National Weather Service Des Moines, IA Gravity Wave Interactions with the 25 May 2008 Parkersburg,...

National Weather ServiceNational Weather ServiceDes Moines, IADes Moines, IA

Gravity Wave Interactions with the 25 May 2008 Gravity Wave Interactions with the 25 May 2008 Parkersburg, Iowa Supercell Parkersburg, Iowa Supercell

The views expressed are those of the author and do not necessarily represent those of the National Weather Service.

2009 Severe Storms & Doppler Radar Conference2009 Severe Storms & Doppler Radar Conference


OutlineOutline•Mesoscale/gravity wave environmentMesoscale/gravity wave environment

•Gravity wave evidence/Nature of gravity waves Gravity wave evidence/Nature of gravity waves

•Web cam and Visible Satellite imagesWeb cam and Visible Satellite images

•Gravity waves/spectrum width evidenceGravity waves/spectrum width evidence

•Gravity waves/mesocyclone evolutionGravity waves/mesocyclone evolution

•Closing commentsClosing comments


MSLP, Surface Observations, Surface Analysis, and Visible Satellite MSLP, Surface Observations, Surface Analysis, and Visible Satellite Imagery, 2200 UTC 25 May 2008 Imagery, 2200 UTC 25 May 2008

((cyan cyan arrow indicates location of Parkersburg)arrow indicates location of Parkersburg)Analysis courtesy of SOO Karl JungbluthAnalysis courtesy of SOO Karl Jungbluth

Mesoscale Parameter Summary 22 UTC 25 May 2008

Parameter SPC Mesoanalysis value Percentile value from Davies/Rassmussen studies

• SRH 0-1 km 180 – 200 m2/s2 near 75th

• SRH 0-3 km 200 - 250 m2/s2 near 60th

• VGP 0-3 km 0.3 -0.4 60th to 75th

• EHI 0-1 km 3-5 off the scale • LCL 750-1000 m 45th to 70th

• LFC 1400-1500m near 50th

• SB CIN 25-50 J/kg 40th to 65th

• 0-3 KM CAPE 100 – 120 J/kg 50-60th

Near storm environment values from SPC Mesoanalysis page compared to studies from Davies (2002) and Rasmussen (2003)


Stable layer

•Visible satellite imagery indicated apparent gravity waves that initiated near Hastings Visible satellite imagery indicated apparent gravity waves that initiated near Hastings and Hebron, Nebraska around 1500 UTC and Hebron, Nebraska around 1500 UTC •Consistent with the synoptic patterns favorable for gravity waves outlined in Schaub Consistent with the synoptic patterns favorable for gravity waves outlined in Schaub (2005), with the initiation region was just ahead of a cold front and in the right-rear quad (2005), with the initiation region was just ahead of a cold front and in the right-rear quad of a 300-mb jet max. of a 300-mb jet max.

A proximity sounding near Fort Dodge, Iowa at A proximity sounding near Fort Dodge, Iowa at 1700 UTC also indicated a stable layer below 800 1700 UTC also indicated a stable layer below 800 mb conducive for ducted gravity wavesmb conducive for ducted gravity waves

Gravity waves are the oscillations of air parcels by the lifting force of buoyancy and Gravity waves are the oscillations of air parcels by the lifting force of buoyancy and the restoring force of gravity.the restoring force of gravity.

Gravity Wave EnvironmentGravity Wave Environment

RUC Bufkit Soundings 21z/22z RUC Bufkit Soundings 21z/22z at Waterlooat Waterloo


Koch and O’Handley (1997) Koch and O’Handley (1997) developed a “duct factor”, developed a “duct factor”, which is a measure of the which is a measure of the duct strength in the stable duct strength in the stable layer, and the degree of layer, and the degree of conditional instability in the conditional instability in the 700-mb to 400-mb layer. 700-mb to 400-mb layer. Values approached 20 Values approached 20 degrees C near Parkersburg degrees C near Parkersburg at 2200 UTC, more than at 2200 UTC, more than sufficient to support gravity sufficient to support gravity wave development and wave development and propagation. propagation.

Koch and Saleeby (2001) indicated a Koch and Saleeby (2001) indicated a Duct Factor of 10 to 15 would support Duct Factor of 10 to 15 would support strong ductingstrong ducting


•Surrounding surface observations indicate this feature was not an Surrounding surface observations indicate this feature was not an outflow boundary, as there was no significant change in wind speed outflow boundary, as there was no significant change in wind speed and direction, or temperature and dewpoint associated with small and direction, or temperature and dewpoint associated with small scale radar featuresscale radar features

•The speed of propagation (around 50-60 kts) was faster than the The speed of propagation (around 50-60 kts) was faster than the mean wind in the layer (WSW under 30 kts)mean wind in the layer (WSW under 30 kts)

