Winter Storm Lexi Leaves Its Mark, More Snow?

(Note- I will begin to use the Weather Channel winter storm names.  The National Weather Service's official position is opposition to these names.  However they are growing in popularity and I find them useful.)
Winter Storm Lexi arrived yesterday and left its mark on Southern New England.  Tragically a 6 year old girl from Canton died when a tree limb fell on her while playing outside.  May you rest in peace Kaleigh Kenyon.  Tree limbs also fell on power lines and left nearly 180,000 customers without power at the height of the storm.  In eastern MA there are still about 50K customers without power.  In Rhode Island it looks like there are approximately 10-15K still in the dark.

MEMA power outages for MA

I don't have a snow total map yet but the highest total in MA was Worcester airport with 12.5".  In CT the big winner with 13" is Staffordville.  In Rhode Island Burrillville checked in with 12".  I am content with my snow map but I would have really nailed it if I made my 5-9" band a 8-12" band as a lot of places came in around 9. 10".  See the full list here for yourself.

NWS Boston seasonal snow round up post storm

So what is next?  First off today is pretty seasonable for February.  Temperatures in the mid to upper 30's with mostly sunny skies giving way to partly cloudy conditions this afternoon.   This will allow for some melting.  The temperatures drop back into the 20's tonight allowing for a refreeze.  Sunday is similar but a tad warmer and less clouds.  Now we turn to Monday.  Given this is a complex set up let me try and set the table.

First here is the upper air pattern this morning at 7 AM

12z NAM 500 mb vort 7 am (image NCEP)

First that jumps out is the complex in the southern plains ready to eject into the Southeastern states.  By tomorrow AM a storm system will develop in the Southwest Atlantic.

WPC surface forecast Sunday 7 AM

While we watch the Panthers pound the Broncos (but hopefully by less than 7) the upper air pattern will evolve to this.  One does not need to be a weather enthusiast to see the strength of this upper level low.  The low is closed and feeding off the gulf stream.

12z NAM 500 mb vort Sunday 7 PM (image NCEP)

This should continue right up the coast right?  Well not exactly.  The potential Tuesday system (more on that later) is moving out of the northern branch of the jet stream and could shunt this storm further east.  The overnight computer guidance largely favors that solution.  The problem is the stakes are high.  If the storm moves 50 miles north and west look what we get.

12z NAM 1000-500 mb thickness, qpf, mslp valid Monday 1 PM (image NCEP)

Temperatures inland will be much colder on Monday so at least we would not have to deal with the cement that fell yesterday.  But in turn snow ratios are higher and more snow falls.  For example here is Monday at the same time as the image above (1 PM Monday)

12z NAM Hires 2 m temps 1 PM Monday (image weatherbell)

Snow would likely start around or just after the AM commute Monday.  As of now Tuesday is complicated.  It depends on what storm number 1 does.  I feel that the threat from Monday is much greater than Tuesday.  So as of now here is my snow map.

Zack Green snowfall impact map Monday

I have to buy the potential of this.  So far this winter guidance has tended to bring storms further north and west as we got closer to the event.  Despite the long standing bias against the NAM it has done well this winter.  I may post tonight but if not I will have a Sunday AM update.  I'll try and figure out the mes of Tuesday today but as for now that appears to have much less potential than Monday.  The next winter storm name is Mars.  Less sexy than Lexi if you ask me.

Questions, comments, concerns, complaints on my facebook page or @zgreenwx on twitter.

-Zack Green

Snow to Continue Into the Afternoon

Good Morning everybody.  I am happy for the school cancellations.  I did not want to upset the teachers I promised a snow day.  Let's look at the current conditions and project the rest of the storm.

The winter storm warning remains in effect until 3 PM.  It has actually expanded north in Southern New Hampshire and into Southern RI

NWS Boston watches and warnings

First lets look at the water vapor satellite loop.  See how the moisture source extends to the Gulf of Mexico all the way into New England.

