2012 Atlantic Hurricane Season Birdseye Discussion #4

By: NCHurricane2009 , 10:32 PM GMT on April 15, 2012

...APRIL 15 2012...
1013 mb low frontal low forms east of Bermuda...subtropical cyclone formation possible beginning on April 17

This is the fourth birdseye discussion of the 2012 Atlantic Hurricane Season. See the previous discussion concerning the idea behind this new type of discussion forum.


This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1323Z-released HPC analysis.

In light blue is upper air anlaysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicating surface lows, Hs indicating surface highs.


This chart is generated using GOES water vapor satellite imagery.

Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

The SW US surface cyclone reponsible for severe weather over western Oklahoma, Kansas, eastern Nebraska, and parts of Iowa yesterday has continued to deepen, and reached 989 mb at the Kansas/Nebraska border as shown in the above charts. The 989 mb cyclone is being supported by strong divergence ahead of the west US upper trough which has now moved into the eastern Rocky Mountains. Vigorous cool air advection behind the 989 mb cyclone in turn has amplified the western US upper trough, and the upper trough now features a vort max (upper low) over western Nebraska. This 989 mb cyclone continues to be dangerous today as it produces southerly flow pushing in low-level warmth/moisture, which collides with cooler upper westerly flow en route to east US upper ridge, favoring directional wind shear and instability for severe weather across Missouri, Iowa, Minnesota, and Arkansas where tornado watches have been in effect. A summary of yesterday's severe weather produced by this 989 mb cyclone is provided in the final section of today's discussion.

Upper divergence is present well SE of the west US upper trough supporting the 989 mb cyclone. Normally the Mexican monsoonal surface trough/low is outside of the scope of the above charts, but this upper divergence has allowed it to be displaced a bit east and be stronger, featuring a 1002 mb center just SW of Texas and a surface trough extending from that 1002 mb center all the way toward Central America.

Upper ridge which has moved into the eastern US yesterday has greatly amplified due to strong warm air advection ahead of aformentioned 989 mb cyclone. The 1029 mb surface ridge supported by the eastern covnergence of the upper ridge has shifted offshore into the west Atlantic and still remains at 1029 mb.

Mentioned briefly in yesterday's North America discussion was a 1005 mb cyclone just NW of Newfoundland, which has now been absorbed by strong cyclone S of Greenland. The cold front ushered in by the now-gone 1005 mb cyclone is strewn east-west across southern Canada and has overspread yesterday's 1001 mb cyclone over SW Ontario. This 1001 mb cyclone has slid east along the south Canada front and deepened to 999 mb while currently present over the southern tip of Hudson Bay in the above charts. Warm air advection ahead (cold air advection behind) the 999 mb cyclone will create a shortwave upper ridge east of it (upper trough west of it). In fact such an upper shortwave ridge is marked in the above charts over Labrador. In turn, divergence between the developing upper shortwave ridge and upper shortwave trough will cause the 999 mb cyclone to gradually strengthen while heading east along the front.

Eastern convergence of the new shortwave upper ridge over Labrador supports weak 1017 mb surface ridge marked nearby in the above charts.

High seas south of Greenland still dominated by intense surface cyclone currently at 985 mb, the same pressure it had 24 hours ago. The cyclone earlier bottomed-out at 962 mb, and is now weakening as the lengthy west Atlantic upper trough axis (offshore of east US) has neared it. This weakening is induced as the axis itself has less upper divergence than the environment east of the axis. Thus expect the cyclone to continue weakening through the next several hours.

Central Atlantic deep-layered ridging has been pushed toward east Atlantic ahead of S Greenland cyclone and its very long oceanic cold front. As predicted yesterday, the northern portion of the upper ridge has amplified into an upper high pressure center over the Azores thanks to continued warm air advection ahead of the S Greenland cyclone. The new upper high has vertically aligned with the strong surface ridge (presently 1032 mb) near the Azores, resulting in a blocking deep-layered high pressure over the Azores. To the southwest of the blocking high is a leftover central Atlantic upper ridge axis supported by continued warm air adection ahead of oceanic cold front extending from the S Greenland cyclone.

A surface trough is added from the Canary Islands to southern Morocco in the 1200Z NHC TAFB analysis (shown in the above charts as well). It appears that this trough is supported by divergence between upper northerlies east of the deep-layered Azores ridge and mainstream mid-latitude upper westerlies.

Cut-off upper low persists in the far east Atlantic midway between Azores and Cape Verdes. Divergence east of the cut-off upper low has been battling dry air that was once produced by what is now the deep-layered ridge over the Azores. The lift created by the upper low's eastern divergence has been successfully "moistening away" the dry air in the region when animating the thermodynamics charts over the last 48 hours. Satellite imagery shows no weather associated with the divergent region of the cut-off upper low, but the observed moistening may allow this to begin at some point. The divergent region of the cut-off upper low will however struggle to produce a surface trough while battling high surface pressures associated with the Azores deep-layered ridge.

1013 mb low has been added by 1200Z TAFB along the cold front extending from the S Greenland cyclone, located well east of Bermuda. The cyclone and lengthy cold front has been supported over the last days by a rather large west Atlantic upper trough offshore of east US. Yesterday's computer model runs suggested that the upper trough would split into a southern cut-off E of Bermuda and northern portion "running away" with S Greenland cyclone. However, this split is expected any time now. The cut-off upper trough E of Bermuda gets trapped between the above-discussed deep-layered Azores ridge and upper ridge over the eastern US mentioned in today's North American discussion. The models predicted the severe-weather producing west US cyclone would amplify the east US upper ridge (with warm air advection), and this indeed has begun over the last 24 hours. As the east US upper ridge continues amplification, this will allow the cut-off upper trough E of Bermuda to amplify into a rather impressive cut-off upper low vortex E of Bermuda by April 17. What is now the new 1013 mb frontal low will be present beneath the divergent east side of the cut-off upper low such that it flourishes eventually into a non-frontal subtropical cyclone. I do not expect subtropical cyclone formation before April 17 as the cold front across the 1013 mb low needs to decay into a non-frontal surface trough in order to classify the system as subtrpoical in the first place. The dissipation of air temperature contrasts across the front (to qualify it as non-frontal) is not an instantaneous process, and therefore no subtropical cyclone is expected before April 17.

The models show the subtropical cyclone making a clockwise loop E of Bermuda while steered by the cut-off upper low vortex from the 17th to 19th. Using today's thermodynamics chart, this keeps the forecasted subtropical cyclone well north of the 26 deg C isotherm, over waters between 20 to 22 deg C. This seems to be the only disadvantage to subtropical cyclogenesis. It is going to take a very cold-temperature upper low to produce instability and convection with surface water/air temps that mild. However, the cut-off upper low vortex E of Bermuda developed by the models seems impressive enough to be up to the challenge...stay tuned!

East-to-west oriented shortwave upper trough still present over the Gulf of Mexico based on latest 200 mb wind barbs in the above charts. Upper convergence north of this upper trough axis, upper convergence southeast of the east US upper ridge, and surface divergence of the west Atlantic 1029 mb ridge are all teaming up to expand the intensity of sinking, dry air across the northern Gulf. This dry air mass has spread into the west Atlantic waters S of Bermuda.

Northern South Amercian monsoon upper ridge continues to be choked by west Atlantic amplified upper trough offshore of US (located due north). Although there is some storm activity remaining with the monsoon, it is not as impressive as it was 72 hours ago.

The following preliminary summary is divided into thirteen convective supercell areas that developed during and after yesterday's discussion.

(Supercell #1) There was a supercell T-storm induced tornado in the late afternoon hours near Salina, Kansas.

