An almost quasi-stationary cold front extending southwestward from the Great Lakes into the central/southern Plains will make slow progress through the day Monday as ridging remains in place to the East.
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The stagnant pattern will allow for additional moist return flow from the Gulf today that will bring increasing shower and thunderstorm chances across portions of the Midwest, Mississippi Valley, and Southern Plains compared to Sunday, especially by Monday night.
Some moderate to locally heavy rainfall is possible along with an isolated threat for some severe thunderstorms.
Greater moisture closer to the central/western Gulf Coast may lead to some more intense downpours from eastern Texas into the Lower Mississippi Valley, with an isolated threat for flash flooding.
A relatively greater threat for a few more scattered instances of flash flooding will exist over southeastern Louisiana where the combination of repeated, back-building thunderstorms producing heavy downpours exists, and a Slight Risk of Excessive Rainfall (level 2/5) has been introduced for the area.
The front will begin to make faster eastward progress by Tuesday, bringing shower and thunderstorm chances into the Ohio/Tennessee Valleys and Southeast.
The chances for heavier rainfall will follow a similar pattern for Monday, with more moderate rainfall for northern locations and a greater chance for locally heavier rainfall and an isolated instance or two of flash flooding from the Lower Mississippi Valley into the Southeast.
A Slight Risk of Excessive Rainfall will also remain in effect for southeastern Louisiana as storms linger.
To the east, another coastal low pressure system is expected to deepen/better organize along the Carolina coast Monday, bringing increasing shower chances spreading northward into the Mid-Atlantic Monday and New England Tuesday.
Some moderate to locally heavy rainfall will be possible, particularly for coastal locations of the Carolinas and Mid-Atlantic Monday.
An energetic upper-level jet stream and another low pressure/frontal system approaching the West Coast will keep unsettled weather in place over northern portions of the West the next couple of days.
Additional heavy higher elevation, mountain snowfall is expected over the southern Cascades into the northern Sierra through Monday.
Moisture spreading inland will help enhance snowfall over portions of the northern Great Basin Monday and into the northern Rockies Tuesday as well, particularly for southern Idaho into western Wyoming.
Snowfall will also linger into the northern Cascades and central Rockies through Monday with generally lighter amounts expected away from the influx of greater moisture.
While most of the accumulating snowfall should be limited to higher elevations, portions of southern Oregon in particular will likely see at least a few inches for inland lower elevation/valley locations as colder air pushes southward and snow levels lower.
Some moderate to locally heavy rainfall is expected for coastal locations of the Pacific Northwest/northern California, particularly near the California/Oregon border.
Widespread much above average, Spring-like high temperatures will persist across the central/eastern U.S.
to start the upcoming work week.
The greatest anomalies of 25-35 degrees will focus on the middle Mississippi Valley northeastward into the Great Lakes and Ohio Valley Monday.
Numerous daily record-tying/breaking highs are possible as temperatures reach into the 70s for most locations.
The cold front pushing through the Midwest will bring temperatures down into the 50s and 60s for the middle Mississippi Valley into the upper Great Lakes Tuesday, though still above average.
Forecast highs range in the 70s and 80s for the southern Plains Monday and Tuesday.
Persistently dry conditions accompanied by lee troughing and gusty winds will keep the threat for wildfires elevated along portions of the southern High Plains according to the Storm Prediction Center at least through Monday.
Along the East Coast, highs are forecast to range between the 40s and 50s for New England, 50s and 60s for the Mid-Atlantic, and 70s to low 80s for the Southeast/Florida.
In the West, highs will remain cooler and below average, ranging from the 30s and 40s in the Pacific Northwest and much of the Interior West, 50s in northern/central California, 60s in southern California, and 60s and 70s into the Desert Southwest.
The coldest spot in the country will be in the northern Rockies/adjacent High Plains, where highs will be in the teens and 20s. ■