Central/Western Summer Medium/Long Range Discussions

[brettjrob]

Both the 12z GFS and ECMWF deterministic trended toward next week's system re-amplifying along the east coast, lending to an Omega-like pattern over the Plains as the much-touted following trough tries to come onshore. Just two runs from 9-11 days out, but I'd temper any excitement about that one, too, for the time being. Persistence says it's not hard to believe we could head into May shut out.

[andyhb]

Well it's not like that thing is going to eject immediately.

[Quincy]

Looking at 00z GFS and 12z Euro, another case of poor timing? Late Wednesday could see a line of storms from OK into KS with the dryline. A sfc low develops over the plains and goes sub-990mb. GFS is meager with moisture (Tds mainly in the 50s) and capping mitigates the threat. The Euro is actually a bit more solid with some low 60 dews making it to the NE/KS border. The kinematic support is really good, as the GFS forecast soundings for central KS showed sharp backing winds and >50kt right down to 850mb. The cap/CINH is kind of ugly though.

Thursday looks a bit too late as the system is strung out by that point, but perhaps further south into OK/TX could see a few storms.

Maybe a localized threat each day, but this might be another case of poor timing.

At least the continued trends for the end of April are very encouraging for a better pattern setting up.

[Ground Scouring]

...

At least the continued trends for the end of April are very encouraging for a better pattern setting up.

Wouldn't the -NAO set-up (Omega block) and weak MJO signal be a problem after next Thursday?

[Superstorm93]

Very narrow D5 

 

 

 

 

ZCZC SPCSWOD48 ALL
ACUS48 KWNS 190838
SPC AC 190838

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0338 AM CDT SAT APR 19 2014

VALID 221200Z - 271200Z

...DISCUSSION...
CONSIDERABLE MODEL VARIABILITY EXISTS BETWEEN THE GFS AND ECMWF AS
WELL AS SINGLE MODEL RUN-TO-RUN DIFFERENCES. EVEN SO THERE APPEARS
TO BE SUPPORT FOR A WELL ESTABLISHED LEE TROUGH/DRYLINE BY MID WEEK
AS SUBSTANTIAL SWLY FLOW AT MID LEVELS OVERSPREADS THE HIGH PLAINS.
CURRENT PATTERN FAVORS A NARROW CORRIDOR OF MOISTURE/INSTABILITY
ACROSS THE HIGH PLAINS FROM NWRN TX...NWD INTO CNTRL NEB. WHILE
DETAILS OF SHORT WAVE TIMING AND PLACEMENT OF SPEED MAXIMUM DIFFER
AMONG THE MODELS...40KT+ SWLY FLOW ALOFT SHOULD PROVE ADEQUATE FOR
SUPERCELL DEVELOPMENT ACROSS THIS REGION. IF A BROADER AND MORE
UNSTABLE WARM SECTOR CAN ESTABLISH ITSELF THEN A MORE SIGNIFICANT
SEVERE EVENT...POSSIBLY OVER MULTIPLE DAYS...COULD ENSUE.
HOWEVER...MODEL VARIABILITY WILL PRECLUDE DELINEATING A SEVERE
THREAT BEYOND WEDNESDAY.

..DARROW.. 04/19/2014

CLICK TO GET WUUS48 PTSD48 PRODUCT

 

[Quincy]

Wouldn't the -NAO set-up (Omega block) and weak MJO signal be a problem after next Thursday?

I'm looking at the overall pattern as we head into May.

 

I like to loosely use 2010 as an analog to this season. Spring 2010 was off to a very slow start with tornado reports, but then thanks in part to a pattern change the reports increased dramatically from late April through mid-June. Our pace so far is actually a very close match to 2010:

With that said, here's a look at the mean May 2010 500mb pattern with anomalies. A ridge over the eastern CONUS with a good trough across the Pacific northwest. This allowed for shortwaves to dig into the ridge and resulted in a string of severe events through May:

 

Now, while the day 8-10 forecasts don't show this specific pattern suddenly developing, the trend is in the right general direction. We finally see a consensus among the models of a eastern Pacific trough moving toward the West Coast. The gradient in the Pacific helps as a strong jet develops. If we can see at least somewhat of an eastern progression with this forecast centered around late April heading into early May, I think we'll have a fair match with 2010 again:

 

Here's another look at the 00z Euro, with the EPS day 10 mean on the left and the OP on the right. If this verifies, it's looking pretty good heading into May.

 

The MJO signal is weak and the upstream blocking is not ideal, but I go back to 2010. That mean 500mb pattern for May featured negative height anomalies east of New England and across extreme southeastern Canada.

[tornadotony]

Wouldn't the -NAO set-up (Omega block) and weak MJO signal be a problem after next Thursday?

