Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Dec 24 2023 08:06:23 FOUS30 KWBC 240806 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 303 AM EST Sun Dec 24 2023 Day 1 Valid 12Z Sun Dec 24 2023 - 12Z Mon Dec 25 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE WESTERN OZARKS THROUGH THE KANSAS CITY METRO AND FOR PORTIONS OF THE CENTRAL GULF COAST... Mid-upper trough is expected to close off at 500 mb by 12Z Christmas Day across the Central Plains. Strong southern stream enhancement (130-150 kt upper jet streak moving across South TX) will boost the deep-layer ascent and south-north ageostrophic low-level moisture/theta-e transport into eastern portions of the Lower MO Valley-Central and Southern Plans as well as the Lower MS Valley and central Gulf Coast region. PWs >1.5" will expand along the Upper TX Coast and across the central-eastern Gulf Coast areas Sun and Sun night, while PWs climbing to 1-1.25" across the Lower MO Valley into the western Ozarks average some 3 to 4 standard deviations above normal across these areas for late December. Two separate Slight Risk areas were maintained from yesterday afternoons Day 2 ERO, with minor adjustments based on the 00Z guidance trends. The first one is across the Gulf Coast from eastern LA and far southern MS-AL to the western FL Panhandle. Over these areas, robust low-level moisture/theta-e transport, aligned low-mid level flow with an anomalous LLJ (favoring increased upwind propagation/backbuilding and thus risk for cell training), and at least modest deep-layer instability (at least 500-1000 J/Kg), will lead to a favorable thermodynamic and kinematic profile for heavy rainfall, especially given the active, vigorous southern stream. 850 mb wind and moisture flux anomalies over these areas peak around 3 standard deviations above normal per both the SREF and GEFS, indicative of a favorably rich thermodynamic profile. Furthermore as noted above, the eastward progression of any pre-frontal quasi-linear convective segments may retard a bit overnight given the vertical shear profiles, i.e. becoming more conducive to training. The second Slight Risk area across eastern KS-western MO into northeast OK and the western Ozarks is also supported by ensemble consensus for robust moisture transport, with 850 mb wind and moisture flux anomalies quite high for late December (between 4 and 5 standard deviations above normal). Deep-layer, elevated instability over this area will be more limited (i.e. MUCAPEs generally less than 500 J/Kg), however at the same time current FFG values are lower over these areas despite the relatively low soil moisture percentiles per the NASA SPoRT analysis. FFG values of 1.5 to 2" in 3 hours is noted across much of the Slight Risk area, while the 00Z CAMs do show isolated stripes of 3+ inches, the bulk of which falling in less than 6 hours. Hurley Day 2 Valid 12Z Mon Dec 25 2023 - 12Z Tue Dec 26 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHEAST... Closed mid-upper low will move very little during day 3 (12Z Christmas-12Z Tue), as upper level difluence increases over the southeastern U.S. The aforementioned subtropical jet will remain quite robust, with 250mb winds between 150-170kts moving into the western and central Gulf Coast regions Monday night. A rather quick uptick in deep-layer ascent and low-level theta-e/moisture transport from the GOMEX is expected, although per the latest GEFS and NAEFS, moisture flux and IVT anomalies start off near +2 early in the period across the FL Panhandle, then decrease thereafter. Also limiting the potential for a Slight or better risk over much of the Southeast region will be the faster progression of the leading cold front, thus increasingly transient quasi-linear convective segments over most areas. One area that does bear monitoring for a possible upgrade to a Slight Risk is across the eastern slope of the Southern Appalachians (northern GA to Upstate SC and western NC). This as the strengthening SE-SSE low-level flow provides some upslope enhancement, as most of the models show a heavier rainfall footprint across this region with areal-average totals between 1.5 and 3.0+ inches. However, any elevated instability will be relatively weak/shallow, with MUCAPEs generally under 500 J/Kg. This will limit the 1 and 3 hourly rainfall rates somewhat, which along with the current low 0-100 cm soil moisture percentiles (less than 20% per NASA SPoRT), will likely lead to a more marginal excessive rainfall threat with the expectation of at most localized short-term runoff issues. Hurley Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8nb9Xn5kKBda6gYNcInOBd1c_r7Ltp1xx2JCfDv_Irw6= dUC-uVH0pImeZlXzSAMyeIsL_sWBghqQvR8cybjJOUyCbLQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8nb9Xn5kKBda6gYNcInOBd1c_r7Ltp1xx2JCfDv_Irw6= dUC-uVH0pImeZlXzSAMyeIsL_sWBghqQvR8cybjJvavmLFE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8nb9Xn5kKBda6gYNcInOBd1c_r7Ltp1xx2JCfDv_Irw6= dUC-uVH0pImeZlXzSAMyeIsL_sWBghqQvR8cybjJVPpuFgA$=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) .