Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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686 FXUS63 KIND 140702 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 302 AM EDT Fri Jun 14 2024 .KEY MESSAGES... - Scattered showers and thunderstorms through daybreak - A few showers or storms over southeast Indiana this afternoon - Dry and seasonable tonight and Saturday - Hot and humid trend starts Sunday...increasing confidence in potentially hazardous heat into next week && .SHORT TERM (Today and Tonight)... Issued at 302 AM EDT Fri Jun 14 2024 Convection that has moved across the forecast area since late Thursday evening is finally weakening as it moves out of our eastern counties as of 0630Z. Despite the drier air and lack of extensive instability over much of the region as the storms moved in...a cluster of stronger cells produced pockets of likely 50-60mph winds tracked from near Crawfordsville southeast across the southwest Indy metro and into Johnson County before weakening. A noted rear inflow jet was a contributor to these stronger winds surging out at the surface as the storms tracked southeast. Temperatures were currently in the mid and upper 60s early this morning with additional scattered convection moving into the northern Wabash Valley. Scattered convection will persist over the next several hours with a low risk for a few showers or storms across southeast portions of the forecast area even into this afternoon as the weak frontal boundary lingers across southern Indiana. A large area of high pressure will expand into the region from the north by late today and bring seasonable temperatures into the first part of the weekend...before the hottest air of the season arrives Sunday into next week. This Morning Additional convection continues to fire across central Illinois and the CAMs are not doing a great job of capturing this. Appears the main catalyst for the renewed convective development is the presence of subtly stronger flow at 850mb with westerly winds near 30kts feeding into the showers and storms. With elevated instability in place and the stronger flow at 850mb expected to persist through daybreak...expect scattered convection to migrate into the forecast area and gradually sag southeast over the next few hours. Locally heavy rainfall will be the primary impact and considering the forecast going forward into next week...any additional rainfall will be welcome through later this morning. The weakening and veering of the 850mb flow as the morning progresses will largely diminish activity. This Afternoon and Tonight The front will be positioned somewhere across the southern half of the forecast area by the afternoon and despite better forcing aloft along the boundary to our east...enough instability and lift in the vicinity of the front to generate a few showers and perhaps a couple thunderstorms over southeast counties through late afternoon. Further north across the forecast area...a noted surge of drier air and subsidence in tandem with a well mixed boundary layer will support some wind gusts through the afternoon with mostly sunny skies developing. The remnant boundary will drop south of the Ohio River tonight with high pressure from the north taking over across central Indiana. Skies will be clear overnight with N/NE winds bringing a refreshing airmass as dewpoints fall back into the 50s. Temps...despite the passage of the front through the afternoon and the progressively drier airmass arriving in its wake...low level thermals are supportive of highs close to if not just a few degrees cooler than Thursday. Expect mid and upper 80s across the forecast area. Lows tonight will be comfortable...falling into the upper 50s and lower 60s. && .LONG TERM (Saturday through Thursday)... Issued at 302 AM EDT Fri Jun 14 2024 Saturday through Next Week **Increasing confidence in an extended period of very hot and humid conditions Sunday through much of next week** Looking back at maximum high temperatures for the month of June across Central Indiana, climatology shows that it`s relatively rare to see highs exceed 95 degrees. And 3 or more consecutive days at or above 95 degrees in June is exceedingly rare for Central Indiana, with only 3 occurrences of that happening in June at KIND (Indianapolis International Airport). The upcoming weather pattern does support consecutive days with highs potentially reaching and exceeding 95 degrees for all of Central Indiana in addition to warm nights in the 70s and humid conditions. Saturday will likely be the "coolest" day over the next week with highs in the mid 80s as the heat dome and best warm air advection still remain to the west across the Plains. 500mb ridging strengthens over the south on Sunday with 500mb heights reaching 593dm over Georgia. Through the rest of the week, upper ridging slowly shifts to the northeast while strengthening with 500mb heights potentially reaching 600dm, indicating an anomalously strong ridge taking hold of the eastern half of the country. The low level ridge and surface high pressure remain east of Indiana during this entire period keeping strongest warm air and moist air advection right over the Ohio Valley. One thing to note, with the center of the high pressure over the NE Conus and Atlantic, the best subsidence and associated low level subsidence inversions will likely remain to the east. Forecast soundings Sunday into early next week show very steep low level lapse rates and deep mixing heights, further increasing confidence that high temperatures could exceed 95 degrees, despite such a humid airmass. This will all translate to near normal temperatures for the Friday night to Saturday night period under the passing northern high... with lows around the low 60s and highs Saturday near the mid-80s amid the light easterly flow. Noticeable transition on tap for Sunday when sun and warm advection are staked to boost all corners of the region to 90-95F...which will be the first 90F+ day for many locations. Slightly hotter conditions are possible Monday per better WAA and morning lows likely starting about 10 degrees higher. Higher confidence in moderate humidity for Monday following longer fetch off the Gulf...bringing the potential for triple-digit heat index values to much of the region. Can not rule out a stray shower Monday but expect the generally capped profile to continue rain-free conditions for most spots. Latest guidance is indicating increasing confidence in a pronounced upper trough over the northwestern CONUS/Canadian plains into the middle of next week, which will help to boost the next bubble of the subtropical H500 ridge over the Midwest, with perhaps a 595 dm height reaching Indiana by the end of the long term. The broad surface ridge is progged to remain over or to the east of the Mid- Atlantic, maintaining the southerly flow into central Indiana. Higher, yet probably not oppressive dewpoints should hold overnight minimums to the 70s...and, when coupled with mainly FEW/SCT clouds, promote diurnal spreads approaching 20 degrees...which should continue the late-June heat wave through at least Thursday. Any potential relief from 90F+ temps would be limited to greater cloud cover should the increasing deep moisture be able to organize above the cap or getting caught under what should be a few showers and a stray thunderstorm through the mid-week. Unfortunately given lack of any approaching wave or forcing confidence in either opportunity for any location will be low. Any breakdown in the strong and broad ridge will likely follow the end of the long term. Indianapolis has only reached 95F as early as June 17 on 11 occasions since 1871...and only twice since 1952 (95F on both 6/4/2011 and 5/28/2018). Indianapolis has only observed five days 92F+ during 6/1 - 6/20 on 11 occasions...and only twice since 1954 (6 in both 1988 and 1994). && .AVIATION (06Z TAF Issuance)... Issued at 1115 PM EDT Thu Jun 13 2024 Impacts: - Thunderstorms around until about 09z - Brief MVFR stratus as front moves out Friday morning/midday Discussion: Thunderstorms are expected to decrease by the predawn hours with impacts to TAF sites possible until then, including gusty winds and brief visibility reductions in heavy rain. Ceilings could lower due to post-frontal stratus at least briefly. VFR conditions will return by early afternoon and prevail through the remainder of the TAF period. && .IND WATCHES/WARNINGS/ADVISORIES...None. && $$ SHORT TERM...Ryan LONG TERM...CM AVIATION...BRB