Evan Lowery Dr. Eric Hoffman Northeast Regional Operational Workshop IX.

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?


FIG 1: Miller (2007)


a. cell-based or gridded VIL? (VIL: cell-based)

b. Limitations of VIL





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)


b. VIL limitations? (Range: 25 – 125 km)



“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)





c. VIL threshold for thunderstorms? (Threshold: 10 kg m-2)


WSR-88D Level III Storm Structure Product (Gray/Portland, ME)



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)





c. VIL threshold for thunderstorms? (Threshold: 10 kg m-2)

d. Which radar product will be used? (Storm Structure)


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



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



NLDN Lightning strikes Vs. VIL values June – August (2005)



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)


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)


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)


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


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)


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


FIG 12: Yearly distribution of thunderstorm cells


Focus on 4 Flow Regimes


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


925 hPa SE Flow Storm Density [count / area * 100]


49 events 274 thunderstorm cells


700 hPa SW Flow Storm Density [count / area * 100]


High Storm Density



700 hPa W Flow Storm Density [count / area * 100]


High Storm Density



700 hPa NW Flow Storm Density [count / area * 100]


High Storm Density



Stability Assessment 700 hPa Flow CAPE [ J / kg ]


CAPE(J/kg)

0 Stable0-1000 Marginally unstable1000-2500 Moderately unstable2500-3500 Very unstable≥3500 Extremely unstable


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


Stability Assessment 700 hPa Flow Total Totals [-]


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


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.

http://amsglossary.allenpress.com/glossary/search?id=vertically-integrated-liquid1

Evan Lowery Dr. Eric Hoffman Northeast Regional Operational Workshop IX.

Documents

Transcript of Evan Lowery Dr. Eric Hoffman Northeast Regional Operational Workshop IX.