####018004548#### FXUS63 KILX 040516 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 1216 AM CDT Sat May 4 2024 .KEY MESSAGES... - Near daily chances for showers and thunderstorms over the next week as a series of fronts advance across the region. The Tuesday through Wednesday period looks particularly active, with medium confidence in thunderstorms capable of producing all severe weather hazards. && .UPDATE... Issued at 917 PM CDT Thu May 2 2024 The surface ridge axis has made eastward progress into Illinois this evening, helping to nudge high clouds eastward into Indiana as well. The back edge of the clouds is mainly covering counties along the Indiana border as of 9 pm, with additional clearing expected in the next few hours. Light and variable winds are expected overnight, under the weak pressure gradient. The main concern is for a possible need to expand the patchy fog across more of our counties than just our far southeast 6 counties south of I-70. There doesn't appear to be enough support in the high res guidance at this point to do that, so will leave the fog coverage as is. Only minor updates were done to sky and wind grids. The remainder of the forecast database remains on track. Shimon && .DISCUSSION... Issued at 127 PM CDT Fri May 3 2024 Current GOES WV imagery depicts a strong upper-level low positioned over western Ontario with more subtle shortwave energy ejecting out of the Great Basin. Model guidance remains in excellent agreement that shortwave energy lifts into the Northern Plains and Upper Midwest regions overnight, ultimately helping to force a synoptic cold front into western Illinois Saturday afternoon. A plume of low-to-mid 60s dewpoints is progged to advect northward ahead of the cold front, and SBCAPE values should be able to achieve 1000-1500 J/kg with CINH eroding in the presence of steep 0-3 km lapse rates (> 7.5 C/km). This all adds up to likely (> 60% chance) thunderstorm development Saturday afternoon along and ahead of the cold front. Coverage of Saturday storms could be limited by somewhat underwhelming deep-layer shear profiles, with much of the area at or below 30 kts in the vicinity of the cold front. Updrafts may struggle to become organized or struggle to stay organized, especially some of the early updrafts, and recent CAMs hint at this as well. Nevertheless, CAPE/Shear profiles are just good enough to support the potential for an isolated severe hail and wind threat. As storms move toward and east of I-55 Saturday evening, the severe potential should gradually fade. This will largely be due to the loss of daytime heating and the lack of a LLJ to help augment instability. This thinking lines up well with SPC's Day 2 Marginal Risk, which ends the threat near the I-57 corridor. Flooding should not be a concern with the Saturday storm event. NBM Mean QPF is around 0.25", and this guidance only offers a 10% chance that rainfall exceeds 0.75", which is well below 3-hour flash flood guidance. The rest of the weekend through Monday should be fairly low drama, with the main frontal zones displaced just to our south. Attention quickly turns to the Tuesday - Wednesday timeframe as persistent, deep southwest flow envelops the region ahead of an elongated upper-level low. While we're running lean on details at this timeframe, the synoptic pattern (kinematics/thermodynamics) being modeled supports a multi- day severe weather threat across portions of the Plains and Midwest. This strong signal in the global models is also reflected in the analogs and machine learning tools for severe weather potential. MJA && .AVIATION... (For the 06z TAFs through 06z Saturday Night) Issued at 1216 AM CDT Sat May 4 2024 VFR conditions will prevail in the near term through mid afternoon on Saturday, under surface high pressure. A non-zero chance of light fog at our eastern TAF sites of DEC/CMI, but better chances of MVFR/IFR fog should remain south of I-70. A weakening line of thunderstorms is projected to impact (70% chance) the western TAF sites (PIA/SPI/BMI/DEC) during the late afternoon through mid- evening time frame, with primarily a 2-3 hour window of thunder. More isolated thunder chances (20%) at CMI. Shimon && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$ ####018005714#### FXUS61 KALY 040517 AFDALY AREA FORECAST DISCUSSION National Weather Service Albany NY 117 AM EDT Sat May 4 2024 .SYNOPSIS... High pressure will provide continued dry conditions through tonight. The high will only move slightly east off the coast through Saturday, with a frontal system slowly approaching from the west. Clouds will increase on Saturday, with chances for showers developing west of the Hudson Valley. Showers will become more likely by Sunday as the system tracks east across the area with cool temperatures. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... .UPDATE...Made some minor adjustments based on current obs. Only chance for a few light showers through the rest of the night will be across the far NW Adirondacks, otherwise dry conditions will persist. Some patchy low stratus clouds may develop in some spots mainly east of the Hudson River, but should be rather sparse in coverage. Mid level clouds will gradually spread eastward from central NY through the night, so did increase cloud cover in the forecast especially west of the Hudson Valley. .PREV DISCUSSION[1006]...An upper level ridge axis will be directly overhead tonight. High pressure off the New England coast will bring largely dry weather across the region with just some patchy mid and high clouds. Forecast soundings and the 00z KALY sounding shows rather dry air in the low-levels, so low cloud development later tonight looks fairly isolated. While most of the precipitation will remain to our west tonight, a few sprinkles may reach portions of Herkimer County after midnight. Temperatures have fallen into the 50s to lower 60s in most areas and remain on track to dip into the 40s to around 50 by daybreak. Light winds and just thin high clouds will allow for some radiational cooling. Lows by daybreak Saturday in the 40s to around 50. && .SHORT TERM /6 AM THIS MORNING THROUGH MONDAY/... The axis of deeper moisture associated with the upper energy and associated warm and cold front will slowly approach through the day Saturday. Sources of guidance/ensembles suggest the leading edge of the deeper cloud cover and any rain is timed for very late Saturday afternoon and night. This suggests more periods of high clouds through the day with steady light south to southeast winds and highs in the 60s to around 70. Showers move into our region from southwest to northeast through the night Saturday night and by daybreak Sunday many areas will see showers. Depending on the timing, the onset of showers in the Capital Region and points north and east may be after daybreak Sunday. Then, clouds and showers across the entire region Sunday, limiting warming. There could be a rumble of thunder but chances are low with a lack of instability. Highs mainly in the 50s Sunday. Rain moves out Sunday night and there cold be a lingering early morning shower Monday. Then, weak cold advection begins with the exit of the upper system and cold front Monday. Highs Monday in the 70s with 60s higher terrain. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... Dry weather continues Tuesday with highs in the 70s. Increasing clouds through the day, with around 70 higher terrain and near 80 mid Hudson Valley and NW CT. By Wednesday through the rest of next week, split upper flow with northern stream upper energy slowly dropping out of Canada and a closed upper low slowly approaching from the northern and central plains. Confluent upper flow and associated moisture advection and low level jet forcing will result in showers and a possible rumble of thunder Tuesday night through Friday. There will be some periods of dry weather but there is a lot of spread in sources of guidance as to the timing of embedded smaller upper impulses and associated focused moisture, low level forcing and areas of showers. Still, the general upper pattern should support unsettled weather. So, again, indicating chances for showers Tuesday night through Friday. The threat for severe weather and/or heavy rain looks limited due to the relatively weak upper dynamics and weak low level forcing. Highs Wednesday in the 70s with 60s higher terrain. Highs Thursday in the 60s to around 70. Highs Friday in the 60s with near 70 mid Hudson Valley and NW CT and some 50s southern Adirondacks. && .AVIATION /05Z SATURDAY THROUGH WEDNESDAY/... Through 00z/Sun...VFR conditions are in place at the TAF sites and look to remain VFR through the upcoming TAF period. High pressure off the New England coast and upper-level energy to our west will bring occasional clouds across the TAF sites, but cigs should remain at or above 5 kft much of the period. Low cloud development looks less likely tonight but will monitor trends. Wind will be southeasterly for much of the TAF period at 4-8 kt tonight and around 10 kt on Saturday. Outlook... Saturday Night: Moderate Operational Impact. Likely SHRA. Sunday: High Operational Impact. Definite SHRA. Sunday Night: High Operational Impact. Likely SHRA. Monday: No Operational Impact. NO SIG WX. Monday Night: No Operational Impact. NO SIG WX. Tuesday: No Operational Impact. NO SIG WX. Tuesday Night: Moderate Operational Impact. Chance of SHRA. Wednesday: High Operational Impact. Likely