Long-awaited update

I don't know of any visitors who aren't from weather forums, but for those who are, usually when the event comes near I'll post my thoughts in forums rather than on my blog, and then compile them following the outbreak. If there is anybody who actually reads this for pleasure, I can point to where I am posting them, but I will only do that if someone posts a comment saying they know of no weather forums.

With that said, the threat seems to be somewhat lessened by a strong longwave trough which has appeared on the progs, near Newfoundland. Just to the west of the ideal. Thus wavelengths, and resulting moisture and instability, will be limited, due to recycled cP air.

First call...Major Outbreak could be on tap

The GFS and Euro now concur: the potential exists for a major outbreak. All the parameters are there. Lower than normal SLP's, strong LLJ, good thermodynamic environment, etc.

Don't think I have much to say anymore, so here's my First Call:



P.S. the threat on the 21st doesn't seems so impressive now as the wave looks like it flattens out after leaving southern California.

Refined threat dates. Has some serious potential IMO.

First of all, I do apologize that the model pic in the last post is outdated. I did not know that even after uploading an image to Blogspot, the image is still active and auto-updating.

A note on the last system -- 1 person was killed in New Orleans, LA as a result of a nocturnal tornado. I pretty much busted on the last system as I didn't anticipate that nocturnal event, which was probably a result of localized enhanced low level shear from the warm front.

OK, onto next week.

As the polar vortex in the northeast begins to retreat, the flow over the CONUS begins to turn more zonal. One thing to keep note is that the ridge over the western CONUS has not been a true block, so to speak, so it is undercut quite nicely (this is unlike Jan. 2003, when the ridge was an Omega block that persisted for entire January, preventing any sort of severe wx). SST's and the ENSO support mild Pacific air beginning to infiltrate the CONUS next week as the Pacific jet stream is allowed to impact the CONUS unobstructed. Thus, the flow begins to turn zonal.

(Note that several significant outbreaks have occurred after this scenario occurred. Several I can think off the top of my head:
4/3/1974
3/13/1990
1/21/1999
3/12/2006
11/10/2002

I suspect that the remains of the cool air allowed for steeper lapse rates than what would be expected, and also, the atmosphere is in a constant state of balance, something I explained when I started the thread on Eastern two weeks before the 11/14-16 tornado outbreak in 2006.

There are other times where it did not occur, but I have explained that in my previous paragraph before the parentheses using Jan 2003 as an example.)

Disturbances will ride along the jet stream. A slight ridge will still remain, which the initial disturbance will cut through. This disturbance could spark the first of possibly two severe wx events. Timeframe: Feb. 20-22. Threat should not be too significant although a localized outbreak is possible. This was the system that I harped on a week ago. However, this is not the big tamale, so to speak.

The first disturbance will leave a perturbation in the flow as the weak ridge retrogrades to the Aleutians. This leads to a trough downstream. All the ingredients come together for a vort lobe or a shortwave to accelerate down the eastern side of the ridge, carving out another trough over the Intermountain west. This is the second system. Timeframe: Feb. 23-26. This could be significant. Since the image I posted, each GFS operational and ensembles run have showed 1) trough digging in the intermountain west and tugging eastward, and 2) a sub-1000 low. Incredible model consistency, and stuff that really deserves watching. How fast the first system goes away will be critical in determining how much return flow will be available for this system. If sufficient, this really has a LOT of potential to be a significant severe wx outbreak from the Plains to the foot of the Appalachians, and from the Gulf Coast all the way up to the Great Lakes.

Basically, after that, I believe there are two options:
1) If the Feb. 23-26 system turns out to be large amplitude and wide, it could merge with the remnants of the Polar Vortex over Canada and draw another shot of cold air over the eastern CONUS, ending the severe wx threat.
2) If the AO (Arctic Oscillation) does not remain negative, zonal flow should begin to dominate; there will be no sufficient Polar Vortex over Canada.
3) The Pacifc could reload, resulting in another outbreak.

In reality, I believe the first option is the most likely at this time to start out March. Looking out REALLY long range, another high-impact event is possible in mid-late March if Scenario 1 verifies. If Scenario 2 or 3 verifies, any additional severe wx events should be relatively localized and small until later in spring (possibly waiting until late April or May).