The 00z Euro shows no signs of omega blocking and the 06z GFS only has it showing up ~228h and onward.  The 00z Euro verbatim is a series of significant to major severe weather outbreaks likely encompassing the entire midsection of the country between the Apps and the Rockies and S of NE/IA/WI in days 6-11.

[andyhb]

Let's also note that there is another huge trough out in the Pacific towards the end of the Euro's run (in behind the one that ejects towards the Plains).

 

The 12z GFS shows a very similar pattern developing, except truncation turns into a mess as usual.

[andyhb]

12z Euro looks pretty darn nasty through 168 hrs with the intense jet streak sliding SE on a very favorable angle (not too steep, not too shallow) to carve out a major western trough. Again, there is a large warm sector building out ahead of it.

 

Edit: Well the Central Pacific ridge deamplifies afterwards, but the door into the central portion of the CONUS is still wide open for that to just slide in there, with no omega blocking to speak of.

[Quincy]

I know the focus may be on the longer-range, but a few Wednesday PM storms could pack a punch ahead of the dryline. GFS is looking pretty good across central/western Kansas. Further north moisture is more marginal. If the cap can be overcome, the GFS parameters look very supportive of supercells. It's a fairly narrow zone, but the signal has been fairly consistent over the last several model runs.

[andyhb]

The 00z Euro can be summed up by lower option of the first image, which then proceeds to lead to well...the second image, although that's not until after a series of events featuring the shortwaves that do eject.

 

[andyhb]

With that said, it appears the 00z run was on the shallow/progressive end of the rest of the ensembles, and let's be honest when saying that ensemble mean is nasty looking in a number of ways.

 

[andyhb]

Changes as expected coming with the 12z Euro, deeper trough being carved out in the west by 144. At 120, there is a 120-130 kt 500 mb jet about to drop into the developing trough.

 

 

Edit: Looks like the first event takes place in between 144 and 168.

[Ground Scouring]

Changes as expected coming with the 12z Euro, deeper trough being carved out in the west by 144. At 120, there is a 120-130 kt 500 mb jet about to drop into the developing trough.

Edit: Looks like the first event takes place in between 144 and 168.

I would still like to see better timing on the ECMWF and, to a lesser extent, on the GFS. The large polar high over the High Plains means that the distance between the departing longwave trough over the Great Lakes and the incoming trough over the West will be important re: the angle and northward projection of moisture return. The ECMWF, in particular, seems (at least as I can see) to hint at development of multiple low centers along the dryline between H144 and H168. Also, the low-level H85 return flow at 12Z 27 April is a bit weaker than I would like to see re: prospects for a bigger event, but much can change. So far the potential seems high but rather localized over the s-ctrl Plains in days six and seven.

[andyhb]

I would still like to see better timing on the ECMWF and, to a lesser extent, on the GFS. The large polar high over the High Plains means that the distance between the departing longwave trough over the Great Lakes and the incoming trough over the West will be important re: the angle and northward projection of moisture return. The ECMWF, in particular, seems (at least as I can see) to hint at development of multiple low centers along the dryline between H144 and H168. Also, the low-level H85 return flow at 12Z 27 April is a bit weaker than I would like to see re: prospects for a bigger event, but much can change. So far the potential seems high but rather localized over the s-ctrl Plains in days six and seven.

 

Timing will certainly change between now and zero hour, I don't think there's much doubt about that.

 

Also, the low level return flow at H85 is >20 kts from the western Gulf for at least two and a half days prior to the trough's ejection, which should be sufficient. Let's also note that the D4/5 system will also help improve deep moisture advection trajectories over the Southern Plains and Lower MS Valley. Both the Euro and GFS indicate large amounts of instability over their respective warm sectors. The bigger threat with the Euro would likely come at 168-204 from the south central Plains into the SE. Be careful when localizing a threat this far out, especially with a volatile looking pattern like this.

[andyhb]

00z Euro appears to be holding serve from 12z through 144, still an incredible deep moisture feed being established from the Central Caribbean in front of this thing.

 

Edit: Holy crap at 168...

[brettjrob]

What a nailbiter next weekend is. There's fairly strong consensus that the pattern goes down the toilet afterward, so a lot hinges on this. It's clear that a very impressive trough will carve into the western CONUS late in the workweek, and that moisture supportive of a high-end event should precede it over parts of the Plains.

 

A lot to get excited about, for sure. However, the midweek system could still amplify over the Northeast early and strongly enough that things get blocky, even leading to a backdoor cold intrusion for the Plains in the worst-case (see 00z GFS). At the other extreme is the 00z ECMWF just coming in, which maintains an awesome warm sector that extends N of I-70.

