Expect "Complete 360" Pattern Change In October

Click on each image to enlarge for better viewing

Its been a long time coming for one of these blogs. I figured this lazy Sunday will be the best time to write one. The blog is going to look at key differences in our Sea Surface Temperature Anomalies (SSTA) between August and September, and it will also look at the rapid changes our upper air pattern (500mb level) is going to go through as we head into October.

A lot has been made about the upcoming El Nino event.

• Will it be moderate, strong, or super? 
• Will it be basin-wide or east-based? 
• Will it reach a plateau then start weakening through the winter?

These are just some of the many questions people are asking. Personally, I have made it a point in the past to not try to figure these things out too early in the season. What the Nino looks like now could look completely different in November. There are many reasons for that. The main one being it's difficult to forecast where the best forcing takes place (how the MJO behaves) along the Equatorial Pacific. 

The SSTA graphic above is for the month of August. Over the month, we saw rapid strengthening in Nino 1+2 region (eastern most based region of the ENSO) and continued warmth in the northern Pac. Lets see if these trends have held to this point. 

Nino Region 1+2 continues to maintain the core of the warmth. While Nino Region 3.4 has warmed slightly...its been a very slow and seemingly difficult process. Also, check out the area of water in the GOA to the NW Pac of the U.S. It looks like it has cooled some, right? 

Take a look at the September (to date) H5 map above. The ridge has been pushed back west allowing for more of a neutral to positive EPO. This has brought cooler weather - or negative H5 heights - to that region. 

The 7-day change in SSTA shows that area of the Pacific continuing to cool. Obviously this it not ideal to see because it could lessen the probability of seeing another winter with a mean -EPO. A

 -EPO these last couple of winters forced, or displaced, the polar air in the Arctic to the eastern CONUS. Then again, with a strong El Nino event currently taking place it is difficult to find analogs that had a ++ENSO with a persistent -EPO over an entire season. We will see if this trend continues into October...but I have a feeling it will not. 

The upper air pattern is going to undergo significant changes this week. 

The beginning of the week is going to feature much of the same weather we have seen the last couple of weeks - zonal flow with temps in the upper 70's to low 80's. Negative heights persist across central/northern Canada and the Southeast US, while positive heights drape through most of the U.S. and eastern Canada. Refer to the September H5 map above to see how incredibly warm east-southeast Canada has been this month. 

Check out where our pattern is headed by the 1st weekend of October. Canada has gone from experiencing negative heights to way above normal heights. The EPO region (Alaska / GOA / NE PAC) is also expected to see a ride resurgence take place. This "blocking" pattern is going to have big effects on our weather here in the northeast. 

• We will enter a normal to below normal temp regime 

• There will be greater rain chances going forward - at times - significant rain

We could see our first significant rain threat of the season by the end of this week or weekend. With abrupt heights changes from negative to positive across Alaska to Canada, waves of vorticity that drop down from Canada will not be able to move much. There will be a lot of vort interaction. This is going to cut-off our flow and potentially bring nasty weather to our area. The H5 map above is an example of what the models are trying to do for next weekend. H5 closes off over the Midwest and an area of low pressure forms off the coast. 

EURO (left) and GGEM (right) are both insisting on a potent rain event next weekend. There are differences in track and storm intensity at this moment. We will have a clearer picture of how this storm envelops by Tuesday. 

Moral of the story:

• El Nino needs to begin looking more like a basin-wide event rather than east-based 
• Cooling SSTA in the North Pac may not last after this pattern change 
• Sustained Fall-like weather will begin the end of this week 
• Potent coastal rain storm likely the end of this week (at least 1" of rain expected) 
• Rain chances should last through much of October

I hope everyone has a fantastic Sunday. 