GOES_east water vapor loop 815 AM

The northeast regional radar shows a lot of precipitation

NWS Northeast regional radar 818 AM

Low pressure has formed along the stalled front offshore

WPC surface analysis 7 AM

The elongated S shape of the cold front is a classic snow signature for New England.  We would be looking at a lot more snow if the stalled boundary in Northern New England was not present.  Look at the temperatures

7 AM 2 m RTMA temps (image weatherbell)

Temperatures in Southern New England are marginal for snow.  Last year when it was so cold the snow was fluffy and it piled up quickly.  This snow will be wet and heavy.   Some colder air is moving into Worcester County so the snow will be slightly lighter there.  So let us time this out.

By noon the radar looks like this

13zHRRR simulated radar valid 12 PM (image weatherbell)

Some light snow will still be around Worcester until 4-5 PM but still going strong in Eastern New England.

13z HRRR simulated radar 6 PM (image weatherbell)

So lets say another 4-7 inches of snow in addition to what is already on the ground in purple/pink below.  This model assumes a 10.1 liquid to snow ratio.  I think that is too high given the heavy nature of the snow so I will cut these a bit

12z HRRR 15 hour snow total

All in all a messy Friday.  Enjoy the day.

Zack Green

Snow Friday AM

UPDATE
Winter storm warning now posted

NWS 3 PM update

Change over from snow to rain begins around 3 AM from west to east.  This is a not a cold system so it will be interesting to watch the rain snow line.

Previous discussion below. 

Living in New England means many things including the Jekyll and Hyde nature of our weather.  Take this week for example.  Temperatures have been in the 50's and 60's.  Last night some folks lost power as heavy rain and roaring winds took down tree branches.  Tomorrow we see snow!  The National Weather Service in Taunton has issued a winter storm watch late tonight into tomorrow afternoon.

NWS Boston hazards

Currently a cold front is draped right across New England.

WPC surface analysis 7 AM

The true Arctic air is locked away behind the cold front in Ontario but it will cool off tonight.  As of 10 AM the New England temps look like this.

RTMA 2 m temps 10 AM (image weatherbell)

The upper air shows southwest flow aloft which explains the mild weather this week

12z NAM 500 mb vort 7 AM (image NCEP)

But see that mess in the Central US?  It will consolidate and add energy to the cold front which will stall offshore.  The ridge in the Atlantic will strengthen and force the trough to take on a negative tilt.

12z NAM 500 mb vort valid 4 AM Friday (image NCEP)

A low will form offshore and move up the coast throwing moisture back along the I-95 corridor.  In Southern New England a dusting to an inch is likely all the way to I-91/84 with heavier snows south of the MA Pike and inside 495.

WPC surface forecast 7 AM Friday

 The latest trends have been for more moisture and the precipitation is moving further west.  So more snow? Well not so fast.  The latest trends have been warmer.  The upper level support is strong so that should allow for a heavy thump of snow.  That will allow for snow to accumulate.  But it will be heavy and moisture laden.  It will not be a fluff bomb.  The Outer Cape and Islands can look for a lot of rain with this system.  Here is my snowcast

Snowcast for Friday

To my friends who are educator's I would expect no school in the 3-5 and 5-9 bands.  The precipitation will begin as warm but switch to snow around 3-4 AM.  The AM commute will stink.  It wraps up early afternoon Friday.  If you need more specific information please ask.

I'll watch the trends and update again tonight if/when the Winter Storm Watches become a warning.

-Zack Green

Tracking the Blizzard (To Be)

I am on record calling the storm off yesterday.  I still believe it is a non event for most of the region but perhaps I was a bit premature in saying just a few flakes here and there.  In fact the South Coast of CT, RI, MA (including Cape and Islands) may see a significant event.  It will be still be hard to get much north of the Pike.  But I can already feel the egg white starting to hit my face.

Me Looking at the data this AM

Here are the National Weather Service watches and warnings for Southern New England this afternoon.  The Vineyard is under a Blizzard Warning!

