textproduct: Wilmington

WHAT HAS CHANGED

No major changes.

KEY MESSAGES

1) A strong storm system will move through the region Tuesday night into Wednesday bringing the potential for multiple rounds of severe weather, flooding, and gusty winds.

2) Wind gusts up to 30-35 mph expected early Friday morning into the evening particulary for Western Central / Central Ohio with isolated gusts potentially reaching 40mph.

3) Warmer and wetter conditions expected Sunday into Monday, potentially transitioning to a rain-snow mix in the early morning hours on Monday.

DISCUSSION

KEY MESSAGE 1) A strong storm system will move through the region Tuesday night into Wednesday bringing the potential for multiple rounds of severe weather, flooding, and gusty winds.

Tuesday night severe threat: Thunderstorm initiation near the southern periphery of Lake Michigan should be in the 4pm timeframe this afternoon, with the developing complex to push southeast into the evening and early overnight hours. This primary cluster should remain north of the ILN forecast area until after 04z, and will be on a weakening trend and lose organization as it progresses into the northern Ohio Valley.

The main potential for severe storms overnight will be south of this main northern Indiana cluster. A 45-55kt LLJ develops overnight which will prompt elevated convection after about 08z. Thunderstorm clusters have the potential to produce large hail, and thunderstorms that do develop can facilitate the mixing of the LLJ down to the surface, so damaging winds are also a threat. Prime timing for this first round of severe storm potential is 08-14z. There isn't an expectation of tornadic storms with this initial elevated cluster.

Wednesday afternoon severe threat: After a potential lull in late morning/very early afternoon, the afternoon threat may be highly conditional on how widespread morning convection is and the extent of late morning/early afternoon clouds. Surface cold front still outside the ILN area by 16z/Noon over northern/Central Indiana into NW Ohio.

Looking at how the CAMs resolve the afternoon convection, only the NSSL WRF seems to amp up the potential for stronger discrete cells, as it's not as robust with the morning convection. Confidence in the extent and severity of the Wednesday afternoon storms is a little shaky as a result. As the cold front pushes SE through the afternoon, the greatest risk area for developing instability and thunderstorm/severe thunderstorms after any lingering morning clouds would likely be along/SE of I-71. In addition to damaging winds and hail, the 16-22z timeframe along/SE of roughly I-71 has the best potential for rotating storms/isolated tornadoes if we destabilize enough.

Wind threat: With the strong LLJ ahead of the main frontal boundary, winds pick up to 35-40mph even outside of any thunderstorms. Held off on a wind advisory at this time, but mentioning this elevated wind threat outside of storms in existing partner messaging.

Heavy Rain/flood threat: Per the HREF, the area with the best potential for multiple rounds of heavy rain appears to be along/north of a Richmond/Dayton/Circleville, with the localized Probability Matched Mean from HREF members yielding a 24 hour potential of 2-3". But this should be with multiple rounds over an area that didn't get flooded last week, so while minor flooding is possible, if multiple rounds remain north of this line, not expecting flash flooding.

KEY MESSAGE 2) Wind gusts up to 30-35 mph expected early Friday morning into the evening particulary for Western Central / Central Ohio with isolated gusts potentially reaching 40mph.

According to the GFS, an intensifying jet streak plans to center itself over central Ohio with a weak positively-tilted trough at the 500mb level. An incoming cold front will pass midday Friday with high pressure following behind with some clearing convection near Western Central OH. Areas of Central Ohio and counties to the west may expect wind gusts up to 35mph and potentially 40mph in isolated areas. Temperature advection earlier in the day favor warm air advection before flow becomes more zonal by the mid-afternoon, bringing in some south-southwest flow. Relative humidities will hover in the 40-50% range. Wind gusts are expected due to the tightening pressure gradient on the southern side as the low dives to the southeast.

KEY MESSAGE 3) Warmer and wetter conditions expected Sunday into Monday, potentially transitioning to a rain-snow mix in the early morning hours on Monday.

A deep, positively-tilted trough on Sunday will begin to shift negatively by the end of Monday. Rain chances begin Sunday evening before potentially shifting to a rain-snow mix in the very early morning hours of Monday as the 540 line follows shortly behind the cold front. Winds, both surface and aloft, will shift from southerly to northerly, bringing in some colder and drier air. Severity of this system is little to none, bringing in around under an inch of snow near Wilmington and upwards of an inch near Cincinnati. Morning commute may be affected by slippery road conditions. Winds center around 10-15 kts during this event, decreasing chances for whiteouts. Pre-frontal rain soundings have SBCAPE stagnant around 0- 600 J/kg with SFC-6km shear around 40-70 kts in varying areas; 700- 500mb lapse rates are looking to maximize around 7 degrees Celsius / km with instability and energy dropping as soon as convection moves into the area. Temperatures will center around 50-60 degrees F midday Sunday before dropping down to the upper 20s and low 30s for the incoming rain-snow precipitation, with highs during the day on Monday only reaching the low 30s. The GFS shows areas of spotty freezing rain around Columbus 06z and areas of sleet near south central Ohio at 09z.

During the transition and front passing, a brief chance of mixed winter precipitation will be possible. There is a chance for light snow accumulations, but details are still to be determined.

AVIATION /18Z TUESDAY THROUGH SATURDAY/

Starting to see some breaks in the MVFR ceilings, so quiet conditions expected through about 06z. As the strengthening LLJ pivots into the region overnight, LLWS expected near/after 06z. Due to lingering low confidence in thunderstorm development after about 07z, kept TSTM mention to PROB30, but then introduced TEMPO groups at all sites, with the narrowest window being KDAY as the frontal boundary approaches toward the very end of the TAF window.

Strong winds outside of thunderstorms mainly after 15z will increase to near 30kts or possibly higher right ahead of the cold front. FROPA after about 20z at the KCVG extended TAF.

OUTLOOK...Sharp wind shift from southwest to northwest is expected between 20Z Wed-00Z Thu, with gusts above 40 kt possible Friday.

ILN WATCHES/WARNINGS/ADVISORIES

OH...None. KY...None. IN...None.