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Day 2 Outlook >
WPC Day 1 Excessive Rainfall Outlook
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
Updated: 1429 UTC Mon Jun 25, 2018
Valid: 15 UTC Jun 25, 2018 - 12 UTC Jun 26, 2018
Day 1 Excessive Rainfall Forecast
Forecast Discussion
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1028 AM EDT Mon Jun 25 2018
Day 1
Valid 15Z Mon Jun 25 2018 - 12Z Tue Jun 26 2018 

1500 UTC update

...Central to eastern Kentucky...
The only change of note made to the initial excessive rainfall 
outlook was to add a slight risk area over portions of eastern KY 
and expand slightly northward the marginal risk area into the 
upper OH river region.  These changes were for convective 
potential ahead of the vort initially over the lower OH Valley 
region that is forecast to push eastward into the upper OH river 
region by this evening.  FFG values are relatively low across 
portions of central to eastern KY ahead of this vort... and with 
heavy rains potential likely late morning through this afternoon 
ahead of this vort...runoff issues are possible.  



A closed low will slowly shift east across NE today. Likely to 
have an expanding area of showers and embedded thunderstorms 
around the center of this low, with cell mergers and locally heavy 
rain rates likely. Instability will likely be a limiting factor, 
but should see just enough to allow for some embedded heavier 
convective cores within the broader area of more stratiform 
rainfall. Portions of northeast NE, southeast SD, southwest MN and 
western IA have seen well above normal rainfall of late, making 
these areas more susceptible to additional flash flood issues. 
Thus, while extreme rainfall totals are not anticipated today, a 
prolonged steady rainfall with embedded heavier rates will still 
likely pose at least some flash flood threat. The general 
consensus amongst the 0z guidance is for localized rainfall totals 
around 2" in three hours, with localized totals through the day 1 
period of 3-4" within the Slight Risk area. 

The Slight Risk was shifted southward with this update, with all 
of the 0z global and high res models shifting in this direction. 
Will maintain a broader Marginal Risk around the Slight. Sometimes 
with closed lows such as this we see some slow moving heavy cells 
develop on the periphery of the system where diurnal heating can 
be maximized...and thus some chance we see some localized flash 
flood issues extend extend further north in SD/MN...with the 
Marginal covering this potential.

Will carry a Slight Risk from portions of northeast OK into 
southern MO and far northern AR. This is to account for potential 
convective development later this afternoon into tonight. The 
closed low to the north will put this area in a corridor of very 
strong upper level divergence. Also will have a slow moving cold 
front draped across this area, with confluent flow increasing 
towards evening as the nocturnal increase of the southerly low 
level jet kicks in. This should support an expanding area of 
convection along/near this front by this evening into the 
overnight hours. Given the slow movement of the front and the 
persistent 850 mb moisture transport into it, the setup does 
appear to support some backbuilding and training. This scenario is 
depicted well by most of the 0z guidance as well...with several of 
the 0z HREF members depicting some 3"+ amounts across this 
corridor. This area has been anomalously dry of late, resulting in 
high FFG. However the training potential suggested by the 
environmental setup, and the signal within the 0z HREF, suggests 
that short term rates may still get high enough to cause some 
flash flood concerns...thus a Slight Risk is warranted.

A tricky convective forecast across this area today. As of 08z 
note one convective cluster moving into eastern KY, with another 
developing over southern IL and western KY. The 0z HREF members 
and recent HRRR/HRRRX runs tend to weaken this lead complex as it 
runs east of the instability axis, and thus focus additional 
development through the day along/ahead of the trailing complex. 
However the lead cluster appears to be maintaining itself more 
than the models would suggest. Still think it will tend to be on a 
downward trend as it heads into the Appalachians, but it very well 
may maintain a bit more than suggested by the guidance. This then 
brings up the question of whether remnant cloud cover from this 
system impacts instability ahead of the next wave. Either way 
likely to have convection with locally heavy rain along this 
corridor, just some uncertainty with the exact timing of heaviest 
amounts, and whether or not an organized flash flood risk ends up 

Will carry a Slight Risk across portions of southeast NC and 
northeast SC. This is where the best chance of merging cells and 
heavier basin averaged rainfall appears to be. As the MCV 
approaches from the west, likely will see at least one organized 
area of convection move east into this area. Also may see 
diurnally driven storms fire ahead of this feature within a 
corridor of low level convergence (possibly aided by sea breeze 
boundaries as well). Thus it is the concern that this lead 
convection ends up merging with a more organized area of 
convection moving in from the west, that warrants a Slight Risk 
issuance. More uncertainty upstream across western NC into 
southwest VA. Considered a Slight Risk here as well, but enough 
uncertainty with how things evolve instability wise, given the 
multiple MCVs in play, to keep it at a Marginal Risk for now. 
Think some flash flood risk certainly exists, but it may end up 
more localized in nature across this area compared to further 
southeast. Will need to closely monitor trends though, as may need 
to upgrade the risk if enough destabilization appears imminent 
resulting in more widespread merging of stronger cells.


Day 1 threat area:

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