Anyhow, some other pros' comments:

DVD on EasternUSWx:

And now, on to the next one.....give it 7-14 days and I think the severe weather crew will be very busy. Just a sneak preview there of what I'm preliminarily beginning to think.

Hoosier4caster on EasternUSWx:

I reappear just to be the bearer of bad news...All sign's pointing to the end of winter for much if not all of the E Conus after the period of 19th to 22nd. Indices have been hinting at this for days...with model representation of the upcoming pattern change. So start gearing up for Svr weather season...its right around the corner! There maybe a brief shot of colder air...but nothing like what we have seen the last few weeks. And no I don't think we are heading for 60s either, just normal to slightly above...as the pattern change is at hand.

Now, the following are images from the Op GFS since the Feb.12, 12Z run, to prove its consistency. You'll have to trust me on the Ensembles, they have been agreeing well.

12Z Feb 12 run:



0Z Feb. 13 run:



12Z Feb. 13 run:




0Z Feb. 14 run:



I hope you get the point. This does not even include today's runs which continue to show this.
After 5 or 6 primary runs that have good support from the Euro and the Ensembles, I think it's a good betting hand.

Update on tomorrow's storm and LR

Tomorrow's storm may be limited by the Gulf action I pointed out yesterday. Once again, SLGT risk looks to prevail. I am concerned the warm front may still lift farther north than expected, and one cannot discount the underestimation of instability that the models have struggled with throughout the winter. So tomorrow's threat is still there despite a more benign look on the 0Z models. I'm not really interested in it though, so I'll skip the details that I planted yesterday.

EDIT (italicized portion): Never mind, I will do some analysis. The latest SPC SWODY1 has peaked my interest.
Right now the dewpoints are meager at best, however. The LLJ is not strong at all - the best dynamics are still far out to the west in western portions of TX. I saw that they wrote of a dynamics driven event, again, I just do not think that is true. However, I am torn.

First of all, moisture transport looks to be not very rapid until 12Z tomorrow. The warm front is still offshore of Houston right now. With that said, by that time, the LLJ could indeed finally start picking up. Either it picks up later and this becomes a nocturnal concern, or it picks up earlier and we get an event from 18Z-3Z. Both options are quite viable, and due to the stability right now, there is concern that the models could underdo the 850mb LLJ. The system in the GOM is already halfway through. One more thing - sats do indicate a possible N-S oriented long outflow boundary left behind in the western Gulf. That could become a significant factor in focusing "junk" convection, or "good" convection (if it lifts north).

Now, the speed shear isn't that great. And there could still be a mini cool front left over in the Yucatan Channel. So, pretty much, it's going to be all dependent on mesoscale features. Boom or bust, I say. When it's dependant on mesoscale features, 9 times out of 10 it will underperform.

The last thing that leads me to err on the side of caution: 10% nonhatched tornado probs at 6Z SWODY1 has never verified.

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Onto the next event, which I will revise my outlook. There are two systems IMO, the first of which seem to be well-modeled on the ECMWF and its ensembles. GFS, I really would not agree as it has been overly trigger happy with cutting off lows the past few days. The second system IMO will be the bigger one. I think that following the second one, a break will arrive in terms of severe.

Approximate dates:
First system...18th thru 20th
Second system...22th thru 26th

I am a bit concerned as the timeframe has been trending later and later, so more than likely, the events may materialize during the latter parts of the timeframes given.

Pattern recognition continues to support major potential. Several things I look for:
1) Polar Vortex breaking down, western ridge undercut, zonal flow
2) Support of amplification of a ridge in the Aleutians vicinity in order to induce a trough digging in the west.
3) An earlier shortwave which allows a slight trough to take hold in the west, which allows the next disturbance to dig more and possibly become negatively tilted.
4) When the time comes, a zonal flow across the Atlantic with slight perturbated shortwave just east of Newfoundland (teleconnects to pos. height anomalies along the east coast)

Note that one more thing, the Nino is switching to a Nina at this time. Indications are that the Nina is going to be strong, as the PDO values were never really strongly positive. That means that the Nino, didn't really act like a Nino. Similar to the 72-73 strong Nino, which was followed by the strongest Nina on record. What does that have to do with this? A Nina favors amplification in the Aleutians vicinity and favors a -PNA. This may be a part of that overall change.

Many of the signals are there. The ensemble mean has been fairly consistent with the following solution.
Starts out with polar vortex reasserting itself after the Eastern snowstorm. That lifts out and the NAO switches to negative.
Pacific energy begins to undercut what is now a very negative AO styled high latitude block. Eventually, some energy makes it to the Pacific NW, but cuts off.
One shortwave does make it through and picks up the cutoff, flinging it east. This produces storm #1.
Second wave comes thru and digs deeply in the wake of storm #1. If this materializes as expected (and I do believe it will), this is the bigger storm.

Now, this is still 2 weeks away granted, but the potential is there. Here's what some pro mets are offering.

Mr. Ed Berry:

At this time most of the CONUS has below normal temperatures with an active storm track from California into the eastern states. During weeks 2-3 I would expect all of this to slowly shift northwest meaning by late this month an active southwest flow storm track across from the Rockies into the Plains would be probable. Cold and moist energetic troughs would be expected to dig into the western and central Rockies and then lift northeast into the Mid/Upper Mississippi Valley. Given the South Pacific signal (and we need to monitor the east Pacific where there are still warm SSTs – at least for now remembering the cold subsurface), a moist subtropical jet with closed lows may interact with this storm track (GSDM 4-1 instead of Stage 1). While late winter storms would occur in the cold sectors, heavy rain and severe storms would be probable for much of the Deep South into the eastern states. In general, this would be an active pattern for much of the lower 48 states. There would be cold to the northwest and warmth for the far southeast. Alaska may stay under the ridge while closed lows may develop near/west of Hawaii. Finally, with variations in amplitude, I could see this type of pattern persisting well into spring.

Mr. Brian Lovern:

One other thing I will throw out, and I'm glad it was brought up earlier, is that this pattern, should it hold into spring, is classic for severe weather. I won't be shocked to see one more cold period in early March after the late February milder turn, but then we should see things flip after that IMO. I also agree with you that a nino is typically not a SE ridge promoter. A nina, all other things equal, is much better for this.

One final note - 0Z OP GFS run shows a massive severe wx outbreak on the 24th. It's the OP GFS, but does support the idea of a severe wx outbreak that I've been harping on for 5 days now.

Switching gears temporarily...

All along, I have been focusing on the threat from Feb. 17-24. I still believe the threat is there even though the models have been shying away from it. Except the Euro, now that it has entered its range.

Now, let's talk about the threat on Monday. Since two posts ago, I've been harping on the threat being minimal. Maybe doubting that call a bit. A few trends on the models have piqued my interest.

1) A small disturbance in the GOM that halts moisture transport on the eastern GOM. It is visible in water vapor imagery. This could become an issue, although I believe GFS may be suffering convective feedback and overdoing it a bit.

2) Strong dynamics, stronger mid level winds and stronger 850 LLJ. This is BIG and weakens the argument of deep layer shear being a problem. HOWEVER, winds in the upper levels are still lacking per the GFS, although not on the NAM. Now is the time where the NAM begins to shine, and this will again be straightened out over the next day.

3) Arctic High is now further north, with the bulk of it over Canada. This could shift southward though again - it is all up to the Polar Vortex over northeast Canada (which the easterners are discussing with regards to a possible snowstorm on Tuesday). But this is a big change from the oppressive arctic high in southern Canada, ready to dive into the Dakotas, that the models were showing a few days ago.

This will NOT be a dynamics driven event - if anything, given climo, the dynamics are lacking and the instability should not be a problem. The forecast soundings are showing minimal instability. I disagree. There's a 40 kt LLJ extending from the Yucatan, and no way are dewpoints merely in the upper 50's (per NAM). Considering 500T's are less than -15°C, that's a signal that instability will perhaps reach 1500 J/kg, perhaps even more if some sunshine comes out (and given the lack of strong forcing and cool mid level temps, along with hints of mid level drying on fcst soundings, that seems likely). Yes, the models show less than ideal temperatures at the surface, but they often underdo WAA. So, with that said, instability I think is there. However, this is only assuming that the arctic high remains up very far north, and the disturbance down in the GOM does not interfere with moisture transport from the Caribbean.

Just given the uncertainties, and the lack of speed shear, a SLGT remains the best call for now. However, with a bit more dynamics and a stronger surface low, I'd go moderate, but there's too many uncertainties for now.

