Forecast Discussion
240 FXUS64 KMEG 181235 AFDMEG Area Forecast Discussion National Weather Service Memphis TN 735 AM CDT Wed Jun 18 2025 ...New AVIATION... .KEY MESSAGES... Updated at 720 AM CDT Wed Jun 18 2025 - A cold front will move through the region this afternoon, bringing a line of strong to severe storms. A Slight Risk of severe weather is in effect for areas along and north of I-40 through the overnight period. - Strong to severe storms may redevelop around sunrise tomorrow, though confidence is much lower in this second round. - Hot and humid conditions will develop late week, with heat indices above 100 degrees by Saturday. && .DISCUSSION... (Today through Tuesday) Issued at 122 AM CDT Wed Jun 18 2025 All is mostly calm across the Mid-South at this hour, save for a few straggling showers still working their way out of the area. We`ll have a brief break this morning in between systems before more active weather moves in this afternoon. A very well organized MCS currently racing across eastern OK is on the leading edge of a surface low that will eventually dig a longwave trough down through the Ozarks this afternoon. The associated cold front is our weather-maker for this evening. A line of showers and thunderstorms will reorganize ahead of this front in the mid to late afternoon hours and continue holding together fairly well throughout the FROPA overnight. Will note that the timing has significantly shifted earlier with the last few CAM runs... With yesterday morning`s forecast, it looked like the convection wouldn`t be at our doorstep until 00Z Thursday (7PM tonight) at the latest, but now it`s looking like the front`s arrival may have sped up to as early as 18Z (1PM) today. If the earlier timing solution is correct, peak heating in the afternoon may help storms pack more of a punch with the added resultant instability. Regardless of the timing, the primary threat for this line of thunderstorms is damaging winds. Especially on the northern end of the risk area near the MO and KY state lines, bulk shear is on the order of 30 kts this afternoon and evening, which provides more than enough organizational support for bowing segments and strong downbursts on the leading edge of the line. With any isolated cells ahead of the main line or even broken segments within the line itself, midlevel lapse rates just over 6 degC/km will support marginally severe hail up to about an inch in diameter. The low level kinematics in play are much weaker, though, which explains why the tornado threat is comparatively much weaker. 00Z HREF puts the mean 0-1 km SRH right at 100 m2/s2 during the frontal passage this afternoon and evening for areas north of I-40. In a moderately sheared environment like this one, that SRH is not necessarily raising any alarm bells, but it`s not something to balk at either. The tornado potential will largely depend on the convective mode: if this remains a well organized QLCS, the tornado potential will be quite low, but if we get more supercellular storms and broken segments, the threat will increase. Despite the earlier arrival time, the front will be rather slow moving overnight. This is the reason for the introduction of a D2/Thursday marginal risk over north Mississippi. Even after the first wave of convection clears the area just after midnight Thursday, the front itself will still be lingering from the ArkLaTex up through eastern Kentucky. By the time the reinforcing airmass arrives and pushes the front out once and for all, more convection will fire up along the boundary by daybreak on Thursday morning. These storms will have a much less favorable environment to work with, namely strong CIN and very weak shear, but the forcing is quite robust and may help storms break out of the capped environment. There will be a very small window of time early Thursday morning where convection in the southeastern part of our CWA can take advantage of the eroding cap before losing all its kinematic support entirely. After the front finally moves out on Thursday morning, the trends quickly shift to lower PoPs and warmer temperatures. A 595 dam midlevel ridge will park itself over the Mid-South by Friday and stay there through the weekend. This heat dome will warrant the first heat headlines of the year at some point in the near future. It may be as early as Friday afternoon in the MS Delta, but heat indices will certainly climb above 105F by Saturday and Sunday, which is our criteria for a Heat Advisory. By Monday, the upper level pattern will deamplify just enough to allow diurnally driven convection to return. 30-40% chance PoPs are in the forecast Monday through Wednesday of next week, mostly in the form of isolated summertime convection. It`ll still be very hot and humid well into the work week, so any showers and thunderstorms that develop will be a nice cooldown from the heat and humidity. CAD && .AVIATION... (12Z TAFS) Issued at 720 AM CDT Wed Jun 18 2025 Low confidence TAF set with respect to timing, intensity, and coverage of TSRA today and tonight. A loosely organized line of storms is quickly approaching KJBR and may move into MEM and MKL by late morning. No hi-res model guidance is currently capturing this activity, so confidence is low beyond this morning. The current thinking is that TSRA will be most likely in the afternoon hours with peak daytime heating. Added a tempo to the northern sites for likely TSRA time. Uncertainty remains as to whether this activity will shift south and east or remain nearly stationary near MEM and MKL. Another round of storms is expected overnight, but will be largely dependent on this afternoon and evening`s activity. AC3 && .FIRE WEATHER... Issued at 122 AM CDT Wed Jun 18 2025 South winds and high humidity will prevail again this afternoon. A cold front will move through this evening, bringing widespread showers and thunderstorms overnight into tomorrow morning. Hot and humid conditions will move in Friday through the weekend with temperatures rising into the lower to mid 90s. && .MEG WATCHES/WARNINGS/ADVISORIES... AR...None. MO...None. MS...None. TN...None. && $$ PUBLIC FORECAST...CAD AVIATION...AC3