. An upper-level shortwave approaching from the west will help to deepen the frontal wave and push the system eastward on Saturday, bringing the threat for heavy rainfall/flash flooding to portions of the Great Lakes southwestward into the Upper Mississippi Valley as an organized complex of storms is expected to follow the system eastward. Some severe thunderstorms will again be possible with a Slight Risk in place mainly for the threat of damaging winds. As the system pushes into New England on Sunday, it brings an elevated risk of flash flooding to the region. Near the Southeast Coast, a small convective low has the potential to bring isolated heavy rainfall/flash flooding over the next couple of days as it moves inland into portions of far northeast Florida and Southeast Georgia. The National Hurricane Center is monitoring it for tropical cyclone development, as it has a 60% chance to become a tropical depression prior to landfall Friday night into Saturday morning. Across the southern Gulf of Mexico, another tropical disturbance has a 60% chance of formation into a tropical depression over the next 2-3 days, and it brings a risk of isolated flash flooding this weekend to areas which received heavy rainfall from Alberto on Wednesday. The warm core high across the Mid-South is expected to shift into the West with time, towards the Four Corners. When combined with moisture brought into the region by the former tropical storm (Alberto), whose remains will be moving west-northwest from southern Baja California into the open North Pacific, monsoon-like afternoon and evening thunderstorms are expected with associated locally heavy rainfall/flash flooding, which would be most problematic in dry washes/arroyos, slot canyons, and locations with burn scars. Some of the storms could also cause haboobs -- dust storms caused by strong, cool thunderstorm outflow. Forecast highs will soar into the 100s on Saturday for portions of the Great Basin and central California Valleys, bringing high temperatures close to record values across northern California and portions of Utah. Heat-related Advisories and Watches have been issued for the central Valleys south into interior southern California. Conditions will also be notably hot over the Desert Southwest on Friday, particularly over central Arizona where Excessive Heat Warnings are in place, with highs into the 110s. Roth/Putnam Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php