SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0253 PM CDT Thu Oct 30 2025 Valid 302000Z - 311200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON ACROSS THE NORTHERN MID-ATLANTIC... ...SUMMARY... Thunderstorms with an isolated damaging wind/tornado threat may occur across parts of the northern Mid-Atlantic through the remainder of the afternoon. ...Northern Mid-Atlantic the remainder of the afternoon... A deep midlevel low will move from the upper OH Valley to NY tonight, as an associated surface cyclone deepens from the Mid-Atlantic into New England and a trailing cold front progresses off the Atlantic coast. There is still a small window of opportunity for low-topped thunderstorms rooted near the surface, mainly across southeast PA and NJ. Weak surface-based CAPE is confined to a narrow warm sector on the nose of the midlevel dry intrusion, and there are attempts at updrafts in this zone. However, the convection is moving northward a little faster than the warm sector, and low-level shear is weaker where buoyancy is relatively maximized. Thus, only a low-end threat for wind damage and/or a weak tornado will persist for the next few hours before ending late this evening. Please see MD #2194 for additional details. Otherwise, isolated lightning flashes will be possible from parts of PA/NY into southern New England in the zone of weak elevated buoyancy and warm advection/forcing for ascent. ..Thompson.. 10/30/2025 .PREV DISCUSSION... /ISSUED 1128 AM CDT Thu Oct 30 2025/ ...Mid-Atlantic/Delmarva... A closed mid/upper-level low over the upper OH Valley will translate northeastward into the Mid-Atlantic and NY today, with a surface cold front expected to continue moving eastward across eastern NC/VA and the southern Mid-Atlantic. As a weak surface low develops northeastward into PA this afternoon/evening, a warm front will likewise attempt to lift northward across eastern PA and NJ. Cloud cover remains prevalent across the warm sector, with only filtered diurnal heating occurring in the presence of modest mid-level lapse rates (reference 12Z IAD sounding). This will temper the degree of surface-based instability which can develop this afternoon, with a notable mid-level dry slot also overspreading the southern Mid-Atlantic per recent water vapor satellite imagery. Even with these thermodynamic limitations, it still appears possible that isolated showers and thunderstorms could develop and spread quickly north-northeastward this afternoon across parts of the Delmarva vicinity into southeast PA and NJ. Strong deep-layer shear noted in recent VWPs from KDOX/KDIX may support organized updrafts with some risk for occasional damaging winds given the strength of the low/mid-level southerly flow. While low-level winds will have a tendency to veer to southwesterly with time this afternoon/evening, a brief tornado appears possible with any sustained updraft that can interact with the northward-advancing warm front. The overall severe threat will likely remain constrained by the poor thermodynamic environment. The primary change made with this update was to trim severe probabilities given the eastward/northward progression of the cold front and mid-level dry slot.
