Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 338 AM EDT Thu Sep 05 2024 Valid 12Z Thu Sep 05 2024 - 12Z Sat Sep 07 2024 ...Very heavy rain and the threat for scattered to numerous instances of flash flooding continues for the Gulf Coast states the next couple of days... ...Dangerous heat wave intensifies over the Southwest and West Coast... Heavy rain and flash flooding remain in the forecast along the Gulf Coast as a stationary front and coastal low drive multiple days of widespread showers and thunderstorms across the region. The elongated area of low pressure and front from the north-central to western Gulf will keep the greatest focus for repeated rounds of storms moving onshore over the central Gulf Coast and upper Texas Gulf Coast today (Thursday), potentially spreading a bit further northward into the Lower Mississippi Valley. Very moist Gulf air continues to contribute to very efficient downpours with these storms, approaching 2-3" per hour in some cases, exacerbating the threat for heavy totals and flash flooding. There is now a Moderate Risk (level 3/4) of Excessive Rainfall for southeastern Louisiana where prior days rainfall has lead to very wet antecedent conditions and brings a locally greater threat for scattered to numerous instances of flash flooding, especially for the urban areas around greater New Orleans. A broader Slight Risk (level 2/4) is in place across the region for additional scattered instances of flash flooding. An approaching upper-level wave will help to shift the focus for heavy rainfall a bit eastward on Friday as the front begins to meander away from the western Gulf and lift northward into southern Georgia, leading to decreasing rain chances further West. Another Slight Risk of Excessive Rainfall extends from the central Gulf Coast eastward through the Florida Panhandle into southern Georgia where a similar threat for intense heavy downpours with repeated rounds of storms will lead to several inches of rain, and the potential for scattered instances of flash flooding. Temperatures will remain well below average across the region north of the frontal boundary and in the presence of widespread rain and cloud cover with mostly upper 70s and low 80s. Some locations may only reach into the low 70s Friday. On the other hand, it will be hot south of the front across the Florida Peninsula, with highs in the low 90s. A Heat Advisory is in place for South Florida where the combination of heat and humidity will lead to heat indices in the 105-110 degree range. A dangerous heat wave will intensify over the Southwest and West Coast the next couple of days with a strong upper-level ridge now settled over the region. Forecast high temperatures Thursday and Friday range from the 110s for the Desert Southwest, low 100s to near 110 for southern California, mid-100s for the central California Valleys, and the 90s to low 100s for central/northern California and into the Pacific Northwest. Several record-tying/breaking highs are possible across the Pacific Northwest. Widespread heat-related warnings and advisories are in place given the heightened threat for heat-related illness to anyone without efficient air conditioning or adequate hydration. While not quite as hot, highs will be well above average and potentially uncomfortable even for some immediate coastal locations with temperatures reaching into the 80s. Elsewhere, a broad area of showers and thunderstorms is expected ahead of a pair of cold fronts passing through the Upper Midwest/Great Lakes, Central Plains, and central/southern High Plains and adjacent Rockies. The greatest chance for some moderate to locally heavy rainfall will be under the influence of an upper-level trough over the Upper Midwest/Great Lakes, and where upslope flow enhances storms over the southern Rockies. A few isolated instances of flash flooding will be possible in the southern Rockies given recent rains and some more sensitive burn scars. Storm chances with moderate to locally heavy rainfall will continue ahead of the front as it pushes eastward through the Great Lakes overnight Thursday and into the Lower Great Lakes/Upper Ohio Valley on Friday. Some storms may begin to spread into the Northeast and Mid-Atlantic by early Saturday morning. Temperature-wise, the passing cold front will bring well below average, Fall-like temperatures to the Northern Plains and Upper Midwest Thursday, with highs in the 60s to low 70s. Temperatures will be rather chilly for the Upper Great Lakes by Friday as highs drop into the 50s. Conditions will be much warmer ahead of the front Thursday over the Midwest and Ohio Valley with highs in the mid-80s to low 90s. The approaching front will bring temperatures down into the 70s for portions of the Midwest Friday. Mild conditions will continue for much of the East Coast through Friday with highs in the upper 70s to low 80s. Putnam Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php