####018008816#### FXUS63 KLSX 040356 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1056 PM CDT Fri May 3 2024 .UPDATE... Issued at 1036 PM CDT Fri May 3 2024 Regional satellite shows skies are clearing over small envelope of the mid-Mississippi Valley, as surface ridging extends from the Great Lakes Region through southeast Missouri. Surface observations show winds range from calm to light and variable through much of the area. These conditions, along with recent rainfall, have provided ample surface moisture resulting in dewpoint depressions that range of 0 to 3 degrees over far southern sections of the CWA. Hi-res soundings plot shallow inversion developing through the early morning hours, which should support the development of patchy fog as far north as I-70. Fog could have greater spread and become dense for a few hours through early Saturday morning over southeast Missouri through sections of southwest Illinois. This has prompted the issuance of a dense fog advisory through 14z. Maples && .KEY MESSAGES... - Isolated strong to severe thunderstorms are possible from 2pm to 7pm Saturday. Hazards include up to 60 mph winds and up to quarter sized hail. - Confidence is increasing in a multi-day severe event taking place in the central U.S early to mid-next week. However, there is still uncertainty regarding details like timing, exact location, and how one day's thunderstorms will impact the next day's severe potential. && .SHORT TERM... (Through Late Saturday Night) Issued at 249 PM CDT Fri May 3 2024 Thursday night/Friday's cold front will continue to slowly buckle northward through the bi-state tonight as a quasi-stationary boundary. Meanwhile, a mid-level shortwave and surface cold front will push east through the Plains, arriving in Mid-Missouri early Saturday afternoon. This system will push the boundary to the northeast and leave us within its warm sector. Because of this, temperatures Saturday will be much warmer than they were today, reaching the mid-70s to mid-80s. Moisture will also pool into the area, mostly along and just ahead of the incoming cold front. Instability will be maximized here with SBCAPE values of 1500-2000 J/kg. Deep layer shear will be lacking, though, ranging from 20-30 kts. Modest CAPE and bulk shear values are expected to result in a severe weather threat much like yesterday - disorganized clusters of outflow dominant cells. Although we're confident in thunderstorm development, strong to severe thunderstorms are expected to be isolated in nature due to them being outflow dominant and likely quick to intensify and even quicker to die. The greatest potential for severe weather will be between 2pm and 7pm as the front is passing through the CWA. In any thunderstorms that become severe, damaging winds of up to 60 mph and up to quarter sized hail are possible. We're confident in the end time of the severe potential, as the front will be close to exiting to the southeast, and that coincides with the downfall of daytime instability. With the lack of appreciable shear, diminishment in instability will be detrimental to the life of any thunderstorm. Saturday night will be relatively chilly for portions of the areas surface high pressure passes to our north. Areas in northeast Missouri and west-central Illinois are forecast to fall into the upper 40s. To the south, further from the influence of the high and under more dense cloud cover, low temperatures may not fall under 60 degrees. Jaja && .LONG TERM... (Sunday through Next Friday) Issued at 249 PM CDT Fri May 3 2024 Sunday will be a relatively quiet opening to the week, almost literally the calm before the storm as we face a potential multi-day severe event between Monday and Wednesday. Despite the relative quiet, wet weather is expected beginning Sunday afternoon and continuing into overnight. This is due to a shortwave passing through the Mid-Mississippi Valley from the southwest and driving a weak surface low through our CWA. This surface low will cause Saturday's remnant cold/stationary front to buckle back north as a warm front with showers with embedded thunderstorms along it and within the system's warm sector. Severe weather is not expected, even earlier in the afternoon, due to weak lift, weak moisture convergence along the front, mid-level subsidence, and minimal instability (<250 J/kg MUCAPE). High temperatures Sunday will be near normal, landing in the 70s areawide. Monday kicks off the potential for multiple days of severe weather extending from the central and southern Plains into the southwestern Great Lakes and western Ohio Valley. A deep mid-level closed low will be responsible for this as it ejects northeast into the Plains on Monday. At the surface, two low pressure systems will develop lee of the Rockies, advecting warm air and moisture into the region ahead of a dryline and developing cold front. The dryline will act as a trigger for convective initiation in the Plains on Monday. On Tuesday, the system as a whole will be further east, and a shortwave and vorticity lobe will swing