December 31, 2020

This Is Your World Today | December 31, 2020

Today is the 366th day of the longest year we've been through in a long time. Fires, floods, tornadoes, excessive heat, bitter cold, massive snows, and hurricanes upon hurricanes upon hurricanes—and that's just the weather. It's hard to find beauty amid the chaos, but it's there if you know where to look.

If you're a longtime reader (hi!), you might remember that I used to write "Here's Your World Today" posts in a previous blogging life. I originally started those posts as filler to get through quiet days, but it turned into an enjoyable (but short-lived) series to gawk at happenings around the world. In that spirit, and 'cause goodness knows we could use it, here's a loosely affiliated sequel: This Is Your World Today.

A: Today's big weathermaker in the United States is this blobular (totally a word) winter storm in the southeast. It's producing severe thunderstorms along the northern Gulf Coast, complete with an enhanced risk for tornadoes across parts of Louisiana and Mississippi. The cold side of the storm will bring snow and ice to communities from Texas north through the Midwest. Temperatures will briefly jump into the 60s along the East Coast before the system's cold front sends things back down to a more reasonable level for the beginning of January.

B: It's tough to see the Great Lakes through the clouds—but they're part of the reason there are clouds there in the first place. It's been such a (relatively) warm couple of months in the eastern United States that there's hardly any ice on the Great Lakes. The latest analysis from NOAA showed that just 2.2 percent of the Great Lakes were covered by ice. Ice cover percentages are usually in the double digits by this point in the winter.

C: A strong cold front moving over relatively warm waters of the Atlantic Ocean is a recipe for brilliant streets of cumulus clouds. These are always a sight on satellite imagery. They form as air warms up near the surface of the ocean, forming cumulus clouds as its rises and gets organized into rows (or "streets") by the prevailing winds. 

D: The Amazon's hot and humid climate affords us the opportunity to admire thousand-mile fields of cumulus clouds. Particularly active days will see raucous thunderstorms blow up over the Amazon, raging and randomly scooting around until the instability of the day wanes after sunset. 

E: Actinoform clouds (a close-up is seen at the top of this post) are a near-daily occurrence in the southern Pacific Ocean. These marine clouds take on a radial pattern, kind of developing littles spokes and trippy chains as they form over frigid waters. These clouds weren't discovered until weather satellites first spotted them—it's hard to see their shape from below—and it's still a bit of an open question why these clouds take on their distinctive shape. Some of the clouds over the northern Atlantic in "C" above are also actinoform clouds.

F: It's the sun! Well, the sun's reflection. Each day for about the next six months, the sun's reflection on the ocean surface will tick a little higher in latitude. Maximum sunlight reached its southernmost extent over the Tropic of Capricorn on last week's winter solstice. It's always cool to watch the sun's reflection glisten across the oceans in long satellite loops. (The loops are too sizeable to upload here, unfortunately.)

G: This swirling low-pressure system in the Bering Sea is the strongest storm in that part of the world in years. The system's central pressure dropped to a staggering 921 mb on Thursday, which is about as low as you'd expect in a powerful category four or category five hurricane. I explained on Forbes yesterday how this storm got so strong—and why it's so different from a hurricane.

H: Hey, look, Hawaii! Very pretty. It's always interesting to look at the islands on satellite imagery because it's obvious which way the winds are blowing. Moist winds blowing out of the northeast dry out as they pass over the islands, leaving clear skies downwind.

[All satellite images from NOAA.]

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December 24, 2020

A Boisterous Windstorm Will Usher In A Frigid Christmas Across Much Of The Eastern U.S.

A coast-to-coast storm will reach its peak tonight as it shoves its way across the eastern United States, bringing some combination of dangerously strong winds, severe thunderstorms, flooding rains, and heavy snow to everyone from the southern tip of Florida to the northern reaches of Maine. This storm will be highly disruptive in many areas as it pushes through.

