Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
157 FXUS63 KIND 072243 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 643 PM EDT Tue May 7 2024 .KEY MESSAGES... - Severe storms expected today, especially during the afternoon and evening. All forms of severe hazards are possible. - Additional severe storms are possible Wednesday afternoon and evening. All forms of severe hazards are again possible. - Heavy rain is possible at times through Wednesday night. Localized flooding will also be possible. - Periodic chances for showers and a few storms late week into early next week. - Normal to slightly below normal temperatures from Thursday into early next week. && .MESOSCALE UPDATE... Issued at 643 PM EDT Tue May 7 2024 Scattered supercells continue to track E and NE over central IN. The earlier cell that was approaching southern Indy metro failed to pulse up as cell mergers occurred more in front flank of cell which may have limited unstable inflow into updraft zone. Nevertheless it remains a core entity as it passes across SE Marion Co. at this time and will continue to monitor as it moves east. Other supercells not showing much low-level rotation at this time. This could be due to slightly more veered boundary-layer flow into the storms, limiting some streamwise vorticity ingestion into updraft zone. Nevertheless, we are getting some good hail cores with occasional 1 inch reports still happening with strongest cells. Most concern over next 1-2 hours would be the storms along/near the I-70 corridor which have unimpeded axis to unstable low-level inflow and reside on the northern gradient of the maximum instability over far SW IN on southward. Storms also are riding along their own created outflow boundary which could possibly promote better convergence and tilting/rotation into the updraft. Will continue to monitor. Issued at 540 PM EDT Tue May 7 2024 Persistent supercell continues to track east across southern and eastern Putnam Co. at this time. Storm has history of 1 inch diameter hail, with isolated report up to ping pong in Putnam along with funnel cloud as relayed by EMA. Still healthy rotation aloft but less so in low-levels. Still not seeing really any cell or shower mergers into southern inflow flank of storm yet although radar now showing some cells developing just to its south and moving NE toward it. Such mergers can enhance low-level streamwise vorticity and rotation potential, subsequently leading to better tornado potential (but not always). WoFS data suggests that some mergers and some cell strengthening may occur as it continues to propagate east toward southern half of Indy metro over next hour, although rain from downwind part of storm will affect Indy area shortly. Will continue to monitor trends on this storm closely. Elsewhere, we are continue to monitor supercell structures over Boone, Clinton, and Tipton counties at this time. More updates to come. Issued at 439 PM EDT Tue May 7 2024 Clouds across Central Indiana are demonstrating some key features as we continue to destabilize the atmosphere. Cirrus shield quickly pivoting east into Ohio, with a couple channels of strongly ascending parcels noted within the deeply agitated cloud layer west of Indy Metro. Another channel of clouds demonstrating some steady vertical ascent. Axis of 0-1km storm relative helicity has continued to be stronger over Central Indiana, with the gradient placed across Central Illinois stretching east/northeast to near Lebanon/Frankfort then continuing northeast. Expect that as the convection presently lifting northeast of Terre Haute. As this convection continues to lift northeast of Vigo county, it should realize the gradient of the 0-1km SRH and persist the convective development. Aircraft data still showing a considerable dry layer above 700mb, which convective towers should easily realize this drier air coupled with the deeper vertical energy and expect continued upscale growth to occur. The combination of enhanced low-lvl helicity and the stronger vertical growth suggests the potential remains for rotating updrafts throughout the next couple of hours and possibly further north lapse rates will be marginally steeper to support hail growth. && .SHORT TERM (This evening through Wednesday)... Issued at 259 PM EDT Tue May 7 2024 Our focus in the short term is the severe weather potential this afternoon. THIS AFTERNOON Synoptic Overview A potent trough and associated jet streak are beginning to edge into Indiana. We`ll find ourselves in the right exit region of the jet streak. Typically, the right exit region isn`t usually considered the best place for large-scale lift. However, we`re dealing with a cyclonically curved jet streak which maintain favorable lift in both the right and left exit regions. The best vorticity advection looks like it will pass to our north. Still, enough divergence exists within the jet streak for synoptic-scale lifting this afternoon. 500mb height falls signify that this large-scale lifting is ongoing. At the surface, a cold front across northwestern Illinois will advance eastward. This feature will provide another source of lift in addition to the dynamics above. A potent low-level jet (35-45kt at 850mb) will advect warm buoyant air back northward eroding what remains of a cold pool/CIN. Rapid destabilization of the planetary boundary layer (PBL) is expected as we head into the afternoon through a combination of advection and solar insolation. Additional lift will arise from the buoyant forces near the surface. As such, thunderstorms are likely once again both along the boundary and within the open warm sector. Convective Mode Now that we`ve reasoned why thunderstorm development is once again expected this afternoon, we can take a look at convective mode and hazard types. Latest RAP analysis shows plenty of low-level shear, and this is corroborated by latest satellite imagery showing billows/waves in the warm sector stratus (17z). RAP soundings depict 0-1km shear over 20kt, with effective bulk shear over 50kt. Hodographs are long, with some curvature in the lowest 3km (especially as one heads further east). The thermal profile shows modest lapse rates with tall CAPE profiles and abundant low-level moisture. NAM/GFS soundings are quite similar. The jet streak aloft is generally perpendicular to the warm sector and cold front. Therefore, multicell clusters and supercells appear to be the most likely storm mode today. Reason being is we have a lot of shear with the best large-scale lift is passing to our north. Additionally, faster flow may still be a bit further west and storms could have poor anvil-level relative outflow (which may promote multicell over supercell). The jet streak will be deeper into the region later in the day as well, so supercell mode may become more prominent after 6pm or so. Linear