Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
660 FOUS30 KWBC 242029 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 429 PM EDT Mon Jun 24 2024 Day 1 Valid 16Z Mon Jun 24 2024 - 12Z Tue Jun 25 2024 ..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF THE UPPER MISSISSIPPI VALLEY AND SOUTHEAST ARIZONA... 16Z Update... Added a Slight Risk from the Twin Cities to the NW corner of IL. ...Upper Mississippi Valley/Upper Great Lakes... A warm sector ahead of the low currently over central SD shifts east over the Upper Midwest today, reaching Lake Michigan tonight. Moisture anomalies in this warm sector area between 1.5 to 2 deviations above normal by this evening setting the stage for a primed environment capable of heavy rainfall. Elevated instability is quite extensive from eastern SD through western IA, but has a rather strong capping inversion. The greater threat for activity is thought to be well represented in the 12Z ARW/ARW2 with afternoon central MN activity shifting southeast in what will become Wly deep layer mean flow with upwind propagation vectors to the southeast, toward northeast IA and southwest WI. This activity may organize into a single, progressive bow like that seen in the 12Z ARW2, but the right end interaction with the focus of the instability and moisture presents concern, given how sensitive this area is from 2-8" rainfall over the past 5 days. There is a local maximum risk of 3" range considering the available atmospheric moisture and prominent ascent pattern focused over the region. Other members of the 12Z HREF suite, the HRRR and FV3LAM offer disparate solutions, with activity focusing farther east over WI. But the 13/14Z HRRRs have shifted their QPF focus south, lending credence to this embedded SLGT upgrade southeast from the MSP metro along the Miss River to NW IL. The Marginal Risk remains in a similar place from southwest MN over the northeast sector of IA and across WI/western U.P. of MI. Should the cap be broken farther south, portions of southeast SD and northwest IA, which are very sensitive to additional rainfall, would see developing activity. This was noted in the Thompson microphysics versions of the 00Z MPAS CAMS from NSSL, so this area will continue to be monitored. ...Southwest... 16Z Update...just a note that despite morning stratus over southeast AZ, WFO TWC agrees to leave the SLGT risk as is... Previous Discussion... A continued pattern of elevated deep layer moisture will preside over much of the Western U.S as a mid-level ridge axis resides just east of the Four Corners with remnant tropical moisture situated on the western flank of the ridge. As a result, another afternoon and evening of scattered convection with access to substantial moisture across the Great Basin to the Mexican border during peak diurnal heating. Destabilization pattern is forecast during the typical climatological period between 17-01z before we see a decay in the overall environment. PWAT indices are running incredibly high across the aforementioned area with 2-4 deviations located over the central Great Basin and western CO interior with deviations closer to +4-5 within AZ leading to enhanced rainfall within any convective cells that develop. The best opportunity for more general storm clusters and organized thunderstorm development will be across Southeast AZ within the topography comprised of the Huachucas down into nearby Sonora. A pronounced theta-E ridge will extend north out of Mexico into the Southeast AZ terrain leading to targeted areas of convection that will be tied to the mountains in the vicinity. Considering the ambient environment, this will allow for local maxima exceeding 2" in some of the more prevalent storms, easily capable of causing flash flood concerns given the more complex terrain and flashy soils. The threat will extend close to the Tuscon urban center where any heavy rain threat could turn quickly into flash flooding within the urbanized setting. This prompted the continuation of the previous SLGT risk as the setup has deviated very little from the previous forecast. Further north and west, the focus for convection is a little more scattered, but the premise stands with such a moisture laden environment. Locally heavy rainfall could spell trouble for locations across the Desert Southwest with the best potential lying within the terrain centered around the Mogollon Rim into Northwest NM. Totals of 1-2" will be plausible in those affected by slow- moving convection tied to the terrain, enough to cause a flash flood concern within the terrain and surrounding locales. ...Northern New England.... Previous Discussion... A digging mid-level shortwave analyzed over Quebec will shift south into Northern New England, eventually closing off into an upper low centered across NH into ME by the afternoon hours. Focused mid- level ascent within an destabilized environment under the low will allow for a generation of convection across northern NH into ME during peak diurnal heating leading to scattered thunderstorms capable of heavy rainfall under any cell development. Storm motions will be weak thanks to being situated under the closed upper reflection, so cell cores will be able to espouse locally heavy rainfall that could bring totals upwards of 2-3" in the most prominent cell structures. Surface low pressure development over ME will drift into the Gulf of Maine creating an easterly low-level moisture feed inland which is part of the expected convergence pattern centered on the leeside