As we've seen out west already, a strong pressure gradient will lead to ripping winds as the system strengthens. The low already produced heavy snow and intense winds across much of the north-central part of the country. Intense winds buffeted communities in the Rockies and on the Plains earlier this week. A significant portion of Minnesota and Iowa endured blizzard conditions during the day on Thursday, whiteout conditions that made driving a fool's errand and simply walking around without getting disoriented just about as difficult.

More snow will fall as the system tracks east. The greatest snowfall totals—read: the greatest chance for a white Christmas—will fall in the Ohio Valley and the Appalachians. Some areas could see a decent li'l snowstorm, with totals exceeding half a foot in higher elevations of West Virginia. Lake effect snow on the eastern shores of the Great Lakes will bring a fresh blanket to communities that are plenty acclimated to those conditions.

Farther east, it'll be rain, storms, and wind. Ugly stuff any time of the year, but just brutal for Christmas Eve. Even though people shouldn't be traveling (NUDGE NUDGE), people will travel anyway, and those folks—hopefully not you, my loving and health-conscious reader—should pay attention to the weather and make plans to quickly get to safety if they roll up on dangerous storms or flash flooding.

Flash flood watches are in effect for a vast swath of the eastern United States, stretching from Tennessee to New England's border with Canada. It's not going to be a tremendous amount of rain, but a few inches of rain will fall quickly—that's a problem on its own, but many of these areas still have snow on the ground from last week's storm, so between existing snowpack, rapid snow melt, and clogged storm drains, some areas could deal with flash flooding.

Severe thunderstorms will be an issue closer to the coast. I went into detail about the threat over at my Forbes column on Wednesday afternoon. There's an enhanced risk for severe weather in parts of eastern North Carolina and Virginia on Thursday afternoon and evening. That's a pretty significant risk for this region this late in the year.

Any thunderstorms that form have the potential to produce damaging wind gusts and tornadoes, especially in the discrete storms that form ahead of the cold front. These individual thunderstorms ahead of the main line have the greatest chance of developing into supercells capable of producing tornadoes.

This storm will likely be remembered for its wind. It's going to be windy. Wiiindy. The wind will follow the track of the low-pressure system from the Mid-South straight through New England on Friday. Widespread wind gusts of 40 to 50 MPH will be the norm across many eastern states, with higher gusts likely in thunderstorms, higher elevations, and communities close to coastlines.

Wind alerts scattered around from Texas to Maine in anticipation of widespread gusty winds. Gusts greater than 60 MPH could be common in parts of New England, which will easily knock out power. Widespread power outages are going to be difficult for power crews to get a handle on, so there's a good chance that many communities will spend Christmas without electricity as a result of this storm.

Make sure you're prepared for a power outage. Keep flashlights (actual, physical flashlights) and plenty of batteries to keep them going for at least several days. Gather some non-perishable, ready-to-eat food and water so you don't scramble to find something to eat if you can't cook anything, keeping in mind that McDonald's and Pizza Hut probably won't have power either. And please be mindful of candles and fireplaces as you try to see and keep warm.

It's going to be tough to keep warm in many areas. That cold front is a doozy. Temperatures plummeted 30-40°F in many areas in the central U.S. High temperatures will struggle to climb above freezing in many parts of the east on Christmas.

Here's the National Weather Service's high temperature forecast for Friday. Some of these high temperatures in New England will occur not long after midnight, plummeting through the morning and day after the cold front passes through. (Temperatures will be quite nice on the Plains, though, as a ridge builds in behind the big storm.)

And here's their low temperature forecast for Friday night:

Brr. The chilly air makes it all the way to southern Florida, which won't escape this burst of cold air without a morning in the mid 40s. 

It's not going to linger for too long—temperatures will slowly moderate after this weekend—but it's going to stick around just long enough to remind you that we're in the throes of winter now.

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December 15, 2020

A Significant Winter Storm Will Plaster The Mid-Atlantic And Northeast This Week

Gird your loaves and invest in milk futures: a snowstorm's comin'. A big one, in fact. Parts of the Mid-Atlantic and Northeast are getting ready for the season's first big-time snowstorm. Some areas will see more snow than they've seen in two years—of course, that's not as impressive as it sounds considering last winter's snows were a dud in the Mid-Atlantic. As we see with so many coastal storms, the precise track of the storm will determine whether you get blanketed by snow or shrouded by bitter disappointment.

