1. July 2013 Jeffrey Nelson 1
TAMDAR Enhanced Forecasting of Cold-Air Damming Events in the
Southeast and Their Associated Characteristics
Jeffrey L. Nelson
Mississippi State University, Starkville, Mississippi
ABSTRACT
The developmentof a cold-air damming scheme caused by the orographic blocking and
stabilization of the atmosphere is still not a well-knownprocess. Cold-air damming detection and
forecasting is a particularly important area of meteorology for Southeastern states. Therefore,the
advancement of forecasting techniques is crucial in aiding municipalities in being adequately
prepared for winter weather events.This study looks to combine the expansive network of
Tropospheric Airborne Meteorological Data Reporting TTAMDAR sensors to some existing cold-air
detection algorithms and perform model comparisons betweenthe Panasonic Weather Solutions
RTFDDA 12km model and the NAM 12 km model. The increased data availabilityprovided by the
TAMDAR network should enhance the algorithms effectivenessin detecting cold-air damming
events.Using t tests and root mean square error analysis to perform statistical analyses on the
mean valuesof meteorological components, including minimum central pressure at several
locations and events across the Southeast, it is hoped a significant improvement will be found with
the addition of the TAMDAR data set over using standard available soundings currently employedin
Cold Air Damming forecasting. The utility of these improved forecasts can greatly assist local
governments in the Southeast in preparing for potential severe winter weather onset from cold-air
damming events.
1. Introduction
Winter weather in the Southeast is a fairly
rare occurrence. Places like Georgia and South
Carolina seldom have true snow days, though
the city may shut down under the threat of a
storm. Ice storms are slightlymore prominent
when the mid layersof the atmosphere
manage to stay just warm enough for
precipitation to remain liquid,while the
surface is at or below freezing.This study
attempts to examine the current methods
used to forecast Cold Air Damming TCAD
events,a case phenomenon for keeping
colder air at the surface, and attempt to

2. 2
improve upon them by using the TAMDAR
network of aircraft-based data to increase the
spatial and temporal availabilityof initial
records. Some questions to investigate are
what are the frequenciesof winter weather
eventsin the Southeast and how many are
also correlated with CAD events? Is there a
notable difference in time of winterfor these
eventsto developas opposed to typical
frontal systems? What other meteorological
phenomenon typically coincide with the
developmentof the CAD eventand how does
it, or not, contribute to more severe winter
weather? Does the additional input data
better predict the life-cycle of a CAD event?
Part of this research will necessitate looking
back at cold air damming eventsover the last
10 years and perform a verification of
forecasts with and without the additional
TAMDAR data. Further attempts will be made
to incorporate more vertical sounding data
into forecast models to determine any other
interactions the cold dome may have with
higher levelsto predict onset and erosion
time frames. A prominent goal of this study is
to determine if the additional data source
makes it possible to create a more precise
climatology, not only betweentraditional CAD
types, but within categories to determine
strengths. It is hoped through this study that
with a significantly more robust data source,
the CAD events can be more accurately
forecasted.
2. Cold-AirDamming Review
Topographicinfluencescanhave varyingeffects
on air flow and subsequentweather patterns.In
particular,alongthe easternside of the
southernAppalachians,stable,coldairbecomes
trappedagainstthe slopescreatingadamming
effect.Inadditiontotrappingcoldair inthis
region,otherphenomena,suchascoastal warm
fronts,backdoorcoldfrontsandcoastal
cyclogenesisare believedtobe initiatedbythis
coldair dammingTRichwien,1980 .Coldair
dammingisunique tonorth-southoriented
mountainchainswhere easterlyflow ismore
likelytobecome blocked.Althoughthe Rockies

