April 12th/13th and 15-16th Severe Weather Thread

[andyhb]

A potentially more substantial severe threat looks to return next Thursday, where a strong shortwave looks to eject ahead of the developing large Eastern Pacific trough. Thanks to relatively good model agreement this far out, the SPC has issued a relatively rare Day 6 area for the Red River Valley northward through large portions of KS and OK, it also hints at the potentially even more significant threat into the weekend as the large western trough itself looks to move eastward. Either way, things look to become more active as this ridge that has caused problems with the last few systems looks to no longer maintain itself as the dominant upper air feature across the CONUS. Will keep this thread focused on the early/mid week events for the time being, while uncertainties with the larger weekend system are worked out to greater detail over the next few days.

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0359 AM CDT SAT APR 07 2012

VALID 101200Z - 151200Z

...DISCUSSION...

MEDIUM RANGE MODELS REMAIN IN GENERAL AGREEMENT EARLY IN THE

EXTENDED OUTLOOK PERIOD...SHOWING A LONGWAVE TROUGH LINGERING OVER

THE ERN STATES THROUGH D5/WED. MEANWHILE...THE ROCKIES RIDGE WILL

SHIFT EWD INTO THE CENTRAL STATES...WHILE THE UPSTREAM ERN PACIFIC

TROUGH ADVANCES INLAND SUPPORTED BY A PROGRESSIVE BASAL SHORTWAVE

TROUGH APPROACHING SRN CA BY THE START OF D5/WED. THIS LATTER

SYSTEM WILL MOVE THROUGH THE FOUR CORNERS TO CENTRAL HIGH PLAINS ON

D5 BREAKING DOWN THE RIDGE OVER THE HIGH PLAINS.

REGIONAL SEVERE WEATHER THREAT AREAS /30 PERCENT OR GREATER/ ARE NOT

EXPECTED ON D4/TUE OR D5/WED...THOUGH SOME SEVERE STORMS CAN BE

EXPECTED ON D4 ACROSS THE SRN PLAINS...SIMILAR TO WHAT IS EXPECTED

ON D3/MON. SEVERE STORMS WILL ALSO BE POSSIBLE ON D5 OVER THE SRN

AND CENTRAL HIGH PLAINS...BUT LIMITED MOISTURE RETURN WITH NWD

EXTENT SHOULD PRECLUDE THE NEED FOR A REGIONAL SEVERE WEATHER

THREAT.

ALTHOUGH THE GFS/ECMWF DIFFER IN THE TRACK OF THE D4/D5 BASAL

SHORTWAVE TROUGH AS IT EMERGES INTO THE PLAINS WITH THE GFS

MAINTAINING A MORE NRN BIAS...EACH MODEL SHOWS STRONGER SWLY FLOW

ACROSS OK/KS DURING D6/THU ATOP STRONGER SLY LLJ. THESE FAVORABLE

WIND FIELDS/DEEP LAYER SHEAR COMBINED WITH MODERATE INSTABILITY

GIVEN MOISTURE RETURN SUPPORTS A REGIONAL SEVERE WEATHER THREAT AREA

ON D6/THU ACROSS MUCH OF OK INTO CENTRAL AND ERN KS.

BEYOND D6...MODELS ARE SUGGESTING ANOTHER ACTIVE SEVERE WEATHER DAY

COULD DEVELOP ON D8/SAT ACROSS THE SRN PLAINS INTO KS AS THE NEXT

PACIFIC TROUGH ADVANCES INLAND INTO THE PLAINS...BUT TIMING

DIFFERENCES PRECLUDES INTRODUCING ANOTHER REGIONAL SEVERE WEATHER

THREAT AREA.

..PETERS.. 04/07/2012

[baroclinic_instability]

I am actually surprised they are highlighting (I ma not questioning their judgment, just surprised) a day 6 for this setup. A lot of potential problems may exist (day 5+) whenever you have deamplifying waves in SW flow flattening a high amplitude shortwave ridge axis.