Best,

Francesco

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Watching Tropical Storm Erika

It has been a remarkably quiet summer season. Sure we dealt with some thunderstorms - at times severe - but for the most part they were your typical summer storms you can expect around the NYC area. Temperatures have been more on the milder side than I expected, but we also had our fair share of cool nights too. Precipitation from normal is below average to date which is what I predicted in my Summer Outlook. I will have a more detailed overview of how well, or poorly, the summer forecast came out sometime in September or early October.

I want to spend some time talking about Tropical Storm Erika. I am not going to go into extreme specifics and depth mainly because there is still a lot of uncertainty surrounding her.

For the most part, guidance is consistent in taking Erika either through or just north of Puerto Rico. Then continuing along the northern periphery of the DR and Cuba. The big question is, at what intensity will she be at once she's west of Puerto Rico? One thing is for sure, Erika is a much stronger and more robust wave than Danny was. She will also be moving into a slightly more favorable environment for further deepening than Danny had to work with. 

GFS 500 mb pattern by the weekend shows your classic Bermuda High which will help steer Erika into the western Atlantic. Will she continue west into either the Gulf or Florida, or will she make the turn north? This is a question I cannot answer at this time. A stronger storm, let's say Hurricane strength, is likely to keep her on a northern trajectory while a weaker storm should keep her chugging west. In the image above, notice I circled the H5 trough which the GFS forecasts to slide into the central Atlantic. If a piece of this trough  clips Erika this weekend, it will likely weaken her and quite possibly kill her altogether (that's pretty harsh word choice). However, if she follows the ridge and moves quickly enough, she could possibly deepen into a major hurricane. 

Major hurricane for a couple of reasons:

1. SST's (sea surface temperatures) in the southwest and western Atlantic are running above normal as shown below. 

     2. The Hurricane models, namely the GFDL, show a sharp rise in intensity by late weekend. The            GFDL has had a decent track record this year. 

     3. The EURO model is very robust with the ridging along the east coast. The Atlantic trough noted          earlier builds behind the ridge and the end result is an impressive rise in heights along the                    eastern CONUS. 

There are other reasons as well, such as the decline in wind shear by early next week (depending on how the ridge plays out), but it's far too early to even speculate on how strong this storm will get and where it will track. Let's watch her over the next few days and I will have a second update - if needed - over the weekend. It is tomato sauce making season in my household so I will be busy one way or another...

-Francesco Paparatto

March Storm(s) Update - Easter Nor'easter?

Hello all - 

Just wanted to give a quick update on the late week storm(s) of which I blogged about on Sunday. Last weekend, the models were showing an impressive -EPO/+PNA couplet for the March 26th-April 1st time frame but that does not appear to be happening anymore. Instead, the EPO ridge is going to break down and the PNA ridge is going to be transient. This is going to keep the April 1st energy to our north instead of digging it south into our area and possibly spawning a coastal storm off our coast. 

The trough coming in behind the cold front on Friday is going to bring another round of well below normal temperatures for this time of year. High's on Saturday will only be in the low 40's, and with a NW wind, it's going to feel like the 30's. There will also be enough H5 energy involved which could spawn a wave of low pressure of the coast. As the trough tilts negative for a bit, this could enhance precipitation along the coast in the form of snow. 

The GFS, along with other models, are showing some snow showers for the area on Saturday afternoon. I would not expect much in accumulation, perhaps a coating to 1" best on grassy surfaces. If the trough is too quick - which is still possible - then we will not see any snow showers. I was never fond of this event for significant snowfall, I was more interested in the April 1st event. 

That event, however, will probably bring little to no impact to our area. Like previously mentioned, the EPO ridge is breaking down and the upper air energy associated with this wave will not dig far enough south into our area. What's most likely to happen is a band of rain or snow showers will trickle over the area on Monday. You can see the 993mb low on the GFS remains well to our north in Upstate NY. The pattern is also progressive, so the western ridge is kind of shoving this system off to the east. 

The Aleutian trough is going to come onshore and push the western ridge east. This is the main reason why the Monday event is likely not to come to fruition, along with the fact we lost the -EPO. Once that Pac. trough comes on land, it's going to turn the overall flow across the U.S. zonal and gradient-like. 