3. 3
can alsoachieve thissetup,the distinctive
featuresalongthe eastcoastmake these events
more influential onlocal weather.The
“backdoor”coldfronthelpstoentrenchthe
coldair furthersouthbyadvancingfroman
atypical direction,the northeastTRichwien,
1980 . Furthermore,the developmentand
persistence of coldairdamminginthe
Southeastcanplaya significantrole inthe types
and strengthof frozenprecipitation.
Bosart’sT1981 studyof the Presidents’Day
stormin 1979 foundthe existence of a“wedge”
of coldair alongthe southernAppalachiansthat
were correlatedwithacoastal warmfront;this
allowedforthe entrainmentof moisturethat
broughtsubstantial precipitationtothe
Southeast.
The Genesisof AtlanticLowsExperiment,
GALE, wascarried outin 1986 totry to
understandthe processesbehindEastCoast
winterstormformation.2out of 13 observed
stormswere attributedtocoldairdamming,
withone classifiedasa long-lastingeventunder
influence of the lowlevel jetonbothsidesof
the AppalachiansTDirksetal.,1988 . Mote etal.
T1997 alsofoundthe existence of alow leveljet
that developsalongthe barrierbetweenthe
coldair dammingandcoastal regionthatassists
incyclogenesis.These findingshelptoconfirm
some of Richwien’searlierworkoncoldair
damming’sinfluence oncoastal cyclogenesis.
Coldair dammingcanbe recognizedby a “U”
shapedridge insealevel pressure maps,aswell
as the presence of a temperaturegradientof
greaterthan “20C fromthe dammingregion
and the coast” TBell &Bosart,1988 . Figure 1
showsa graphicrepresentationof the flow
regime alonganorographicbarrieras itrelates
to coldair damming.These eventsare more
typical duringlate fall andearlywinterwhile the
waterisstill verywarmcomparedto the land
and amountto 3 to 5 eventspermonthTBell
and Bosart,1988 . Some additional synoptic
featuresassociatedwithcoldairdamming
include aparenthighthat islocatedtothe
northeastof the dammingregion;however,
precipitationcanalsostarta dammingeventby
evaporative coolingthatwill increase the

4. 4
surface pressure THartfield,1998 .Baileyetal.
T2003 additionallynotedthatevaporative
coolingcanenhance stabilitywhichcan instigate
or intensifycoldairdamming.Once the
dammingeventisinplace,freezingrainevents
are a commonoccurrence where the mid-level
moisture staysliquidjustabovethe colddome
before refreezingasitentersthe belowfreezing
surface layerTRauberet.al,2000 . As statedin
ChangnonT2003 , manyof the ice stormsin his
studywere relatedto “airmassinteractionswith
the AppalachianMountains”.Moreover,Hunter
etal.T2001 documentedanexceptiontotheir
studywhere ice accumulationwasdue toa cold
air dammingeventinsteadof aslowmoving
frontal system,while the existence of asplit-
front, “whichoccursas a midlevel baroclinic
zone advancesaheadof a coldfront”, can bring
additional precipitationtothe dammingregion
TBrennanetal.,2003 .
Fig.1 Coldair dammingeventmodel.
Importantthingstonote are the sloping
inversionthathelpstokeepthe air
stable,also,the low-level wind
maximumthattransportsthe coldair
southwestalongthe mountainslopes
TBell &Bosart, 1988 .
The methodologyinthe currentinvestigation
will use acombinationof algorithmsand
statistical equationstodetermine the viabilityof
forecastingtechniquestodayandthe utilityof
addinginTAMDAR dataintothe traditional pool
of National WeatherService radiosonde datato
improve andbetterclarifythe specifictype of
CAD eventthatisoccurring.Indeterminingthe
existence of acoldair dammingevent,Bell&
BosartT1988 utilizedthe Froude numberto
determine the amountof energyaparcel
neededtomove overthe mountaintopthrough
the equationF2
= U2
/TN2
H2
,where Uisflow

5. 5
normal to the obstacle,N isthe Brunt-Väisälä
frequencyandH isthe obstacle height.Lower
Froude numbers,ingeneral under2.5,indicate
blockedparcelsTBell,1988 ,butfor the
Appalachian studyregion,computedvaluesin
the range of 0.3 to0.4 are more common
TForbesetal.,1987 . Byexaminingupperlevel
jetstreaks,Uccellini &KocinT1987 ,propose
that areasof increasedheavyprecipitationcan
be identifiedwithinthe dammingregion. A
similaralgorithmasdevelopedbyBaileyet
al.T2003 to determinethe existence of acold
air dammingeventwill be employedoverthe
lasttenyears.Thisalgorithmutilizedhourly
surface observations,butneglectedsoundings
due to the sparse nature of the grid.The current
studywill incorporatethe use of National
WeatherService soundingsinadditiontothe
TAMDAR networkof soundingstosubstantially
increase the available inputdataforthe
algorithm.Accordingtothe Baileyetal.T2003
study, the classiccoldair dammingevent
typicallyhasa parenthighwitha central
pressure greaterthan1030 mb.This will be
usedas a base numberto identifypotential
developmentof coldairdamming.The
hypothesisforthisstudyisthatthe additional
vertical, as well assurface baseddata,will
improve the forecastingabilityof coldair
dammingeventsandenhance the algorithm’s
capabilities. Especiallyinthe case of Baileyet
al.,whose workonthe detectionalgorithmwill
be the inspiration forthe currentstudy,the
precedingresearchall playsagreaterrole ina
deeperunderstandingof cold-airdammingand
itsrelatedprocesses.Exploringthesevarious
topicsensuresawell-roundedknowledgeof the
phenomenaathandand increasesthe
likelihoodof successof the currentendeavor.
3. Data and Methodology
To try to improve the algorithmdevelopedby
Baileyetal.T2003 ,additional spatial and
temporal datawill be utilizedtoenhance the
algorithm’scapabilities.One of the underlying
equationsusedtodeterminethe extentof
blockage isthe Froude number. Thisfigure is
foundbydeterminingthe amountof kinetic
energy thatisrequiredtoovercome abarrier.

6. 6
The value will be validover the lengthof the
barrierand the lowerthe Froude number,the
strongerthe blockingpattern.A studybyForbes
etal.T1987 foundFroude numbersfor
Appalachiancoldairdammingtobe in the
range of 0.3 and 0.4. Forthis reason,the current
studywill use 0.4 as an upperthresholdwhen
determiningdammingepisodes.Events
determinedtodisplaythe blockingcriteriaof a
Froude numberbelow0.4will thenbe
examinedfurtherwithinthe dammingdetection
algorithm. The Baileyetal.T2003 algorithm
usestransectsacrossmultiple locationsinthe
southeasttodeterminethe differencesin
pressure fromthe Appalachianstothe coast,
figure 2. Three horizontal transectsthrough
Knoxville-Greenville-Charleston,Bristol-
Greensboro-WilmingtonandCharleston,WV-
Lynchburg-Norfolkandone vertical transect
fromGreensburg-Greensboro-Richmondwere
chosenfora representative areaof the coldair
dammingregion.
Figure 2 – Graphical depictionof transects
selectedinthe Baileyetal.T2003 paper.
In addition,these were the onlylocationswhere
sufficientobservationswere able tobe obtained
fromthe National WeatherService. Moreover,
the lack inavailabilityof vertical soundings
limitedthe studytoonlysurface observations.
Bell andBosartT1988 foundthatthe calculation
of Laplacians,eithersealevelpressure or
potential temperature,fromstationsfromthe
mountainstothe coastgave a measureable
value forthe strengthof the colddome
associatedwiththe CADevent.These were
calculatedthroughthe equation
∇2 𝑥 =
𝑥3−𝑥2
𝑑2−3
−
𝑥2−𝑥1
𝑑1−2
1
2
(𝑑2−3+𝑑1−2)
T1
where x is the sea level pressureforthe
denotedlocationsanddis the distance
betweeneachlocationTBaileyetal.,2003 . The

