November 29, 2019

A Major Winter Storm Could Bring Blizzard To Northern Plains, Significant Snow To Northeast

A major winter storm will move across the northern United States through early next week, producing a solid blanket of snow from the northern Plains to the Northeast. The heaviest snow will fall on the Dakotas and across the Upper Midwest, where a huge swath of land could see more than 12" of snow by the time the storm is over. Disruptive snowfall totals are also likely across a large portion of the interior Northeast early next week.

The developing storm will come from the same trough that generated the record-breaking low-pressure system in California and Oregon earlier this week. The storm broke the all-time record low air pressure reading for the state of California, with a pressure of 973.4 mb recorded in Crescent City on Tuesday night.

Northern Plains and Upper Midwest

Heavy snow will continue to spread across the north-central United States on Friday night, ending from west to east by Sunday night as the storm scoots east across the Great Lakes.

The National Weather Service predicts more than a foot of snow for a decent chunk of real estate, including the cities of Pierre, Fargo, Grand Forks, and Duluth. Duluth could wind up "winning" the snowfall contest as a result of snowfall enhanced by lake effect snow off of Lake Superior. The city could see a foot-and-a-half of snow by the end of the storm.

Strong, gusty winds associated with the developing winter storm could lead to blizzard conditions in parts of Wyoming, Nebraska, and South Dakota, including Rapid City. A blizzard warning is also in effect in and around Duluth as a result of strong winds blowing off of Lake Superior. A blizzard occurs when sustained winds of 35 MPH and blowing snow reduce visibility to one-quarter of a mile for three consecutive hours. Not only is travel almost impossible during blizzard conditions, but a whiteout can easily disorient someone even on a short trip from the front door to the mailbox.


December will begin with the first major snowstorm of the season across much of the interior Northeast as a winter storm threatens to produce more than a foot of snow at higher elevations. This could be a long-duration winter storm, with precipitation beginning on Sunday evening and lasting through the first half of Tuesday in some areas. This is a winter-hardened part of the country, but more than half a foot of snow is difficult to deal with if road crews can't keep up with snowfall rates.

Heavy snowfall totals will come perilously close to the major cities along the I-95 corridor. The gradient between a lot and a little could be especially apparent in Boston, where the current forecast calls for minor accumulations along the coast, but more than 6" of snow just west of the city. A small nudge either way in the storm's track could have a big impact on who sees decent snowfall totals.

It's worth noting that the snowfall forecast above only runs through 7:00 PM EST on Monday, December 2. It's possible that accumulating snow may continue after that cutoff in some areas, so those additional accumulations aren't covered by the National Weather Service's forecast above.

Freezing Rain

It's not all going to be picturesque snow and fluffy drifts. Warmer air on the southern end of the system could allow precipitation to fall as freezing rain for a time, potentially leading to a crust of ice up to one-tenth of an inch thick on exposed surfaces. The greatest threat for freezing rain exists in central and western Pennsylvania, southwestern New York, southern Ontario, and parts of northeast Pennsylvania and northern Michigan.

Even the tiniest coating of ice can make travel by vehicle or foot almost impossible. A crust of ice beneath snow will make a snow-covered street deceptively slick, and freezing rain on top of snow can dramatically increase the weight of the snow and make shoveling a much more intensive task.

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November 25, 2019

Four Different Weather Headaches Will Snarl Thanksgiving Travel This Week

It wouldn't be Thanksgiving week without nasty weather. Several storms will move across the country through the holiday weekend, providing ample opportunities for disruption to airline and highway travel just in time for the holiday rush. It's a good idea to take the next day or two to prepare for travel snarls in advance so you're not stuck halfway between home and a turkey dinner.

Headache #1: Major Pacific Storm | Timing: Tues-Weds

GFS model guidance showing the strong low off the coast of Oregon on Tuesday evening. Source: Tropical Tidbits

A powerful storm will move across parts of Oregon and California on Tuesday evening, bringing the potential for damaging winds, heavy rain, and several feet of mountain snows through Thanksgiving. Heavy snow will make it difficult, if not impossible, to drive across the mountains on Wednesday, which will severely hamper traffic on one of the busiest travel days of the year.

The National Weather Service in Medford, Oregon, characterized the storm in unambiguous terms on Monday night: "this low is unprecedented in its strength and track." A strong jet stream diving south over the Pacific Northwest will allow a developing low-pressure system to rapidly strengthen over the next day or so. The low's minimum central pressure could get down into the low 970s, which would be impressive for a hurricane let alone an extratropical cyclone in this part of the country.

