Weather across America

(NATIONAL) Heavy rain with the potential for flash flooding and severe weather expected in the Southeast, light to moderate precipitation chances in the Midwest and Northeast, lingering snow chances over the Rockies, and a powerful storm system to carry heavy snow and rainfall threat to California.

Gulf moisture will continue to flow northward over a quasi-stationary front draped across the Southeast helping to fuel widespread shower and thunderstorms Sunday night into Monday. The anomalously high moisture in the low levels will support moderate to strong CAPE values increasing the potential for heavy rain rates of 1"+ per hour. In addition, the quasi-stationary nature of the front will lead to the risk for repeated, overlapping storm development and motions that will contribute to heavier rainfall accumulations, with totals between 2-4", locally higher, possible.

A Moderate Risk of Excessive Rainfall (level 3/4) has been issued across portions of central Alabama to Georgia where the favorable conditions for heavy rainfall are most likely to contribute to the risk for instances of flash flooding. The moderate to strong CAPE values as well as strong winds aloft and strengthening low-level shear will also lead to the potential some of these storms will be severe. The Storm Prediction Center has outlined a Moderate Risk of Severe Weather (level 4/5) from central Louisiana east through south-central Mississippi and central Alabama where supercell thunderstorms may produce a few strong tornadoes and very large hail. 

Shower and thunderstorm chances will continue into Monday, focusing more towards the Gulf Coast as the front begins to shift southward. The more progressive motion of the front as well as weaker winds aloft will keep the risk for flash flooding and severe weather lower than Sunday, with a Slight Risk of Severe Weather across portions of southern Georgia into far southern South Carolina. High temperatures will generally be above average across the South on Monday, with mid-70s to low 80s forecast.

Conditions will be a bit warmer south of the quasi-stationary front and shower activity, with highs in the upper 80s to low 90s in Florida. Things cool down across much of the Southeast on Tuesday after the cold front pushes through. Weak shortwave energy may spawn a surface wave along the central Gulf Coast on Tuesday, leading to the renewed potential for heavy rainfall and flash flooding along across region.

A frontal system pushing eastward across the Midwest will bring light showers to the Ohio Valley and a light wintry mix to portions of the Upper Midwest and Lower Great Lakes Sunday night. Upper level energy will help to better organize an area of low pressure associated with the quasi-stationary front to the south, with the system pushing northeastward into the Mid-Atlantic.  

Light to moderate rain showers are forecast for coastal locations of the region Monday, with a wintry mix further northwest over the Interior Northeast. Highs will generally be seasonable for New England and the northern Mid-Atlantic, with 40s and 50s expected. Temperatures moderate across the Mid-Atlantic beginning on Monday.

A frontal boundary lingering along the Northern/Central Rockies with general upslope flow will keep snow chances up across the region the next couple of days. Locally heavy snowfall will continue over higher elevations in the Northern Rockies, with an additional 6-12" possible through Monday afternoon. Higher elevations in the mountains of the Great Basin and Central Rockies will also see additional snowfall accumulations.

Snow chances have come up Monday across portions of the Central High Plains as the front pushes further into the region. Meanwhile, a powerful Pacific storm system will begin to approach the West Coast on Monday.

Moisture spreading inland will significantly increase precipitation chances across northern California and the Pacific Northwest. Moderate to locally heavy rainfall will be possible along the coast, with locally heavy snow beginning for the northern coastal Ranges of California and the southern half of the Cascades. 

Heavy rain and snow will continue to overspread the region Tuesday. Persistent mean troughing aloft will keep temperatures much below average across the West. Highs will range from the 30s and 40s for the Great Basin and Northern/Central Rockies, the 40s and 50s for the Pacific Northwest/northern California and the Southern Rockies, and the upper 50s to low 70s for southern California and the Desert Southwest.