NWS Boston Afternoon watches and warnings

A winter storm warning has been posted in pink.  Although we are missing out on 95% of the storm it is still very impressive.  Here is the NWS snowfall forecast for the Northeast US

NDFD NWS snowfall forecasts through Sunday 1 PM

This is pretty wild and will likely crack the top 15 snowstorms of all time when accounting for population and snow totals.  The storm is a beauty on satellite

GOES_East water vapor loop valid 815 AM (image NOAA)

The radar as of 4 PM

NWS Northeast regional radar loop

High pressure and dry air stops this beast from making a ton of noise in New England.  But it does look like the South Coast is going to get rocked.  I was wrong to write this baby off completely yesterday.  Weather is humbling.  So the snow will start to fly around noon time South to North.

My forecast

I think a lot of places along the south coast see around 7-8 inches.  I'll update again tomorrow AM.

-Zack

Cancel the Storm

UPDATE- I am leaving this post.  One must take the good and the bad in forecasting.  Below is my apology to my facebook friends.

Feb 2010- predict 8-12 we get 0. Jan 2016 predict 0 we get 6". 2 of my worst forecasts ever. I'll be better Facebook friends who read my weather posts. Sorry about this one I messed up.


Enjoy the weekend New England- no storm for us.  A few flakes at the coast but put the plows away.  Most of the energy will transfer to a secondary low well out to sea. Likely wind advisory criteria on the Cape and Islands Sunday with blustery conditions for the rest of Southern New England.  There are still high tides astronomically this weekend so some minor coastal flooding is possible in flood prone areas.

GO PATS

-Zack Green

Wednesday Update

When watching the news or searching facebook it is important to know who is providing the information and where it is they are talking about.  No one in Southern New England is promising 2 feet of snow unless it is a 12 year old wish casting online.  When the news is talking about a historic storm they are referring to the DMV (DC, Maryland, Virginia).  See my post yesterday for a larger discussion on the evolution of the storm.

General Overview 
The energy that will be responsible for the storm is now onshore.  It is a weak frontal system in the Pacific Northwest.  This energy will dive southeast towards the four corners and combine with another piece of energy in Texas (circled).

06z NAM 500 mb vort 1 PM Wed (image NCEP)

This will lead to a surface storm that should produce showers and thunderstorms along the Gulf Coast states.

WPC surface forecast Thursday 7 AM

We went over this yesterday.  So now the question is why won't the storm come all the way up the East Coast?  The first answer is it develops and closes off too quickly.  Let us review the 2015 January Blizzard 500 mb set up and also show the set up for this storm.

First up- 1.25.15
Notice how the energy is much further north.  The ridge out west is more pronounced and this energy is already ready to round the base of the trough.

1.25.15 12z NAM 500 mb vort for 7 am (image NCEP)

 Now I want to show the storm as it gets to the east coast.  The trough has a strong negative tilt but the low has not yet closed off yet at 500 mb

1.25.15 12z NAM 500 mb valid at 7 PM Monday 1.26 (image NCEP)

Now let me show you what the surface looked like at 7 PM that Monday night.

WPC surface analysis Monday January 26, 2015 7 PM

In contrast when the 500 mb trough is in a similar location Friday look at the huge differences

12z GFS 500 mb vort valid Saturday 7 am (image NCEP)

The low is already closed off so meteorologically speaking the storm is peaking.  This is when DC, Balt, Richmond etc are being pounded with snow.  Here is the surface chart forecast for Saturday AM

WPC surface forecast Saturday 7 AM

 Why won't this storm just continue up the coast?  First of all the high pressure in Quebec will help force it to the east north east.  The upper level system will start to be elongated as well and multiple low pressure centers will form.  This lows will compete for the energy and odds are one of the lows closer to the gulf stream will win out.  From experience I was burned in a situation like this in 2010.  I was in college in Advanced Forecasting and the Mid Atlantic was forecast to get a huge snowstorm.  We believed it would come up the coast and give Southern New England a good 8-12 inches of snow.  Nearly the entire class busted.  If the upper level low looked like this

12z NAM 1.25.15 valid Tuesday January 27, 2015 (image NCEP)

THEN PERFECT!  Unfortunately by Sunday morning it will look something like this

12z GFS 500 mb vort valid Sunday 7 Am (image NCEP)

 With all those competing maximums snow will not make it very far into Southern New England, if at all.

