40 th national weather association annual meeting oklahoma city, ok october 20 th, 2015 chris melick...
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40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
Chris Melick1,2, Patrick Marsh1, Andy Dean1, Israel L. Jirak1, and Steven J. Weiss1
1NOAA/NWS/NCEP/Storm Prediction Center2CIMMS, University of Oklahoma
Norman, OK
Lightning Characteristics and Relationship to Preliminary Local
Storm Reports
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
INTRODUCTION
• The National Weather Service (NWS) Storm Prediction Center (SPC) is responsible for forecasting lightning and severe thunderstorms, as well as for other high impact hazardous weather (including fire and winter precipitation)
• For SPC, observations serve crucial role given short-term nature for many of the products issued– Mesoscale Discussions (MD)/Watches focus on few
hours after issuance – Provide Situational Awareness– Evaluation and Verification
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
MOTIVATION• NWS defines a severe thunderstorm to contain
wind gusts ≥ 50 kt, hail ≥ 1” in diameter, and/or any tornado – However, all thunderstorms (regardless of
severity) still also require presence of lightning.– While relatively rare, winter thunderstorms can
occur where lightning is coincident with frozen precipitation (e.g., thundersnow)
• More detailed information about convective cells can be provided by combining observational networks – Total [Cloud-to-Ground (CG) and Intra-Cloud (IC)]
Lightning– Preliminary Local Storm Reports (LSRs)– Others not examined here (e.g., Radar and
Satellite, ASOS/AWOS)
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
• The relationship between preliminary LSRs and total lightning flash data is explored using time-matched, high-resolution gridded data from 2014.
• The purpose is to provide some initial statistical characteristics of the lightning data when stratified by geographic region, time of year, and type of flash (IC or CG).
• Details on the location and frequency of active lightning grid points relative to severe and winter type reports are also explored.
MOTIVATION
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
Lightning Data at SPC• SPC has access to real-time data feeds from two
vendors:A. Vaisala’s National Lightning Detection Network
(NLDN)B. Earth Networks Total Lightning Network (ENTLN)
• SPC also gets quality-controlled (QC) NLDN CG flashes for prior year.
• Transition from CG Total Lightning• For 30 years, CG lightning flash data used at SPC to
monitor on-going convective systems (Bothwell 2014). • CG part is small in Total Lightning when compared
with IC. Further, IC flashes often precedes CG flashes in convective initiation (MacGorman and Rust 1998).
• Concern addressed as SPC acquired Total Lightning data in late 2012.
• For current work, characteristics from the QC CG NLDN data for 2014 will be contrasted to the CG and IC flash counts from ENTLN
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
Local Storm Reports (LSRs)
Local Storm Reports (LSRs) – Routinely used at SPC for decades
• Preliminary but quick way to summarize recent/current weather events.
• Traditionally, focus placed on Severe (tornado, wind, hail) LSRs
• Recently, SPC developed LSR decoder to include Winter weather related type reports (Sullivan et al. 2014).
• NEW: Snow, Heavy Snow, Freezing Rain, Sleet, Blizzard, Ice Storm
• All LSR types examined here for 2014 except for Blizzard and Ice Storm as they comprise a very small proportion of the Winter sample size
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
DATA PROCESSING
• For all of 2014, Hourly Bins created for: 1. CG/IC/TOTAL ENTLN and QC CG NLDN Flash
counts 2. Separate tallies of Total Severe LSRs and Total
Winter LSRs
• Placed on nearest 0.04deg x 0.04deg Lat-Lon grid point
• Analysis domain restricted to continental United States
• QC of problem data reduced sample size to 8712 hours (363 days).
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
QC CG NLDN > CG ENTLN
SUMMER: IC SLOPE INCREASES
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
• 89% of ENTLN Detections are IC
• NLDN (QC CG) has 1.22 times more detections than ENTLN CG
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
CG ENTLN QC CG NLDNDIFFERENCE FIELD: QC CG NLDN – CG ENTLN
More areas in US where NLDN > ENTLN (RED)
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
CG ENTLN IC ENTLN
Extensive, much higher IC compared to CGIC > 1000 in FL/Gulf Coast/Missouri Valley
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
CG ENTLN IC ENTLNTOTAL ENTLN
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
DATA PROCESSING
• For an effective comparison, binary (1/0) event grids in both observation datasets were constructed by specifying thresholds.
• For the LSRs, a severe object was recorded if ≥ 1 reports occurred within the hour. Similarly, the case of ≥ 1 Flashes indicated a grid point with an active thunderstorm.
• Grid-point Matching of Event Grids Results in 2x2 Table:
LSR with Lightning LSR with NO Lightning
Lightning with NO LSR
Neither Lightning nor LSR
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
LIGHTNING AND LSRs: MATCHING ILLUSTRATION
Nearest Grid Point versus Neighborhood
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
Nearest Grid Point MatchingLTNG (Blue dots) with LSRs (Red Stars)
LSR but NO LTG
LSR with LTG
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
Neighborhood MatchingLTNG (Blue dots) with LSRs (Red Stars)
ROI: 40-KM
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
Lightning DatasetQC CG NLDN
CG ENTLN
IC ENTLN
TOTAL ENTLN
Percentage of ALL Severe LSRs with Lightning [%] (n = 21,194 grid points)
97.462 97.211 97.933 98.014
Lightning DatasetQC CG NLDN
CG ENTLN
IC ENTLN
TOTAL ENTLN
Percentage of ALL Winter LSRs with Lightning [%] (n = 64,332 grid points)
0.555 0.622 0.639 0.759
2014 Domain Percentages: Neighborhood Lightning with Severe LSRs (Top) and Winter LSRs (Bottom)
Better Relationship with Total Lightning: Higher percentages!
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
Severe LSRs with NO LightningCounts of ≥ 1 Objects within 40-
km ROIQC CG NLDN (Left) Versus Total ENTLN
(Right)
Less Severe LSR Events without Total Lightning compared to just CG!
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
Winter LSRs with LightningCounts of ≥ 1 Objects within 40-
km ROIQC CG NLDN (Left) Versus Total ENTLN
(Right)
More Winter LSR Events with Total Lightning compared to just CG!
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
SUMMARY
• 2014 Bulk Lightning Datasets:– Hourly, High-resolution CG/IC Lightning
Flash Grid – Observations linked to LSRs by defining
“Active” Objects
• The use of NLDN/ENTLN permitted:1. A systematic evaluation and comparison of
annual lightning properties from different detection networks
2. Identifying contrast in thunderstorms by incorporating IC in Total lightning versus just using CG flashes
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
CONCLUSIONS• Flash Counts of ENTLN and NLDN show:
– Similar CG pattern but NLDN detection 1.22 x more than ENTLN
– IC more extensive/numerous than CG across US as IC portion of Total Lightning was large [~0.89]
– FL/Gulf Coast highest frequency TSTM location with secondary max more evident with IC in Missouri Valley
• Relationship between Lightning and LSRs:– Severe (Winter) LSRs consistently (rarely) coincide
with CG/IC Flashes as greater (less) than 97% (1%) of grid points meet criteria.
– Still, better relationship found by incorporating IC in Total Flashes
– Density of Severe LSRs occurring without lightning greatest in Mid-Atlantic States. Principal locations of Winter LSRs occurring with lightning in Central/Southern Plains, near Great Lakes, and Rocky Mountains
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
FUTURE WORK
• Some Items to Explore:1. Diurnal: Which hour has most lightning and strongest correlation? 2. Seasonal: Highest frequency of lightning with winter LSRs?3. Methodology: Does relationship increase with time-window?4. Case study: What distinguishes a success mode of LSRs in close
proximity to lightning flashes from a null scenario?
ACKNOWLEDGMENTS
This work was prepared with funding provided by NOAA/Office of Oceanic and Atmospheric Research under NOAA-University of Oklahoma Cooperative Agreement #NA11OAR4320072, U.S. Department of
Commerce. The statements, findings, conclusions, and recommendations are those of the author(s)
and do not necessarily reflect the views of NOAA or the U.S. Department of Commerce.
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
WINTER
SEVERE
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
Lightning with Severe LSRsCounts of ≥ 1 Hours within 40-km ROI
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
Winter LSRs with NO LightningCounts of ≥ 1 Hours within 40-km ROI
40th National Weather Association Annual Meeting Oklahoma City, OK
October 20th, 2015
WINTER
SEVERE
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