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Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
741 FOUS30 KWBC 151812 AAA QPFERD Excessive Rainfall Discussion...UPDATED NWS Weather Prediction Center College Park MD 212 PM EDT Mon Jul 15 2024 Day 1 Valid 185Z Mon Jul 15 2024 - 12Z Tue Jul 16 2024 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR ACROSS PORTIONS OF NORTHERN ILLINOIS, INCLUDING THE CHICAGO METRO... ..1810Z Update... In coordination with the local Chicago WFO, a targeted upgrade to a Moderate Risk was made to encompass much of Northern IL, including the Rockford and Chicago metro areas. Previous 48 hrs have been impactful across the aforementioned area with locally 5-10" of rainfall from a succession of three MCS as they moved through the area. Despite the overall progressive nature of the expected complex later today, the antecedent conditions coupled with rates of 1-3"/hr over very saturated soils and flood prone urban corridors were enough to warrant a targeted upgrade to the MDT risk across that area. Kleebauer ...16Z Update Summary... The SLGT risk across the Midwest was expanded in all directions with a greater emphasis to the north, south, and east where the forecast track of the next convective complex will likely cause some enhanced flash flood issues during its progression. A MRGL risk was added across portions of Southern New England for isolated flash flood within a zone of enhanced convergence. The MRGL risk across the Northeast was expanded a bit further east as well to reflect some of the trends within the QPF field on recent CAMs as they have a better handle on the approaching shortwave and remnant MCV currently pushing through Southeast Ontario. The MRGL risk across the Southwest was linked and expanded somewhat to encompass the higher instability reflection across the region where isolated flash flood concerns will be plausible. ...Midwest through the Ohio Valley... Area convection within the Upper Mississippi Valley is in the process of weakening with some of the remnant energy expected to pivot southeast within the mean flow aloft. A cold front at the surface is analyzed over Southwest MN with a surface low expected to motion to the northeast into the Northern Great Lakes by the evening. The cold front will slide to the southeast allowing for increasing convergence within the confines of a building moist/unstable axis present between Eastern IA and points east encompassing most of Southern WI through Northern IL. These areas have been impacted significantly leading into the upcoming convective pattern with some remnant flooding still located within portions of Rockford and Chicago after the succession of 3 MCS`s the past 48 hrs. The priming of the soils in conjunction with the incoming wave of convection is concerning as the threat will lean on the higher-end of potential impacts given the current situation. Convection will fire late this afternoon and quickly grow upscale as it moves from Eastern IA into Southern WI and Northern IL, a similar path to the previous complex that impacted the area last night. Those areas that were hit previously will maintain the SLGT risk from prior forecast with a higher end wording on locally significant impacts possible across the corridor from Rockford over into Chicago and the surrounding suburbs. The cold front will propagate south with the assistance from cold pool generation from the expected complex. After 00z, increasing LLJ presence will play a significant role in enhancing the rainfall potential within the confines of the boundary as the flow shifts parallel to the front allowing for convective training and backbuilding to occur on the upwind flank of the complex. This has been a consistent signature within the latest CAMs with the HREF blended mean QPF footprint depicting the potential pretty well across the IA/IL border south of Davenport to points east into western IN. This is a relevant signature given the synoptic and mesoscale evolution anticipated with an enhanced probability field accompanying within that zone of interest. The two primary areas will lie within that northern and southwest flank of the complex. Neighborhood probabilities for at least 2" are very high within both corridors with a solid 40-70% outline within both areas. The 1" EAS signatures were also more robust in those zones with some lighter 2" signatures in the same region. Considering those variables, there was enough confidence to maintain the SLGT risk and including some higher-end SLGT wording within those two corridors above. The SLGT was also expanded to the east over portions of Southern MI through Northern and Central IN as the complex will continue propagating eastward overnight with locally heavy rainfall in-of those areas downstream. There is a potential for a targeted upgrade within portions of Northern IL if the setup repeats or has a higher impact across the areas where they have been hit recently leading to greater sensitivities to flood concerns. ...Southern New England... A small, but fairly substantial mid-level perturbation will advect eastward into Southern New England from the west, entering an area of modest low-level convergence and sufficient surface buoyancy located within parts of Northern CT up through Central MA later this afternoon. A fairly substantial boundary layer moisture presence