April 14-17th Severe Weather (Day 3 Mod)

[baroclinic_instability]

I will say the NAM is exhibiting a few thoughts that wxmann brought up earlier...elevated early DMC outflow substantially affecting the position of the front. I suspect that is why the NAM is so incredibly far S for the 00z run.

[baroclinic_instability]

I'm sure the NAM generation of precip Wed morning doesn't help the NW progress of the front either.

You just beat me to it. ^^

[OKpowdah]

Notice in the forecast soundings just behind the front, the inversion isn't as severe as last week's case. Last week was a super impressive arctic airmass for April and the density current definitely just plowed it southward. Not the same this time.

[baroclinic_instability]

FWIW, both the 21z WRF-NMM and ARW for SREF are clear into N Ok with the front.

[baroclinic_instability]

00z Canadian RGEM follows what the global has been simulating all along...a front sliding into central KS. It has been a while since I have seen such a huge discrepancy in the guidance...we are talking upwards of 300-350 mile differences 48 hours out.

[baroclinic_instability]

00z RGEM. 

For anyone interested, prinsburgwx from C/W up in MN has a nice model page using GEMPAK graphics. http://www.plainsweather.com/wxmap/model/

[brettjrob]

00z RGEM. 

For anyone interested, prinsburgwx from C/W up in MN has a nice model page using GEMPAK graphics. http://www.plainsweather.com/wxmap/model/

 

 

That basically screams outbreak for W OK taken literally. Very little warm sector contamination prior to 18z.

 

One concern I have aside from the cold air is a relative weakness in the flow magnitude around H2-H3. I've even seen some forecast soundings where H5 speeds are faster than anvil-level, which could be problematic. But it's tricky business trying to guess whether that will actually mitigate the tornado threat with large, favorable low-level hodographs and strong deep-layer shear.

[tornadotony]

Thursday could be a significant, widespread severe weather and tornado outbreak all the way from Arkansas to NE Illinois/NW Indiana, and perhaps spreading across the Ohio and Tennessee Valleys overnight.  I'm not feeling the best, so I'm gonna keep this on the shorter side (ha) but this is by far the most promising severe weather setup of the year and deserves some attention.

 

The current water vapor/mesoanalysis loop from COD (cool stuff!) shows one shortwave trough lifting out of the center of the country, with a sprawling trough digging into the west.  Things to note:

 

1) The first trough lifting in that manner usually means quality warm sector (definitely the case here)

2) The trough out west is VERY broad-based.

 

A look at the current sfc map along the Gulf Coast is all that's needed to know we'll have plenty of water vapor available.

 

 

So, we'll have a nice broad-based trough and a ton of humidity available.  So, what's going to happen with it?  That part's a little tricky.  A couple things to watch:

 

1) What happens Wednesday?  We've obviously seen convection from the day before modulate the next day's event (both for more severe and less severe weather), but that's not the only key for Wednesday.  The key is cyclogenesis, namely where does it occur and how strong is it?  If the NAM and Euro solutions are more correct, it will be farther south, and likely slightly weaker, which may lead to slight slower/weaker intensification of the cyclone on Thursday.  Also, where the baroclinic zone sets up may play a role in dictating low track and northward extent of severe threat.  However, with such a strong baroclinic zone, we may very well see a mesolow form and propagate to the NE, backing winds at the sfc and increasing the threat for the northern areas even more (the NAM does this).  This is the biggest question.  My leaning is toward a NAM/Euro solution.  I've been burned time after time after time not buying into either 1) surging cold air masses/density currents undercutting convection or 2) a lingering near-sfc cold air mass sticking around longer than expected.  The solution on the NAM for Wednesday very much reminds me of previous setups with such a cold frontal orientation on the plains, such as last Wednesday (although that was an even stronger density current) and, more importantly/pertinently, 2/10/09, which though it had the Lone Grove EF4 and Edmond EF2 was largely an underperforming event because the sharp baroclinic zone, which did retreat NW that morning, ended up being reinforced by the Edmund supercell and the cells that followed it, such that each cell became elevated pretty quickly after forming (until Lone Grove).  I won't get fooled again.  That said, I think there are some differences with Wednesday's event that make it more likely to produce, especially late evening overnight, given good BL humidity, a strong LLJ, and good mid-level lapse rates, so I won't write it off yet.  But I think Thursday is by far the bigger threat overall.