With that said, here's my first call for Febrary 12-13. The threat on the 12th is mainly west of AL, 13th to the east.



Note: See Text - as the primary low occludes and the secondary coastal low (which leads to the snowstorm) forms, the severe threat should diminish. Still, enough instability should remain over Florida for a marginal threat.

Confidence increased, details in post

The chances of a severe wx outbreak affecting the CONUS has been raised to 25%, give or take. The GFS and its ensembles are really latching onto this idea of a strong Pacific jet stream carving out a trough over the intermountain west. A LOT can still go wrong, and these are still thoughts, not a true forecast.

Just wanted to add something regarding overall teleconnection patterns, although I'm really not good at them though. First of all, the SST's over near Japan are above normal. The temperature gradient between the Bering Sea and the central north Pacific is greater than usual (negative sea sfc temp anomalies over the Bering Sea and positive over areas further south). Negative anomalies are still strong over the Gulf of Alaska. These signs suggest that a stronger Pacific jet stream is favored. In addition, my current research indicates big but brief spurts of tornado activity are favored as an El Nino weakens. Otherwise an El Nino favors a quiet tornado season. As this current el nino weakens, this outbreak goes along with Nino climo.

As of right now, my preliminary call is for an event from Feb. 17-24. Many big events have happened on the 21st before, but that is just pure coincidence. Could this be a repeat?

SSTA's:




12Z operational GFS (BTW, it's extremely dumb to use post 300-hr GFS unless the pattern and the ensembles support what it shows. This is mainly just for future verification.)


I am in the process of attaching the ensembles.

EDIT 2-14-07: For those who read this blog (how many?), I apologize for not attaching the ensembles. I've had it on my hard disk, so here it is:
Click to animate


One last thing - I feel a SLGT risk could still verify for the Day 4-5 event, but again, the arctic high to the north is not a recipe for a major outbreak.

More thoughts for the next few weeks

Last post verified in terms of intensity with a significant outbreak in central Florida which killed 20 people and attracted national news. However, the warm front did not far as north as I expected, which led to a personal bust in location.

Onto the next event which the SPC already has outlined for a risk.
http://www.spc.noaa.gov/products/exper/day4-8/

However, I believe the talk of the event will eventually just be that, talk with no verification. Taking the GFS verbatim, yes it screams major severe wx outbreak. But the GFS isn't too good in terms of verification. Major problem: 1) speed shear which often is associated with strong winter tornadoes is lacking, and 2) strong arctic sfc high across the eastern U.S. The OP GFS does not show this, but the European and the ensembles do. The second issue is by far the bigger one, and IMO will keep this from being a significant event except for fish. Given that the OP GFS has a bias of underdoing cold and warm air advection (specifically in this case CAA associated with an Arctic High that the GFS seems to be underdoing), it can be thrown out.

Of bigger concern for me is a possible event following the one mentioned above. Another shortwave will dive into the CONUS but IMO that will also be moisture starved. It is a possible event after that that is of concern to me. The signals are weak, but after contemplating this for a few weeks, I decided to post my thinking here. Won't go into detail but it seems big events happen after cold outbreaks. But there are a few conditions: first of all, the polar vortex over Hudson Bay has to move out for good. That in itself will be hard to achieve if the Arctic Oscillation (AO) does not rise back to neutral or positive. The ensembles are divided. I'm still researching on synoptic conditions that lead to synoptically-evident setups but there seems to be a subtle correlation.

Up until last weekend, the correlation was weak enough and the ensembles pessimistic enough so that I pretty much forgot about it. Originally I was thinking Feb 10-17 to be the timeframe. I'm going to move that down a week. Again, it's a mere possibility, and the mesoscale is always the key. However, the ensembles seem to be going more gung-ho around the 240-348 hr (yes, very far out!), and if there a synoptic setup in February that is clearly classic enough to support some big fireworks, this in my opinion is it. Longwave in western CONUS, longwave east of Newfoundland, and below normal SLP's across the CONUS are the general signs for synoptically evident event in the cool season months.

One final note - "El Nino rains" may finally begin for SoCal late this weekend after an excruciatingly dry rainy season so far. I'm not paying too much attention to that for now. Possible snowstorm for the NE next week as well.