Check this out, though. Guidance is suggesting the -EPO could make a comeback around the 5th of April. If this is true, you can expect another injection of cold air into the U.S. around that time frame with a large storm potential. The MJO is still active and propagating through cold phases, and the STJ could possibly play a role in a possible storm around the 6th. 

The GFS and EURO agree about the EPO tanking negative again around the 4th of April. The long range is suggesting there could be a large coastal storm to deal with around this time. I do NOT feel the dominant precipitation type along the coast will be snow at this time, but if the dynamics are impressive enough, that could certainly pull enough cold air to the coast. Still too early to make any determinations. The pattern could stay progressive (if the EPO never goes negative) in which case we probably will not even see a storm. I'll be sure to keep everyone updated. 

In the meantime, thunderstorms likely Thursday afternoon (not severe) with the return of colder weather this weekend. Some snow on Saturday is possible but nothing significant. 

Enjoy the rest of your week and have a great weekend!

-Francesco Paparatto

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April Ra...Snow Showers Bring May Flowers

It is safe to say after the widespread 4 to 7 inch snowfall a couple of days ago, winter is in no hurry to leave this year. While we should see temperatures warm up into the mid to upper 50's this week, that's just another tease from Mother Nature since we're likely to get colder - and potentially snowy - again! 

The two time frames to watch for the threat of additional snowfall are March 28th-29th and March 31st-April 1st:

(Click on image to enlarge and read text at the bottom)

This 500mb heights/vorticity graphic from today's 12z GFS valid March 27th shows the ridge-trough combo with a potent piece of H5 energy digging into the mid-section of the country. There is some confluent energy leftover northern New England (which will be responsible to bringing us some rain this Thursday) that is keeping heights along the east coast flat. The mid-level trough is positively tilted and the overall flow across the country is progressive. 

(Click on the image to enlarge and read text)

This graphic is now valid for March 29th and you'll notice the mid-level trough is no longer positively tilted, however, the H5 energy is very strung out. There are 2 main reasons why this trough de-amplifies: 

1. Western ridge retrogrades to connect with another mid-level ridge near the EPO region and the flow turns progressive for a period of time 

     2. An even stronger piece of H5 energy (circled) is about to dig into the eastern CONUS which               disturbs the flow ahead of it. 

Here is a look at just the 500mb height anomalies valid March 29th. The full latitude ridge in the west is impressive, but it's too little too late for the March 29th east coast storm as it's already well off the coast at this time. What I am interested in is whether the next piece of energy (notice the kink in the flow around North Dakota) digs into the eastern U.S. in response to the -EPO/+PNA and brings a Miller B storm to the area around April 1st. 

Getting back to the March 29th, you can see the GFS shows an impressive system but it's well offshore. 

(Click on the image to enlarge and read text)

The 12z EURO also keeps the March 29th system offshore. The mid-level trough is simply too positive and the flow is too progressive to get anything going off the coast. Notice it also has a very potent piece of H5 energy entering the country in the upper Midwest. With all that ridging in the west, I would be surprised it that energy does not trend further south and east over the next few days and show a sizable storm off the east coast around April 1st of the Miller B variety. There may not be enough blocking to get a Miller B system to work out for our area, but if the -EPO/+PNA amplification is real I do feel we still have a shot. Obviously New England is in better position than we are, but you never know. 

The 12z GGEM is more robust with the east coast storm bringing rain to I-95 and snow to the interior northeast. Its evolution aloft is very ugly. The mid-level trough broadens out and the energy elongates over the east coast. It's basically just a wave of low pressure riding up the coast. 

CONCLUSION - MARCH 28TH-29TH STORM

Remember this scenario the GGEM was showing last week with a closed off H5 and a sub 980mb storm at the surface? I doubt very much guidance trends back to this solution. As I just explained, the lack of blocking and the retrograde of the western ridge is keeping the overall flow too progressive. 