[thewxmann]

I feel like SPC's really been much more bullish on the Day 3-8 outlook ever since the March 2 event. Maybe they had some in-house discussion about the outlooks?

[Superstorm93]

...STRONG/DYNAMIC

SHORTWAVES ROUND THE BASE OF THE WEST COAST TROUGH AND TRACK

TOWARDS THE PLAINS ON THURSDAY AND SATURDAY...GULF MOISTURE IS

TAPPED...LEADING TO ADDITIONAL ROUNDS OF POSSIBLY SEVERE

THUNDERSTORMS

Saturday certainly looks interesting.

[Chicago Storm]

I'm more interested in what happens from Thurs into next weekend...chase wise.

[wx_chip]

Mid-week introduces persistant troughing in the west for quite some time. The placement and strength of these will all be influenced greatly by where and how strong the ridge over the mid-west sets up to be. Should it shift west more or deepen greater than expected, the severe wx threat would be greatly mitigated.

Chip

[andyhb]

Mid-week introduces persistant troughing in the west for quite some time. The placement and strength of these will all be influenced greatly by where and how strong the ridge over the mid-west sets up to be. Should it shift west more or deepen greater than expected, the severe wx threat would be greatly mitigated.

I see very little reason for it to be as strong as it has been for the past few systems.

I am actually surprised they are highlighting (I ma not questioning their judgment, just surprised) a day 6 for this setup. A lot of potential problems may exist (day 5+) whenever you have deamplifying waves in SW flow flattening a high amplitude shortwave ridge axis.

I was certainly more concerned about the first system with the 12z Euro's verbatim yesterday, that thing was nasty.

Pretty impressive look on the 12z GFS with the big late week system...

Added the weekend to the thread, considering what I've been seeing with the several runs of the GFS/Euro/ensembles over the past few days. The thread can also probably be limited to Thursday on at this point, any severe threads for the Monday-Wednesday threats can be made if they should be needed to.

12z GFS ensembles at 156, some of them are even more impressive than the OP (Particularly member P003). Most of the ones that hold back on the trough on Friday eject it on Saturday in some form.

Seeing a sub-995 mb SLP on an ensemble mean 156 hrs out tends to be an indication of trouble...

[andyhb]

DDC putting in some impressive wording for Friday/next weekend:

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE DODGE CITY KS

1200 PM CDT SAT APR 7 2012

.LONG TERM...(SUNDAY THROUGH FRIDAY)

ISSUED AT 418 AM CDT SAT APR 7 2012

AFTER THIS SYSTEM PASSES,

UPPER-LEVEL TROUGHINESS WILL RELOAD ACROSS THE WESTERN UNITED

STATES. WITH PLENTY OF LOW-LEVEL MOISTURE CLOSE BY, THUNDERSTORMS

WILL BE A POSSIBILITY AS THIS SYSTEM GETS CLOSER BY FRIDAY NIGHT OR

SATURDAY. THESE STORMS HAVE A MUCH BETTER CHANCE OF BEING SEVERE. IN

FACT, THE SURFACE AND UPPER-LEVEL PATTERN ALONG WITH MOISTURE

AVAILABILITY WILL ALL BE NEARLY IDEAL FOR OUTBREAKS OF SEVERE

THUNDERSTORMS NEXT WEEKEND. OF COURSE, GIVEN THAT THIS IS STILL A

WEEK AWAY, IT IS NOT CLEAR EXACTLY WHERE IN THE PLAINS THE

SEVERE WEATHER WOULD BE CONCENTRATED.

TornadoTitans' blog: http://www.tornadotitans.com/blog/2012/04/07/169-prime-time-chasing-next-week

[Chinook]

I bet you could make an argument that there will be severe weather on Thursday, Friday, and Saturday.

[andyhb]

Maybe Sunday too...this trough looks pretty damn large, so accordingly it's going to have multiple vort maxes/shortwaves/ULLs rotating around it.

[PatrickSumner]

Maybe Sunday too...this trough looks pretty damn large, so accordingly it's going to have multiple vort maxes/shortwaves/ULLs rotating around it.

