National Weather Service
Area Forecast Discussion

142 AM EDT Tue May 21 2019
SYNOPSIS
High pressure will build south into the Ohio Valley tonight. As the the high moves to the east of the area on Tuesday night, a warm front will begin to move northeast toward the Ohio Valley. This warm front will push northeast across the region on Wednesday, bringing a chance of showers and thunderstorms. Cool conditions on Tuesday will transition to warm and more humid weather on Wednesday.



NEAR TERM
UNTIL 6 AM THIS MORNING
Lower clouds may persist in west central Ohio through the rest of the night. Meanwhile cirrus will continue to spread across the area, likely becoming thicker towards daybreak. Only minor adjustments to temperatures through the rest of the period.



SHORT TERM
6 AM THIS MORNING THROUGH 6 PM WEDNESDAY
On Tuesday, the center of surface ridge will move east toward the eastern Great Lakes. Considerable mid and high level clouds will gradually lift to the north during the afternoon while locations along and south of the Ohio River scatter. Winds will have shifted to the east around 10 knots. Given a cool start, easterly flow, and considerable clouds, temperatures across the north will remain on the cool side, while afternoon sun across the south will allow for warmer temperatures. Highs will range from near 60 far north to the lower 70s along and south of the Ohio River.

A strong occluding system will lift north toward the central Plains Tuesday night while the mid level ridge continues to build north. This will allow a warm front to our southwest to begin to push northeast. Ongoing convection well to our west across the mid Mississippi River Valley will move east overnight, but should weaken as it does. We could see a shower or thunderstorm encroach our western zones late from the weakening convection. Overnight lows will occur by early morning Tuesday night, then begin to rise some toward sunrise Wednesday. Lows will range from the lower 50 to mid 50s north with mid to upper 50s expected along and south of the Ohio River.



LONG TERM
WEDNESDAY NIGHT THROUGH MONDAY
By Tuesday night into early Wednesday, the remnants of what once was a cohesive and well-formed convective line across the mid-Missouri Valley will nudge eastward closer to the local area but will most likely do so in a weakening state as the source impulse/disturbance essentially becomes sheared-out as it progresses into an increasingly hostile environment characterized by a midlevel ridge axis centered from eastern TN northward into eastern MI. As such, precipitation chances will decrease west to east Wednesday morning with the nudging of the pseudo-warm front east across the area, with just chance PoPs during the day as the remnants of the disturbance push east through the region. Increasing low-level instby during the afternoon hours, attendant with the influx of BL moisture-rich air, will occur with at least the potential for a remnant outflow/storm- scale boundary lingering about the area -- which may provide a focus for re-initiation of storms during the afternoon hours across central and western portions of the ILN FA. With relatively weak forcing overall, however, the coverage is expected to remain isolated to scattered in nature even during peak diurnal heating.

Even with the inherent uncertainties in convective re- initiation locations on Wednesday afternoon, the expansion of the ridge across the Gulf States and southeast U.S. will yield an increasingly large, warm, and humid airmass across both the Tennessee and Ohio Valleys midweek and beyond.

By Thursday, the upper level ridge across the southeast will strengthen considerably -- and this has been, and continues to be, supported both in deterministic and ensemble datasets among multiple synoptic-based modeling systems. However, a midlevel disturbance progressing eastward along the northern periphery of this ridge may provide enough focus for ascent to allow for scattered showers and storms again during the day on Thursday. This being said, there remains considerable variations in the global model suite handling of this system and the potential implications on convective coverage locally. However, with at least some focus for ascent and more than enough surface-based instby, do think that storm activity will be more widespread Thursday (especially compared to Wednesday). And even after the midlevel impulse moves through, a very weak front will likely become laid out in a west-east orientation across the northern Ohio Valley -- which in and of itself may provide enough surface convergence to keep scattered storm activity going further into the overnight period into very early Friday morning -- especially across central Ohio and points northward.

The positioning of the strong ridge over the southeast U.S. will undoubtedly have implications on the sensible weather locally for the end of the workweek into the upcoming weekend -- as it at the very least appears like the center of the ridge will stay well south of the Ohio Valley. This setup does lend itself to the potential for embedded disturbances riding along the northern fringes of the ridge, which would act to keep a daily chance of showers and thunderstorms in the forecast (especially across the northern reaches of the Ohio Valley) opposed to going with a hotter/drier solution for Friday through the end of the long term period. This being said, the oscillation of the weak frontal boundary about the northern Ohio Valley is not being handled well at this time by long range guidance in terms of its orientation and associated progressions/retreats from Friday through early next week. The ECMWF continues to show a further north mean frontal position /with attendant corridor of favored repeated rounds of showers/storms/ while the GFS trend of a wetter/stormier pattern for the local area continues from run-to-run. Am leaning right now toward the GFS solution of daily chances of showers/storms being maintained in the ILN FA with the Ohio Valley positioned more squarely on the fringes of the ridge. Although these kinds of patterns can be deceivingly active for us here locally, did not want to jump too much on precipitation chances given inherent uncertainties in timing and placement of the aforementioned oscillating front -- the evolution of which will be dictated by the expanse (or lack thereof) midlevel ridging northward into the region. Nevertheless, the pattern for the end of the week into the weekend may very well feature multiple rounds of storms for the Ohio Valley -- the specifics of which may not come into better focus for at least several days. Nevertheless, the prospect of having midlevel disturbances pivot about the ridge axis amidst an inherently unstable airmass will be watched in the coming days for the potential for episodic thunderstorms for an extended period of time late in the week.

With all of this being said, confidence remains high in a very warm and humid airmass building into the region from Wednesday through the end of the long term period -- with highs in the 80s/near 90 and lows in the 60s. These temperature trends of course will inevitably be augmented by associated complexes of storms at times during this period. However, the overall pattern supports an extended stretch of above normal temperatures for much of the region.



AVIATION
06Z TUESDAY THROUGH SATURDAY
VFR will prevail through the TAF period. High and then mid clouds will spread across the region through much of the period with clouds scattering towards 00Z. Winds will veer to the east and be around 10 kt.



OUTLOOK

Thunderstorms possible Wednesday and Thursday, and again Saturday.



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