through our region. The cold front will be further east as well, shifting the severe threat into our area. Guidance across the board is in consensus that instability, deep layer shear, moisture, and synoptic level dynamics will all be favorable for severe weather on Tuesday and again on Wednesday as the cold front continues its eastward advancement. With the environment that may be in place, no hazard can be discounted at this point. Of course, this multi-day event begins four days out from now, so there's uncertainty to discuss. Firstly, although WPC cluster analysis shows consistency amidst guidance in the mid-level trough/closed low early next week (positioning, strength, size), there are differences in the phasing that impact the mid-level flow and thus impact the timing of the overall system. For a multi-day system like this, a faster or slower passage of the system could increase or decrease our potential for severe and/or lengthen or shorten our window for it. A faster frontal passage may shift Wednesday's severe threat further east and out of our CWA, whereas a slower frontal passage may extend our severe threat into Thursday. There's also the question of how/if severe weather to our west impacts our severe weather threat for the following day (Monday into Tuesday and Tuesday into Wednesday). Overnight low-level jets may cause ongoing convection to continue into the next morning, potentially dampening the potential for severe that day. The opposite scenario is also equally as likely - thunderstorms dying in the evening could lay down outflow boundaries and open up the potential for rapid destabilization the next day, increasing our chances for severe. All of this to say despite the very favorable synoptic set-up for severe, there's still plenty of variability that could sway our severe potential and its timing. Jaja && .AVIATION... (For the 06z TAFs through 06z Saturday Night) Issued at 1036 PM CDT Fri May 3 2024 The only change since the last TAF update is the increasing potential for fog development early Saturday morning. The potential for dense fog should remain over southeast Missouri and far southwest Illinois. However, patchy fog could develop as far north as I-70, including the metro terminals. The sites to monitor will be KSUS/KCPS, as recent observations show winds have gone calm at KSUS. TAFs do not include the mention of fog, but may later be amended if trends continue in this direction. The main impact will stem from thunderstorm potential Saturday, progressing west to east along and ahead of an advancing cold front. Thunderstorm potential still look highest after 18z through about 00z. Cloud bases remain at VFR level through much of the period until the cold front pushed through Saturday evening, at which time a brief period of MVFR ceilings are likely to accompany the front. Outside of this, any conditions lower than VFR will depend on direct impacts from thunderstorms. Maples && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Dense Fog Advisory until 9 AM CDT Saturday for Iron MO-Madison MO-Reynolds MO-Saint Francois MO-Sainte Genevieve MO. IL...Dense Fog Advisory until 9 AM CDT Saturday for Randolph IL- Washington IL. && $$ WFO LSX ####018007635#### FXUS61 KPHI 040357 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1157 PM EDT Fri May 3 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/... No significant changes to prior forecast. Will make some adjustments based on the latest obs. The current forecast continues to remain challenging due to pesky marine layer over the Coastal Plain. An expansive ridge of high pressure is building into eastern Canada with the southwestward periphery of this feature extending back into the Mid-Atlantic. In fact guidance actually depicts this feature strengthening slightly over our area during the next 24 hours. Meanwhile though, this ridge has resulted in easterly flow that has brought in a low deck of some marine stratus into much of NJ, DE, and even extending at times into portions of eastern PA. Finally, there is a frontal system that's approaching from the west with some showers however, it will take some time for these showers to get into the area over the weekend as it runs up against the ridge in place. The upshot of all this is that skies are variable across the area with the marine stratus eroding back to the east while high cirrus continues over western areas. Regardless, it will remain precip free though through the evening. Overnight, however, shortwave energy will ride over the top of the upper level ridge centered over the east and help to push showers from the west closer to the region. This could bring a few light showers into parts of Delmarva and eastern PA by daybreak. Otherwise, clouds thicken through the night with lows getting down mainly into the upper 40s to around 50. For Saturday, low pressure moves eastward towards the Great Lakes driven by an advancing upper level trough. As this occurs, showers well ahead of it will continuing to try making inroads into our area while running up against the