AT2k Design BBS Message Area
Casually read the BBS message area using an easy to use interface. Messages are categorized exactly like they are on the BBS. You may post new messages or reply to existing messages! You are not logged in. Login here for full access privileges. |
Previous Message | Next Message | Back to General Weather-related Discussi... <-- <--- | Return to Home Page |
|
||||||
From | To | Subject | Date/Time | |||
![]() |
Mike Powell | All | HVYRAIN: Excess Rain D2-3 |
August 2, 2025 6:20 PM * |
||
FOUS30 KWBC 022000 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 400 PM EDT Sat Aug 2 2025 Day 2 Valid 12Z Sun Aug 03 2025 - 12Z Mon Aug 04 2025 ...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHEAST/GULF COAST AND SOUTHERN PLAINS... ...Southeast/Gulf Coast... The cold front from Saturday will continue to waver along the Gulf Coast as a stationary front Sunday in response to subtle additional height falls as the trough extending from the Northeast continues to subtly amplify. The trough axis may reach the Gulf Coast Sunday evening, but flatten at the same time in response to an elongated ridge draped across the Gulf. Moisture pooled along this front will remain impressive as PWs remain above 2.25 inches with deep column saturation noted via moist-adiabatic lapse rates through the depth of the column indicating tall-skinny CAPE which is progged to reach above 1000 J/kg during peak heating. Convergence along the front into these thermodynamics will support another day of slow moving convection noted by 0-6km mean winds of just 5-10 kts pointed to the east, with rainfall rates likely eclipsing 2"/hr at times (HREF 50-60% chance) supported by warm cloud depths nearing 15,000 ft to produce efficient warm-rain collision processes. Late in the aftn and into the evening, a shortwave is progged to rotate beneath the trough and pivot E/NE from the FL Panhandle into eastern GA, coincident with a surge in bulk shear up to 35 kts. This could support some more widespread convection with organization into clusters/multi-cells. With weak storm motions in place, any collisions/organization during this time could briefly pulse up rain rates even more significantly, while also leading to longer temporal duration or repeating rounds of these rain rates. Where this occurs, the HREF and REFS both indicate a 70-90% chance of 3"/24hrs and locally a 40-70% chance of more than 5"/24hrs. This rain will be falling atop areas that will likely receive significant rainfall on D1 as well, further enhancing the threat for flash flooding. Although this region generally takes a lot of rainfall to flood, the setup appears to support a higher than typical SLGT risk especially from the FL Panhandle through coastal GA. Otherwise, scattered thunderstorms with intense rain rates could produce instances of flash flooding on Sunday. The guidance has a secondary area of maximum rainfall potential along a westward advancing surface trough through northern AL into central TN which may require an upgrade in the ERO with later issuances since 3"/24hr probabilities peak at 40-50%, but this correlated with 3-hr FFG exceedance that is just 10-15%. At this time opted to maintain the MRGL risk and re-evaluate with new guidance for a possible upgrade overnight or on the D1 Sunday. ...Plains... The elongated stationary front aligned north to south from MT through TX will weaken Sunday, but leave at least a weak convergence boundary as it decays. Mid-level flow upstream of this feature will gradually become more W/NW as it gets squeezed between an amplifying ridge over the Southwest and a trough across Canada. Within this pinched flow, multiple shortwaves/vorticity impulses will shift eastward, interacting with the front to cause another day of convective development across the High Plains and into the Plains, with several MCSs possible beneath any of the stronger impulses. While there is considerable spread and thus uncertainty in the placement of any of these MCSs, each of them will likely contain intense rain rates of 1-2"/hr (locally higher) in response to meridional 850mb flow drawing elevated thermodynamics northward. From TX to MN a ribbon of PWs of 1.25 to 1.75 inches will overlap a plume of MUCAPE above 2000 J/kg and bulk shear of 25-35 kts to support the intense rainfall rates. While the CAMs are generally suggestive of forward propagating features that will limit the duration of heavy rainfall, locally