 

2) What about the free warm sector?  Will we see discrete development?  This is a tough question.  The 00z NAM and GFS support the idea of discrete or semi-discrete activity ahead of the front, with the GFS painting blotchy QPF output and the NAM leaning maybe toward multiple bands of convection.  With a strong jet max rounding the base of the trough and a pretty strong cold front, I'd expect a good chance of gravity wave formation in the warm sector that could/should lead to convection firing ahead of the front.  And with shear vectors not exactly parallel to the front (e.g. 72h on the NAM), I could certainly see some discrete activity (in fact, shear vectors tend to veer even more overnight, which may promote sustained semi-discrete activity even within the main line along the front).  Note that I am using the NAM in these examples, but this is consistent with previous GFS and NAM output.  Also of note is that the models have been trending toward a more neutral to even slightly-negative tilt solution, which would promote better large-scale forcing for ascent in the free warm sector.

 

All in all, there are still plenty of question marks, but I think Thursday holds a pretty high ceiling.  With a large portion of the warm sector likely to see 1500-2000J/kg of CAPE (cloud dependent, of course (point 1)), a strong isallobaric wind component due to the intensifying system, plenty of humidity, and at least a reasonable trough orientation, the potential is there for a very widespread (areal) severe weather event, with a good shot at some significant severe weather including wind damage and perhaps a few strong tornadoes, even if embedded in a QLCS.

[tornadotony]

I'm concerned too, but Tony's rationale leaves a bit to be desired. I guess every single time there's a significant thermal boundary involved in a setup, we'll have to keep in mind that cold air is denser, so expect it to get shoved to Brownsville or Miami by the day of.

 

Honestly, gun to my head, I imagine the NAM is closer to reality than the GFS. But even if we get a 20% GFS/80% NAM compromise, I don't understand how it's the death knell for a significant threat. The Red River Valley has looked quite impressive all along, and still does, even on the NAM (barring a couple unrelated caveats).

 

I guess it's possible the front ends up running from Abilene to Ft. Smith, in which case this really is an epic bust. But right now there's not much indication of that.

See my latest rambling post for a better explanation of the point I failed to make.

[baroclinic_instability]

That basically screams outbreak for W OK taken literally. Very little warm sector contamination prior to 18z.

 

One concern I have aside from the cold air is a relative weakness in the flow magnitude around H2-H3. I've even seen some forecast soundings where H5 speeds are faster than anvil-level, which could be problematic. But it's tricky business trying to guess whether that will actually mitigate the tornado threat with large, favorable low-level hodographs and strong deep-layer shear.

Yeah you make a good point with respect to anvil level flow. And it is worth mentioning again, since we are talking the upper jet (and it will be driving quite a bit of dryline convergence/SE synoptic inflow), the GFS has a far more substantial and better oriented STJ nosing well into the plains by 00z Thu. But there is a feedback process in the models. The farthest N with the front will tend to allow more interaction with the baroclinic wave to the NW...and much stronger and more substantial cyclogenesis/low level wind fields. 

[baroclinic_instability]

Thursday could be a significant, widespread severe weather and tornado outbreak all the way from Arkansas to NE Illinois/NW Indiana, and perhaps spreading across the Ohio and Tennessee Valleys overnight.  I'm not feeling the best, so I'm gonna keep this on the shorter side (ha) but this is by far the most promising severe weather setup of the year and deserves some attention.

 

The current water vapor/mesoanalysis loop from COD (cool stuff!) shows one shortwave trough lifting out of the center of the country, with a sprawling trough digging into the west.  Things to note:

 

1) The first trough lifting in that manner usually means quality warm sector (definitely the case here)

2) The trough out west is VERY broad-based.

 

A look at the current sfc map along the Gulf Coast is all that's needed to know we'll have plenty of water vapor available.

