## Q ual i t at i ve E pi s ode A nal ys i s f or 2002 O zone Seas on

E pi s ode of J une 10-12, 2002

Ju n e 10 : A t 0000 U T C, a t c ol d front i s a na l yz e d i n nort he rn P A

. T hi s bounda ry dri ft s s l i ght l y

s out h a nd be c om e s s t a t i ona ry a l ong a D ove r-Ba l t i m ore -P i t t s burgh l i ne by 1200 U T C. V i s i bl e

i m a ge s s how c l e a r s ki e s w i t h hi nt s of ha z e a t 1600 U T C w i t h onl y s ha l l ow c um ul us de ve l opi ng

by 1800 U T C. S urfa c e re port s a t 1800 U T C ha ve s c a t t e re d re port s of ha z e i n t he W a s hi ngt on

a re a a nd m ore w i de s pre a d re port s w e s t of t he A ppa l a c hi a ns

. T he uppe r a i r pa t t e rn i s c onduc i ve

t o t he de ve l opm e nt of a hi gh oz one pe ri od w i t h hi gh pre s s ure a t 850 m b c e nt e re d ove r K Y a nd a

m ode s t ri dge w e s t of t he re gi on a t 500 m b. T he fore c a s t ba c k t ra j e c t ori e s a re c ons i s t e nt w i t h

s t a nda rd hi gh oz one c a s e s w i t h w e s t e rl y fl ow

. U ps t re a m oz one a t 1500 U T C a t t he s ourc e of t he

ba c k t ra j e c t ori e s on J une 9 i s s t rongl y e nha nc e d

– i n t he 70-80 ppb (1-hour a ve ra ge ) ra nge

.

W i de s pre a d Code O ra nge c onc e nt ra t i ons a re found s out h of t he front a l bounda ry.

Ju n e 11 : T he s l ow m ovi ng/ ne a r s t a t i ona ry front a l bounda ry ha s now t a ke n t he form of a

re t re a t i ng w a rm front a nd i s w e l l i nt o N e w E ngl a nd a t 1800 U T C w i t h a n A ppa l a c hi a n l e e t rough

(A L T ) a na l yz e d from Ba l t i m ore t o nort he rn N C. A broa d ri dge a t 850 m b s t re t c he s from A L t o

t he D e l m a rva w i t h t he 500 m b ri dge a xi s re m a i ni ng j us t w e s t of t he m i d-A t l a nt i c

. H i gh oz one

c onc e nt ra t i ons a re re port e d ri ght a l ong t he I-95 Corri dor w i t h s c a t t e re d Code Re d c onc e nt ra t i ons

.

T he fore c a s t ba c k t ra

j e c t ori e s s how a s hi ft from w e s t -nort hw e s t e rl y fl ow t o a l ong-Corri dor. T he

1200 U T C s oundi ng a t D ul l e s A i rport

, V A (IA D ) s how e d c ont i nui ng w e s t e rl y fl ow t hrough t he

de pt h of t he bounda ry l a ye r w i t h a ve ry s t rong c a p a t 660 m b. A re s i dua l m i xe d l a ye r, oft e n

found i n a s s oc i a t i on w i t h hi gh oz one c a s e s , i s a l s o s e e n.

Ju n e 12 : O z one c onc e nt ra t i ons fa l l re gi on-w i de on J une 12 w i t h s t rong s out hw e s t w i nds

obs e rve d. F ore c a s t ba c k t ra j e c t ori e s s ugge s t ve ry fa s t fl ow ba c ki ng furt he r t o t he s out hw e s t t ha n

t he pre vi ous t w o da ys

. Conve c t i on de ve l ops by a ft e rnoon a c ros s c e nt ra l P A w i t h a s ubs t a nt i a l

c i rrus c l oud s hi e l d m ovi ng i nt o t he m i d-A t l a nt i c i n a dva nc e of t he ra i n.

E pi s ode of J une 22-26:

D uri ng t hi s e pi s ode

, t he m i d-A t l a nt i c i s s a ndw i c he d be t w e e n t w o s ys t e m s

. F i rs t

, a vi gorous l ow

t ha t c ros s e s s out he rn Ca na da on J une 20-21 a nd, s e c ond, a n uppe r l e ve l l ow t ha t de ve l ops ove r

t he s out he a s t e rn U S a nd t he n dri ft s w e s t w a rd w i t h t i m e

. A s m a l l a re a of hi gh pre s s ure i s w e dge d

be t w e e n t he s ys t e m s a nd t he hi ghe s t oz one c onc e nt ra t i ons a re found be ne a t h t hi s hi gh pre s s ure

w e dge

.