I know this thread is in the Central/Western section, but is there a threat for the Ohio Valley/Great Lakes region? Which day in particular would be of interest if so?

[andyhb]

I know this thread is in the Central/Western section, but is there a threat for the Ohio Valley/Great Lakes region? Which day in particular would be of interest if so?

I would've posted it there if there was. The GL/OV/SE possible threat of this system is bit more dependent on the ridge's movement/deamplification than the Plains/Ozarks portion. For now will keep this in C/W. If any threat does manifest further east it would probably be on Saturday to Monday/Tuesday.

Not to get frisky, but you seem to post this exact thing every time there is any possible severe threat somewhere around the CONUS...

[PatrickSumner]

I would've posted it there if there was. The GL/OV/SE possible threat of this system is bit more dependent on the ridge's movement/deamplification than the Plains/Ozarks portion. For now will keep this in C/W. If any threat does manifest further east it would probably be on Saturday to Monday/Tuesday.

Not to get frisky, but you seem to post this exact thing every time there is any possible severe threat somewhere around the CONUS...

I'll be sure not to ask anymore questions. I cannot believe how rude and insensitive a majority of people are on this forum. Good day.

[andyhb]

Um...how was my post rude or insensitive at all?

[Thundersnow12]

I would've posted it there if there was. The GL/OV/SE possible threat of this system is bit more dependent on the ridge's movement/deamplification than the Plains/Ozarks portion. For now will keep this in C/W. If any threat does manifest further east it would probably be on Saturday to Monday/Tuesday.

Not to get frisky, but you seem to post this exact thing every time there is any possible severe threat somewhere around the CONUS...

Damn dude...can i pick apart you now?

[andyhb]

With the second part, I'm simply making an observation, something similar to what hm did in a previous thread.

Every one of your posts in this thread have been something like this. Take some time and read what others are saying and you'd get your answer.

The first part I guess could taken across as a little uncalled for, but I don't think it was that insensitive, just stating that if there was one in the GL/OV, I would've posted it there.

[Srain]

~sigh~

[Indystorm]

Very powerful jet rounding the trough in this indicated time frame. If this pans out we certainly won't have to worry about lack of upper air support as was a concern with some recent opportunities.

[andyhb]

Very powerful jet rounding the trough in this indicated time frame. If this pans out we certainly won't have to worry about lack of upper air support as was a concern with some recent opportunities.

Agreed strongly.

[Chinook]

Um...how was my post rude or insensitive at all?

Please don't get into a flame war after one question was asked. Remember, the Western/Central Forum is friendly.... unlike some other regional forums.

[Crazieman]

Even the typically cold-water splashing ICT is somewhat bullish on this event.

THURSDAY-SATURDAY...THOUGH THERE REMAINS CONSIDERABLE UNCERTAINTY

SURROUNDING SPECIFIC DETAILS...MEDIUM RANGE CONSENSUS CONTINUES TO

SUGGEST A FAIRLY ACTIVE PATTERN SEVERE WEATHER-WISE COULD SET UP

ACROSS MID-AMERICA LATE WEEK INTO THE WEEKEND...AS A WESTERN CONUS

LONGWAVE TROUGH EJECTS VARIOUS SHORTWAVES NORTHEAST ONTO THE PLAINS.

FORECASTED INSTABILITY AND SHEAR PARAMETERS WOULD SUPPORT SEVERE

WEATHER...POSSIBLY HIGHER END ACTIVITY. HOWEVER...RUN-TO-RUN AND

MODEL-TO-MODEL CONSISTENCY REMAINS POOR. PLEASE CHECK BACK OVER THE

NEXT FEW DAYS AS DETAILS SHOULD START TO BECOME CLEARER.

[jdrenken]

The potential is definitely there...pending the feature hitting the West Coast will determine specifics for the first segment.

Uploaded with ImageShack.us

[andyhb]

Please don't get into a flame war after one question was asked. Remember, the Western/Central Forum is friendly.... unlike some other regional forums.

Yeah I didn't mean to come across that way.

