Subj : HVYRAIN: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jul 06 2023 07:49:39 FOUS30 KWBC 060749 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 348 AM EDT Thu Jul 06 2023 Day 1 Valid 01Z Thu Jul 06 2023 - 12Z Thu Jul 06 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE CENTRAL/SOUTHERN PLAINS, AS WELL AS, NORTHERN LOUISIANA INTO MISSISSIPPI... .......North/Central High Plains into the Central/Southern Plains... Current RADAR, Satellite and observational trends suggest a few clusters or larger complex should be ongoing across central OK with some embedded training thunderstorms capable of producing 2-4" totals and flash flooding. Though late morning diurnal minimum should result in a reduction in rainfall rates and flash flooding potential, especially in crossing areas of recent dryness of SE OK. As such, the inherited Slight Risk area was adjusted slightly eastward to account for some of this timing.=20 By afternoon/evening, strong upslope flow will return with new clusters of thunderstorms developing toward nightfall across E CO with strong southerly to southeasterly LLJ increasing to 35-40kts after 00z. Moisture flux values become very anomalous given the 45 to 60 degrees of directional convergence and increase of 1.25 to 1.75" total Pwats as the shortwave height-falls reach the Rockies. 00z Hi-Res CAMs (and ongoing convection) suggest an expansion of the Slight Risk toward the south and west. There did remain some guidance suggesting of a secondary enhanced band of mid-level convection along the northern edge of a developing MCS toward the end of the Day 1 period. Guidance did also shift slight west and south and so have adjusted the Slight Risk area into the OK/northeast TX panhandle to account for this trend.=20 A second cluster further north is expected to evolve out of N WY/SE MT with strong thunderstorms and potential training profiles crossing into southwest SD and western Nebraska. Greatest QPF signal appears to align with the Sand Hills, and so a broad Marginal Risk encompasses the region with the exclusion of the core of the Sand Hills. ....Southern Arkansas/Northern Louisiana... Evolving convective clusters/complex mentioned in section above will be down-trending by late morning crossing E OK/AR, but the MCV will continue to remain providing some structure for enhanced convergence and perhaps some weak DPVA for ascent as instability once again builds downstream. Banded convection along the leading edge may support short-term training as well as producing some outflow boundaries for additional development through the evening/early overnight hours. This is important, as a surge of western Gulf moisture is forecast to arrive across E TX/N LA by evening increased deep moisture availability as well as potential orthogonal moisture flux convergence to outflow boundaries or ongoing convection in proximity to the MCV. Strong collision/cell mergers may allow for short-term increase in rainfall rates up to 2.5-3"/hr (as 00z HREF probability for 2"/hr rates is about 40-60%) with 60-70% probability of 3" across N LA/SW MS. As such, in coordination with local forecast offices, have placed a small Slight Risk across the area of enhanced probabilities and Hi-Res CAM QPF signal. ....Texas Gulf Coast... GOES-E SWIR shows a fairly compact MCV/low level tropical wave south southeast of Brownsville with the start of a north-south line of convection along/just west of the circulation axis.=20 Strong south-southeasterly low level flow is expected to be generally convergent along the eastern side of the circulation aligned with early morning instability axis within the Western Gulf. There is ample uncertainty to its further evolution which is contingent on the next cycle of this convergence/deep convection is just starting to manifest with the north-south line of convection. There is Hi-Res CAM signals to suggest best convergence and convection will remain along and just offshore the south Texas coast, though a wave of thunderstorms is highly plausible to slide northward toward the Upper Texas coast by mid-morning into early afternoon with spotty rates of 2-2.5"/hr; eventually sliding north-northeast into LA. Additionally, depending on how close early morning convection develops, much of Southern Texas may have increased low-level Theta-E, while remaining cloud free increasing