####018008448#### FXUS61 KPHI 041420 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1020 AM EDT Sat May 4 2024 .SYNOPSIS... High pressure over New England will maintain an onshore flow through the next few days. A series of cold fronts approaches from the west through the weekend, with the second (and stronger of the two) front stalling out nearby by early next week. The stalled front lifts north as a warm front at some point in the Tuesday/Wednesday timeframe, bringing a return to above normal temperatures. && .NEAR TERM /THROUGH TONIGHT/... 10 AM update...Made some tweaks to forecast based on latest guidance, but not a whole lot changed, just nudged temps down, cloud cover up. POPs are tricky given showers seem to be progressing a bit faster than most guidance, with the GGEM being somewhat closer to reality it would appear. Even the GGEM has the first band dying out over southern NJ in the next few hours, so won't get too aggressive with POPs today just yet, especially given its quite light rain. That said, if this trend continues, might have to make some more upward adjustments across the area as the rain doesn't seem like its too eager to stop moving northeast. Previous discussion... Scattered showers continue over portions of Delmarva, though lightning has ended, and showers are not producing the brief downpours they did earlier. These showers will continue to wind down this morning. The base of high pressure centered over New England extends down into the Mid-Atlantic. An old warm front lies over the Appalachians, and a cold front is moving through the Great Lakes and into the Ohio Valley. High pressure slowly lifts to the north and east throughout the day today and into tonight. Several shortwaves will approach from the west, pushing those frontal boundaries towards the local forecast area. Some marine stratus will continue to spread over portions of New Jersey and southern Delaware. That stratus will dissipate later this morning, but skies remain cloudy through the day as showers continue to develop well west of the region. Those showers will slowly track east, not making it into the far western portions of the forecast area until late in the afternoon and early evening. A cool day with highs in the 50s to low 60s, which will be some 10 to 15 degrees below normal for this time of year. Best chances for showers will be during the overnight period tonight, mainly for inland areas as those frontal boundaries wash out as they approach. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... A cold front approaches from the west on Sunday. With a slower approach, showers will mainly be north and west of the Philly metro through the morning, before pushing over the rest of the area through the afternoon and evening. The marine airmass in place will keep things stable, and really not expecting much in terms of thunder or heavy rainfall Sunday/Sunday night. Rainfall amounts will generally be around a quarter to three quarters of an inch of rain, spread out over a rather large period, so not expecting much in terms of hydro concerns. Temperatures will be in the upper 50s/low 60s, though some spots in the Delmarva will get into the upper 60s/low 70s. Temperatures won't drop much on Sunday Night, likely staying in the 50s. For Monday, temperatures moderate as a weak west/southwesterly flow takes over. The first of several shortwaves next week is expected to traverse the area, with some showers and thunderstorms potentially developing in the afternoon and evening. Some of the model soundings show decent instability with marginal shear, so can't rule out a strong to severe thunderstorm late Monday. However, not expecting the threat to be widespread at all. Will continue to monitor as we get in range of CAM guidance. Best chance to see any convection will be over Delmarva and southern New Jersey. Temperatures will be in the upper 70s/low 80s on Monday with mid to upper 50s/low 60s on Monday Night. && .LONG TERM /TUESDAY THROUGH FRIDAY/... Unsettled conditions are expected for most of the week as a rather progressive pattern will be in place. Several shortwaves are expected to pass over the region. Lift will also be aided by a stalled boundary bisecting the area that will meander for the middle and end of next week. The front looks to venture northward on Tuesday into Wednesday, resulting in a period of above normal temperatures with upper 70s/low 80s expected. With a relatively warm and moist airmass in place, incoming shortwaves could potentially spark some showers and thunderstorms Tuesday/Wednesday PM. Wednesday afternoon/evening looks to be the most active in terms of convective weather, though too early to see if severe weather is on the table. The stalled boundary retreats southward towards the end of the week with onshore flow likely taking