Active Pattern To Bring Anomalous Warmth East And Heavy Precipitation from Four Corners to New England

When a ridge of high pressure stubbornly sits over the same region, it generally brings dry weather and above average temperatures. A ridge causes sinking motion in the atmosphere, preventing deep clouds and precipitation from developing. However, along the edges of the ridge, or what I sometimes refer to as the periphery of the ridge, embedded disturbances in the flow will induce precipitation, some of which can be moderate to heavy. Notice the latest 72-hour rainfall totals (March 14-17 at 8am ET). Aside from localized convection, Florida and areas near the Gulf and Southeast coasts have remained dry through the period, due to sinking motion caused by the ridge. On the other hand, parts of the Southern Plains, Mississippi Valley, Tennessee Valley, Ohio Valley, and Mid-Atlantic have experienced wet conditions along the ridge’s periphery.   

Rainfall totals over the last 72 hours (March 14-17 at 8am ET)

Another hotspot for heavy precipitation over the last few days has been across California and other western regions. An upper-level low pressure system developed this past weekend and continues to slide southeastward along the West Coast. When a low becomes detached from the main flow, they tend to meander for a while and not move all that much. Eventually though, they get absorbed back into the main flow and make their way eastward/northeastward, which will happen by mid-week.

The evolution and track of the upper-level low will have an effect on the weather for the remainder of the week nationwide. As the feature approaches the Four Corners region on Wednesday, precipitation will develop and spread across the region. Mountainous regions across the Colorado Plateau have a high probability of picking up at least 4 inches of snow from Wednesday into Thursday, but accumulations will likely exceed at foot across the higher elevations. As the upper low moves northeastward into Colorado and then into the central Plains on Thursday, a surface low will develop just east of the Colorado Rockies. As the surface low moves across the central Plains and into the upper Midwest/Great Lakes region, a swath of accumulating snow will fall from Nebraska and the Dakotas into the far upper Midwest on Thursday going into early Friday.

The probability of snowfall accumulations exceeding 4 inches from late Wednesday into late Thursday

Also, the eastward progression of the upper low will amplify the ridge across the eastern U.S., which will drive up the temperatures substantially as the rest of the week progresses. Across the Southern Plains, Mid-South, Southeast, and Tennessee, temperatures will surge well into the 70s and into the 80s across parts of the area on Wednesday. The first round of moderate to heavy rain/storms associated with an embedded weaker disturbance will move across parts of the Southern Plains, Missouri Valley, Ohio Valley, and Kentucky/northern Tennessee on Wednesday. The rain will continue spreading northeastward into the Mid-Atlantic and lower half of New England later Wednesday into early Thursday. Some accumulating snow could fall across higher elevations regions in New England. The warm front will continue advancing northward on Thursday and Friday, expanding the warmth as far north as the Ohio Valley and Mid-Atlantic on Thursday and into the Great Lakes region/New England by late Thursday/early Friday. In fact, temperatures will probably increase overnight going into Friday across part of the Great Lakes region and western New England. Another round of rain/storms will move across similar regions in the Thursday/Friday timeframe ahead of an approaching cold front.

Green/yellow shaded regions have the high probability of having flash flooding on Wednesday or Wednesday night
Green/yellow shaded regions have the high probability of having flash flooding on Thursday or Thursday night

The cold front will sweep across most of the eastern U.S. by Friday/early Saturday, which will briefly usher in winter-like temperatures. Unfortunately, the cold front will take it sweet time fully moving through the Southeast; thus, expect Saturday to bring another day of 70s/80s across most of the Southeast outside of the Tennessee Valley and parts of the Mid-South. In fact, the cold front will likely stall out somewhere close to the Gulf Coast and northern Florida, so Florida and possibly surrounding regions just north may not experience much relief from the anomalous warmth.

Projected departure from average temperatures on Saturday morning