any of these could produce some short-term training, especially where any MCVs and lingering boundaries can track. Uncertainty is high in where this is most likely, but the REFS and HREF suggest a slightly higher potential from north Texas into central KS, as well as across portions of eastern SD/ND into Minnesota. The large inherited SLGT risk for TX/OK/KS was cosmetically adjusted, but further refinements are likely (with a reduction of category also possible) as confidence in MCS placement becomes more clear. Across MN, a targeted SLGT risk was considered where HREF and REFS probabilities for 5"/24 hrs peak above 15% as storms slow/regenerate beneath a deformation axis downstream of a mid- level closed low. Confidence is modest across this area, but 24-hr LPMM from the HREF is 3-4", so FFG exceedance potential appears higher than surrounding areas. However, there is still a lot of placement uncertainty among the available models, and some concern that instability won't be sufficient to support multiple rounds of heavy rain. While a SLGT risk is still possible with later issuances, after coordination with WFO DLH opted to maintain the MRGL risk at this time. Weiss Day 3 Valid 12Z Mon Aug 04 2025 - 12Z Tue Aug 05 2025 ...THERE ARE MARGINAL RISK AREAS FOR THE NORTHERN ROCKIES, NORTHERN PLAINS/MINNESOTA, AND THE SOUTHEAST... ...Southeast... Moisture streaming northeast ahead of the longwave trough axis will maintain unsettled conditions and widespread showers/thunderstorms from southern AL through GA and coastal SC. There is quite a bit of uncertainty in the placement of the heaviest axis of QPF on D3 owing to uncertainty in accompanying mid-level impulses progged to lift out of the Gulf on Monday, and this limits confidence from upgrading the inherited MRGL risk to a SLGT risk at this time. However, with PWs likely continuing at 2-2.25 inches overlapping MUCAPE of more than 1000 J/kg, rainfall rates of 1-2"/hr or more are likely within any convection that develops and then tracks northeast. Some repeating rounds are possible, but SREF/GEFS/ECENS probabilities for 3"/24hrs are all quite modest at this time, and the EC/EC-AIFS is north of the other guidance which could allow the heaviest rain D3 to not overlap the heaviest rainfall footprint from D1-2. For these reasons the MRGL risk was maintained and adjusted, but a SLGT risk may be needed with later issuances. ...Northern Plains... The closed mid-level low responsible for areas of heavy rainfall Sunday will continue to lift northeast and weaken on Monday. The weakening of this feature will result in less ascent, but a lingering boundary in its wake could still produce enhanced low- level convergence, primarily across Minnesota. The threat for heavy rainfall appears lower D3 than D2, as both ascent and thermodynamics are reduced, but locally rainfall rates in excess of 1"/hr are possible, with a secondary surge in convection possible late in response to 850mb winds reaching 20-30 kts converging into the region. With FFG likely to be lowered from antecedent rainfall D1 and D2, isolated excessive rainfall impacts will again be possible on Monday. ...Northern Rockies... A shortwave moving northeast across ID/MT will help amplify a trough shifting into the Northern High Plains on Monday. This will drive enhanced ascent into the already broad synoptically forced lift, helping to spawn a weak wave of low pressure tracking into the High Plains the latter half of D3. Low-level southeasterly flow will draw elevated PWs and MUCAPE into the region aiding a moistening column from high-level SW flow emerging from the Pacific. The result of this will likely be showers and thunderstorms moving progressively eastward from the Northern Rockies through the northern High Plains. With PW anomalies +1 to +1.5 sigma above the climo mean, rainfall rates may reach 1"/hr at times, which despite the anticipated progressive nature of these cells, could produce isolated impacts due to runoff. Weiss $$ --- SBBSecho 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (618:250/1) |
||||||
|
Previous Message | Next Message | Back to General Weather-related Discussi... <-- <--- | Return to Home Page |
![]() Execution Time: 0.0133 seconds If you experience any problems with this website or need help, contact the webmaster. VADV-PHP Copyright © 2002-2025 Steve Winn, Aspect Technologies. All Rights Reserved. Virtual Advanced Copyright © 1995-1997 Roland De Graaf. |