textproduct: Cleveland

WHAT HAS CHANGED

Another Heat Advisory has been issued for Wednesday, but this time it encompasses more of north central and NE Ohio.

KEY MESSAGES

1) The hottest day of this stretch will be Wednesday, with peak heat indices in the 95 to 105 degree range leading to Major HeatRisk (level 3 of 4) areawide.

2) Gradual cooling Thursday through the weekend with periodic chances for showers and thunderstorms. The greatest potential will be Friday and Saturday.

DISCUSSION

KEY MESSAGE 1... A large bubble of hot and humid air is becoming established across the region this afternoon as an elongated and anomalous H5 ridge averaging 600 DAM temporarily builds into the Great Lakes. Afternoon satellite and water vapor loops show this ridge currently centered over southern portions of Minnesota and Wisconsin, and the center will slide SE into the Ohio and Tennessee Valleys by late Wednesday. The position and movement of this H5 ridge center will make for a different type of heat compared to the late June/early July event.

First, the westerly mid/upper flow on the northern periphery of the ridge will direct the warmest temperatures (averaging 26 C at 850 mb) across the northern and central Great Lakes tonight and Wednesday. Some of this will drop SE across our region Wednesday as the ridge center moves southeastward, but generally expect the hottest air temperatures to occur in Lower Michigan. Second, the airmass circulating NW to SE across the region will lead to lower max dew points compared to the previous heat event, with dew points expected to peak in the upper 60s/low 70s Wednesday. This should cap max heat indices in the 95 to 105 F range (warmest in NW Ohio). With all of this being said, Wednesday will be the hottest day of this stretch with major HeatRisk impacts (level 3 of 4) expected for vulnerable populations, but we are not looking at extreme impacts this time since the worst conditions will be north of the area. Issued a Heat Advisory for Wednesday for all counties in the CWA except for Lake, Geauga, Ashtabula, Erie, and Crawford since an onshore component to the low-level flow should help to keep temps and heat indices lower there.

KEY MESSAGE 2... The mid/upper ridge will start to become suppressed farther SW into the Ohio and Tennessee Valleys Wednesday night and Thursday in response to a mid/upper trough deepening over eastern Canada. This trough will continue to slowly deepen through the Great Lakes and suppress/retrograde the ridge Friday through the weekend. As this process occurs, gradually cooler and less humid conditions will drop into the area. An initial frontal boundary sagging through the southern Great Lakes and Upper Ohio Valley Wednesday night and Thursday will advect notably lower dew points across the region for Thursday and Friday as low-level flow turns northerly and surface high pressure builds down into the eastern Great Lakes. Although air temperatures will still be very warm Thursday and Friday (mid 80s to low 90s), the lower dew points will keep heat indices lower. The real cooling when air temperatures will drop will occur by Sunday into early next week as the mid/upper trough further deepens.

The other aspect that this changing weather pattern will bring is the potential for convection. The initial sagging front Wednesday night will interact with moderate to strong instability beneath a stout EML. The latest HREF and RRFS continue to show uncertainty, but there is an increasing signal for some widely scattered convection Wednesday night if the cap can break, so added chance POPS. The better potential for convection will occur Friday over the SW portions of the CWA and Saturday over more of the area as the frontal boundary slowly lifts back northeastward in response to a couple of shortwaves dropping through the developing NW flow aloft. We are not currently outlooked for severe weather, but would not be surprised to see it in future outlooks since the combination of at least moderate instability and increasing upper jet support/shear could support organized convection, especially Saturday. The biggest uncertainty lies with convective evolution and timing, as the pattern supports upstream MCS activity potentially dropping SE through the region at times in addition to local development. Conditions will gradually trend drier Sunday through early next week as the trough deepens and pushes the frontal boundary south allowing Canadian high pressure to build in.

AVIATION /18Z Tuesday THROUGH Sunday/

VFR across the TAF sites this evening with mainly VFR to persist through the TAF period. Main concern going forward will be the potential for lower vsbys starting Wednesday night as upper- level wildfire smoke may begin to filter down near the surface. Have introduced 5sm hz for CLE towards the end of the TAF period late Wednesday evening. Additional hz mentions may need to be added at other TAF sites if trends persist.

Winds are generally out of the west to southwest this evening, 5 to 8 knots. Winds will subside to 5 knots or less overnight, before increasing and shifting to the west to northwest Wednesday afternoon, 8 to 12 knots. A few brief gusts up to 20 knots are possible at CLE/ERI.

Outlook...Non-VFR visibility possible Wednesday night and Thursday due to wildfire smoke. Non-VFR likely Friday night through Saturday in showers and thunderstorms.

MARINE

Elevated southwest flow will continue over Lake Erie this afternoon and evening with high pressure advancing eastward and increasing the pressure gradient over the lake. The highest waves will continue out of the nearshore zones with a flavor of 2 to 3 ft closer to the NW PA/NE OH shoreline. As high pressure advances east for Wednesday, southwest flow will continue and diminish. A cold front will move east for Wednesday night into Thursday and stall out across the lake. This will flip flow to the north/northeast on Thursday. This boundary will remain across the lake on Friday, maintaining weak east flow. Several low pressure systems will move through the region over the weekend, strengthening southwest flow at times and bringing intermittent storm chances.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Heat Advisory until 8 PM EDT this evening for OHZ003-006>011- 017>019. Heat Advisory from noon to 8 PM EDT Wednesday for OHZ003- 006>011-017>023-027>033-036>038-047. PA...None. MARINE...None.