of the higher terrain in central and western ME. This corridor is being depicted as the target for the heaviest precip potential with 00z HREF neighborhood probabilities for at least 2" signaling values between 60-80% encompassing the above area. The signal for 3" drops off a bit, but still has a central point of 25-35% situated across central and south-central ME. Considering the setup and convective mode for rainfall, a MRGL risk was kept from previous forecast. Kleebauer/Jackson Day 2 Valid 12Z Tue Jun 25 2024 - 12Z Wed Jun 26 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF LOWER MISSOURI AND MID-MISSISSIPPI VALLEYS... ...Central Plains through the Midwest... An overnight organized thunderstorm complex is likely to be over portions MI by 12Z Tuesday with outflow/ongoing convection over northern IL into IA. However, the 12Z consensus is for this early morning activity to be progressive from Chicago and east with an afternoon/evening round focusing ahead of a cold front associated with the low currently over the Dakotas. That places later day development over southern IA into MO/the KC metro. Therefore, the Slight Risk that was over northern IN/southern MI and Chicago has been shifted southwest of these areas. Uncertainty remains with this organized development tonight, as evidenced by the 18Z HRRR which is farther east with its track (over WI) compared to mid- morning runs like the 15Z which were move in line with a farther west solution. So positioning of the Slight Risk for Tuesday retains a fair amount of uncertainty. A plume of 1.75-2" PW from the central Plains into the Mid-Miss Valley is about 2 sigma above normal and the presence of the cold front should allow capping concerns (present today over the northern Plains) to be alleviated a bit. Please stay tuned for further updates on the area of greatest heavy rain focus, but as of now the risk areas look to be south of the northern tier areas hard hit by heavy rain in recent days. ...Southwest... Mid-level ridge across the Southwestern US will amplify up the northern Rockies from a high centered over the AZ/NM border Tuesday afternoon before drifting east through Wednesday. This will expand the convective focus area farther north in UT. PWAT anomalies are still exceptional, 2-4 deviations above normal from SoCal through the southern Great Basin, across AZ to central NM and much of UT/western CO. Slow storm motions under the ridge should allow locally heavy rainfall upwards of 1"/hr in the most substantial updrafts. Slot canyons, arroyos, burn scars, and complex topography over the interior will continue to be the zones of highest opportunity for flash flooding with any urbanized areas also residing in the threat window. Given the broad coverage of mostly isolated activity, the Marginal Risk is maintained for now. continuity. Jackson Day 3 Valid 12Z Wed Jun 26 2024 - 12Z Thu Jun 27 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR TERRAIN IN CENTRAL NEW MEXICO... ...Southwest into the Central High Plains... The focus for diurnally-driven scattered thunderstorms shifts a bit east Wednesday as the high center drifts over central NM with the axis to the central High Plains. Elevated moisture accompanies this eastward shift with PWs 1-3 standard deviations above normal across these areas. Terrain will continue to be the convective focus with the broad Marginal Risk maintained. In coordination with WFOs ABQ and EPZ, a Slight Risk is raised for central NM terrain from the Sangre de Cristos to the Sacramento Mtns where ongoing concerns with burn scars persist. A more organized convective scheme is likely over the portions of the Central High Plains as a mid-level shortwave trough approaches from the Northwest, allowing moisture to surge up the Plains later Wednesday. Organized thunderstorms are possible over the central High Plains with the focus a bit north from the previous forecast, mainly covering western Neb/KS into SD. Will continue to assess whether the Marginal Risk needs to expand north of the Nebraska Sandhills. ...Northeast through lower Mississippi Valley... A cold front progresses east and south from the Central Plains into the Ohio Valley Wednesday with organized thunderstorms likely across the Ohio Valley up through the Northeast and down over the Mid-South to the central Gulf Coast. This expansive area features elevated moisture and plentiful surface instability to allow heavy rainfall within any convective cores along and ahead of the approaching cold front. Over the Northeast, there is a combination of the approaching front and a broad area ahead of right-entrance region of an amplifying jet over Southeast Canada which will create a widespread convective setup by Wednesday afternoon into the overnight. Heavy rain with localized amounts over 2" can be expected in places where convection is most prevalent/repeating. Guidance did tick north a bit which allow the Marginal Risk to be removed for portions of the central Mid-Atlantic (which are experiencing a rapid onset drought). However, urban area sensitivity to heavy rain is not much affected by drought, so the Washington DC metro area may yet warrant a Marginal Risk. Also, progressive activity down to the central Gulf Coast warranted expanding the Marginal to the central Gulf Coast, which is in agreement with AI models such as the ECMWF- AIFS which generally handle heavy QPF footprints well (with the magnitude better depicted in global deterministics. Jackson 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