Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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974 FXUS63 KIND 020412 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 1212 AM EDT Thu May 2 2024 .KEY MESSAGES... - Multiple chances for showers and storms throughout much of the forecast period, with continued above normal temperatures. - Repeated rounds of rainfall may lead to redevelopment of flooding. && .FORECAST UPDATE... Issued at 957 PM EDT Wed May 1 2024 Isolated convection had diminished across central Indiana this evening, with a few showers south of the area. The front remains across the southern half of the forecast area, with dewpoints in the 40s north of the front and in the 60s south of it. The front will remain across the area tonight. An area of thunderstorms south of St Louis at the moment is moving northeast and looks to be associated with some upper energy moving through. This convection should weaken as it moves into less favorable conditions and the diurnal lessening of instability. Models are all over the place with this convection, ranging from high coverage of overnight to nothing. Feel that there will likely be some isolated convection remaining by the time it moves through given a little upper support, so expanded slight chance PoPs to much of the area at some point overnight. PoPs can be adjusted further once the trend in the convection becomes more clear later tonight. Otherwise adjusted sky cover based on latest trends, and tweaked temperatures as needed based on latest observational trends. && .SHORT TERM (This evening through Thursday)... Issued at 300 PM EDT Wed May 1 2024 Latest satellite imagery shows high clouds streaming across Indiana, which are the result of upstream convective activity. The clouds are thin enough for a good view of the diurnal cumulus development currently taking place. These clouds should not be enough to prevent highs from climbing into the low 80s for much of the area. Going forward, a weak cold front is sliding in from the northwest. Surface observations show this front partially through central Indiana as of 2pm. The parent vort max is well to the north and east, and any large-scale forcing is essentially absent. Nevertheless, dew points are in the low 60s south of the front and enough buoyancy may exist for some isolated showers or thunderstorms. Model soundings show little in the way of shear (under 30kt effective), but relatively steep lapse rates (7.0-7.5 C/Km). Enough DCAPE may be present for a quick downburst should any convective core gain sufficient mass. Confidence in this occurring is very low (less than 15 percent) but is worth mentioning. Overnight, the front stalls across the area and begins to retreat northward as a warm front by morning. Throughout this time, however, the risk of an isolated shower or storm continues. Overall, the overnight hours should feature gradually veering winds and occasional mid to high-level cloudiness. During the day Thursday, the now-warm front is expected to push northward with renewed warm air advection. Temperatures at 850mb reach between 15-20C which, combined with efficient boundary layer mixing, could lead to surface temps well into the 80s. A few locations may even make a push for 90 especially closer to the Ohio River. && .LONG TERM (Thursday night through Wednesday)... Issued at 300 PM EDT Wed May 1 2024 The warm and active stretch of weather is expected to continue into next week, as large scale pattern characterized by broad upper level troughing over much of the country and mean subtropical ridging over the southeastern CONUS remains in place. While this will require PoPs throughout much if not all of the long term period, precipitation will be primarily convective in nature, and significantly dependent upon mesoscale influences generally poorly resolved on such time scales. There will be ample opportunity for precipitation, but plenty of dry periods as well - but NWP limitations and inconsistencies preclude more detail, precision, or confidence in the long term forecast for any one particular time frame. All that said, the highest chances for showers and thunderstorms will be Friday, and then again on Monday into Tuesday, as these are the times when a general guidance consensus exists that frontal boundary passage and upper level support will be present to promote more widespread precipitation. While there is no major signal for excessive precipitation in either ensemble situational awareness tables or experimental machine learning, the area is already fairly wet and streamflows remain elevated in most areas, particularly western and southwestern Indiana, so repeated rounds of precipitation will have at least modest potential to lead to renewed flooding concerns, and this will require close monitoring. Hydrologic ensemble data do have signal for this potential. Severe storm wise, there again is little signal for significant concerns until late in the period, when machine learning data and CIPS analogs do show some signal toward Tuesday into Wednesday of next week - though uncertainty is quite high given all the aforementioned caveats. Temperatures will remain fairly warm throughout the period, with highs generally in the mid 70s to mid 80s and lows in the mid 50s to mid 60s. These will obviously be highly dependent on evolution and timing of potential convection and/or absence/presence thereof. See little opportunity for improvement over blend approach at this time. && .AVIATION (06Z TAF Issuance)... Issued at 1212 AM EDT Thu May 2 2024 Impacts: - VFR Conditions expected for much of the forecast period. - Convection possible on Thursday afternoon and evening. - MVFR/IFR conditions possible in any convection that strikes a TAf site. - Confidence for showers/storms is low. Discussion: Isolated convection was found over southern IL early this morning. HRRR suggests that will push north and dissipate in the next few hours as high pressure remains across Central Indiana. Thus the ongoing VFR conditions and stray CI clouds are expected to continue across the TAF sites through the night. The high pressure system will drift east of the TAF sites on Thursday, allowing the return of a warmer and a more humid air mass across Central Indiana. Forecast soundings by afternoon suggest attainable convective temperatures with CAPE over 2000 J/KG. Thus VFR CU development will be expected during the afternoon and evening and TSRA should be possible. However confidence for specific timing and locations is low. Thus a large window of VCTS will be used. On Thursday Night, the HRRR suggests continued sct showers and storms across the area, arriving from the middle Mississippi valley. For now, have used VCSH to account for these passing showers with lower VFR Cigs. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...50 SHORT TERM...Eckhoff LONG TERM...Nield AVIATION...Puma