Hydrometeorological Discussion
Issued by NWS Tuscaloosa, AL
Issued by NWS Tuscaloosa, AL
465 AGUS74 KWCO 181521 HMDNWC National Hydrologic Discussion - EXPERIMENTAL NWS National Water Center - Tuscaloosa AL 1015 AM CDT THU JUL 18 2024 .Synopsis... Flash and urban flooding in the Lower Mississippi Valley, ArkLaTex and Southeast... River flooding is ongoing in the Midwest and Great Lakes... Monsoon activity increases this week in the Southwest... Flooding possible in Puerto Rico, Guam, and in the Eastern Carolinas... Isolated small stream and river flooding in portions of Alaska... .Discussion... .Lower Mississippi Valley, ArkLaTex and Southeast... Moderate to locally heavy rainfall is possible through the remainder of the week into next week, bringing localized flash and urban flooding impacts. These factors will likely lead to rapid stream rises and pluvial flooding of typical flood prone or low-lying areas. Regions include TX, LA, AR, MS, and AL. Antecedent conditions are generally on the drier side, less than 55% with local areas closer to 75% (0 - 10 cm, NASA SPoRT), suggesting confidence in primarily urban impacts. .Midwest and Great Lakes... Scattered minor to isolated moderate and major river flooding is ongoing and forecast, primarily in portions of northern IL, northern IN, and southern WI. While the majority of these rivers have crested, some are expected to crest through late week and fall out of flood stage shortly thereafter. A few rivers in the slower drainage basins are forecast to linger into the weekend. Generally dry conditions settle in for the remainder of the week, allowing unimpeded recessions to continue. .Southwest... Increasing coverage and intensity of monsoon rains could lead to flash flooding along arroyos and complex terrain, along with urban flooding, particularly in NM, western AZ, and southern CO where the heaviest rainfall is forecast. Slow moving convection may cause flash flooding issues, especially over the usual vulnerable areas like burn scars, dry washes, and slot canyons. Localized heavy rainfall of 2 - 4" remains possible into next week for this region. This will likely increase the threat for locally significant impacts in these areas, as intense rainfall on hydrophobic soils will enhance runoff conditions. .Eastern Carolinas... Flash and urban flooding will be possible in response to several rounds of moderate to locally heavy rainfall that will impact the region starting today and through early next week. Soils are generally dry (55% 0 - 10 cm RSM, NASA SPoRT) and streamflows are normal to much below normal for all days of the year. While this rainfall would be beneficial for much of the area, repeated rounds of heavy rainfall could still overwhelm soil conditions and enhance runoff. Urban areas and areas of poor drainage are the primary concern for this event with small stream response being less likely unless training occurs. This is further backed by low flows on streams and absent NWM MRF high flow signals providing additional confidence of ample in-channel storage and soil infiltration availability. .Alaska... Localized minor flooding as well as significant river rises are possible in rivers, creeks and streams near Juneau, AK. Flooding caused by previous rain and snowmelt continues through the end of the week as an increase in snow and ice melt into glacier-fed rivers situated at the foothills of steep terrain heightens the threat of small stream and river responses in the area, particularly the Chilkat River. .Puerto Rico... A return of heavy rainfall with isolated urban and small stream flooding impacts is possible on day 3 (Sat) for the interior portions of the island. Previous rainfall has wetted the soils in the northwestern and extreme eastern area of the island (NASA SPoRT) however, there is available storage capacity to handle forecast rainfall, and streamflows are generally near normal for this time of the year (USGS). .Guam... Heavy rainfall is possible through day 3 (Sat) due to a surface troughing pattern developing over the Mariana Islands, likely causing flash, urban, and small stream flooding. Low-lying and poor drainage areas, including roadways, are most vulnerable. //Kirkpatrick $$