91 replies to this topic

[Jim Martin]

What an explosive 0z NAM sounding for Topeka, KS valid at 7pm cdt Thursday evening...

[andyhb]

Hmm...

[brettjrob]

Looks like a marginal setup characterized by high CAPE, decent directional shear (at least E of that sounding location), and poor deep-layer shear magnitudes -- in other words, something you'd see day-to-day in late May or June. Could certainly get a surprise or two out of it. Tomorrow also looks similarly interesting across northern KS, with a boundary in play.

[andyhb]

Looks like a marginal setup characterized by high CAPE, decent directional shear (at least E of that sounding location), and poor deep-layer shear magnitudes -- in other words, something you'd see day-to-day in late May or June. Could certainly get a surprise or two out of it. Tomorrow also looks similarly interesting across northern KS, with a boundary in play.

00z NAM actually has some rather impressive deep shear magnitudes (40-60 kts) roughly in East Central/NE KS, West Central/NW MO, SW IA and SE NE on Thursday, especially considering the amount of instability present in the sounding Jim posted.

Here's a dandy of a sounding at Kansas City 00z Thursday evening, more than 90 degrees of turning between the sfc and H5:

[MnWeatherman]

I'm thinking it's a chase worthy system for eastern Kansas/Nebraska

[Thundersnow12]

0z GFS also coming in stronger with that mid-level wave that moves across NE on Thursday which is leading to better wind fields to work with.

[David Reimer]

Weak mid-levels on Wednesday will likely limit any tornado threat and make many of the storms high precipitation. Thursday looks to have some directional shear issues. Honestly, I'm more interested in some potential caprock supercells on Thursday and Friday. Again, no tornado threat but I'm always up for some Caprock supercells.

[andyhb]

I'm thinking it's a chase worthy system for eastern Kansas/Nebraska

If something like the NAM verifies, then I'd have to agree, probably would include Western MO and SW IA possibly too in that zone.

[andyhb]

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1259 AM CDT WED MAR 28 2012

VALID 291200Z - 301200Z

...THERE IS A SLGT RISK OF SVR TSTMS MID AND LOWER MO VALLEY AND
VICINITY...

...SYNOPSIS...
AS A SHORT-WAVE TROUGH MOVES OFF THE NORTHEAST U.S. COAST AND THE
MAIN NERN PACIFIC TROUGH REMAINS OVER THE GULF OF AK...DEAMPLIFYING
FLOW FIELD ALOFT IS FORECAST ACROSS THE U.S. -- WITH THE SHORT-WAVE
TROUGH EXITING THE ROCKIES ACTING TO FLATTEN THE PERSISTENT CENTRAL
U.S. RIDGE.

AT THE SURFACE...A WEAK LOW DEVELOPING INVOF THE MID MO VALLEY WILL
BE THE PRIMARY FEATURE ASSOCIATED WITH MORE ROBUST CONVECTIVE
ACTIVITY THIS PERIOD.

...MID AND LOWER MO VALLEY AND VICINITY...
AREAS OF SCATTERED TO ISOLATED SHOWERS AND THUNDERSTORMS MAY BE
ONGOING AT THE START OF THE PERIOD...WITHIN TWO ZONES OF WARM
ADVECTION -- ONE INTO ERN KS/WRN MO NEAR THE NOSE OF A SWLY BRANCH
OF THE LOW-LEVEL JET...AND ONE OVER THE ERN DAKOTAS REGION IN
CONJUNCTION WITH A SECOND/MORE SLY BRANCH OF THE JET.

AS LARGE-SCALE RIDGING IS SUPPRESSED BY A SHORT-WAVE TROUGH
APPROACHING FROM THE WEST AND WITH DIURNAL HEATING ASSISTING IN
AFTERNOON DESTABILIZATION...NEW STORM DEVELOPMENT IS EXPECTED TO
OCCUR -- LIKELY FOCUSED NEAR A WEAK SURFACE LOW PROGGED TO RESIDE
INVOF THE MID MO VALLEY. WITH TIME...EWD PROGRESS OF THE UPPER
SYSTEM WILL RESULT IN A STEADY EWD/SEWD SHIFT OF THE
CONVECTION...WHICH IS EXPECTED TO SPREAD ACROSS MO AND EVENTUALLY
INTO WRN MO.

WITH AMPLY STRONG/VEERING FLOW WITH HEIGHT ACROSS THIS REGION
SUPPORTING UPDRAFT ORGANIZATION...A FEW SUPERCELLS WILL LIKELY
EVOLVE DURING THE AFTERNOON WITH HAIL AND LOCALLY DAMAGING WINDS THE
MAIN THREATS. OVERNIGHT...STORMS MAY CONGEAL INTO AN MCS --
POSSIBLY ACCOMPANIED BY DAMAGING WIND POTENTIAL AS THE SYSTEM
CROSSES THE MO AND LATER THE MID MS VALLEY.

..GOSS.. 03/28/2012

[Jim Martin]

Here is the 06z NAM sounding for Topeka KS valid Thursday evening at 7pm cdt. Parameters are still up there. There is still some turning of the wind.

[brettjrob]

Here is the 06z NAM sounding for Topeka KS valid Thursday evening at 7pm cdt. Parameters are still up there. There is still some turning of the wind.

Now that's impressive. Much more backing of low-level flow, leading to a near-classic hodograph shape. Hard to ignore >250 m^2 s^-2 of 0-1 km SRH in the presence of high CAPE. The only limiting factor on that forecast sounding is weak storm-relative flow upstairs, but I'd still expect a decent tornado threat if the environment depicted there verifies.

[Thundersnow12]

this was from the 0z 4km WRF

[OceanStWx]

this was from the 0z 4km WRF

This is for later tonight though right?

I was just posting in the 26-28th thread about this area. I just modified the 12z TOP sounding based off their forecast high around Salina and dewpoints in the low 60s. It's a pretty classic loaded gun, and over 3000 J/kg CAPE. Nice and fat in the hail growth zone too.

[OceanStWx]

Posted this in the other severe thread...

Not sure if this is the best place for it (the date is right but the region is a little off in the title), so feel free to move this to the 3/29 thread if you think that is more appropriate.

Subtle disturbance is lifting north across Kansas right now. If you loop a visible satellite you can even see the cyclonic rotation of the low level clouds as they drift north.



Decent environment is setting up along I-70, as heating and moistening of the boundary layer takes place. This disturbance lifting north should only serve to enhance the convergence to its N/NE, right in the Salina vicinity. Very steep mid level lapse rates could produce some monster hail, but low level parameters are such that a tornado or two is entirely possible.

[OceanStWx]

 KTOP_19z.jpg   172.01K   1 downloads

Modified KTOP sounding. Used the 19z obs for Salina, and profiler winds from Hillsboro to modify the hodograph.

[OceanStWx]

Some cells southwest of Topeka are approaching severe thresholds aloft, however dual-pol data showing that there is significant melting occurring below the freezing level. Very high ZDR values suggest a rain/hail mix, or more likely wet hail. Plus, KDP values are extreme, and this commonly happens with wet hail.

[tornadotony]

Some cells southwest of Topeka are approaching severe thresholds aloft, however dual-pol data showing that there is significant melting occurring below the freezing level. Very high ZDR values suggest a rain/hail mix, or more likely wet hail. Plus, KDP values are extreme, and this commonly happens with wet hail.

Very strong mid-level couplet.

[Thundersnow12]

This is for later tonight though right?

I was just posting in the 26-28th thread about this area. I just modified the 12z TOP sounding based off their forecast high around Salina and dewpoints in the low 60s. It's a pretty classic loaded gun, and over 3000 J/kg CAPE. Nice and fat in the hail growth zone too.

correct.

svr warning out now for sw of TOP.

[Thundersnow12]

base ref at the sfc and the strong mid-level meso

[OceanStWx]

 KTWX_2158.png   672.9K   0 downloads

70 dBZ over 20kft, near zero ZDR in the vicinity as well. Good sign for large hail aloft.

Also if you look to the west of that hail signature on the elevation angle just below it, you'll see a ZDR column (high ZDR - liquid water) indicating where the updraft is.

[SouthernNJ]

I would imagine it is quite scary in Harveyville right about now.
Does not even have to be a particularly intense storm either.

[Jim Martin]

From radar data... it appears the damaging hail core is just E of Harveyville. If I recall correctly... didn't they get a tornado there earlier this year?

[OceanStWx]

I would imagine it is quite scary in Harveyville right about now.
Does not even have to be a particularly intense storm either.

Quite the opposite, that cell has another impressive ZDR column (strong updraft), and that is just now starting to manifest in hail reaching the ground. This is not of the "wet" variety either, ZDR values are near zero so this is mostly just hail east of I-335. Probably getting upwards of significant hail size too.

[Buckeye05]

From radar data... it appears the damaging hail core is just E of Harveyville. If I recall correctly... didn't they get a tornado there earlier this year?

Yeah, large EF2 damaged or destroyed most of the structures there and killed 1 person during the Feb 29 outbreak.

[Jim Martin]

Is it me... or is this supercell starting to split?

[Thundersnow12]

Is it me... or is this supercell starting to split?

it looks like the western updraft threw off a left split that died and now the eastern updraft is becoming more dominant.

[Jim Martin]

This is what I was just referring to about this supercell...

[Jim Martin]

It appears the supercell S of Topeka is turning to the right some... velocities have increased as well on latest scan...

[SouthernNJ]

Looks like some big hail possible around the Scranton KS area.

[OceanStWx]

This is what I was just referring to about this supercell...

Both are showing mid level cyclonic rotation, so the northwestern cell is not a split of the southeastern one in all likelihood. I do believe the northwestern cell tried to throw off a left split, which did quickly weaken though.

[SouthernNJ]

The storm southwest of Manhattan KS is also beginning to rotate
a bit as it attempts to strengthen.

[OceanStWx]

 KTWX_2213.png   1.15MB   1 downloads

To further illustrate the left split (which occurred about a half hour ago) here is a dual-pol aided four panel.

You can see three (albeit one very weak) SRM couplets in the bottom left window. One west of Burlingame, one west of Harveyville (both cyclonic) and another north of Eskridge (very weak, and anticyclonic). One the top right window, you can see ZDR at 4.4 degrees (about 5-7kft depending on which cell you are sampling). You can see three ZDR columns, indicating where the respective updrafts are. I have placed the red marker on top of the left split updraft, while the other two are again west of Harveyville, and Burlingame.

[OceanStWx]

The storm near Scranton is actually trying to gets its act together in the lower levels now. Weak, but slowly organizing meso at 0.5 degrees now.

[Thundersnow12]

awesome overshooting top with the storm south of EMP.

[OceanStWx]

awesome overshooting top with the storm south of EMP.

This is my favorite time of day for the visible satellite.