The Setup

A trough in the jet stream will drive the formation of the low-pressure system that will become our mid-week winter storm. A low-pressure system will develop in the Carolinas on Tuesday night and move up the coast through Thursday. The system will have plenty of moisture and cold air to work with, so there's not much wishy-washiness about whether or not the system will produce big snowfall totals. There's going to be a sharp cutoff between blockbuster snows and a nuisance, so the ultimate track of the storm will make a big difference on who sees huge snows or a cold rain.

The Timing

Rain will begin over the southeast on Tuesday night and Wednesday morning as the low-pressure system starts to develop. The storm will pick up intensity in a hurry as it approaches the Mid-Atlantic, which is when wintry precipitation will start on the northern side of the storm.

Freezing rain will likely begin in western North Carolina and parts of western Virginia on Wednesday morning and afternoon. Temperatures will eventually climb above freezing across areas expecting freezing rain, so the question will be how long it takes the subfreezing air at the surface to erode. The longer it sticks around, the thicker the crust of ice will grow. It shouldn't be a big ice storm, but any crust of ice is dangerous when there's ice on the roads and if tree limbs or power lines snap under the weight. Temperatures should—should!—climb above freezing by late afternoon across most areas expecting ice.

Farther north, the snow will begin on Wednesday afternoon west of D.C. and spread north through the afternoon and evening hours. Precipitation will taper off on Thursday morning from west to east. 

The Track

Six runs of the GFS model showing how tiny shifts in the storm's position can move around the rain/snow line. SOURCE:

Track track track. Track? Track. Okay, I got that word out of my system. It'll be like Edith and the cling peaches. Won't say that word again.

The structure of coastal storms like this is usually pretty textbook. The rain/snow line follows close to the tra—uh, path—of the center of the low-pressure system, so you wind up with rain to the south/east and snow to the north/west. You get a pretty heavy shield of snow to the northwest of the low that accounts for the greatest snowfall totals. If that line sets up near I-95, you wind up with those memorable storms that immobilize big cities for an entire week.

Since precipitation type and totals are so heavily dependent on the storm's motion, getting it right is crucial to the forecast. If the storm moves 20 miles to the right or to the left of what was forecast, the rain/snow line and shield of heavy snow will follow suit. That could result in surprises and disappointments.

Right now, it's likely that any jog in the storm's motion would be a northerly jog, which would push the heaviest snowfall totals north.

The Snow

Speaking of surprises and disappointments, check out that tremendous cutoff between lots of snow and not much at all. That's why even a tiny shift in the storm's motion could result in a tremendous difference in snowfall amounts for these densely populated communities.

Right now, the National Weather Service's forecast calls for more than a foot of snow from northwestern Virginia to southern Connecticut, which is a vast swath of real estate at risk of seeing a great deal of snow. The greatest totals are likely in central Maryland, eastern Pennsylvania, northern New Jersey, and the Hudson Valley in New York—these areas could see more than a foot-and-a-half of snow by the end of the storm.

Again, it won't take much for that sharp cutoff in totals to nudge a dozen or two miles to the right or to the left, which could have big implications for densely populated communities along I-95. When you're preparing for a storm, it's always best to prepare for the worst so you're ready no matter what happens.

The Weather Prediction Center's new Winter Storm Severity Index (WSSI) shows major to extreme impacts across areas expecting more than a foot of snow. The greatest disruptions are likely in eastern Pennsylvania and northern New Jersey, where a combination of deep snow on the ground and the weight of the snow on trees, power lines, and flat roofs could cause major issues.

Across the hardest hit areas, travel will be all but impossible during and immediately after the storm. It could take several days for crews to reach residential areas. Hopefully the fact that travel is at a minimum and work/school is predominately conducted at home these days will make it easier for crews to safely clear the roads in a reasonable amount of time.

Now that most trees have lost their leaves and the snow isn't going to be particularly wet, there shouldn't be a widespread risk for power outages, but this much snow built up on power lines and tree limbs could lead to some power outages.

