Use of TAMDAR Data in a Convective Weather Event

Saturday, May 21, 2005

Background InformationBackground Information

TAMDAR was used by meteorologists at the TAMDAR was used by meteorologists at the NWS office in Sioux Falls, South Dakota during NWS office in Sioux Falls, South Dakota during an an expectedexpected convective event on May 21, 2005. convective event on May 21, 2005.

Model soundings suggested that a mid level cap Model soundings suggested that a mid level cap would erode during the late afternoon, resulting would erode during the late afternoon, resulting in strong or severe thunderstorms.in strong or severe thunderstorms.

The Storm Prediction Center (SPC) had this The Storm Prediction Center (SPC) had this area in a Convective Outlook, and later issued a area in a Convective Outlook, and later issued a Tornado Watch. Tornado Watch.

Background InformationBackground Information

Sioux Falls forecasters looked at TAMDAR Sioux Falls forecasters looked at TAMDAR soundings from Sioux City, Iowa during the late soundings from Sioux City, Iowa during the late afternoon and early evening hours.afternoon and early evening hours.

The soundings showed a mid level cap that would be The soundings showed a mid level cap that would be nearly impossible to overcome by expected surface nearly impossible to overcome by expected surface heating. Therefore, they lowered the probability of heating. Therefore, they lowered the probability of thunderstorms in their local forecasts. thunderstorms in their local forecasts.

Based upon the observation that the cap would be Based upon the observation that the cap would be too strong to overcome, they coordinated with SPC too strong to overcome, they coordinated with SPC to leave six of their counties out of the tornado to leave six of their counties out of the tornado watch.  No severe weather occurred in those watch.  No severe weather occurred in those counties. counties.

Sioux Falls Forecast AreaSioux Falls Forecast Area

The Sioux Falls NWS is responsible for severe weather warnings for these counties

Surface Map 12ZSurface Map 12Z 5/21/20055/21/2005A surface low was moving east towards Minnesota. The easternDakotas, westernMinnesota, easternNebraska and western Iowa were forecast to be in thewarm sector in thelate afternoon.

12Z Model forecastsoundings suggestedmid level cap wouldbe overcome in thelate afternoon, withCapes of 2-3,000 J/kgand significant shear

SPC Day 1 OutlookSPC Day 1 Outlook

SPC correctly identified the significant cap SPC correctly identified the significant cap over the Plains states in this 1630UTC over the Plains states in this 1630UTC update.update.

Models forecast cap to be overcome by Models forecast cap to be overcome by strong surface heating and mid level strong surface heating and mid level cooling in the late afternoon.cooling in the late afternoon.

CAPE and shear profiles from models CAPE and shear profiles from models suggested that thunderstorms that suggested that thunderstorms that resulted could be severe. resulted could be severe.

SPC Day 1 OutlookSPC Day 1 Outlook

DAY 1 CONVECTIVE OUTLOOKNWS STORM PREDICTION CENTER NORMAN OK1120 AM CDT SAT MAY 21 2005 VALID 211630Z - 221200Z...NE/IA/KS/MO... MORNING SOUNDINGS CONFIRM THAT A SUBSTANTIAL CAP CURRENTLY ACROSSTHE PLAINS ASELEVATED MIX LAYER HAS SPREAD EWD OVERNIGHT WITH VERYSTEEP MID LEVEL LAPSE RATES. 50KT LOW LEVEL JET AHEAD OF COLD FRONTWILL RAPIDLY INCREASE LOW LEVEL MOISTURE NWD THRU CENTRAL PLAINSTHIS AFTERNOON. WHILE NAM SEEMS A LITTLE AGGRESSIVE ON MOISTURETRANSPORT...GIVEN THE OBSERVED DEWPOINTS RISING THRU THE 60S FACROSS CENTRAL KS...SUBSTANTIALDESTABILIZATION IS EXPECTED AHEAD OFCOLD FRONT BY MID/LATE AFTN AS FAR N AS ERN NEB/WRN IA. EROSION OF THE EXISTING STRONG CAP WILL TAKE PLACE THIS AFTERNOONTHRU STRONG SURFACE HEATING AND LARGE SCALE VERTICAL MOTION AHEAD OFFRONT AND APPROACHINGUPPER TROUGH. BY LATE AFTERNOON WITH MLCAPES BETWEEN 2000-3000 J/KG COUPLED…

Radar and satellite data at 18ZRadar and satellite data at 18Z

18Z radar from Omaha showed scattered 18Z radar from Omaha showed scattered showers over northern and central Iowa.showers over northern and central Iowa.

