May 26th, 2000 MCS Event Across Northern and Central Missouri

During the evening of 26 May 2000 (after 00 UTC 05/27/00) a large mature linear convective line 
extended from far northern Missouri through central sections of the state.  The convective line already produced isolated wind damage over parts of northwest through parts of west-central Missouri.  We tested the utility of the MARC velocity signature to identify or further fine-tune potential areas where damaging winds may occur along the larger convective line echo pattern.

(A) Brief Synoptic Overview


Fig. 1 - 0200 UTC 27 May 2000 surface analysis.

The convective squall line traveled along and north of a warm frontal boundary which extended from an area of low pressure near St. 
Missouri to just south of St. Louis and eastward into western Kentucky.  Surface dewpoints of 73F pooled near and south of the 
warm front.  The 
squall line at 0200 UTC (shown in purple) extended from 30 km west of Kirksville MO (IRK) to Sedalia MO (SZL).   The 
squall line traveled along and north of the warm frontal boundary throughout much of its lifetime.

Fig. 2 - 0000 UTC 27 May 2000 Skew-T Log-P from Springfield MO (KSGF).  Magnitude of
Surface-based Convective Available Potential Energy (CAPE) was 2512 J/Kg.
 Magnitude of 0-3 km Bulk Shear was 14 m/s (moderate shear). 
Surface - 500 mb delta theta-e was 

(B) WSR-88D Imagery from KLSX

Fig. 3 - WSR-88D plan view reflectivity imagery (0.5 degree slice)
for 0217 UTC from KLSX.  Reflectivity values are in dBZ. 

At 0217 UTC, a large squall line extended from near Kirksville Missouri (IRK) to 10 km west of Sedalia, Missouri.  Several small poorly
defined bowing segments, embedded within the larger squall line, were identified from Kirksville to Macon Missouri.  The warm frontal 
boundary at this time stretched from just north of Jefferson City (JEF) to just south of St. Louis.  Note the development of new convection 
from Columbia, Missouri northeast through Mexico, Missouri just north of the warm frontal boundary.

Fig. 4 - May 27, 2000 at 0247 UTC: WSR-88D reflectivity image (0.5 degree slice) (left);
 storm-relative velocity image (right) from KLSX.
Range rings are 50 nm.  White arrows point to the location of MARC at this time. 

The WSR-88D reflectivity image at 0247 UTC (0.5 degree slice) from KLSX shows two small embedded bowing segments within the 
larger squall line.  The northern most segment was moving across northern Shelby county while the second segment traveled across 
northern and central parts of Monroe county.  The MARC velocity signature is identified at three locations (white arrows); (a) along 
the leading edge of the northern segment (central Shelby county - 12 Kft AGL), (b) along the northern part of the second segment 
(northern Monroe county - 11 Kft AGL) and (c) with the convective cluster near Harrisburg Missouri or 15 to 20 km northwest of Columbia 
(northwest Boone county 11 Kft AGL).  Two critical points must be raised with the two northern MARC signatures; 1) the viewing angle is 
becoming more critical with the far northern MARC velocity signature where the magnitude of MARC is likely underestimated, and 2) an 
enhanced local area of MARC is identified over the northern part of the second bowing segment.  With an increasing number of cases, 
our studies have shown that these enhanced areas may be linked to more intense surface wind damage.

Fig. 5 - May 27, 2000, 0303 UTC; Four panel presentation reflectivity / Storm-relative velocity
(SRM) images.  Top reflectivity / SRM velocity images (1.5 degree slice);
 Bottom reflectivity / SRM velocity images (0.5 degree slice).