In fact, if the forecast air pressures come to pass, the storm could break all-time record low air pressure readings in southwestern Oregon and northwestern California. According to the Weather Prediction Center, the all-time record low air pressure at Medford, Oregon, was 978.0 mb, and 978.7 in Eureka, California. It's likely that these records would fall if the core of the low moved over or very close to one of these stations.

Source: NWS Medford

Damaging winds are a serious threat from a system this strong. Wind gusts in excess of 70 MPH are possible along and near the coast in southwestern Oregon and northwestern California. Higher gusts are likely at higher elevations. Winds this strong will easily knock down trees and power lines, potentially leading to widespread power outages. Trees and limbs falling across roads will pose a hazard to vehicles and homes.

Heavy Rain

This will be a fast-moving storm, which doesn't give it much time to drop a ton of rain all at once. (Remember, steady rain quenches the ground but torrential rain runs off before it can soak in.) The latest forecast from the Weather Prediction Center shows more than an inch of rain across most lower elevations in southern Oregon and northern California.

Heavy Snows

This storm will produce several feet of snow in the mountains of eastern California, which is great news for ski resorts but terrible news for travelers who are hoping to drive east for the long holiday weekend. It's worth considering alternate plans for Thanksgiving if you're planning to cross the mountains on a road like I-80.

Headache #2: Central U.S. Winter Storm | Timing: Tues-Weds

A classic winter storm developing along the Front Range on Monday evening will move toward the Great Lakes through Wednesday, blanketing a stretch between Denver and Marquette with a solid, shovelable snow. Thunderstorms and high winds will follow a cold front across the southern Plains through Tuesday evening, bringing the potential for severe thunderstorms to the lower Mississippi River Valley.

It's already snowing in Colorado and Wyoming, where communities like Boulder, Fort Collins, and Cheyenne, could wind up with a foot or more of snow by the time the storm is over on Tuesday evening. The storm will continue producing snow across the central Plains as it makes its way toward the Great Lakes. Another burst of 12"+ totals is possible in northern Wisconsin and Michigan's Upper Peninsula, where the storm's snow is enhanced by Lake Superior.

The warmer side of the system will produce high winds across the southern Plains, where high winds warnings are in effect for much of eastern New Mexico, western Oklahoma, and the Texas Panhandle in anticipation of wind gusts as high as 70 MPH after the cold front passes through on Tuesday. High winds and dry air will lead to an increased threat for wildfires across these areas.

Severe thunderstorms are possible in the lower Mississippi River Valley on Tuesday evening as the cold front pushes into warm, humid air. The Storm Prediction Center painted a slight risk across the area, which includes St. Louis, Little Rock, and Memphis. The storms are likely going to develop along the cold front in the form of one or more broken squall lines, posing the threat for damaging wind gusts and possibly a couple of tornadoes. Tornadoes are most likely in broken lines, where individual thunderstorms have an easier time tapping into low-level rotation.

Headache #3: SoCal Rain | Timing: Weds-Sat

Source: NWS San Diego

An inch or two of rain isn't too big of a deal for us east of the Rockies, but it's an errand-stopping ordeal in southern California. Heavy rain and maybe even a few rumbles of thunder are possible in southern California as a surge of moisture moves across the southwestern United States later this week. Several inches of rain could fall in southern California beginning on Wednesday and lasting through Saturday. Flash flooding is possible if the rain falls too quickly, especially in areas that saw wildfires in recent years.

It's likely that the rain will lead to flight delays at LAX just in time for the busiest flying day of the year. Rainy, gloomy weather requires air traffic controllers to slow down operations so they can safely maneuver the planes as they're arriving and departing. Pilots and controllers need a little breathing room in the rain, and it takes a little longer for planes to stop on wet runways. Even a small slowdown will cause a ripple effect of delays and cancellations down the line, since individual planes often complete so many legs in a day.

Headache #4: Southwest Snowstorm | Timing: Thurs-Fri

Source: NWS Flagstaff

A significant winter storm will unfold at higher elevations in Arizona, where several feet of snow could fall from the Grand Canyon to the White Mountains. Flagstaff could see more than two feet of snow by the beginning of the weekend. This kind of snow will snarl traffic along highways that traverse the northern half of Arizona. Crews should have the roads clear and open again in time for folks to head back home this weekend.