over, at least along the coastal plain. Depending on where this stalled boundary sets up will have implications on temperatures and thunderstorm potential on Thursday/Friday. Areas near and east of the front will be under the influence of the marine layer with cooler and more stable air, while areas west of the boundary are more unstable with warmer temperatures. A deepening trough will begin to move into the Mid- Atlantic, with a series of shortwaves/frontal systems moving through both Thursday/Friday. Both days will feature temperatures near/below normal, depending on where this lingering boundary sets up. Important to note that there remains a lot of uncertainty with the long-term forecast as models tend to struggle with a progressive pattern like this, and the placement of this boundary that will hang around through next week. As mentioned before, where that boundary sets up will have large implications on the forecast. We look to potentially shake this unsettled pattern once a sweeping cold front comes through late next week/early next weekend. && .AVIATION /14Z SATURDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of Today...Most CIGs have lifted to VFR, though MVFR/IFR conditions at KACY will remain MVFR/IFR for most of the day. Slowed progress of MVFR return, but will need to watch progress of rain as there are lower cigs further west where rain has been falling longer, though guidance mostly indicates this first round should dissipate toward midday. MVFR CIGs will spread from west to east starting at KRDG/KABE tonight. E to SE winds 10 to 15 kt. Low confidence. Tonight...MVFR/IFR conditions in stratus/BR/SHRA tonight. E winds 5 to 10 kt. Low confidence. Outlook... Sunday through Sunday Night...MVFR/IFR conditions expected with low ceilings. Reduced visibility likely with showers. Monday through Monday Night...Conditions gradually improve as the day goes on, likely back to VFR, though some showers/thunderstorms develop for the afternoon/evening, with restrictions possible if any storms move over the terminals. Tuesday through Tuesday Night...Primarily VFR though some restrictions possible with 20-40% chance of SHRA. Wednesday...Sub-VFR conditions possible (30-50%) with scattered showers/thunderstorms expected, especially in the afternoon/evening. && .MARINE... Sub-Small Craft Advisory conditions on tap today and tonight with E to SE winds 10 to 15 kt with gusts up to 20 kt and 3 to 4 ft seas. There is the potential for localized marine dense fog early this morning for areas south of Little Egg Inlet. Otherwise, mostly cloudy. Some showers may result in VSBY restrictions tonight. Outlook... Sunday through Wednesday...No long-fused marine headlines anticipated, though periods of showers/thunderstorms possible on the waters. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ SYNOPSIS...Hoeflich NEAR TERM...MPS/RCM SHORT TERM...Hoeflich LONG TERM...Hoeflich AVIATION...Hoeflich/MPS/RCM MARINE...Hoeflich/MPS/RCM ####018012301#### FXUS63 KLOT 041421 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 921 AM CDT Sat May 4 2024 .KEY MESSAGES... - A line of scattered thunderstorms is expected to cross the area late this afternoon into mid-evening, with locally strong to severe wind gusts to 60 mph possible. - Periodic shower and thunderstorm chances are expected next week. There is a potential for strong to severe storms along with a locally heavy rainfall threat on Tuesday. && .UPDATE... Issued at 921 AM CDT Sat May 4 2024 A recent hand surface analysis reveals a 1009mb surface low pressure system centered in central Iowa ahead of a cold front arcing southward across far eastern Kansas and central Oklahoma. An MCV is evident ahead of the front just to the northeast of Kansas City along the nose of a developing instability plume arcing northward along the backside of a surface high pressure system centered over southern Ontario. A narrow line of showers and storms approaching the Mississippi River continues to outpace the developing instability gradient and cold front to the west, and accordingly, should continue to decay. With that said, we can't rule out a shower survives as far east as I-39 by early afternoon. The forecast for this afternoon and evening appears to be on track. Pockets of clearing ahead of the cold front and northward-progressing instability plume will allow for steepening low-level lapse rates and eroding inhibition. As a result, showers and thunderstorms appear poised to erupt along and ahead of the front this afternoon near the Mississippi River and spread eastward into northern Illinois and eventually northern Indiana this evening (reaching I-39 in the 5 to 7 pm timeframe, Chicago metro in the 6 to 8 pm timeframe, and northern Indiana in the 7-9 pm timeframe). With the upper-level jet displaced to our north, thunderstorms