 

 

So, we'll have a nice broad-based trough and a ton of humidity available.  So, what's going to happen with it?  That part's a little tricky.  A couple things to watch:

 

1) What happens Wednesday?  We've obviously seen convection from the day before modulate the next day's event (both for more severe and less severe weather), but that's not the only key for Wednesday.  The key is cyclogenesis, namely where does it occur and how strong is it?  If the NAM and Euro solutions are more correct, it will be farther south, and likely slightly weaker, which may lead to slight slower/weaker intensification of the cyclone on Thursday.  Also, where the baroclinic zone sets up may play a role in dictating low track and northward extent of severe threat.  However, with such a strong baroclinic zone, we may very well see a mesolow form and propagate to the NE, backing winds at the sfc and increasing the threat for the northern areas even more (the NAM does this).  This is the biggest question.  My leaning is toward a NAM/Euro solution.  I've been burned time after time after time not buying into either 1) surging cold air masses/density currents undercutting convection or 2) a lingering near-sfc cold air mass sticking around longer than expected.  The solution on the NAM for Wednesday very much reminds me of previous setups with such a cold frontal orientation on the plains, such as last Wednesday (although that was an even stronger density current) and, more importantly/pertinently, 2/10/09, which though it had the Lone Grove EF4 and Edmond EF2 was largely an underperforming event because the sharp baroclinic zone, which did retreat NW that morning, ended up being reinforced by the Edmund supercell and the cells that followed it, such that each cell became elevated pretty quickly after forming (until Lone Grove).  I won't get fooled again.  That said, I think there are some differences with Wednesday's event that make it more likely to produce, especially late evening overnight, given good BL humidity, a strong LLJ, and good mid-level lapse rates, so I won't write it off yet.  But I think Thursday is by far the bigger threat overall.

 

2) What about the free warm sector?  Will we see discrete development?  This is a tough question.  The 00z NAM and GFS support the idea of discrete or semi-discrete activity ahead of the front, with the GFS painting blotchy QPF output and the NAM leaning maybe toward multiple bands of convection.  With a strong jet max rounding the base of the trough and a pretty strong cold front, I'd expect a good chance of gravity wave formation in the warm sector that could/should lead to convection firing ahead of the front.  And with shear vectors not exactly parallel to the front (e.g. 72h on the NAM), I could certainly see some discrete activity (in fact, shear vectors tend to veer even more overnight, which may promote sustained semi-discrete activity even within the main line along the front).  Note that I am using the NAM in these examples, but this is consistent with previous GFS and NAM output.  Also of note is that the models have been trending toward a more neutral to even slightly-negative tilt solution, which would promote better large-scale forcing for ascent in the free warm sector.

 

All in all, there are still plenty of question marks, but I think Thursday holds a pretty high ceiling.  With a large portion of the warm sector likely to see 1500-2000J/kg of CAPE (cloud dependent, of course (point 1)), a strong isallobaric wind component due to the intensifying system, plenty of humidity, and at least a reasonable trough orientation, the potential is there for a very widespread (areal) severe weather event, with a good shot at some significant severe weather including wind damage and perhaps a few strong tornadoes, even if embedded in a QLCS.

Yes, spot on with the bold. There is a clear feedback process here in the varying solutions, and keying in on where the front tracks is crucial to severity and coverage.

[Ian]

looks like spc likes wed still: https://twitter.com/GCarbin/status/323992042030108672

[prinsburg_wx]

MODEL DIAGNOSTIC DISCUSSION

NWS WEATHER PREDICTION CENTER COLLEGE PARK MD

1221 AM EDT TUE APR 16 2013

VALID APR 16/0000 UTC THRU APR 19/1200 UTC

DEEP CYCLONE DEVELOPING IN THE MIDWEST/PLAINS THU INTO FRI...

WEAK FRONTAL WAVE RIPPLING THROUGH MICHIGAN THURSDAY...