•The stable layer necessary for continued ducting of the gravity The stable layer necessary for continued ducting of the gravity waves was likely well elevated at least initially (FOD sounding), waves was likely well elevated at least initially (FOD sounding), perhaps explaining why there were no significant pressure perhaps explaining why there were no significant pressure perturbations in this area. The atmosphere would also have a difficult perturbations in this area. The atmosphere would also have a difficult time responding with significant pressure changes given the fast time responding with significant pressure changes given the fast movement of the waves. (Coleman, 2009)movement of the waves. (Coleman, 2009)

•As the waves approached Parkersburg, proximity soundings indicate As the waves approached Parkersburg, proximity soundings indicate the stable layer lowering, and pressure perturbations were noted at the stable layer lowering, and pressure perturbations were noted at several locationsseveral locations

Gravity Wave Evidence/Nature of Gravity WavesGravity Wave Evidence/Nature of Gravity Waves


ASOS observations at the Waterloo Airport indicate a familiar pattern associated with gravity ASOS observations at the Waterloo Airport indicate a familiar pattern associated with gravity waves, with surface pressure rises near the wave ridge and pressure falls near the wave waves, with surface pressure rises near the wave ridge and pressure falls near the wave trough (Schaub 2005trough (Schaub 2005)

SPECI KALO 252142Z 2142Z 16011G18KT 5SM HZ BKN017 24/21 A2971 RMK AO2 LTG DSNT W-N PRESRR PRESRR METAR KALO 252154Z 2154Z 14014KT 5SM VCTS HZ SCT019 BKN023 BKN028 24/21 A2967 RMK AO2 LTG DSNT SW-N TSB50 PRESFRPRESFR SLP044 T02390206

2235z 81kt wind gust

Initial tornado at 2146Z south of

Aplington

tornado moves into Parkersburg at 2156Z

1-minute Pressure perturbations from ASOS/AWOS sites around Parkersburg1-minute Pressure perturbations from ASOS/AWOS sites around Parkersburg


Tama webcam loop from Tama webcam loop from Iowa Environmental Iowa Environmental

MesonetMesonet

Visible Imagery from 2140 ZVisible Imagery from 2140 Z

T


1st wave2nd wave

wave movement

Visible satellite imagery, 1955 UTC 25 May 2008

Storms fired just east of Fort Dodge around 2000 UTC, right after the Storms fired just east of Fort Dodge around 2000 UTC, right after the second gravity wave moved through, and near a pre-frontal trough second gravity wave moved through, and near a pre-frontal trough


T

Visible satellite imagery, 2140 UTCVisible satellite imagery, 2140 UTC

By 2140 UTC, just prior to tornado formation, the lead gravity wave By 2140 UTC, just prior to tornado formation, the lead gravity wave had pushed east of the primary warm front, which extended north to had pushed east of the primary warm front, which extended north to south near the location of the first tornadosouth near the location of the first tornado

22ndnd gravity wave gravity wave not apparent on not apparent on visible imagery,visible imagery,position position estimated from estimated from Spectrum Width Spectrum Width datadata


Visible Satellite Imagery Loop 1915Z - 2115Z Visible Satellite Imagery Loop 1915Z - 2115Z


T

•The lead gravity wave continued to hold together as it moved northeast of Parkersburg, but The lead gravity wave continued to hold together as it moved northeast of Parkersburg, but the second wave had become imperceptible using base reflectivity and velocity data, and the second wave had become imperceptible using base reflectivity and velocity data, and visible satellite imageryvisible satellite imagery•However, an analysis of WSR-88D spectrum width data revealed that the second wave was However, an analysis of WSR-88D spectrum width data revealed that the second wave was still intact through the time when the first tornado developed still intact through the time when the first tornado developed

The tornado The tornado developed just after developed just after the second wave the second wave (dashed yellow line) (dashed yellow line) passed. A nearly passed. A nearly stationary fine line stationary fine line (red solid line) likely (red solid line) likely indicates the position indicates the position of the primary north-of the primary north-to-south oriented to-south oriented warm frontwarm front

0.5 degree Spectrum Width, 2141 UTC (yellow T 0.5 degree Spectrum Width, 2141 UTC (yellow T indicates location of initial tornado ~2146 UTCindicates location of initial tornado ~2146 UTC


0.5 deg Spectrum Width Loop 2100Z – 2217Z0.5 deg Spectrum Width Loop 2100Z – 2217Z



Coleman and Knupp(2008) reviewed a number of cases in which gravity waves intersected Coleman and Knupp(2008) reviewed a number of cases in which gravity waves intersected with supercell thunderstorms, and presented evidence that a gravity wave can act to with supercell thunderstorms, and presented evidence that a gravity wave can act to strengthen a mesocyclone in two ways: 1) wind convergence ahead of wave ridges causes strengthen a mesocyclone in two ways: 1) wind convergence ahead of wave ridges causes enhanced stretching of vertical vorticity and 2) enhancement of streamwise horizontal enhanced stretching of vertical vorticity and 2) enhancement of streamwise horizontal vorticity in the storm inflow, which is then tilted into the vertical. vorticity in the storm inflow, which is then tilted into the vertical.

Wave motionWave motionSR Inflow SR Inflow vectorvector

25 May 2008 situation25 May 2008 situation


2141Z2141Z 2146Z2146Z

2137Z2137Z2132Z2132Z

Interaction between the 2Interaction between the 2ndnd gravity wave and mesocyclone gravity wave and mesocyclone


0.5 deg SRM Loop 2100Z – 2217Z0.5 deg SRM Loop 2100Z – 2217Z


Closing CommentsClosing CommentsClosing CommentsClosing Comments• Difficult to determine precise contribution of gravity waves to Difficult to determine precise contribution of gravity waves to

mesocyclone intensification in this case, given the ideal mesocyclone intensification in this case, given the ideal environmentenvironment

• No other storms in the area became tornadic…did the gravity No other storms in the area became tornadic…did the gravity waves jump start the process, or was that storm simply in the best waves jump start the process, or was that storm simply in the best mesoscale environment with unrestricted inflow?mesoscale environment with unrestricted inflow?

• These gravity waves were identified well before the Parkersburg These gravity waves were identified well before the Parkersburg tornado…but very difficult to project ahead when and where the tornado…but very difficult to project ahead when and where the waves will be interacting with important features. Increased role for waves will be interacting with important features. Increased role for SWAN?SWAN?

• Future research: Future research: What are the differences in contribution to What are the differences in contribution to mesocyclone intensification between elevated gravity waves, and mesocyclone intensification between elevated gravity waves, and those based in the storm inflow layer?those based in the storm inflow layer?


AcknowledgementsAcknowledgements

•Karl Jungbluth, WFO Des Moines Science OfficerKarl Jungbluth, WFO Des Moines Science Officer

•Marc Russell, WFO Dodge City Forecaster/Marc Russell, WFO Dodge City Forecaster/Former WFO Des Moines Met. InternFormer WFO Des Moines Met. Intern

•WFO Des Moines StaffWFO Des Moines Staff

•Dr. Tim Coleman, University of Alabama-HuntsvilleDr. Tim Coleman, University of Alabama-Huntsville


Gravity Wave Interactions with the 25 May 2008 Gravity Wave Interactions with the 25 May 2008 Parkersburg, Iowa Supercell Parkersburg, Iowa Supercell

The views expressed are those of the author and do not necessarily represent those of the National Weather Service.

2009 Severe Storms & Doppler Radar Conference2009 Severe Storms & Doppler Radar Conference

Any questions?Any questions?

[email protected]@noaa.gov


ReferencesReferences

Coleman T.A., Knupp K.R., 2008: The Interactions of Gravity Waves with Mesocyclones: Coleman T.A., Knupp K.R., 2008: The Interactions of Gravity Waves with Mesocyclones: Preliminary Observations and Theory. Preliminary Observations and Theory. Monthly Weather ReviewMonthly Weather Review: In Press: In Press

___________, 2009: Personal communication. ___________, 2009: Personal communication.

Davies, J.M., 2002: On low-level thermodynamic parameters associated with tornadic and Davies, J.M., 2002: On low-level thermodynamic parameters associated with tornadic and non-tornadic supercells. Preprints, non-tornadic supercells. Preprints, 2121stst Conf. on Severe Local Storms, Conf. on Severe Local Storms, San Antonio, TX, San Antonio, TX, Amer. Meteor. Soc., 603-606. Amer. Meteor. Soc., 603-606.

Koch, S. E., and C. O’Handley, 1997: Operational forecasting and detection of mesoscale Koch, S. E., and C. O’Handley, 1997: Operational forecasting and detection of mesoscale gravity waves. gravity waves. Wea. Forecasting, Wea. Forecasting, 1212, 253-281., 253-281.

________, and S. Saleeby, 2001: An automated system for the analysis of gravity waves and ________, and S. Saleeby, 2001: An automated system for the analysis of gravity waves and other mesoscale phenomena. other mesoscale phenomena. Wea. ForecastingWea. Forecasting, , 1616, 661-679., 661-679.

Rasmussen, E.N., 2003: Refined supercell and tornado forecast parameters. Rasmussen, E.N., 2003: Refined supercell and tornado forecast parameters. Wea. Wea. Forecasting, Forecasting, 1818, 530–535., 530–535.

Schaub, Jr., W.R.: Gravity Waves: Those Important to Operational Weather Forecasting. Schaub, Jr., W.R.: Gravity Waves: Those Important to Operational Weather Forecasting. Forecasting Note, 28 February, 2005.Forecasting Note, 28 February, 2005.

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