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Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
411 FOUS30 KWBC 192001 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 401 PM EDT Fri Jul 19 2024 Day 1 Valid 16Z Fri Jul 19 2024 - 12Z Sat Jul 20 2024 ...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHWEST, SOUTHERN ROCKIES, CENTRAL HIGH PLAINS, AND EASTERN CAROLINAS... ...16z Update... Primary changes for this update include a Slight Risk introduction for portions of the central High Plains (northwest KS and surrounding portions of NE/CO) and the expansion of the Slight Risk over portions of the Southern Rockies to include more of the Southwest (along the higher terrain of the Mogollon Mountains/Rim into southwest NM and southeast AZ). For the former, the 12z HREF PMM indicates the potential for 3-5" localized totals (with 5-yr ARI exceedance probs between 20-40%). For the latter, 40-km neighborhood exceedance probs from the HREF indicate ~20% odds of localized 2" exceedance. Otherwise overall meteorological thinking remains unchanged from below, and only minor tweaks based on observational and model trends. Churchill ...Previous Discussion... ...Carolinas... The cold front from the past few days will become quasi-stationary across the Carolinas with a strong low-level convergence signature focused from Northeast NC down through Central SC in the Piedmont. Areal PWATs are sufficient for heavy rainfall potential with anomalies nestled between 1-1.5 deviations above normal with values between 1.8-2.2" focused over the above area. Current mean QPF is right around 1-1.5" with some smaller maxima located across multiple portions of the Carolinas which is reflective of the overall convective environment. The primary signature of note for the potential is heavily based in the latest probability fields with EAS signatures between 25-40% for at least 1" present through much of the Eastern Carolinas with the max confined to the eastern extent of the Piedmont down to around Columbia, an urban area more prone for flash flooding historically. Neighborhood probabilities for at least 3" show multiple areas between 50-70% with another max located within the escarpment of SC/NC/TN where models are depicting some terrain focused convection later this afternoon. There are some minor signals for at least 5" totals within the confines of the Eastern Carolinas as well signaling a general maximum of up to 6" in any cells. Area hodographs indicate a weak steering pattern which would lead to either slow moving, or even stationary storms that could enhance the local threat further as the storm motions would only be accelerated through outflow propagation. The SLGT risk from the previous forecast was maintained with some expansion over the northern and southern fringes to match the recent trends within the probability fields. ...Southern Rockies... General persistence will create another day of locally heavy rainfall threats located within the Southern Rockies with a southern expansion down closer to the NM Bootheel as noted within the convective QPF footprint. The area will see another round of diurnally driven convection with more mid-level perturbations rounding the eastern flank of the ridge, moving overhead during the peak of diurnal heating. This will create an enhancement within the large scale ascent pattern along with the already favorable instability field with the theta-E ridge bisecting much of Central and Northern NM. Local totals of 1-2" with a few spots seeing higher amounts are forecast across the terrain down into the northern extent of the Bootheel near Gila National Forest. Probabilities for at least 1" are relatively higher when gauging the neighborhood probability output with some scattered signals for at least 2" in portions of Central NM. The combination of multi-day impact within complex terrain and remnant burn scars exacerbating the flash flood concerns was plenty of reason to extend the SLGT risk maintain general continuity. Kleebauer Day 2 Valid 12Z Sat Jul 20 2024 - 12Z Sun Jul 21 2024 ...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHERN ROCKIES AND SOUTHWEST... ...20z Update... The Slight Risk over the Southern Rockies has been expanded southwestward to include the high terrain of the Mogollon Mountains/Rim from southwest NM into southeast AZ, as well as lower elevations downstream into southeast AZ (including Tuscon and surroundings). The expectation is for a bit more convective coverage relative to Day 1, due to minor weakening/westward shift in the upper-level ridge. This should also allow for a bit more storm movement, which may reduce residence time of higher rates a bit, but perhaps more significantly this can allow for more storm propagation into the low elevations of southeast AZ. A skillful proxy for flash flood impacts across the southwest is the 2" exceedance threshold from the HREF (40-km neighborhood method), which exceeds 20% across the bulk expanded Slight Risk. Outside of this region, changes/tweaks to the outlook were minimal. Churchill ...Previous Discussion... ...Southern Rockies... A pattern of persistence within the mid and upper-levels will lead to an ongoing threat of convective development in-of the Southern Rockies and adjacent terrain of NM due to primed environmental destabilization coinciding with a progression of mid-level vortices streaming down the eastern flank of the ridge across the Western U.S. Theta-E