Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Feb 15 2025 15:46:35 FOUS30 KWBC 151544 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1044 AM EST Sat Feb 15 2025 Day 1 Valid 16Z Sat Feb 15 2025 - 12Z Sun Feb 16 2025 ....THERE IS A HIGH RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE LOWER MISSISSIPPI, TENNESSEE, AND OHIO VALLEYS... 16Z Update: Current radar/sat composite this morning shows our continued axis of training moderate to heavy rainfall within the confines of a combination stationary front extending north through the Lower Mississippi Valley, arcing east-northeast into northern TN through KY within a west-east oriented surface boundary that denotes a sharp gradient within the thermal profiles present. 12z mesoanalysis has a strong 85H LLJ analyzed across northeast AR up through northwest TN into the far southwest reaches of KY. The overall placement and magnitude of the LLJ has led to a significant moisture advection regime in-of the Tennessee and Ohio Valley's with PWATs running between 1.3-1.6" when assessing the latest 12z RAOB's across the Lower Mississippi into the Tennessee Valley corridor. Expectation is for the flow to remain parallel in nature of the above frontal alignment with repeating elevated convective signatures moving northeast within the confines of the boundary. For a more detailed depiction on the current setup and expected=20 impacts, see MPD #0038 for more information. Widespread 2-4" totals are already observed within the corridor=20 extending from Jonesboro, AR up through Union City, TN through=20 south-central KY. This axis is sufficiently within the current High Risk in place lending confidence in the current positioning of the risk area and the likely area of highest impact. Considering the=20 FFW's in place across the western TN/KY border, the High Risk=20 placement will maintain general continuity with a very small=20 adjustment on the southwest and southern flank of the risk area to=20 account for the latest radar/hi-res trends.=20 Further to the southwest, there's increasing concern for heavier training echoes to impact areas of central AR and points northeast that would be sufficient for an expansion of the MDT risk just to the southeast of Little Rock. A tight theta-E gradient within that corridor will likely lead to a sufficient low-level convergence regime later this evening with the approach of the front and has merit within the latest 12z suite of CAMs. There's also more=20 consensus on a further southwest extension of convection between=20 21-03z just before and in tandem with the approaching cold front=20 this evening. Considering the environment being primed through the=20 afternoon ahead of the falling height pattern to the west, an=20 expansion of the MDT/SLGT/MRGL risk areas have been expanded to=20 account for the current evolution and short term trends.=20 Further north and east, a stronger push of deep layer moisture has allowed for the heavy rain footprint across north-central TN through much of central and eastern KY to be a little more robust than what was anticipated for this stage of the evolution. Reports out of JKL WFO domain correlate to a more impactful event brewing further downstream than what was currently forecast, albeit still within the margin of error on the longitudinal push of heavier QPF. The MDT risk was expanded a bit further east to account for what is occurring over eastern KY this morning and expected continuation of heavy rainfall as well as collaboration with the JKL WFO.=20 The remainder of the forecast is on track with significant rainfall all but certain for a large portion of the Lower Mississippi and Ohio Valley's. Expect a large expanse of flash flood and areal flood warnings within heavily primed areas across the region. Confidence remains very high for potential life-threatening flash flooding occurring in the above areas.=20 Kleebauer ...Previous Discussion..=20 Confidence remains high that repeating rounds of heavy rainfall will produce very heavy accumulations, resulting in numerous to widespread flash flooding across portions of the lower Mississippi, Ohio, and Tennessee Valleys today into the overnight. The greatest threat for life-threatening flash flooding remains centered over parts of western Tennessee and Kentucky. The 00Z models showed a slight southern shift, but overall remained consistent, indicating widespread amounts of 3-6 inches extending from northeastern Arkansas to eastern Kentucky, with locally heavier amounts, especially across portions of western Tennessee and Kentucky. Increasing southwesterly flow ahead of an amplifying shortwave trough moving across the southern Plains will support an environment anomalous for mid-February, with PWs climbing to around 1.5 inches along a 60+ kt low level jet extending across the lower Mississippi Valley into the Tennessee and Ohio valleys. This strong jet aligned nearly along a slow-moving front, extending east from the Mississippi through the Ohio Valley, will support training, redeveloping storms along the boundary beginning later this morning. Storms will continue to train through the afternoon, with some intensification expected during the late afternoon/evening ahead of a low moving into Arkansas, which is forecast deepen in response to the sharpening mid-level shortwave and increasing divergence along the right-entrance region of the upper jet. These storms are expected to train across western Tennessee and Kentucky ahead of the advancing low, adding additional heavy amounts to the region. Guidance shows a convective line beginning advance steadily east during the overnight, but not before several inches of rain will have likely fallen across parts of the region. Given the model consistency and the likelihood for heavy, highly- impactful amounts, a High Risk was maintained across portions of western Tennessee and Kentucky and into the far southeastern extent of Missouri and northeastern Arkansas. A slight southern adjustment was made to the area, reflecting a small shift in the model QPF and where the HREF shows the highest neighborhood probabilities for 5 inches or more. But overall, the area remains similar to the previous Day 2. A similar southward adjustment was made to the Moderate Risk as well. Further to the south, trimmed back the Slight Risk east of Louisiana into the Southeast, where guidance indicates the progressive nature of the convection developing across the region tonight will help limit amounts and the potential for widespread flash flooding. Pereira Day 2 Valid 12Z Sun Feb 16 2025 - 12Z Mon Feb 17 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF THE MID-ATLANTIC... A Marginal Risk was maintained across portions of the Mid-Atlantic, mainly as a reflection of the potential for brief, heavy rains advancing along the cold front moving across the region early in the period. While these storms are expected to be progressive, with widespread additional heavy totals not expected, moist soils further saturated by rain in the previous period may encourage isolated flash flooding responses, especially across portions of southwestern to central Virginia. Pereira Day 3 Valid 12Z Mon Feb 17 2025 - 12Z Tue Feb 18 2025 The probability of rainfall exceeding flash flood guidance is less than five percent. Pereira Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9FJHjnWaJ9UImZ9AP0UcPHl9-Lr796amZEYq1Bq7nnPj= zGbfuAfynYh5Tf_ACb-bJW6dYQALdOH8TMh4TjwqSPCAMbk$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9FJHjnWaJ9UImZ9AP0UcPHl9-Lr796amZEYq1Bq7nnPj= zGbfuAfynYh5Tf_ACb-bJW6dYQALdOH8TMh4TjwqZO5VEwE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9FJHjnWaJ9UImZ9AP0UcPHl9-Lr796amZEYq1Bq7nnPj= zGbfuAfynYh5Tf_ACb-bJW6dYQALdOH8TMh4TjwqpaGMw18$=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) .