Severe Weather Potential For the 29th of Feb

That is correct you are reading the title correctly. The biggest area of concern is going to be from Ohio into the SE with another smaller area shaded in gray equivalent to a 5% risk. This is based on the most recent run of the SREF and short range guidance.

An occluded area of low pressure will be heading across the great lakes and this will be lifting a warm front towards the region sending warm southerly flow ahead in the mid levels and also at the surface across areas like Western PA . In SW PA for example temperatures will be between 50 –60 but then you head east and you are in the 30s..

It will be this cold front that will be heading towards the region that will be responsible for the severe weather. The trigger so to speak..

Because of cloud cover and ongoing precipitation ..this will likely hinder the severe weather to some extent. With limited CAPE ..the greatest severe threat appears to be Strong Winds….

Final Update for Feb 29-March 1st Storm System

This is the final map before the system arrives other then the Severe Weather Potential map that will be issued this evening.
The models at 12 Z today came in warmer ..The ECM also has a toasty BL. To toasty for the big cities such as NYC and KPHL.
Essentially what we are dealing with is a teleconnection driven event where there is a vertically stacked low moving to the Great Lakes with a warm front lifting N and a cold front moving to the east.
A secondary low develops along the frontal system.
Strong WAA and southerly flow out in advance of this frontal system..
Strong temperature gradient as parts of SW PA will be 50-60 while further east temperatures will be 30-40 range...
This temperature gradient could cause severe weather across western Pa with the advancing cold front..
Big cities such as KPHL and KNYC are looking at a mainly rain event
NW NJ would be in the 1-3 zone along with ice..
Greatest Snow accumulations will be North of PA in Central NY and into Northern New England..
The snow and ice accumulations in PA will be mainly the highest elevations..

Feb 29-March 1st Updated Scenario Map…First Call

The above is the updated scenario map. 

Low pressure is going to be moving out of the Rockies region and move ENE towards the Great lakes region.

This is going to allow warm air advection to spread across the area. A warm front will be lifting towards the area and from the low pressure area a cold front will then also be crossing the region.

It’s the warm southerly flow at the mid levels and the surface in the SW part of PA with the advancing cold front that will bring the the chance of some thunderstorms into the region ..some of which could be severe.

There will be a cold sector to this storm in the beginning as the warm air advection moves into the region. This is thanks to a high pressure in SE Canada providing an area of confluence. However..the warm air advection will end up winning out and the greatest snow accumulations will be NY state and North and east and even some of that region will also be seeing potential for ICE.

For the ABE region we are expecting precipitation to begin as snow and sleet but will transition over to rain relatively quickly. Further to the north the WAA will have a slower time transitioning the moisture to rain so we can see 2-4 inches into NE PA along with some ICE in the range of .10 with some isolated amounts that could reach .25

The big cities such as NYC and KPHL we are anticipating a mainly rain scenario for this system.

The teleconnections never supported a further south and east solution and this is something that we never bought into despite the better model guidance of the ECM suggesting so.

One thing we have learned is that teleconnections drive the weather pattern & determine ending results.

Stay tuned for further updates.

Update On Feb 29-Mar 1st 2012 Storm.

We are going to hold off on any discussion to go along with this map. For technical discussion see the previous blog in reference to the teleconnections and what they support.

Earlier in the afternoon on Sunday the NWS had issues a Hazardous Weather Outlook and was pretty bullish on a plowable snowfall along with some ice.

This was from that HWO

SNOW...SLEET AND FREEZING RAIN ARE EXPECTED WEDNESDAY INTO THURSDAY.
SIGNIFICANT SNOW/SLEET ACCUMULATIONS ARE LIKELY WITH A CHANCE THAT
SOME OF THE SNOW AND SLEET WILL FALL HEAVILY FOR A TIME WEDNESDAY.
THIS LOOKS TO HAVE POTENTIAL TO BE A PLOWABLE EVENT.

We had mentioned on our Facebook that we were not biting on to this nor in agreement with this. The teleconnections support a further north and warmer scenario then a further south and colder scenario..We felt that they jumped the gun and were to bullish..

We still feel that way..All the guidance tonight from the GFS to the UKMET to the GGEM to the ECM have come in much warmer aloft and at the surface as well…

We are issuing this scenario map. Keep in mind that even the area where we have as the best chance for snow and sleet accumulating may also change to rain…

The big cities such as KNYC look to be primarily rain. KPHL primarily rain.

NW NJ would be in the snow/sleet light blue category…

The problem has always been when you have a vertically stacked low going into the the Midwest towards the lakes region this never bodes well for the Northern Mid Atlantic region. You have southerly flow ahead with the Warm Air Advection Over running and any secondary that develops would develop either to late or too far north for the region.

The other issue is that there just is not any really cold air around with the NAO & AO + and a PNA on the decline.

What could go wrong?

When you are dealing with over running events …sometime to majority of the time the precipitation moves in faster then modeled. We actually took this in consideration when making this scenario map because the thermal profiles upper levels and lower levels are not as supportive of what we have pasted as a scenario. This scenario is subject to change and ..potentially not for the better for snow lovers in the Northern Mid Atlantic…

Mid Week Storm System What Is In Store?

This is the question that is burning up the internet right now as to what is going to happen with the mid week storm system. Will this be a snowstorm or will this be a cold rain storm or will this be a snow changing to rain storm. Well..we are going to attempt to answer this question with many maps from the guidance tonight from the GFS to the GGEM to the UKMET to the ECM and even the Nogaps..We are even going to look at the teleconections and see what these suggest as well.

So we will take a look at the teleonnections first..

Now the first thing we notice is that the Arctic Oscillation is positive.  Now many people may not understand what a positive or a negative AO means so here is the definition explained..

“In the negative phase, the polar low pressure system (also known as the polar vortex) over the Arctic is weaker, which results in weaker upper level winds (the westerlies). The result of the weaker westerlies is that cold, Arctic air is able to push farther south into the U.S., while the storm track also remains farther south. The opposite is true when the AO is positive: the polar circulation is stronger which forces cold air and storms to remain farther north. “

So according to the definition above a positive AO indicates a further north storm track and cold air is also locked further to the north and not able to dive as far south..

Now this is the North Atlantic Oscillation and what you can see by the above is that the NAO is positive. What exactly does this mean?

“

During a positive NAO there is a strengthening of the Icelandic low and Azores high. This strengthening results in an increased pressure gradient over the North Atlantic, which cause the westerlies to increase in strength. The increased westerlies allow cold air to drain off the North American continent rather than letting it build up and move south.

• Above average geopotential heights  are observed over the eastern U.S., which correlates to above average temperatures

• The eastern U.S. often sees a wetter pattern with stronger storms during the winter season in this phase due to increased upper level winds”

Well..what we see here is that there is no mechanism to keep colder air in place and that it leads to above average heights which correlate to above average temperatures. We also see that it also leads to stronger storms during the winter season.

So pretty much so far we are seeing two teleconnections that are against a snowstorm.

The PNA you can see is on the declining slide into negative territory. What does this mean?

“The negative phase of the PNA pattern features below average geopotential heights over the western U.S., and above average geopotential heights across the eastern U.S. This results in deep troughing over the western U.S., which allows cold air from western Canada to drain southward into this region. In the eastern U.S., warm, moist air from the Gulf of Mexico and the Atlantic Ocean is able to travel northward, often resulting in above normal temperatures “

This generally means that the colder air will be situated across the west and warmer then average temperatures will be across the east. In other words the exact opposite of a + PNA which would put the trough in the east and ridging into the west. Ridging into the west would result in stronger amplification of the pattern.

So we have a + NAO & a + AO along with a PNA going into the negative state. All this points to milder conditions in the east…a  lack of a mechanism to lock in any colder air (blocking) and the pattern to be progressive but with the coldest air into the west or Pacific Northwest region.

So the teleconnections themselves suggest a further north storm track with lack of cold air having the staying power…

So lets look at the guidance and see what it is suggesting and we are going to look at 90-120 hours on the guidance.

First up the GFS..

Now, what we see here is a primary that is heading towards the Great Lakes. This never bodes well for east coast snowstorms..Why? When you have a low cutting to the west and becoming vertically stacked such as is you have a warm southerly flow going out ahead of the main system. And we see this happening on the GFS with the only area at 90 hrs. cold enough for winter precipitation would be NE PA into Northern New Jersey and of course north of that area. (Remember + AO and + NAO where it provides the colder air and the storm track?)

However what happens is by 96 hrs. that 850 line goes north and we have a change over to rain in those locations.

By 108 hrs. we have a secondary develop from the primary but it develops to far north( + AO + NAO)  to have any major effect on PA.. So we have a wintry precipitation change to rain and end up with mainly a rain event in the PA/NJ area…

Now this is the link to the GGEM precipitation images and it covers thru 120 hours. (click here)

What we notice here is that it is along the same line of thinking with beginning as snow/ice across the same regions but then changes to rain and then rain along the coast in places like NYC..

We see one difference here in that the GGEM does not really develop a secondary but more or less moves a weak batch of moisture thru and this weak batch of moisture is mainly rain along the coast in places like NYC that could end as some flurries or sleet… Of course further north of those regions we are talking a more winter type event. Again remember the effects of the teleconnections in place.

UKMET we see is along the same lines as the GFS for the most part with the primary to the west at 96 hrs. with ridging into the east and it develops the secondary and is pretty far north at 120 hours out.

Even the progressive biased NOGAPS is in agreement with the above first part of the system and for the second half it ends up more or less closer to the GGEM with just w weaker batch of moisture moving across the region..

Finally this brings us to the ECM..

Well… from looking at this image we see the ECM as well brings warmer southerly flow into the region and it also begins off as snow in generally the same areas prior to this time frame but with the 850s this warm at 96 hrs. it would indicate a change over in the PA NJ regions..but now we see where the ECM becomes different at 120 hours..

Now the ECM is further south with the secondary then the rest of the guidance. Many people look at this model as the most accurate model ..however..the model is alone in being this far south and furthermore ..this southern solution for the secondary ..does not fit with the telconnections that are in place. Furthermore interestingly enough is when you turn to the ensemble means..

We are looking at a further NE position of that low and more progressive which is more fitting of the pattern.

So in summary..with the teleconnections in place and the southerly flow out ahead of the system and the lack of any locking mechanism for the colder air to stay in place..the best case scenario for winter weather lovers is a snow or snow/ice mix changing over to rain and the most prone areas for this to occur would be Northeast PA into Northern New Jersey..Of course north of that region has the best potential for a winter storm.

This is based on the guidance above along with the teleconnections & pattern that is in place. Speaking of pattern..this is what CPC put out earlier in the day yesterday..

This storm is probably winter last hurrah comparable to Custards last stand.

Later tonight we will put out a scenario map ! Stay tuned!

The Week Ahead in Weather!

The week ahead in weather …the detailed forecast will be in specific to ABE…

As you can see by the map above this is for the first 21 days of the month of February..

The 22nd day at ABE will also fall above normal with a high 1 degree shy of 60 at 59 degrees which ended with a +13 over all departure on the day..

This warm weather is going to continue over the next few days…and then it will take a turn to more seasonal levels before once again warming back up.

Generally a weak frontal system is moving thru the region currently but a low will travel from the Midwest into New England and this will drag a strong cold front thru the area on Friday in the afternoon hours. This low pressure and front will bring rain to the area of ABE..and most of PA as there is to much southerly flow ahead of this low..

So the forecast looks generally like this:

Today: Showers possible early then clouds with times of sunshine ..warm day once again with highs near 60

Tonight: Rain will be developing and this rain will last into Friday morning and winds will become gusty with gusts to about 30 MPH… Temperatures on Friday will be once again around 60 degrees.

Saturday : Partly to Mostly cloudy with possible rain showers  Temperature 40-45

Sunday thru Tuesday …Fair weather with temperatures ranging 40-45 Sunday and then moderating to 45-50 Monday and Tuesday…

Midweek depends on the next system involved coming from the SW…Right now we are leaning more towards a warmer scenario then a colder scenario but plenty of time to watch that system..

2012 Preliminary Hurricane Outlook

The above is the outlook for the 2012 Tropical Season for the Atlantic and the Eastern Seaboard.

The following is the AMO which is in its positive phase: (Atlantic Multidecadal Oscillation)

Since the mid 1990's we have been in a warm phase of the AMO. Warm Phase of the AMO has been found to increase Atlantic Hurricanes along with there intensity due to the ocean temperatures being warmer then normal. It acts as a fuel aiding development of the Tropical Cyclones.

Latest ENSO models seem to indicate that we will be dealing with a neutral to a weak El Niño for the 2012 Tropical Season..

As you can see using the years of history from 1950-2001 ..in El Nino years (top image) there are indeed some land falling tropical systems. However, most would suggest recurve out over the Atlantic ocean. The bottom image (tracks in blue) is for a La Nina year and we do not think  that this will be the case for this season.

Now when we look at the tracks for Neutral years things do indeed become a quite bit more interesting along the east coast.

So, even though we think that things will be less active compared to last year ..the tracks of the systems could be quite interesting compared to last season.

Pattern Update–Persistence Continues to be the KEY!

The above is the first 19 days of Feb ..just shy of being 3 weeks into the month. As you can see…the look of this map and the departures looks no different from November, December or January…

The moral of the story is that every single time a pattern change was signaled to occur by long range guidance it simply has not occurred..

Snowfall is well below normal ..in locations such as ABE without counting October towards the winter snowfall we are approximately 18 inches below normal.

Our original winter forecast we have already admitted that it was going to bust and bust horribly but we were in good company as the majority of winter forecasts busted just as badly.

When we did revise the winter forecast at the end of December and released on January 1st we did indeed nail it from that point on with the warmer then normal and less snowfall then normal. The original however…failed and failed bad but we will still do a actual verification at the end of March…

So where are we going from here? There are some main weather media outlets that are still talking about cold and snow and the pattern changing in March etc..Is this true? Or are these folks just holding out hope because there has been a lack of snow and a lack of cold and they just want this to occur? Or is there a chance that March will come out cold and snowier?

Well…if one has been following the GFS it was suggesting that things could indeed get snowier and colder. However…caution must be advised because we have seen the GFS do this ALL winter long and it has failed to materialize.

So lets look at the teleconnections to see where we are heading..

From the images above we see three things:

1. A positive Arctic oscillation

2. A negative Pacific North American Oscillation (PNA)

3. A positive North Atlantic Oscillation (NAO)

If you are a cold and a snow lover these signals are the complete opposite of what you want to see for cold and snow in the east.

These signals indicate at the very least a continuation of the pattern that we have had all winter along which is times of cooler then normal to seasonal weather in an over all above normal temperature regime.

When we look at the guidance we see that the ECM fits the teleconnections the best by showing an over all warmer pattern with the shots of cooler weather.

And then more into the longer range..

In the first set of images we would not be shocked to see temperatures near or into the 60s…and in the second set of images we would not be shocked to see temperatures in or around the 70 degree mark if the day 9 scenario were to verify as depicted..

Of course some may cling on to the GFS and what it shows as of 12 Z ..

However…if one were to look at the teleconnections above what we see indicated would be closer to the ECM in reality then the GFS. When looking at the GFS one has to remember in the long range it has a KNOWN cold bias.

The moral of the story is essentially spring has sprung but there will still be shots of cooler weather. For those in PA ..snow chances are dwindling down and we here think that the chances of seeing any significant east coast snowstorm in PA the rest of this winter is at around 10%.

There is a high likely hood that the rest of the winter season will continue to produce warmer then normal temperatures overall & continue with the below normal snowfall.

Latest Thoughts on the System for the 19-20th ..Feb 2012

Starting yesterday at 12 Z basically all the guidance started to trend south with the system around the 19-20th. The 18 Z GFS continued with the south trend and the 00z guidance also continued the south trend with one exception to the guidance being the 00z NAM.

However…as we look at all the models at hour 72 you will notice that they are all in fairly good agreement with the position of this system. The difference with the NAM and to a lesser extent the GFS is the north extent of the QPF shield which gets into southern PA..

Lets look at the guidance…

Now in the above images we have all the guidance from the 00z GFS/GGEM/UKMET/ECM/NOGAPS. You can see that they generally agree on the low position at 72 hrs. with probably the ECM being the most south of the solutions.

Now this image above is the 00z ECM ensemble means and it basically supports the operational run . It can be argued that the system on the means is just a touch NE of the op at the same time ..However..for this system to effect PA and Northeast ..you do not want the means to show a touch NE but more N then anything.

We are going to attempt to show WHY this is not going to make it any further to the north then what we are seeing on the guidance and we are going to use the ECM @ 48 hrs. to show this…

First thing we notice is the 50/50 low and this is part of the problem in that the 50/50 low is to strong which causes a NW flow behind the Northern stream system (that all the guidance trended faster with) which causes the NW flow or confluence to NOT allow the heights to rise on the east coast. Which leaves us with..

Black lines indicate the flow which is ENE…

Another problem is lack of a + PNA ridge that goes across the west into Canada as the white line represents. If this would have occurred we would be looking at a sizeable storm coming up the coast. However ..we do not have this happening…

Third the lack of blocking. Even if we had a full phase between the northern stream and the southern stream..with a positive NAO in place there really would be nothing to stop this from cutting west.

So instead of having the heights rise along the east coast…we are left with lower heights due to the NW flow or confluence from the 50/50 low and this system has no choice but to follow the steering flow ENE and off the coast around Hatteras and bring the Mid Atlantic region a decent snowfall…

As of 6 Z the NAM ..while still bringing some light QPF north of the PA/MD border has really backed off and gone more south and east as well coming into harmony with the rest of the 00z models.

One thing is certain as you can see by the radar image above that this system is not going to have a lack of moisture. And I would not be surprised if we see a very expansive moisture shield with this system..

So with over whelming guidance support to suggest this system has little fanfare to the north of the PA/MD border …taking a blend of the guidance with less emphasis on the ECM but more emphasis instead on the ECM means this would be the most likely area that has the potential to see a heavy wet snowfall…

At this time we think that around 4-8 inches of snow could fall across the area that is in blue..

We will continue to monitor this system for any changes but with the NAM as of 6 Z now coming in more suppressed we pretty much feel that the models are coming into agreement on the ultimate track and resulting location of the storm…

Potential Exists For A Moderate To Perhaps Major Snowstorm Feb 19-20th- But Where?

We feel the above title is most fitting that for the end of the weekend that a moderate to perhaps Major Snowstorm could occur but the question that needs to be answered is what region is going to benefit from this system. Will it be the Mid Atlantic and Northern Mid Atlantic or will it be the Northern Mid Atlantic and the Northeast…or will this simply go off the coast of Hatteras and out to sea. All these have been shown on model solutions over the past few days.

The exact track of this system is still up in there air on the latest guidance and we are going to take a look at that in operational model form as well as ensemble model form..However before we do that lets take a look at the teleconnections that are in place..

For starters lets look at the MJO or the Madden Julian Oscillation.

The above images tell us that we are in phase 1 of the MJO and the bottom image is the 500 mb temp anomalies and you can see that across the east it represents more in the way of seasonal weather.

The above is the Arctic Oscillation and normally you want to see this teleconnection with showing in a negative direction . However, what this shows is a positive AO …but around the time of the storm this dips to neutral. What this means is that there should be seasonably cold air around at the time of the storm. However..nothing that would be considered arctic cold and that should not be too surprising considering how mild this winter has been.

The PNA or Pacific North American Oscillation looks to be positive and looks to stay positive thru the duration of the time frame in discussion. So this is a favorable teleconnection for trying to get a storm up the eastern seaboard..

Generally what a + PNA will do is set up ridging into the west coast , sometimes into western Canada and then form a trough along the east. So what this teleconnection suggests is that we will have a trough along the east in this time frame.

