####018009101#### FXUS62 KGSP 162131 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 531 PM EDT Fri May 16 2025 .SYNOPSIS... Very warm and humid conditions remain in place through tonight as a cold front sends a line of showers and thunderstorms across the area late tonight into Saturday morning. The front stalls in the vicinity of the area Saturday through early next week, keeping a relatively active pattern in place. && .NEAR TERM /THROUGH SATURDAY/... Key Messages: 1) Severe Thunderstorm Watch has been cancelled for this afternoon/evening. 2) A line of strong-to-severe thunderstorms is expected to impact the mountains late tonight, with the threat decreasing eastward. 3) Temps around 10 degrees above normal. As of 521 PM EDT Friday: The cap appears to have won the battle, with not a singel storm having initiated over the Piedmont in the last few hours, and round 1 of severe potential essentially over for the afternoon and early evening. Severe Thunderstorm Watch #261 has been cancelled. Expect quiet conditions the next few hours, as attention turns upstream, to organized convection now underway across southern Illinois and western Kentucky. Afternoon soundings there depict a more robust convective environment, with a weaker/nonexistent cap and thus a similar but more accessible parameter space. The latest hi-res guidance is remains in fairly good agreement on quasi-linear convection accelerating cross Tennessee late this evening along a robust coldpool...but likely weakening upon its arrival in the Appalachians after midnight. The big question then becomes whether convection can reorganize along the cold pool as it moves off the high terrain into the foothills and Piedmont during the pre-dawn hours. The environment east of the mountains is expected to remain largely capped...arguing against the potential for reorganization. Additionally, shear parameters are strong...and studies have shown that strong shear cam actually be detrimental for regeneration along a terrain-crossing cold pool. Nevertheless, there's more than enough uncertainty to advertise chance PoPs east of the mountains. While the main severe wx threat overnight will be from damaging wind gusts...low level shear will be adequate for brief spin-ups, mainly across the TN border counties. The cold pool will effectively push a frontal boundary through the CWA Saturday morning, leaving behind lower theta-E air (mainly manifest as lower surface dewpoints). As such, forecast soundings during the daylight hours feature much weaker instability, and CAMs develop little in the way of diurnal convection. Therefore, after some lingering token small morning PoPs, chances drop to less than 20% across most of the area during the afternoon. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... As of 130 PM EDT Friday: Most of the model guidance are in agreement with the synoptic frontal boundary completing a full fropa across the CFWA and stalling south of the I-20 corridor by Saturday evening as the vertically stacked parent low sets up shop over the northeastern CONUS. The frontal boundary will be draped from the Southern Plains through the Lower MS Valley and Deep South Saturday night as the cold front becomes reactivated when convection initiates over the Southern Plains and Ozarks Saturday evening before becoming clustered and translating east. The flow aloft becomes more progressive Sunday into Monday as a digging upper low over the western CONUS carves out a ridge over the central CONUS, while orientating the flow from the northwest to southeast across the CFWA. Early Sunday morning, the flow aloft won't be fully established, but a potential decaying MCS could make a run at the southwest mountains and Savannah River Valley. Model guidance differ with the overall evolution, with the ECMWF/CMC indicating very little SBCAPE, while the NAM/GFS show a couple hundred J/kg of SBCAPE as it slips towards the area. Kept some mentionable PoPs in this region of the CFWA as a result, while any convective debris could alter afternoon highs on Sunday, but warm thicknesses and slightly lower dewpoints (upper 50s-lower 60s) will help afternoon highs top out ~5 degrees above normal. Deep layer northwesterly flow becomes better established later Sunday as the upper ridge axis gradually shifts over the MS Valley, while an upper low churns over the western CONUS and the other upper low meanders over New England, creating an Omega-like blocking pattern. In this case, drier air will filter into the area, but convective initiation on the leeside of the western upper low and dryline across the Plains will create an assembly line for the activity to grow upscale and make a couple of MCS runs towards the CFWA during the early part of next week with the first MCS possibly tracking towards the area sometime on Monday. Confidence is low on the exact timing and placement of the MCS, but the synoptic setup is favorable and will likely throw a monkey wrench into the temperature and PoP forecast with the associated QPF response and convective debris. However, higher heights build into the area by early next week and should keep temperatures on track to rise a category or so above normal outside of the monkey wrench. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... As of 230 PM EDT Friday: The upper ridge gradually shifts further east towards the eastern-third of the CONUS, while breaking down as the upper low over the western CONUS gets pushed from behind as a Pacific Northwest jet punches in. This will disorientate the northwesterly regime, but guidance try to send one more MCS towards the region late Monday into Tuesday, but will likely hit the northern tier of the CFWA this time around or miss to the north altogether. Diffluent flow aloft becomes better establish later Tuesday into Wednesday as the ridge continues to slide eastward and the upper low deepens into a closed low, which eventually becomes established across the Great Lakes region. Expect an increase in deep layer shear as a result, which will coincide with daily diurnal instability to help instigate strong to severe storms ahead of an encroaching frontal boundary. Model guidance also show a potent shortwave rounding the base of the closed low Wednesday into early Thursday to help the frontal boundary advance eastward and complete a fropa sometime during the first half of Thursday. Drier air is expected behind the front as broad cyclonic flow aloft remains in place and low-level CAA filters in with weak high pressure, setting the stage for a post-frontal regime by the latter half of the forecast period. Northwesterly flow will commence and could produce a few orographically enhanced showers along the TN border. Continued northwesterly flow pattern remains in place through the end of the forecast period and could make the area vulnerable to another favorable MCS pattern, but likely to become more set and stone after D7. Temperatures will be at or slightly above normal Tuesday and Wednesday, before the post-frontal regime allows temperatures to fall a category or so below normal Thursday and Friday. && .AVIATION /22Z FRIDAY THROUGH WEDNESDAY/... At KCLT and elsewhere: VFR is forecast through the period. Isolated thunderstorms are possible late this afternoon near KHKY, but the probability of a storm in the vicinity is around 20%, and therefore not worthy of a TAF mention. A line of thunderstorms organizing over the TN/OH Valleys later this afternoon/evening is expected to begin weakening as it moves E/SE across east TN and western NC late this evening into the early part of the overnight. At this time, it is not clear whether this convection will hold together long enough to reach any of the TAF sites. Nevertheless, Prob30s for TSRA are warranted at most sites at some point between 06-12Z Saturday. Gusty winds are likely if the convection holds together. (Even if the convection doesn't hold together, remnant outflow boundary may still be capable of gusty winds.) Otherwise, S/SW winds are expected to increase to around 10 kts by this evening...generally persisting through tonight before increasing to 10-15 kts with higher gusts by early afternoon Sat. Outlook: The potential for mainly diurnal convection increases again Sunday, with chances continuing through the middle of next week. Early morning fog/low stratus will be possible, especially in the mountain valleys and in locations where appreciable rain fell the previous afternoon/evening. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...CAC NEAR TERM...JDL/MPR SHORT TERM...CAC LONG TERM...CAC AVIATION...JDL ####018009206#### FXUS61 KPHI 162134 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 534 PM EDT Fri May 16 2025 .SYNOPSIS... Periods of showers, thunderstorms, and humidity continue through Saturday morning ahead of a strong cold front that passes through Saturday afternoon into Saturday evening. High pressure builds into the area on Sunday and persists into Tuesday before another period of unsettled weather returns Wednesday into Thursday. && .NEAR TERM /THROUGH SATURDAY/... 530 PM update... Severe Thunderstorm Watch in effect for central and southern areas as next incoming MCS moving toward region presently. Severe warnings may be imminent for southern areas, though uncertainty about how far north and east activity can maintain strength given how well worked over the atmosphere was and because we're about to lose daylight. 4PM discussion... A second round of severe weather is possible late this afternoon and into tonight as another MCS moves east from the southern Ohio River Valley across Virginia and into the DC Metro. This MCS is expected to bring a cluster of storms across the Delmarva tonight, potentially impacting portions of southeast PA and southern NJ again. This MCS also looks to interact with the residual outflow boundary from our severe storms late this morning and early this afternoon. In fact, convection has fired up along this outflow boundary already across central PA. There remains ample untapped instability (2000-3000 J/kg CAPE) across south central PA, northern VA, and the western Delmarva Peninsula. Furthermore, skies have cleared out rapidly this afternoon, allowing for some locations to see some atmospheric destabilization again. Damaging wind gusts with some possible hail will be the main concerns, but another tornado or two cannot be ruled out with this second round of severe storms. The second round of severe potential will be around 5-9pm. Overnight, there may still be some convection ongoing into the evening but this should diminish with time leading to another brief lull. Once again, there could be some low clouds, mist, and fog that form due to the continuing moist environment. The action won't be over though because another decaying MCS may move into the area sometime overnight into early Saturday morning. There remains a lot of uncertainty on this though and depends on how storms pan out across Missouri and Kentucky tonight. Otherwise, it will be a mild, muggy night with lows mainly in the 60s. The aforementioned MCS arrives across the region around daybreak. A bit of uncertainty still remains with how strong this MCS will remain by the time it reaches the Delaware Valley, but the chance for showers and storms certainly remains possible. Skies should be partly to mostly cloudy through the morning however, before clearing out by early afternoon. Temperatures will climb into the 80s for most areas with dew points in the low to mid 60s making it feel quite uncomfortable outside. The cold front will continue to make its way east through the afternoon where isolated to scattered thunderstorms will re-develop by the afternoon. That said, the latest guidance is less aggressive with storm development Saturday afternoon. While some instability will be around, upper level forcing will be weaker and drier air aloft may limit any widespread convective initiation. As of now, storms tomorrow will likely be more isolated to scattered in nature with a marginal chance for storms to become severe. If so, gusty winds and hail will be the main concern. && .