Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
753 FOUS30 KWBC 180819 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 419 AM EDT Sat May 18 2024 Day 1 Valid 12Z Sat May 18 2024 - 12Z Sun May 19 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHEAST/CENTRAL GULF COAST... ...Southern Alabama/Georgia into the Florida Panhandle... Mid-level trough/weak closed low over the Lower MS Valley/Mid- South this morning will continue eastward across southern TN today and into the southern Appalachians by early Sunday. On its southeast side, a stream of mid- level impulses will move across the FL Panhandle and southern AL/GA today ahead of a cold front that will finally clear through the area by tomorrow. SW flow out of the Gulf will maintain relatively high precipitable water values (~1.75" or +1.5-2 sigma) into the region ahead of the trough and surface front, with more impressive 850-700mb moisture flux anomalies into the region (+3 to +4 sigma). With ongoing convection over southern LA moving eastward, expect this to continue past 12Z along the I-10 corridor from southern MS eastward through early afternoon. Thereafter, models suggest a loss of mid-level vorticity dynamics to sustain heavier rainfall but this may be underdone given the approach of the cold front with still sufficient moisture available. Slight Risk outline was generally constrained to the higher probabilities of >2" QPF in the 12-18Z period this morning. Broader Marginal Risk covers much of the rest of the Southeast into the Carolinas where isolated heavier rain rates are possible. Trimmed away the northern/northeastern side of the Marginal Risk where instability is low (or non-existent) on easterly flow. Fracasso Day 2 Valid 12Z Mon May 20 2024 - 12Z Tue May 21 2024 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE CENTRAL PLAINS/CORN BELT... Broad SW flow over the central Plains across the Corn Belt will bring in increasing moisture to the region on Sunday with a surface frontal boundary hung up over Iowa. Mid-level vorticity will exit the central Rockies and moves across the central Plains as precipitable water values rise to around 1.50" (+1.5-2 sigma) with some instability in the afternoon/early evening (500-2000J/kg) that could yield some 1"/hr rates (per 00Z HREF thru 00Z Mon) which are near FFG values over Iowa and nearby areas. The region has been fairly dry the past week (most of the region has had about 50% of the normal rainfall) so much of the rain will be beneficial, but given 1-hr FFG values near 1"/hr (between MCI-OMA- DSM), maintained the Marginal Risk outline for the region. Higher probabilities exist farther southwest into central Kansas (to where the Marginal was extended), but FFG values are higher as well (2"/hr). 12Z CAM guidance through 12Z Mon may shed a little more light on the higher rainfall potential over the entire 24 hours. Fracasso Day 3 Valid 12Z Mon May 20 2024 - 12Z Tue May 21 2024 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE CENTRAL PLAINS/CORN BELT... Upper pattern remains fairly similar to D2 across the Plains, with broad SW flow over the region. One wave will exit through the Upper Midwest as troughing over the West deepens via northern and incoming southern stream vorticity. Upper diffluence east of the Rockies will support widespread showers/storms over the central Plains Monday into Monday night along the stalled surface boundary, with sufficient moisture in place and sfc CAPE 500-1500J/kg. Heaviest rainfall per the ensembles lie over western Nebraska (Sand Hills) where FFG values are highest, so focused the area to the southeast and east into Iowa where rainfall on D2 may lower FFG values a bit (from already somewhat lower numbers). Fracasso Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt