Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Apr 09 2024 09:02:48 FOUS30 KWBC 090902 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 502 AM EDT Tue Apr 9 2024 Day 1 Valid 12Z Tue Apr 09 2024 - 12Z Wed Apr 10 2024 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE SOUTHERN MISSISSIPPI VALLEY... BLUF: Compared to yesterday afternoon's Day 2 ERO, there's a slight expansion of the Marginal Risk area across OK, northwest AR, and southern MO. Otherwise, the Slight Risk area was largely unchanged, while the Moderate Risk was shifted south of ArkLaTex into the southern Piney Woods of eastern TX, though northern LA and into the ArkLaMis. The trends in the guidance, particularly the high-res CAMs, has resulted in a southward shift in the heavier QPF footprints, largely owing to the deep-layer CAPE trends (greater farther south) and thus the impact on short-term rainfall rates (highest farther south). Deep-layer forcing ahead of the amplifying southern stream trough pivoting into the southern Plains by Wednesday morning will cover quite a bit of real estate, with the broad diffluent flow aloft and coupled left exit/right entrance region forcing from the southern stream/northern stream jet streaks respectively. For this region the Marginal and even Slight Risk areas remain quite large. However, within the Moderate Risk area will be an overlap with a more favorable thermodynamic profile as 850 mb moisture flux/transport anomalies get closer to +3 standard deviations above normal, PWs to 1.75+ inches, and MUCAPEs closer to 1000 J/Kg. Within the Moderate Risk area, the latest (00Z) HREF indicates the highest probabilities...between 25-40+ percent...of 24hr QPF exceeding 5 inches, with 15-25+ percent probs of exceeding 8 inches. Hurley Day 2 Valid 12Z Wed Apr 10 2024 - 12Z Thu Apr 11 2024 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER A PORTION OF THE MID-SOUTH TOWARDS THE FLORIDA PANHANDLE... BLUF: No significant changes made from yesterday's Day 3 ERO. Once again per coordination with local WFO's, given the continued progressive nature of the convective pattern from the latest 00Z guidance (including the 60hr FV3 and RRFS), have maintained a rather targeted Moderate Risk area over the area (including central AL that will most likely see significant rainfall during a larger portion of the forecast period). This area continues to align well with the highest areal-average QPF per WPC and the NBM (2.5 to 4+ inches). However this remains a low confidence ERO forecast, especially given the progressive nature of the convection as with the upper trough and surface front. In addition, some of the extended CAMs, including the 00Z FV3 and RRFS, are now farther south with the heavier rainfall footprint during the Day 2 period (12Z Wed-12Z Thu), i.e. closer to the Gulf Coast. For now, again per collaboration with the WFOs, have opted to maintain continuity with only minor adjustments, with the anticipation of better clarity in the guidance over the next couple of forecast cycles as the event gets within all of the high-res windows. Hurley Day 3 Valid 12Z Thu Apr 11 2024 - 12Z Fri Apr 12 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF THE APPALACHIANS TO WEST OF THE I-95 CORRIDOR FROM THE MID ATLANTIC TO NORTHEAST... BLUF: Have scaled back on both the Slight and Marginal Risk areas compared to yesterday's Day 4 ERO. Guidance has trended down with the QPF across the outlook areas, despite the favorable deep-layer forcing ahead of the upper trough which will become more negatively tilted with time. Despite 850-700 mb moisture flux anomalies peaking aoa 4 standard deviations above normal, the swift progression of the upper trough and surface=20 front will inhibit the potential and areal extent of flash flooding. By the same token, there is some deep-layer instability noted per the guidance, especially within the Slight Risk area (generally under 1000 J/Kg). This will allow for more intense short-term rainfall rates, which again could pose a localized (or slightly more enhanced) threat for short term runoff issues, despite the faster eastward progression of pre-frontal quasi-=20 linear segments and thus a more limited risk for cell training=20 during the period. Hurley Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4fP9xkRA1guY0MlQAgGabAI8qU9FwkDHz5kpfDIHDrEB= vH3A4EttfVl4cOhcztR8QpE8XKIAvzZ0AR2D7LjhycEobrU$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4fP9xkRA1guY0MlQAgGabAI8qU9FwkDHz5kpfDIHDrEB= vH3A4EttfVl4cOhcztR8QpE8XKIAvzZ0AR2D7LjhIXYYJUc$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4fP9xkRA1guY0MlQAgGabAI8qU9FwkDHz5kpfDIHDrEB= vH3A4EttfVl4cOhcztR8QpE8XKIAvzZ0AR2D7LjhIApBekE$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .