11 replies to this topic

[TNE]

The first and main thing is to know the pattern and then to know the focal point. The focal point refers to the time period when two things are present. 1.Cut-off energy originating in the Southwest United States. 2. An extensive cold front (moving all the way down into FL) are present.

The 'extensive surface cold front/ temperature gradient' typically arrives shortly AFTER or DURING the Cut-Off passing in the East...It is associated with the Polar Energy.
.
During Example: October 29 2011 Historic East Coast Snowstorm. Most likely chance for a phase.
After Example (Most common scenario this winter): January 26 2012. No phasing in the East with the upstream energy...Cut-Off moves into the area first (with the leading trough acting as a cold front) and then the polar energy wraps around behind it.

1.The main idea is to have a phase like we did in October--the cut-off in the subtropical flow phasing with the polar energy aloft.

2.If the phase between the cut-off and the polar energy does NOT occur aloft, we are looking at a rainstorm and 50s or the storm passing to our south and east. Most of the energy phasing into the leading trough moving in as a cold front.

3.A partial phase (polar energy catching up to some subtropical energy aloft) will allow some snow to develop in selected areas to the south and to the east (e.g., South Jersey Event that occurred early on January 10, 2012).

1.Forecasted Threat in Similar Pattern (February 24-26 Potential Winter Storm):
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2.Previous Threat in Similar Pattern (January 26, Most Common Scenario This Winter):
1.Cut-Off phases with the leading trough, it comes in first and delivers the warm, subtropical air to most of the East.
2. Polar Energy (located Upstream--*see below*) moves into the East BEHIND the CUT-OFF.
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3.East Coast Historic Snowstorm This Winter Pattern (October 30, 2011)... Example of how a complete phase looks like aloft:
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4.Future Threat Revisited:
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About: Partially Phased Polar Energy and the cut-off itself remains detached from the Upstream Energy. The good news is that the two upper troughs present are aligned, which indicates POTENTIAL for complete phasing and a strong storm from that point on. Please remember that this is only one run...it can trend either way, really...

There is a lot to consider and we might be looking at 1. rain /50s, 2. nothing, or 3. some snow. This thread is for everybody to chime in and to have some fun.


TNE

[uncle W]

nice post...I thought we would have seen a similar storm to October 29th by now...We are running out of time and I would hate to see it come in April if it comes at all...

[phlwx]

the big storm could be an apps runner if the 12z's are right. pretty warm run in general from the guidance.

[Ellinwood]

Given what we've been seeing in the pattern and with the models trying to resolve the complicated UL energy interaction, I wouldn't be trying to forecast/guess at anything more than 72 hours out. There's decent model support at the moment for it, but I wouldn't be planting any ideas in anyone's head yet.

[Amped]

Nice analysis. SE ridge and dominant NRN stream looks to kill any chances S of Albany, NY. ECMWF has a 972mb low over MT Washington @144.

[Amped]

00z GFS says nice tornado outbreak. Any snow is in Mich and Canada.

[TNE]

Same Time, Different American Models.
 nam_namer_084_300_wnd_ht--DURING.gif   142.63K   3 downloads NAM
 GFS_AFTER.gif   130.28K   2 downloads GFS
I am at work so I will have to make this quick.

Title: DURING VS AFTER SOLUTIOUNS FOR THE BIG EVENT.

About:

One solution is to have the cut-off energy phasing with the leading trough, which is the warm solution [2]. Most of the surface development occurs on the warm side, ahead or along the cold front. The complete phasing occurs AFTERWARDS (in Canada ...) but in this case the full phase occurs over the Great Lakes and all of the subtropical energy moves up the front into Southeast US. The cold air comes in afterwards as it happened many times before. This is the leading solution this winter and is notable the soltuon on the 00z GFS and the 00z ECMWF.

The other solution is to have the cut-off phase with the upstream energy behind the cold front, which is the cold solution [1]. This will allow surface development to occur on the cold side as you can see in the images above. The potential for this solution is notable on the NAM (1 st Image) , please use my mark-up as guidance. This solution signifies complete phasing near the East Coast and would be similar to the October 29, 2011 event in this pattern.

TNE

[TNE]

This is what I mean at work.

EDIT for Scenario 1:
The complete phasing occurs AFTERWARDS OR NOWHERE AT ALL (in Canada) but in this case the full phase occurs over the Great Lakes and all of the subtropical energy moves up the front in Central US/ Eastern US. The cold air comes in afterwards as it happened many times before. This is the leading solution this winter and is notable the soltuon on the 00z GFS and the 00z ECMWF.


The thing I want to point out is that the full phase occurs OVER THE LAKES AND NOT IN CANADA OR NOWHERE. We had phasing occuring in the East last winter but no so much (OR EVER) this winter. The storm on GFS might be the strongest one we had all winter (despite it being warm). A Great Lakes Low might signify severe weather as a lot of warm air moves ahead of the front. Most of the energy is along the front for areas up north . However, the heaviest convection is located in the south (associated with the cut-off Low in the subtropical stream ) and is clogging up most of the warm sector. The dynamics are best further north and there is more dry air to work with.The surface low drops from 992MB-4AM FRIDAY to 980MB-4PM FRIDAY as the cold front passes NYC.


I guess we will see what happens but it might be time to put on the severe weather hat. The severe weather aspect on the warm side of this winter storm might be more promising than anything else.

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[TNE]

What is happening now is we are trending toward the colder solution. The 18z GFS is trending toward the 12z/18z NAM. There is cut-off energy that does not phase with the leading trough, and that cut-off energy that moves toward the coast (as depicted below) is the main point for the phasing that occurs along the front. The phasing occurs along the East Coast or the front that has stalled, and the surface cyclogenesis is occurring along the coast with the cut-off feature and not with the primary polar low over the Lakes. The degree of cold air available behind the front and the severity of the cyclogenesis will now depend on the TILT of the UPPER TROUGH. If the upper trough gains a negative tilt sooner, it will allow for a classic system to form along the coast.

Interesting weather event, strong weather event, and a great learning experience. No matter the outcome, it was worth forecasting. Thank you.

NAM SOLUTION AND GFS TRACK OF THE CUT-OFF LOW:

1.NAM
 nam_namer_084_850_temp_ht.gif   72.99K   0 downloads  nam_namer_084_300_wnd_ht (1).gif   74.19K   0 downloads

Note: The track of the POTENTIAL "cut-off" energy is similar but in the most recent model run the energy is with the cut-off and not with the Polar Low over the Lakes. >>
2.PREVIOUS GFS TRACK:
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 gfs_namer_096_850_vort_ht (1).gif   79.27K   0 downloads
2.CURRENT GFS TRACK:
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1.NEW GFS RUN--THERE IS CUT-OFF ENERGY AND THE COASTAL DEVELOPMENT ALONG AND BEHIND FRONT (as it approaches the Northeast) IS PRIMARY:
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2.OLD GFS RUN--THERE IS NO CUT-OFF ENERGY (all of the energy moves into the leading trough and cold front, and the polar low becomes the center for the phase...as the warm air takes over the area):
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[TNE]

Severe Wind Threat Potential Early Friday Morning for our Area? Yes, No, Maybe?
I used the short-term forecast on the NAM as well as the February 17, 2006 analog.

The energy that is undergoing intensification in this event is associated with the vort-max highlighted below. The best divergence would be near this feature. Another thing I want to point out is the lack of surface development anywhere else in the warm sector except near the warm front. The warm front is the trigger for development ahead of the cold front, which is why I believe along or near the warm front would be the best area to see any development, and the strongest development will be just ahead of the intensifying vort-max.

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1.Here is the 00z NAM:
Pay attention to where the vort-max in the Northeast is going and where the warm front is most likely positioned (also notice that most of the development is centered near or ahead of the warm front). ...There is hardly any development anywhere else, and in the Northeast the strongest development is right near the Low's center.
click to animate
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2.I compared the Skew-T in LGA for Fri./5AM to the only severe weather event that occurred in February in New York. That event occurred early on February 17 2006. The event I believe is similar in how it develops the leading trough and how it develops the Polar Low in the Northeast. The way I knew for sure is by taking a sounding from the 2006 event. I also found 2006 to be a good match for our weather overall.

Skew-T for LGA on Friday at 10 UTC:
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Sounding for ALB on February 17, 2006 at 12 UTC:
February 17, 2006 Severe Wind Event:
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Here is the Mesoscale Discussion issued by the SPC at 913AM of Feb. 17 06:
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MESOSCALE DISCUSSION 0155
NWS STORM PREDICTION CENTER NORMAN OK
0913 AM CST FRI FEB 17 2006

AREAS AFFECTED...ERN NY...SRN VT...SRN NH...WRN MA...WRN CT

CONCERNING...SEVERE THUNDERSTORM POTENTIAL

VALID 171513Z - 171715Z

...DAMAGING WINDS MAY ACCOMPANY NARROW BAND OF THUNDERSTORMS...

STRONG PRESSURE RISES ARE NOTED ACROSS UPSTATE NY IN THE WAKE OF
FAST MOVING LINE OF THUNDERSTORMS. ACTIVITY HAS DEVELOPED SEVERAL
BOW-TYPE STRUCTURES IN THE HUDSON VALLEY THAT ARE RACING EWD IN
EXCESS OF 50KT. THIS CONVECTION WILL CONTINUE EWD INTO THE HIGHER
ELEVATION REGION OF SRN MA INTO WRN CT...ESPECIALLY GIVEN THE NARROW
ZONE OF CLEARING/HEATING OBSERVED AHEAD OF THE LINE. LIGHTNING
SHOULD DECREASE WITH THIS ACTIVITY DOWNSTREAM...ALTHOUGH STRONG
WINDS MAY CONTINUE IN A BROAD SENSE BEHIND THE WIND SHIFT. WW NOT
ANTICIPATED DUE TO LIMITED AREAL EXTENT/TIME OF EXPECTED SEVERE
THREAT.

..DARROW.. 02/17/2006


ATTN...WFO...GYX...BOX...BTV...OKX...ALY...BGM...

41537476 43767297 43357188 41407329

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3.The SPC strongly believes that the severe threat will be in the South on Friday. I would have agreed if the cut-off energy phased in. The problem now I think is that the instability might remain low in the south and the dynamics are intensifying (propagating) up to the north instead toward the south. The gamble here is that the NAM does indicate some subtropical energy rushing ahead of the front in areas of the South and that does create some instability during the day.

IMO It has been hard to forecast the cut-off energy or the subtropical energy that gets phased into the leading trough so far (a great deal of inconsistency has tormented the models with this feature for the last couple of days). Why take any gamble with the subtropical energy is something that I am wondering about...

SPC Day 4 Outlook for Friday:
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A THREAT FOR SIGNIFICANT SEVERE STORMS WILL LIKELY PERSIST OVER ERN
PORTIONS OF THE SERN STATES FROM NRN FL...GA INTO THE CAROLINAS AND
THE DELMARVA REGION IN ASSOCIATION WITH AMPLIFYING UPPER TROUGH AND
ATTENDANT STRENGTHENING KINEMATIC FIELDS WITHIN MOIST WARM SECTOR.

[TNE]

12z NAM has some convection ahead of the strong front...Right behind the cold front the NAM indicates potential for strong wind gusts in the afternoon(greater than 55-60). Something to watch for.

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[TNE]

Winter Storm 02/24-

First Severe Threat of the Season (Warm Sector Discussion)?

I just looked at the most recent data from the NAM. This will be my last update before the event.
The key would be who gets into the warm sector. The best divergence for surface development passes through DCA, PHL, Into lower Jersey. 700mb image shows high omega values with potential for clearing just ahead of the convection at 21z (in the lower-half of New Jersey). Timing of the cold front or prefrontal boundary looks really good at this point [3-6/5-9PM respectively], which supports the idea of having any convection AT ALL.

There is potential for high effective shear in this region, and instability values might be near 500-1000 j/kg (surface CAPE) in the warm sector and the Lifted Index probably around -1C. Overall the pressure drops by about 4MB in the warm sector prior to the high omega values, with a strong jet streak overhead.

The highest potential for strong storms might be in this area IMO, but the SPC believes it will be in the Southeast US...Any conflicting views or supporting views would be appreciated.


Graphs to support my call (using the 00z/12z NAM):

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Instability for Convection:
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