At 0303 UTC, the far northern bowing segment moved into northern Marion and southern Lewis counties in northeast Missouri while the 
second bowing segment entered southeast Shelby - northeast Monroe counties.  Strong reflectivity gradients along the storm's forward 
flank suggested the presence of strong updrafts with this storm.  Further southwest, a third linear segment entered western Audrain 
county.  Similar to the Monroe county storm, strong reflectivity gradients along the storm's forward flank was suggestive of strong updrafts.
The SRM velocity image at 0.5 degree slice (lower right) showed a nearly continuous narrow ribbon of outbound velocities along the 
convective line's leading flank (light blue arrows).  This narrow ribbon is a reflection of the squall line's updraft current.  During my 
participation in the North Dakota Cloud Modification project (late 1970s), pilots I directed along the leading edge of convective lines near
cloud base generally reported nearly a smooth - continuous current of rising air (region of updraft / 800 - 1000 ft/min).  However, in 
some cases, pilots reported local pockets (e.g. 2 - 4 miles long) of stronger updrafts (e.g. 1500 - 2000 ft/min rise) embedded within the 
larger rising current.  Some of these local pockets of stronger updrafts were directly downshear from the storm's high reflectivity core 
region.  The brighter green inbound SRM velocities (37 kts) over northern Boone and western Audrain counties reflect  the southern
storm's mesoscale rear inflow.  The SRM velocity image at 1.5 degree slice showed two regions of MARC over northeast Monroe and 
northeast Boone counties.  The magnitude of MARC increased to 43 m/s (northeast Boone - 5.18 km/ 17 Kft), and 30 m/s (northeast 
Monroe - 5.2 km/17.2 Kft) respectively from 0247 UTC image.  Based on MARC values from the preceding two volume scans and the 
current 0303 UTC images, severe thunderstorm warnings were issued for northern Monroe, southern Shelby and the western half of 
Audrain counties.

Fig. 6 - May 27, 2000, 0313 UTC; Four panel presentation of reflectivity / storm-relative velocity (SRM)
image from KLSX.  Top reflectivity / SRM velocity images (1.5 degree slice);
 lower reflectivity / SRM velocityimages (0.5 degree slice).

The four panel presentation at 0313 UTC in Fig. 6 shows the second of the first two original small bowing segments embedded with the 
larger squall line moving into southern Marion and northern Ralls counties in northeast Missouri.  A third linear segment began to show a 
bowing structure at this time as it traveled across was moving across west-central Audrain county.  Reflectivity values exceeding 60 dBZ 
were common with each convective segment.  The viewing angle of the northern bowing segment (Ralls county storm) became 
increasingly more critical in viewing the MARC velocity signature.  A relatively strong magnitude of MARC (32 m/s - 1.5 degree slice) is 
observed along the southern flank of this bowing segment.  The third convective segment over western Audrain county continued to
reveal a strong low-level reflectivity gradient along the leading edge of the segment suggesting the presence of a strong
updraft / 
downdraft structure. 
Strong radial convergence was detected at the 1.5 degree slice (45 m/s (
near location of the blue arrow).  The blue 
arrow on the 0.5 degree SRM slice shows the storm's advancing cold pool.  The region of inbounds extending from the location of
MARC upwind (northwest) to the Audrain - Monroe county line continues to reflect the presence of a mesoscale rear inflow.  Damaging 
winds occurred 3 to 5 minutes after 0313 UTC over parts of Mexico, Missouri.

Fig. 7 - WSR-88D reflectivity (left) and storm-relative velocity (right) cross-sections along the
 300 degree radial from 79 nm to 56 nm away from KLSX at 0313 UTC 27 May 2000.
The cross-section is taken nearly orthogonal to the
convective line over central Audrain county.

Reflectivity and storm-relative velocity cross-sections were taken along the 300 degree radial at 0313 UTC over central Audrain county.  
The reflectivity cross-section revealed multicell evolution with a new convective tower between 10 and 12 nm and Weak Echo Region 
(WER) along the storm's forward flank.  The later stages of a mature storm is noted  between 7 and 10 nm with a descending high 
reflectivity core below 14 Kft.  Storm-relative velocity cross-section shows the MARC velocity signature at an altitiude between 10 to 15 
Kft (12 nm) just below the developing new convective tower and in the vicinity of the WER.  The strongest convective outflows (medium 
green color) appeared to be associated with the descending high reflectivity core (7 - 10 nm).  Two other interesting velocity features 
were also identified with this cross-section.  First, the initial surge of the convective system's cold pool accelerated downwind (eastward) 
to near 14 nm (or 3 nm) downwind from the mature storm (descending high reflectivity core.  Convective outflows associated with MCSs 
can be as deep as 5 to 7 kft (Burgess 1999).  Secondly, local outbound velocity maximums embedded with the MCS's  front-to-rear flow 
are detected at an altitude of 21 - 25 kft (10 - 11 nm) and again near 21 - 23 kft (8 nm).  Smull and Houze (1985) have documented these 
local velocity maximums with MCS events across south-central Kansas during the Pre-Storm Project.


