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HRRR and the Mid-Mississippi Valley Severe and Heavy rainfall event
of
13-14 October 2014
By
Richard H. Grumm
National Weather Service State College, PA
contributions by
Charles Ross
1. Overview
A deep 500 hPa trough (Fig. 1) moved across the central United States from 13-14 October
2014. The flow between the deep trough and downstream ridge allowed a surge of warm moist
air into the Mid-Mississippi Valley (MMV: Fig. 2) with a strong southerly 850 hPa low-level jet
(LLJ: Fig. 3). The strong southerly flow resulted in a widespread rainfall event (Fig. 4) and
severe weather from Illinois to the Gulf of Mexico (Fig. 5). The maximum rainfall was on the
order of 100 mm in portions of Mississippi and Alabama.
The strong southerly jet (Fig. 3) and implied strong shear is often associated with the Maddox
Synoptic rainfall event type (Maddox et al. 1979) and is often associated with quasi-linear
convective systems (QLCS: Atkin et. al 2004 & 2005). The composite radar (Fig. 6) shows that a
QLCS did in fact traverse the region. How well this feature was forecast by the NCEP 3km
HRRR will be explored.
This case is used to show the larger scale pattern which contained strong southerly winds and
high PW values. This resulted in relatively high CAPE (Fig. 7) from the lower to MMV
producing heavy rainfall and severe weather with tornadoes as far north as Illinois (Fig. 5). It
should be noted that the CFSR appears to under estimate CAPE relative to the HRRR and GFS
00-hour forecasts.
This study will also show some forecast issues relative to the NCEP 16km SREF verse the
convective allowing HRRR. The HRRR can show the mode of convection and where the more
intense rainfall and convection may occur in short forecast ranges. Rapidly refreshed convective
allowing models (Juanzhen et al. 2014: Fig. 1) can improve short-range QPFs verse traditional
cold started models.
2. Methods and Data
The NCEP 3km HRRR and 16km SREF were used to show the evolution of the rainfall and
precipitation. The HRRR had the added value of showing the “evolution” of the radar and
convection. The 0.5 degree CFSR was used to construct the larger scale pattern.
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Radar data was retrieved from then multi-sensor (MRMS) site to evaluate and make loops of
the evolving convection and rainfall
The rainfall images in plain view were produced using the Stage-IV data and plotted using
GrADS.
3. SREF
The SREF and other NCEP models did relatively well predicting the pattern and the potential for
both a heavy rainfall event and severe weather event. Six SREF forecasts of CAPE all valid near
the height of the QLCS event at 2100 UTC 13 October 2014 (Fig. 8) bear out the surge of high
PW air (Fig. 2) and are related to the SREF forecasts of the surge of high PW air (Fig. 9) and a
strong LLJ (Fig. 10) with strong shear. The shear and CAPE were important ingredients to the
convection and the development of the QLCS system and the tornadoes in Illinois.
The resulting pattern produced locally heavy rainfall in the SREF (Fig. 11-13) in a general northsouth pattern along and ahead of the cold front with some hints of a wraparound rainband farther
north in the cold air. The 12-hour probabilities of 25 mm showed a high probability along a
north-south axis (Fig. 11). The 12-hour SREF mean (Fig. 12) showed a broader area of rainfall
and some uncertainty with the regions susceptible to heavy rainfall. The ensemble mean in both
the 12 and 24 hour periods showed the north-south band and an axis of heavy rainfall in the cold
conveyor belt. The 24 hour totals showed some areas of over 50mm in both the convection ahead
of the front and in the cold conveyor rain area (Fig. 13e-f). The short-term nature of these 50 mm
forecasts implied a slow but steady convergence to get the higher amounts in extremely short
forecast ranges.
The SREF did reasonably well the pattern for heavy rainfall and convection. The next section
examines how the NCEP 3km HRRR performed.
4. NCEP 3km HRRR
The hourly convective evolution in the 1500 UTC 13 October 2014 HRRR is shown in Figure
14. These data showed the potential details of the rainfall evolution capturing the QLCS system
in the MMV and the wrap-around rainband. Relative to the radar (Fig. 6-lower panel) the 15Z
HRRR was slow to move the convective line across the Mississippi river.
Six successive HRRR runs (Fig. 15) and the verifying 2100 UTC radar (Fig. 16) show the
evolution of the QLCS system as forecast and observed. The salient point for this event was how
well the HRRR captured the convective mode and how well the HRRR tracked the system to the
east. At times the HRRR was slow relative to the observed radar.
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Compared the SREF QPFs and probabilities of heavy rainfall (Fig. 11-13) it was apparent that
the HRRR showed a faster evolution of the heavy rainfall to the east than implied in the SREF
forecasts ending at 0000 UTC 14 October. The 1800 UTC HRRR (Fig. 17) near the mid-point of
the forecasts in Figure 11, show that the heavy rainfall and convection was well into Mississippi
from 2200 through 0000 UTC. The HRRR QPF in the periods was not shown.
5. Summary
A strongly forced heavy rainfall and convective event impacted the central United States on 1314 October 2014. The strong LLJ and high CAPE lead to a severe weather event in the lower
and MMV’s. Tornadoes were observed as far north as Illinois, though most of the observed
severe weather was in the form of strong winds from a QLCS. The larger scale pattern was a
pattern often associated with both heavy rain and QLCS.
The NCEP 16km SREF did relatively well predicted the pattern and thus the areas of heavy
rainfall. The system is too coarse to predicted convective mode though along and ahead of the
cold front the SREF predicted the ingredients for convection including strong low-level winds
and shear and relatively high CAPE. The SREF also produced rainfall in the region implying
ascent to realize the convection.
The SREF 24 hour totals showed some areas of over 50mm in both the convection ahead of the
front and in the cold conveyor rain area (Fig. 13e-f). The short-term nature of these 50 mm
forecasts implied a slow but steady convergence to get the higher amounts in extremely short
forecast ranges. Clearly, as forecast length decreases, new data improves the SREF short-term
forecasts. But with a cold start and 6-hourly updates this effect is not as dramatic as that shown
in the HRRR which is updated hourly.
The rapidly updated HRRR with radar used to hot-start the model, provided relatively good
guidance as the nature of the convective evolutions. The HRRR also produced the wrap-around
band and handled a weak short-wave ahead of the QLCS which produced rain over portions of
Florida, Alabama and Georgia. The power of rapidly updated forecasts and convective allowing
models has been shown to provide skill in predicting convective mode. Several studies
(Weisman et al. 2013) have shown the power the convective allowing models to simulate historic
derechoes to include 8 May 2009 super derecho. A more recent study showed the ability of the
HRR to simulate the historic eastern United States derecho of 30 June 20121.
Clearly, the HRRR provides excellent guidance with regard to convective mode and system
evolutions. However, relative to the radar there are considerable issues with timing and the
convective details. The system is not perfect but represents an historic leap forward in short-term
1
Morris Weisman provided output from simulations of the historic 30 June 2012 derecho and his related talk is
available on line from this AMS link: https://ams.confex.com/ams/15MESO/webprogram/Paper227825.html
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forecasting and an opportunity to improve short-term forecasting. There are also issues to learn
from such as the transition from coarse models such as the SREF to the HRRR.
Comparing successive HRRR forecasts to the latest 6 SREF forecasts implied the SREF was too
slow to move the heavy rainfall eastward. The 18Z HRRR was shown relative to the SREF 12
hour QPF in the 1200 to 0000 UTC window. The HRRR indicated that the more intense rainfall
had moved east of the SREF area of heavy rainfall. Though not pointed out, the HRRR also
showed little in terms of QPF and intense “radar” in the western area of heavy rainfall implied by
the SREF. This implies an opportunity to use the HRRR and to study using the HRRR to
improve upon these coarser cold-started model and ensemble forecast systems. The key point:
rapid updates in the QPF and radar often create some conflict in the QPF and PoPs provided
by models which are not rapidly updated and imply the potential to improve short-term
forecasting.
6. Acknowledgements
7. References
Atkins N. T., J. M. Arnott, R. W. Przybylinski, R. A. Wolf, and B. D. Ketcham, 2004:
Vortex structure and evolution within bow echoes. Part I: Single-Doppler and damage
analysis of the 29 June 1998 derecho. Mon. Wea. Rev., 132, 2224–2242.
Atkins, N.T., C.S. Bouchard, R.W. Przybylinski, R.J. Trapp, and G. Schmocker, 2005:
Damaging Surface Wind Mechanisms within the 10 June 2003 Saint Louis Bow Echo
during BAMEX. Mon. Wea. Rev., 133, 2275–2296.
Juanzhen Sun, Ming Xue, James W. Wilson, Isztar Zawadzki, Sue P. Ballard, Jeanette OnvleeHooimeyer, Paul Joe, Dale M. Barker, Ping-Wah Li, Brian Golding, Mei Xu, and James Pinto,
2014: Use of NWP for Nowcasting Convective Precipitation: Recent Progress and
Challenges. Bull. Amer. Meteor. Soc., 95, 409–426.
doi: http://dx.doi.org/10.1175/BAMS-D-11-00263.1
Maddox,R.A., C.F Chappell, and L.R. Hoxit. 1979: Synoptic and meso-alpha aspects of
flash flood events. Bull. Amer. Meteor. Soc., 60, 115-123.
Morris L. Weisman, Clark Evans, and Lance Bosart, 2013: The 8 May 2009 Superderecho:
Analysis of a Real-Time Explicit Convective Forecast. Wea. Forecasting, 28, 863–892.
doi: http://dx.doi.org/10.1175/WAF-D-12-00023.1
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8.
http://www.erh.noaa.gov/ctp/hydro/events/lws_ms/loop.html
https://docs.google.com/a/noaa.gov/spreadsheets/d/1YUUO5x1dSEFOIZhuK1izZYiEfc6OhI6OVb_Zjeing
kg/edit?usp=sharing
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Figure 1. CFS 500 hPa height and standardized anomalies from a) 1200 UTC 8 October through f) 1200 UTC 14 October 2014. Contours every
60 m and anomalies as in color bar. Return to text.
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Figure 2. As in Figure 1 except for precipitable water (mm) and precipitable water anomalies in 6-hour increments for a) 0000 UTC 13 to f)
0600 UTC 14 October 2014. Return to text.
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Figure 3. As in Figure 2 except for 850 hPa winds (ms-1) and v-wind anomalies. Return to text..
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Figure 4. Stage-IV rainfall in(mm) for the period of 0000 UTC 13 to 0000 UTC 14 October 2014. Return to text.
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Figure 5. Storm reports by type for the 24 hour period ending at 1200 UTC 14 September 2014. Return to text.
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Figure 6. NMQ site composite reflectivity showing the character of the convection as it moved
across the Mid and lower Mississippi Valley at 1500 and 1900 UTC 13 October 2014. Return to
text.
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Figure 7. As in Figure 3 except for layered CAPE. Values greater than 400JK-1 shaded. Return to text.
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Figure 8. NCEP SREF ensemble mean CAPE valid at 2100 UTC 13 October from 6 SREF runs initialized at a) 0900 UTC 12 October through f)
1500 UTC 13 October 2014. Return to text.
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Figure 9. As in Figure 8 except for PWAT. Return to text.
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Figure 10. As in Figure 8 except for v-wind in ms-1. Return to text.
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Figure 11. The probability of 25mm or more QPF from 1200 UTC 13 October through 0000 UTC 14 October 2014 from NCEP SREF initialized at
a) 2100 UTC 12 October through f) 0900 UTC 13 October 2014. Return to text.
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Figure 12. As in Figure 11 except the SREF mean QPF and each members 25mm contour. Return to text.
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Figure 13. As in Figure 12 except the 24 hour total and the 50 mm contours from each SREF member. Return to text.
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Figure 14. NCEP 1500 UTC HRRR showing estimate composite reflectivity (dBZ) in hourly increments from a) 1900 UTC through f) 0000 UTC 13-14
October 2014. Return to text.
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Figure 15. As in Figure 14 except for showing conditions from 6 HRRR from a) 1500 UTC through f) 18000 UTC 13 October valid at 2100 UTC 13
October 2014. Return to text.
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Figure 16. As in Figure 6 except valid at 2100 UTC for comparison to Figure 15. Return to text.
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Figure 17. As in Figure 15 except for the 1800 UTC HRRR showing forecasts in hourly increments from a) 1900 UTC through f) 0000 UTC 13-14
October 2014.. Return to text.