A shortwave trough will support repeated rounds of convection to develop across the southern tier of the country over the next few days.
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Tonight appears to be the worst of it from a heavy rainfall and severe weather standpoint as anomalous moisture and significant instability make their way into the region.
A Moderate Risk (level 3/4) of Excessive Rainfall leading to Flash Flooding is in effect for portions of eastern Texas, Louisiana and southwest-to-central Mississippi, where the confluence of moisture, instability and lift along the surface front will be greatest.
In addition to the Moderate Risk of Excessive Rainfall, a Slight Risk (level 2/4) of Severe Thunderstorms is in effect over the Central Gulf Coast where a few tornadoes and severe-wind gusts are possible.
The primary Flash Flood risk pivots into parts of the Southeast and Southern Appalachians while remaining over the central Gulf Coast.
The Severe threat remains for the Lower Mississippi Valley and Southeast, but at a lower/Marginal risk.
The anomalous moisture plume emanating from the Gulf of Mexico will spread into the Northeast tonight ahead of the approaching low pressure system over the Ohio Valley.
Rain showers in the warm sector are likely for much of the Northeast and Lower Great Lakes tonight while freezing rain gets going over parts of Vermont, New Hampshire and southern Maine.
Freezing rain accumulations aren't expected to eclipse 0.1".
Light snow will occur over central and northern Maine.
Conditions should improve by Thursday afternoon for the Northeast.
Abnormally warm temperatures are likely to spread into the East Coast and Ohio/Tennessee Valleys over the next few days.
Low temperature anomalies between 40-50 degrees above average will lead to widespread records being broken tonight and Thursday night.
Elsewhere, low pressure in the West will produce snow showers over the Cascades, Sierra and Rockies over the next couple of days. ■
A clipper system will move quickly across the northern Plains into the Midwest Friday and the Northeast by Saturday, bringing a wintry mix of rain and snow showers ahead of a sweeping cold front.