Administrators NorthGeorgiaWX Posted August 4 Administrators Posted August 4 SPC 1730Z Day 2 Outlook Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1233 PM CDT Sun Aug 04 2024 Valid 051200Z - 061200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM NORTHERN FL INTO EASTERN GA AND SOUTHERN SC...ACROSS PORTIONS OF THE UPPER MIDWEST...AND FROM THE UPPER OH VALLEY INTO NEW ENGLAND... ...SUMMARY... A few severe thunderstorms are possible Monday into Monday night from the Upper Ohio Valley into New England, across portions of the Upper Midwest, and from northern Florida into southern Georgia and southeast South Carolina. ...Synopsis... A belt of enhanced westerlies is forecast to extend across the length US/Canada border, from the Pacific Northwest through the northern Plains/Upper Midwest and Northeast. Several shortwave troughs will be embedded within these westerlies, the most prominent of which is a wave that is forecast to progress quickly from central Ontario through southern Quebec and northern ME. Another, low-amplitude shortwave trough is expected to move through the northern Plains, Upper Midwest, and Upper Great Lakes. Expansive upper ridging is expected to remain centered over the Four Corners, extending from the southern Great Basin vicinity through the lower MS Valley. Tropical Cyclone Debby is expected to move between the eastern periphery of the Four Corners ridge and subtropical ridging over the western Atlantic, progressing across northern FL and reaching the southeast GA/southern SC vicinity by early Tuesday morning. Surface pattern early Monday is expected to feature a low over the central SD/NE border vicinity, with a stationary front extending eastward from this low across central IA, northern IL, and southern Lower MI before arcing more northeastward along the St. Lawrence Valley to another low over New Brunswick. Eastern portion of this front is expected to progress southeastward across the Northeast throughout the day, while the portion of the front closer to the SD/NE surface low transitions to a warm front amid southerly low-level flow ahead of the low. A cold front will extend westward from the SD/NE surface low into eastern WY, where it intersects lee troughing extending across the northern and central High Plains. This front is expected to push southward across the central Plains as the low progresses eastward/southeastward through IA. ...Northern FL into southern GA and far southern SC... Tropical cyclone Debby is forecast to progress across northern FL throughout the day, reaching the southeast GA/southern SC vicinity by early Tuesday morning. Strong low-level flow attendant to this system will support the potential for tornadoes within deeper, more persistent updrafts. These updrafts are most likely in the areas where dewpoints exceed 74/75 deg F. This appears most likely across northern FL and southeast GA. However, a more westerly track would allow this more favorable low-level moisture to penetrate inland more of southern GA and perhaps even southern SC. 5-percent tornado probabilities were adjusted northward to account for this possibility. ...Northern OH Valley through the Northeast/New England... Thunderstorm development is anticipated Monday afternoon along the length of the cold front extending from ME into northern IN/OH. Dewpoints ranging from the mid 60s across central ME to the low 70s across IN/OH will support moderate buoyancy, with the strongest buoyancy across the OH Valley where greater low-level moisture exists. Moderate mid-level flow will extend across the region as well, with the stronger flow and greater vertical shear expected across New England. While there is some displacement between the strongest shear and greatest buoyancy, there is still enough overlap to support scattered strong to severe storms, including even some supercells across New England. Damaging gusts will be the primary severe hazard. ...Upper Midwest... Late afternoon/evening thunderstorm development is expected near the surface low and associated warm front moving across IA. The airmass will be very unstable, supported by temperatures in the upper 80s/low 90s and dewpoints in the mid 70s. Even so, there is some question whether true warm sector storms will initiate, given the potential for significant mixing and warm mid-level temperatures. Storms north of the warm front could still pose a severe risk, with large hail and damaging gusts as the primary threats. A surface-based, warm sector storm would have these threat as well, but with an added potential for very large hail and potentially even a tornado or two, given the potential for a supercellular mode. After the initial cellular mode, a quick transition to a more linear/forward-propagating mode is expected. ...Northern Rockies... A low-amplitude shortwave trough is forecast to move through the northern periphery of the ridge across the northern Rockies Monday afternoon. Ascent and increased mid-level moisture attendant to this wave combined with orographic ascent and deep boundary-layer mixing will help support afternoon/evening thunderstorms. Deep-layer vertical shear is strong enough to some organized, more persistent updrafts. High storm bases and steep low-level lapse rates will help support damaging gusts with the strongest storms. ..Mosier.. 08/04/2024 Read more View the full article Quote
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