An 18Z satellite picture showed clear skies An 18Z satellite picture showed clear skies over western Iowa and the eastern over western Iowa and the eastern Dakotas, except for developing cumulus.Dakotas, except for developing cumulus.

These cumulus were expected to develop These cumulus were expected to develop into thunderstorms as the cap was broken. into thunderstorms as the cap was broken.

Radar from Omaha at 18ZRadar from Omaha at 18Z

Radar shows scattered showers over northern and central Iowa at 1800Z. Eastern Nebraska and Southwest Iowa arecurrently free of echoes.

Visible satellite picture at 18ZVisible satellite picture at 18Z

Visible satellite picturefrom 18Z shows somecumulus clouds forming over the easternDakotas, easternNebraska and westernIowa.

These clouds will laterhave little verticalextent due to the mid level capping inversion

A Waiting Game…A Waiting Game…

Now NWS WFOs in the outlook area must Now NWS WFOs in the outlook area must wait and see whether mid level cap over wait and see whether mid level cap over the Iowa, Minnesota and eastern the Iowa, Minnesota and eastern Nebraska can be broken. Nebraska can be broken.

Until recently, forecasters had no real time Until recently, forecasters had no real time way of assessing cap strengthway of assessing cap strength

TAMDAR and MDCRS data are now TAMDAR and MDCRS data are now available, and can help meteorologists available, and can help meteorologists determine convective potential in real time.determine convective potential in real time.

TAMDAR data 19Z-22ZTAMDAR data 19Z-22Z

Map showing flight paths of TAMDAR equipped aircraft 19-22Z May 21, 2005. From FSL Aircraft Web Page http://acweb.fsl.noaa.gov/java

This TAMDAR sounding from Sioux City at 1940Z shows strong directional TAMDAR sounding from Sioux City at 1940Z shows strong directionaland speed wind shear, but a mid level capping inversion that would prevent and speed wind shear, but a mid level capping inversion that would prevent severe thunderstorms from forming. severe thunderstorms from forming.

ResultsResults

Forecasters at the Sioux Falls office viewed the Forecasters at the Sioux Falls office viewed the TAMDAR data in the NSHARP program to TAMDAR data in the NSHARP program to further refine the convective potential.further refine the convective potential.

They determined that the cap would not likely be They determined that the cap would not likely be overcome, despite model forecasts suggesting it overcome, despite model forecasts suggesting it would. would. Therefore, they lowered the probability of Therefore, they lowered the probability of thunderstorms in their local forecasts.thunderstorms in their local forecasts.

They also They also coordinated with SPC to leave six of coordinated with SPC to leave six of their counties out of a tornado watch that was their counties out of a tornado watch that was issued. issued. 

Tornado Watch IssuedTornado Watch Issued

The Sioux Falls NWSasked the Storm Prediction Center toleave six counties of their forecast area out of a Tornado Watch that was issued during the late afternoon. The SPC agreed, and no severeweather occurred in those counties.

Preliminary severe weather reports Preliminary severe weather reports May 21, 2005May 21, 2005

The lack of severe weather reports from the tornado watch area shows that the mid level inversion was indeed too strong to get severe weather.

SummarySummary

TAMDAR was useful in showing that the model TAMDAR was useful in showing that the model soundings were incorrect in forecasting the mid soundings were incorrect in forecasting the mid level cap to be broken.level cap to be broken.

Sioux Falls and SPC meteorologists were able Sioux Falls and SPC meteorologists were able to improve their forecasts by leaving parts of to improve their forecasts by leaving parts of South Dakota and Iowa out of the Tornado South Dakota and Iowa out of the Tornado Watch. Watch.

Other WFOs may have been able to improve Other WFOs may have been able to improve their forecasts if they had used the TAMDAR their forecasts if they had used the TAMDAR data. data.