[andyhb]

Friday and Saturday both look pretty impressive across the Plains and perhaps into the Ozarks on the 00z GFS.

Actually Saturday looks to bring moisture quite far north, there's 65 dews all the way into Northern IA. These large positively tilted troughs that eject strong upper/mid level speed maxes on their east side tend to create a lot of problems.

12z SPC MARS popping some big numbers for Friday/Saturday, especially on the PWAT analogs:

Sunday looking good too.

[nwburbschaser]

The models will be interesting to watch leading up to this. Hopefully the models come into agreement early on this because I want to get out this weekend, but if I want to get Friday off work then this Monday is the deadline to decide.

Always tough early in the year not to jump the gun and use a personal day whenever a weekend set up starts looking good.

[Indystorm]

Any time I see a 110-130 knot 300 mb jet streak in the Plains with other parameters starting to come into place like I do for an extended period late this coming week per this 00z GFS I go into heads up mode.

[andyhb]

All three major models and many of the ensembles agreeing on a substantial looking threat at some point from Friday to Sunday, GGEM is a bit slower and brings the main threat Sunday and Monday.

[andyhb]

First time I've seen the Day 7 in quite awhile:

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0359 AM CDT SUN APR 08 2012

VALID 111200Z - 161200Z

...DISCUSSION...

ALTHOUGH MEDIUM RANGE MODELS /00Z ECMWF AND GFS/ DIFFER IN THE TRACK

OF A TROUGH INTO THE CENTRAL U.S. ON D5/THU AND TO SOME DEGREE ON

D7/SAT...THESE MODELS DO AGREE IN A PATTERN CHANGE ACROSS THE CONUS

FROM MID WEEK TO NEXT WEEKEND. A BLOCKING PATTERN WITH A NWLY FLOW

REGIME OVER THE CENTRAL TO SERN U.S. WILL PERSIST INTO D4/WED WITH A

THREAT FOR SEVERE STORMS ACROSS THE SRN AND CENTRAL HIGH PLAINS.

THE PATTERN CHANGE BEGINS ON D5 AS SWLY FLOW DEVELOPS INTO THE

PLAINS DOWNSTREAM OF A LONGWAVE TROUGH EVOLVING OVER THE WRN STATES

THROUGH THE REST OF THE EXTENDED PERIOD.

FOR D5/THU...THE GFS AND ECMWF CONTINUE TO DIFFER WITH THE TRACK OF

THE SHORTWAVE TROUGH FROM LATE D4/WED THROUGH D5. ALTHOUGH THE GFS

IS MAINTAINING A NRN TRACK BIAS WITH WEAKER FORCING ACROSS

KS/OK...THE WARM SECTORS IN EACH MODEL ARE SIMILAR. NORMALLY THESE

TYPES OF MODEL VARIANCES IN THE MID-UPPER LEVELS WOULD RESULT IN NOT

INCLUDING A REGIONAL SEVERE WEATHER THREAT AREA. HOWEVER...GFS

FORECAST SOUNDINGS SUGGEST THE POTENTIAL FOR SUPERCELLS ALONG THE

DRY LINE...BUT WITH LOWER COVERAGE. THIS FACTOR COMBINED WITH THE

FORECAST FOR STRONGER WIND FIELDS PER THE ECMWF SUGGESTS THE

REGIONAL SEVERE WEATHER THREAT AREA WILL BE MAINTAINED INTO D5 WITH

THE POTENTIAL FOR LARGE HAIL AND TORNADOES.

THE MODEL DIFFERENCES WITH THE TRACK OF THE D5/THU TROUGH AFFECT THE

SEVERE WEATHER FORECAST FOR D6/FRI...WITH THE GFS FAVORING A MORE

NRN TRACK ACROSS KS/NEB INTO IA...WHILE THE ECMWF INDICATED A

GREATER THREAT FARTHER TO THE SSE.

FOR D7/SAT...THE GFS/ECMWF ARE IN BETTER AGREEMENT AGAIN WITH

RESPECT TO THE DISTRIBUTION OF LOW LEVEL MOISTURE AND WARM SECTOR

SETUP ACROSS TX INTO KS. GREATEST JUXTAPOSITION OF INSTABILITY AND

STRONG DEEP LAYER SHEAR SUPPORTS ANOTHER REGIONAL SEVERE WEATHER

THREAT AREA SIMILAR TO D5 ACROSS OK/KS.

..PETERS.. 04/08/2012

Morning AFDs beginning to hit a bit harder on the threat:

TSA:

MODEL EVOLUTION OVER THE PAST 24 HOURS HAS STRENGTHENED A PROGGED

DEVELOPING TROUGH ALONG THE WESTERN CONUS LATE IN THE WEEK. THIS

SYSTEM SHOULD BEGIN TO AFFECT THE FORECAST AREA BY FRIDAY INTO THE

WEEKEND. THE CURRENT PROGGED PATTERN WOULD SUPPORT SEVERE WEATHER

AND/OR A HEAVY RAINFALL EVENT ACROSS OUR AREA. THIS POTENTIAL WILL

BE MONITORED CLOSELY AS THE WEEK PROGRESSES.

OUN:

ACTIVE WEATHER

PATTERN WILL CONTINUE THROUGH MIDWEEK WITH FRONTAL BOUNDARY AND

MOISTURE LINGERING IN THE AREA. BY LATER IN THE WEEK UPPER RIDGE

AXIS SHIFTS EASTWARD WITH UPPER TROUGH DEVELOPING OVER THE WESTERN

U.S. THUNDERSTORM CHANCES WILL CONTINUE INTO THE WEEKEND AS THIS

SYSTEM MOVES SLOWLY EASTWARD WITH PATTERN FAVORABLE FOR SEVERE

STORM DEVELOPMENT.

ICT:

REST OF WORK-WEEK:

OVERALL THE OUTLOOK FOR THESE PERIODS IS ESSENTIALLY UNCHANGED. THE HIGH

AMPLITUDE RIDGE WILL GET FORCED E FROM ROCKIES ACROSS THE GREAT PLAINS

DURING MID-WEEK AS A MID-UPR CYCLONE IS PROGGED TO STRENGTHEN OVER WY &

MT WHERE IT MAY GYRATE THE LATTER HALF OF THE WEEK. LWR-DECK TROFFING

WILL STRENGTHEN CONSIDERABLY DURING THESE PERIODS TO ENABLE RICH GULF

MOISTURE TO STREAM NORTH ACROSS THE SRN & CNTRL PLAINS. WITH DEEP-LAYER

SHEAR GREATLY INCREASING THE SVR TSRA POTENTIAL IS LIKEWISE INCREASING

FOR MOST OF KS THU & THU NGT.

NEXT WEEKEND:

THE NEXT MID-UPR WAVE IS PROGGED TO DIG SHARPLY OVER THE WEST COAST FRI

NGT BEFORE UNDERGOING CYCLOGENESIS AS IT PUSHES E OVER THE GREAT BASIN.

A STRONG ~120KT UPR-LVL JET MAX WILL ROUND THE BASE OF THE TROF & SPREAD

NE OVER KS SAT & SAT NGT. AS RESULT SVR TSRA POTENTIAL MAY EXTENDED WELL

INTO NEXT WEEKEND. STAY TUNED>

DDC:

