Oppressive heat and humidity continues across much of the South.
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Severe storms will be possible in the Northeast, central Plains, and Mid Mississippi Valley.
Heavy rain that could cause significant flash flooding is likely from southeastern Missouri to central Alabama and for parts of the north Plains.
Meanwhile, fire weather threats continue in the south Plains and Northwest.
Indicators for a potentially very significant rainfall continue to sound across northwestern SD primarily, but also into southwestern ND.
100 year ARI values (which represent total rainfall between 4 and 5 inches of rain) have spiked over 60% for a small portion of northwestern SD, with a 50% area into far southern ND.
This is now considered a high end Moderate Risk area.
The broader Moderate Risk has been expanded north and east to include more of the steady but still stratiform rainfall ongoing across west central ND, with the Slight Risk brought nearly to the Canadian border, as the steady rain is likely to amount to 1 3 inches, but will be falling over a longer period of time.
This will still be a highly unusual amount of rain, but for northwestern ND may fall just slow enough that the river systems can mostly handle it.
Such is not expected to be the case further south, where instability both from daytime heating, but far more significantly from the advection of high theta e air continuously into the vertically stacked and intensifying low over SD will likely make for much higher rainfall rates in thunderstorms, which are expected to largely overwhelm the low FFG values between 1 and 1.5 inches in an hour over much of the Moderate Risk area as storms capable of producing 2 inch/hour rainfall rates are possible this afternoon and evening.
The Slight and Marginal Risks were expanded to include more of OR and ID, where there's good signal for 1 3 inches of rain on persistent easterly upslope flow, and the Marginal into OR where light to moderate rain has been ongoing all morning and convection is expected to continue developing this afternoon.
The Slight Risk across northern and eastern MO is mostly in place for an expected MCS that will develop this afternoon with the initial thunderstorms appearing to form currently and evening and move over the area, with a leading squall line followed by training convection.
This area has been quite hard hit in recent days, and more rainfall is occurring presently, though fortunately is largely moving at a fast pace.
This area will be monitored into the evening for a potential Moderate Risk upgrade as well.
The Slight Risk over the area matches messaging with the ongoing Flood Watches across portions of northeast NY and all of VT, NH, and southern ME.
Training storms are beginning to develop with an MCV moving into ME and new convection forming presently across NY, which will move across the region this afternoon.
After heavier than expected flooding in VT last night, the Slight Risk looks good for this region with no significant changes planned.
Anomalous moisture combined with favorable forcing for ascent associated with shortwave energy moving through the region will keep an active/unsettled pattern in place and the threat of heavy rainfall and flash flooding.
The notable difference however from yesterday's Day 2 ERO was an uptick in the rainfall along the NC/VA coastline as a weak shortwave approaches from the west later today.
Extended the Marginal risk area to cover the potential that some flooding or run off problems occur.
On the other hand flash flood guidance is very high which should help mitigate any concerns. ■