Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jun 07 2023 15:57:04 FOUS30 KWBC 071557 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1156 AM EDT Wed Jun 07 2023 Day 1 Valid 16Z Wed Jun 07 2023 - 12Z Thu Jun 08 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE SOUTHERN HIGH PLAINS NORTHWEST INTO THE LEE OF THE CENTRAL ROCKIES AND ACROSS NORTHWEST WYOMING INTO SOUTH CENTRAL MONTANA... ....Southern Plains through the Northern Rockies... Another day of scattered to widespread diurnal convection is likely across much of the High Plains and Intermountain West as the blocking synoptic pattern remains entrenched across the area. An expansive ridge centered over the Northern Plains and an anomalous closed low over the Great Basin will sandwich this area, driving persistent moist advection from the Gulf of Mexico to push PW anomalies to +2 to +3 standard deviations according to the NAEFS ensemble tables. The corridor of highest PWs will be collocated with MUCAPE of 500-1000 J/kg, and lay beneath a persistent upper deformation axis, to favorably produce aftn thunderstorms today. Weak impulses embedded within the flow will likely yield areas of greater coverage, but with minimal overall bulk shear, storms should generally remain disorganized today, which is echoed by the simulated reflectivity among the various high-res members. This suggests that the broad MRGL risk inherited from overnight remains warranted as any of these storms could have rain rates above 1"/hr atop soils that are saturated from 7-day rainfall of 300-600% resulting in anomalous streamflows. The only significant adjustment to the MRGL risk area was to expand it east into the western Hill Country and RGV of TX where guidance indicates an MCS may develop tonight with heavy rain rates falling atop locally more sensitive soils. The inherited SLGT risks were adjusted only cosmetically as they still highlight the two areas of greatest concern. The first, from the Front Range of the Rockies south into the TX Panhandle is driven primarily by the most saturated antecedent soils from repeated days of heavy rainfall. This has lowered FFG to 1-1.5"/3hrs in many areas, which has a 20-30% of being exceeded according to the HREF. While coverage/organization of convection may not be overly impressive here, the high risk of runoff leading to flash flooding persists due to the more compromised soils. Additionally, for the smaller SLGT risk across WY/MT, this area is more firmly embedded within the greatest PW anomalies, and FFG is reduced even more to as low as 0.5"/3hrs due to recent heavy rains. Any storms that move across this area could quickly produce runoff to renew flash flooding. ....Northern Sierra/Northern California into portions of the Great Basin... The anomalous closed upper low over CA this morning will begin to drift northward while slowly filling today. The total latitude and height gain will be pretty minimal today however, so significant forcing for showers and isolated thunderstorms is still expected across northern CA and into the Great Basin. The most significant adjustment today should be a reduction in coverage over central CA which did experience heavy rain on Tuesday, so the MRGL risk has been trimmed just slightly from the south. However, the overlap of impressive PWs noted by NAEFS standardized anomalies reaching above +2 sigma and MUCAPE as high as 1000 J/kg will still support efficient rain rates reaching 1"/hr in the scattered slow moving convection. Across the Northern Sierra and northern coastal ranges, 24-hr rainfall has been more than 2 inches in some areas according to MRMS, compounding already wet soils noted by high USGS streamflow anomalies and elevated CPC soil moisture. The HREF has a more aggressive signal today for more than 3 inches across the Klamath Mountain as well, which, while still only 10-20%, suggests a higher-end MRGL risk for runoff and isolated flash flooding than the past few days. ....South Florida... Increasingly confluent mid-level flow across Florida will push a modest shortwave northeast today, combining with the tail of a 70-90kt upper jet streak to produce deep layer ascent. This lift will act upon an environment with PWs rising above 1.75 inches and MUCAPE above 2000 J/kg to support scattered thunderstorms with rainfall rates exceeding 2"/hr. The important environmental difference today compared to earlier in the week is forecast 0-6km bulk shear reaching 30-35 kts, sufficient for storm organization. This combined with Corfidi vectors aligned to the mean wind to imply training indicates that rainfall duration may be lengthened in some areas today, and the HREF neighborhood probabilities suggests the potential for 3-5 inches of rain in some areas. Although FFG is high, 7-day rainfall has been 150-300% of normal, suggesting the soils have at least a subtly higher threat for runoff resulting in flash flooding. This will be most likely if any training or organized cells can move across urban areas, especially on the Gold Coast where the pinned sea breeze may enhance rates and duration today. ....Northern Plains/Upper Midwest... Stationary front positioned north-to-south across the Dakotas will begin to weak today, but continue to provide an impetus for ascent and scattered thunderstorms this aftn. The environment around the front will be thermodynamically favorable for heavy rain noted by PW anomalies around +2 sigma according to NAEFS ensemble tables and a ribbon of MUCAPE reaching 2000 J/kg. This will fuel convection with rain rates that could reach 2"/hr according to the HREF probabilities. Storm motions will generally be around 10 kts, but aligned to the front so some training is possible. Despite the expected scattered nature of convection this aftn, training of these rain rates could produce locally more than 3" of rain, which will fall atop soils still primed noted