will be limited to "pulse" like single-cell behavior. However, somewhat linear forcing ahead of the cold front, as well as relatively dry low- level moisture profiles, will afford efficient amalgamation of surface outflow/cold pools and support "upscale growth" of initial single-cell thunderstorms into gusty multicell clusters. While the environment doesn't appear supportive of widespread severe weather, prospects for a wall of 45-55 mph wind gusts along the leading edge of any consolidated thunderstorm outflows appears to be increasing this evening. Where thunderstorm pulses are most intense, locally damaging wind gusts of 60-65 mph may occur, as well. We'll have to keep a close eye on the integrity of the aforementioned MCV as it tracks toward central Illinois this afternoon, as it may provide just the oomph needed for a more focused threat area for damaging winds. Updated products have been sent. Borchardt && .DISCUSSION... Issued at 314 AM CDT Sat May 4 2024 Through Sunday: A retreating surface ridge extending southwestward across the western Great Lakes will give way to ongoing lee cyclogenesis ahead of a mid-level trough entering the central Great Plains early this morning. Robust convection from northern OK into western IA has likely enhanced the trough, with multiple MCVs evident along this corridor. An associated cold front just behind this convection will become the main focus for storm potential into our area later this afternoon into this evening. Surface dew point trends today will be an important factor on the coverage and intensity of storms into the forecast area. Friday's weak cold front has since stalled across central Illinois and will jump northward in response to diurnal warming and moistening today. However, the magnitude of moistening primarily from evapotranspiration remains less clear this afternoon. Current thought is daytime mixing into a very dry layer above the growing PBL will with offset rising dew points or at least reduce the depth of moisture sufficient for development and maintenance of convection. Have opted to use only scattered thunderstorm wording even as some CAMs depict higher coverage as a result of higher modeled dew points. While it is expected that a more prominent MCV currently near Omaha will lift NE within the broader mid-level steering flow this morning, the extreme southern influence of this MCV may clip the northwest CWA late this morning. Capping should remain far too high to support convection this far southeast, but isolated attempts at convection may reach as close as far northwest Illinois. Overall expectations are for a line of broken showers and storms to develop/intensify roughly along and around the Mississippi River by mid-afternoon within a pre-frontal ribbon of higher theta-e air. Coverage of thunderstorms should then begin a slow downward trend across the forecast area late afternoon through mid-evening as the drier pre-storm environment becomes less favorable with time. However, given an increasing reservoir of DCAPE with eastward extent across the CWA, the potential for strong to locally severe wind gusts may actually maximize across the west half of the CWA up to and through sunset. The antecedent dry air ahead of these storms combined with diurnal mixing of low-level moisture speaks to this wind risk, with the strongest winds likely occurring with any existing loosely organized multi-cell cluster or collapsing cores as storm intensity wanes with time. After the storms and cold front clear the forecast area by early Sunday morning, dry and cooler conditions are expected through the remainder of the period. Kluber Sunday Night through Friday: Quiet weather starts the period Sunday night, as surface high pressure is progged to be drifting east across the Great Lakes region. Farther south, guidance continues to depict mid-level short wave approaching IL late, though it is deamplifying as it moves into the short wave upper level ridge axis. Forecast soundings depict very dry low and mid-levels initially in place across the forecast area, though persistent isentropic ascent and associated warm/moist advection does eventually produce saturation and precipitation development into central IL/IN and the LOT/ILX border region after midnight. Mid-level lapse rates are unimpressive in forecast sounding guidance, suggesting little/no thunder threat. Showers are expected to persist into Monday across the southern parts of the cwa as the mid-level wave continues its transit of the area. NBM blended pop guidance appears to spread too far north in this scenario, and note that much of the EPS/GEPS/GFS ensembles are dry along/north of the I-88 corridor through the day across northern IL. Farther west, guidance continues to depict a deep upper level trough across the western CONUS, within