Quantitative Precipitation Forecast
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200 FOUS30 KWBC 070050 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 850 PM EDT Thu Jun 6 2024 Day 1 Valid 01Z Fri Jun 07 2024 - 12Z Fri Jun 07 2024 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHEAST AS WELL AS THE TEXAS PANHANDLE AND PORTIONS OF WESTERN OKLAHOMA... ...01Z update... ...Texas Panhandle Area... A new Marginal Risk area was introduced with this update for the Texas Panhandle and portions of western Oklahoma. A stationary front draped across the area is providing a localized source of lift for a pool of moisture running into the boundary from the south. Nearly stationary storms have been developing along it as a result...leaving a line of storms from western Oklahoma to far eastern New Mexico. Some of the CAMs guidance has captured the spirit of the storms, with HREF guidance suggesting a 20% chance of 3 inches of rain across the southern Texas Panhandle through 7am/12Z Friday. For that reason, the Marginal Risk has been hoisted. ...Northeast... A cold front sweeping across New England continues to provide the forcing for an area of moderate rain with embedded heavier convection. Most of the storms are moving quick enough that any resultant flash flooding should be isolated. A separate line of storms is just north of NYC, but these storms too are moving along and only producing isolated rates to 3/4 inch per hour, so flash flooding from these should also be very isolated, if it happens at all. Wegman ...16Z Update... Little change was made to the inherited risk area as the prospects for flooding remain similar to the previous forecast(s) as backed by hi-res probability fields and associated numerical output. The latest HREF signals maintain relative continuity with the area across New England and over the southern Mid Atlantic as the primary focal points for convective based flash flooding this afternoon and evening. A small shift in the MRGL was necessitated over portions of coastal southern New England due to a small, but formidable axis of convergence along a warm front bisecting the coasts of RI over into southeastern MA. Rainfall rates have reached upwards of 2-2.5"/hr at times within the band of heavy rainfall. While not overly convective in nature, anomalous low to mid-level moisture with a zone of enhanced 925-850mb frontogenesis aligned parallel to the coastal plain has provided a tongue of precip totals breaching 1.5-2" over the aforementioned areas. The setup will eventually vacate the area and end the threat, but current radar presentations indicate at least another hour or two of potential before the threat subsides. This was the greatest change from the previous forecast. Otherwise, general continuity with the threat across the Mid Atlantic evolving from convection along and just ahead of an approaching cold front. Heavy rain over northern New England is due to primed upper forcing within a broad axis of diffluence present downstream of a potent shortwave trough swinging through the Great Lakes and adjacent Ontario Province. Kleebauer ...Previous Discussion... ...Mid Atlantic to Northeast... A slow moving cold front, currently analyzed across portions of the Ohio Valley and Appalachians, will cross through the Mid Atlantic and Northeast today into tonight. Meanwhile, a warm front will continue lifting northward through the Northeast this morning before stalling or slowing across southern New England this afternoon. The airmass will be quite moist, with the latest guidance pointing toward PWs well above normal (exceeding 95th percentile) with values over 1.75" from the Mid-Atlantic into southern New England and near 1.5" across northern NY and portions of VT/NH. This morning there should be an initial round of locally heavy downpours with the warm front passage across southern NY and southern New England, which could bring localized flooding concerns with rain rates exceeding 1"/hr. A second round is then expected for the afternoon/evening with the approaching cold front but also could train/repeat with the warm front stalling nearby. Convective initiation is likely between 16-18Z across western NY and PA with a line of showers and thunderstorms moving east/northeast through the remainder of the day. The latest HREF probabilities for 24-hr totals of at least 2" are spotty but show some signal exceeding 40-50 percent in locations form eastern/northern NY and southern New England). Probabilities for hourly totals of 1-2" are slight (under 30 percent). Further south into the Mid-Atlantic, higher moisture ahead of the cold front and sufficiently warm temperatures will support a line or two of stronger showers and thunderstorms during the afternoon/evening hours. Some of these will be capable of producing heavy downpours, particularly from the I-95 corridor from Baltimore to Richmond and eastward including southeast VA where the 2" HREF neighborhood probabilities are locally higher near 50 percent. Taylor Day 2 Valid 12Z Fri Jun 07 2024 - 12Z Sat Jun 08 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF EASTERN KANSAS AND WESTERN MISSOURI... ...20Z Update... Minor adjustments were made to the inherited SLGT risk across the central plains. Recent trends favor an axis of heavy rain a tad further north within the confines of an increasingly favorable theta-E surge on the western fringe of a surface ridge positioned over the Tennessee Valley. HREF probabilities for totals >2" signal a greater likelihood of the heaviest totals bisecting the KS/NE/MO/IA border, in-line with the recent ML output for location of the heaviest