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November 22, 2019

Tropical Storm Sebastien Keeps Fighting The Odds To Survive In The Atlantic Ocean

Tropical Storm Sebastien is still trucking along in the central Atlantic Ocean with maximum sustained winds of 65 MPH. Forecasters expected the storm to absorb into a cold front by Thursday morning, didn't! It kept going, and going, and going. Thankfully, it's safe to gawk and laugh at the relative tenacity of this storm—it's far out in the middle of the Atlantic Ocean, and it poses no threat to land.

Sebastien formed on Tuesday morning from a tropical disturbance that found a pocket of favorable conditions a few hundred miles northeast of the Caribbean Sea. As I documented over at Forbes early Wednesday morning, the storm was originally expected to be a short-lived blip that just padded the 2019 hurricane season's numbers.

But it persisted.

We're now in day 4 of Tropical Storm Sebastien's joyride over the central Atlantic. It looked like the storm was going to absorb into a cold front moving across the western Atlantic Ocean and that would be that. What happened instead, however, is that Sebastien both slowed down and managed to stay ahead of the encroaching cold front, keeping it in a favorable environment much longer than expected.

The good folks at the NHC keep expressing their astonishment at the storm's persistence. The advisory headlines from Friday evening read "more of the same from Sebastien" and "tenacious Sebastien does not know it's November and refuses to weaken."

Tropical Storm Sebastien is still a fairly lopsided storm. Wind shear has kept all of its thunderstorm activity on northeastern side of the center of circulation, leaving a well-defined but totally naked surface swirl visible on satellite imagery.

The storm's luck will run out soon. Sebastien is running out of warm water to fuel its thunderstorms, and we'll eventually see the thunderstorms weaken enough that wind shear rips them away from the center of circulation, killing the storm once and for all. The NHC's forecast calls for Sebastien to weaken this weekend and finally dissipate on Sunday.

[Top Image: NOAA]

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November 17, 2019

A Coastal Storm Could Bring Freezing Rain To New England On Monday

A nor'easter that brought heavy rain, high winds, and coastal flooding to the Carolinas this weekend could produce a period of freezing rain in New England early next week. The latest forecasts don't call for a full-fledged ice storm, but even a thin crust of ice is dangerous on exposed surfaces.

The storm is quite the looker on satellite imagery today. You can clearly see the low-pressure system's center of circulation as the system wraps up and moves north. Sunday's 1:00 PM EST analysis from the Weather Prediction Center put the storm's minimum central pressure around 994 mb, and its pressure should hold steady or drop a little as it moves toward Atlantic Canada over the next couple of days.

Carolinas Rain And Wind

This is the same system responsible for all the cloudy, drizzly, rainy weather we've seen in the southeast for the past couple of days. The system managed to grow more organized once it left the coast, which is good news for folks in the eastern Carolinas, since double-digit rainfall totals occurred just a few dozen miles off the coast near the NC/SC border.

A cold rain is miserable enough, but this storm was downright windy, too. Winds gusted as high as 36 MPH in Greensboro, N.C., and gusts hit 60 MPH on the state's Outer Banks. The wind and waves led to coastal flooding in areas like Charleston; the water at the Charleston Harbor tide gauge came within a quarter of an inch of major flood stage at high tide on Sunday morning. The outer banks also saw significant storm surge flooding and beach erosion, with some roads in Rodanthe, N.C., completely covered by water and sand early Sunday.

Potential Freezing Rain In New England

The storm is picking up speed as it moves away from the Carolinas, eventually making a wide hook into Atlantic Canada over the next couple of days. The biggest threat from this storm is freezing rain, which could coat most of New England and parts of Quebec and New Brunswick through Tuesday. Winter weather advisories are in effect for most of New England in anticipation of freezing rain on Monday and Monday night.

The best chance for a glaze of ice near the coast will exist on Monday morning before temperature jut above freezing and it all turns to a cold, miserable rain. A greater chance for freezing rain exists inland, where temperatures near the surface should stay at or below freezing for the duration of the storm.

Steady freezing rain will begin in interior New England on Monday evening and continue through the night before changing over to snow. The Weather Prediction Center's most likely ice accretion forecast shows the potential for 0.10" of ice from freezing rain, which is enough to leave a solid, snappable crust on exposed surfaces. This won't rise to the level of a full-fledged ice storm, but even a thin glaze of ice is dangerous for motorists and pedestrians, especially when it's dark and you can't see the slippery surfaces.

Why Ice Instead Of Snow?

Why will the storm start as freezing rain even though temperatures are below freezing at the surface? As the storm draws closer, it'll begin to wrap around a layer of warm air a few thousand feet above the surface. You can see this pretty well in the weather models.

