Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
508 FOUS30 KWBC 232005 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 405 PM EDT Sun Jun 23 2024 Day 1 Valid 16Z Sun Jun 23 2024 - 12Z Mon Jun 24 2024 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE NORTHEAST TO THE OHIO VALLEY, SOUTH TEXAS, AND THE SOUTHWEST... ...Northeast to Ohio Valley... Models continue to show the eastward push of a well defined surface low across far southeast Canada into far northern NY state and northern New England. Strong isentropic lift ahead of this low in the plume of anomalous PW values over the northeast have pushed an initial round of moderate rains across Northern New England this morning. This will then be followed by developing convection along the associated cold front this afternoon/evening pushing across the Northeast, Ohio Valley, and Mid-Atlantic. Continuous moderate rainfall with rates peaking around an inch per hour are likely across far northern Maine, but limited instability has decreased the flash flood threat. The Slight Risk was dropped for this reason, but isolated flooding concerns remain. For portions of Upstate New York, Vermont, and New Hampshire, organized convection in the form of at least a few supercells is likely due to MLCAPE of 1500-2000 J/kg and curved hodographs. This could lead to brief instances of intense rainfall rates above 2" per hour, but fast storm motions should limit the flash flood threat somewhat. 12z HREF neighborhood probabilities depict 30-45% chances for at least 2" in 6-hours (ending 00z tonight) across NH and VT. Simulated radars from the latest hi res guidance suggest that the frontal convection Sunday afternoon/evening extending into the Ohio Valley will be fairly progressive, limiting the flash flood potential elsewhere as well. ...Southwest... Anomalous PW values forecast to remain in place for the upcoming day 1 period from southern California into the Southwest, with values as high 5 standard deviations above the mean across southern Arizona and southwest California. Similar to what occurred on Saturday, another round of scattered convection likely over much of Arizona into portions of New Mexico and southern Utah. Models are beginning to show some convective potential in southern California also, with the marginal remaining across this region. There remains low confidence in where any isolated runoff issues may occur, but there are HREF neighborhood probabilities as high as 60-80% for 1" amounts and 10-40% for 2" amounts in south-central Arizona suggesting some isolated runoff issues possible. Placement agreement is not good in the latest hi res with HREF EAS for 1" mostly less than 10% and near zero for 2". The previous marginal was expanded northward to include more of eastern Utah and western Colorado given the similar setup compared to Saturday, CAMs simulated reflectivity, and current satellite trends. ...Far South Texas... Surface low pressure across the southwest Gulf of Mexico forecast to push westward and inland into northeast Mexico day 1. Persistent east southeasterly low level flow expected to the north of the low in an axis of PW values 2-2.5". Models again are showing the heaviest totals remaining south of the U.S./Mexican border across northeast Mexico, with scattered convection again likely into far South Texas on the north side of the qpf axes. HREF neighborhood probabilities are high for 1 and 2"+ amounts across far South Texas, but the EAS probabilities are highest for 1"+ and 2"+ amounts to the south of the U.S. border. Given no big changes overall to the pattern, the marginal risk was maintained over far South Texas for isolated runoff issues. Snell/Oravec Day 2 Valid 12Z Mon Jun 24 2024 - 12Z Tue Jun 25 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF SOUTHEAST ARIZONA... ...Southwest... A Slight Risk was introduced for the day 2 period (12z Mon to 12z Tue) across parts of southeast AZ, including the greater Tucson region. PW values will remain highly anomalous (above the 95th climatological percentile and +5 standard deviations) from southern California into the Southwest with a continuation of weak forcing under the upper ridge axis stretching from the Southern/Central Plains into the Southwest. An influx of deeper moisture throughout the mid-levels is likely on Monday associated with a tropical disturbance entering northeast Mexico today. This added moisture when combined with sufficient instability should create greater coverage in convection through the afternoon and evening hours across southern and southeastern AZ. 12z HREF neighborhood probabilities for at least 2" of rain support this concept, with 40-60% chances in the Slight