textproduct: Cleveland

WHAT HAS CHANGED

No significant changes to the forecast with the morning update.

KEY MESSAGES

1) A few rounds of showers and thunderstorms are expected today through Friday night, with a chance for a few strong storms east of I-71 between 2 and 7 PM today.

2) Significant heat and humidity builds next week, with heat indices likely exceeding 100 degrees, especially in Northwest Ohio.

DISCUSSION

KEY MESSAGE 1... Broad mid/upper longwave troughing continues across the northern tier of the CONUS this morning, with a significant shortwave dropping through its base. Early morning water vapor loops and RAP analysis depict the axis of this low amplitude shortwave over Wisconsin and northern Illinois, and it remains on track to progress through the central Great Lakes this afternoon and evening, with an associated surface low passing across northern Lower Michigan and Lake Huron. The latest RAP and other hi-res guidance have come into agreement on an evening cold frontal passage, and that is diurnally favorable for some scattered, strong to severe convection.

First off this morning, decaying showers are working eastward across portions of northern Ohio and Lake Erie. This activity is being sustained by a 20-30 knot low-level jet focusing modest moisture advection and isentropic ascent as a warm front lifts northward. Consensus among the CAMS is that some of this may rejuvenate near the south shore of Lake Erie early this morning as the low-level jet impinges on the lifting warm front, and this will likely prolong periods of light showers, sprinkles, and cloud cover through 15 or 16Z. That continues to add uncertainty with how the afternoon and evening convection will play out ahead of the cold front since it will disrupt surface heating of what is already not a very warm and moist airmass by summertime standards. The thinking is that a messy convective evolution will take place, with numerous multicell clusters initiating along differential heating boundaries this afternoon and evening. This will make for a lot of scattered convection instead of a more organized line, but strong deep layer (0-6 Km) effective bulk shear of 40-50 knots in response to an impressive 90-100 knot H3 jet streak will allow for some short line segments and bows capable of locally damaging winds if enough instability can be realized. A W to WNW shear vector orientation normal to the convective clusters as well as fairly dry mid- levels depicted in RAP forecast soundings will aid in some bows and wind production, and the strength of the shear also supports some hail. The latest SWODY1 Marginal Risk (level 1 of 5) has been expanded into most of our CWA east of the I-75 corridor, and this is very reasonable given the dynamics and likelihood of numerous, scattered multicell clusters. The number of severe storms will depend on how much sunshine can break through this afternoon. The latest HREF suggests MLCAPE reaching around 1000 J/Kg this afternoon, but this could be about 500 joules higher or lower depending on cloud cover. In terms of timing, convection should start to initiate after 17Z, with the strongest clusters likely between 18 and 23Z as the activity propagates west to east.

The cold front will briefly settle near the Ohio River Valley tonight and Friday morning allowing our area to dry out as surface ridging attempts to build down from the north. The drying will be short lived as another mid/upper shortwave ignites a wave of surface low pressure. This low will move out of the Mid Mississippi Valley Friday morning and will pass across central Ohio Friday night. As the low tracks along the frontal boundary, it will lift slightly back northward Friday and Friday night. Strong moisture advection from a 35-40 knot low-level jet in the Ohio Valley combined with isentropic ascent will result in a large area of rain showers spreading back into our area north of the retreating boundary Friday afternoon and Friday night, with the steadiest rain south of a Findlay to Warren line. Rainfall amounts between 0.50 and 1 inch are possible the closer one gets to U.S 30. Any lingering showers will end by mid Saturday morning as a stronger Canadian high builds down across the Great Lakes and pushes the front back into the Ohio River Valley.

KEY MESSAGE 2... The mid/upper longwave trough that has covered the northern tier of late will continue to influence our region through Saturday, although it will be slowly retreating into New England as a large subtropical ridge builds across the central CONUS in response to a developing deep trough west of the Rockies. This will keep near to below normal temperatures in place today through Saturday, with highs mostly in the upper 70s to around 80. However, the central CONUS ridge will further expand and drift into the Mid Mississippi Valley Sunday and eventually the Ohio and Tennessee Valleys by the middle of next week. This will result in a major pattern change to heat and humidity. The past couple runs of the deterministic ECMWF and GFS have an anomalously strong 500 mb high of 595-598 DM centered near the Ohio Valley by Tuesday and Wednesday, with 850 mb temps as warm as 25 C. This would support high temperatures in the mid 90s or higher, but how hot we get ultimately depends on the strength and position of the ridge and any cloud cover from nearby convective complexes rotating around the ridge (ring of fire). Nevertheless, people should focus on heat related impacts rather than the exact high temperature. Dew points will be in the 70s by Monday, and that will be the case much of next week. This will likely lead to heat indices near 100 F even if air temperatures are just in the low 90s, and the cumulative effect of 3 or more consecutive days with heat indices that high will result in major heat related impacts. This is similar to the first hot spell of the season because it has been so cool the past 2 weeks that people will need to acclimate to the heat all over again. Early season heat is usually more dangerous, so precautions will need to be taken to stay cool and hydrated next week if spending time outdoors. The latest CPC outlooks have a moderate risk for excessive heat next week, and the NWS HeatRisk map is already showing widespread major impacts, so the main message continues to be that a period of significant, prolonged heat and humidity is looking likely next week.

AVIATION /12Z Thursday THROUGH Monday/

Showers are pushing east across northern Ohio this morning and will continue east over the next several hours. Overall, rain is light and conditions are staying VFR. Some isolated MVFR has popped up here and there over western and central Ohio and could allow for some brief MVFR at KMFD. Additional showers and some storms are expected to develop across the area this afternoon with the most likely spots being KCAK, KYNG, and KERI and have maintained some TEMPO groups for IFR in thunderstorms. Any development further west is more conditional and have maintained PROB30s for thunder at KCLE and KMFD. Rain and storms will clear to the east this evening with a cold front moving through the region and high pressure building from the north. Some fog may try to materialize toward the end of the TAF period and have started some MVFR mist mentions.

Outlook...Non-VFR possible in showers and thunderstorms Friday afternoon through Friday night with some lingering activity potentially continuing into Saturday.

MARINE

Southerly flow will be expected over Lake Erie today ahead of a low pressure system and associated cold front moving through the region. Winds will shift to the southwest then west tonight with the cold frontal passage. Overall, winds will remain light, or 5 to 15 kts. High pressure briefly building from the north will allow for light and variable winds over the lake for the first half of Friday. For Friday night into Saturday, a low pressure system will move through the Ohio Valley and winds will favor an east to northeast flavor. At their worst, winds could be northeast at 10 to 15 kts and allow for some 2+ ft waves. High pressure will build from the north starting on Saturday night. Winds will remain light out of the east through Sunday and then shift to the southeast as the system moves over the eastern Great Lakes. Overall, marine headlines are not expected at this time.

CLE WATCHES/WARNINGS/ADVISORIES

OH...None. PA...None. MARINE...None.