Quantitative Precipitation Forecast
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977 FOUS30 KWBC 111953 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 353 PM EDT Tue Jun 11 2024 Day 1 Valid 16Z Tue Jun 11 2024 - 12Z Wed Jun 12 2024 ...16Z Update... Changes within the respected risk areas across the Southern Plains and Florida were minimal with minor adjustments on the northern edges of each risk. Florida continues to carry the SLGT risk with heavy rain potential lasting through the period with the heaviest QPF focus in-of the western FL coast, especially across southwest FL where local maxes of 6-9" of rainfall are plausible. The key in limiting the flash flood threat will be maintaining the current rates with general hourly rainfall currently between 0.5-1.25"/hr, a far cry from what would constitute concern within the Peninsula. Antecedent conditions leading in were very dry, so the initial wave of moderate to heavy rain has been beneficial and will continue through the period with some breaks at times later this evening. The SLGT risk has the best definition over the coastal urban centers with the primary locations from Sarasota down to Naples as the targets for flash flooding. The sandier soils in the affected area(s) across central and southern FL will deter major impacts outside those urban centers that come underneath a stronger heavy rain core. Those will be more isolated in nature and certainly not enough consensus on when/where those would occur. The SLGT risk is justified due to forecast totals and potential, but any upgrades are highly contingent on near term convective evolution. The Southern Plains continues to be impacted by a propagating MCS this morning. More on the setup in an updated sub-heading below.... ...Previous Discussion... ...Southern Florida... A steady influx of tropical moisture, with PW anomalies up to +3.5 standard deviations will trigger scattered to widespread convection across southern and central Florida. With the stalled front positioned to the north in a west-east orientation the environment will be favorable for slow moving capable of producing several inches of rain. Some of the highest totals are expected to focus from Tampa Bay to the Keys during this period. Areal averages of 2 to 5 inches are forecast with very isolated locations possibly receiving 6 to 9 inches. The Keys and southwest portions of the peninsula will have the greater risk for excessive rainfall (Slight Risk) and associated flash flooding, but the threat extends to the southeast coast and into portions of central Florida as well. Campbell/Kleebauer ...Southern Plains... Nocturnal MCS continues to push southeast, likely riding along a stationary boundary analyzed from north-central TX down through the central and eastern portion of the state as it extends near the Gulf coast around Houston and arcs back along the remainder of the Gulf coast to the east. Guidance has picked up on the MCS and it`s general forward motion over the past succession of runs with some general continuity and consensus on expected impacts. Totals over north-central TX have been mainly between 1-2" within the zone of impact, but a few stronger cores embedded within the bowing segment and on the edges of the complex have aided in totals closer to 3" with an anomalous 6+" total over Seymour, TX due to a bookend vorticity that stalled over the area with a remnant boundary influencing the evolution. These types of maxima are plausible in the setup today, but will be highly localized with most of the areas in the path of the complex likely seeing more along the 1-2" range with locally higher in those more complex evolutions. 12z HREF was pretty bullish in the neighborhood probability fields with some 40-45% readings for at least 5" where the MCS is currently located and moving towards. Observations over the area show the hi-res deterministic reading a bit hot, but still within a reasonable margin of error on the current rates. Debated an upgrade to a SLGT risk for central TX, but with more of an isolated prospect for flash flooding, decided to maintain continuity with the MRGL risk. The forward motion of the MCS is also a deterrent on the higher potential as areas will likely see 30 min to an hour of heavier rain before settling. However, like the areas to the north that received the higher totals this morning, if there is a more defined concern with those types of outcomes downstream in the MCS path, there could very well be a targeted SLGT risk upgrade if the setup is warranted. Recent ML output from the First Guess fields are still holding firm on a MRGL risk in place as well, so the necessity to upgrade was entertained, but passed on. We will continue to monitor closely. Kleebauer Day 2 Valid 12Z Wed Jun 12 2024 - 12Z Thu Jun 13 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR SOUTHERN FLORIDA... ...20Z Update... Continuity was maintained for all the risk areas with only some minor adjustments necessary as the general pattern evolution remains consistent from run-to-run to limit any notable changes. The heavy rain across the southern half of the Florida Peninsula will continue with the best flash flood threats confined to the coastal urban corridors, especially over southwest FL from St Petersburg down through Naples. 