National Weather Service
Area Forecast Discussion

1042 AM EDT Tue Jun 18 2019
SYNOPSIS
A stalled frontal boundary draped across Ohio and Indiana, and numerous ripples of energy moving through the Ohio Valley will combine to produce more showers and thunderstorms today. Some of the storms could produce heavy rain and the flooding threat will continue. Activity will be on the decrease tonight before strengthening low pressure approaches the area Wednesday night and Thursday. This will induce more showers and storms across the area. Little rest for the weary in terms of rain chances into the weekend as an extremely moist airmass will continue to be situated across the Ohio Valley, with frequent disturbances moving through offering chances of showers and storms.



NEAR TERM
UNTIL 6 PM THIS EVENING
Active pattern continues today. Primary hazard will be flooding/flash flooding into the evening hours, although isolated strong to even damaging wind gusts can`t be ruled out in the strongest storms this afternoon.

Radar imagery at 14Z shows two areas of rain. First area resides from around Auglaize County east into Union County. Rain in this area has been persistent and slow-moving. Expect this area to diminish/dissipate by midday, per most high resolution guidance, but until then high water issues will continue. Second area resides across the Tri-State area eastward into south- central Ohio. While this area has also been persistent, it has better forward propagation than the northern area, and will continue pressing to the east over the next few hours. Given the saturated ground, localized high water problems may also occur in association with this area.

For the afternoon, upstream convection over southern Indiana/central Kentucky likely will hold together in some fashion, moving across the southern CWA this afternoon. In addition, as models suggest some instability for the afternoon (possibly aoa 1000 J/kg), expect an increase in convection most likely closest to the vicinity of the residual front draped across the CWA. While larger scale upper air support/shear to promote severe is lacking, given the high moisture content the strongest updrafts could produce locally strong or even damaging wind gusts. But the bigger concern obviously will heavy rainfall leading to continued or renewed flooding problems. A flash flood watch continues across the CWA -- until 2 PM in the north and 8 PM further south. Will strongly consider extending the northern portion of the Watch beyond that expiration time.

All grids for today have been updated -- main change is for PoPs/Wx based on latest radar trends/expectations and guidance from most recent high resolution models.



SHORT TERM
6 PM THIS EVENING THROUGH WEDNESDAY NIGHT
Dare we say a break in the action? This time period will feature a ||relative/ minimum in shower and thunderstorm activity due to an overall minimum in shortwave trough action and subtle height rises over the Ohio Valley. Given anomalous moisture in place, still can`t rule out a few meandering showers/storms in a loosely focused sense, but don`t see a concentrated rain threat through Wednesday morning. Rain chances return in earnest Wednesday afternoon and especially Wednesday night as next upper trough shifts into the forecast area. There is timing/strength issues in the NWP with this trough, with 18.00Z NAM seemingly an outlier in comparison to ECMWF/GFS which are slower and a little weaker. Either way, increasingly strong flow brings enhanced moisture transport back into the forecast area from south to north on Wednesday afternoon and especially Wednesday night via a strong low level jet and background forcing for ascent. Should see a large complex of showers/storms develop to the west and move into the forecast area later Wednesday night - and some of this could be strong to severe given increasingly favorable shear profiles and a still extremely moist airmass. SWODY2 has expanded convective risks into the ILN CWA and we could see this continue to increase as timing differences get resolved. Could be an active night in the Ohio Valley given low/mid level shear profiles and overall synoptic setup.



LONG TERM
THURSDAY THROUGH MONDAY
Would like to say the pattern is going to offer some breaks - but we just don`t see much in the way of a respite. Friday offers the best chance of dry weather in the wake of the strong wave on Wednesday night/Thursday, as decent subsidence signal shifts through the flow. Next shortwave trough and returning warm/moist advection along and north of the re-developing stalled frontal zone will likely allow an MCS to form Friday evening in the Corn Belt and this will drop southeast on an increasing feed of southerly flow. Could be a decent MCS knocking on our door late Friday night/Saturday morning. Good agreement in 18.00Z GFS/ECMWF in this scenario. Saturday/Sunday/Monday all look potentially active as numerous shortwaves move through the Ohio Valley as extremely moist airmass remains in place, and heat slowly builds.



AVIATION
13Z TUESDAY THROUGH SATURDAY
12Z TAF forecast is one of low confidence in terms of ceilings and visibility this morning ||through about 15Z/ and then again tonight ||after about 04Z/. This morning - there are a considerable number of sites reporting IFR even LIFR in wake of rain last night and weak winds near a weakly convergent frontal boundary. Sites have been bouncing from IFR to VFR and back again, so a very difficult forecast out of the gate given the pockets of IFR amidst conditions which are largely VFR. In addition, a large area of showers is moving toward the Ohio River this morning and will overspread CVG/LUK, and possibly ILN as well before turning east. Additional showers are just north of CMH/LCK. These should stay north of these two sites but are close enough for concern given heavy downpours.

Once the morning showers pull east and out of the area, the remaining weak frontal boundary will likely see some showers and storms redevelop - but coverage is not expected to be high enough to carry as a predominant weather type. So have VCSH in the afternoon hours especially south of I-70.

The weakly convergent front will again be a source for low clouds and fog overnight much like we are seeing this morning. Hard to say whether this will manifest more as a low stratus deck with minor visibility reductions, or if it will come in heavier and lower in terms of visibility. For now have played an MVFR scenario but this may need to be trended lower in future updates.



OUTLOOK

Thunderstorms will be possible through Thursday, and again Friday night into Saturday.



HYDROLOGY
It`s no secret by now that the ILN CWA is saturated and waterlogged to the point that any thunderstorm complex/rain band is going to cause runoff issues. This potential remains in play today with slow moving/low centroid heavy rain elements dominated by warm rain processes. Several rivers already in flood and many are running high. Flash Flood Watch remains in effect until early afternoon area-wide, and into the evening in the south/central portions of the CWA. 3-5" have been common in many areas in the last 3 or 4 days, and could easily see another 2-4" through the rest of the week and into the weekend with the various thunderstorm complexes. Given crops have been slow to be planted ||a historically slow planting season/ many fields are still not covered with vegetation thus runoff will continue to be higher than normal. Expect more instances of river flooding and flash flooding in the next 3-5 days.



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