11/30 Mo Mo: Winter Update

Today's Mo Mo blog is going to give you an update on how the long range pattern is looking heading into Meteorological Winter. 

Buongiorno,

I hope everyone had a nice Thanksgiving break. Hard to believe Christmas is a short few weeks away. It sure did not feel like Christmas these last few days or even weeks. Temperatures have been averaging well above normal. This looks to continue into the first couple of weeks of December which is not surprising under a pattern driven by a strong El Nino. 

SHORT RANGE - Week of November 29th

I do not want to spend too much time speaking about short term weather. Expect gloomy and rainy conditions Tuesday and Wednesday this week. A low pressure system will cut off to our west sending mild Gulf air and moisture northward into our area. 

Anywhere from half an inch to one inch of rainfall is likely. The weather will clear by Thursday and temperatures will also take a dip into the mid to upper 40's. Temps will hover around 50, plus or minus a few degrees, into the weekend with clear conditions expected. 

MEDIUM RANGE - Week of December 6th

Another storm system is expected to impact the area exactly 1 week from this week's storm, approximately Tuesday December 8th into Wednesday December 9th. 

12z EURO 500mb vorticity / heights valid Monday December 7th:

As of this moment, the EURO and GFS models are in fair agreement of a storm cutting off well to our west again. What is different with this system compared to the one we'll get rain from this week is the low pressure system does not track into Chicago and the Great Lakes. Instead, it tracks into the Northeast. It's likely to cut North and West of I-95 which will send warm air advection into the coast. Normally a storm track this time of year NW of I-95 could bring wintry weather to the interior Northeast, but with the Polar Jet forecasted to be in central Canada (2nd image) there is no cold air to be found. Additionally, we're probably looking at increased rainfall amounts with this system in excess of 1 inch. However, storms have trended weaker / drier this year so we'll see how we look by next week's Mo Mo blog. For now, expect more rain and mild temps early next week too. 

LONG RANGE - Winter Pattern Update

With Meteorological Winter beginning Tuesday (Met Winter is Dec 1st to Mar 1st),  I figured it would be a good time to check up on the pattern. Please give my Winter Outlook a read if you have not already so you have an idea of how I expect the winter pattern to progress through each month. 

SSTA's in the Pacific still shows a raging El Nino over the Equatorial Pacific and a +PDO, defined by the above normal SSTA's in the Northeast Pacific Ocean. 

ENSO tracker of each Nino region from StormVista over the last month suggests El Nino has strengthened through November. As of last week, the ONI value for Nino region 3.4 was 3.1*C. To put that in perspective, not even the Super Nino of 1997-1998 saw an ONI value get that high. Averaged over the entire winter 1997-1998 is lijely still to come out on top. The reason why there's a bit more optimism surrounding this winter if you're a winter weather fan is because most forecasters, including myself, believe this El Nino event will peak / weaken sooner than the 97' event. As Nino weakens, so does the Sub-Tropical Jet stream thus allowing the Polar Jet Stream to have more influence on the overall pattern (i.e. driving cold air into the central & eastern CONUS). 

The image on the left is a 500mb height anomaly composite of +PDO and strong El Nino years for the month of December (thanks to Isotherm for pulling image off the ESRL site). In case you can not read the years, they are: 1957, 1965, 1982, and 1997. On the right is the forecasted 500mb height anomalies in the 8-10 day range from the EURO and GFS models. The yellow circles are intended to easily show the similarities between those strong El Nino December's and our upcoming December pattern. What's most common between these three images is all agree on the placement of the Alaskan Vortex, which keeps the EPO positive and helps spread mild Pacific air into the country. Therefore, it's not a surprise my Winter Outlook along with many others called for a warm start to the Meteorological Winter. The million dollar questions are:

1. When does El Nino peak? 

2. When does the Alaskan Vortex retrograde to the Aleutians and promote ridging into the NE PAC and western U.S.? 

3. When will the AO and NAO go negative, if at all? 

Let's start with #1. One way I like to tell if the current El Nino is close to peaking is by evaluating the state of the trade winds and monitoring the trends of ONI (Oceanic Nino Index) in each Nino region (there are 4 of them) over the last month or so. 

The CFS forecast (solid black line is present time) is predicting a series of Kelvin Waves (purple) and Rosby Waves (green) to intersect over the International Dateline (180). I circled where that is expected to happen for a visual understanding. 