12z GEFS snowfall through Sunday 7 PM (image weatherbell)

Very few members have any snow at all and this has been consistent for days.  This is a DC snow storm which happens in El Nino's.  So my call is this..

Snowcast props

 I am honestly being generous.  It's probably a 5% chance of a plowable snow from the MA/CT/RI border to the pike, if that.  The snow would fall Saturday PM if it does so I'll keep an eye on it but my recommendation is to keep all plans.   For entertainment here is the storm I busted on in 2010

Feb 4-7 nor'easter 2010 NESIS

The map should look similar when all is said in done (just shifted south a bit).

As always questions, comments, complaints, concerns on facebook or twitter.  One more update tomorrow to officially write this one off.

-Zack Green

Thoughts on Weekend Storm

I have chosen to avoid the hype for the potential major winter storm this weekend.  Now is the time to add some general thoughts.  I am leaning towards a modest snowstorm in Southern New England with the jackpot well to our south.  Our friends in the DMV have been thirsty for a blockbuster snowstorm and it looks like they will get it. 

General Overview
The energy associated with this storm has not yet entered the US.  When it does tonight expect the weather guidance to really lock onto a solution.  As it stands there is pretty remarkable agreement that something will happen along the east coast.  Lets track the upper air energy

06z GFS 500 mb vort valid 10 am Tuesday (image NCEP)

I've drawn the general track of the upper level energy.   It is likely I have drawn it a bit far to the north. It will strengthen as it gets into Dixie and will pick up Gulf and Atlantic moisture.  At the surface the "storm" is not much to look at as of right now.  But by Thursday a weak surface low should be moving across Texas

WPC surface forecast Thursday 7 AM

Fast forward 24 hours and we see a building Western ridge and a deepening eastern trough.  On Friday the original surface low will begin to reform near the Atlantic coast as the system runs up against the Appalachians.

06z GFS 500 mb vort Friday 8 am (image NCEP)

 See the surface chart at the same time and notice the banana high in the Midwest extending into Ontario.  This locks the cold air in pace and gives most places on the cold side of the storm all snow.

WPC surface forecast Friday 7 AM

At this point its time to watch how the upper air evolves.  The American GFS which I have been using to show upper air diverges from the European (which I can't show $$) in small but significant ways.  The 500 mb low closes off further north on the GFS allowing for more moisture into Southern New England.  The EURO closes off further south the northward extent of the moisture is much less.  The low feeds off a 300 mb jet max which is further south and east on the EURO.  I tend to agree with the EURO because that high pressure in Ontario will slide into Quebec/Northern New England.

WPC surface forecast Saturday 7 AM

So up to this point I have high confidence in a major storm for the Mid Atlantic- a true mauler.  The high pressure is in a pretty sweet spot for SNE- though I would like it just a bit further north.  That high will limit how far north the storm can come and will in turn force it out.  Now that usually is a good thing but this storm may not make the 40/70 benchmark which is the sweetspot for Southern New England storms.  This scenario means the Southern New England coast will take a battering.  With a full moon Saturday tides will already be high.  Add in this storm and there is potential for moderate-major coastal flooding. 

WPC 5 day precipitation totals through Sunday 7 AM

This chart shows the sharp cut off with moisture.  The ski resorts will not do well with this storm.  Here is my snow potential.  I will work on wind/coastal impacts later this week but the threat looks to be substantial in SE MA.

Snow threat guess- Zack Green

Today I will watch the upper air trends and surface tracks and try to narrow this down more.  Please do not go crazy and cancel plans.  The storm is 120 hours out.  Friday and Friday night look fine for our region.  Saturday afternoon looks to be the target start time but experience tells me this will fluctuate.  Twitter/facebook for questions

-Zack Green