Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
870 FOUS30 KWBC 140053 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 853 PM EDT Sat Jul 13 2024 Day 1 Valid 01Z Sun Jul 14 2024 - 12Z Sun Jul 14 2024 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE UPPER MIDWEST, FOUR CORNERS REGION, AND SOUTHWEST... ...Upper Midwest... ...0100 UTC Update... Very few changes made to the previous Marginal Risk area based on the latest observational and mesoanalysis trends, along with the more recent HRRR, HREF, and RRFS deterministic and probabilistic guidance. Pre-frontal QLCS currently diving through southeast MN and southern WI. Behind it, another swath of convection closer to the surface front is trying to grow upscale across far eastern SD and northwest MN, where mixed-layer CAPEs remain a robust 2000-3000 J/Kg. The latest high-res guidance maintains a heavy rainfall threat through the overnight, albeit based on the spread in the CAMs with QPF, and the isolated nature of the 2-3+ inch totals, expect the risk for flash flooding to remain localized. ...Four Corners into parts of the Southwest... ...0100 UTC Update... Expanded the Marginal Risk considerably based on the current radar and satellite trends, along with the latest mesoanalysis profiles. Monsoonal moisture is responsible for TPW and 850-700 mb moisture flux anomalies between 2-2.5 standard deviations above normal across interior CA and the southern Great Basin. Based on the latest HREF and RRFS probabilities of 1 hr QPF >0.50", expect the flash flood risk to wane considerably after 0300Z. Hurley Day 2 Valid 12Z Sun Jul 14 2024 - 12Z Mon Jul 15 2024 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE NORTHERN PLAINS AND THE GREAT LAKES AS WELL AS FOR PORTIONS OF THE SOUTHWEST... ...20Z Update Summary... MRGL risks across the northern tier of the U.S and the Southwestern U.S were maintained with some modest adjustments based on the updated probability fields from the HREF/NBM, as well as the overall QPF footprint from the global blends and ensemble bias correction guidance. ...Northern Plains and Great Lakes... Current MRGL risk area within the Northern Plains to Great Lakes region was generally maintained outside some minor adjustments on the southern and western flank of the risk area. Several shortwaves and smaller mid-level perturbations will ripple through the flow with the 5H trough axis aligned from central ND and points southeast. A couple areas currently stand out as the primary regions of interest within the broad MRGL risk area. The first across southern Lake Michigan over Southeast WI through Southern MI where the the expected complex at the end of D1 is anticipated to move towards leading initial impact on D2. Forward propagation speed is still expected to be on the quicker side, so this could limit the flash flood aspects considering the deep moisture presence to be somewhat tame (+1 standard deviation PWATs) compared to what we`ve seen in the past. The key will be for any MCV development that provide more of a targeted area for persistent, heavy rainfall returns. As of now, the general pattern looks to yield more 1-2" rainfall in the corridor of impact with the higher end at 3" given the low-end neighborhood probabilities for the 3" marker (15-25%). This typically correlates with a solid MRGL risk, just on the edge of a SLGT towards the southeast areas off Lake Michigan. Further upstream, a stronger mid-level shortwave will enter into northern ND as it pivots southeast out of Canada creating a more dynamic environment capable of stronger storms with better shear and large scale ascent. Areal PWATs are still not as favorable compared to what you would want to see for higher impacts, however the threat for a quick 1-2" is possible over the Northern Plains between Bismarck and Grand Forks up to the Canadian border. Current UFVS based First Guess fields remain insistent on the MRGL, but would not be surprised for a small, targeted SLGT risk as we enter into D1. 1hr and 3hr FFG exceedance probabilities are still on the lower end for the potential, but any uptick in the signal could induce the upgrade if the overall synoptic setup persists. Kleebauer ...Southwest... Atmospheric moisture will increase across the region as compared to today by Sunday. This will result in both an increase in coverage and intensity of the resultant storms across this area today. That said, the trends in the guidance have been flat. There`s somewhat higher certainty that storms will concentrate along the Mogollon Rim of Arizona, so that region is in a higher- end Marginal with potential for an upgrade to a Slight with future updates. Isolated to scattered convective signatures will also be present over the southern edge of Pima and adjacent Santa Cruz counties as monsoonal convection ignites over Sonora with outflow generation moving northward towards the border with some convective redevelopment across the above areas. A few of the CAMs are more robust over for convective development with heavy rain signatures that would be conducive for flash flood concerns in the complex terrain embedded within the southern parts of the above counties. That will be a setup to monitor as thunderstorm risks stemming from Mexican outflows is very variable and can easily be a boom or bust type scenario when it comes to expected rainfall. Elsewhere to the north over northern AZ/NM into UT/CO will be isolated flash flood concerns due to the location of slot canyons that will be most susceptible rapid onset flooding. Coverage is pretty isolated at this time given the forecast, but a targeted upgrade may be warranted if radar trends allow. Wegman/Kleebauer Day 3 Valid 12Z Mon Jul 15 2024 - 12Z Tue Jul 16 2024 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE UPPER GREAT LAKES AND FOUR CORNERS REGION... ...20Z Update Summary... Only minor changes were made to the orientation of both inherited MRGL risk areas across the Great Lakes and Southwestern U.S. ...Upper Great Lakes... The threat across the lakes is subject to a lot of convective variability with several shortwaves still traversing the region with multi-cell clusters and the occasional MCS making an appearance that would provide a local uptick in the precip seen during the period. There is a hint that a more organized convective regime may develop in-of southern Lake Michigan with a cold front advancing overhead allowing for a better surface convergence pattern working with favorable environmental shear and mean flow shifting more parallel to the boundary creating an axis of for potential training. This is becoming a little better defined within the deterministic output and is expressed in the ensemble QPF footprint with a QPF max generally positioned over Northern IL into Southwest MI. This would be the area for a SLGT risk if the conditions remain favorable and the synoptic evolution doesn`t change with regards to frontal positioning and timing. Those details will become more focused in time, so updates could very well have an upgrade in future forecast packages. For now, continuity was chosen given the questions of variability and potential shifts in the synoptic pattern. Kleebauer ...Four Corners... Monsoonal flow may shift a little bit east away from northwestern Arizona and southern Utah and focus closer to the AZ/NM border while extending north across much of central Colorado. Storms that form will once again likely be tied to the terrain, which with burn scars may result in locally significant flash flooding if the storms are strong enough and remain stationary, but with still minimal organization there is not enough certainty to upgrade to a Slight at this time, but the potential is there for future updates. Wegman 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