If we overlay OLR (Outgoing Longwave Radiation) onto the same map, we notice negative anomalies showing up between 180 and west of 120W which points to convection, or enhanced thunderstorm activity, to continue over that area. This promotes tropical forcing which could eventually lead to transient ridging over the western U.S. within the next 2 weeks. 

Taking the equatorial waves into consideration as well as the OLR forecast from the CFS when looking at 850mb zonal wind anomalies, it's no surprise strong WWB (westerly wind bursts) are expected over the International Dateline and just west of 120W. This is an indication winds will shift from blowing east to west (normal state of winds over the Equatorial Pac) to west to east and that will help transfer warm water to the central ENSO regions. Additionally, the blue shadings east of 120W suggest easterly winds to persist over the east-central and eastern-most ENSO regions. This is a pretty good indication temperatures will / already have stopped warming over Nino regions 1+2 as there is no mechanism for the warming to continue.

While the easterlies are a promising sign Nino regions 1+2 and possibly 3 have stopped warming, it remains to be seen if that's the case for Nino region 3.4. These charts suggest there is still room for additional warming but notice the amplitudes of these WWB's are not nearly as strong as they were in October and early November. The latest ONI values have not been released yet. Once they are, I will be sure to provide everyone an update on the forum. They will give us a good indication if we've finally reached a peak. I do believe there's still room for the central / western Nino regions to warm given the state of the MJO and trade winds, but a peak should come by early to mid-December which puts us in a pretty good place for the 2nd half of winter. 

Other then studying ENSO and Pac/Atl SSTA's, we can also analyze the Stratosphere, the layer of our atmosphere just above the Troposphere. One specific activity we look for is known as Sudden Stratospheric Warming Event (SSWE), which is when temperatures in the Stratosphere warm to rapid levels in a short period of time. The end result, no matter how we got there, is either a displacement or split of the Stratospheric Polar Vortex. As a result, this weakens the Tropospheric PV and allows it to move out of the Arctic into the southern latitudes of Canada. This typically, but not always, takes the AO from a positive phase to a negative one and allows cold air to filter from the Arctic into central / eastern Canada and eventually the U.S. 

Talking about the Stratosphere is an area of Meteorology I am still getting to understand. I know the basics of how certain wind patterns in the Polar Stratosphere, typically measured by the QBO, can impact our weather in the Troposphere (layer of atmosphere where we live). That said, much of the discussion that will take place is broad-based and high level.

A current look of temperatures at 10hPa in our Stratosphere shows it to be very cold. Between 10hPa and 30hPa is typically known as the "middle Stratosphere" and is exactly where we want to see warming take place. Notice how expansive the colder than normal temperatures are which is an indication this years' Polar Vortex in the Stratosphere is very strong. 

Here's another graph showing temps at the 50hPa level. Notice how much colder 2015-2016 is compared to last season (solid blue line) and the mean (solid black line). By now you understand the Stratosphere is COLD and we need to see it warm up if we want it to influence our PV in the Troposphere. On a side note, it's not surprising to some the Stratosphere is running colder than normal. The QBO, a measure of Stratospheric Winds, is currently in a positive state which means westerly winds. Historically, westerlies strengthen the Stratospheric Polar Vortex. The 30mb QBO value for the month of October was +13.38. Not anomalously positive but positive nonetheless. 

Heat Flux helps us understand wave forcing (wave 1 and wave 2) while Momentum Flux points to their meridional (north-south) state. The intensity and duration of wave 1 or wave 2 forcing often tells us if a SSWE is taking place. The best way to explain "wave 1" and "wave 2" is by counting the ridges and troughs in geopotential heights around the world within the latitudes that the Stratosphere is located in. Wave 1 forcing typically points to PV displacement while Wave 2 signifies PV split. 

This graphic shows Geopotential Heights and Temperatures at 30hPa level at 216 hours from the EURO. It's forecasting the Stratospheric PV to remain strong with little to no wave 1 forcing (or warming) taking place.  

A look at EPV, or Eliassen-Palm Vectors, represent vertical forcing that takes place through the Troposphere into the Stratosphere. The direction (look at the arrows) and magnitude (size of the arrow - how far north along the Y-Axis they extend) tells us if vertical forcing exists, and if so, how strong it is. The further north, or poleward, the arrows are pointing the better it is for Polar Vortex weakening. We had a minor event before Thanksgiving but given the EURO forecast we just saw it clearly had little to no impact on the PV. 