PREFERENCE:  00Z GFS WITH A DASH OF 12Z CANADIAN LATE

CONFIDENCE:  SLIGHTLY ABOVE AVERAGE

THE GUIDANCE SHOWS ISSUES WITH THE FIRST WAVE MOVING THROUGH

MICHIGAN THURSDAY, WITH THE 12Z UKMET AND 00Z NAM TRACKING THE

SYSTEM MORE EASTWARD DUE TO THEIR STRONGER NORTHERN STREAM

SHORTWAVE IN CANADA WHICH FLATTENS THE TOP OF THE BROAD/STRONG

MID-LEVEL RIDGE -- A MODEL BIAS OCCASIONALLY SEEN IN ALL THE

GUIDANCE.  WITH THIS FIRST SYSTEM, A COMPROMISE OF THE 00Z GFS/21Z

SREF MEAN LOOKS IDEAL AND HAS THE GREATEST 12Z GLOBAL ENSEMBLE

SUPPORT.

WITH THE MAIN EVENT -- THE DEEP CYCLONE FORMING IN THE MIDWEST

THURSDAY INTO FRIDAY -- THE 12Z UKMET REMAINS ON THE

SLOW/AMPLIFIED END OF THE GUIDANCE.  WHEREAS SUNDAY IT HAD NO 12Z

GLOBAL ENSEMBLE SUPPORT, IT HAS PICKED UP THE SUPPORT OF ONE-TENTH

OF THE GLOBAL ENSEMBLE GUIDANCE ON THE MONDAY 12Z RUN, WHICH IS

NOT ENOUGH TO BELIEVE QUITE YET.  DUE TO THE DISTANCE BETWEEN THE

NORTHERN STREAM SHORTWAVE IN SOUTHERN CANADA AND THE ENERGY IN THE

PLAINS/MIDWEST, A CLOSED CYCLONE MAKES SENSE, THOUGH THERE REMAINS

A BIT OF SPREAD WITH THE 00Z NAM THE FARTHEST SOUTH (THOUGH IT

DOES LIE WITHIN THE 12Z GLOBAL ENSEMBLE SPREAD USING THE 5400

METER 500 HPA HEIGHT LINE AS A GUIDE).  THE 12Z ECMWF AND ITS

ENSEMBLE MEAN, ALONG WITH THE 21Z SREF MEAN APPEAR TO PLACE TOO

MUCH DISTANCE BETWEEN THE MID-LEVEL CYCLONE AND THE SURFACE

REFLECTION OF THE FEATURE, SO WILL NOT CONSIDER THEM CONTENDERS.

A SOLUTION ON THE SOUTHWEST CORNER OF THE BEST GLOBAL ENSEMBLE

CLUSTERING APPEARS BEST HERE, IN CASE THE GUIDANCE CLOSES OFF THE

SYSTEM SOONER ON LATER RUNS.  THIS LEADS TO A 00Z GFS/12Z CANADIAN

COMPROMISE, WITH SLIGHTLY ABOVE AVERAGE CONFIDENCE CONSIDERING THE

GOOD DAY-TO-DAY CONTINUITY IN THIS IDEA AND PREFERENCE AND THE

SYSTEM'S AMPLIFIED NATURE.

 

 

[baroclinic_instability]

looks like spc likes wed still: https://twitter.com/GCarbin/status/323992042030108672

When Carbin gets excited that usually isn't a good sign. He never struck me as the type to become excitable for no reason.

[Ian]

When Carbin gets excited that usually isn't a good sign. He never struck me as the type to become excitable for no reason.

Think 1990 was mentioned before April 14 too. Not by him per se. Given the guidance discrepancy hard to run to the top but unless he's learned the magic of social media in his limited tweets.. Definitely worth consideration.

[thewxmann]

Yes Tony does make a good point -- frontal position will be highly dependent on location of sfc cyclogenesis on Wed. But with a sprawling 1025+ high to the north, why would cyclogenesis occur in KS rather than TX? The 0Z GFS has shifted ever so slightly south, as has the NAM, but delta-(frontal position) remains more or less consistent. But the trend is clear. The NAM is probably too far south, but somewhere in the southern TX Panhandle looks about right.

 

The bigger issue here is that there will be plenty of lift due to the dual upper jet structure, and as has been mentioned, any convection that develops in the cold sector will reinforce the front and halt northward progression. And the models are ridiculously bad at forecasting this. So actually it almost seems prudent to forecast low position, interpolate frontal position from that and from other model output, and then just shift the resulting front south by 50-100 miles. 