Ju n e 22 : T he s t rong s ys t e m t ha t c ros s e d Ca na da e a rl i e r i n t he pe ri od ha s now w e a ke ne d a nd

m ove d j us t nort he a s t of M E (500 m b). A s pra w l i ng a re a of hi gh pre s s ure a t 850 m b i s found

from IN e a s t t o j us t s out h of L ong Is l a nd. A t t he s urfa c e a t 1200 U T C, hi gh pre s s ure i s l oc a t e d

ove r W V

. T he front a l bounda ry a s s oc i a t e d w i t h t he de pa rt i ng Ca na di a n s ys t e m i s qua s i

s t a t i ona ry ove r N e w E ngl a nd a nd nort he rn N Y

. F urt he r s out h, t he uppe r l e ve l l ow ove r t he

e a s t e rn G ul f of M e xi c o ha s re s ul t e d i n t he de ve l opm e nt of a c oa s t a l t rough w i t h s us t a i ne d

e a s t e rl y w i nds re a c hi ng a s fa r nort h a s N C. T he oz one pa t t e rn t hi s da y fol l ow s t he s ynopt i c

s i t ua t i on c l os e l y w i t h good a i r qua l i t y nort h of t he front a l bounda ry a nd s out h a c ros s V A a nd N Cw he re t he m a ri t i m e i nfl ow i s s t ronge s t

. In t he W a s hi ngt on, D C a re a a w i de ra nge of

c onc e nt ra t i ons i s found. Conc e nt ra t i ons ra nge from Code G re e n i n t he nort hw e s t s uburbs t o

uppe r Code O ra nge i n t he ne a r s out he rn s uburbs

.

S ki e s a re ge ne ra l l y c l e a r a c ros s t he W a s hi ngt on re gi on w i t h s om e s ha l l ow c um ul us de ve l opi ng

by a ft e rnoon. T he 1200 U T C IA D s oundi ng s how e d l i ght s out hw e s t w i nds be ne a t h t he s urfa c e

ba s e d i nve rs i on w i t h e a s t e rl y fl ow a l oft a nd a ve ry s t rong c a p a t 820 m b. T he a i r m a s s i s

re l a t i ve l y dry for t he s e a s on (62-63 ○ F ).

Ju n e 23 : A re a s of good a i r qua l i t y (Code G re e n) a re a ga i n found i n t he W a s hi ngt on a re a w i t h

no 8-hour oz one vi ol a t i ons on t hi s da y. T he ve ry c l e a n m a ri t i m e a i r m a s s a s s oc i a t e d w i t h t he

c oa s t a l t rough a nd a s s oc i a t e d uppe r l e ve l l ow i s s e e n ove r V A

. T he fore c a s t ba c k t ra j e c t ori e s

s how a c ompl e x t ra ns port pa t t e rn w i t h a n offs hore c ompone nt a t 500 m

. Ba c k t ra j e c t ori e s ba s e d

on a na l ys i s fi e l d a re roughl y s i m i l a r w i t h a w e a ke r m a ri t i m e c om pone nt

. T he m orni ng IA D

s oundi ng a ga i n ha s a

s t rong i nve rs i on ba s e d a t 850 m b w i t h l i ght a nd va ri a bl e w i nds be ne a t h i t

.

Ju n e 24: By m i d-a ft e rnoon on J une 23, l ow pre s s ure de ve l ops a l ong a front a l bounda ry nort h of

t he W a s hi ngt on a re a

. T hi s s ys t e m de ve l ops qui c kl y s o t ha t

, by 1200 U T C on J une 24, a

re i nforc e d c ol d front ha s pus he d t o j us t nort h of N e w Y ork Ci t y. By 1800 U T C, t he bounda ry i s

qua s i -s t a t i ona ry a c ros s nort he rn N J a nd c e nt ra l P A w i t h s c a t t e re d c onve c t i on oc c urri ng a c ros s

c e nt ra l P A

. S c a t t e re d ha z e i s re port e d s out h of t hi s front a l bounda ry i n t he m orni ng hours

,

pe rs i s t i ng i nt o a ft e rnoon. T he 1200 U T C IA D s oundi ng s how s a re s i dua l i nve rs i on pre s e nt a t

800 m b t hough m uc h w e a ke r t ha n t he t w o pre vi ous da ys . A n e l e va t e d m i xe d l a ye r i s e vi de nt j us t

be ne a t h t he i nve rs i on. T he hi ghe s t oz one c onc e nt ra t i ons a re orga ni z e d i n a w e s t -t o-e a s t ba nd

a c ros s O H a nd P A i nt o N J a nd M D

. S c a t t e re d Code Re d c onc e nt ra t i ons a re found e a s t a nd

nort he a s t of W a s hi ngt on, D C.