ridge is forecast to shift focus across NM with the tongue of elevated instability generally confined to the terrain extending from the Bootheel up through the Sangre de Cristos. Scattered to numerous thunderstorms will be capable of locally heavy rainfall that will interact with complex terrain and the burn scars littered across the Southern Rockies down to the Sacramento Mountains. Areal QPF average between 0.75-1.5" is forecast with a few locations potentially seeing upwards of 2" which would easily cause issues no matter where they occur given the lower FFGs situated across the state. Considering the ongoing impacts from prior periods and the convective coverage anticipated, maintained the previous SLGT risk with some broadening of the risk area to reflect the concerns even outside the terrain focused areas. ...Southeast to Southern Mid Atlantic... Persistent surface front bisecting much of the Southeastern U.S up through the Southern Mid Atlantic will continue the threat of scattered thunderstorms capable of locally heavy rainfall with some training prospects within the confines of the quasi-stationary boundary. The QPF footprint is a shotgun of small QPF maxima reflective of the potential with less of any organized threat and more of a widespread convective pattern that favors some locally greater impacts, but remaining on the low to middle grounds of the MRGL threshold. Unlike the previous period, a lack of stronger mid-level vorticity will negate the higher end potential as the ascent pattern is mainly limited to boundary layer destabilization and low-level convergence within the front. The previous MRGL risk was maintained with some minor adjustments. Kleebauer Day 3 Valid 12Z Sun Jul 21 2024 - 12Z Mon Jul 22 2024 ...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHERN ROCKIES AND SOUTHWEST... ...20z Update... Similar to the updates on Days 1 and 2, some expansion of the Slight Risk was made from the Southern Rockies into the Southwest. While overall convective coverage and intensity has the potential to be a bit greater on Sunday, confidence is not as high given the lack of hi-res guidance during this time frame. The expanded Slight was confined to the more confident higher terrain areas of NM (and some surrounding portions of CO/AZ). These areas are where a bias corrected blend of the ensemble guidance suggests localized totals of 1-3", and corresponds with many sensitive burn scars which have been the focus for locally significant flooding impacts. Otherwise, only minor adjustments were made to the Marginal Risk areas. Churchill ...Previous Discussion... ...Southern Rockies... Mid-level ridge axis will begin sliding eastward with building heights centered over the Lower Colorado River Basin into the southern portion of the Great Basin. A multitude of mid-level vortices will continue to plunge down the eastern flank of the ridge and interact with ample surface destabilization located within the Southern Rockies. With steep low to mid-level lapse rates and prominent moisture anomalies running close to 1-2 deviations above normal, convective threats will induce periods of moderate to heavy rainfall within the general confines of the Southern Rockies with emphasis on the Sangre de Cristos and the Northern fringe of the Sacramentos. There will also be an extension of convective concerns down closer to the NM Bootheel within the Gila National Forest just to the north of Silver City. Areal QPF within the means are consistent with 0.75-1.25" with some bias corrected maxes exceeding 2" in spots, mainly over Northern NM. With the successive period of heavy rainfall potential within the terrain and remnant burn scars, the threat remains well within the SLGT risk range inherited from prior forecast. Thus, outside some adjustment within the fringes to reflect QPF trends, the SLGT risk was majority continuity. ...Mid-Atlantic to Central Gulf Coast... A mid-level trough will begin to carve out across the Central Plains with a lingering stationary front still bisecting much of the Southeast into the Southern Mid Atlantic. Broad extent of thunderstorm chances will remain stagnant in terms of placement and potential impact with greater effects generally relegated to focal points near higher surface convergence patterns and deep layer moisture field present in any given area. Scattered to numerous thunderstorms are forecast across TX to the Central Gulf Coast during the afternoon on Sunday with locally heavy rainfall plausible in any cells that develop. General 1-2" are possible in any convective signal, however the area over the Central Gulf has the best chance for heavier returns due to a deeper moisture field located along the Gulf. These areas do have a higher FFG however, so the threat is on the lower end of MRGL during the period, along with the area across TX. Continued threat of heavy rainfall is forecast across the Southern Mid Atlantic where multiple shortwaves will enter the region and enhance regional ascent within the convergence corridor near the stationary front. The main area of impact is subject to some variability at range due to the forecast frontal placement being a major part of where training convection could develop. The MRGL risk across the area was broad but worthy of the current location given the setup. An upgrade is possible pending the convective evolution over the previous period. Kleebauer 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