Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Nov 13 2023 20:08:58 FOUS30 KWBC 132008 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 308 PM EST Mon Nov 13 2023 Day 1 Valid 16Z Mon Nov 13 2023 - 12Z Tue Nov 14 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. 1600 UTC Update -- Based on the latest observational trends, along with the 12Z CAMs (including the HREF exceedance probabilities), per collaboration with the WFOs along the western-central Gulf Coast, have removed the Marginal Risk in the Day 1 ERO update. Instability, even elevated, is seriously lacking north of the front per the latest SPC mesoanalysis, and is expected to remain as such as the surface low and associated fronts remain offshore. With the anafrontal rainfall largely stratiform, the 12Z HREF 25%+ probabilities of >0.5"/hr remain offshore, while probs of 1+ in/hr are even farther offshore over the Gulf where the better instability is present.=20 Hurley Day 2 Valid 12Z Tue Nov 14 2023 - 12Z Wed Nov 15 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM SOUTHEASTERN LOUISIANA TO WESTERN PORTIONS OF THE FLORIDA PANHANDLE... 2000 UTC Update -- Based on the latest (12Z) guidance and trends, including the full CAM suite, have pared the Marginal Risk area to areas along the Gulf Coast (including New Orleans and Mobile). Latest high-res ensemble means and PQPFs show the 24hr 2+ inch totals (and higher probabilities) mainly over the Gulf and coastal parishes in south-central to southeast LA (south of New Orleans). This is where 12Z HREF probabilities are highest (aoa 40%) of 1+ in/hr rainfall rates, particularly in the latter half of the D2 period (after 00Z Wed), while also highest (40-70%-plus) with 24 hr probs of at least 3.00". Overall a longer duration rainfall, though once again with hints of more convective contribution near the coast (esp. Louisiana) as MUCAPEs of 250-500 J/Kg get drawn in closer to coast per the latest HREF. Hurley Previous discussion below... Surface low will continue to propagate eastward along a stationary boundary centered offshore of the Central Gulf Coast. Elevated PWAT anomalies between 2-2.5 deviations above normal will remain fixed to the coastal areas of LA/MS with a shift eastward into southern AL and the FL Panhandle by later in the period. The general lack of convective potential will curb the threat of flash flooding for most as prime instability remains offshore, but urbanized areas within the southeast LA Parishes and along I-10 to the western FL Panhandle could exhibit some localized flooding concerns over the course of Tuesday afternoon and evening. With coastal flooding increasingly likely over the the far southeast Parishes in LA, the potential for flooding is highest within that corridor, including the city of New Orleans. There is some discrepancy in the forecast between ensemble guidance with the NBM maintaining a stronger signature of heavy rainfall along the central LA coastal areas on Tuesday morning and the GEFS/ECS/ENSBC all shifted a bit to the east. NBM is likely seeing a feedback from the NAM suite and some of the hi-res depictions inflating the totals for areas east of Lake Charles. Decided to refrain from too much deviation on the western flank of the MRGL risk over LA, but did nudge a bit to at least account for the potential. Forecast totals of 1-3" will be common along the Central Gulf Coast with the highest totals remaining along and south of the I-10 corridor, especially between New Orleans over to Mobile.=20 Kleebauer Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!88cLbHSqbBpnOhxZZ0t_MZw410ncvogeuh1spr-pk-6K= 3OoaUyhGDuP3oFf104dKOhpGwGtm4d1FVupT08aSj21nBeM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!88cLbHSqbBpnOhxZZ0t_MZw410ncvogeuh1spr-pk-6K= 3OoaUyhGDuP3oFf104dKOhpGwGtm4d1FVupT08aSC8nIysI$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!88cLbHSqbBpnOhxZZ0t_MZw410ncvogeuh1spr-pk-6K= 3OoaUyhGDuP3oFf104dKOhpGwGtm4d1FVupT08aSORjfx-E$=20 $$ =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .