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


andyhb

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Wow, the 00z ECMWF would be a blockbuster outbreak across the Plains, as would the 00Z UKMET run. As mentioned before, it looks like the GFS is on its own island now w.r.t. not ejecting a piece of the trough on Saturday. Still 4 days out, so there's a lot of details to be resolved, and those details are going to be important because the ejection of the vort max is necessary to amplify the low-level wind fields for the low-level shear. But the Saturday event in particular has a very high ceiling IMO.

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While on the discussion about Saturday, I feel it relevant to point out we have several high-profile events ongoing this weekend in D/FW. One of those events is NASCAR at Texas Motor Speedway, which is northwest of Fort Worth.

:unsure::yikes: That doesn't sound good.

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Thursday looks awesome. Large hodos and dryline/warm front setup can't get any better. SPC feeling a bit timid...should beef it up by tomorrow.

One word >> Moisture.

But yeah if that possible caveat works itself out, (like the NAM suggests) then Thursday could be big in the region where some of those soundings were pulled earlier.

Either way, this is the type of setup with fast moving Plains storms where I become very concerned regarding chaser convergence, since if that Saturday setup verifies, the amount of chasers out is going to be insane.

I mean, a possible significant outbreak in prime chaser country, on the weekend...

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Friday. Timmer should also be concerned considering these things could be targeting where he lives.

2iux3wz.jpg

...OK/KS...

A DRY LINE IS EXPECTED TO EXTEND SWD FROM THE NEB SURFACE LOW

THROUGH CENTRAL KS...WRN OK...THEN SWWD INTO SW TX AT 12Z FRI.

GFS/ECMWF SUGGEST THIS BOUNDARY SHIFTS A LITTLE EWD FRI MORNING...

BUT BACKING/STRENGTHENING LOW LEVEL WINDS IN RESPONSE TO SURFACE

PRESSURE FALLS WITH THE LEE TROUGH ARE EXPECTED TO SUPPORT MOISTURE

RETREATING WNWWD. SURFACE DEWPOINTS IN THE LOWER 60S SHOULD EXTEND

INTO WRN/NWRN OK BY LATE FRI AFTERNOON AND THEN INTO CENTRAL KS FRI

EVENING AS THE SLY LLJ UNDERGOES FURTHER STRENGTHENING.

MOST MODELS INDICATED CONVECTION/TSTM DEVELOPMENT COULD OCCUR PRIOR

TO PEAK HEATING /BY 18Z/ ACROSS THE WARM SECTOR FROM N TX THROUGH OK

TO ERN KS. INCREASING INSTABILITY AND SUFFICIENT DEEP LAYER SHEAR

WOULD SUPPORT ORGANIZED STRONG TO SEVERE STORMS WITH THIS ACTIVITY.

ADDITIONAL TSTM DEVELOPMENT IS THEN EXPECTED WNWWD LATER FRI

AFTERNOON AS THE BOUNDARY LAYER MOISTENS ALONG AND E OF THE

RETREATING DRY LINE. STRONG SURFACE HEATING INVOF THIS BOUNDARY AND

BENEATH STEEP MIDLEVEL LAPSE RATES SHOULD ALLOW FOR STRONGER

INSTABILITY. STRENGTHENING SWLY MIDLEVEL AND SLY LOW LEVEL WINDS

ACROSS WILL RESULT IN EFFECTIVE BULK SHEAR UP TO 50 KT ORIENTED

PERPENDICULAR TO THE DRY LINE LINE...SUPPORTING THE POTENTIAL FOR

TORNADIC SUPERCELLS WITH ADDITIONAL THREATS FOR VERY LARGE HAIL AND

DAMAGING WINDS. GIVEN THE STRENGTHENING WIND FIELDS INTO THE

EVENING...SEVERE WEATHER THREATS ARE EXPECTED TO PERSIST AFTER DARK

INCLUDING A THREAT FOR TORNADOES.

THE EARLY WAVE AND IMPACT OF THE MORNING/EARLY AFTERNOON STORMS

COULD AFFECT OVERALL DESTABILIZATION...AND THUS LOWER PROBABILITIES

WILL BE MAINTAINED...BUT HIGHER PROBABILITIES MAY BE NEEDED IN LATER

OUTLOOKS.

..PETERS.. 04/11/2012

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And the latest Day 4-8 maintains a large area for Saturday.

29bfwae.jpg

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0400 AM CDT WED APR 11 2012

VALID 141200Z - 191200Z

...DISCUSSION...

THE GFS/ECMWF EACH MAINTAIN A TROUGH IN THE WEST WITH SWLY FLOW

EXPECTED TO BE STRONGER THAN D3/FRI ACROSS OK/KS TO MO/IA...WHILE

THE STRONGEST FLOW ON D5/SUN GENERALLY EXTENDS FROM W TX INTO KS.

THE GFS CLOSES A LOW ACROSS THE FOUR CORNERS REGION ON D4 SHIFTING

IT ENEWD INTO CO/NM ON D5/SUN...WHILE THE ECMWF MAINTAINS THE SRN

EXTENT OF THE WRN TROUGH AS AN OPEN WAVE. DESPITE THESE

DIFFERENCES...THE OVERALL MOISTURE DISTRIBUTION WITHIN THE WARM

SECTOR IS SIMILAR FOR D4 WITH A SURFACE LOW LOCATED ACROSS WRN KS IN

AGREEMENT WITH THE MREF. GIVEN THESE SIMILARITIES FOR D4 WITH EACH

MODEL INDICATING STRONG VERTICALLY VEERING WIND FIELDS...A REGIONAL

SEVERE WEATHER THREAT AREA WILL BE MAINTAINED FOR SAT APR 14 FROM N

TX THROUGH MUCH OF OK...CENTRAL/ERN KS INTO NWRN MO/SWRN IA/SERN

NEB. TORNADIC SUPERCELLS ALONG WITH VERY LARGE HAIL AND DAMAGING

WINDS CAN BE EXPECTED ACROSS THIS REGION.

MODEL DIFFERENCES BEYOND D5 PRECLUDE THE INCLUSION OF ANY ADDITIONAL

REGIONAL SEVERE WEATHER THREAT AREAS AS THE WRN TROUGH SHIFTS EWD.

STRONG TO SEVERE STORMS MAY OCCUR EACH DAY AS EXTENSIVE CONVECTION

IS EXPECTED FROM PARTS OF TX THROUGH THE LOWER-MID MS VALLEY TO OH

VALLEY THROUGH EARLY NEXT WEEK.

..PETERS.. 04/11/2012

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This is why the SPC is holding back on highlighting areas after Day 4. It's also another reason why I've been on the mindset that the NHC needs to continue Pacific Flights during the severe weather season. No sampling means model variability!

post-1598-0-05910300-1334147281.jpg

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This is why the SPC is holding back on highlighting areas after Day 4. It's also another reason why I've been on the mindset that the NHC needs to continue Pacific Flights during the severe weather season. No sampling means model variability!

The NHC does not task flights for the Pacific for severe weather or winter storms. Also with budget constraints, NOAA G-IV missions are becoming very difficult to come by.

Edit to add: We probably need to extend the severe threat for the 16th as well...;)

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Here is an overlay I have of 0-4 km theta-e lapse rates and 300 mb jet speed. Generally speaking the overlap in the two is good for severe weather.

This is the 11/06z GFS run, and it is the first to really show the overlap along the warm front in Iowa into Illinois. Between 70 and 90 knots on the southern fringe of the main jet core over the top of -4 to -5 deg/km would be more than sufficient for warm frontal action.

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Although it's the 16th, eastern TX could be kind of interesting with that setup.

I agree. The local chatter (EWX/HGX/FWD/LCH/SHV) has been rather interesting for several days for points along and E of the I-35 Corridor.

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0zNAMHLCSounding.png

Here is the Hill City, KS 0z NAM sounding valid at 7pm cdt Thursday evening.

I know I'm late on this, but wow. I haven't seen as many soundings as many others here but that is astounding... Not incredibly amazing on the instability front but the wind profile looks as good as it possibly could.

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While on the discussion about Saturday, I feel it relevant to point out we have several high-profile events ongoing this weekend in D/FW. One of those events is NASCAR at Texas Motor Speedway, which is northwest of Fort Worth.

Verbatim, Euro QPF is nuisance rains until after the race should be over Saturday night. AFW is the location for looking up forecast soundings, only ~5 miles from TMS.

I'm glass half full optimistic that the races themselves will be ok. The large crowd that attends in motor homes and will no doubt stay at least until Sunday morning might be another issue.

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I'm in awe of the 12z NAM. I've never seen a multi-day event quite like this forecast for the southern Plains, no matter the time of year. Saturday has the makings of a monster day that could find its way onto lists with impressive company. Confidence in that sort of outcome is beginning to increase, too, with prior convective evolution the only major caveat I see right now.

I think if a student were asked to draw a classic OK/KS outbreak scenario and traced the kinematics and thermodynamics from the 12z NAM for 00z Sunday, they'd get extra credit.

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I'm in awe of the 12z NAM. I've never seen a multi-day event quite like this forecast for the southern Plains, no matter the time of year. Saturday has the makings of a monster day that could find its way onto lists with impressive company. Confidence in that sort of outcome is beginning to increase, too, with prior convective evolution the only major caveat I see right now.

I think if a student were asked to draw a classic OK/KS outbreak scenario and traced the kinematics and thermodynamics from the 12z NAM for 00z Sunday, they'd get extra credit.

Kansas I-35 corridor, >2000 J/Kg MUCape, 25 m/s (~50 knots) deep layer shear, and backed low level winds, I almosr regret being away from the TV/computer Saturday evening.

NAMCN_CE2012041112F084.gif

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While we're talking about high profile events, the Oklahoma Sooners have their Red & White spring football game at 2 p.m. on Saturday, so about 30,000 extra people will be in Norman...

Same deal in Lincoln, Nebraska. Nebraska Cornhuskers football Spring game - kickoff at 1 pm. Add another 50,000 or so to Lincoln, all trying to drive home to various places in Omaha, Grand Island, Hastings, Kansas City, etc... at 5 pm.

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Confidence in that sort of outcome is beginning to increase, too, with prior convective evolution the only major caveat I see right now.

With the strength of theta-e inflow I'm not sure how much that is going to negatively affect this, there also could be major OFB problems here.

I just saved that image that Ed posted, that is disgusting...

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