SHRA...TSRA. && .ALY WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. MA...None. VT...None. && $$ SYNOPSIS...NAS NEAR TERM...NAS/JPV/Rathbun SHORT TERM...NAS LONG TERM...NAS AVIATION...Rathbun ####018009911#### FXUS63 KLMK 040518 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 118 AM EDT Sat May 4 2024 .KEY MESSAGES... * Isolated shower and thunderstorm possible this afternoon. Slow moving storm motion and moderate to heavy rain expected with any storm. * Showers and thunderstorms will be more scattered on Saturday, though forecast confidence in exact timing and coverage remains low. * Increasing potential for strong to severe thunderstorms and flooding next Tuesday through Thursday, though confidence in details is still low. && .UPDATE... Issued at 944 PM EDT Fri May 3 2024 As of 0130z, WSR-88D continues to show a few lingering isolated showers and thunderstorms, mainly over the Bluegrass. Weak sfc low and associated inverted sfc trough will continue to push east. Given the rain from this evening, high PWAT values around 1.50" and dew points in the low/mid 60s some patchy fog as well as drizzle associated with low stratus is possible during the overnight. Only made a few minor adjustments to the grids and the forecast to account for the patchy fog and updated PoP grids to account for some isolated light rain and or even a possible brief rumble of thunder. && .SHORT TERM /THROUGH SUNDAY/... Issued at 328 PM EDT Fri May 3 2024 ========== This Afternoon ========== The cold front is located just north of the Ohio River this afternoon, with our area within the warm sector of the system. Mostly cloudy sky cover has kept temps cooler than in previous days, with highs so far in the low 70s. However, the airmass is muggy enough to develop some marginal instability, with ACARS data from SDF showing over 500 J/kg of MLCAPE. Convective temps are close to the mid 70s, so if we can reach another degree or two we could see isolated convection fire up along the front or in the warm sector. We are already seeing some showers redevelop down towards Bowling Green, as well as along the front closer to Huntingburg, IN. Probability of thunder for this afternoon peaks around 50%, so coverage will be mainly isolated, and not everyone will see a thunderstorm. For those that do see storm activity in the next few hours, moderate to heavy downpours will be expected thanks to the PWATs around 1.5 inches. Additionally, very weak flow and shear will promote unorganized and very slow storm motions in addition to the lightning threat this afternoon. ========== Tonight ========== Around sunset and into tonight, precip coverage will begin to diminish as our daytime heating is lost. The cold front appears to wash out tonight, leaving no real source of lift in place. However, those high PWATs will linger, so will need to keep at least a slight chance through the night. However, better chances for additional showers come in the morning hours. Temps will be mild tonight, with lows only reaching the low to mid 60s. With the muggy airmass in place, and saturated grounds from recent rains, there should be a good chance for low stratus and fog tomorrow morning. After sunrise, stratus and fog will burn off. ========== Saturday ========== Another weak mid-level impulse should lift northeast from the south into the region tomorrow morning. This will bring additional rounds of isolated to scattered showers in the morning, with the greatest chances to the east of I-65. The forecast for tomorrow afternoon remains complicated in regard to shower and storm activity without much of a trigger mechanism in place. As mentioned earlier, the cold front will have washed out, leaving behind a moist and unstable airmass across the region. There will likely be some weakening mid-level vorticity left over from the morning impulse from the south, but overall the greater forcing will be up towards the Great Lakes later in the day. It'll be another muggy day, with dewpoints possibly reaching the upper 60s, with 12z HREF favoring 75-80% chance for dewpoints over 65F. PWATs don't appear to be as high as today, but still between 1.25-1.4" possible. However, sfc temperatures will be much warmer with highs hitting the upper 70s and possibly even the low 80s in some locations. This should lead to more potential instability during the afternoon, with forecast soundings suggesting between 1000-2000 J/kg of SBCAPE possible. Convection initiation tomorrow afternoon will probably be driven by differential heating boundaries or other mesoscale features present at the time. Due to this continued uncertainty, will continue with broad brush PoPs for the entire region. Severe thunderstorms are not expected due to another day of weak flow aloft. Storms that do form will be fairly slow movers, with storm motions generally less than 20 mph expected. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Issued at 328 PM EDT Fri May 3 2024 Synopsis...The medium-range forecast starts on Sunday by featuring an expansive mid-level ridge over the central and eastern US as mid- level shortwave energy lifts from Upper Midwest to Canada. Further west, a strong mid- to upper-level trough will move onshore from the Pacific eventually amplifying across the western two-thirds of the country by the middle of next week. The ensuing broad cyclonic circulation will allow the upper jet to stretch closer to the Ohio Valley while periodic shortwave energy rotate around the trough axis. As a result, there is a chance of organized, strong to severe storms for several days next week across the Lower Ohio Valley as the main trough meanders around the Plains. Model Evaluation/Confidence...Confidence in synoptic weather pattern has continue to increase as CMC/ECMWF/GFS deterministic models agree fairly well on the position and evolution of the main features (trough/ridge). On the other hand, confidence decreases in the timing and intensity of individual shortwave troughs embedded within the larger trough circulation impacting the ability to indicate the exact times of the severe weather risks. Nonetheless, the CSU and NCAR machine learning algorithms have been consistent at depicting, at least, low probabilities of severe weather for the Tuesday- Thursday timeframe. Sat Night - Sunday...A slight chance of showers and storms will continue Saturday night into sunrise on Sunday as a weak frontal boundary approaches the area overnight. The second half of Sunday morning and early afternoon looks drier as the diffuse boundary stalls close to the Ohio River. Another low chance of showers and storms might be in place late Sunday afternoon and early evening ahead and along the frontal wave provided that cloud coverage diminishes and solar radiation destabilizes the BL to yield CI once convective temperatures are met. Given the weak steering flow, mesoscale boundary interactions could play an important role for convective initiation and maintenance. Sun Night - Monday...An increase in shower intensity and coverage can be expected Sunday night into Monday morning as a southern- stream shortwave trough moves from the southern Plains to the Ohio Valley. GFS forecast soundings show increasing moisture profile with overall decreasing instability and warming mid-level temperatures. Therefore, there could be a chance of brief moderate to heavy rainfall with low thunder probabilities. This vorticity wave will push the stalled frontal boundary further north, so the shower coverage should decrease towards the afternoon and evening given the lack of any substantial forcing mechanism. Tuesday - Friday...As mentioned above, chances of strong to severe storms will be on the rise during the Tuesday-Thursday timeframe owing to the increasing shear associated to the incoming upper jet, the presence of moderately high instability values, and sufficient forcing provided by the periodic mid-level shortwave troughs. Although confidence in timing and details on type of severe risk are low at the moment, available medium-range CAM guidance (GFDL-SHIELD) hint at a multi-day overnight severe threat on Tue and Wed night with probabilities displaced further south for Thu night. A flooding risk cannot be ruled out either given the convective nature and duration of the weather events. && .AVIATION /06Z TAFS THROUGH 12Z SUNDAY/... Issued at 116 AM EDT Sat May 4 2024 Complicated and low confidence forecast for the TAF period. A weak frontal boundary is currently stalled across the region and local obs indicate MVFR/IFR cigs near the convergence zone of the front. As we go toward dawn, low level moisture in the form of stratus should build down and widespread MVFR/IFR cigs/vis should be present across all TAF sites. Localized LIFR cigs are possible. One caveat to this forecast is that if the stratus does not become as widespread as models indicate, we could see dense fog develop instead given light winds and moist soils/ground from recent rain. The morning stratus/fog will be slow to burn off and lift, and it may not be until early afternoon that all sites get to VFR levels. Moisture trapped near the top of the boundary layer will keep a BKN strato-cu deck going for most of the day. Isolated to scattered storms will also be possible in the afternoon, with the highest chances for precipitation generally east of the I-65 corridor. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ UPDATE...BTN SHORT TERM...CJP LONG TERM...ALL AVIATION...DM