by USGS streamflows that are above the 90th percentile, especially in eastern ND. The MRGL risk was extended into MN as well which, despite having soils that can likely handle more rain, could also experience a flash flood risk tonight. The high-res simulated reflectivity has some consensus in developing an MCS type event late tonight along a potent CAPE gradient and the elevated front to the east. This could result in training 2"/hr rates, and the HREF has some higher EAS probabilities for 2" tonight. Confidence is not extremely high for this event, and it is possible some further adjustments to this ERO area will be needed later today. Weiss Day 2 Valid 12Z Thu Jun 08 2023 - 12Z Fri Jun 09 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHERN ROCKIES INTO THE NORTHERN HIGH PLAINS... ....Northern Rockies into portions of the Northern High Plains... The slow moving closed low pushing out of central CA into southwest NV at the end of day 1 will accelerate to the north across the Great Basin and into the Northern Rockies. While the closed low does weaken, strong upper difluence continues to its northeast. Model consensus is for the heaviest precip potential to be shifting into the Northern Rockies/Northern High Plains day 2 where this strong upper difluence will coincide with strengthening low level easterly flow. This strengthening low level moisture flux will raise PW values to 2.5 to 3+ standard deviations above the mean, supporting potential for widespread heavy precipitation. The previous slight risk area was expanded slightly northward toward northern ID as per model qpf consensus and southward across the lower ffg values regions of northwest WY and corresponds with model consensus heavy rain potential region. ....Sierra/Northern CA/Great Basin into the Central Rockies... No changes made to the previous marginal risk area stretching across the Sierra, northern CA, the Great Basin and into Central Rockies. Another day of widespread scattered convection likely to the east of the Great Basin/Northern Rockies trof and west of the Northern Plains upper High. PW values will remain anomalous across much of this region with continued pockets of upper difluence enhancing uvvs and supporting additional isolated 1"+ rainfall totals. ....South FL... There are not anticipated any significant changes to the overall pattern from the Gulf of Mexico across South Florida from the day 1 to day 2 period. PW values will remain near seasonal norms 1.75-2". Continued favorable right entrance region jet dynamics from the sub-tropical jet stretching from the southeast Gulf into the Bahamas will continue to accentuate lift across South Florida. The continued moist low level west southwest flow will support potential for training of cells and isolated runoff issues from 1-2" rainfall amounts in a brief time, especially if the training occurs over urbanized regions of southeast FL. Expanded the previous marginal risk area westward from the southeast urban regions to be consistent with out day 1 outlook, although believe the greatest flash flood risk will be urbanized again day 2. Oravec Day 3 Valid 12Z Fri Jun 09 2023 - 12Z Sat Jun 10 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHERN ROCKIES AND NORTHERN HIGH PLAINS... ....Northern Rockies into the Northern High Plains... Continued weakening expected to the previous day 2 closed low moving through the Great Basin during day 3 as the remaining height falls shear more to the north in response to the mean trof reforming farther to the southwest along the central CA coast.=20 While the mid to upper level center is shearing apart day 3, there still is an axis of above average PW values stretching from the Northern High Plains into the Northern Rockies in response to continued anomalous easterly moisture flux. This will support potential for heavy rains from northeast WA state, northern ID into northwest MT. A slight risk was drawn where there is overlap to potentially heavy day 3 rains and anomalous rainfall amounts over the past few weeks. This corresponds to a slight risk over WFO TFX, far western GGW and northwest BYZ.=20 With reformation of the mean trof off the central CA coast during day 3, additional scattered convection again likely from the Sierra, northeast into northern CA, the Great Basin and Northern Rockies. Locally heavy rainfall totals possible across these areas, with isolated flash flooding possible across high stream flow areas of the Sierra or burn scar regions across the remainder of the marginal risk area. ....Southern to Central High Plains... While the western mean trof reforms farther to the west day 3 off the central CA coast, there still forecast to be a stream of height falls pushing across the Southern to Central Rockies into the Southern to Central High Plains. These height falls should strengthen the southerly flow across the Southern to Central Plains, evident by a 850-700 mb moisture flux anomaly axis developing late Fri into early Sat over the Southern to Central High Plains. Model consensus is for a convective max axis from southeast CO, western to southern KS into northern OK. While it has been wet over portions of the Southern and Central High Plains lately, these areas have been relatively drier. For this and low confidence in day 3 qpf max placement, only a marginal risk is depicted across the Central to Southern Plains. Oravec Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6lEDUO9JmskadZsZxSoh7K3jMSe4CQA-BhRiJ6nhOKNT= E0qx7prMwltBsThhI6tqPLhRjLkupb36SRudc_bTftVe0GQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6lEDUO9JmskadZsZxSoh7K3jMSe4CQA-BhRiJ6nhOKNT= E0qx7prMwltBsThhI6tqPLhRjLkupb36SRudc_bToiF9P20$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6lEDUO9JmskadZsZxSoh7K3jMSe4CQA-BhRiJ6nhOKNT= E0qx7prMwltBsThhI6tqPLhRjLkupb36SRudc_bTMHd0Ej8$=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) .