textproduct: Wilmington

WHAT HAS CHANGED

Increased confidence for thunderstorms over the weekend.

KEY MESSAGES

1) High confidence in extreme heat through Friday.

2) Chances for showers and thunderstorms increase over the holiday weekend, while heat and humidity continues.

DISCUSSION

KEY MESSAGE 1)

Center of the 1020 500mb ridge remains anchored over the Ohio Valley as of this writing and is not forecast to shift much over the next 24 hours. Mass subsidence resulting in clear skies and sinking/ compressing air continues to contribute to our early July heat wave.

Daytime highs today reach the mid 90s again with very sticky Tds in the 70s; this results in heat indices between 100 and 105 for the entire CWA on Thursday. Areas along I-70 and north may feel a subtle afternoon breeze (closer to the pressure gradient) of around 5-10 MPH, but it won't be enough to alleviate the extreme heat.

Tomorrow night will be a similar story. Overnight lows in the mid 70s offering little relief. Patchy fog will once again be possible, especially in river valley regions, given very moist airmass and calm conditions (and corn sweat).

By Friday daytime hours, we start to see some subtle changes to our stagnant high pressure as the upper level ridge begins to break down somewhat. Unfortunately, change is slow and at the surface, we'll still be feeling the effects of the heat. Extreme Heat Warning continues through Friday at 8 PM, as daytime heat indices reach the lower 100s. With that being said, as the ridge dampens a little, this allows PoPs to be reintroduced to the forecast Friday afternoon and evening. See next key message.

KEY MESSAGE 2) By Friday afternoon, there is good consensus between the big three (ECMWF, GFS, Canadian) that the 500mb ridge will be dampening with the center of it shifting slightly eastward. This acts to bring somewhat more zonal upper level flow back over the Great Lakes region and allow for shortwave disturbances to potentially reintroduce PoPs back into our forecast.

Unfortunately, there is no strong forcing forecast at the moment so confidence on storms/ timing/ placement is quite low. However, there is a signal for some convection Friday night between a handful of deterministic guidance. MPASA, RRFS, HRRR, and even the GFS all paint scattered convection Friday evening. With upper level forcing being quite limited, not overly concerned about an organized severe threat, but damaging winds may occur with collapsing storms, given the very high DCAPE and CAPE environment. Similarly, the extremely moist airmass in place will allow for heavy downpours with any storms. With it being a holiday weekend and plenty of people outside, wanted to start highlighting the thunderstorm/ lightning threat early.

As we move into the 4th, confidence in the forecast decreases both in terms of heat and thunderstorm coverage. The Ohio Valley will be well under zonal flow by then and the environment won't be as capped as previous days. Diurnal thunderstorm activity is expected, though it's a bit early to determine where. This uncertainty translates to heat products as well. The warm and humid airmass will be slowly shifting southward and much of our area may still have heat indices in the upper 90s to low 100s. Of course, thunderstorm activity would disrupt diurnal heating and act to lower temps. At this point, it's a bit too early to make a decision on any headlines. However, it will still be a hot and humid day (with a chance for storms)! Plan accordingly for your Independence Day.

Looking ahead at the long range guidance, the unsettled pattern continues with additional chances for convection. A somewhat larger shortwave may arrive early next week, pulling in some cooler (ish) temperatures, but much remains to be determined at this point.

AVIATION /10Z THURSDAY THROUGH MONDAY/

Handful of sites still reporting patchy fog, with LUK being the most problematic. Kept them at LIFR through 12Z or so. Fog should burn off quickly this morning as the sun rises. Some patchy cu are possible as are some cirrus drifting by, but otherwise mostly clear skies are expected today. Similar conditions are expected overnight tonight and patchy fog will once again develop.

Winds out of the southwest reach 8-10 knots for northern TAF sites (KDAY, KCMH, KLCK) while southern TAF sites remain around 5 knots. Winds decrease overnight tonight to calm or light and variable.

OUTLOOK...Thunderstorms are possible Friday and into next week.

ILN WATCHES/WARNINGS/ADVISORIES

OH...Extreme Heat Warning until 8 PM EDT Friday for OHZ026-034-035- 042>046-051>056-060>065-070>074-077>082-088. KY...Extreme Heat Warning until 8 PM EDT Friday for KYZ089>100. IN...Extreme Heat Warning until 8 PM EDT Friday for INZ050-058-059-066- 073>075-080.