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... The cold front will push off the coast by Saturday night and the threat for storms wanes in addition to the loss of daytime heating. Nighttime lows will be in the mid 50s to low 60s. Sunday is looking like the better half of the weekend as tranquil weather returns with the upper trough moving further east. Partly to mostly cloudy skies are expected with dry conditions and lower humidity. Perhaps an isolated shower is possible north and west, but general thinking is most of the area will stay dry. The one thing to note is winds will increase as diurnal mixing occurs as the area lies wedged between systems resulting in a tightening pressure gradient. Wind gusts up 30-35 mph will be possible. Gusts will diminish into Sunday night under mostly clear skies. Despite the windy conditions, high temperatures should mainly be in the 70s (with 60s in the Poconos). && .LONG TERM /MONDAY THROUGH FRIDAY/... By Monday, low pressure over the Canadian Maritimes will begin to move further east into the North Atlantic. At the same time, high pressure will settle over the Mid-Atlantic before moving offshore on Tuesday. Aloft, the area will be situated under northwest flow in wake of exiting upper trough. All in all, a tranquil weather period is in store with mostly clear skies, light winds and dry weather. By Tuesday night and through the middle of the week, our attention will turn to our next weather system which will take aim at the area. Global and ensemble guidance both feature a deep upper trough moving into the Great Lakes/Northeast region around the middle of the week with a potential coastal low developing before moving up towards New England. This would indicate another period of unsettled weather with periods of rain starting as early as Tuesday night, and more so on Wednesday and Thursday. Still quite a ways out from this potential, so have generally stuck with NBM guidance and capped rain chances at chance (~30-50%). In terms of temperatures, we'll encounter temperatures around average on Monday, before dipping below average for Tuesday through Thursday as the area remains situated within the deep upper trough. && .AVIATION /22Z FRIDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of today...A lull in showers and thunderstorms this afternoon before another round of storms may arrive late afternoon and early evening. Second round will mainly impact all terminals except ABE. Skies will be mostly clear, but a low scattered deck may cause brief moments of MVFR/IFR conditions right over the terminals. Generally S to SSE flow less than 10 kts for the rest of the afternoon, but stronger gusts in thunderstorms. Tonight...Any showers/storms diminish through the evening with with the potential for low cigs and low visbys once again due to stratus, mist and fog. Low MVFR or IFR appears likely. More showers and storms could move in late. S to SW winds around 5 knots. Low confidence. Saturday...Sub VFR conditions possible early in the morning with showers and storms around. Otherwise, primarily VFR expected. Isolated to showers and thunderstorms possible in the afternoon afternoon and early evening. Winds WSW around 10-15 kts with gusts to 20 kts. Low confidence on showers and storms in the morning; moderate confidence otherwise. Outlook... Saturday night...VFR. Winds W to WNW 10 kts or less. Sunday through Tuesday...VFR. Gusty winds up to 25-30 kt possible on Sunday. Otherwise, no significant weather expected. && .MARINE... Generally sub SCA except storms tonight into early Saturday morning could produce locally strong winds. A few isolated showers and storms possible Saturday afternoon. SW winds gust to around 15-20 kts in the afternoon, but no headlines expected. Outlook... Saturday night...No marine headlines expected. Sunday through Sunday night...SCA conditions possible due to wind gusts up to 25 kt. Monday through Tuesday...No marine headlines expected. Rip current... Currently projecting low risk of rip currents over the weekend based on low wave heights of 1-2 feet and winds shifting offshore at 10-15 mph. && .TIDES/COASTAL FLOODING... The Coastal Flood Advisory for northwestern Burlington and lower Bucks Counties has been extended until 8 AM Saturday. Minor coastal flooding is expected with the early morning high tide this morning and on Saturday. It's possible minor coastal flooding may occur on Sunday as well, where further extensions may be needed. For areas of the lower tidal Delaware River near Philadelphia may encounter spotty minor coastal flooding through Saturday, but should fall short of advisory levels. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Coastal Flood Advisory until 8 AM EDT Saturday for PAZ106. NJ...Coastal Flood Advisory until 8 AM EDT Saturday for NJZ019. DE...None. MD...None. MARINE...None. && $$ SYNOPSIS...MJL NEAR TERM...Fitzsimmons/MJL/RCM SHORT TERM...DeSilva LONG TERM...DeSilva AVIATION...DeSilva/Fitzsimmons MARINE...DeSilva/Fitzsimmons/RCM TIDES/COASTAL FLOODING...