 

With that said, this is a completely different animal from the last system. The models want to swing a subtle wave across N. TX around 18-21Z, so no matter where the front is, it won't be a warm sector cap bust. Which brings up another issue -- if storms fire too early and stabilize the warm sector, all the discussion of the front and what-not might end up being for naught.

[andyhb]

With that said, this is a completely different animal from the last system. The models want to swing a subtle wave across N. TX around 18-21Z, so no matter where the front is, it won't be a warm sector cap bust. Which brings up another issue -- if storms fire too early and stabilize the warm sector, all the discussion of the front and what-not might end up being for naught.

 

I'm not sure if you are referring to storms earlier in the day than this, but those storms (via the influence of the aforementioned shortwave) would be initiating within a fairly potent environment already by that time taken any of the guidance (yes the LLJ will still have some strength to gain, but there is still plenty of low level shear at least being advertised).

[thewxmann]

On a tangential note, Andy, where did you get those Euro maps on the last page?

[andyhb]

On a tangential note, Andy, where did you get those Euro maps on the last page?

 

Wunderground Wundermap, screen-capped them, then uploaded to Imageshack.

[cyclone77]

On a tangential note, Andy, where did you get those Euro maps on the last page?

 

http://www.wunderground.com/wundermap/

[JoMo]

SPC Day 2 is out. Looks a lot like the Day 3 was.

 

http://kamala.cod.edu/spc/

[thewxmann]

Wunderground Wundermap, screen-capped them, then uploaded to Imageshack. 

 

 

http://www.wunderground.com/wundermap/

 

Thank you, great link to have.

[andyhb]

Darrow highlights everyone's points nicely in the outlook, I'll note that he is considering GFS forecast soundings for OK/TX, which are showing substantially more CAPE than the NAM soundings (over the areas unaffected by the anafront, of course) over a larger area.

 

It appears the NAM/Euro front setup is favored, but the GFS' ambient environment over the unaffected warm sector is favored as well.

 