12z HREF signals are still fairly robust with neighborhood probabilities for at least 5" in totals for the period running between 70-90% within the aforementioned corridor along the Florida Gulf Coast. Waves of heavy rain will move inland off the adjacent Gulf with general rates running between 1-2"/hr within heavier cells with some localized 3-4"/hr rates possible based on the probabilistic fields of the HREF and upper quartile of the NBM. The multi-day event will lead to heightened concerns for flooding, but pure flash flooding will still remain within the SLGT risk category thanks to the elevated FFG`s that are climatologically favored over the Peninsula. The urban areas are the most likely to see any flash flood risks due to impervious surfaces with the sandy soils likely to absorb much of the rain during the period, especially with any small breaks in the precip shield. The other areas of concern across the Midwest and Texas are generally MRGL with local rainfall totals likely within the 1-2" range in the affected areas with maxes more around 3" for each region in question. Convection over the Midwest will have the most dynamical support with the approach of a shortwave trough and associated cold front that will enhance surface forcing along with the favored upper pattern. The progressive nature of the precip will deter higher end impacts, however some backbuilding is plausible over southern MN into northern IA that could enhance local totals towards that upper threshold mentioned previously. This is noted on a few hi-res deterministic and falls within the 90-99th percentile of outcomes in the blend. Considering this is more localized, the threat remains on the MRGL level with a chance at a targeted upgrade pending short term convective evolution. Further south, pulse convection will occur with the passage of a weak mid-level vorticity maximum that will swing southeast around the eastern flank of a mid-level ridge that will shift eastward from the Southwestern U.S. A few spots could see a quick 1-2" of rainfall, but will be highly localized. Considering the rainfall from the previous period, some places could still be wet and more conducive for flooding concerns. This is highly contingent on what falls this evening and there`s a chance this risk area is voided, or shrinks in size. Kleebauer ...Previous Discussion... ...Southern Florida... The stalled front will sag a little to the south during this period but the heavy rain will persist across South Florida. PW values of 2 inches will hold steady across the peninsula and will maintain very efficient rain and rain rates across the nearly saturated rural and urban areas. Areal averages will again be 2 to 4 inches with local maxes up to 8 inches possible. A Slight Risk for Southern Florida and the Keys remains in effect along with a Marginal Risk for Central Florida. The nature of this multi-day event with storm total rainfall amounts potentially rising into the double digits, there may be the need for an upgrade in future updates. ...Texas... Convection will continue to shift south and east while reducing areal coverage during this period. Most of the thunderstorms will focus across eastern portions of the Hill Country and points east. While amounts are on the lower end the recent rains will have increased soil saturation thus lowering the amount of rain needed to become problematic. The Marginal Risk was maintained for an isolated threat for flooding concerns for portions of central and eastern Texas toward the Mid and Upper Coast. ...Upper Mississippi Valley... A Marginal Risk was introduced for portions of Minnesota, Wisconsin and Iowa where soils have been nearly saturated from multiple instances of recent rainfall. Showers and thunderstorms are expected to accompany a passing cold front through the northern tier states, potentially spreading 1 to 3 inches over the sensitive area and may lead to isolated areas of flooding. Campbell Day 3 Valid 12Z Thu Jun 13 2024 - 12Z Fri Jun 14 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR SOUTHERN FLORIDA... ...20Z Update... No changes were necessary for the previous D3 issuance as model continuity maintains the areas over the central Midwest and Florida as the primary areas of note for flash flood concerns. Recent bias corrected QPF across the southern FL Peninsula remains aggressive with totals approaching 2-4" across the southwest urban corridors with 1-3" expanding further inland. This will likely lead to some areas in FL seeing over 12" of precipitation in the span of 3-days, a substantial amount even with a consideration for it being in Florida. Rates are still a factor in maintaining the area in a SLGT risk as the FFG`s, while expected to decrease, will likely remain within the 2.5-3"/hr range for any expected flash flood threat keeping the threat tied to the coast for greater impact. As of now, there was not enough of a signal to warrant an upgrade. The central Midwest through IL/IN will see the pattern evolve upstream to overhead by Thursday afternoon and evening with a shortwave progression bisecting the region along with a cold front moving through on the base of a low moving through the northern Great Lakes in to Ontario. Local totals of 2-3" are possible across parts of the aforementioned area with the heaviest rain likely tied to convection along the frontal boundary. The threat is still a question mark on the latitudinal extent of the precip field as much of the setup is contingent on the placement of the front. Ensemble guidance is generally impacting northern IL down into the central portion of IL/IN, so there was no reason to deviate from the previous forecast. Thus, the MRGL was maintained over the same general area from the past forecast. Kleebauer ...Previous Discussion... ...Florida... Little change in the environment and pattern across FLorida. Thunderstorms will continue to focus across South Florida and the Keys bringing another 1 to 3 inches to the area. WPC has 3-day forecast accumulation of 2 to 12 inches from north to south across the peninsula with isolated higher amounts. A Slight Risk is in place from Tampa Bay to Melbourne metros and south to the Keys. A Marginal Risk area covers central Florida. ...Midwest... Thunderstorms will pass from the Upper Mississippi Valley into the Midwest/western Ohio Valley as the cold front progresses eastward. Areal averages of 1 to 3 inches will be possible across this part of the country where recent rains have left soils nearly saturated. Rain may become excessive and lead to isolated instances flooding. A Marginal Risk was maintained from the previous day 4 forecast and spans from eastern Iowa/northeast Missouri to southwest Michigan and northern Indiana. Campbell 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