Now, here is the North Atlantic Oscillation or the NAO and interestingly enough this teleconnection more or less supports a system that would be further north and west.

Generally when storms end up being suppressed it is due to two main reasons teleconnection wise:

A. The NAO is strongly negative which creates very strong confluence over the east/ northeast

B, In tandem with this the AO is strongly negative which tends to help shear or dampen and crush the systems to the south of the Mid Atlantic Northeast region.

Notice we do not have either of those occurring at the present time with the upcoming system.

So in summary of the teleconnections we have the following:

A. MJO Phase 1 favorable

B. PNA positive which is favorable

C. AO which is positive dropping to neutral which is not the greatest but not the worse it just means that this will be a stale air mass over the region instead of fresh arctic supply..

D. The NAO . The NAO being positive argues for more of a NW track closer to the coast…not necessarily to the benchmark but indeed a further NW track .

So now lets look at the guidance and the ensemble guidance and see what solutions if any hold up to what the teleconnections suggest..

This is the 00z GGEM. While this has made a shift to the NW over all…this model is mainly a brush to the northern Mid Atlantic area..with the main storm occurring south of the Mason Dixon line. However..you will notice that this model also is about 12 hrs. slower then the rest of guidance so we will consider this a unlikely solution due to timing issue compared to other guidance.

The above is the 00z UKMET and this is similar in its depiction at least where it ends up at 96 hrs. as the GGEM but it is 12 hrs. faster then the GGEM. This also lines up fairly well with the ensemble means of both the GFS and ECM as you will see.

This is the GFS..this is the operational run and as you can see thus far it is pretty much the furthest NW of any model and the reason why is because it phases in the northern het stream disturbance with the southern stream SW over the southeast. This run is also colder then previous runs because it is not as AMPED up compared to other solutions..

00z ECM is very similar to the GFS in low position ( a little south) however the 00z ECM has taken a major trend with the northern stream disturbance towards the GFS which can be seen in the first 24-30 hrs. of the 00z ECM.

Verbatim about .37 gets to KPHL and only .07 at ABE and NYC..However this is greater QPF then the 12 Z run. Also important to keep in mind is the 12 Z means were more amped and north of the op yesterday afternoon.

So now we are going to look at the three models GGEM/GFS /ECM in the form of the ensembles at 96 hrs..

Now the last image is the GGEM means and you will notice that the means are Southeast..however you will also notice that they are about 12 hrs. faster then the OP GGEM. We are considering these means of the GGEM as lower probability because the model is clearly struggling with timing issues as evident in the difference between the OP and means.

Now the top image is the GFS and the middle is the ECM ensemble means and you can see that they are in fairly well agreement. The main difference is that the ECM is more AMPED then the GFS ..Which is kind of interesting considering the ECM means is a smoothed version of 51 members versus the GFS 12 members. The means of the ECM are also slightly more North as well compared to 12 Z ECM means.

In Summary the teleconnections would support more of a NW track up along the coast with the NAO positive and the PNA positive ..

We do not think the teleonnections are supportive of a system that would be south and east and miss the region..but the ultimate outcome will depend on Phase or no phase of the two streams..If there is no phase then it is very possible that this ends up being a Mid Atlantic storm with nothing but clouds north of the Mason Dixon line.. as it would slide ENE from the Hatteras Area..

If we have a full phase then we could be looking at more of an inland solution because of the positive NAO. With no blocking in place (other then temp block from the 50/50 low) this would then become a primarily rain maker for the big cities along the coast with heavier snows inland..

So there are a lot of questions to be answered yet ..but right now we are leaning towards the following scenario based on the ensemble means and teleconnections..

This much we will say…if this storm does come up the coast in a more northerly fashion that the surface temperatures will be in the low to mid 30s but the 850s supportive of snow. What this means is this would be a heavy wet low liquid to ratio snow and if this does come to fruition then it could become not only travel problems but also problems with trees and wires down due to the snow being heavy and wet..

So the potential is on the table but the exact track is in the air yet and whether we phase or partial or no phase at all.

Stay tuned we will continue to monitor and follow this potential winter weather event!