It's likely that the snowpack will stick around for a while after the storm—it doesn't look like there are any significant warmups on the way for the eastern states.

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December 4, 2020

The Season's First Big Nor'easter Could Bring A Foot Of Snow To Interior New England

The first significant nor'easter of the season will bring heavy snow to parts of New England this weekend. It's got everything: a sharp cutoff in totals, uncertain snow amounts, and small changes in the storm's path having a big impact on what ultimately happens. Hey, at least we're not talking about hurricanes anymore, right?

The storm that will become the nor'easter—which, by the way, doesn't have a name, since we don't name winter storms in the United States—will get its act together tonight over the southeastern states. Precipitation will begin as heavy rain and thunderstorms in the Carolinas as the low-pressure system organizes and starts to move toward the coast.

Here's what to expect.

Rain And Severe Thunderstorms

Heavy rain and thunderstorms will begin to overspread the Carolinas tonight through early Saturday morning. Not only will the rain be quite heavy at times—with a quick inch or so of rain possible—but there's a possibility for severe thunderstorms in eastern North Carolina.

The Storm Prediction Center issued a slight risk for severe weather across the far eastern portion of the state through Saturday morning, with a marginal risk extending westward into the Piedmont Triad.

The greatest risk will be damaging wind gusts of 60 MPH, but tornadoes are possible, especially in the slight risk area in eastern N.C. There will be enough wind shear on the eastern side of the developing nor'easter that discrete thunderstorms ahead of the main line could rotate and produce tornadoes.

Elsewhere, it's just a heavy rain threat. Precipitation will fall as rain across most inland and coastal areas until you reach deep into New England. Even areas that could see snow at the end of the storm, such as Boston and Portland, will see rain for most of the storm.

The heaviest totals are likely along the coast—Cape Cod could see up to two inches of rain by the end of the storm. This isn't a blockbuster rain event, but it could cause some flooding issues, especially where any storm drains are clogged by fallen leaves.


Plenty of cold air over interior New England will ensure that the northwestern side of the storm will produce the first decent snowstorm of the year for the region. The latest forecast from the National Weather Service calls for more than half a foot of snow through much of Massachusetts, Vermont, New Hampshire, and Maine, with the greatest totals likely from northern New Hampshire northward into Quebec. Augusta, Maine, could see more than a foot of snow by the end of the storm.

Precipitation will begin as rain on Saturday, quickly changing over to snow as the evening wears on. Snow will continue through Sunday afternoon as the storm pulls away into Atlantic Canada. There's a decent chance that rain will end as snow near the coast, possibly bringing a light blanket of snow to Boston.

The first big snow of the year is a big deal no matter where you live because it takes a little while to acclimate yourself to shoveling, walking, and driving in the stuff. The Weather Prediction Center's new Winter Storm Severity Index (WSSI) calls for minor to moderate impacts across the region, mostly for a combination of snow amounts and the "snow load," which is the weight of wet snow on trees, power lines, and roofs. This is going to be a wet snow, so that'll increase the risk for downed tree limbs, power outages, and it'll make it more difficult to shovel.

It's important to remember one of the rules of winter weather forecasting: small changes in storm track have a big effect on the final result. This especially holds true for nor'easters. If the storm moves one or two dozen miles to the east or west of what forecasters expect, it would move the axis of heavy snow accordingly. That could mean that areas expecting minor (or no) accumulations wind up with a shovelable snow, while areas bracing for a big thump get less than expected. Keep checking forecasts this weekend so you're ready if things change in your area.


It's going to get pretty windy behind the system. Gusts of 40 MPH are possible well behind the system into the Carolinas, which could lead to sporadic power outages where trees, already stressed by the parade of storms this summer and fall, struggle to keep their grip in the wet soil.

Up north, gusty winds will follow the snow on Sunday. Wet snow is bad enough on tree limbs and power lines, but the added stress of gusty winds could cause some issues. The risk for power outages ticks up with heavier totals, so folks from Worcester, Massachusetts, north through interior Maine should be ready for at least a day or so without power, just in case.

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