The conversation with the Stratosphere extends way more than what I just talked about. However, these are the basics and as of now they show a very cold / strong Stratospheric PV. Until this changes, our AO and NAO will remain positive and the strong El Nino will continue being the dominant force in our overall weather pattern. Something I should mention which is pretty important is the above normal Eurasian SAI (snow advanced index) should lead to increased energy interaction between the Troposphere and Stratosphere in the form of latent heat release. Once High Pressure takes over in Siberia and temps gradually warm, the melting process should send "heat" into the Stratosphere and possibly begin the process toward a SSWE. There's another dimension to this - which I am still learning about - that consists of Rosby waves and their interaction with land masses (mountain torque) that could also effect the rate in which our Stratosphere warms. 

It will be interesting to follow the Stratosphere in the weeks to come. Historically, strong El Nino events deliver SSWE's between end of December to mid-January. The earlier the better for our winter prospects. 

CONCLUSION 

1. Rain Tuesday and Wednesday this week with above normal temps early then falling back to average for a couple of days. 

2. More rain likely early next week with above normal temps expected to last. 

3. Possible shot of cold air mid-month thanks to the tropical forcing taking place over the Dateline. More to come of that in next week's Mo Mo. 

Fino la prossima volta (until next time), 

Francesco Paparatto 

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Mo Mo Update: November 23rd

Good Morning, 

For those who are not familiar with these Monday Morning (aka "Mo Mo") blogs, I decided to put one out every Monday morning to highlight the upcoming weeks weather and a bit of the long range. This week is especially important because it's one of the busiest travel weeks of the year. Thanksgiving! 

Short Range

The first few days of the week will feature dry weather but some pretty cold temperatures, especially in the morning. High's around the Tri-State area will be in the mid to upper 40's between today and Wednesday with low's in the 20's and low 30's. 

A low pressure system developed off the coast yesterday. The baroclinic zone remained well offshore keeping precip out to sea. As the storm moved north into extreme eastern Canada, a trough sneaked in behind to settle over the northeast. Notable by winds shifting to the northwest allowing to transfer cold air from Canada into our area. 

Here is a look at what the EURO is predicting for temps valid 7am Tuesday (left) and Wednesday (right) morning. Both images show temps in the upper 20's to low 30's, which is pretty cold for this time of year. 

Thanksgiving Day

500mb Height Anomalies from the 12z EPS show an elongated ridge over the eastern CONUS. This promotes the southwest flow to take over and bring mild temps into our area, possibly getting into the 60's around NYC Metro! The very fast northern jet boots out the High Pressure that was there earlier in the week to our north which would have helped combat winds from turning to the south. This gives the deep anomalous trough over the west more power to raise heights over the east coast. 

It is also looking like a dry week and Thanksgiving is expected over the eastern U.S. High Pressure is in control until we get to early Saturday morning. A weak cold front will come through bringing little to no rain while also taking temperatures back down to average.

December 1st Storm? 

The EURO and GFS suggest there will be an east coast storm to track on December 1st. The question on everyone's mind of course is will there be snow associated with it? Let's check out the upper air pattern.

The Sub-Tropical Jet is once again looking to rear its head. Of course, that is not surprising given the strong El Nino we have going on over the Tropical Pacific. The above is the 12z EPS showing the ridge axis over west-central Canada and a weak trough over the east. The deep trough over the Aleutians is impressive but centered a little too far east. This disallows the PNA from going positive while shunning the Canadian ridge east. Right away you'll notice there is not a cold air source to work with. A lot of the cold that is over our area at this time is moderated or antecedent from pieces of energy that break off the Aleutian trough and travel east. As long as the ridge axis is over central Canada and the AO is positive, it will be difficult to get an arctic express connection from Siberia into the eastern U.S.

The GFS cuts the storm to our west while trying to transfer energy to the coast. Boundary layer temps warm up in this scenario which would promote rain for most across the northeast. The EURO keeps the 500mb vort far enough south that by the time a phase occurs the surface low is right on or just off the east coast. In this scenario, wintry weather has a chance to impact areas all the way to the coast. As the storm deepens, it pulls cold air to the coast and changes rain to a heavy wet snow. Dynamic cooling plays a big role in this event since we're not working with an arctic air mass. 