(Supercell #2) Well SE of Dodge City, Kansas...a supercell T-storm produced a tornado tornado headed first toward Greensburg. It passed just 2 miles NW of Greensburg and was spotted by observers at night. The tornado then moved thru Fellsburg...heading toward Trousdale...Belpre, and then Macksville. A tornado emergency was issued for Macksville. Afterwards, the destructive tornado moving just north of Saint John and was about to head toward Hudson. After Hudson, the tornado headed toward Lyons & just N of Sterling but with a weaker radar signature. Affiliate KSN news (from Witchita, Kansas) reported power flashes at 10:03 PM CDT according to a storm chaser just west of Lyons.. signs that the tornado was regaining strength. KSN news reported power flashes in Lyons at 10:16 PM CDT. After clearing Lyons, the tornado headed toward rural grounds...but its long range track eventually threatened Salina and eventually Abilene, Kansas. A new tornado warning at 10:41 PM CDT was issued for this tornado just SSW of Salina. It was doing damage near Smolan, a town well south of Salina. The hail core NW of tornado center was hitting Salina at 11:00 PM CDT. Hail core then moves into Solomon (midway between Abilene and Salina) along I-70 at 11:18 PM CDT. The tornado signature was weakening on radar along I-70 at 11:18 PM CDT. Tornado signature collapses into multiple disorganized hooks along I-70 at Abeline & Solomon, which indicated tornado dissipation by 11:24 PM CDT. Tornado re-established itself by 11:32 PM CDT at a position just north of Abeline. Sloppy tornado signatures north of Chapman & Abeline at 11:35 PM CDT. Not long after...the tornado warnings with this supercell were finally cancelled.

(Supercell #3) A supercell T-storm in east Reno County Kansas (Hutchinson area) produced a tornado...and was heading NE toward Hillsboro and passing NW of Marion. Later, radar suggested it passed south of Herington. At 9:22 PM CDT...tornado was 4 miles north of Wilsey moving NE in east-central Kansas. At 9:35 PM CDT...radar image posted showing weaker/dissipating tornado signature that was passing northwest of Council Grove and east of Herington.

(Supercell #4) A vigorous supercell T-storm produced a new tornado starting near Woodward, OK during the late afternoon. Shortly thereafter, it passed by Waynoka, Dacoma, and then later moved toward Manchseter area of Oklahoma. On its way toward Manchester, affiliate News9 aired dramatic footage including an explosion of a gas tank & multiple vortices. Before heading toward Manchester, OK, it passed just N of Byron. After passing just NW of Manchester, it moved across Oklahoma border into south-central Kansas. It is making a bee-line to southern Witchita, KS. On its way toward Witchita...it produced an extremely impressive velocity doppler signature south of Argonia. At 9:33 PM CDT...velocity doppler signature was closing in on Conway Springs and Belle Plaine with bee-line still toward Witchita. It was at this time affiliate KSN reported the sounding of tornado sirens in Witchita. At 10:00 PM CDT...two circulations were spotted on radar heading into Clearwater & Conway Springs as the supercell neared Witchita. AT 10:13 PM CDT...the tornado re-established itself as a single circulation just NE of Clearwater and heading NNE to downtown Witchita. SW Witchita reported powerflashes at 10:15 PM CDT according to KSN. A tornado emergency was issued for Witchita...the largest tornado emergency issued during the evening considering the population of the area. KSN reported reported power outages in SW Witchita at 10:22 PM CDT. At 10:24 PM CDT...tornado spotted on I-35 turnpike with the apperance of a dangerous wedge. The tornado banked NE at 10:29 PM CDT such that it will move through SE Witchita and along the I-35 turnpike. Along the turnkpike, the tornado moving NE toward Andover by 10:39 PM CDT. Next was Towanda and El Dorado, Kansas by 10:42 PM CDT. Radar showed the tornado signature on top of El Dorado at 11:00 PM CDT. AT 11:20 PM CDT, the tornado signature was parelleing I-35 moving NE en-route to pass south of Cassoday & into rural areas of NW Greenwood county, then rural SE Chase County, and then a tornado warning was issued in southern Lyon County by 11:50 PM CDT. By midnight thru 12:12 AM CDT, the storm looked disorganized in S Lyon county and south of Emporia. Its tornado warning was finally dropped by 12:30 AM CDT, making it the longest-track tornado of the event.

