A Plethora of Winter Storm Potentials to Monitor

Ice storm potential next week

Synopsis

A longwave trough with quite a broad base will remain almost stationary across the northern half of the U.S. this upcoming week into at least next week. A ridge will persist just off the West Coast, while a block sits over western Greenland. Another ridge will remain positioned over the southeastern quadrant of the U.S. This ridge will initially keep temperatures well above average across the Southeast; however, northern troughing will prohibit the ridge from amplifying unabated. A baroclinic zone will become established across the Southern Plains, Mid-South, Missouri Valley, Tennessee Valley, Southeast, Ohio Valley, and Mid-Atlantic. This setup will bring several opportunities for snow, ice, and rain across the mentioned regions over the next two weeks.

We discussed around a week ago how longwave troughing can suppress the storm track too far southward to bring any meaningful wintry precipitation. Instead, conditions are generally very dry and cold. If you recall, model guidance had a lobe of the tropospheric polar vortex digging as far south as the Tennessee Valley for early this week. Instead, we got a flatter trough with some Southeast ridging. In most guidance now, we’re stuck with a long-lasting broad-based trough that likely won’t keep the southern stream storm track suppressed.

Temperature outlook february 14-18, 2021
Probability of above/below average temperatures over February 14-18, 2021

Cross polar flow extending from Siberia over into western Canada has allowed Arctic air to pool over western Canada. That brutally cold airmass has already begun spilling into the upper Plains and Midwest. But essentially, we now have the available cold air to tap as numerous storm systems parade from the Southwest/Southern Plains in an east or northeastward direction. One major drawback to the expected pattern configuration is that ice (sleet/freezing rain) could become the more predominant frozen precipitation-type across the Southern Plains, Mid-South, Southeast, and even into the lower Ohio Valley and Mid-Atlantic. With broad troughing centered across the central U.S. and a Southeast ridge to the east, southwesterly flow will transport warm air above the surface. However, Canadian high pressure will wrap around very cold air at the surface. This will produce atmospheric profiles that support sleet/freezing rain versus snow.  

Systems We’re Currently Watching

We have a slew of systems we’re currently watching that will bring impacts in the foreseeable future. We’re going to post articles and social media updates on each system individually, but we will introduce those threats here.

February 10-12, 2021 (Wed.-Fri.): Shortwaves embedded in mostly westerly flow will bring widespread precipitation across the Southern Plains, Mid-South, Missouri Valley, Southeast, Tennessee, along and south of the Ohio River, and the Mid-Atlantic. Canadian high pressure has continued to advect cold air at the surface across northern portions of where precipitation will develop. We expect a prolonged period of sleet/freezing rain to fall across northern Texas, central/eastern Oklahoma, northern/central Arkansas, lower Missouri, western Tennessee, upper Mississippi, and Kentucky. North of the Ohio River and areas across much of the Mid-Atlantic will experience mostly snow, although lower and central parts of the Virginias may get a mixture of snow/ice. For areas south, expect rain.

February 13-14, 2021 (Weekend): Forecast model guidance indicates HIGH uncertainty for this potential event. The outcome of this potential winter storm depends on the interaction of three features: a shortwave entering lower California late week, a shortwave entering the Pacific Northwest around the same time, and a lobe of the tropospheric polar vortex spinning over the northern Plains/Midwest. The European model continues to indicate that the California wave gets suppressed so far south that it passes across the Gulf of Mexico. This feature would bring rainy conditions to Florida and areas along and relatively close to the Gulf coast over much of the weekend. On the other hand, the GFS often has the California wave phasing with the Pacific Northwest wave somewhere over the central U.S. This scenario would result in the phased systems eventually taking on a northeastward trajectory. This scenario would potentially bring a significant winter storm to the central/southern Plains, the Mid-South, the Missouri Valley, the lower Midwest, the Ohio Valley, the lower Great Lakes, and Northeast over the weekend. I will admit that this is a tough forecast, and at the moment, I need additional time to study this event.

February 15-17, 2021 (Mon.-Wed.): A strong shortwave will enter the western U.S. later in the weekend and dig southeastward into the Four Corners region. As the wave continues eastward, the tropospheric polar vortex lobe will move eastward across the Great Lakes and Northeast. These two features will create a region of confluent flow across the Ohio Valley and Mid-Atlantic/New England, which will support Canadian high pressure moving eastward into the Northeast. This high will likely result in cold air damming as far south as the Carolinas and Georgia. A surface low will likely develop along the Gulf coast in response to the shortwave approaching the region. Cold air will already be in place across the Southern Plains, Mid-South, and much of Tennessee to support wintry precipitation. With cold air damming in place, the Carolinas, northern Georgia, and northeastern Alabama need to closely monitor the potential for an ice storm next week. This system could potentially bring an impactful winter storms to parts of the Ohio Valley, Mid-Atlantic, and (maybe) the Northeast. We have about a week to get into specifics. I advise against making any changes to current plans until confidence increases over the next two to three days.

High-Impact Nor’easter to Impact the Mid-Atlantic and New England

GFS parallel snow accumulations

Brief Synopsis

This week’s storm system of interest has now moved away from the West Coast and begun to dig into the Four Corners region. The vigorous shortwave will continue amplifying across the Southern Plains on Tuesday. By Wednesday, it’ll begin lifting east northeastward across the Mid-South, Mississippi Valley, and Tennessee Valley. Later Wednesday, the wave will push into the Ohio Valley, the Mid-Atlantic, and New England, bringing a powerful winter storm along the East Coast from Wednesday into Thursday.

Timing

After dropping snow across the Rockies, precipitation will develop along and ahead of the shortwave across the central and southern Plains on Tuesday. The wave will trigger the development of a surface low along the Gulf coast on Wednesday, as a large swath of precipitation overspreads the Southeast, Tennessee Valley, Ohio Valley, and Mid-Atlantic. Precipitation will then begin to overspread southeastern New England by Wednesday evening, continuing into Thursday. Rain and possible storm development in the warm sector of the system will aid in the amplification of a downstream ridge. The strength of this ridge will determine how closely the surface low rides along the Mid-Atlantic and southeastern New England coast after departing North Carolina and Virginia.

Expected position of the surface low off the Mid-Atlantic coast on Wednesday evening

Forecast Model Discussion

The operational, along with many of its ensemble members, have continued to show a more southern track of the surface low, primarily due to a weaker downstream ridge. In such a scenario, the axis of heaviest snowfall rates and accumulations would occur from around D.C. (and northern Virginia) to Philly to Long Island to Cape Cod. Areas just northwest of this line would still get noteworthy but lower amounts. The GFS-parallel, a version of the GFS still in its testing phase, has consistently been the northern outlier. This solution would largely be a miss for D.C., Philly, New York City, Long Island, and Cape Cod, but copious amounts of snow would fall northwest of this line, including over Boston.

Projected 24hr Snowfall accumulations from Wednesday morning to Thursday morning, according to the GFS-parallel model. Additional snow will fall across parts of New England Thursday afternoon.

The European model, along with the shorter-range 12km NAM, has the surface low trekking quite close to the Mid-Atlantic after moving just offshore. Both models keep the low far enough off the southeastern New England coast for the heaviest snow accumulations to still fall over Philly, NYC, Long Island, and Cape Cod.  

Most model guidance indicates that downstream ridging mid-week will be flattened by the current storm system exiting New England today. However, this ridge should be more amplified than what models suggest. For that reason, I gave the GFS-parallel and the shorter-range RGEM model (not discussed above) more weight in the snow accumulation forecast below. If there’s not a northward shift in most model guidance by tomorrow afternoon, I’ll adjust my forecast to align more closely with the operational GFS, European, and other short-range guidance.

Matthew’s Snowfall Accumulation Forecast for Select Cities

Washington, D.C.: 1-3 inches

Philly: 3-6 inches

New York City: 3-6 inches

Long Island: 1-3 inches

Providence, RI: 12-18 inches

Boston: 12-18 inches

Cape Cod: 1-3 inches

Download Firsthand Weather’s Southern Snow App Today

Please consider downloading Firsthand Weather’s newFREE app: SOUTHERN SNOW (Link). This app will notify you when there are winter weather alerts in your area. Also get updates on the latest snowfall accumulations from your local National Weather Service, along with detailed forecast discussions from Firsthand Weather.

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Major Winter Storm, Mid-Atlantic and Northeast

When we last left this subject, we had Tornadoes, snow, ice, and me pulling my hair out over the newest NAM model giving Boston a foot of snow.    Oh New England, what am I going to do with you?

rain and snow

On to Virginia and the Mid Atlantic!!

West Virginia and Virginia:

Moving north from my last post into Virginia, only the Southeast portions of the state will get straight rain, most areas will have cold air being brought down for what could be a historic blizzard for portions of the state.

Blizzard Warnings are in effect for Charles, St. Mary, Calvert, Prince William, Manasas, Stafford, Spotsylvania and King George Counties.  This warning is from 1 PM Friday to 6 AM Sunday.  Heavy snow will begin Friday afternoon and while it may mix with sleet for a time east if I-95, It will change back to all snow Saturday afternoon.  18 to 24 inches of snow are expected in this region with the lower amounts near the bay.  Winds will be gusting up to 55 mph in  this area and I would strongly advise that no one in this region head out Friday night.

Winter Storm Warnings are in effect from Southeast West Virginia along and north of highway 460 towards Lynchburg and on to Appomattox.  16 to 24 inches of snow will fall in this area with the highest amounts in the Blue Ridge region. Snow will be heaviest during the mid-morning through midafternoon hours and gusty winds will reduce visibilities down to 0 in the higher terrain.

Further South and East, Central Virginia and the Interior Northern Neck region will have snow picking up late Friday morning and getting heavy at times during the afternoon and evening.  Sleet and Freezing rain may mix in some as the original low pressure system moves the west of this area before dying out as the secondary pushes north.  This changeover and possible change to rain on Saturday will help keep totals down in the 7-15 inch range with the higher totals in the Piedmont regions of central Virginia to the West and North of Richmond.

Down in the Southeast corner of the state, interior regions near Emporia, Wakefield and Williamsburg will see even lesser amounts as sleet and rain mix in with the snow.  After the mix, this area will turn to rain and have seen 2-5 inches of snow.  Though a fresh coating to an inch may occur as the precipitation changes back to snow on the backside of the low.

Heading back to West Virginia,  Central and Northwest areas of the state and including Western portions of Maryland from Hagerstown West, are set to see 18-24 inches of snow between Friday afternoon and Saturday evening.  Snow will be at its heaviest overnight Friday with strong Northeast winds reducing visibilities and making some roads in the mountains impassable.

Maryland D.C. and Delaware

Jumping over to the Eastern shore of Maryland.  The Southern tip of the Eastern shore will see snow begin Early Friday afternoon, but for those in Dorchester County, the warm oceans will mix in sleet and freezing rain before changing over to all rain for a time but additional snow accumulations are expected by Saturday afternoon and into Saturday night, leaving the county with about 6-12 inches of snow.  Even lower amounts are expected towards Wicomico and Somerset counties, as well as Inland Sussex County in Maryland, and Cape May County and Coastal Ocean County in New Jersey, where 2 to 6 inches may fall and Winter Storm Watches are in effect.  Sleet and then Rain will be a major factor in this area as temperatures climb into the upper 30s late Friday and stay that way through Saturday afternoon.  Worcester County will see very little snow and ice and accumulations of less than 2 inches are expected before the changeover to rain in this area.

For the remainder of the Eastern Shore and Kent and New Castle Delaware, 10 to 16 inches of snow is possible from Friday night into Sunday morning.  Blizzard conditions are possible during the day on Saturday as heavy snow, high winds, and cold temperatures combine before tapering off.

For the remainder of Maryland and D.C, Blizzard Warnings are in effect from 3 PM Friday until 6 AM Sunday, expect starting at 6 PM near Baltimore.   The Eastern Suburbs of DC and Baltimore can expect 18 to 24 inches of snow as sleet mixes in along and east of 95, but the western suburbs are in the bullseye as 24 to 30 inches of snow will fall where sleet does not mix with the snow.  Winds will gust to 50 mph creating whiteout conditions overnight Friday.  Anyone living in this area will want to be off the roads by early to mid-Friday afternoon.

rain and snow

Pennsylvania, New Jersey and New York:

Much of the action with this system will take place in Southern and Eastern Pennsylvania.

In the West, Winter Weather Advisories are in effect for Washington, Westmoreland, Allegheny, and Indiana Counties including Pittsburgh for 4-6 inches of snow beginning on Friday afternoon and ending late Saturday afternoon.  Just east of there, Cambria, Blair, Huntington, Mifflin, Juniata and Schuylkill Counties are under Winter Storm Watches for 4-8 inches of snow during the same time period.  From Greene County over to York County and up to Dauphin and Lebanon Counties, Winter Storm Warnings are in effect for 6 to 12 inches of snow with as much as 24 inches along the Maryland border in places.

The bullseye region for here is from Philadelphia down to just inland of Atlantic City up through Trenton, Newark, New York City and out to Long Island.  Blizzard Watches are in effect for 8-16 inches of snow.  Less by the coastlines and more inland.  Blizzard conditions are possible during the day and evening on Saturday as heavy snow, winds as high as 40 mph, and cold temperatures combine before tapering off.

For Counties further inland, a line from the city of Reading, through Allentown and Morristown to West Milford and into Peekskill New York and the rest of the Lower Hudson Valley, Winter Storm Watches are in effect for 4-10 inches of snow beginning late on Friday or Early Saturday before tapering off Sunday morning.  This snow is expected to be very heavy and wet which reduces the chances of blowing and drifting snow.

New England:

Data on New England snowfall continues to change by the hour.  The gradient of snowfall in this location is massive and a difference of just 20 miles in the track of the storm can be the difference between no snow and half a foot.  Model outputs from earlier today gave Providence a foot of snow while giving Boston less than an inch and model data on whether or not this region will get hit is all over the place.

close shave

What I can tell you is this, Maine, Vermont and New Hampshire are simply too far north to get in on this system.  The real question, and I do not yet have a good answer for readers in these locations, is what will happen in Southern New England. Any snowfall that does occur here will not arrive until Saturday afternoon and would taper off late Sunday.  So I will be up bright and early to begin looking at the 6Z and 12 Z runs of the models.  Consensus or not this region will have a forecast by Friday.

 

Please be aware that strong winds and coastal flooding will be a risk from North Carolina all the way through New England on the astronomically high tide.

 

Thank you for sticking with us on this incredibly busy day.  We will see you bright and early Friday.

 

Robert Millette

Meteorologist

Firsthand Weather

Major, Possibly Historic, Winter Storm On The Way

There are is definitely a lot to discuss with the upcoming Friday/Saturday winter storm that could end up being significant and potentially historic. While it has become certain that there will be a big winter storm, the uncertainty lies in determining the overall storm track and placement of heaviest snowfall accumulations. Given that it’s only Tuesday night, a lot can change on specifics, so it’s important to keep that in mind, especially when reading any forecasts that are based entirely on forecast models. I know I bring this up a lot, but I always want my audience to be aware of the limitations of such an approach. I’ll be discussing the various solutions that are being shown on the latest model guidance, but in addition, I’ll be pointing out specifics that the models may not be handling well with this system. Due to the complex nature of this upcoming system, I may be required to do a follow-up article that includes some changes, if needed.

Discussion (Friday through Weekend System):

A vigorous shortwave (disturbance) will be moving into the Pacific Northwest, and as it moves southeastward, it will dig into the Southern Plains. A surface low will move/develop over the Plains in response to this disturbance and move eastward across the Southeast, as this disturbance treks eastward. This will eventually trigger the development of a long-wave trough in the eastern U.S., and colder air should begin getting wrapped around the low pressure system. This energy will eventually transfer to the coast, and a coastal low should move up the coast.

There is higher than average confidence on how this system will evolve, but the specifics on the exact track are going to be difficult to nail down. The GFS model and most of its ensembles, along with the Canadian model, have the original surface low moving up through Tennessee before its energy gets transferred to the coast. The European model is now showing a more southerly track across the Gulf Coast states, which would allow for some accumulating snow to fall farther to the south and would shift the core of heaviest snowfall farther south, also. On almost all guidance that I have seen, a pretty stout warm nose is initially present well north into eastern Tennessee and even southern regions of Kentucky. This is likely due to the placement of the original surface low and the orientation of the long-wave trough.

To complicate this forecast even further, a cold air damming scenario could set up east of the Appalachians, allowing temperatures to stay below freezing at the surface in places, despite the warm air advection that will likely try to pump northward, overrunning this cold. This sets up a tricky forecast from Northeast Georgia, parts of Upstate South Carolina/extending east and central-east North Carolina (excluding the coast) Even with the system taking a more northerly track, the colder air at the surface may not get out quickly enough before a nasty ice situation unfolds across the mentioned areas.

The latest Canadian represents this possible ice situation well on Friday:

Canadian ice

Snowfall will likely start falling across northern and central Arkansas Thursday night going into Friday and expand into parts of southern Missouri and into the western third of Tennessee. Snow will eventually spread eastward into Kentucky and parts of the lower Ohio Valley through Friday and eventually expand into the Mid-Atlantic states including West Virginia, Virginia, North Carolina, Washington, D.C., and into the Mid-Atlantic states later on Friday going into Saturday. Southern Pennsylvania, including Philadelphia could be hit hard, along with parts of New England, especially along the coast. This is going to be a slow-moving system, and backend snow could fall as far south as the northern third of Mississippi, Alabama, Georgia, much of Tennessee, and into northern parts of South Carolina. Depending on track, there will likely be a region of very heavy snowfall amounts falling, including many of the regions that I just mentioned. This system has the potential to rival or beat some of the historical winter storms of the past and is looking similar to the January 1996 blizzard.

Just To Reiterate A Few Points:

• The European model has been depicting a more southern track. I’m skeptical of this solution currently, although I’m not ruling it out entirely. If there is a southern trend in the track, snowfall accumulations would likely fall farther south and the heaviest snowfall accumulations would shift south. This would also exclude the most northern regions mentioned in this article from getting heavier accumulations.
• A warm nose extending as far north as eastern Tennessee could cause many of these regions to get rain before possibly seeing a transition to some snow (possibly heavy) on the backend of this system. Accumulations would be possible but not as heavy as in surrounding regions.
• Due to cold air damming, an icy situation could setup initially across northeastern parts of Georgia, Upstate SC and possibly extending eastward across the state and into central-eastern portions of North Carolina (excluding the coast). A transition to snow could eventually occur in these regions, with higher accumulations occurring the farther north one goes.
• The core of heaviest snow accumulations could fall somewhere from northern Arkansas/southern Missouri into northwest and north-central Tennessee, across Kentucky, and particularly into the Mid-Atlantic states extending into parts of North Carolina. Many regions in this zone could be measuring snow in feet before all is said and done.

I will continue to monitor this situation closely. I posted a map that shows a 72-hour snowfall output map based on 15 previous winter storms that look similar to this one, courtesy of CIPS Analog Guidance:

snowstorm analog

Just keep in mind that I’m expecting snow to fall west of this region as mentioned in my article, but I did want to show you this map.

Anyway, I will definitely have to make edits to this forecast, since it’s a difficult and tricky forecast. Someone is going to get hit very hard with this winter storm, and at this point, it’s a matter of determining where. More updates to come. . .