Fig. 8 - Tracks of MARC identified with the May 26, 2000 MCS event.
W represents locations of wind damage.  A signifies location of
hail and dashed lines indicate location of tornadic damage tracks.

The map above shows wind damage reports and traces of where a persistent MARC velocity signature was identified; traces A - G (Fig 
8).  We will take a closer look at traces D and E and their respective time-height MARC traces.  It is important to note that the surface 
warm frontal boundary during this period extended from near St. Joseph to just south of Columbia and southeast to just south of St. Louis,
Missouri at this time.  It is difficult to determine the depth of the stable layer, however MARC traces (B, E, and G) located further
north and away from the warm frontal boundary are likely over a region of a deeper low-level stable layer.

Fig. 9 - (a) represents Trace D time-height cross-section of MARC across northern Boone through central Audrain counties
in central Missouri.  (b) represents Trace E time-height cross-section of MARC across northern Monroe through northern
Ralls counties in northeast Missouri.  Magnitudes of MARC are in (m/s).  W represents time of wind damage.

Characteristics of the magnitudes of MARC for traces D and E are shown above (Fig. 9a and 9b respectively).  Trace D initially showed that
MARC magnitudes were near or just below 25 m/s at the lowest two elevation slices for the period 0242 and 0247 UTC.  At the 1.5 degree
elevation slice, values of MARC increased to 31 m/s at 5.5 km (0253 UTC) suggesting a increased potential for damaging winds.  A 
second and significant increase in MARC magnitudes on the 1.5 degree slice is observed after 0258 UTC where velocity differentials
increased from 29 to 43 m/s (5.2 and 4.9 km (17.2 - 16.0 Kft) respectively).  The trend of significantly higher values further add credence for 
a higher damaging winds threat.  Wind damage occurred just after 0313 UTC in the city of Mexico, Missouri or approximately 21 minutes 
after values exceeded 25 m/s.

Trace E, north of Trace D, is located in a region where a deeper low-level stable layer of air is likely present.  At the initial starting point of 
Trace E over northwest Monroe county, MARC values of 40 m/s were observed near 3 km suggesting strong radial convergence in the 
vicinity of the storm's WER (northern flank of the storm).  Such magnitudes would suggest a high probability of damaging winds.  However, 
in this case, one needs to be aware of a stable layer near the surface.  Can convective-scale downdrafts penetrate through this stable 
layer?  At the next volume scan, magnitudes of MARC fell to 30 m/s, still suggesting the probability of damaging winds.  Isolated wind 
damage did occur between Traces E and C over north-central Monroe county at approximately 0255 UTC.  Between 0258 and 0308 UTC, 
MARC values of 30 to 35 m/s at and just below 5 km were detected and continued to suggest the potential for damaging winds.  The storm
during this period (not shown) showed signs of bowing with a rear inflow notch along the trailing flank.  At approximately 0305 UTC, a 
second isolated report of wind damage occurred over northeast Monroe county.  Beyond 0308 UTC, MARC magnitudes continued to 30 
m/s between altitudes of 4 and 5 km along the southern part of the bowing structure, even with an increasingly poorer viewing angle with 
time.  From many of our earlier observations, we found the strongest magnitudes of MARC at or just below 5 km (18 Kft).  This case further 
supports our earlier findings.  The consistent strong values of MARC between 4 and 5 km (0308 to 0323 UTC)  continue to suggest the 
potential for damaging winds.  Isolated reports of wind damage occurred for a third time with this storm at and after 0323 UTC over
northern Ralls county Missouri.

Fig. 10 - Map of wind damage reports (W), and tornado tracks from central Missouri
through west-central Illinois.  Squall Line positions are denoted approximately
every 30 minutes.

Fig. 10 is a map showing, squall line positions every 30 minutes, reports of damaging winds (W), and hail (A).  Dashed lines signify
location of tornadic damage.  The squall line positions show a broad bowing structure entering northeast through central Missouri around 
0300 UTC.  One hour later (0400 UTC) two smaller bowing segments are observed over Pike county Missouri and Pike county Illinois.  
Smaller bands of scattered smaller convection extended orthogonal to the bowing segments.  More information on the issue of 
tornadogenesis with this case will be forth-coming in Group 2 "Intensifying Stage of MCS Evolution."

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