DAY 2 CONVECTIVE OUTLOOK    NWS STORM PREDICTION CENTER NORMAN OK  1215 AM CDT TUE APR 16 2013    VALID 171200Z - 181200Z    ...THERE IS A MDT RISK OF SVR TSTMS ACROSS OK INTO EXTREME SERN  KS...    ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK FROM  WCNTRL TX TO IL...     ..SRN PLAINS TO MID MS VALLEY    SIGNIFICANT LARGE SCALE DIFFLUENCE IS EXPECTED TO OVERSPREAD THE SRN  PLAINS WEDNESDAY AS UPPER TROUGH SHIFTS INTO THE ROCKIES.  MODELS  CONTINUE TO SUGGEST A CORRIDOR OF 500MB FLOW IN EXCESS OF 50KT WILL  SPREAD ACROSS A MOISTENING WARM SECTOR THAT SHOULD BECOME QUITE  UNSTABLE BY MID DAY.  INCREASING LARGE SCALE ASCENT AND FAVORABLE  BUOYANCY SUGGEST A CONSIDERABLE AMOUNT OF CONVECTION WILL ULTIMATELY  EVOLVE ACROSS THE BODY OF OK...NEWD INTO THE MID MS VALLEY...MUCH OF  IT POTENTIALLY SEVERE.    AS UPPER TROUGH APPROACHES THE SRN PLAINS THERE IS REASON TO BELIEVE  EARLY FRONTAL SURGE WILL STALL NEAR THE RED RIVER THEN ADVANCE NWD  AS A WARM FRONT DURING THE DAY2 PERIOD.  THERE IS SOME UNCERTAINTY  HOW FAR NORTH THIS BOUNDARY WILL RETREAT WITH THE GFS THE MOST  AGGRESSIVE ALLOWING WARM FRONT TO ULTIMATELY REACH THE I-70 CORRIDOR  ACROSS KS.  WHILE THIS MODEL HAS CONSISTENTLY FORECAST THIS SCENARIO  CURRENT AIRMASS ACROSS THE CNTRL PLAINS IS DISTURBINGLY COLD AND ANY  WARM ADVECTION PRECIPITATION ACROSS KS DURING THE DAY1 PERIOD MAY  PREVENT THE WARM SECTOR FROM ADVANCING NORTH OF THE OK BORDER.  BOTH  THE NAM AND ECMWF MAINTAIN A MORE SLY POSITION AND FOR THIS REASON  HAVE OPTED TO PERPETUATE ENHANCED SEVERE RISK PRIMARILY ACROSS OK  WITH PERHAPS A NEED TO EXTEND HIGHER PROBS INTO PORTIONS OF NWRN TX.    LATEST THINKING IS LOW LEVEL WARM ADVECTION WILL LIKELY AID EARLY  MORNING ELEVATED TSTMS...POSSIBLY SEVERE...ACROSS KS INTO NRN MO.   DIURNAL HEATING ACROSS THE WARM SECTOR WILL CONTRIBUTE TO  DESTABILIZATION AS FAIRLY MOIST LOW LEVELS...DEW POINTS WELL INTO  THE 60S...CONTRIBUTE TO SBCAPE IN EXCESS OF 2000 J/KG.  STRONGEST  HEATING IS EXPECTED ALONG DRYLINE WHICH SHOULD ESTABLISH ITSELF OVER  WRN OK/NWRN TX AND INSTABILITY JUST EAST OF THIS BOUNDARY SHOULD  APPROACH 3000 J/KG.  GFS FORECAST SOUNDINGS ARE QUITE IMPRESSIVE  NEAR THE DRYLINE WITH STRONG VEERING WIND PROFILES WITH HEIGHT AND  LOW LCLS.  IF WARM FRONT INDEED RETREATS TOWARD THE KS BORDER  DISCRETE SUPERCELLS SHOULD EVOLVE ALONG THE DRYLINE WHICH SHOULD  TRACK ENEWD INTO THE BODY OF OK.  REGARDLESS...INCREASING DIFFLUENCE  ALOFT WILL CONTRIBUTE TO NUMEROUS TSTMS INTO THE OVERNIGHT HOURS  AIDED BY 50-60KT SLY LLJ.    AN EXTENSIVE CORRIDOR OF FRONTAL CONVECTION IS EXPECTED TO EXTEND  NEWD ACROSS SERN KS/MO INTO PORTIONS OF WCNTRL IL.  THIS ACTIVITY  SHOULD BE WELL ORGANIZED ALONG THE WIND SHIFT BY LATE EVENING BEFORE  ADVANCING DOWNSTREAM WITH PROGRESSIVE BOUNDARY.    LARGE HAIL...DAMAGING WINDS...AND ISOLATED TORNADOES ARE POSSIBLE  ACROSS THE SEVERE RISK REGION...ESPECIALLY OK INTO PORTIONS OF NWRN  TX.    ..DARROW.. 04/16/2013

[chase_stormz]

central to southern ok definitely has high risk "potential" imo

[andyhb]

00z Euro is nasty looking throughout most of OK on Wednesday, retreated the cold front a bit compared to the 12z/00z last night runs (nowhere close to the 00z NAM's southward extent). 992 hPa low in the TX Panhandle and an almost 60 kt wind max at H85.

[chase_stormz]

00z Euro is nasty looking throughout most of OK on Wednesday, retreated the cold front a bit compared to the 12z/00z last night runs (nowhere close to the 00z NAM's southward extent). 992 hPa low in the TX Panhandle and an almost 60 kt wind max at H85.

 

wow any way we can get images?

[andyhb]

http://www.instantweathermaps.com/ECMWF-php/ecmwf.php

[yoda]

Got to admit i was perplexed by the "disturbingly cold" comment... is that a new kind of cold or something?

[MnWeatherman]

"Isolated tornadoes," huh?

[baroclinic_instability]

Got to admit i was perplexed by the "disturbingly cold" comment... is that a new kind of cold or something?

I think that was his way of saying, "we think the warm front may surge northward, but we aren't sure, so we will make it sound colder than it is to add emphasis".