What needs to happen to get a coastal storm:

1. Get better consolidation of H5 energy within the mid-level trough instead of seeing it escape out to sea. 
2. Maintain ridge amplification in the western U.S. to prevent the overall flow from becoming too progressive. 
3. Get a piece of northern stream energy to phase into the trough to help reamplify it and possibly turn neutral-negative in time.

Will it happen? It could, but at this time I am not confident. We'll see how things trend through the course of this week. I kind of like the April Fool's Day time frame a little better. As long as the -EPO/+PNA couplet maintains amplification beyond March 30th, I think that set-up could produce a Miller B for someone in the northeast region. 

COLD TEMPERATURES 

The intrusion of both those mid-level trough's (March 27th and April 1st) means colder than normal temperatures yet again for the area. 

The MJO is currently in phase 8 and heading into octant 1. 

Composite's of an MJO in phase 1 for early April show negative heights anomalies over the east coast. The evolution shown aloft by guidance to keep the area colder than normal from the end of March into the 1st week of April makes sense. 

Temp. departures will range anywhere from -5*F to as much as -10*F below normal for the NYC Metro area during the aforementioned time period. 

If neither the March 29th nor April 1st storms work out, I do feel it would be awfully difficult to see accumulating snowfall again this season given that the MJO would likely be headed into phase 2 by then. Long range guidance is already suggestion the western ridge to spread east by April 6th or so. We'll see what happens!

Enjoy the rest of your Sunday evening! 

-Francesco Paparatto

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Will Winter Go Out With A Bang?

Do not hold your breath if you are looking for 50 & 60-degree spring days. While the last week has been pleasant and has given us a taste of spring, it seems that was just an early April Fools joke from Mother Nature as winter looks to make a comeback later this week. 

Negative OLR anomalies, or wetter than normal conditions, are currently seen from the Dateline to Hawaii. These bursts of convection near the Dateline that propagate east is what is causing our MJO to enter enhanced phases. 

The green contours, again centered near the Dateline to Hawaii, show where precipitation is favorable to develop. In this case, we're seeing some strong cyclones in the Tropical Pacific along with some enhanced convection along the Equator. 

The current observations explained above is the reason why we are seeing the MJO amplify into phases 7, 8, and possibly 1. What does this mean for the rest of March into April? We should continue seeing persistent riding over the EPO and PNA regions. In turn, this should keep our area either at normal or below normal from a temperature standpoint. 

MJO phase 8 composite's for the month of March show a large Aleutian trough helping to promote a -EPO/+PNA. Also, there is a signal for a -NAO/-AO couplet. 

The GFS by the end of this week shows a split-flow over the west with the aforementioned signals in place. However, the core of the negative height anomalies look to remain to our north. The northern stream energies are disorganized which is keeping the trough stretched out and heights along the east coast flat. In this type of set-up, you will not see any east coast storms trying to come up the coast. 

Fast forward to the 22nd of March and this set-up is starting to look a little more organized. There is clear amplification in the trough but it needs more separation with the upper low south of Greenland. If the models can retrograde the western ridge a bit and help position the trough axis a bit west of where it's currently shown, that could go a long way in getting a coastal storm to pop off our coast.

At the surface, the 12z EURO is trying to show a storm in the 21st-22nd time period. With favorable looking teleconnections, namely the NAO and MJO, there is a high likelihood of a storm developing at that time. 

The 00z GFS is also trying to hint at something in this time frame. 

It's important to keep in mind that by late March the average temp. for Central Park is between 46-49 degrees F. So even temp. departures 10 degrees below normal will still keep the area above freezing. Whatever storm comes our way, we will need an impressive cold air source to accompany it and for the system itself to be as potent as possible to manufacture some of its own cold air and force dynamic cooling. Given that we are still in the 7-10 day time frame, I would not even look at the surface right now rather pay closer attention to how the upper levels trend. 