which a strong, negative-tilt short wave develops a closed upper low over the northern high plains by Monday night. Along with a series of short waves propagating around the southeast periphery of the upper circulation and upper level diffluence ahead of a strong cyclonically-curved upper jet, this sets the stage for southerly low level warm/moist advection from the western Gulf into the mid-Mississippi Valley and upper Midwest Monday night, with a northward lifting warm front spreading into the area into Tuesday morning. Thus shower and thunderstorm chances look to ramp-up into the forecast area from the west especially after midnight and into Tuesday morning. While the primary upper/surface lows will be well to our northwest Tuesday, guidance continues to depict a strong mid-level jet is progged to spread east across the area during the day, with a surface wave developing along an occluding cold front approaching the Mississippi Valley later in the day. Combined with a warm, moist and conditionally unstable low- level air mass, additional thunderstorms (potentially strong to severe) are likely within the region Tuesday afternoon/evening. In addition to severe weather, high precipitable water values around 1.75 inches will support locally heavy rainfall will be possible especially if storms train over a particular area. SPC and WPC outlooks for Tuesday for both severe and heavy rainfall potential continue to appear appropriate at this distance. The upper trough is forecast to drift east across the upper Midwest and northern Great Lakes region during the mid and late week period, maintaining an active weather pattern across our forecast area. While the primary low-level theta-E axis will shift southeast of the forecast area Wednesday through Friday, a series of short waves rotating through the southern periphery of the upper Midwest upper low will likely produce additional periods of showers and thunderstorms, especially during the diurnally more favorable afternoon and evening hours. Temperatures will remain above average through most of the period, with daytime highs in the 70s to low 80s (Tuesday and Wednesday have the potential to be the warmest days). Cooler, more average temperatures are expected by Friday, with highs in the mid-60s. Ratzer && .AVIATION /12Z TAFS THROUGH 18Z SUNDAY/... Issued at 607 AM CDT Sat May 4 2024 Aviation Key Messages: - IFR stratus may approach KGYY from the east this morning, but should lift/scatter as it does. - Scattered gusty thunderstorms this afternoon/early evening. - MVFR ceilings likely behind a cold front late tonight into Sunday morning. - Winds become southeast this morning, then south-southwest around midday. Winds may become somewhat variable behind storms this evening, before shifting north-northeast behind the cold front tonight, and eventually northeast Sunday morning. Weak surface low pressure was over south central IA this morning, with a cold front trailing into the southern Plains. This low and cold front will move east-northeast to the western Great Lakes by early this evening, with high pressure building eastward into the region Sunday morning. Early this morning, an area of LIFR stratus/fog had developed across MI and far northern IN, and was moving west-northwest. With the sun already up and mixing commencing, expect that this will lift and scatter especially over northwest IN, though will approach KGYY as it does so. Can't completely rule out a brief period of IFR conditions there, but think the stratus deck will scatter prior to reaching the airport. Otherwise, southeast winds will eventually turn south-southwest across the terminals by midday, under thickening VFR high clouds. Earlier high-res model runs had moved the lake breeze inland through KORD and KMDW later this afternoon, but have since backed off of that solution and it now appears the boundary will remain east of those airports. Farther west, an area of showers and thunderstorms was noted across southern MN/IA and MO. Expectation is that these storms will weaken, with dissipation across southern IA/MO this morning. Scattered storms are then expected to redevelop this afternoon in the vicinity of the MS river, then push east across northern IL. Storms are expected to reach KRFD around 21Z, and the metro terminals 23-00Z, albeit in a gradually weakening state. Storms may produce wind gusts in excess of 30 kts. Winds may become a bit variable behind the storms later this evening, though the gradient would support a westerly direction. The cold front will then bring a wind shift to the north- northwest overnight, with winds eventually turning northeast Sunday morning. An extensive area of MVFR ceilings will likely follow the cold front, lingering into Sunday morning. Ratzer && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago