A winter storm with the potential for embedded blizzard conditions is now moving up the Atlantic coast of the United States. Very heavy snow is likely over most of New England today and tomorrow. Thousands of flights out of Boston, New York, and other airports in the northeastern U.S. have either been canceled or delayed as a result of this potentially historic storm.

This afternoon’s WRF model run gives most of Massachusetts, Connecticut, and Rhode Island 15-30″ of snow through 7am Sunday:

This afternoon’s higher-resolution WRF model gives 2’+ of snow to the Boston area by 1am Sunday:

This morning’s GFS model is more conservative with snowfall totals through 7am Sunday but still gives most of New England 10-20″ of snow:

Precisioncast, our in-house model, paints 2’+ of snow through the the weekend in and around Boston:

Blizzard Warnings, Winter Storm Warnings, and Winter Weather Advisories cover all of New England and parts of the Mid-Atlantic:

Why is so much attention being given to this winter storm? The simple answer is it will likely be historic. 27.5″ is the most amount of snow Boston has seen from a single storm (February 16-18, 2003). Many near Boston will likely see 2’+ of snow for the entire event. Compare that to our snowiest winter on record in Cincinnati (January 1978):

Travel is highly discouraged or temporarily against the law in parts of Massachusetts, Connecticut, and Rhode Island. This storm will make headlines!

The top story on the national news this weekend will be a nor’easter pounding New England and the Mid-Atlantic with heavy snow. Models have been reasonably consistent on giving the Boston area at least a foot of snow from Friday through Sunday, but some models are more aggressive than others.

So what’s the latest thinking on how much snow Massachusetts, Connecticut, Maine, New York, New Hampshire, and Vermont are going to get? Let’s start with the snowfall forecast from this morning’s NAM model (through 7am Sunday morning):

The NAM model says most will get 10-20″ of snow, and some (in the shades of white and dark green) will see 30-40″ of storm total snowfall accumulation. A higher-resolution of this morning’s NAM model run shows similar amounts of snow, but with some higher totals in New Hampshire:

Next up is last night’s GFS model snowfall forecast (through 7am Sunday):

The GFS is clearly not as aggressive with snowfall totals; it gives most of New England 2-10″ of snow with 10-20″ for eastern Massachusetts and downwind of Lake Ontario and Erie. What does last night’s ECMWF think for snowfall amounts Friday through Sunday? Here’s your answer:

Essentially, the ECMWF model is a blend of the latest GFS and the NAM model runs; the ECMWF gives most of New England 2-10″ of snow and the Boston area 20-30″ of snow.

WSI’s RPM model from 7am this morning gives most of New England 5-15″ of snow and areas close to the coast 2’+:

The 4am run of the RPM model looks similar, but different enough to give New England forecasters something to think about:

It is worth noting the the NAM, GFS, and ECMWF maps above assume a 10:1 snow-to-liquid ratio. In other words, the snowfall charts are made with the assumption that 0.1″ of liquid output from the models is equal to 1.5″ of snow in the same spot. This is a low-end approximation for this scenario. Models suggest snow-to-liquid ratios will be closer 15:1 or even 20:1 in spots Friday, Saturday, and early Sunday. This means that the snowfall maps above may be underdoing the amount of snow in spots this weekend.

Analogs (comparing this system to others in the past) suggests most of New England is likely going to get 12-24″ of snow. One of the strongest analogs to this upcoming event is the February 12, 1983 blizzard…which turned New York City into this: http://youtu.be/U9LiWVXpqg4

I don’t envy meteorologists making localized snowfall forecasts for the Mid-Atlantic and New England. This will be a tough forecast. This storm has the potential to be historic not only for snow amounts but also for it’s minimum pressure (how deep the center of low pressure gets). I wish forecasters along the East Coast the best of luck with this one!

Yesterday evening in the weather center, it became very clear that stratus clouds moving in from the north were moving our way, and those clouds were going to be tough to shake today. Why did the forecast need to be adjusted from thinking earlier this week? The answer comes from an understanding in how the temperature changes going away from the ground.

In meteorology, we learn what is going on in the upper-levels of the atmosphere by launching weather balloons across the county. One of those balloons was launched this morning at the National Weather Service forecast office in Wilmington. Meteorologists see wind, temperature, and dewpoint trends from the ground to the upper-levels of the atmosphere on a diagram called a Skew-T. This is the Skew-T from Wilmington from 7am this morning:

Unless you’re a weather aficionado, you may not be able to make sense of much of much on this diagram. The black line at the bottom of the plot represents the ground and the top of the plot represents the upper-levels of the atmosphere. The red line is the temperature, the green line is the dewpoint, and the black lines in a row on the right side of the plot represent the wind direction and speed. Let’s simplify it…and just look at the temperature in Wilmington at the ground and aloft around 7am this morning:

In the graph above, you can see the temperature rise and fall between the ground and 18,000 feet above the ground. Usually, the temperature decreases going away from the ground. In this morning’s case, we see temperatures decrease rising from the ground to 5,000 feet up. Between 10,000 and 15,000 feet above the ground, the temperature increases. In meteorology, this is called a temperature inversion:

A temperature inversion is another way of saying there is a layer of stable air above the ground. When clouds are trapped below this layer of stable air, they are often slow (and in some cases, very slow) to mix with drier air in the atmosphere, including above the temperature inversion:

As of 3:45pm, this temperature inversion is holding tough, and clouds persist in and around Cincinnati, while ample sun is found over most of central and eastern Kentucky:

These temperature inversions make forecasting the weather tricky. A difference of 1-3° in  the temperature at any given point above the ground can make the difference between quick clearing and slow clearing. Little to no clearing is forecast through mid-evening.

Two disturbances will push through the Ohio Valley between now and midnight; the first will move through over the next couple of hours, and the second will move through later this evening. A satellite and radar snapshot as of 3:55pm shows these two pieces of upper-level energy approaching the Cincinnati area:

The latest HRRR model’s forecast radar product has flurries favored northeast of the Tri-State around 9pm tonight:

Only flurries are forecast in the Tri-State this evening; little to no accumulation is forecast in and around the Tri-State. The latest run of Precisioncast gives no Tri-State community accumulating snow through tomorrow morning:

The latest run of Microcast gives us little to no accumulation through tomorrow morning:

Fog and dense fog will be a concern tomorrow morning. Visibilities in spots may be under a 1/2 or even 1/4 of a mile. Once the fog dissipates, ample sunshine is forecast Wednesday. Clouds will increase tomorrow night and Thursday, and a line of showers will sweep through Thursday night and early Friday. The best chance for rain in the next week will be late Sunday and Monday.

While rain will come and go in the week ahead, near or above average temperatures are forecast through the weekend. This morning’s ECMWF model has warm air surging into the Ohio Valley ahead of Thursday night’s cold front:

We should make it into the 50s Thursday afternoon. Some colder air will swing into the Ohio Valley Friday and Saturday (highs will be 40-45° each day), but warmth returns to the Tri-State by Sunday night and early Monday:

Temperatures will likely each into the 50s both Sunday and Monday afternoon. The latest ECMWF and GFS models bring another shot of cold air into the Tri-State by Tuesday or Wednesday next week.

The Cincinnati area remains under a SLIGHT risk for severe storms late tonight and early Wednesday; the Storm Prediction Center has placed the southwestern Ohio Valley, the southeastern Mississippi Valley, and much of the Mid-South under a MODERATE risk for severe storms tonight and early Wednesday:

This morning’s model runs suggests damaging straight-line winds will be the main severe weather threat in the Tri-State early tomorrow. A line of showers and thunderstorms has already formed over the Mississippi Valley and southern Plains; this line will be pushing east through the night and tomorrow. The latest high-resolution WRF model has a squall line along the Wabash and Mississippi River at 1am tonight:

By 7am, the WRF has the squall line (and perhaps a secondary line showers and thunderstorms) moving the Tri-State:

By 1pm Wednesday, the WRF has rain and thunderstorms moving east of Cincinnati and through the Mid-Atlantic/Carolinas:

The WRF has a large swath of 60mph+ winds just above the ground (in orange and bright red) in the western Ohio Valley by midnight ET:

By 4am, that swath of gusty to damaging winds has pushed east into the Tri-State:

Strong winds may proceed storms late tonight.

Even the latest HRRR model has damaging winds (near the arrow and as thunderstorms come through) in southern Illinois, southwestern Indiana, and western Kentucky by midnight:

While the best tornado threat will be well southwest of the Tri-State early Wednesday, the tornado threat (while it is small) can’t be ruled out. SPC’s version of the WRF model has the best potential for rotating thunderstorm updrafts along the Mississippi River at 1am tonight:

By 6am, the WRF suggest there may be some rotation in thunderstorms moving through the Tri-State:

Summary

Damaging straight-line wind continues to be the main severe weather threat locally early Wednesday. Tornadoes and large hail will secondary threats, with the greatest threat for each staying southwest of the Tri-State. Showers and thunderstorms will be moving through tomorrow morning between 2 and 11am, with the best threat for rain and storms (including strong and/or severe storms) between 5 and 9am.

Please stay safe and weather aware tonight and early Wednesday. Having a NOAA Weather Radio on and programmed correctly could save your life!

The next 24 hours will be fairly quiet in the Ohio Valley, but a threat for storms continues in the Ohio Valley Tuesday night and early Wednesday. Severe weather is not a guarantee, but the threat for severe weather has increased since yesterday.

This morning’s WRF model suggests clusters of thunderstorms will be northwest of the Tri-State for mid-afternoon Tuesday:

Also note the line of showers and thunderstorms organizing in the Mississippi Valley tomorrow afternoon. This morning’s WRF model has that line of showers and thunderstorms (and perhaps some individual cells ahead of the line) moving into the western half of the Tri-State by 4am Wednesday:

The WRF model has this line of showers and thunderstorms moving east of Cincinnati by 10am Wednesday:

As I mentioned in yesterday’s blog post, damaging winds will be the main severe weather threat early Wednesday morning. One indication of this is the strength of the wind 5,000 feet above the ground; this morning’s NAM model shows 60-80 knot (70-95mph) winds 5,000 feet above the Tri-State at 7am Wednesday:

This morning’s GFS model has winds about as strong at 1am Wednesday in the Ohio Valley:

If these winds can be transferred down to the ground, storms may produce damage.

When it comes to wind shear, the speed shear (the change in wind speeds going away from the ground) is impressive but the directional shear (often needed for tornadoes and defined as the change in the wind direction going away from the ground) is not as impressive. For this reason, the latest SREF model from the Storm Prediction Center has the best tornado support along the Mississippi River at 1am Wednesday (Cincinnati is the blue dot):

Summary

Damaging straight-line winds will be the main concern with any strong storms in the area early Wednesday morning. Storms will likely arrive in the Tri-State in a weakening mode, but storms may still be strong or even severe. Large hail and heavy rain are secondary threats with the strongest storms, and the tornado threat is the lowest threat. Be prepared for heavy rain and gusty winds during Wednesday morning’s commute.

Last last week, there were indications from computer forecast models that there would be some instability available for thunderstorms  in the Ohio Valley Tuesday night and Wednesday. Based on upper-level support alone, the support for heavy rain Tuesday night and Wednesday has been in the forecast since last Friday. The thunderstorm threat will need to be monitored closely nearing mid-week.

For now, the severe weather threat in the Tri-State is not a major concern, but strong or severe storms can’t be ruled out. The main reason why severe weather will be favored outside of the Tri-State will be the time of day. The latest round of model data suggests the cold front – the surface feature supporting the chance for thunderstorms early Wednesday in the heart of the Ohio Valley – will be moving through during the early morning commute Wednesday, as NOAA’s Hydrometeorological Prediction Center shows in their latest forecast surface analysis:

If this cold front was moving through during the afternoon (when instability and the temperature would be higher), the risk for severe weather would be noticeably higher. Since the cold front (and it’s associated thunderstorms) will be moving through late at night, instability will be lower, which tends to support a lower severe weather threat.

This morning, the Storm Prediction Center felt the best severe weather threat Tuesday morning through Wednesday morning was west of the Tri-State, where greater instability and low-level moisture would be focused:

This is a rather large “slight risk” area from the Storm Prediction Center. While not likely, they may be looking to issue a moderate risk in the Ark-La-Tex, where shear and dewpoints will be elevated and the tornado/large hail threat will be higher. The Storm Prediction Center, though, is likely going to wait until more model runs complete before making adjustments and/or issuing a moderate risk. SPC has placed much of the Mid-Atlantic and Carolinas under an enhanced risk for severe storms Wednesday morning and afternoon (highlighted in red):

The Tri-State has not been placed the Tri-State under a slight or enhanced risk for severe weather yet, but that may change.

One thing I’ll be watching as new models come in is the strength of winds aloft, especially 5,000 feet or so above the ground. Without going into great detail, strong winds 5,000 feet or so above the ground often serves as a signal that damaging straight-line winds are possible in an otherwise favorable thunderstorm environment. In other words, these strong winds aloft don’t always mean an area will see damaging winds, but it is a concern when thunderstorms are forecast.

So what do the winds look like 5,000 above the ground Tuesday night and Wednesday? This morning’s NAM forecast model suggest winds will be roughly 50-60 knots (60-70mph) overhead at 7am Wednesday morning (Indiana, Ohio, and Kentucky are on the right half of the screen):

These are fast winds! This morning’s GFS model also suggests winds will be 50-60 knots (60-70mph) 5,000 above the ground at 7am Wednesday morning:

In heavy rain, most – if not all – of these winds tend to be mixed down to the ground, and we can get blasted with strong or severe winds. In this particular setup, this is not a guarantee, but it is something to watch. 

With storms gradually weakening to our west late Tuesday as instability drops, our severe weather threat is conditional. This morning’s high-resolution WRF model has numerous showers and thunderstorms to our west by 4pm Tuesday:

The latest high-resolution WRF model has showers and thunderstorms congealing into a line by 1am Wednesday:

While the high-resolution WRF model doesn’t go out through the morning commute Wednesday, a slightly lower resolution WRF model does…and here’s what it thinks the radar will look like by 7am Wednesday:

With this “future radar” product painting yellow and red colors in our area, heavy rain is a concern, but this also highlights the potential for a solid line of strong or severe thunderstorms to sweep through the Tri-State.

Summary

There is still uncertainty about the strength and timing thunderstorms Tuesday night and early Wednesday. The time of day tends to favor weaker storms, but strong winds above the ground suggest gusty or damaging winds are possible with any strong storm that is able to form.

Models suggest better support for severe storms (higher dewpoints, great shear, better instability, and stronger lift) will be closer to the Mississippi River. There are also indications from the newest computer model runs that we will get “cut off” from Gulf moisture that will fuel thunderstorms.

Storms will likely be in a weakening mode as they arrive in the Tri-State late Tuesday night and Wednesday. At this time, isolated strong storms appear more likely than a widespread severe weather event.

Stay tuned for updates! I hope to have a new blog entry up tomorrow…

The area of low pressure that gave the Tri-State a quick shot of snow is heading east in a hurry; high pressure over the Mississippi Valley is already moving in from the west. The clearing line along the Indiana/Illinois border now will be moving into the Tri-State early this evening. By late evening, the sky overhead will be clear to partly cloudy. Tonight’s hour-by-hour forecast shows temperatures falling into the upper teens late:

High pressure will settle into the Ohio Valley Saturday. With high pressure nearby, ample sunshine is forecast tomorrow morning, and a partly cloudy sky is forecast Saturday afternoon:

High pressure will push east Saturday night and early Sunday, allowing low pressure to move in from the west. Mid- and high-level clouds will increase Saturday night, and only filtered sun is expected Sunday. Sunday’s hour-by-hour forecast shows a mix of freezing rain, sleet, snow, and rain developing in the Tri-State Sunday afternoon:

Temperatures will be above freezing most if not all of Sunday night, so the mix of precipitation types will likely transition to all rain by early Monday morning. Only rain is forecast Monday afternoon through Wednesday. While there are large model discrepancies in next week’s forecast, the latest GFS forecast model shows some limited instability (shown in purple) in the Tri-State Wednesday afternoon:

For this reason, a mention of thunderstorms will be put into the forecast Wednesday.

Cold air is likely to return late next week. Little to no snow accumulation is expected Thursday as a cold front sweeps through the Ohio Valley.

Two different areas of low pressure and a large upper-level disturbance approaching the Ohio and Tennessee Valley tonight will produce snow in the Tri-State tomorrow. This is not going to be a big winter storm, but accumulation will be widespread.

The National Weather Service has posted a Winter Weather Advisory for the Tri-State. This advisory will be in effect from 6am to 5pm Friday:

The heaviest snow will likely fall between 9am and 3pm.

This morning’s Microcast model run has a good handle on the timing of snow Friday. At 8am Friday, light snow will be moving in from the west:

By noon Friday, Microcast suggests snow will be widespread:

By late Friday afternoon, Microcast shows snow exiting the Tri-State:

By early Friday evening, most in the Tri-State will get 1-2″ of snow accumulation; some will see 2-2.5″ of accumulation. Overall, Microcast has a good handle on amounts, but amounts for specific towns on this map are approximate:

As new model data comes in, we will adjust totals through the night and early tomorrow. Please be careful traveling tomorrow!