 

For now, the 00z GEFS mean would suggest the operational run is on the pessimistic extreme, thankfully. But I wouldn't let my guard down or assume that this system will amount to anything at all just yet, in light of the seasonal trend. I sure hope it does, along with every other chaser on the planet who's seen the latest progs heading into early May.

 

[andyhb]

Um...it keeps going at 192, look out Dixie Alley.

 

It's pretty safe to say that the 00z Euro would likely be a major multi-day outbreak across multiple sub-forums.

[Radtechwxman]

man this is a real nail biter for the upcoming weekend. euro obviously would spell a significant outbreak and gfs says not so much. yes moisture looks to be in place. I just wish there were more spacing in between systems. as brett was saying, def could see an intrusion of cold air if we see the mid-week system re-amplify in the Northeast. euro seems to be performing better later than the gfs. didn't the gfs cave into the euro for our mid-week system? I went ahead and requested off the weekend in case the best case scenario pans out. im hoping that large high pressure doesn't settle into the Midwest like gfs keeps showing

[Quincy]

Even the latest GEFS mean analogs aren't too shabby, despite a less "optimistic" operational run:

[tornadotony]

The op GFS is garbage.  Total horse****.  It can't even remain consistent with itself run-to-run, let alone with its ensembles or the Euro.  It's getting 0% considering from me right now.

[jojo762]

The op GFS is garbage.  Total horse****.  It can't even remain consistent with itself run-to-run, let alone with its ensembles or the Euro.  It's getting 0% considering from me right now.

The major differences, and scenarios between the GFS and EURO right now are amazing. One shows Major outbreak, the other shows a good setup for thundershowers. ECMWF and UKMET seem to be in decent agreement, and have actually been consistent, meanwhile the GFS completely jumped ship on this 4 runs ago.

[Radtechwxman]

I totally agree with you guys. GFS seems a bit crazy of a solution. the GFS caved to the euro for the mid week storm. euro also looks to have better support from its ensembles and the ukmet model. but not going to lie it is worrisome to see the gfs lock onto this idea of a blocky pattern and backdoor crashing cf. eventually one of these models has to cave to the other.

[brettjrob]

I'm not sure that the GFS is completely off on its own island, even though it is the worst-case scenario right now.

 

Last night's 00z suite, time sensitive:

 

ECMWF vs. GFS: http://meteocentre.com/models/explorateur.php?mod2=gfs&run2=00&stn2=PNM&hh2=144〈=en&map=na&stn=PNM&run=00&mod=ecmwf&hh=144&comp=2&fixhh=1〈=en

 

ECMWF vs. GGEM: http://meteocentre.com/models/explorateur.php?mod=ecmwf&run=00&stn=PNM&hh=144&map=na&stn2=PNM&run2=00&mod2=gemglb&hh2=144&comp=2&fixhh=1〈=en

 

ECMWF vs. UKMET: http://meteocentre.com/models/explorateur.php?mod2=ukmet&run2=00&stn2=PNM&hh2=144〈=en&map=na&stn=PNM&run=00&mod=ecmwf&hh=144&comp=2&fixhh=1〈=en

 

The Euro stands alone in maintaining near-zonal flow over New England next Saturday, allowing the energy to eject quickly into the Plains before the trough starts getting "pinched."

 

If we're trying to stay positive, the Euro also stood alone (I think) regarding the timing and evolution of the midweek system a few days ago, bringing it through the Plains quickly on Wednesday when the GFS wasn't progressive enough. All the other models eventually caved to that.

[andyhb]

It also was by far the best solution in the mid range regarding 4/3 and 4/6-7, the GFS had the 4/6-7 system basically as a coastal for IIRC up to 72-96 hours out.

[andyhb]

HPC Mid-range evaluation.

 

..GUIDANCE EVALUATION  
 
EARLY IN THE FCST THERE IS RELATIVELY GOOD CONTINUITY AGREEMENT  
WITH SYSTEMS OF INTEREST... FAIRLY STG LOW PRES DEPARTING FROM THE  
CANADIAN MARITIMES... COMPLEX AREA OF LOW PRESSURE TRACKING EWD  
FROM THE NRN TIER AND TRAILING FRONT... AND SYSTEM INITIALLY OFF  
THE PAC NW COAST. AN AVG OF LATEST GFS/ECMWF SOLNS IS FAIRLY  
CLOSE TO CONTINUITY.  
 
