085 FXUS63 KIND 071054 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 654 AM EDT Sun Aug 7 2022 ...Updated Aviation Discussion... .Short Term...(Today through Monday) Issued at 252 AM EDT Sun Aug 7 2022 Through Sunrise into This Morning Very quiet conditions prevail across the region as of 2am. Some lingering storms across southern Indiana, down by the Ohio River, continue but pose little threat to our CWA for the time being. Aside from the occasional low stratocumulus cloud, most locations have been enjoying a generally clear night. Upstream, a large convective complex has developed across northeastern Iowa and southern Wisconsin. An extensive area of cirrus is expanding east and southward from this system. Currently thinking that this cloud layer will work its way into northern Indiana, and eventually into central Indiana. Upper-level flow is very weak from Indianapolis southward, so any cirrus that works its way into our northern counties will have a difficult time spreading any further south. Cirrus may actually spread southwestward as it rounds the periphery of an expansive upper-level high situated to our west. Additionally, the clear skies have allowed temperatures to cool enough for some patchy fog to develop just across the state line in Ohio. Fog is also possible across Indiana by sunrise as relative humidities are around 90 percent in most locations. Fog should not be as widespread as the previous overnight, since slightly drier low- level air is filtering in from the south. Otherwise, another warm and humid morning is in store with lows in the lower 70s. Today into Tonight Starting with the synoptic scale pattern, we find ourselves on the outskirts of a large upper-level ridge that is centered over northeast Nebraska. As mentioned before, upper-level flow is very weak (500mb flow around 10 kts). Faster flow aloft can be found just north of the ridge, across the Great Lakes region. A shortwave trough embedded within the mostly zonal flow is currently ejecting from the northern Rockies and should be over the Great Lakes by late tonight. This feature is expected to generate a weak surface low which will then race northeastward into Canada. A cold front associated with this low should then sweep southward late tonight into Monday morning. Looking back towards the mesoscale, we turn our attention to the convective complex to our northwest. This system has been gradually propagating southeast, and is now entering northern Illinois. The main question is: will this system be able to sustain itself into Indiana? Examining the environment ahead of it, we see a nocturnal low-level jet around 20kts, MLCAPE around 1000 J/kg, and rich low- level moisture to 850 mb. Mid-level flow is lacking, however, with less than 10kts above 700mb according to recent ACARS soundings out of Indianapolis. Flow is a bit better to the north, however. Given this environment, a southeastward propagating MCS may be able to make some headway into northern Indiana...but will find itself in an increasingly difficult environment as it heads south. With diminishing mid-level flow and a weakening LLJ, the system should become cold pool dominant. The best chance of experiencing any impacts from this system will be across our northwestern counties late in the morning or early afternoon. Dry mid-level air may lead to some gusty outflow winds within stronger cells. Lingering clouds and stratiform rain could persist for northern locations as well. Further south, a moisture-rich environment should quickly destabilize during the day as temperatures rise to around 90. Pop-up convection is possible in most locations, but may concentrate near any lingering outflow boundaries from late morning and early afternoon convection associated with the dying MCS. The weak flow aloft should prevent storms from organizing into anything more than a multicell cluster. Some lingering mid-level dry air may lead to a brief downburst as cells collapse upon themselves. Convection should diminish during the evening as instability is lost. CAMs show some lingering convection into the night, mainly across central and northern counties, and this may be a response to a re- intensification of the LLJ and associated moisture advection. Additionally, a convectively augmented vort max and an uptick in mid- level flow may enhance lift during the overnight hours. This factor, however, will largely be dependent on how today's convective situation plays out. && .Long Term...(Monday night through Saturday) Issued at 252 AM EDT Sun Aug 7 2022 * Shower and Thunderstorm Chances Monday Night through Tuesday * Dry weather returns on Wednesday through Friday * Rain chances return Saturday Monday Night through Tuesday... On Monday night and Tuesday, the models show a short wave sagging southward across Indiana from the upper midwest. A strong area of high pressure aloft will continue to be developing across the Western United States, along with a building ridge axis aloft over the Rockies. This large high aloft will result in northwest flow aloft through Saturday. However on Monday Night through Tuesday an associated cold front is expected to slowly sag southward across Central Indiana, providing a focus for lower level convergence. Ahead of the cold front, the warm and humid air mass that has been in place for the past several days will still be present, providing plenty of moisture for shower and storm development with the surface front and upper wave. Forecast soundings show a very saturated column as the front passes with Pwats around 2.00 inches. Of note, available CAPE does appear to diminish on Monday Night after heating is lost. Thus precip on Monday night should be more showery with more isolated thunder. Given all of this, we will trend toward high pops on Monday night and Tuesday as these features slowly pass to the south. By Tuesday night, strong subsidence and drying is seen within the column. Wednesday through Friday... The previously mentioned cold front is shown to sag to Tennessee on Wednesday, as stronger high pressure builds aloft over the Rockies and a strong lee side NW flow develops over the upper midwest, spilling into the Ohio Valley. Associated strong high pressure is suggested to develop over the upper midwest and slowly push to the Great lakes on Friday. This will result in mainly northerly surface flow on Wednesday and Thursday, before transitioning toward a easterly flow on Friday. Aloft with the NW flow, a few short waves are depicted to ride the ridge and push across Central Indiana through this time. However, deep moisture looks to remain a problem as the surface high blocks any gulf moisture and subsidence on the lee side of the ridge aloft remains dominant. Thus will trend toward a dry forecast with highs in the middle 80s along with less humid conditions compared to recent days. Saturday... Little change is seen within the overall pattern for Saturday. The strong high aloft is still parked over the western United States, providing NW flow aloft to Indiana and the Ohio Valley. Again, some forcing dynamics are suggested to ride the ridge and push across Indiana on Saturday. This time however, the surface high is suggested to be northeast of Central Indiana, allowing warmer and more humid southerly return flow to begin. Thus given this return of moisture, some low chance pops for rain appear reasonable at this point. && .Aviation...(12Z TAF Issuance) Issued at 653 AM EDT Sun Aug 7 2022 Impacts: * Mostly VFR through tonight * Scattered showers and isolated thunderstorms, mainly north of a HUF to IND line Discussion: High cirrus clouds around 25k ft have spread in from upstream convection to our north. These clouds should persist throughout the day. Fog has held off for the most part, with all terminals reporting VFR conditions. VFR conditions are expected to continue most of the day today. Diurnal cumulus development is expected with cloud based between 3k and 4k ft. Leftover showers from the aforementioned upstream convection may spread southward as the day goes on. Added a period of VCSH to the northern terminals. Thunder is also possible with this activity, but confidence isn't high enough to warrant inclusion in the TAFs. Showers remain possible overnight, as a cold front approaches from the north. Any showers or storms may produce brief periods of MVFR conditions. Surface winds are expected to retain a south to southwesterly direction throughout the forecast period, with speeds generally 5 to 10 kts. A few gusts around 15 kts are possible this afternoon upon peak boundary layer mixing. && .IND WATCHES/WARNINGS/ADVISORIES...None. && $$ Short Term...Eckhoff Long Term...Puma Aviation...Eckhoff