The above image is from a program called BUFKIT, which uses model data to simulate the SKEW-T charts that meteorologists use to plot out upper-air data from weather balloons. A SKEW-T chart shows the temperature, moisture, and wind speed through a column of the atmosphere. It's like looking at a cross-section with all the data plotted out for you.

The red line on the right traces the temperature through the atmosphere, while the green line traces the dew point through the atmosphere. The altitude on this chart is measured in feet above ground level. This particular graphic shows the GFS model's view of the atmosphere over Montpelier, Vermont, at 8:00 PM EST on Monday. I've highlighted the layers of the atmosphere that are above- and below-freezing.

If this model scenario pans out, the surface temperature in Montpelier at 8 PM on Monday would be about 28°F. However, the air temperature about 2,000 feet above ground level peaks at about 38°F.

Snow will fall until it reaches about 6,000 feet above ground level, at which point it'll start to meet air that's above freezing. Any snowflakes that fall into the thick layer of above-freezing air above Montpelier will completely melt into a liquid raindrop. The raindrop will begin to cool below freezing once it enters that shallow layer of 28°F air right at the surface, freezing on contact with any exposed surfaces.

This nose of warm air across interior New England will slowly erode through Monday night until the entire atmosphere is below freezing, at which point the freezing rain (and possibly some sleet) changes over to all snow. The National Weather Service expects that a couple of inches of snow will fall in northern Vermont and New Hampshire, with up to five inches of snow possible near the Canadian border in northern Maine.

[Top Image: NOAA]

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November 11, 2019

Mother Nature Cashes In On Your Heat Relief Pleas With A Bitter November Cold Snap

Remember all those tweets and posts about how you'll do anything to make the summer heat stop? Time to pay up. The season's first deep shot of cold air will cover much of the United States and Canada this week. Temperatures will plunge firmly into winter territory for most areas east of the Rockies, but not before a significant early-season snowstorm blankets parts of the Great Lakes and Northeast.

The pattern we'll see this week is more common in the winter than in the middle of November. A strong trough will move south from northern Canada, allowing a pent-up pool of Arctic chilliness to flow toward lower latitudes.

Here Comes The Cold

An animated look at NWS forecast high temperatures between Monday (Nov 11) and Thursday (Nov 14).

The leading edge of the cold air is already draped over the northern Plains and Upper Midwest, where lows on Monday morning will dip below zero in some areas.

An animated look at forecast high temperatures this week makes it pretty easy to follow the track of the upper-level trough as it pivots south from Canada. This won't be a sustained cold outbreak like we'd see in the dead of winter, but it's going to be pretty darn cold nonetheless.

Our cold front will race all the way to the Gulf of Mexico by Tuesday, leaving only southern Florida untouched by the chilly weather. High temperatures on Tuesday and Wednesday could break dozens of record low maximum temperatures, or the coldest high temperature on record for the date.

Temperatures will struggle to climb above freezing during the day on Tuesday as far south as Memphis, and the season's first freeze will reach all the way to the Gulf of Mexico a couple of weeks ahead of schedule. The average first freeze in Mobile occurs on November 25.

A stiff wind behind the cold front lead to below-zero wind chill values across the northern states, with wind chills dipping into the teens in the southeast.

This is a solid chill for so early in the season. It may not seem like too big of a deal to most of us, but consider how the cold temperatures and even colder wind chills will affect vulnerable populations like those who are homeless, folks who live without heat, and children who have to walk to school without warm clothing. This kind of cold can lead to hypothermia in short order.

Northern Border Snowstorm

A low-pressure system developing along the cold front will produce a swath of heavy snow across the Great Lakes and New England, largely straddling the U.S./Canadian border. Communities from Lake Erie to Atlantic Canada could see double-digit snowfall totals by the time the storm winds down on Wednesday and Thursday.

The latest forecast from local National Weather Service offices shows heavy snow along the northern borders from Ohio to Maine. While it doesn't show up on this NWS-generated forecast, snowfall totals will be just as high across the Canadian border in Ontario, Quebec, and New Brunswick.

Forecasters expect significant snowfall totals in places like Cleveland, Erie, Buffalo, and Burlington. It's not too unusual to see heavy snow along the lakes in November, but this will be more widespread than a true lake effect event. Burlington, Vermont, could see a storm total snowfall accumulation of 9 inches, which would be one of the greatest snowfalls ever recorded this early in the season.

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