WITH THE TROUGH MOVING INTO THE WEST BY THE START OF THE WEEKEND  
LATEST GFS/CMC RUNS ARE FARTHEST SWD WITH AN EMBEDDED CLOSED LOW  
WHILE ECMWF RUNS HAVE TENDED TO MAINTAIN AN OPEN TROUGH THROUGH  
THE WEST AND WAIT UNTIL ENERGY REACHES THE PLAINS TO CLOSE OFF A  
LOW. RESPECTIVE ENSEMBLE SYSTEMS GENERALLY REFLECT THE  
OPERATIONAL IDEAS WITH GEFS/CMC MEMBERS SHOWING MORE TROUGH  
AMPLITUDE AS A WHOLE RELATIVE TO ECMWF MEMBERS. IN THE PAST  
COUPLE WEEKS THERE HAVE BEEN AT TWO WRN TROUGHS THAT HAVE TURNED  
OUT TO BE LESS AMPLIFIED THAN SOME GFS/GEFS SOLNS... WITH ANY  
EMBEDDED UPR LOW WELL NWD. THUS PREFER TO MINIMIZE USE OF  
OPERATIONAL GFS RUNS WITH ONLY MINORITY INCLUSION OF THE 06Z GEFS  
IN THE UPDATED FCST.  
 
MEANWHILE SOLNS DISPLAY INCREASING DISPERSION WITH TIME FOR NERN  
CONUS TROUGH AMPLITUDE AND RESULTING LATITUDE FOR THE SFC FRONT  
OVER THE ERN HALF OF THE LOWER 48. RELATIVE TO THE FULL RANGE OF  
GUIDANCE 00Z/06Z GFS RUNS ARE RATHER AMPLIFIED WITH THE TROUGH  
ALOFT/SWD WITH THE TRACK OF THE EMBEDDED UPR LOW AND SWD WITH THE  
SFC FRONT. WHILE REMAINING SOLNS ARE LESS AMPLIFIED ALOFT THERE  
HAS BEEN SOME APPARENT OSCILLATION IN RECENT CYCLES WITH EVEN THE  
ECMWF MEAN TENDING TO BRING THE ERN CONUS SFC FRONT FARTHER NWD  
LATE IN THE PERIOD IN 00Z RUNS THAN 12Z VERSIONS.  
 
LOOKING AT MULTI-DAY MEANS AT D+8... THE MOST COMMON FEATURES ARE  
AN AREA OF POSITIVE HGT ANOMALIES OVER/NEAR HUDSON BAY AND  
NEGATIVE ANOMALIES OVER THE NERN PAC. WHILE TELECONNECTIONS  
RELATIVE TO THESE TWO FEATURES YIELD DIFFERENT RESULTS OVER THE  
WRN-CNTRL CONUS THERE IS A COMMON THEME OF TROUGHING CLOSER TO THE  
EAST COAST... WHICH LEADS TO SOME SKEPTICISM OF THE 00Z  
ECMWF/ECMWF MEAN THAT BRING THE SFC FRONT RATHER FAR NWD DUE TO  
HIGHER HGTS ALOFT. ON THE OTHER HAND RECENT HISTORY SUGGESTS GFS  
RUNS COULD BE OVERDONE WITH TROUGH AMPLITUDE. AT THIS TIME THE  
BEST OPTION IS AN INTERMEDIATE SOLN THAT INCLUDES ONLY HALF  
WEIGHTING OF THE 00Z ENSEMBLE MEANS ALONG WITH 50 PCT OF THE MORE  
SUPPRESSED WPC CONTINUITY.

[brettjrob]

Thanks for posting that discussion. Almost every word is very pertinent to our concerns for central US impacts 4/26-28. It sounds like they favor a compromise regarding frontal placement and associated eastern trough amplitude.

 

FWIW, the 12z GFS coming in shifted the New England closed low a lot farther east, which does wonders for warm sector extent. Man, Saturday could be epic High Plains action if everything falls into place.

[andyhb]

First time I've seen this from the revamped SPC MARS, and remember this is working off the GFS side.

 

[Thundersnow12]

Yeah the spacing is much better on the 12z GFS

 

[Ground Scouring]

Thanks for posting that discussion. Almost every word is very pertinent to our concerns for central US impacts 4/26-28. It sounds like they favor a compromise regarding frontal placement and associated eastern trough amplitude.

 

FWIW, the 12z GFS coming in shifted the New England closed low a lot farther east, which does wonders for warm sector extent. Man, Saturday could be epic High Plains action if everything falls into place.

I'm still rather skeptical, given that the HPC discussion mentioned the fact that even a blend of the GFS and ECMWF ensembles supports a strong polar surface high near Hudson Bay. It's better but far from ideal re: moisture return and could well bust. Additionally, while the 12Z GFS shifts the NE low farther east, it also shows a deeper low, thereby keeping the surface warm front from retreating northward. If, on the other hand, the ECMWF trends toward a broader-based trough, and if the GFS continues to shift the NE low farther east, then I'll consider getting excited. But not now. I'll need to wait for persistence. (I'm personally favoring the ECMWF's handling of the trough, but not by much.)