Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/08/19

Area Forecast Discussion
National Weather Service Denver/Boulder CO
820 PM MDT Wed Aug 7 2019 .UPDATE... Issued at 820 PM MDT Wed Aug 7 2019 Forecast is evolving pretty much as expected this evening with the strongest storms organizing over the eastern plains, roughly from eastern Adams County through Lincoln county, and moving eastward. The stronger storms are still producing heavy rain and some hail, Storms may still produce heavy rain through midnight as they move eastward into the higher Td (lower 60s) air and increasing low level jet. Meanwhile, weaker convection in the Denver area is already dissipating. We still expect a few showers and isolated storms, however, as the weak short wave rotates eastward out of Utah and across southern Wyoming/northern Colorado overnight. Thursday is shaping up to be a wetter day (afternoon) with heavier rainfall from storms as Precipitable Water (PW) values increase. This is also handled well in the current forecast. && .SHORT TERM...(This evening through Thursday) Issued at 337 PM MDT Wed Aug 7 2019 Increasing moisture under an upper ridge is moving into Colorado visible on satellite imagery as well as precipitable water values up from yesterday. According to the latest ACARS soundings and the current convective activity, a cap still resides from this morning`s cool push into the plains. Plenty of showers and storms firing over the mountains, but they diminish as they head out over the plains. Clearer skies over the plains should still allow for a couple more degrees of heating which should weaken the cap as well as stronger storms to the north and south of our forecast area should send out some outflow for additional forcing. Therefore still keeping the scattered to numerous showers and thunderstorms later this afternoon pushing east over the plains through the rest of the evening. Weak CAPE values over the urban corridor and mountains increases east over the plains, though some models keeping CIN over the far northeastern corner. Best chance for stronger storms looks to be keying into Washington County. A shortwave noted over Utah will round the ridge and push into the forecast area this evening, extending the chance of showers and storms across the area through midnight, with the chance continuing over the eastern plains through sunrise. An MCS will likely develop east of our area late tonight into tomorrow morning, which should end up sending back moist outflow into the area, helped along by high surface pressure over the northern plains. This will increase upslope flow, with an already moist airmass in place. Showers may be ongoing over the mountains overnight and into Thursday morning with just a slight bit of sun needed to get the plains going again. PW values should increase slightly over today over the mountains and urban corridor, with higher values near 1.4 over the northeastern plains. Slightly warmer temperatures east of the Palmer Divide combined with upslope flow and influx of moisture will increase CAPE values into the 1500-2200 J/kg range in this area. Therefore, storms that form or move into that area will have the potential for heavy rain, hence the slight chance of excessive rainfall forecast from WPC. Temperatures tomorrow will be about 2 to 8 degrees F cooler than today`s readings, and should drop several degrees below climatologically normal for the date. .LONG TERM...(Thursday night through Wednesday) Issued at 337 PM MDT Wed Aug 7 2019 Medium range models continue showing a prolonged period with the potential for heavy rainfall from afternoon shower activity each day. Early in the forecast period, the upper level ridge will be centered over eastern Colorado which will allow for a strong surge of sub-tropical moisture to move over the state. Precipitable water values should be high, and winds aloft will be weak, leading to the formation of slow moving thunderstorms that are laden with moisture. shower activity Thursday evening should be left over from afternoon initiation over the mountains that moves out onto the plains. A similar setup should be in place Friday afternoon, but with a little more southwesterly flow aloft. Heavy rainfall will again be a threat, from the foothills out onto the plains. Over the weekend, the moist southwesterly flow aloft will continue as the upper ridge axis shifts eastward over the Central Plains. More afternoons with the threat of heavy rain will exist. The GFS shows an embedded short wave trough rotating over the state Sunday afternoon to further help the organization of the developing convection. For next week, the flow aloft across Colorado is expected to be more westerly, but models also show that sub-tropical moisture will continue feeding into the region from the southwest. Until we see stronger upper level ridging develop over Arizona and Nevada, it seems that the monsoonal flow of moisture will continue over the desert southwest. Until then, the cycle of afternoon and evening thunderstorms over northern Colorado will continue. Temperatures through this period should be around normal for early to mid August, with high temperatures on the plains reaching the mid 80s to lower 90s before afternoon shower activity develops and brings some cooling. As the afternoons of heavy rain accumulate, then the threat for flash flooding will begin to increase. No highlights at this point. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 820 PM MDT Wed Aug 7 2019 Shower and storm chances are slowly decreasing this evening, but an isolated storm still possible til about 06Z. East/northeast winds at KDEN and KAPA will transition to normal south/southwest winds slowly through 06Z-08Z. There may be a weak frontal passage/surge 12Z-15Z Thursday which will bring a chance of stratus development with IFR/MVFR ceilings possible, otherwise VFR conditions should prevail through about 21Z Thursday. Thunderstorm chances will then increase considerably by 21Z Thursday under a more moist and unstable airmass, with VIS and CIG restrictions and gusty/variable winds to 35-40 knots under the stronger storms. && .HYDROLOGY... Issued at 820 PM MDT Wed Aug 7 2019 Storms with locally heavy rain may produce minor flooding in rural areas on the eastern plains until about midnight. On Thursday, due to the influx of moisture into the area, as well as instability, storms will be able to produce rainfall rates of 1 to 2 inches per hour, especially near and east of the Palmer Divide. This could create localized flooding issues in the aforementioned area. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Barjenbruch SHORT TERM...Kriederman LONG TERM...Dankers AVIATION...Barjenbruch HYDROLOGY...Kriederman/Barjenbruch
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1026 PM CDT Wed Aug 7 2019 .UPDATE... 841 PM CDT Continue to monitor thunderstorm potential tonight, mainly after midnight, across portions of northern IL. Thunderstorms of interest are currently across central WI, developing along surface trough/front. This trough/front is expected to sag south through the overnight hours, with the potential for thunderstorms to increase across the CWA. However, the large scale ascent, which the current development across WI is feeling at this time, will stay to the north. So, do anticipate a diminishing trend with any southward moving storms as well as coverage to lower with mainly dry conditions expected for most areas. That being said, with the front swinging through, can`t completely rule out isolated development tonight along it and have maintained mention of thunder in the forecast. Expect lower level instability to decrease tonight, and if anything does develop, don`t anticipate any strong/severe storms. Rodriguez && .SHORT TERM... 227 PM CDT Through Tonight... The forecast and reasoning for tonight has changed very little. There remains potential for some scattered, semi-organized storms moving into northern Illinois, more so far northeast Illinois, and far northwest Indiana after 10 p.m. tonight. A few of these storms if organized could produce 40+ mph gusts. A normal August afternoon with temperatures in the mid 80s area- wide and a scattering of cumulus, along with a lake breeze struggling to advance inland. There has been some clumping of cumulus along the lake breeze convergence but aircraft sounding data indicate any towering updrafts would be narrow with dry air entrainment and that has been the case. This lake breeze should retreat late afternoon with downtown Chicago likely to jump from the upper 70s to mid 80s sometime between 5-7 p.m. A 1004 mb surface low just north of Green Bay is steering a cold front southeastward across northwest Wisconsin and resulting in scattered thunderstorms. Convective sustenance parameters are in place for the storms to uptick through early evening into central and eastern Wisconsin with shear profiles favoring some organization into an MCS, which convective allowing models generally support. This would be most favored to be on a trajectory to move over central Lake Michigan and into Michigan and not our area. Further west of this -- more upstream of the forecast area -- more orthogonal shear orientation with respect to the initializing boundary would support scattered to loosely organized convection. This should track southeast with any convective segments that surge southeast most capable of the stronger winds, and that is possible as far south into the northern CWA given the stronger mid to upper level winds. But the storms will be fighting waning instability, and the instability already is marginal over northern Illinois and far northwest Indiana. Feel that the best chance of storms (around 50 percent) is in far northern suburbs of Chicago (Lake Co area). Any convection that does make it into the area should be weakening and/or moving out of northwest Indiana by 3-4 a.m. The cold front should move through overnight/pre-dawn time period, also in a weakening phase. MTF && .LONG TERM... 218 PM CDT Thursday through Wednesday... For much of the long term period the main feature impacting the weather across northern Illinois and northwestern Indiana will be a large, sprawling high pressure system dropping out of Canada Thursday night and then spreading across the Middle/Upper Mississippi Valley Friday through Saturday. Temperatures will be near seasonal normals, but given the continental polar air mass associated with the surface high, dewpoints should be lower than normal for for mid-August. While there is some concern that a few scattered shra/tsra could develop along the cold front expected to push through the region during the Short Term forecast period at the most favorably diurnal time, Thursday afternoon, the higher chances for more widespread pcpn will come later in the period. The next chance for pcpn should be Saturday night as the longer range guidance continues to advertise a weak shortwave rippling through the northwest flow aloft that will be entrenched across the area, between upper ridging over the wrn CONUS and broad long wave troughing over the ern CONUS. The upper ridge is expected to build east through the weekend and into early next week. This will set up more zonal flow aloft across the Midwest. the longer range guidance indicates a series of waves rippling through the strengthening wly flow aloft, but confidence in timing of individual waves will quickly diminish as the upper flow becomes more zonal. So, while the official forecast will indicate periodic chances for showers and thunderstorms from Sunday afternoon into Tuesday night, confidence in exact timing of any individual wave is low and there will likely be periods of dry weather intermixed with the chances for pcpn. Also, lake breeze development will likely be an almost daily occurrence, so daytime highs along the lakefront will be a little lower than inland highs. && .AVIATION... For the 03Z amendment... Elected to add a period of showers and temporary wind shift centered on the 06z timeframe to account for the activity working south across Wisconsin. Still have low confidence that this line will hold together as it moves into a less favorable environment, thus the choice to omit thunder at this time. Later trends may require a different approach, either to add thunder or remove the mention of showers altogether. A potential wind shift to the northwest would appear to be short lived and should not have significant operational impacts, especially at this time of night. For the 00Z TAFs... Pockets of convection well north of the area across Wisconsin could work their way into the local terminals overnight with the approach of an associated cold front but trends are not appearing favorable for this activity to hold together. If it does it would most likely be overnight when traffic demands are lowest, and then departing the area by the time traffic picks up in the morning. Otherwise expect VFR with persistent west to northwest winds, diminishing overnight and likely gusting again tomorrow to around 20 kts. Lenning && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO