Good evening from Southern Connecticut Weather.
There's no rest for us as we track another significant storm that will impact the state tomorrow. The signal for this one has also been on the guidance for a while, and as I wrote earlier in my update earlier, this is a truly massive storm responsible for virtually every watch or warning east of the Rockies. While the Midwest will deal with the cold blizzard side of the storm, we will be on the eastern side and as a result we have a mostly rain and wind event. While some snow is possible tomorrow afternoon in interior CT with minor accumulation in the higher elevations due to the cold we currently have in place, the main story is the warm side. Let's dive in.
There's no rest for us as we track another significant storm that will impact the state tomorrow. The signal for this one has also been on the guidance for a while, and as I wrote earlier in my update earlier, this is a truly massive storm responsible for virtually every watch or warning east of the Rockies. While the Midwest will deal with the cold blizzard side of the storm, we will be on the eastern side and as a result we have a mostly rain and wind event. While some snow is possible tomorrow afternoon in interior CT with minor accumulation in the higher elevations due to the cold we currently have in place, the main story is the warm side. Let's dive in.
Above: the latest WPC Excessive Rainfall Outlook, which has virtually all of CT under a moderate risk of excessive rainfall. With the state seeing more than 150% of normal precipitation in the last 30 days, another heavy rain event is on the way. Image courtesy of Pivotal Weather.
Overall Setup
The overall setup is straightforward. A big time storm is rapidly developing in the Midwest and will become even stronger as it moves northeast. Unlike our last storm, we have a retreating high is not enough blocking in place to keep this moving east and off the coast. As a result, this cuts west as it explosively develops, creating a truly massive wind field and strong cold and warm sectors.
Precipitation rapidly approaches tomorrow, but the first half of the day looks quiet. With cold in place but retreating, some parts of interior CT may see snow before a quick transition to rain. While some minor accumulation is possible in the hill towns (coating-2"), little to no accumulation is expected elsewhere.
Heavy rain comes in tomorrow night along with strong winds and as the storm moves to our north a squall line will develop along the front to bring more heavy rain and possible damaging wind early Wednesday.
Timing
The precipitation, starting as rain in most of Connecticut and as snow in colder and elevated spots in interior northern Connecticut should begin between 1-5pm. The wind will also gradually pick up starting early afternoon, though the worst wind is not until late night. Expect a wet commute as the rain begins. Rain and wind will increase in intensity tomorrow night, and the worst of the storm is expected between midnight and 5am.
Heavy rain and wind gradually diminishes between 5-7am, and while some scattered showers will linger later into the morning the storm will effectively be over.
The overall setup is straightforward. A big time storm is rapidly developing in the Midwest and will become even stronger as it moves northeast. Unlike our last storm, we have a retreating high is not enough blocking in place to keep this moving east and off the coast. As a result, this cuts west as it explosively develops, creating a truly massive wind field and strong cold and warm sectors.
Precipitation rapidly approaches tomorrow, but the first half of the day looks quiet. With cold in place but retreating, some parts of interior CT may see snow before a quick transition to rain. While some minor accumulation is possible in the hill towns (coating-2"), little to no accumulation is expected elsewhere.
Heavy rain comes in tomorrow night along with strong winds and as the storm moves to our north a squall line will develop along the front to bring more heavy rain and possible damaging wind early Wednesday.
Timing
The precipitation, starting as rain in most of Connecticut and as snow in colder and elevated spots in interior northern Connecticut should begin between 1-5pm. The wind will also gradually pick up starting early afternoon, though the worst wind is not until late night. Expect a wet commute as the rain begins. Rain and wind will increase in intensity tomorrow night, and the worst of the storm is expected between midnight and 5am.
Heavy rain and wind gradually diminishes between 5-7am, and while some scattered showers will linger later into the morning the storm will effectively be over.
Above: the 18z GFS depicting the storm evolution tomorrow and early Wednesday. The guidance generally agrees that very heavy rain arrives tomorrow night and peaks during the early morning hours before tapering off around sunrise.
Impacts
This is a multi-hazard event, and we have a number of watches and warnings as a result. The highest confidence is in the rain and flooding risk, followed by coastal flooding and wind.
Rainfall/Flooding
This is most likely to be the headline of the storm. We've had a lot of rain the last month, and with a water laden snowfall just yesterday we have a problem. The rainfall is likely to be very heavy with moisture content 2-3SD above normal. We expect the state to see another 2-4" event with most of the rain falling overnight and early morning as the storm quickly moves through the region. Some isolated areas could see even higher totals.
This kind of rainfall would trigger flood watches by itself given our recent wet streak, but the potential is raised even more by the rapid snow melt that is coming as temperatures quickly rise late tomorrow and Wednesday. Most of what we see outside should melt rapidly which will create significant flooding issues.
If you have a basement that floods or a storm drain that's clogged, you will want to take action in case your street or the area around your house becomes waterlogged. Not only are soils saturated, in some places they are frozen given the recent cold and snowfall. That may create runoff issues. Rivers, streams, and streets are at risk of flooding from the heavy rain and snow melt.
Below is the national blend of models (NBM) showing the computer model consensus for rainfall tomorrow and Wednesday. Most see 2-4" of rain.
This is a multi-hazard event, and we have a number of watches and warnings as a result. The highest confidence is in the rain and flooding risk, followed by coastal flooding and wind.
Rainfall/Flooding
This is most likely to be the headline of the storm. We've had a lot of rain the last month, and with a water laden snowfall just yesterday we have a problem. The rainfall is likely to be very heavy with moisture content 2-3SD above normal. We expect the state to see another 2-4" event with most of the rain falling overnight and early morning as the storm quickly moves through the region. Some isolated areas could see even higher totals.
This kind of rainfall would trigger flood watches by itself given our recent wet streak, but the potential is raised even more by the rapid snow melt that is coming as temperatures quickly rise late tomorrow and Wednesday. Most of what we see outside should melt rapidly which will create significant flooding issues.
If you have a basement that floods or a storm drain that's clogged, you will want to take action in case your street or the area around your house becomes waterlogged. Not only are soils saturated, in some places they are frozen given the recent cold and snowfall. That may create runoff issues. Rivers, streams, and streets are at risk of flooding from the heavy rain and snow melt.
Below is the national blend of models (NBM) showing the computer model consensus for rainfall tomorrow and Wednesday. Most see 2-4" of rain.
Coastal Flooding
We have coastal flood warnings for the shoreline as this is likely to bring strong onshore flow from southeasterly and southerly winds. Minor to moderate flooding will be possible, so if you are at the immediate coast pay close attention to the water level.
Wind
The least confidence is in the wind forecast. The thing that exacerbates the flooding potential also keeps inland CT at least at less risk of truly high end wind gusts. The snowpack will melt, but in doing so will help to reinforce an inversion. Inversions help prevent the mixing of air that would normally bring some of the strongest winds aloft to the surface. There is a strong low level jet, so to prevent damaging winds inland you really want to prevent mixing. This is why many of our wintertime wind events do not become high end.
Along the shoreline, it's a different story. With most areas not receiving much snow, the snow pack should melt quickly and with proximity to the coast, coastline areas could see significant wind gusts. What may help here are the cooler sea surface temperatures in Long Island Sound.
As a result, our wind forecast is a little more muted than it might otherwise be.
We expect maximum wind gusts inland to peak between 40-50mph. This includes the interior sections of Fairfield, New Haven, and Middlesex Counties. For the entire coastline and interior New London County--the place where the high wind warnings exist in southern CT, we expect peak gusts of 50-65mph.
With peak wind gusts in this range, scattered to widespread power outages are possible. Everyone should go the general preparation you would for a moderate wind event.
There is a wild card however. Some of the high resolution guidance is trying to show what looks like convection in the squall line that ends the heavy rain. Convection can mix down stronger LLJ winds, so this is something to watch very closely. If we do have convection early Wednesday morning wind gusts even inland can briefly become high end, exceeding our forecast. This is a low likelihood, perhaps around 20%, but it is worth mentioning.
We have coastal flood warnings for the shoreline as this is likely to bring strong onshore flow from southeasterly and southerly winds. Minor to moderate flooding will be possible, so if you are at the immediate coast pay close attention to the water level.
Wind
The least confidence is in the wind forecast. The thing that exacerbates the flooding potential also keeps inland CT at least at less risk of truly high end wind gusts. The snowpack will melt, but in doing so will help to reinforce an inversion. Inversions help prevent the mixing of air that would normally bring some of the strongest winds aloft to the surface. There is a strong low level jet, so to prevent damaging winds inland you really want to prevent mixing. This is why many of our wintertime wind events do not become high end.
Along the shoreline, it's a different story. With most areas not receiving much snow, the snow pack should melt quickly and with proximity to the coast, coastline areas could see significant wind gusts. What may help here are the cooler sea surface temperatures in Long Island Sound.
As a result, our wind forecast is a little more muted than it might otherwise be.
We expect maximum wind gusts inland to peak between 40-50mph. This includes the interior sections of Fairfield, New Haven, and Middlesex Counties. For the entire coastline and interior New London County--the place where the high wind warnings exist in southern CT, we expect peak gusts of 50-65mph.
With peak wind gusts in this range, scattered to widespread power outages are possible. Everyone should go the general preparation you would for a moderate wind event.
There is a wild card however. Some of the high resolution guidance is trying to show what looks like convection in the squall line that ends the heavy rain. Convection can mix down stronger LLJ winds, so this is something to watch very closely. If we do have convection early Wednesday morning wind gusts even inland can briefly become high end, exceeding our forecast. This is a low likelihood, perhaps around 20%, but it is worth mentioning.
Above: the latest high resolution NAM, showing the evolution of the storm over CT. Note how the very end has a squall line like appearance. If that were to occur, higher end wind gusts could occur in advance of it.
Overall Impact
This is likely to be a high impact storm. The flooding potential is higher than usual with heavy rain coming in over a relative few hours and rapid snow melt. The wind potential is moderate, but could quickly become higher if there is convection at the end of the event.
Scattered to locally widespread power outages are most likely in southern CT where the winds will be highest. Wednesday may bring widespread delays and cancellations.
After this storm, we turn our eyes to another big storm signal for the weekend...
As always, please like, share, and interact with us on our social media--on Facebook to share our discussions, and follow us on Twitter @southernctwx to retweet our posts. Hit the buttons below to join.
Thank you for reading SCW.
-DB
Overall Impact
This is likely to be a high impact storm. The flooding potential is higher than usual with heavy rain coming in over a relative few hours and rapid snow melt. The wind potential is moderate, but could quickly become higher if there is convection at the end of the event.
Scattered to locally widespread power outages are most likely in southern CT where the winds will be highest. Wednesday may bring widespread delays and cancellations.
After this storm, we turn our eyes to another big storm signal for the weekend...
As always, please like, share, and interact with us on our social media--on Facebook to share our discussions, and follow us on Twitter @southernctwx to retweet our posts. Hit the buttons below to join.
Thank you for reading SCW.
-DB