THIS SHORTWAVE TROUGH WILL

BE PASSING ACROSS THE CENTRAL PLAINS IN NEGATIVE TILT FASHION BY

THURSDAY AS THE MAIN LONGWAVE TROUGH STILL HANGS BACK NEAR THE WEST

COAST. THE ECMWF IS THE FURTHEST SOUTH WITH THIS SHORTWAVE TROUGH

WHILE THE GFS/GEM ARE FURTHER NORTH. GIVEN THE PROGRESSIVENESS OF

THIS SYSTEM AND THE STRONG ZONAL MOMENTUM, IT WILL BE VERY DIFFICULT

TO GET THUNDERSTORMS WEST OF THE 100TH MERIDIAN. CURRENT THINKING IS

THAT THE THUNDERSTORM ACTIVITY ON THURSDAY AFTERNOON AHEAD OF THE

DRYLINE AND WARM FRONT WILL BE ALONG AND EAST OF A LINE FROM HAYS TO

MEDICINE LODGE, AND POSSIBLY FURTHER EAST THAN THIS. GIVEN THE

STRONG SHEAR AND HIGH DEWPOINTS, THESE STORMS COULD BE SEVERE WITH

LARGE HAIL AND POSSIBLY EVEN TORNADOES. ONE LIMITING FACTORS FOR

HIGH-END SEVERE COULD BE THE PRESENCE OF WIDESPREAD STRATUS IN THE

WARM SECTOR, WITH ONLY A NARROW CORRIDOR OF STRONG INSTABILITY AHEAD

OF THE DRYLINE. AFTER THIS SYSTEM PASSES, A WEAK COLD FRONT MAY PUSH

THROUGH SOUTHWEST KANSAS. HOW FAR SOUTH THIS FRONT GETS WILL DEPEND

ON THE SOUTHERN EXTENT OF THE SHORTWAVE TROUGH WHICH WE ALREADY SAID

WAS NOT AT ALL CERTAIN. BUT BEHIND THIS SYSTEM, FAIR WEATHER SHOULD

PREVAIL ON FRIDAY WITH FAIRLY MILD HIGH TEMPERATURES IN THE 60S TO

70S.

THE MAIN LONGWAVE TROUGH WILL BEGIN TO MOVE EASTWARD INTO THE

SOUTHWESTERN UNITED STATES BY SATURDAY. LOW-LEVEL MOISTURE WILL

ADVECT NORTHWARD ONCE AGAIN AHEAD OF THIS SYSTEM INTO SOUTH CENTRAL

AND CENTRAL KANSAS. AGAIN, GIVEN THE STRENGTH OF THIS SYSTEM AND

STRONG WEST-SOUTHWESTERLY MOMENTUM AT MID-LEVELS, THE BEST CHANCE OF

SEVERE STORMS WILL AGAIN BE ALONG AND EAST OF A LINE FROM HAYS TO

MEDICINE LODGE, WITH MINIMAL CHANCES IN FAR WESTERN KANSAS.

SGF:

THERE COULD BE SOME

SEVERE WEATHER ACROSS THE CENTRAL PLAINS STATES BY THURSDAY

HIGHLIGHTED WITH SPC DAY 6 OUTLOOK BUT TOO EARLY TO SAY IF THIS

ACTIVITY WILL MOVE INTO THE OZARKS REGION. THIS WILL BE SOMETHING

TO WATCH OVER THE NEXT FEW DAYS.

THE MODEL GUIDANCE IS SUGGESTING A MORE ACTIVE WEATHER PATTERN FOR

THE AREA NEXT WEEKEND WITH A STRONGER AND MORE SOUTHERN TRACK

SYSTEM MOVING OUT ACROSS THE CENTRAL PLAINS INTO THE MIDWEST NEXT

WEEKEND. THIS COULD BE A BETTER SETUP FOR SOME SEVERE WEATHER FOR

THE REGION. IT IS TOO EARLY TO PINPOINT DOWN TIMING AND DETAILS

BUT IT WILL BE SOMETHING TO WATCH IN LATER MODEL GUIDANCE AS WE

GET CLOSER TO NEXT WEEKEND. OVERALL...EXPECT A MORE ACTIVE AND

STORMY WEATHER PATTERN FOR LATE NEXT WEEK WITH TEMPERATURES

WARMING UP ABOVE NORMAL.

[thewxmann]

Has SPC ever issued a Day 7 area?

[andyhb]

I remember they would issue extended period threats covering more than one day, although I'm pretty sure last year did not have a 7 day risk issued at all (or even a 6 day risk). I'm pressed to remember whether 2010 did either. I remember 2/5/08 had a 6 day risk area highlighted. 4/27 last year was 5 days.

Ah found one, 5/31 of 2008 for June 6th.