(Supercell #5) Large T-storm cluster with bow echo was seen in Iowa with radar. Frequent rotation within the bow echo near Des Moines...however bow echo continues east with no tornado warnings ever issued.

(Supercell #6) A supercell in northern Oklahoma put down tornado near Alva/Cherokee eventually taking a track toward Witchita, Kansas. This circulation was overtaken by the tornado that crossed the border from Manchester, OK (supercell #4) before it had a chance to get to Witchita, and it was suprecell #4 as discussed above that would eventually hit Witchita.

(Supercell #7) Severe T-storm with hook echo south of Hastings, Nebraska just before 10:00 PM CDT. This T-storm cluster produced a tornado warning just north of Lincoln, Nebraska by 11:42 PM CDT. This storm loses tornado warning by 12:03 AM CDT while en-route to pass just south of Omaha, Nebraska. Again it gets tornado warned from 12:40 to 1:09 AM CDT as it crosses the Nebraska border just E of Omaha into west-central Iowa & just west of Atlantic, Iowa. This final tornado warning was brief and tornado signature was disorganized.

(Supercell #8) Off the west side of supercell #2...new tornado warning for Geneseo, Kansas at 10:53 PM CDT. The new circulation was east of Claflin and west of Geneseo heading to Geneseo. Later at 10:59 PM CDT, Lorraine just NW of Geneseo under a potential tornado touchdown with tornadic circulation wraped in heavy rain according to radar. At 11:10 PM CDT...Geneseo was spared as the tornado passed north of the city and was heading ENE. At 11:20 PM CDT...the tornado was now heading toward the Salina area. Brookville, Bavaria, and Salina were on its path at 11:31 PM CDT...& KSN reported NCAR had spoted the torando. By 11:59 PM CDT...circulation moving into Salina but less organized on radar. Warning was cancelled shorlty after midnight local time.

(Supercell #9) New tornado warning at 12:03 AM CDT just SE of Metador in north-central Texas. Tornado warning was short-lived

(Suprecell #10) New tornado warning at 12:03 AM CDT just SE of Gage, Oklahoma heading toward Woodward, Oklahoma. This new tornado was en-route to work its way toward Alva near where supercell #6 went. By 12:19 AM CDT, the tornado was moving into the Woodward area. By 12:29 AM CDT...the tornado signature dangerously directly on top of Woodward, OK. By 1:14 AM CDT, tornado signature appears to be passing well NW of Alva. The dissipating tornado crosses the Oklahoma border into just S of Medicine Lodge, KS by 1:39 AM CDT. Reports the following morning indicated five fatalities due to the direct strike of this tornado upon Woodward.

(Suprecell #11) New tornado warning around 12:18 AM CDT near Elk City, OK tracking ENE eventually en route to pass just north of Clinton, OK. Tornado warning gone by 12:34 AM CDT as it becomes indistinct within nearby squall line. Tornado warning re-issued on it by 12:45 AM CDT as it is slated to pass well north of Clinton. Once again loses tornado warning and re-assimilates into the squall line by 1:39 AM CDT.

(Supercell #12) Major rapid devlelopment of hook echo passing thru Wakefield, Kansas, and a tornado warning by 12:54 AM CDT. This is remnants of supercell #8. Eventually this impressive tornado signature passed just north of Manhattan, Kansas. By 1:34 AM CDT...it still has impressive radar bean-shaped signature while sliding ENE between Manhattan and Marysville. Minutes later, tornado signature much less impressive and dissipating.

(Supercell #13) New tornado warning just southeast of Medicine Lodge, KS passing thru the SE half of that city and tracking NE. Tornado warning SE of Medicine lodge is removed by 1:11 AM CDT.

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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