Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/27/21

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
959 PM CDT Thu Aug 26 2021 .UPDATE... 947 PM CDT Evening updates include lowering pops overnight across parts of the cwa. Convective evolution overnight continues to be unclear, though it appears the best focus for much of the night will be west and northwest of the forecast area across parts of IA and MN. Have eased pops to generally slight chance across our far east and southeastern counties and kept chances in the west, mostly after midnight for the majority of the area. Had a few isolated weak thunderstorms develop along the lake breeze this afternoon, and along outflow boundaries across our southeastern cwa. These have faded with the loss of diurnal heating. Currently, local air mass is generally capped with respect to near-surface based parcels. South-southwesterly low level jet back to our west across central/western IA and MN will likely be the driving feature for renewed convective development overnight, with RAP mesoanalysis depicting the best organized deep moist convergence from far northern NE across northwest IA and southern MN. Some recent convective development noted across northwest IA in fact within the low level jet axis. While CAM guidance has not been very helpful of late, latest 00Z 3km NAM and recent HRRR runs do focus on the IA/MN border region overnight for best thunderstorm coverage. The LOT cwa will be on the far eastern periphery of the low level jet, thus not expecting significant coverage for the most part. Elevated showers/embedded thunder with MCV across eastern IA will likely move into northwest/north central IL later this evening/overnight, though better potential for stronger convective development looks to remain off to the west. Some potential may exist for remnants of southern MN/northern IA MCS to push into the area Friday morning in a decaying form. Based on this have maintained going chance pops across north central IL from late evening into the overnight hours, while have decreased pops across the east/southeast to slight chances. Otherwise, no significant changes made to forecast through Friday morning. Ratzer && .SHORT TERM... 302 PM CDT Through Friday night... Main concerns are low confidence convective trends (especially tonight into Friday morning) and heat and humidity on Friday afternoon. In the near term, main areas of concern are near the lake breeze convergence and in the vicinity of the remnant MCV over the east and southeast CWA. Have seen pulse convection into our southernmost counties, with the somewhat more organized convection farther south over ILX and IND CWAs. Recent AMDAR soundings, visible satellite, day cloud phase RGB, and radar trends indicate the cap has eroded or is in the process of eroding near the lake breeze. Still think that coverage and organization will be less than yesterday but expect a few widely scattered storms until sunset. Lack of deep layer shear today vs the more supportive shear with MCV yesterday will make lightning, heavy downpours/localized flooding, and brief likely non-severe downbursts the main threats. Turning to the thunderstorm threat tonight, unfortunately confidence continues to be quite low. Thus far, the upstream convection from central IA to southern MN hasn`t really taken off this afternoon. There appears to be a weak short-wave near the southeast IA/southeast MN border assisting the ongoing convection, with the RAP initializing this and passing it north of us through Wisconsin this evening. If organization doesn`t increase with signs of MCS development and cold pool formation from this activity this evening, the chances of organized convection tonight drop off drastically given modest height falls focused north of the area. It`s possible thunderstorms to the northwest from one of the various waves over the Upper MS Valley and northern Plains congeals and pushes in later overnight, but confidence is too low to put stock in this scenario. Due to the low predictability nature of convection evolution tonight, lowered PoPs a bit from previous and show them increasing to mid to high chance overnight. If any organized/semi-organized convection moves in tonight, main threat would be wind gusts strong enough to down tree limbs. High PWAT air mass and large MUCAPE reservoir would also be supportive of at least localized flooding in the presence of deep moist convection. Trends *should* become more clear with time by this evening. Held onto chance PoPs Friday morning for the possibility of showers and thunderstorms lingering from overnight activity to the extent that it occurs. Thereafter, Friday afternoon will be hot and humid but otherwise could turn out more quiet as low level winds will increase and likely keep lake breeze development at bay, with unidirectional south-southwest winds also limiting low- level convergence across the area. In addition, modest mid-level height rises are forecast and a majority of the models advect in some pretty dry air in the 700-500 mb layer. Forecast low level thermal progs from 925 to 850 mb support highs near low to the lower 90s, with some upside potential if the afternoon ends up mostly sunny. With dew points back up in the lower to mid 70s this yields forecast maximum heat indices of the upper 90s to lower 100s (with overperforming temps bringing values closer to 105F advisory criteria). Friday night, the support for thunderstorms will primarily be across the Upper MS Valley and central and northern Wisconsin closer to the stalled frontal boundary and where short-wave forcing will be focused. Most locations have a dry forecast, except the Wisconsin state line counties where some slight chances are indicated to account for wiggle room if storms form a bit farther south than expected. Any thunderstorms that form later tomorrow-tomorrow night would have a lower end threat to become strong to severe (mainly wind threat) over far north central Illinois with up to 20-25 kt of deep layer shear forecast. Castro && .LONG TERM... 305 PM CDT Saturday through Thursday... Forecast thinking for the long term period has not changed. Hot and humid conditions will persist through the weekend then trending "cooler" next week with periodic shower and thunderstorm chances through at least Monday. The upper ridge continues to amplify in advance of an approaching upper shortwave trough. In response to this, 850 temperatures around 20C move overhead again, and this will support surface temps into the lower 90s areawide. This combined with yet another day of dewpoints in the lower to mid 70s will result in heat indices around 100 degrees. There will be some breezes out there which should help some with the heat. A few isolated to widely scattered thunderstorms are possible on Saturday afternoon. Details for Sunday into Monday are a little less certain and will depend greatly on the timing of the arrival of the upper wave and associated surface cold front. At this time, this looks to move through late Sunday night into Monday. Thus have another warm day forecast with highs in the upper 80s. Model guidance has development out ahead of the main cold front Monday afternoon and early evening with additional storms moving through with the cold front overnight. Once the cold front moves through, temperatures through at least the first half of next week will be closer to normal in the lower 80s with east northeast winds off the lake keeping lakeside areas in the upper 70s. The front does look to stall out somewhere across central IL/IN on Monday with showers and thunderstorms possible mainly south of I-80. We then trend cooler with generally low chances for thunderstorms. Will note that uncertainty in the upper pattern and precip chances increases by midweek with potential influences from a tropical system in the Gulf. Petr/KJB KJB && .AVIATION... For the 03Z TAFs... Update at 03Z: Observational and forecast model trends have backed away from convection overnight, favoring expansive thunderstorms along the IA/MN border. Accordingly, we removed the TEMPO groups for thunder at all terminals. Depending on how organized convection becomes upstream overnight, some form of remnants may try to sneak in late Friday morning or early afternoon, but will withhold on any mention in favor of watching trends overnight. Borchardt Previous Discussion issued at 00Z: The primary forecast concerns through the next 24 to 30 hours are as follows: * Isolated thunder chances through the next few hours * Chances for additional thunderstorms overnight * Potential for an easterly wind shift Friday afternoon Isolated showers and a few storms continue to percolate along a lake breeze stretching from near DPA/ORD/MDW to IGQ. With waning instability (e.g. setting sun), coverage should continue to wane over the next few hours, but opted to hold onto VCTS at the Chicago terminals through 01Z just to be safe. Attention then turns toward Iowa where thunderstorms are developing along the intersection of the nose of a 30+ kt 850mb low-level jet and a residual outflow boundary. Forecast model guidance continues to perform poorly with convective evolution tonight, though with continued low-level forcing (aided by the approach of a subtle upper-level wave over the central Plains), convection will likely continue to develop if not "grow upscale" with time with eastward motion into at least southern Wisconsin. The greatest uncertainty lies with how far south the convection will develop, so for now opted to maintain the inherited TEMPO for thunder at all terminals, but slide the timing back toward the predawn hours of Friday. Should a more organized system develop tonight, strong northwesterly winds would become an increasing concern, especially at RFD. Finally, depending on convective coverage tonight and whether the brunt passes to the north into Wisconsin, a northeasterly wind shift off Lake Michigan cannot be ruled out particularity during the early afternoon hours of Friday at ORD/MDW/GYY/DPA. After collaboration with CWSU ZAU, opted to withhold formal mention for now in place of watching convective trends over the next few hours. Otherwise, light winds will prevail tonight, with a southerly to southwesterly direction preferred tomorrow during daylight hours. Borchardt/Doom && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at Follow us on Facebook, Twitter, and YouTube at:
Area Forecast Discussion...UPDATED
National Weather Service Little Rock AR
632 PM CDT Thu Aug 26 2021 .UPDATE... Updated to include the 00Z aviation discussion. && .AVIATION... VFR conditions expected through the period with L/V winds overnight, becoming E to SE around 10 kts by late morning Friday. SCT to BKN cumulus aoa 4 kft will develop by afternoon and dissipate near sunset. && .PREV DISCUSSION...(ISSUED 235 PM CDT Thu Aug 26 2021) SHORT TERM...Tonight Through Saturday Currently, isolated showers and storms are developing in easterly flow over southern/eastern Arkansas. These will continue to move westward in the vicinity of a weak surface boundary, but should be diminishing this evening as we lose the heat of the day. Over the course of the short term periods, deep layer humidity will increase, with winds becoming more southeasterly and the gradient increasing as something comes this way. This will result in cooler temperatures Friday and Saturday (and I use that term loosely). While heat index values could approach or briefly exceed 100 to 105, it doesn`t appear it will be prolonged or widespread enough to warrant a Heat Advisory. So, that being said, we`re planning on letting the current advisory expire this evening. With increasing humidity, we will see increasing clouds. Upper level ridging will start to break down. So without further ado, here`s info about that something I mentioned that`s coming this way...or at least in the direction of the Central Gulf Coast... LONG TERM...Saturday Night Through Thursday To begin the period, an upper level ridge is expected to be located to the east of the CWA. Afternoon convection is possible through the period associated with diurnal heating. Temperatures look to become more average through the long term period as the upper level ridge pushes away from the CWA, as mentioned already. High temperatures are expected to be in the mid 80s to lower 90s across the state with lows temperatures in the lower 70s. Heat index values look to stay in the lower 90s across much of the state. Now for the main weather feature in the long term period. Here is what we know...As we approach the the beginning and middle of the period, all eyes will be on the tropics. Currently, Tropical Depression Nine is located in the Caribbean, just to the west of Jamaica. Latest model guidance continues to develop TD Nine into a tropical storm then hurricane as it moves into the Gulf of Mexico. The vast majority of major operational and ensemble guidance develops TD 9 into to a hurricane, making landfall along the Gulf Coast, with a bullseye around Louisiana. Some uncertainties in the forecast are with the exact track and intensity of Tropical Depression Nine. A major difference right now is seen among some major operational models on track and timing. Currently, the GFS is slightly faster than the Euro setting up a Sunday night landfall rather than a early Monday morning landfall. Part of this may be in part to the Euro hinting at a landfall farther to the west than the GFS causing TD 9 to spend more time over the Gulf waters. These differences are likely to be figured out over the next couple of days as aircraft recon go out and sample the storm in addition to more frequent upper air launches sampling the environment ahead of the storm. What does all of this mean for our CWA? The track will be key over the next couple of days in determining if the CWA gets impacted and if The farther to the east of the CWA that the storm makes landfall would minimize impacts as the eastern half of a tropical cyclone tends to be more impactful. At this point it is way too early to pinpoint impacts (or not) to the CWA. So what can you do now? Continue to monitor the National Hurricane Center and local National Weather Service office for up-to-date information regarding TD 9. && .LZK Watches/Warnings/Advisories...NONE. && $$ Aviation...DTC