evan lowery dr. eric hoffman northeast regional operational workshop ix
TRANSCRIPT
Evan LoweryDr. Eric Hoffman
Northeast Regional Operational Workshop IX
- Northern New England thunderstorms pose a forecasting challenge
- Large-scale flow has often been used as a forecasting tool
- Few thunderstorm climatologies have been completed across northern New England
How does large-scale flow affect the development and intensity of northern New England thunderstorms during the warm-season
months April – September (2003 – 2007)?
Questions
1. How can thunderstorms be identified and monitored?
2. How can the pre-convective environment be analyzed?
3. How can large-scale flow be identified for each thunderstorm cell?
4. How can results be objectively analyzed?
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
“Vertically integrated liquid (VIL) water content of thunderstorms has been shown to be a good indicator for the potential of severe weather.” Winston and Ruthi (1986) Grasso and Hilgendorf (2001)
a. cell-based or gridded VIL?
b. VIL limitations
c. VIL threshold for thunderstorms?
d. Which radar product will be used?
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
FIG 1: Miller (2007)
1. How can thunderstorms be identified and monitored?
a. cell-based or gridded VIL? (VIL: cell-based)
b. Limitations of VIL
c. VIL threshold for thunderstorms?
d. Which radar product will be used?
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
1. How can thunderstorms be identified and monitored?
FIG 2: Miller and Sirvakta (2007)
25 km 125 km
FIG 3: Brown (2000)
25 km 125 km
25 km from RDA
125 km from RDA
How does large-scale flow affect the development and intensity of northern New
England thunderstorms?
FIG 4: VIL sampling region (25 – 125 km from KGYX)
a. cell-based or gridded VIL? (VIL: cell-based)
b. VIL limitations? (Range: 25 – 125 km)
c. VIL threshold for thunderstorms?
d. Which radar product will be used?
“VIL values in organized convective cells usually exceeded 10 kg m-2.” Kitzmiller et al. (1995) Brimelow (2006)
“A VIL threshold of 25-30 kg m-2 was effective at correctly identifying those storms associated with the severe hail over central Alberta.” Brimelow (2006)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
1. How can thunderstorms be identified and monitored?
a. cell-based or gridded VIL? (VIL: cell-based)
b. VIL limitations? (Range: 25 – 125 km)
c. VIL threshold for thunderstorms? (Threshold: 10 kg m-2)
d. Which radar product will be used?
WSR-88D Level III Storm Structure Product (Gray/Portland, ME)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
1. How can thunderstorms be identified and monitored?
FIG 4: NCDC Java NEXRAD Viewer (Short range reflectivity 06/19/2006)FIG 5: NCDC Java NEXRAD Viewer (Short range reflectivity 06/19/2006)FIG 6: NCDC Java NEXRAD Viewer (Storm structure product 06/19/2006)FIG 7: NCDC Java NEXRAD Viewer (Storm structure product 06/19/2006)
FIG 8: NCDC Java NEXRAD Viewer (Storm structure alphanumeric table 06/19/2006)FIG 9: NCDC Java NEXRAD Viewer (Storm structure alphanumeric table 06/19/2006)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
WSR-88D Level III Storm Structure Product (Gray/Portland, ME)
a. cell-based or gridded VIL? (VIL: cell-based)
b. VIL limitations? (Range: 25 – 125 km)
c. VIL threshold for thunderstorms? (Threshold: 10 kg m-2)
d. Which radar product will be used? (Storm Structure)
WSR-88D Level III Storm Structure Product (Gray/Portland, ME)
How accurately can the storm structure product track storms?
“The results show that cells above 40 dBz have a 68% of being detected and that cells with reflectivities above 50 dBz have a 96% chance of being detected.” Johnson et al. 1998
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
1. How can thunderstorms be identified and monitored?
CRITERIA
VIL: cell-based
Range: 25 – 125 km from GYX
Min VIL: 10 kg m-2
Min Reflectivity: 50 dBz
Min Duration: > 1 Volume scan
WSR-88D Product: Storm Structure
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
1. How can thunderstorms be identified and monitored?
NLDN Lightning strikes Vs. VIL values June – August (2005)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
1. How can thunderstorms be identified and monitored?
FIG 10: VIL (kg m-2) Vs. Lightning Count (%)
Proximity Soundings
a. Def. proximity sounding?
“Proximity refers to events which are required to occur within 3 h of the sounding time and within 100 nautical miles (185 km) in space. Craven (2001), Craven et al. (2002a,b), and Brooks (2003)
b. Which Reanalysis dataset should be used?