mode may be possible in the evening as the front/pressure trough becomes a bit more parallel with the shear vector. Hazard Type and Timing In terms of hazard type, we have an "all of the above" situation this afternoon. Abundant buoyancy and shear in the lowest 1km should promote tornado potential, with the possibility of a strong tornado. Additionally, tall CAPE profiles with fast flow through the Hail Growth Zone upward will promote a large to very large hail threat. Dry mid-level air may lead to DCAPE values over 1000J/kg allowing for efficient downward momentum transfer and a damaging wind threat. These hazards are most likely within supercells that develop. In terms of timing, given the lack of a cap in the model soundings...it seems probable that convection fires up rather early in the afternoon. As of 17z, lIssued at 439 PM EDT Tue May 7 2024ow- level stratus still has a wavy appearance signifying low-level stability...though this is beginning to change. Satellite trends show convective rolls and a few towers beginning to develop over northern Illinois. The most probable timing of convective redevelopment is between 18-21z. TONIGHT High-res guidance generally shows convective activity exiting the area before 06z. As mentioned above, some linear convective mode is possible in the evening...and if the line orients itself parallel to the shear vector then storm training may occur. This may promote a heavy rainfall threat. This seems most probable in the south and eastern portions of our CWA. Surface winds diminish quickly after sunset and another round of overnight fog is possible as PBL inversion develops. Wednesday`s severe weather threat will be covered in the Long Range Discussion below. && .LONG TERM (Wednesday night through Tuesday)... Issued at 259 PM EDT Tue May 7 2024 WEDNESDAY/WEDNESDAY NIGHT... BOTTOM LINE UP FRONT - Another day of potentially significant severe weather is likely Wednesday, with all hazards possible, though the corridor of highest severe potential may be further to our south/southwest as opposed to today. Central Indiana will begin the day on the cool side of the effective warm front, which will likely lay somewhere along a Kansas City - Paducah line and points east/southeastward by daybreak, though the eastward extent becomes a bit more uncertain as this portion of the boundary may be convectively reinforced. All models, including CAMs, show this boundary pushing steadily back northward through the day on Wednesday, though there is decent variability in how quickly this occurs and what that means for destabilization and evolution of tomorrow`s rounds of convection. The rough consensus appears to be that the front will get as far north as the I-70 corridor or thereabout by late afternoon, though convection will very likely be in progress by this time, as minimal inhibition is expected within the warm sector. Convection may then push eastward and perhaps even east/southeastward as potential upscale growth occurs, cold pools become established and storms begin to ride the instability gradient along the boundary, which may be held up on its northward lift by this activity, which is a failure mode for severe episodes we`ve seen in this area several times before. The lack of capping may also contribute to a variety of convective modes, with discrete storms ahead of any possible QLCS segments, though all hazards look to be on the table - with relative threat of each hazard depending significantly upon these modes. Shear will not be an issue, as deep layer and low level bulk shear numbers are more than adequate for organized storms across the area, especially along the boundary - and significant instability will be present within the warm sector. It appears that convection will fire fairly early in the day over western Missouri into NE Oklahoma/NW Arkansas, initially moving eastward or even ENE-ward with the mean flow, with a gradual shift to eastward motion and then ESE-ward with time as convection organizes and begins to modify the environment. Focus area over the last 24 hours has shifted south somewhat, and given the CAM guidance and uncertainties with respect to warm frontal progress/airmass recovery further northward into central Indiana, this appears reasonable. If QLCS mode becomes predominant early in the day, this activity may well skirt across the southern portions of central Indiana in late afternoon/early evening as it moves eastward and then begins to develop southeastward along the instability gradient. However far north the warm front manages to progress, any convection near and along it, particularly discrete cells, will have the potential for tornadoes, possibly significant, though again, the most likely corridor for this appears to be just off to our south/southwest at this time. Significant rainfall potential will exist with this activity, and a hydrologic threat will require monitoring tomorrow into tomorrow night, dependent upon storm track and evolution. THURSDAY - TUESDAY... BOTTOM LINE UP FRONT - Cooler with periodic shower/storm chances through the rest of the forecast period. Lingering shower and storm chances will accompany a secondary cold front and the upper level trough axis as it passes through the region on Thursday, and periodic shower chances will be necessary throughout the remainder of the long term as individual waves within the larger upper level cyclonic flow impinge upon the region. Temperatures will be cooler, perhaps significantly so, late in the week and into the weekend, though some recovery back into the mid to perhaps upper 70s appears likely by early next week as the large scale upper trough pulls northeastward and heights begin to build locally/flow becomes quasizonal. && .AVIATION (18Z TAF Issuance)... Issued at 146 PM EDT Tue May 7 2024 Impacts: - Good confidence more PM thunderstorms will develop and move across before coverage decreases or ends and flying conditions improve - General wind gusts to 25+ knots this afternoon - Gusts to 50+ knots and large hail possible in severe storms this afternoon and evening - Patchy fog possible overnight Discussion: Thunderstorm re-development is expected this afternoon. Strong and severe thunderstorms are possible with this activity, and very poor flying conditions are likely within or near any shower/storm. Winds will become gusty and switch to the S and SW during the day with gusts to 20+ knots away from convection up to 50+ knots in severe storms. After storms exit the area, skies should clear and some patchy fog may form overnight. Winds may go light and variable for a time. Wednesday will feature increasing clouds and a renewed storm threat shortly beyond the end of the current TAF period. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ MESOSCALE...Funk SHORT TERM...Eckhoff LONG TERM...Nield AVIATION...Eckhoff