is reflected within the current observed PWATs and surface dew points located across all of the area. Diurnal destabilization and the approach of the mid-level reflection will allow for the development of a line of convection across the above areas, riding east-northeast within the confines of a sharp theta-E gradient aligned over basically the I-90 corridor. Considering the environment and some of the probability signals being a bit robust over the highlighted area. In coordination with the local BOX WFO, a small MRGL risk was added over portions of Southern New England, not including greater Boston or Southeast MA. Kleebauer ...Southwest... Monsoon moisture will fuel another day of afternoon showers and thunderstorms, with isolated flash flooding remaining a concern from southeastern Arizona and southwestern New Mexico into the Mogollon Rim. Models have been underplaying the convection development further to the west into southern California. Considering a somewhat decent signal with the SBCAPE fields off the recent CAMs and PWAT anomalies within the interior of SoCal and Southern NV, have expanded the MRGL risk and connected the separated risk areas to become a more uniform MRGL over the region. Pereira/Kleebauer Day 2 Valid 12Z Tue Jul 16 2024 - 12Z Wed Jul 17 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MID MISSISSIPPI AND OHIO VALLEYS... ...Central Plains to the Northeast... As a broad upper trough begins to amplify over the Great Lakes, the associated surface boundary and accompanying moisture pool will become a focus for showers and storms and the potential for heavy rainfall amounts. Southwesterly inflow into the front will support PWs climbing upwards of 2 inches from the mid Mississippi Valley eastward into the Ohio Valley. This is also where the guidance shows the best mid-to-upper level forcing, raising the potential for west-to-east training storms and heavy accumulations. The general model consensus shows the greater threat has shifted a little further south and east, but is overall close to the previous axis. Therefore, a Slight Risk was maintained from central Missouri eastward to far western Pennsylvania. Some of the deterministic guidance do show amounts that would raise Moderate Risk concerns. However, given the model spread, opted not to include any upgrades at this point. While the model consensus indicates the greater threat for widespread moderate to heavy amounts is further east, there is a notable signal for locally heavy amounts developing over the central High Plains, especially over eastern Colorado and western Kansas. Mid-level energy spilling off the top of the ridge and interacting with upslope flow and moisture pooling along the western edge of the surface front will likely support storms developing along the high terrain before moving eastward. While differing in the details, most models show at least locally heavy rainfall amounts, raising at least isolated flash flooding concerns across the region. ...Southwest... Greater coverage of isolated to scattered diurnal convection is expected as the upper high currently in place weakens. This will allow more showers and storms to develop further to the north, extending the threat for isolated flash flooding across a greater portion of northern Arizona and New Mexico. Pereira Day 3 Valid 12Z Wed Jul 17 2024 - 12Z Thu Jul 18 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF COLORADO AND NEW MEXICO... ...Southwest to the central and southern Rockies... A Slight Risk was introduced from south-central Colorado to central New Mexico, where moist upslope flow will support increasing coverage of showers and storms and locally heavy amounts. This will raise the potential for flash flooding, especially across vulnerable areas. Guidance indicates a notable increase in low level moisture transport, raising PW anomalies to 1.5 standard deviations above normal across central New Mexico. This moisture along with weak flow aloft and daytime heating, is expected to support slow-moving storms capable of producing heavy rainfall rates. Vulnerable areas, including burn scars, urbanized areas, and areas of complex terrain will be most susceptible to flash flooding. Elsewhere, the potential for diurnal convection producing at least isolated concerns for heavy rainfall and flash flooding will continue to expand across the Southwest. ...Southern Plains to the Northeast... Widespread coverage of moderate to locally heavy amounts, extending from Oklahoma and northern Texas all the way to the Mid Atlantic and southern New England, can be expected as a cold front continues to drop slowly south through the central and eastern U.S. this period. Model spread contributed to the decision to maintain a broad Marginal Risk across this region for now. However, there are some model signals that an upgrade to a Slight Risk may be required across some areas at some point. This includes areas from eastern Oklahoma through northern Arkansas, where some of the deterministic models show heavy amounts developing as mid-level energy moving through the base of the trough interacts with a deeper moisture pool (PWs ~2 inches) along the front. Other areas include portions of the Ohio Valley and the Mid Atlantic, where there are signals for at least locally heavy amounts as well. Pereira 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