NWS State College Case Examples Central Plains Severe and

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Central Plains Severe and heavy rainfall Event of 16-17 June 2014
By
Richard H. Grumm
National Weather Service State College, PA
1. Overview
A significant severe weather event affected the central Plains on 16-17 June 2014 (Fig. 1). In the
afternoon hours of 16 June a supercell developed in eastern Nebraska, south of the main line of
storms. This storm produced deadly and destructive “twin tornadoes” near Pilger, Nebraska.
The storms developed in an environment with high convective available potential energy (CAPE:
Fig. 2) and with a second surge of above normal precipitable water (Fig. 3). The second surge of
high CAPE around 1800 UTC 16 June was accompanied by and enhanced 850 hPa jet (Fig. 4).
The 850 hPa winds were +2 to +3s above normal at 1800 UTC 16 June peaking at over +4s at
both 0000 and 0600 UTC on 17 June 2014 (Fig. 4e-f). Hourly RAP13km data showed the strong
and persistent 850 hPa jet as it evolved from 1700 through 2200 UTC 17 June 2014 (Fig. 5). The
strong low-level jet was played a role in the convective evolution and the resulting Mesoscale
Convective System which evolved over the course of the period from about 2200 UTC 16 June
through 1200 UTC 17 June 2014.
As in many convective events and heavy rainfall events, a large ridge was present south and east
of the affected area and a trough was located upstream of the same region (Fig. 6). The larger
scale synoptic pattern had a “return flow” appearance allowing moisture from the Gulf to move
around the western flanks of the larger scale ridge. This “ring-of-fire” pattern is often a pattern
know to favor both severe weather and heavy rainfall (Bodner et al. 2011; Junker et al 1999).
The 24-hour rainfall (Fig. 7) showed the heavy rainfall from eastern Nebraska and across Iowa
and portions of adjacent States.
This short note will document the severe and heavy rainfall event of 16-17 June 2014. The
pattern has been shown to be one associated with heavy rainfall. The following sections focus on
some of the severe weather and features which contributed to both the heavy rainfall and the
severe weather.
2. Twin Tornados Omaha Radar
The KOAX radar at 20:11 UTC (Fig. 8) shows the supercell developing northwest of the radar
and the line of storms farther north, over KFSD which would evolve into the heavy rainfall
producing MCC. The northern line slowed move to the southeast as the supercell storm moved
to the east-northeast (Fig. 8 lower panel).
A zoomed in view destructive Pilger twin tornadic storm is shown at 2042 UTC (Fig. 9). The
storm had rotation and a pendant on the southwest flank of the storm. The dual-pol products,
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specifically CC showed a broad region of non-meteorological targets in the large mesocyclone as
the storm passed over Pilger (Fig.10) and moved to the northeast. The 2126 UTC (Fig. 11) CC
and SRM showed the strong mesocyclone and region of non-meteorological targets as the storm
moved northeast of Pilger.
The Associated Press (AP) reported 2 dead after the twin tornadoes flattened the Nebraska town.
The reports carried by many news services included dramatic video of the tornadoes and the
massive destruction.
3. MCS heavy rain, flooding and severe
The cold cloud tops with the twin-tornadoes were clearly visible in the 0015 UTC GOES-IR
imager (Fig. 12). By 0230 UTC a well-defined MCS was present over northeastern Nebraska
with the cold cloud shield extending into Iowa. The MCS developing to the east over eastern
Iowa and Illinois implied the deep moisture and well developed “ring-of-fire” family of MCS
activity.
The MCS became quite massive with two regions of intense lightning by 0615 and 0715 UTC
(Fig. 13). The MCS to the east over Wisconsin and Illinois was also producing considerably
lightning and rainfall. The impact of the MCC’s on the rainfall and severe weather (Fig. 14)
shows the regions of rain and heavy rainfall with severe weather overlaid 1. Clearly, these to
MCS’ produced heavy rainfall and the supercell which became part of the larger MCC
contributed to the region of 64 to 192 mm of estimated rainfall. Most of the severe reports were
associated with the larger MCC with fewer reports with the smaller MCS over Iowa, Illinois and
Wisconsin.
4. Summary
A pattern known to be conducive for both heavy rainfall and severe convection produced a
significant severe weather event and heavy rainfall on 16-17 June 2014 weather (Fig. 14). The
combination of strong flow between a ridge to the east and trough to the east allowed for a surge
of deep moisture and instability. The result was a family of MCSs over the upper-Midwest. The
data shown here imply that the larger MCC developed from the supercell which produced the
deadly twin-tornadoes in northeastern Nebraska.
This case and many others demonstrate the value of understanding the pattern and the significant
contribution MCS provide to the precipitation climatologies. The pattern was relatively well
predicted and thus the concept of rain and at least moderately heavy rainfall was indicated by the
NCEP models (not shown). Additionally, to better predict severe weather and eventually move
toward a warn-on-forecast concept (Stensrud et al. 2009) convective allowing models and
convective allowing ensembles will be required.