corridor of precip. The upper quartile of outcomes is generally within the 3-5" range thanks to the progressive nature of the expected complex as it initiates over northern NE by the late afternoon, driving southeast into MO by the end of the period. Expected rates are forecast to top out between 2-3"/hr at peak intensity, although the probabilistic output of generally 20-30% for at least 2"/hr on the latest HREF neighborhood probability intervals remains highly scattered in nature signifying less of widespread higher rates in the complex and more of a few embedded heavy cells intertwined within the main core. In either case, the prospects for localized flash flooding are high enough to warrant the continuation of the SLGT risk with only some minor shifts on the northern periphery of the risk areas based off current ML and ensemble output of the heaviest precip core. Kleebauer ...Previous Discussion... The setup continues to look favorable for a heavy rainfall event across portions of the Southern/Central Plains Friday/Friday night. A strong ridge of high pressure will remain anchored over Mexico/Texas and along the periphery of this ridge, shortwave energy is expected to ripple through out of the Rockies into the Plains Friday afternoon/night. Meanwhile, a cold front passing through today (Thursday) is expected to return/lift back through as a warm front Friday/Friday night, bringing a surge of higher moisture with it as low level flow increases. The combination of this moisture transport, favorable dynamics (including right entrance lift) will likely initiate a complex of thunderstorms that then dive south/southeast along the instability gradient into KS/MO. For this forecast cycle, the guidance remains in pretty good agreement overall, with perhaps a nudge to the south compared to the past 24 hours though the relative magnitude/amounts of QPF have trended down somewhat and the latest ensemble guidance supports lower QPF in general. There appears to be enough support to maintain the Slight based on the environmental ingredients and synoptic setup, but the risk probably leans toward the lower end of the probability range for now. Taylor Day 3 Valid 12Z Sat Jun 08 2024 - 12Z Sun Jun 09 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHERN PLAINS TO MID MISSISSIPPI VALLEY... ...20Z Update... Recent consensus amongst global deterministic and associated ensembles continues to pin a corridor of heavy rainfall potential across eastern KS extending into central and southern MO. This signal aligns perfectly within a forecasted theta-E maximum that advects poleward Saturday afternoon and evening with an approaching cold front to the north providing ample surface convergence as we enter peak diurnal instability. As mentioned in the previous forecast, environment will be ripe for heavy rain thanks to an anomalous low to mid-level moisture flux that will jettison PWATs to well-above normal levels. The moist environment coupled with favorable low to mid-level dynamics will be plentiful for incite a swath of heavy convection along and ahead of the surface front that will be moving into the area. Current ensemble blends, including the NBM and bias corrected ensemble pinpoint a mean of 2-2.5" of rainfall across eastern KS into south-central MO with the areal extent of at least 1" encompassing the area 75-100 miles surrounding. The biggest change to the previous forecast was mainly the positioning of the SLGT being a bit further south from current consensus, so the shift north was in response to the recent northward deviation of previous forecasts with ample support from pretty much all global deterministic and ensembles. A lot of the pattern is contingent on the meridional push of the advancing cold front, so we`ll be keeping a close eye on the general model output for the boundary in question as that will dictate eventual SLGT risk location and latitudinal expanse of the risk area(s) across the plains. There was little change in numerical output for the secondary area of interest across the Front Range where general consensus points to isolated heavy thunderstorms capable of 1-3" of rain falling in any given storm that materializes along the terrain in CO/WY. Kleebauer ...Previous Discussion... A wavy frontal boundary is expected to settle across portions of the Southern Plains eastward into the Mid Mississippi Valley while aloft the quasi zonal/northeast flow continues with periodic shortwave energies moving through. A pool of higher moisture will remain along/ahead of the frontal boundaries and is likely to be characterized by PWs well above 1.5" and approaching 2", particularly across portions of MO/AR. This higher moisture combined with the lift/convergence and instability due to peak heating should spark a few rounds of strong thunderstorm complexes that track east/southeast across the risk area. There remains model spread in placement (north vs. south) and magnitudes as well, and some of the uncertainty will be tied to how the previous day (Friday/Friday night) plays out but the consensus remains favorable for an area of heavy rainfall that could lead to scattered instances of flash flooding, especially as some of these areas are still running above normal for soil moisture anomalies. Further west, moisture banking against the terrain of the Front Range combined with daytime peak heating and shortwave trough energy moving through will lead to isolated/scattered showers and thunderstorms, some of which will be slower moving and produce intense rain rates and isolated/localized flash flooding. Taylor 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