WHAT TO WATCH:

1. 21st-26th time frame for 1-2 storms. Both of these systems have the potential to bring wintry weather to the area, however, it will be extremely difficult to do given the time of year. A lot needs to go our way. 
• Can the -NAO help slow down the flow and keep the ridge axis positioned favorably in the west, while also helping to develop a coastal storm? 
• Will there be enough cold air for the storm to work with? We need to see better trough amplification on the models moving forward. 
• Will we see a wave eject out of the STJ? We need to give the northern branch something to work with out of the south or else whatever storm comes our way will remain weak (likely too warm). 
2. The general 18th-31st time period should see mainly normal to below normal temps. due to the blocking developing in the Atlantic & Pacific. Remember, below normal this time of year is probably temps. in the upper 30's to low 40's. I am not confident in anything colder than that during the day, just yet. 

CONFIDENCE:

Personally, I thought the upper air pattern looked better a few days ago than it does right now. The trough being advertised does not impress me and the lack of STJ interaction is a little concerning if you're looking for a winter weather event. Therefore, I am at low confidence for a winter storm in the 21st-26th time frame but high confidence for a coastal to develop. Those N&W of I-95 are in a much better spot to see wintry weather the end of this month. 

We'll see what happens...still quite some time to go. Will be monitoring the H5 pattern closely in the meantime. 

Have a great St. Patty's Day...if that's your thing. 

-Francesco Paparatto 

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Last Minute Critical Storm Trends - March 5th Snowstorm

A stretched out frontal system from the east coast all the way to Texas is set to move into our area around Midnight and bring moderate to heavy snow accumulations. Once the mid-level trough containing the H5 s/w energy tracks to the Great Lakes Thursday morning, it will help strengthen dynamics in the mid to upper atmosphere to produce impressive snow rates generated by frontogenesis. The upward motion in our atmosphere is what will help spread precipitation as far north as southern New England. 

Check out these latest developments:

6z GFS H5 vorticity map valid 1pm Thursday

18z GFS H5 vorticity map valid 1pm Thursday

The difference between these 2 images is quite remarkable considering the event will begin around Midnight. In the morning GFS run, H5 trough over the Ohio Valley is faster (progressive), shows strung out energy, which results in lower heights over the east coast. 

On the afternoon run of the GFS, the mid-level trough is slower, steeper, more consolidated which allows heights to rise along the east coast. This is huge because any waves of energy that develop along the draped front along the east coast will ride further north into NYC Metro and southern New England instead of tracking to the south. 

What happens as a result with the upper level jet streak?

6z GFS valid 4pm Thursday:

18z GFS valid 4pm Thursday:

Wow! The 6z GFS basically weakened the jet streak and had it placed over the area, while the 18z GFS is much more impressive with it and has it positioned much more favorably to our N&W so the best dynamics get into our area. 

Speaking of dynamics...

What happens as a result with the H7 frontogenic forcing?

6z GFS valid 7am Thursday:

18z GFS valid 7am Thursday:

There is now lift getting into EPA, NNJ, NYC, southern NY, and CT. 

What does all this mean? 

A new snow map will be released at 10pm to account for these last minute changes in the atmosphere. I noticed with the 12z runs there were subtle changes but I did not expect that to continue into the evening runs. The GFS also has support from the reliable RGEM, as well as, the SREFS, CMC & EURO models. Areas in NEPA, NNJ, southern NY into CT can expect higher snow amounts as a result. 

Stay tuned on the forums for the latest!! 

-Francesco Paparatto

P.S. latest HRRR has rain changing to snow from west to east between Midnight and 2am. By 7am, heavy snow is falling over the area.

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Wild Weather Week Could End With Big Snowstorm

One storm out - another two to go. 