1
Due to colors and sizes most of the severe weather is difficult to visualize and clearly, no reports were observed
outside of the precipitation shield.
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An experimental product produced by NSSL using a storm scale ensemble of opportunity
(SSEO: Sobash et al. 2011) was made available for this event. The Storm Prediction Center
(SPC) also provides some real-time experimental SSEO products. A quick example (Fig. 15) 2 is
provided here of an experimental project and the verification of the updraft Helicity (UH). The
grey lines are the verification data and the lower right panel shows the verification. In the
forecast panels, from each high resolution convective allowing models the models UH is
displayed with the magenta lines showing the UH with maxima over 75 and the shading shows
all UH tracks. These UH tracks are used as proxy data for strong updraft cores and the potential
for supercell evolutions. Figure 16 shows a blow up of two of the forecast models.
The critical point is that most of the forecast models predicted the evolution of UH cores where
the MCS and supercell evolutions occurred, aiding with the mode of convection. Clearly, there
were no significant storms in the Carolinas. But over the Midwest the guidance along with
knowledge larger scale favorable pattern shows promise (Fig. 15). The NSS-ARW had a
considerable region and probability of UH cores over 75 focused over northern Iowa. The
CONNUS-NMM showed different shape to the high UH region shifted to the west (Fig. 16).
Nearly all the convective allowing models suggested the potential for severe weather and
supercell storm evolution in the region affected by severe weather. Optimistically, these
products and the models from which they are extracted from will improve and thus improve the
ability to predicted and anticipated severe future severe events.
5. Acknowledements
Thanks to the Albany map for information and data on the event. James Correia Jr provided the
SSEO data and a description of these data.
6. References
Associated Press, 2014: 2 Dead after Tornadoes Flatten Tiny Nebraska Town, and similar stories
17-18 June 2014.
Bodner, M. J., N. W. Junker, R. H. Grumm, and R. S. Schumacher, 2011: Comparison of
atmospheric circulation patterns during the 2008 and 1993 historic Midwest floods.
Natl. Wea. Dig., 35, 103-119. [Abstract]
Junker, N. W., R. S. Schneider and S. L. Fauver, 1999: Study of heavy rainfall events
during the Great Midwest Flood of 1993. Wea. Forecasting, 14, 701-712.
Stensrud, D. J., and Coauthors, 2009: Convective-scale warn-on forecast system. Bull. Amer.
Meteor. Soc., 90, 1487–1499.
2
Thanks to James Correia Jr for the data and permission to display the data. Affiliations OU CIMMS and SPC HWT
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Sobash, Ryan A., John S. Kain, David R. Bright, Andrew R. Dean, Michael C. Coniglio, Steven
J. Weiss, 2011: Probabilistic Forecast Guidance for Severe Thunderstorms Based on the
Identification of Extreme Phenomena in Convection-Allowing Model Forecasts. Wea.
Forecasting, 26, 714–728. doi: http://dx.doi.org/10.1175/WAF-D-10-05046.1
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Figure 1. GFS 00-hour forecast of 500 heights and severe weather ending at 1200 UTC 17
June 2014. Return to text.
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Figure 2. As in Figure 1 except GFS 0 0 hour forecasts of CAPE in 6-hour increments form a) 0000 UTC 16 June through f) 0600 UTC 17 June 2014. Return to text.
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Figure 3. Return to text.
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Figure 4. Return to text.
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Figure 5 Return to text.
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Figure 6. Return to text.
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Figure 7. NMQ Q2 data showing estimated rainfall (in) for the 24 hour period ending at 1200 UTC 17 June 2014. Return to text.
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Figure 8. 0.5 degree horizontal reflectivity from KOAX radar at 2011 and 2058 UTC 16
June 2014. Return to text.
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Figure 9. 0.5 degree Z and SRM at 2042 UTC and 2104 UTC. Return to text.
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Figure 10. KOAX 0.5 degree CC and Z at 2115 UTC. Note region of “blue “on-meteorological targets in the hook echo implied by the
Z data. Loops of these data implied at times two distinct regions of no meteorological target areas in the broad mesocyclone.
Yellow arrow in CC helps define the region of interest. Return to text.
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Figure 11. As in Figure 10 except for SRM instead of Z and valid at 2126 UTC. Return to text.
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Figure 12. GOES IR of evolving MCS showing the cold tops with the tornadic storm at 0015 UTC and
the MCS it became by 0230 UTC. Lightning is green. Return to text.
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Figure 13. As in Figure 12 except for 0630 and 0715 UTC. Return to text.
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Figure 14. Stage-IV estimated rainfall (shaded) and contours in black along with SPC severe weather plots by type. . Return to text.
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Figure 15. Experimental Forecasts form 5 SEO models with the model names in each panel. The lower right panel is the verifying UH. The grey lines
in each forecast panel shows the verification. The magenta lines (see blow-up in Fig. 16) and shading show the UH cores over 75 and all UH cores
respectively. Return to text. Image provided by James Correia, OU CIMMS and SPC HWT .
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Figure 16. As in 15 except enlargement of the middle top 2 panels. Return to text.