stubborn surface high that will be slow to move out. The upshot is some scattered showers will likely make it in at times, especially over eastern PA and Delmarva and especially getting into the second half of the day (POPs here by late day generally 40 to 60 percent). Otherwise it will be a mostly cloudy and cool day with continuing easterly winds and highs only making it to the upper 50s to low 60s. && .SHORT TERM /SUNDAY THROUGH MONDAY/... Saturday night will featured continued marine flow from the east as the approaching front from the west washes out. Thus, expect areas near the coast to be mostly dry and cool, with a better chance of showers inland due to the nearby stalled front. Lows mostly in the upper 40s. Next, stronger front approaches from the west Sunday, but its approach looks slower, so have slowed the progress of higher POPs into the area. Looks like best chance of widespread showers is late day and at night Sunday night. With the marine layer likely to hold fairly firm, chance of thunder looks minimal, and severe weather risk appears zero. Highs 50s north, 60s south, perhaps near 70 far southern DE and adjacent parts of MD. Rain showers move out on Monday morning, though again opted for slower timing given trend. Marine layer looks like it is at least somewhat disrupted as flow turns westerly and a warm front tries to lift north, allowing temps to potentially rise to the 70s for most and near 80 southern DE/adjacent MD. Guidance now wants to generate some convection in the afternoon, and given the warmer and more humid air mass, its not out of the question we have a few stronger cells, but at this point there doesn't appear to be a significant severe wx or flood risk. && .LONG TERM /MONDAY NIGHT THROUGH THURSDAY/... Unsettled weather continues through the week ahead. The front that lifts north thru the area Monday doesn't get far, and looks to even slide back south a little Tuesday, though at this point still looks likely mostly 70s. Another approaching shortwave and proximity of the front could spark off a shower or t-storm, but right now looks like low coverage. Front lifts a little further north behind that shortwave Wednesday, allowing temps to rise a bit. With it remaining nearby and another front approaching from the north, the odds of some aft/eve convection increases a bit. Highs closer to 80. Guidance is trending towards the return of a marine layer behind said front for Thursday and Friday, with a cooling trend in temps. A passing wave may produce some better shower coverage Thursday as well, so we have highest POPs in the long term on Thursday. Friday trend is a little drier but still a marine influence. It should be noted that with the wavering front nearby all week and several weak waves, its possible the details of the forecast are notably different from how they currently appear, so check back for updates frequently. Guidance is very mixed presently. && .AVIATION /04Z SATURDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...Different conditions expected for each terminal tonight. For KRDG/KABE, expect VFR through 05-06Z, before becoming MVFR CIGs after 07-08Z. For KTTN/KPNE/KPHL/KILG, expect a mixture of VFR/MVFR CIGs through 07-08Z, before becoming MVFR CIGs after 08-09Z. For KMIV/KACY, expect MVFR CIGs through 05-06Z, becoming IFR CIGs after 06Z. East winds around 3-8 kt. Low confidence, especially with the timing of lowering ceilings. Saturday...Mainly MVFR for all terminals. There is indication a brief period of VFR CIGs are possible during the afternoon for all terminals except KMIV/KACY. Otherwise, just some scattered showers. East-Southeast winds around 8-13 kt. Moderate confidence. Outlook... Saturday Night through Sunday Night...Restrictions expected with showers moving through, with CIGs as low as IFR possible. Best chance of showers is late Sunday/Sunday night. Monday through Wednesday...Primarily VFR though some restrictions possible with any showers. 20-40% chance of showers through this period. && .MARINE... Seas at 44009 are subsiding to less than 5 feet, so will cancel the Small Craft Advisory that was set to expire at midnight. Winds will continue to diminish to 10 to 15 knots and seas around 3 to 4 feet. Little change is expected on Saturday. There is the potential for some dense marine fog early Saturday morning especially south of Little Egg Inlet, otherwise, just mostly cloudy skies are expected. Outlook... Saturday night through Wednesday...No marine headlines anticipated. Showers/thunderstorms possible on the waters Sunday through Sunday night. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ SYNOPSIS...Fitzsimmons/Hoeflich/RCM NEAR TERM...DeSilva/Fitzsimmons/MPS SHORT TERM...RCM LONG TERM...RCM AVIATION...DeSilva/Fitzsimmons/MPS/RCM MARINE...DeSilva/Fitzsimmons/MPS/RCM ####018005788#### FXUS63 KDTX 040357 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1157 PM EDT Fri May 3 2024 .KEY MESSAGES... - High pressure fills in Saturday supporting mainly dry conditions ahead of the next weak cold front to bring showers and a few thunderstorms to SE MI late in the day through Sunday. - Seasonably warm temperatures expected through early next week with high temperatures in the low to mid 70s and lows in the 50s. && .AVIATION... The late afternoon and evening band of showers collapsed with the cold front while exiting into Ontario leaving the forecast up to clouds and fog late tonight through morning. Weak high pressure on an axis across northern Lake Huron and northern Lower Mi maintains a flow of cool and moist NE wind into SE Mi augmented by the cold water of Lake Huron. Just enough pressure gradient remains for wind speed in the 5 to 10 kt range favoring borderline LIFR/IFR stratus with a lighter fog component overall. The stratus plume expands westward from remnants of the cold front mainly affecting PTK, FNT, and MBS. NE wind direction aligned with the Ontario peninsula guards the DTW corridor from more than stray coverage. Wind veering SE directs clouds into western/northern Lower Mi during the morning while following a standard diurnal trend into a low end broken VFR ceiling for the afternoon. A stray shower is possible late in the day and closer to the interior of Lower Mi as Friday's cold front stalls in Ohio and then moves back northward as a warm front into Saturday evening. For DTW/D21 Convection... Thunderstorms are not expected late tonight through the morning. Very low potential for a thunderstorm with limited coverage by late afternoon precludes a mention in the forecast at this time. DTW THRESHOLD PROBABILITIES... * Low for thunderstorms late afternoon and Saturday evening. * Moderate for ceiling 5000 ft or less late tonight and high by afternoon. && .PREV DISCUSSION... Issued at 346 PM EDT Fri May 3 2024 DISCUSSION... Broken line of showers currently extends from roughly Saginaw to Coldwater, with no observed lightning activity at issuance. Instability has been the main limiting factor thus far, with MLCAPE holding aob 250 J/kg and observed temperatures generally in the mid to upper 60s. Pockets of sunshine ahead of the line may increase instability enough through the evening to support a few embedded thunderstorms, but for now storm tops have struggled to even reach the freezing level. Slow eastward progression of the line (15-20 mph) and waning instability after 00z with loss of diurnal heating may prevent the line from even getting to easternmost portions of the cwa. Post-frontal subsidence introduces a deep layer of static stability to the column overnight, most prominent near the Tri Cities and Thumb. In these locations, patchy fog is expected especially as onshore flow emerges from Lake Huron. Elsewhere, weaker inversion and poor decoupling signal suggest stratus or more localized fog development Saturday morning. Otherwise, a drier day is in store Saturday for SE MI. Upstream, a surface low lifts toward Lake Superior which effectively draws the theta-e axis back into lower Michigan by Saturday afternoon which boosts temperatures into the mid 70s. The boost to boundary layer conditions will be enough to build surface-based instability, but any convective initiation will depend on localized convergence or lake breezes. So at this point, just a stray shower or thunderstorm will be possible Saturday afternoon. Broader convective coverage is expected early Sunday morning as the surface low sweeps another cold front across the cwa. Persistent lack of mid-upper level jet support and modest elevated instability suggest showers and a few thunderstorms to be possible Sunday morning before clearing out by mid-day. Mid-level ridging then holds steady through middle of next week ahead of a strong Pacific disturbance which will be the next opportunity for widespread precipitation. High temperatures will remain comfortably in the 70s as an open Gulf and southwest flow keep conditions above average for early May standards. MARINE... A line of showers will continue to work east across the central Great Lakes this afternoon as a weak cold front pushes through. Isolated thunderstorms are possible, but severe storms are not expected. Light northeast wind will occur behind the front tonight with mainly dry conditions as a localized area of high pressure builds in. Will monitor observational trends over Lake Huron where conditions may be favorable for areas of dense marine fog to form overnight into Saturday morning. Winds then gradually organize out of the southeast on Saturday as the high departs east. Southerly winds up to 20 knots develop Saturday night ahead of the next cold front that will sweep through on Sunday. Scattered showers and storms will accompany the front with winds turning northwesterly behind it Sunday afternoon. High pressure then builds in to bring quiet marine conditions for the early work week. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...Dense Fog Advisory until noon EDT Saturday for LHZ361>363-421-422- 441>443-462>464. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....BT DISCUSSION...MV MARINE.......TF You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.