overall instability along the Coastal Plain. Aggressive models such as the HRRR suggest bands of thunderstorms rotating onshore, while other solutions suggest perhaps one band. Still, trends are increasing for enhanced rainfall across S TX, with fairly high consensus for 30-50% of 3" or greater from Corpus Christi and south. However, the placement and timing remain uncertain enough to expand the Marginal Risk of Excessive Rainfall to the Mexico boarder without delineating a Slight Risk area at this time. The potential exists for a future upgrade to a Slight Risk if trends continue to increase in coverage/magnitude of rainfall in the area. ....Central Great Lakes into Ohio and Tennessee Valleys... At the base of broad synoptic scale trough, that currently dominates northern and central Canada, is a shortwave sliding through the central Great Lakes with an attendant cold front that extends into the mid to lower Mississippi Valley. Deep layer moisture plume resides along/ahead of the front with 1.5-1.75" of total PWats; and ample day-time heating should support stronger thunderstorms with the capability of increased rain-rate potential (2"/hr). A weak surface wave should exist in the LP of MI just ahead of the core of the shortwave, this should allow for the best enhanced potential for repeating thunderstorms and highest localized rainfall totals throughout the length of the front with isolated 2-3" totals possible. HREF probability fields denote a slightly higher potential in the thumb and toward Detroit.=20 Currently, the signal appears to fall just below level to justify an upgrade to Slight Risk at this time, but observational and 12z guidance trends will be monitored for any upgrade later today. ....Coastal North Carolina/Southeastern Virginia... At the start of the forecast period, a few thunderstorms may be ongoing in the vicinity of the Outer Banks in proximity to the core and southeastern quadrant of an exiting shortwave trof. Very high moisture exists with Total PWats AoA 2.0-2.25" with slightly lower values but still at or above normal through the Mid-Atlantic. As the shortwave presses eastward, increased insolation from clear skies along the western edge will allow for the return of increased instability. Weak but deeper layer northeasterly flow should provide some enhanced convergence to break out additional round or two of thunderstorms from the Necks of eastern VA southward across E North Carolina (generally east of I-95). Weak steering flow should allow for some increased duration and isolated spots of 2"/hr rates; 00z HREF depicts 2"/3hr of 40-50% across these portions of VA/NC to support a Marginal Risk. To add to the potential, AHPS 2-week precipitation anomalies are 200-300% of normal in spots across the area, suggesting above normal soil saturation for reduced infiltration and increased runoff in those intense rainfall rates. ....Southeastern Peninsular Florida... South Florida resides in the trailing end of an exiting weak mid-level trof centers off the Outer Banks of NC, while only Surface to boundary layer southeasterly trades will resist eastward progression. Overall moisture is at or slightly above normal with 2.25" total PWats within the trof. Activation of the western sea-breeze should be the focus for early thunderstorms, while the eastern/southeastern sea-breeze will be weaker and likely later to develop by mid-day. As such, increased instability and slow eastward progression of the thunderstorms will start to merge/collide across the eastern quarter of the peninsula toward late afternoon. 00z HREF signals driven by ARW members, suggest strong 3"+/3hrs probability signals between 21-00z across the highlighted Marginal Risk with 25-35% potential of exceeding 5" in the vicinity of the I-95 corridor from Cape Canaveral southward. Gallina Day 2 The Day 2 outlook will be updated by 0830Z. 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!8a7mF80picTXURRfpi6EdVdxPwYLIiCHyglZDdMX5mIl= VJN_j03GbphWkke7J4JUp5K4p-oWefy4kOJF-AhMjk5pzYI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8a7mF80picTXURRfpi6EdVdxPwYLIiCHyglZDdMX5mIl= VJN_j03GbphWkke7J4JUp5K4p-oWefy4kOJF-AhMVDq7wwE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8a7mF80picTXURRfpi6EdVdxPwYLIiCHyglZDdMX5mIl= VJN_j03GbphWkke7J4JUp5K4p-oWefy4kOJF-AhMmni0wmo$=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) .