Storm Prediction Center Day 4-8 Severe Weather Outlook Page (2024)

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NCEP Quarterly Newsletter

 ZCZC SPCSWOD48 ALL ACUS48 KWNS 110850 SPC AC 110850 Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0350 AM CDT Thu Jul 11 2024 Valid 141200Z - 191200Z ...DISCUSSION... An upper-level ridge will remain in place over much of the western and central CONUS through at least early next week. Multiple mid-level impulses are expected to traverse the anticyclonic flow over the northern CONUS through at least Days 4-5 (Sunday-Monday). These impulses may be accompanied by multiple rounds of strong to severe thunderstorms given continued low-level WAA/moisture advection along the eastern periphery of a regenerating EML. By days 6-7 (Tuesday-Wednesday), a mid-level trough will amplify over the Great Lakes, with a surface cold front expected to sweep southward across the northern Plains into the Northeast, promoting showers and thunderstorms (perhaps strong to severe), but also clearing out the low-level moisture, EML, and associated buoyancy in the process. ...Days 4-5 (Sunday-Monday)... Medium-range guidance consensus shows a mid-level impulse approaching the Great Lakes region from the northern Plains on Sunday (albeit later than earlier model runs). While both the latest ECMWF and GFS agree on the mid-level impulse overspreading the nose of the WAA (and associated 3000-4000 J/kg MUCAPE) over the Upper MS Valley on Sunday, the later arrival of the mid-level impulse past peak afternoon heating results in a complex forecast. The GFS depicts potential convection over the northern Great Lakes by late afternoon/early evening while the ECMWF develops precipitation over central/southern MN that rapidly progress to the WI/IL border. While it is unclear which scenario will unfold, both regimes involve organized convection traversing an axis of strong to extreme instability amid adequate deep-layer shear to support a severe threat. This includes the possibility of a severe-wind producing MCS, warranting a broad 15 percent area. Substantial modifications may be needed to this highlight in later outlooks as mesoscale details and associated placement of key baroclinic boundaries becomes evident. The latest ECMWF and GFS depicts a more pronounced mid-level trough traversing the Upper MS Valley by afternoon peak heating on Day 5 (Monday). Continued low-level moisture advection from the south, beneath a regenerating plume of steep mid-level lapse rates from the west, will support another day of strong to extreme instability overspreading the Upper Midwest. This time, stronger deep-layer shear with the better-timed mid-level impulse will coincide with the instability axis, fostering an environment favorable for severe storms. Given impacts from Day 4 (Sunday) convection, it is unclear how and where mesoscale low-level boundaries will become established over the Midwest, and these will be key to supporting a severe threat (including the possibility of severe wind-producing bow-echo MCSs). 15 percent highlights have been added over the general area where both the GFS and ECMWF agree on precipitation occurring with overlapping favorable vertical wind shear and strong/extreme instability. Like Sunday though, the highlights provided for Monday will likely need substantial modification based on later-known placement of important mesoscale meteorological features. ...Days 6-7 (Tuesday-Wednesday)... ECMWF and GFS are in general agreement in thunderstorms initiating along and ahead of a surface cold front, anywhere from the northern Plains to the Northeast states in the Days 6-7 (Tuesday-Wednesday) time frame. These storms would traverse a buoyancy axis, possibly becoming strong or even severe in the process. However, great uncertainty exists on precisely where and when the greatest severe threat would materialize, since there is more disagreement among medium-range guidance members compared to earlier days. Furthermore, details on severe placement and timing still hinge on the evolution of earlier thunderstorm events (i.e. where baroclinic boundaries are left behind). When taking into account both model disagreements and uncertainties of preceding convective influences, severe probabilities have been withheld this outlook. ..Squitieri.. 07/11/2024 CLICK TO GET WUUS48 PTSD48 PRODUCT