Risk. Additionally, the sensitive urban locations in and around Tucson prompts a greater risk for scattered flash floods and runoff issues. Elsewhere throughout the Southwest, the updated outlook included expanding the marginal northward throughout south-central Utah and southwest CO (including the slot canyon region of UT). This maintains the trend of slow- moving convection occurring across sensitive terrain the last few days, while the weather pattern remaining mostly the same through day 2. It`s expected isolated heavy rainfall and flooding concerns will continue to exist across the broad region of the Southwest and Four Corners. ...Upper Mississippi Valley/Upper Great Lakes... The surface frontal boundary oriented northwest to southeast from the Northern Plains into the Mid Missouri Valley at the start of day 2 will begin to push back to the northeast toward the Upper Mississippi Valley/Upper Lakes region. Strengthening south southwesterly low level flow into this front will raise PW values to 1.5-2" along and to the northeast of the front. Shortwave energy pushing eastward across the Northern Plains toward the Upper Mississippi Valley will help strengthen isentropic lift over this front and support for overrunning convection. There is not a lot of agreement on placement of any heavy precip totals, but overall some potential given the favorable MCS set up. There is potential for heavy day 2 rains to overlap where recent heavy rains fell across southern MN/northern IA and into northern IL. An upgrade to slight may be necessary in later issuances if better model agreement places heavy rain along the southern part of the current marginal. ...Northern Maine.... Surface low pressure moving through the Northeast day 1 will slow in response to the closing off mid to upper level center across northern NY State and northern New England day 2. A comma head/deformation precip band likely to form to the northeast of this closing off mid to upper level low, spreading potentially heavy precip into portions of northern Maine Monday. Developing storms will likely be slow-moving and have 1-2" PWs and up to 1000 J/kg of MUCAPE to work with. 12z HREF 1-hour neighborhood probabilities during the afternoon hours are modest (30-50%) for 1" amounts over central Maine and extreme northern NH. There are also low probabilities (10-30%) for greater than 3" of rain in 6 hours (ending 00z Mon night). This rainfall may overlap the heavy totals from day 1 as well and increase the isolated flash flood threat. Snell/Oravec Day 3 Valid 12Z Tue Jun 25 2024 - 12Z Wed Jun 26 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MIDWEST... In the wake of the warm front pressing northeastward across the Upper Mississippi Valley/Upper Lakes region day 2, the associated cold front will be dropping southeast from the Northern Plains into the Upper Mississippi Valley/Upper Lakes region day 3. Additional convection likely to develop in the axis of high PWs pooling along the front that becomes more west to east oriented. Convection may train in a west to east direction parallel to this front as the low level flow will also be westerly along and ahead of the boundary. There still is spread in model qpf details, but the multi model ensemble qpf mean and latest NBM do show potential for heavy amounts across areas of far southern WI/eastern IA and northern IL that have received heavy rainfall recently. Across these areas, a slight risk is depicted, with the only change this update to shave the northern portion due to a southward trend in better qpf coverage. A broad marginal risk was maintained surrounding this slight risk area to cover the current model qpf spread. ...Southwest... No significant large scale changes expected during day 3 over the Southwest besides the gradual northward lifting of anomalous PWs into parts of UT. PW values 3-4+ standard deviations above the mean will persist from southern California, into the Southwest and southern Great Basin in a region of continued weak forcing under the building closed high over the Southwest. Widespread scattered diurnal convection again possible across these areas, with continued low confidence in any qpf details. Given the increased PWs over the central Great Basin on day 3 the marginal was expanded northward in a similar orientation as day 2. There is some elevated concern that convection could be widespread enough to create scattered flash flooding throughout the slot canyon region of south-central Utah. This area will likely be monitored for a targeted upgrade over the next few days should sufficient instability show up in CAMs and greater qpf coverage. Snell/Oravec 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