7. 7
surface pressure was “normalized”tosealevel
pressure forall locationstoaccountfor
differencesinelevationbythe equation
ln 𝑝 𝑠𝑙 = ln 𝑝 𝑠𝑡𝑛 +
𝑔
𝑅 𝑑 𝑇𝑣
𝑧 𝑠𝑡𝑛 T2
where Rd is the dry gasconstant,Tv is the virtual
temperature atthe station,andz isthe
elevationof the stationTBaileyetal.,2003 . Bell
and BosartT1988 foundthatthe Laplacianof
sealevel pressure providedanumerical value to
associate tothe strengthof the colddome ina
dammingevent. Thiscurrentstudywill use
similarthresholdsasdefinedbyBaileyet
al.T2003 to determinethe existence of acold
air dammingevent.Theseinclude the presence
of a parenthighpressure centernorthof 40N
and between100and 65W. The central
pressure mustalsoexceed1030mb.Because
additional datawill be ingestedtothe
algorithm,some subsequentlibertieswiththe
original studywill be taken.Forinstance,cold
air dammingeventswill be limitedto events
that are classicdiabaticallyenhanced,meaning
precipitationwithin6hours of onset,anddry
onsetevents.Also, the time frame studied has
beenreduced tobetweenNovemberand
March, the highestfrequencyof eventsfound
by Baileyetal.T2003 ,as opposedtothe entire
year.For the currentstudy,a historical
examinationusingthe National WeatherService
EasternRegionHeadquartersStormArchive to
find coldair dammingeventswill be conducted
overthe past 10 yearssince the lasttime this
algorithmwasused.Subsequently,datawill be
collectedfromthe same National Weather
Service officesoverthe last10 yearstorepeat
the previousexperiment.Inaddition,
TroposphericAirborne Meteorological DAta
Reporting,or TAMDAR,fromPanasonicWeather
Solutionswill be usedtoperformasecondary
teston the same time periodfromthe same
and additional locationswithasubstantially
greaterdatasetthanwhatcan be foundfrom
traditional soundingdata.Thisdatawill be used
to enhance the traditional informationfound
fromthe National WeatherService toattempt
to enhance the detectionof dammingevents.
Furthermore,the abundance of thisdatawill
alsoprovide foramore robustdatasetof upper

8. 8
air observationstoattempttointroduce a
vertical profile of the coldair dammingevents.
Hourlysurface datawill be retrievedfromthe
National ClimaticData Centerforthe same
stationsas the original studyandfurther
analysiswill determinethe bestlocationsto
extractthe TAMDAR datato give the bestspatial
and temporal representationof the study
region.The TAMDARmodel datawill be
retrievedfromthe PanasonicWeatherSolutions
RTFDDA model andprocessedthroughthe
dammingdetectionalgorithmasdiscussed in
Baileyetal.T2003 throughthe GridAnalysisand
DisplaySystem,GrADS,software package.
Statistical analyses,includingrootmeansquare
errortests,will be performedonseveral
parametersfrombothalgorithmrunscompared
to data fromactual events.A comparisonof the
average central pressure fromaparticularevent
will be comparedagainstthe forecastpressure
average forthe NAM12 km model as well as
againstthe TAMDARenhancedRTFDDA model,
to determinethe significance level of addingthe
extradata.It isfurtherhopedthata 3-D
representationof the colddome canbe created
usingthe vertical profilesprovidedbythe
TAMDAR data.Due to the increaseddensityof
observationsandspatial coverage of the
dammingregion,alayeredapproachis
proposedusingthe difference in mandatory
levelsof pressure andobservingthe difference
indew pointat the surface.Particularlyin
diabaticallyenhancedevents,abetterforecast
of the topof the colddome may leadtobetter
precipitationforecasts,especiallyin
distinguishingbetweenfrozenorliquid
precipitation. Thisstudywill focusonthe
developmentof the CADevent,butadditional
studieswithstatistical analyses performedon
timingof precipitationonset,aswell as
examininganycorrelationbetweencolddome
heightandintensitytoprecipitationtype may
be conductedinthe future.Figure 3showsthe
locationsof airportswiththe TAMDAR fleet,
alongside agraphicrepresentationof select
flightsovera weekend.Fromthisgraphicalone,
it can be seenthe copiousamountof
informationthatcanbe extractedacrossthis

9. 9
coldair dammingregion. UnlikeNational
WeatherService offices,the TAMDARnetwork
continuestoexpand,increasingthe available
dataset, whichinturn will improve the forecast
processandself-updateasnewandadditional
data ismade accessible.
Figure 3 – The top image depictsairport
locationswhere TAMDARequippedaircraftfly
intoand are possible pointsof interestfor
observations.The bottomimage depictsthe
flightcoverage of TAMDARaircraftsoverthe
coldair dammingstudyregionovera48 hour
period.
4. Results
It ishopedthat the improvedforecastsof cold-
air dammingeventswill allow forcitymanagers
and emergencymanagementtobetterprepare
forsignificantfrozenprecipitationeventsthat
typicallyaccompanythese phenomena.
Statistical analyses,includingrootmeansquare
calculations, were performedoneachof the
eventsinthis study.Thiswill helpnarrowdown
the more significantandthreateningeventsto
betterdeterminethe usefulness of the TAMDAR
enhancedforecasts.Furthermore,asimple
differenceanalysiswasconductedbetweenthe
NAM12km forecastmodel andthe Panasonic
WeatherRTFDDA 12km model. The additional
data providedbythe TAMDARnetworkhas
beenshowntoimprove the accuracyof
forecastsinmanyotherstudiesTFischer,2006,
Sun& Zhang,2006, Szoke etal.,2006 . Similar
resultswere found inthe currentinvestigation
to the extentthatthe synopticpatternaheadof
a cold-airdammingeventcanbe anticipated
sooner.Thiscan allow forecasterstodetermine
othersignificantparameters,suchasmoisture

