Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
023 FOUS30 KWBC 292019 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 419 PM EDT Sat Jun 29 2024 Day 1 Valid 16Z Sat Jun 29 2024 - 12Z Sun Jun 30 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHERN HIGH PLAINS AND THE LOWER GREAT LAKES/OHIO VALLEY... ...16Z Update... ...Northern New York... The most significant change with the midday update is to downgrade the Slight Risk area inherited across northern New York. While an area of rainfall across western New York is still on its way, rates with the embedded rainfall have been low enough that by the time the rainfall gets to northern New York, instability should be low enough to prevent high enough rainfall rates to cause any more than isolated flash flooding, consistent with a Marginal Risk area. Much better forcing will be south and west of the area. Further, antecedent soil moisture conditions are right about normal for this time of year based on NASA Sport satellite imagery. Thus, the abundance of flora in the Adirondacks and eastern Lake Ontario region are likely to handle the 1/2 to 3/4 inch per hour rainfall rates expected with ease. ...Northwestern Pennsylvania and surrounding areas... The Slight Risk area for this region remains largely unchanged...save a small expansion into central/eastern Pennsylvania per latest guidance suggesting that the overnight MCS that will first hit northwestern PA will continue ESE across the center of the state. Much of northwestern PA has been hit hard over the last week with multiple rounds of heavy rain, so soil conditions are favorable for the development of additional flash flooding with this afternoon and evening`s convection. ...Northeastern New Mexico and the Oklahoma Panhandle... Training convection over this area late this afternoon and potentially through much of tonight is likely to cause additional flash flooding concerns in an area that has also been hard hit with heavy rain in recent days. The Slight Risk area was expanded eastward to cover the central Oklahoma Panhandle in coordination with AMA/Amarillo, TX forecast office, as well as the southwest corner of Kansas. Wegman ...Previous Discussion... ...Northeast US... The better chance for organized heavy ton potentially excessive rainfall looks to be the the Northeast US as deep moisture advects into the region ahead of a shortwave trough propagating eastward across the international border. Backing flow aloft ahead of the trough will draw deep moisture into the region...as shown by precipitable water values approaching 2 inches over the eastern Great Lakes region early in the period and values at or above 1.75 inches as far north as upstate New York by late afternoon helping to foster an environment supportive of some downpours and cell training. By later in the day as the deep moisture arrives in upstate New York...there is still some question as to whether or not the convection will be elevated or rooted closer to the surface...but enough mesoscale forcing in an atmosphere with precipitable water values at or above 2 inches around time of maximum heating suggests sufficiently intense rainfall rates to maintain both Slight Risk areas. ...High Plains of New Mexico into Colorado... Model signal persists for isolated to scattered convection later this afternoon and evening as low level flow turns upslope behind a cold front. Above normal moisture as shown by surface dewpoints temperatures around 60 degs should be in place beneath steep lapse rates...supporting local downpours and at least some potential for flash flooding especially from burn scars and in normally dry washes. Bann Day 2 Valid 12Z Sun Jun 30 2024 - 12Z Mon Jul 01 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHWEST US AND SOUTHERN HIGH PLAINS... ...2030Z Update... ...Southwestern Colorado... Following the latest guidance trends, the Slight Risk area was shifted north. This puts more of southwestern Colorado, really hard hit with heavy rains over the past several days in line for another heavy rain event. There remains some uncertainty with amounts...and as is typical for the area...at any time will be highly dependent on where individual cells can form. Training once again is a distinct possibility, especially given the continued anomalously high PWATs. ...Southern Arizona... Daily showers and thunderstorms associated with the persistent thermal low and continued anomalous moisture will once again threaten widely scattered instances of flash flooding again Sunday afternoon as the storms that form over the area are slow-moving but will have plenty of moisture and instability supporting them. ...East Coast... A cold front will be advancing east across the Appalachians on Sunday, with a very moisture rich environment currently in place along the east coast ahead of it. The big question will be which method of forcing ahead of the cold front will result in the most storms capable of flash flooding, and where along the east coast will they form. The latest guidance suggests southern New England and the Tidewater of VA and NC are more likely to see the higher rainfall rates, but as convection remains very difficult to forecast this remains to be seen. The Marginal was expanded north to cover all of southern New England and Long Island with this update. Wegman ...Previous Discussion... ...Southwestern US... Moisture will continue to be drawn northward around the western flank if a mid level high located over the Southern Plains. Model guidance brings precipitable water values in excess of 1.75 inches back into southern Arizona by Sunday afternoon. Expanded the Marginal risk area to the west of the previous outlook to fit better with placement of the highest precipitable water values shown by the NCEP guidance by 01/00Z...although thinking is that the southeastern part of Arizona has the