“It is expected that the NARR data set will show the mesoscale detail in weather systems, particularly severe weather, that the coarser NCEP/NCAR GR would miss.” Grumm (2005)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
2. How can the pre-convective environment be analyzed?
700 hPa is “the first mandatory pressure level that is clearly above the underlying terrain.” Wasula and Bosart (2002)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
3. How can large-scale flow be identified for each thunderstorm?
Radar Data Objective Analysis
Interpolation Method: Isotropic Barnes Analysis
wq = exp(-r’2/k)k = k*[(2Δaz)2
max]Trapp and Doswell (2000)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
4. How can results be objectively analyzed?
k 32.8
k* 0.5
2Δaz 232km [1o (π/180)]
grid spacing 4 km
radius of influence
3 * grid spacing
min. # obs 3
R = 232 km
- Find radar indicated start time
- Find location of Max intensification (ΔVIL/Δt)
- Find location of Max intensity (VIL)
- Find location of Max Weakening (ΔVIL/Δt)
- Find radar indicated end time
- Download relevant NARR data
- Identify large-scale flow (925, 700 hPa) per storm
- Stratify results by large-scale flow
Monitoring Storm Cell Intensity
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)- 231 events
- 3238 thunderstorm cells meet criteria
- 700 hPa Flow: (SW=1921, W=651, NW=599, SE=45, NE=22)
FIG 11: Thunderstorm cells per flow regime (700 hPa)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)
Yearly, Monthly, and Diurnal distribution
FIG 13: Monthly distribution of thunderstorm cellsFIG 14: Diurnal distribution of thunderstorm cells
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
FIG 12: Yearly distribution of thunderstorm cells
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)
Focus on 4 Flow Regimes
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
Level, Flow # Events # Thunderstorm cells
925 hPa, SE 49 274
700 hPa, SW 150 1921
700 hPa, W 79 651
700 hPa, NW 73 599
Northern New England Terrain Map
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)
925 hPa SE Flow Storm Density [count / area * 100]
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
49 events 274 thunderstorm cells
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)
700 hPa SW Flow Storm Density [count / area * 100]
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
High Storm Density
150 events 1921 thunderstorm cells
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)
700 hPa W Flow Storm Density [count / area * 100]
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
High Storm Density
79 events 651 thunderstorm cells
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)
700 hPa NW Flow Storm Density [count / area * 100]
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
High Storm Density
73 events 599 thunderstorm cells
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)
Stability Assessment 700 hPa Flow CAPE [ J / kg ]
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
CAPE(J/kg)
0 Stable0-1000 Marginally unstable1000-2500 Moderately unstable2500-3500 Very unstable≥3500 Extremely unstable
150 events 1921 thunderstorm cells
79 events 651 thunderstorm cells73 events 599 thunderstorm cells
Highest CAPE values south of mountains and away from
coast
FIG 15: Avg CAPE per 700 hPa Flow Regime
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)
Stability Assessment 700 hPa Flow Total Totals [-]
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
Total Totals Index
44 Thunderstorms50 Severe thunderstorms possible≥ 55 Severe thunderstorms likely,
tornadoes possible
TT = (T850 + Td850) - (2 * T500)43 53
FIG 15: Avg. TT per 700 hPa Flow
FIG 26: Total Totals Histogram (700 hPa SW Flow)
SW Flow has the largest number of thunderstorm cells
925 hPa SE Flow thunderstorm cells develop along mountains
700 hPa SW, W, NW Flow localized concentrations of thunderstorm cells
Total Totals low variability across all flow regimesOngoing Research
- Compare:Severe Vs. non-severe daysShort, medium, long duration storms
- Generate soundingsSevere Vs. non-severe daysShort, medium, long duration storms
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
AMS Glossary (2007). Definition of Vertically Integrated Liquid (VIL). Retrieved February 9, 2007 from http://amsglossary.allenpress.com/glossary/search?id=vertically-integrated-liquid1 Brimelow,C.,G.W. Reuter,2006: Spatial Forecasts of Maximum Hail Size Using Prognostic Model Soundings and HAILCAST. Weather
and Forecasting, 21, Issue 2, 206-219. Brooks,H.E,J.W. Lee,J.P. Craven,2003: The spatial distribution of severe thunderstorm and tornado environments from global reanalysis
data. Atmospheric Research., 67-68, 73-94. Brown, R. A., V. T. Wood, 2000: Improved WSR-88D Scanning Strategies for Convective Storms. Weather & Forecasting, 15 Issue 2, 208-220. Johnson, J. T., P. L. MacKeen, 1998: The Storm Cell Identification and Tracking Algorithm: An Enhanced
WSR-88D Algorithm. Weather & Forecasting, 13 Issue 2, 263-276. Kitzmiller, D. H., W. E. McGovern, and R. F. Saffle, 1995: TheWSR-88D severe weather potential algorithm. Wea. Forecasting,10, 141–
159.
Miller, S. T. K., Class Lecture (28 Mar 2007)
Trapp, R.J., C.A. Doswell: Radar Data Objective Analysis. Journal of Atm. Sci., 17, 105-120. Wasula, C. W., L. F. Bosart, 2002: The Influence of Terrain on the Severe Weather Distribution across Interior Eastern New York and
Western New England. Weather & Forecasting, 17 Issue 6, 1277-1289. Winston H. A., L. J. Ruthi, 1986: Evaluation of RADAP II Severe-Storm-Detection Algorithms. Bulletin of the American Meteorological Society, 67 Issue 2, 145-150.