10. 10
availabilityandthe potential forseverewinter
weatherevents,includingice storms.
Table 1 shows the root mean square
values calculated for four differentcold air
damming events. In each event,the RMSE
value for the RTFDDA TAMDAR model had a
lower error value as compared to the actual
pressure analysis for the event. Despite the
small sample size, a t test can be run on these
two samples to determine if the difference is
statistically significant. For these two datasets,
the resultant P-value is 0.004 indicating that
the difference betweenthe two model
performances is statistically differentand the
TAMDAR model is closer to the actual event.
RMSE Thpa for
TAMDAR
Model
RMSE Thpa
for NAM
Model
2009
Event
1.34 3.86
2010
Event
2.73 5.14
2013
Event
1.64 3.20
2014
Event
3.29 4.58
Table 1 – Root mean square error
computation for the TAMDAR and NAM 12km
model versus actual event.
Graphically examiningthe differences in the
mean sea level pressure and dew point values
further depicts the advantages of the
TAMDAR enhanced RTFDDA model. The
positive difference values, circled in red, in
the mean sea level pressure graphic, figure 4,
show the greatest anomalies just to the east
of the Appalachian Mountains in North
Carolina and Virginia.This indicates that the
TAMDAR model was able to better interpret
the strength of the damming event over the
NAM 12 km. Another interesting point to this
graphic is the presence of the blue region in
southern North Carolina and eastern South
Carolina. This is likelya depiction of the
coastal warm front advancing across the
damming region. This can provide an extra
indication of where the heaviest precipitation
may occur and allow forecasters to further
concentrate on the precipitation type in this
area.

11. 11
Figure 4 – Difference betweenNAMand
TAMDAR 12km modelsinreference tomeansea
level pressure.
Anotherimportantparameterto
considerduringacoldair dammingeventisthe
amountof moisture presentthatcancreate
frozenprecipitation.Figure 5depictsacoldair
dammingeventfrom2014 inthe Southeast
where overaninchof ice accumulation
occurredalongthe Georgia/SouthCarolina
border. The circledregionindicatesanareaof
the greatestpositive anomalieswherethe
TAMDAR enhancedmodel hasindicatedhigher
dewpointvalues.Thisparticularsystemwas
well forecast,butforborderline precipitating
events,the additional TAMDARdatamaybe
able to predictthe occurrence of wintry
weatherata greaterresolutionorpossiblywith
a greaterleadtime.
Figure 5 – Difference betweenNAMand
TAMDAR model for2 meterdew point.Greens
to yellowsindicate positive difference.Circled
area indicatesgreatesticing forthisevent.
Future researchishopedtobe
performedonadditional parameters,including
temperature throughoutthe colddome,winds
and a betterquantificationof precipitation
values.Investigatingotherphenomenon,such
as the coastal warm front,anditsimpact on
sensible weather,orevenCADerosion,would
be useful additional workwiththe additionof
the TAMDAR dataset.Itwouldalsobe pertinent
to compare againstothermodels,includingthe
EURO that may show more reliable
performance toobtainanaccurate measure of
the TAMDAR model’scapabilities.Expanding

12. 12
the numberof eventswill alsogiveamore
comprehensivestatistictothe viabilityof the
TAMDAR modelsoverothers.
Acknowledgements:Special thankstoAllan
Huffman,Pete ChildsandHeatherRichardson
withPanasonicWeatherSolutionsforhelp
runningthe TAMDARmodel and generatingthe
graphics.Additional thankstoDr. Gary
Lackmann forprovidingfurtherinsightand
backgroundintothe Baileyetal.study.
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