higher risk of excessive rainfall. The extent and placement of cloud cover that lingers from convection on Saturday will influence where convection fires on Sunday and where the greater risk of excessive rainfall occurs. So largely maintained the Marginal in Arizona with a focused Slight Risk in the southeastern part of the state. The plume of moisture will be pulled north and eastward into parts of New Mexico and Colorado with a corresponding risk of excessive rainfall in the terrain given the steepening lapse rates at the time of maximum heating. ...Northern Plains... A mid- level trough will be moving out of the Northwestern US and emerging from the northern Rockies by Sunday afternoon helping to focus late day convection. Any convection will be able to tap deeper moisture over the far eastern Montana and the western Dakotas...especially given increasing moisture transport into the region by a strengthening low level jet during the evening. with at least some concern for convection to persist into the night given the model shear profile. Eastern U.S.... Maintained a Marginal Risk of excessive rainfall along and south of a front extending from off-shore into the Mid-Atlantic region into the Tennessee Valley. The GFS and NAM both focus the axis of 2.0 to 2.3 inches precipitable water values and nearly 1500 J per kg of CAPE along and immediately south of the front. The resulting updrafts should be able to result in some intense rainfall rates. Given modest flow...at best...cell motion should be slow enough that isolated problems due to run off and flooding of poor drainage areas is a concern despite high flash flood guidance. Bann Day 3 Valid 12Z Mon Jul 01 2024 - 12Z Tue Jul 02 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE UPPER MIDWEST... ...2030Z Update... ...Upper Midwest... No major changes were needed with this update. A cold front moving across the northern Plains will stall out as far as its southward extent goes as it moves over far eastern Nebraska through western Wisconsin. With the typical strengthening of the LLJ Monday night, shower and thunderstorm activity along the stalled out front is expected to increase in coverage and intensity as plentiful Gulf moisture with the LLJ runs into the front. As always with convection, especially with that that forms along a front, the positioning of the front is critical with where the heaviest rain develops. The front looks to be much closer to parallel to the southwesterly LLJ this time around which should allow for faster storm movement, even if there is some training the farther east you go, as well as a smaller area of where the storms remain "stuck". Due to continued significant uncertainty with where the front and storms form, no significant changes were needed. The guidance tends to trend southward with these heavy rain bullseyes, so the Slight was expanded southward to cover much of Iowa. A higher-end Slight is considered in effect for the area from northeastern Nebraska ENE to western WI, primarily due to very favorable antecedent soil moisture conditions in this area. Hopefully additional southward shifts will occur with future updates, so that the same areas still recovering from recent flooding along the IA/MN border aren`t hit again by the same weather pattern. ...Low Country of the Southeast... The stalling out cold front moving across the Northeast and Mid- Atlantic on Sunday looks to get hung up right along the coast. This may result in multiple inches of rain from storms that form along the front Monday afternoon and evening. While the Marginal remains in place pending how much activity is seen in the area on Sunday, wetter conditions from the storms on Sunday in the area may result in a needed targeted Slight upgrade for Monday, particularly in more urban areas such as Charleston, SC and Savannah. ...Four Corners... No major changes here as the Marginal remains largely in place with the monsoon in full swing. Once again there may be additional rainfall targeted at the mountains of southwest Colorado, which may require an upgrade in the area...particularly if the storms on Sunday overperform, as Monday for now appears to be the lesser of the two days. Wegman ...Previous Discussion... ...Upper Midwest... The area of low pressure the brings a risk of excessive rainfall to parts of the northern plains on Day 2 will continue eastward and bring a risk of excessive rainfall to portions of the Upper Midwest on Monday and Monday night. Low level winds will back in response to height falls and result in 1.75 to nearly 2 inch precipitable water values into the central and eastern Dakotas early Monday. Despite the fact that overall forecast rainfall totals are currently expected to be in the 1-2 inch range, it is expected to fall on ground that is highly saturated in many cases, which would be an aggravating factor when it comes to flooding potential. Therefore, the Slight Risk remained in place. ...Southwest... Monsoonal flow will support another round of late day and evening convection on Monday. Continued uncertainty in the extent of cloud cover lingering from convection on Sunday and what impacts that has in terms of where convection sets up limits confidence in hoisting a Slight Risk at this point although there is not much uncertainty as to the supply of deep moisture being drawn up into Arizona and then northeastward around the upper high into New Mexico and Colorado. ...Southeast US... While most of the showers and thunderstorms will be shunted into the Atlantic as a mid-level trough continues to push the eastern US cold front eastward...models still suggest the front will be hugging the Carolina coast early on Monday with lingering risk of some heavy rainfall. Maintained the Marginal Risk here from the medium range period without much change. Bann Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt