In the eastern third of the United States, repeated heavy downpours, capable of flooding, are forecast to surge northward between late Wednesday and early Friday, drawing moisture from the Gulf of Mexico. Widespread heavy rainfall is possible from the lower Appalachians up the East Coast along the Interstate 95 corridor, with a wintry mix and snow likely in interior New England.
The Weather Prediction Center writes that the availability of atmospheric moisture and the speed of the jet stream “could break some records” Thursday.
Snow from Texas to Maine
The storm has already produced snow and ice in regions unaccustomed to it deep into Texas.
Thundersleet struck Abilene, Tex., while San Angelo awaited its first measurable snowfall since 2015. After hitting 72 degrees Monday, the city recorded snow by Tuesday night. The dramatic cold front behind winter’s sudden visitation produced shelf clouds that swallowed many towns in the Lone Star State.
Snow will continue over the Interstate 20 corridor in Texas through Wednesday evening, adding an additional 1 to 3 inches to overnight totals.
Winter storm warnings stretch continuously from Texas into Illinois. (Winter weather advisories and winter storm watches extend farther north through the northern Ohio Valley into the Northeast.)
Oklahoma City and Tulsa could see snow totals of 3 to 5 inches atop a dangerous glaze of ice. Will Rogers World Airport in Oklahoma City measured 3.2 inches of snow before 7 a.m. Wednesday, setting a daily snowfall record before the sun even came up. And more snow was on the way.
Even Chicago will get into the action, particularly southeast of the metro. Two or three inches is possible through the overnight into early Thursday morning. That snow will paint a stripe into New England by Thursday midmorning through afternoon.
Severe Southern weather
A few dangerous thunderstorms are possible during the coming days ahead of a strong cold front. It’s the same front that plunged Denver from the mid-70s to just 16 degrees between Sunday afternoon and Monday night, leading to car accidents on snow and ice-covered roads that a day before had been soaking up the springlike temperatures.
As cool temperatures aloft overspread milder air to the east, scattered thunderstorms will erupt over eastern Louisiana, Mississippi and Alabama on Wednesday, where the National Weather Service has declared a slight risk of severe storms.
While moisture-rich warm air from the Gulf of Mexico will increase the amount of fuel for storms, other ingredients for severe storms are less pronounced. As a result, severe storms will tend to be more isolated to scattered rather than widespread.
The chance of severe storms increases Thursday. The Storm Prediction Center has outlined a zone of enhanced risk of severe weather (level 3 out of 5) from the Florida capital north to the southern Carolina Piedmont.
A strong low-level jet stream will race from south to north, carrying with it plentiful moisture and enhancing the amount of shear — a change in wind speed and direction with altitude — needed to brew more violent storms. Scattered bouts of damaging wind are anticipated, although a few tornadoes across the region can’t be ruled out. A few storms could even reach as far north as the Delmarva Peninsula.
Eventually, the storms — which by then may have congealed into a semi-continuous squall line ― will move off the coast early Friday.
Flooding rains in the East
This system is teeming with moisture, the atmosphere’s predicted water vapor content staggering by February standards.
The howling jet stream will behave like a conveyor belt, dragging a ribbon of exceptionally humid air north from the tropics ahead of the cold front. That will fuel very heavy downpours and favor flooding rains in a number of locales.
Meteorologists use a value called the PWAT, or Precipitable WATer Indices, to put the amount of moisture embedded within this air mass into perspective. The PWAT describes the amount of water contained in a column of atmosphere if every last drop could be squeezed out of the air. (Keep in mind this doesn’t translate to maximum rainfall, as the air mass will continually be “refreshed” from the south as more rain keeps falling.)
The maximum PWAT ever recorded in Washington, D.C., during February is 1.44 inches. PWATs on Thursday are expected to surpass 1.35 inches, and likely flirt with or exceed the record. The same is true in Greensboro, N.C., where the February record is 1.47 inches. When PWATs approach record territory, it’s a surefire sign that heavy rain is on the way.
There’s a chance Thursday could be Greensboro’s wettest February day in history, the previous record of 2.59 inches set in 1916 in jeopardy.
The first waves of heavy rain will predominantly affect Mississippi, Alabama, western Georgia and eastern Tennessee on Wednesday. A bit of localized enhancement is possible in the Appalachian foothills, where a Flash Flood Watch is in effect.
Morning bands of light to moderate rain with a few embedded downpours are possible in the Mid-Atlantic on Thursday morning. Then, a heavier slug of rainfall will arrive late Thursday evening and last through the overnight, with improving conditions during the day Friday.
A widespread 2 to 3 inches is possible, with a few 4 to 6 inch pockets in northern Georgia, the Smoky Mountains and the western Carolinas. Isolated to widely-scattered flash flooding is possible, while urban and small stream flooding in many areas is likely.
Wintry mischief in the Northeast
In New England, recent data has indicated a somewhat colder air mass associated with the storm. As such, more in the way of snow and sleet is anticipated.
Significant snowfall, up to 6 to 12 inches (with locally higher amounts), is possible in northern New England, including northern Maine, New Hampshire and northeast Vermont.
Areas farther south from northern Pennsylvania into interior Massachusetts will see a wintry mix late Wednesday night into Thursday morning before changing to rain.
A period of heavier snow is likely in interior New York state and interior New England behind the cold front Friday as a zone of low pressure intensifies near the coast.
The storm’s final act: Newfoundland
It’s been a marathon month in Newfoundland, replete with relentless winter storms and record-shattering blizzards. Now, another powerhouse storm is on the way.
An “atmospheric river” will transport water vapor to the Canadian Maritimes all the way from the tropics. The same water that produces snow and ice in Newfoundland this weekend probably made its trip north from the Yucatán Peninsula in Mexico, or even deeper within the tropics.
It just goes to show you: With weather and climate, everything is connected.