At this time, I'm not a believer in the EURO scenario. I give more credence to the GFS trying to cut the primary low to our west. I also feel that if the storm did decide to take a EURO route, it has a good chance of going out to sea. The ridge axis is too far east for my liking and the flow over the east looks too fast for any storm to get organized. If the EURO maintains its position over the next couple of days then I will take it more seriously and look further into why it has a chance to be right. 

Long Range

The top image is of the 12z EPS valid December 7th and the bottom is 12z GEFS for same time frame. We are looking pretty far out so take both these representations of 500mb heights with a grain of salt, but this looks pretty close to what I was thinking for December when I created my Winter Outlook. Initially this may look warm with all the reds and oranges, but the heights over the eastern U.S. are fairly neutral on both pieces of guidance. The warmest temp departures are in central and eastern Canada with slightly above normal across northern New England and upper Midwest. The Northeast and Mid-Atlantic are near normal. Like I said earlier in the blog, any cold air masses getting into the northeast are likely moderated because of the large Canadian ridge. 

If we look at the latest run of the CFS American Seasonal model and what it had for December regarding 500mb heights anomalies, you cans see it's pretty close to what the GEFS and EPS are showing. Aleutian trough, Canadian ridge, +NAO, and biggest departures over central and eastern Canada. 

With guidance in fair agreement, I am expecting December to go as planned with temps finishing above normal for the area when all is said and done. There is no wintry weather on the horizon anytime soon, though the December 1st threat bares watching still. 

Next Monday, we'll look at the state of our Stratosphere, progression of El Nino, and an update to latest long range guidance. We'll also have a clear idea of what our sensible weather will be on December 1st. 

Enjoy your week. I wish everyone a Happy Thanksgiving. 

Take Care,

Frank

November 16th Mo Mo

Good Morning,

Welcome to the first "Mo Mo" blog of the season. The intention of these "Monday Morning" blogs is to briefly update you on near term weather and long term pattern changes. Sometimes I struggle to find time during the work week to put out detailed posts. These updates every Monday Morning should help.

The Week Ahead

The first few days of the week will be dry with temps around average. There is a powerful storm taking aim at the Midwest that will bring snow to the Denver area and severe weather to the Plains. The strong upper low will force positive heights over the eastern seaboard.

Despite the impressive height anomalies, temperatures around the Tri-State area will remain on the cooler side. There is a nice area of High Pressure to our north preventing winds from blowing out of the south-southwest. Instead, they'll be blowing from the north-northeast which will keep our temps comfortable.

Once the surface low pressure system cuts into Central Canada, a cold front will approach the area Thursday and bring us rain. Not a whole lot of rain is expected, possibly .25-.75." Start time looks to be mid morning into early Friday morning. 

Behind the cold front, cooler temperatures can be expected again. Looking to be in the upper 40's to low 50's with low's in the 30's (above freezing). The weekend also looks dry. 

Thanksgiving Week

Our first cold blast of the season will occur during this week. A potent upper level trough is expected to track over the eastern U.S. This is in response to the ridging forming over the Northeast Pac. and western U.S. Temps Sunday the 22nd through Wednesday the 25th will only be in the 30's and 40's. Low's will get down into the 20's, possibly teens for those N&W of NYC. There is upper level energy wrapped around the trough that may lead to scattered snow showers at the surface. The day to watch for our first snow flakes of the season will be Sunday into Monday. I'll keep everyone updated on the forum. 

You'll notice the 500mb height anomaly map below actually shows a bunch of ridges and troughs scattered across the Northern Hemisphere next week. You can see the trough I talked about over the Great Lakes / Northeast regions. It is pretty typical during strong El Nino events to see a progressive pattern early on. This means, not one particular trough or ridge is likely to "lock" into place over a specific area. The "line keeps moving" with these features until wavelengths finish undergoing seasonal change. In other words, the overall pattern continues being progressive. 

Thanksgiving Day forecast is tough to call right now. There is significant differences between the GFS (left) and EURO (right). The GFS keeps the trough over the east longer, while the EURO takes the next trough from the Pacific and barrels it into the west U.S. This forces the ridge to move over the east and likely bring some rain to our area. Since the Pacific Jet has been very strong and the pattern remains progressive, I am inclined to believe the GFS at this time. That said, my confidence is low and the Thanksgiving forecast will be much clearer by next week's Mo Mo blog. 

At a later day this week, I want to issue another blog to update everyone on the status of our El Nino and what it means for Winter. Have a great day! 

Have a nice day,

Frank Paparatto