Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
030 FOUS30 KWBC 110824 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 424 AM EDT Sat May 11 2024 Day 1 Valid 12Z Sat May 11 2024 - 12Z Sun May 12 2024 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHERN HIGH PLAINS INTO PARTS OF CENTRAL AND SOUTH TEXAS... ...Summary... Vigorous upper level shortwave trough moving slowly across the Four Corners region and southern Rockies will lead to a quick influx of deep-layer forcing and moisture across the southern High Plains in eastern NM, much of the TX Cap Rock-Rolling Plains, and into the TX Hill Country and parts of South TX. The Marginal Risk of excessive rainfall from yesterday`s Day 2 ERO was expanded a bit into parts of South TX based on the latest guidance trends, where the potential exists for isolated instances of flash flooding. ...Eastern NM into portions of Western and Central TX... Ahead of the approaching upper shortwave trough, a gradual uptick in difluence aloft will ensue across the outlook area. Strengthening low-level moist S-SE inflow will also take place Sat- Sat night along and east of the dryline, as 850 mb moisture flux anomalies peak between 2-2.5 standard deviations above normal. Convection forming off the terrain will obtain quite a bit of forward propagation given the strong deep-layer shear profile, therefore cell training is not a concern per the simulated reflectivity guidance form the models. However, available deep- layer instability (mixed-layer CAPEs at least 500-1000 J/Kg over the northern portion of the Marginal area...1500-2500+ J/Kg south) along with PWs averaging 2 standard deviations above normal will favor maximum rain rates of 1-1.5"/hr and 1.5-2.0"+/3hr underneath the strongest cores. Supported by the latest CSU ERO first guess guidance, runoff from these stronger storms will pose an isolated or localized risk for flash flooding, even with the antecedent dry soils over parts of the outlook area. Hurley Day 2 Valid 12Z Sun May 12 2024 - 12Z Mon May 13 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF CENTRAL AND EASTERN TEXAS INTO THE LOWER MISSISSIPPI VALLEY... ...Summary... Mid-upper level trough traversing the Central-Southern Plains north of the Red River will lead to a surge of deepening instability and moisture from the western Gulf of Mexico as a warm front pushes into eastern TX and southwest LA. Favorable dynamic and thermodynamic profiles will result in widespread convection across central-eastern portions of TX into parts of the Lower MS Valley, where a high-end Slight Risk of excessive rainfall is anticipated Sunday and Sunday night. ...Central-Southern Plains and Portions of the Lower Mississippi Valley to the Mid-Upper TX and western LA Gulf Coast... The latest guidance (00Z 5/11 model cycle) showed a bit of an uptick in the exit region forcing ahead of the approaching mid- upper level trough, at least in terms of the low-level ageostrophic response across central-eastern TX into the Lower MS. Valley. More specifically, the ensembles now show 850 mb southerly flow anomalies getting to 2-2.5 standard deviations above normal (a little more robust compared to yesterday`s guidance). Meanwhile, at the same time 850-700 mb moisture flux anomalies top out between +2.5-3.0, which is also an uptick from yesterday`s model progs. The duration of the best moisture transport/anomalous moisture flux within the lower-mid levels remains rather transient however, while the degree of kinematic and thermodynamic response east of the upper trough does seem to be mitigated by the absence of a more robust subtropical jet streak. An uptick in low-level frontogenesis along the warm front is still anticipated however via the right- entrance region of a 90-100 kt upper jet streak traversing the Southern Plains and TN Valley. This will also help retard the warm front`s east-northeastward progression. Largely elevated, convection will become more widespread downwind of the warm front in a favorable deep-layer warm/moist advection pattern off the western Gulf of Mexico. The lingering low-level frontogenesis/slow progression of the surface front will allow for some cell training, especially across parts of central-eastern TX which had received quite a bit of rain over the past week. Over this region eastward through western LA, believe the ERO risk will be more of a "high end" Slight (i.e. at least 25% risk of rainfall exceeding FFG within 25 miles of a point). Within the Slight Risk area, 00Z models show pockets of 3-5+ inches of rain during day 2 within this area, with the 00Z RRFS noting a narrow band of 6-8" totals just south-southwest of the ArkLaTex, including Longview TX and Shreveport LA. For now, given the areal spread in the guidance in terms of the heavy rainfall footprints, have opted to not hoist a Moderate Risk. Later shifts can re-evaluate the need for a targeted Moderate Risk based on the most recent observational and model trends. Hurley Day 3 Valid 12Z Mon May 13 2024 - 12Z Tue May 14 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE GULF COAST REGION TO SOUTHERN PORTIONS OF THE MID-SOUTH FROM EASTERN TEXAS TO THE FLORIDA PANHANDLE... ...Summary... The aforementioned mid-upper level trough and corresponding surface low/frontal systems are expected to pivot slowly into the Mid Mississippi Valley by Monday night will continue to foster a heavy rainfall -- which by Day 3 (Mon-Mon night) will shift a little farther east to the central Gulf Coast region. Compared to yesterday`s Day 4 ERO, only minor changes were made to the Slight and Marginal Risk areas. ...Lower-Mid Mississippi Valley, Parts of the Midwest, Much of the Gulf Coast Region, Parts of the Southeast... As with the Day 2 ERO, anticipate at least a high-end Slight Risk, which for Day 3 would be across the Gulf Coast region from eastern LA and southern MS-AL to the western FL Panhandle. Buckling upper flow ahead of the trough will help to bolster the low-level frontogenesis for a bit ahead of the advancing cold front, and while while the anomalies and percentiles have come up per the global guidance, forecast confidence for a prolonged period of strong low-level southerly inflow/moisture transport off the Gulf, which helps justify a Day 3 Moderate Risk ERO, remains low. Latest CSU ML first guess fields support that thinking as well. Could certainly see at least 2 rounds of more organized convection; one more elevated ahead of the advancing warm front, with the next perhaps a QLCS ahead of the cold front. However in either case given the shear profiles, the storms should be moving relatively swiftly given the degree of forward propagation inferred with westerly Corfidi Vectors averaging 20-30 kts through the Day 3 period. Model guidance 1 and 3 hour QPF progs Mon-Mon night all show this. Also, there`s a legitimate chance that the second round of heavier rain (ahead of the cold front) may be farther south than the first round. Suspect ultimately there could be a Moderate Risk hoisted over a relatively small/targeted area, but given the aforementioned considerations along with the areal spread in the guidance QPFs, the forecast confidence to hoist a Moderate Risk at this point (Day 3 forecast) is too low. Hurley 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