A potent ice and snow storm effected the northeast today. Parts of Long Island are going to end up between the 5-8" range while most of the area will receive 3-6". Central and coastal NJ are seeing quite a bit of ice - over 1/4" reported in some spots - which is making driving conditions treacherous. Power outages are popping up across NJ with numerous accidents also confirmed. Please take it slow on the roads tomorrow morning. One of the reasons why my final call snow map included a "jackpot" area of 4-7" of snow across NNJ - NYC - north shore of LI - southern CT for this storm was because of the qpf outputs the high-res short range models were showing. Further investigating showed that frontogenesis was pretty strong over areas north of the baroclinic zone which happened to set up across central NJ. There was also an H5 ULL swinging across the region which helped enhance precipitation. While some areas did not do so great in PA, this was still a great storm and a fun one to track. 

Tuesday Ice to Rain Storm

Today's system is going to deepen over Nova Scotia into a cyclone. Once it phases with the mid-level trough in eastern Canada, that will help usher in very cold temps. into our area Monday night. Low's are expected to get down into the teens. Another mid-level trough is going to drop into the upper Midwest by Tuesday night. Ahead of it, there will be a surface low pressure system that cuts into the Great Lakes. Due to the arctic air mass left behind from today's system, precipitation Tuesday afternoon may start as snow before quickly changing to ice then plain rain. Low-level cold has been poorly advertised on the models this year so I do feel a widespread region from PA to NJ/NY will see an extensive period of sleet & freezing rain. 

The GFS at 7pm Tuesday is showing a sub 1000mb low cutting into the G/L with a warm front approaching the area. Before the front gets here and brings us temps in the 40's with rain, the initial batch of precip. will fall as snow or ice. 

The RGEM is also showing wintry precipitation overspreading the region Tuesday afternoon before the changeover to rain. I think a solid .10-.25" of ice is possible for most of PA into NY-NJ (including NYC). Coastal NJ and LI I think should be ok and see mainly plain rain. Their surface temps. are expected to be warmer. I would not be surprised though if that changes on future guidance given the low-level cold. 

Wednesday Night Into Thursday Morning Godzilla? 

The system during this time frame has Godzilla potential - meaning it has a high ceiling to produce snow amounts greater than 12". This does not mean it will, however. This is a very tricky set-up and one that also has high bust potential. 

Once again, we will not be dealing with a well-defined surface low. Instead, this is likely to be an overrunning event caused by strong southwest winds coming out of the southeast and helping to bring up Gulf moisture. The Tuesday night storm is going to leave behind a cold front draped along the east coast. A mid-level trough is going to drop into the upper Midwest on Wednesday containing very potent upper air energy at its base. 

Ahead of the positively tilted trough is our stalled cold front along with some mild air over the east coast. The trough itself will not only help enhance precipitation along the coast due to the potency of the H5 vorts, but it will also bring with it an arctic air mass. Once these two features combine, that should result in a very weak surface low to develop with plenty of Gulf moisture to work with and possibly stream into our area. 

The 250mb level jet streak being advertised is also impressive and positioned favorably to bring about intense dynamics. What will be key is determining the timing of when the cold air reaches the coast. It's very possible that most of us start as rain Wednesday night then transition over to snow by Thursday morning. This is most likely from NYC and points south. It is worth noting the EPS and GEFS have been very bullish with this overrunning event. Some members are showing well over 12" of snow in some spots. 

Given the factors outlined above, I am beginning to feel strongly that someone will see a significant snowfall out of this. Whether it's the coastal Mid-Atlantic or the Northeast remains to be seen. Latest guidance is starting to indicate overrunning getting as far west as State College, PA and spreading east into our area with temps crashing into the teens. If this is the case, we'll see a significant snow event. 

What to watch for:

1. Timing with the mid-level trough for when it reaches the east coast (hopefully not too late!)

2. Timing of the cold air (also hopefully not too late!)

3. Positioning of the H25 jet streak 

4. Intensity of the PVA embedded within the trough 

I believe those 4 factors are essential to how this system plays out. 

We'll see what happens! 

-Francesco Paparatto 

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