Convective Outlook
— Day 4-8
Discussion
All ensemble guidance suites are in broad agreement that the central US ridge will once again build westward in response to the development of a eastern North America long-wave trough during the forecast period. However, significant differences exist within and between ensembles regarding the timing and exact nature of this transition.
At the start of the forecast period, a frontal boundary will be pushing south and west in the wake of a strong short-wave trough that moved across New England in the prior days. The trend over the past 48 hours is for this front to push farther south and west, bringing a continental dry airmass into New England and portions of the Mid-Atlantic. For example, several days ago ensemble guidance was in good agreement that the front would be draped across the Mid-Atlantic on Friday. Many, but not all, of the recent runs now push the front south into southern Virginia and northern North Carolina. This results in significant uncertainty regarding the potential severe weather environment on Friday (Day 5) across the Mid-Atlantic. For example, the GEFS mean temperature for Washington D.C. is 93F on Friday afternoon, while the EPS mean temperature is 102F. However, both ensembles have dewpoint temperatures in the 50Fs.
Given the increasing uncertainty as to the location of the surface boundary on Friday and the overall quality of the severe weather environment, unconditional 15% severe probabilities for Friday are removed with this forecast. It is possible that severe probabilities may be reintroduced in later outlooks should it become apparent that the surface boundary washes out earlier than expected and quality low-level moisture is able to return sooner.
That said, the front should begin to dissipate by Saturday in response to a mid-level trough digging southeast across the Great Lakes. This will allow rich boundary-layer moisture to advect northeastward into the Mid-Atlantic and southern New England. This increase in boundary-layer moisture and strong diurnal heating will allow for afternoon MUCAPE values between 1000-2000 J/kg, perhaps locally higher on Saturday and into Sunday.
This unstable and vertically sheared environment will be ripe for thunderstorm/severe thunderstorm development ahead of any digging mid-level trough. However, as alluded to previously, the timing, magnitude, and number of these troughs is highly variable within the ensemble guidance, leading to too little confidence to pinpoint where and when unconditional severe probabilities should be added. As confidence in the timing, track, and strength of these embedded troughs becomes clear, severe probabilities will likely be needed somewhere across the region stretching from the Upper Midwest southeast into the Mid-Atlantic for one or more days.
000 ACUS48 KWNS 130907 SWOD48 SPC AC 130905 Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0405 AM CDT Mon Jul 13 2026 Valid 161200Z - 211200Z ...DISCUSSION... All ensemble guidance suites are in broad agreement that the central US ridge will once again build westward in response to the development of a eastern North America long-wave trough during the forecast period. However, significant differences exist within and between ensembles regarding the timing and exact nature of this transition. At the start of the forecast period, a frontal boundary will be pushing south and west in the wake of a strong short-wave trough that moved across New England in the prior days. The trend over the past 48 hours is for this front to push farther south and west, bringing a continental dry airmass into New England and portions of the Mid-Atlantic. For example, several days ago ensemble guidance was in good agreement that the front would be draped across the Mid-Atlantic on Friday. Many, but not all, of the recent runs now push the front south into southern Virginia and northern North Carolina. This results in significant uncertainty regarding the potential severe weather environment on Friday (Day 5) across the Mid-Atlantic. For example, the GEFS mean temperature for Washington D.C. is 93F on Friday afternoon, while the EPS mean temperature is 102F. However, both ensembles have dewpoint temperatures in the 50Fs. Given the increasing uncertainty as to the location of the surface boundary on Friday and the overall quality of the severe weather environment, unconditional 15% severe probabilities for Friday are removed with this forecast. It is possible that severe probabilities may be reintroduced in later outlooks should it become apparent that the surface boundary washes out earlier than expected and quality low-level moisture is able to return sooner. That said, the front should begin to dissipate by Saturday in response to a mid-level trough digging southeast across the Great Lakes. This will allow rich boundary-layer moisture to advect northeastward into the Mid-Atlantic and southern New England. This increase in boundary-layer moisture and strong diurnal heating will allow for afternoon MUCAPE values between 1000-2000 J/kg, perhaps locally higher on Saturday and into Sunday. This unstable and vertically sheared environment will be ripe for thunderstorm/severe thunderstorm development ahead of any digging mid-level trough. However, as alluded to previously, the timing, magnitude, and number of these troughs is highly variable within the ensemble guidance, leading to too little confidence to pinpoint where and when unconditional severe probabilities should be added. As confidence in the timing, track, and strength of these embedded troughs becomes clear, severe probabilities will likely be needed somewhere across the region stretching from the Upper Midwest southeast into the Mid-Atlantic for one or more days. ..Marsh.. 07/13/2026