Ju n e 25 : T he front a l bounda ry t ha t w a s dri ve n s out hw a rd on J une 24 re a c he s a s fa r a s s out he rn

N J by 1200 U T C be fore re t urni ng nort hw a rd by m i d-a ft e rnoon. S c a t t e re d Code Re d

c onc e nt ra t i ons a re pre s e nt i n t he W a s hi ngt on a re a

. T he m os t unus ua l a s pe c t of t he oz one fi e l d

on t hi s da y i s t he pre s e nc e of Code Re d c onc e nt ra t i ons ove r t he urba n c e nt e r of W a s hi ngt on.

H a z e re port s a re w i de s pre a d a nd fore c a s t ba c k t ra j e c t ori e s a re l e s s c ompl e x t ha n pre vi ous da ys

w i t h s t a nda rd w e s t -nort hw e s t fl ow w i t hi n t he bounda ry l a ye r.

Ju n e 26 : T he e pi s ode e nds on J une 26 w he n t he uppe r l e ve l ri dge be gi ns t o fl a t t e n. T hi s a l l ow s

for i nc re a s e d bounda ry l a ye r w i nds a nd a m uc h m ore uns t a bl e a t m os phe re

. T he 1200 U T C IA D

s oundi ng i s ne a rl y dry a di a ba t i c on J une 26 i n t he bounda ry l a ye r w i t h s t rong S W w i nds

t hroughout (10-15 knot s ra nge ). T he uns t a bl e a i r m a s s re s ul t s i n c onve c t i on de ve l opi ng a l ong

t he Bl ue Ri dge s by 1900 U T C w i t h w i de s pre a d c onve c t i on l a t e r i n t he a ft e rnoon.

E pi s ode of J ul y 1-3, 2002

A re l a t i ve l y m i l d oz one e pi s ode w i t h s t rong l oc a l pe a ks on J ul y 2, 2002. T he pe a k 1-hour oz one

c onc e nt ra t i on i n t he W a s hi ngt on a re a w a s 158 ppbv i n t he W a s hi ngt on a re a on J ul y 2, 2002.

W i de s pre a d one -hour e xc e e da nc e s on J ul y 2, 2002 w e re re port e d ne a r W a s hi ngt on, D C.

T hroughout t he e pi s ode

, t he hi ghe s t c onc e nt ra t i ons w e re found a l ong a nd e a s t of t he I-95

Corri dor w i t h l ow e r c onc e nt ra t i ons furt he r w e s t

.T he hi gh oz one e ve nt of J une 22-26, 2002 e nde d w i t h a n uppe r l e ve l t rough c ros s i ng t he

nort he a s t e rn U S

. T he t rough e xi t e d t he re gi on fa i rl y ra pi dl y but t he t ra ns i t i on t o a ri dgi ng

pa t t e rn w a s c om pl i c a t e d by a s m a l l “ c ut off’ l ow l e ft be hi nd by t he t rough ove r N e w E ngl a nd.

T hi s l ow dri ft e d onl y s l ow l y e a s t w a rd t o ne a r N ova S c ot i a by J ul y 2, 2002. S urfa c e w i nds w e re

nort h t o nort he a s t on J une 29, 2002 be c om i ng s out hw e s t e a rl y on J une 30, 2002.

Ju l y 1 : T he 1200 U T C s urfa c e a na l ys i s s how s a fa i rl y s t a nda rd hi gh oz one pa t t e rn. T he c e nt e r

of hi gh pre s s ure i s l oc a t e d i n w e s t e rn V A w i t h a ve ry w e a k pre s s ure gra di e nt a c ros s t he re gi on.

A t 850 m b, hi gh pre s s ure i s c e nt e re d furt he r w e s t ove r w e s t e rn T N w i t h a w e a k t rough e xi t i ng

N e w E ngl a nd. A s i m i l a r pa t t e rn i s pre s e nt a t 500 m b a l t hough t he pre s e nc e of a l i nge ri ng c l os e d

l ow j us t e a s t of M a i ne s ugge s t s t ha t t he pa t t e rn w i l l re m a i n s t a t i ona ry i n t he s hort t e rm not

a l l ow i ng t he ri dge t o bui l d qui c kl y e a s t

.

O z one c onc e nt ra t i ons i n t he W a s hi ngt on, D C re gi on w e re re l a t i ve l y hi gh (86-87 ppbv 8-hour

a ve ra ge ) on t he pre c e di ng da y (J une 30), a nd ba c k t ra j e c t ori e s s ugge s t e d s l ow t ra ns port a l ong

a nd s l i ght l y w e s t of t he I-95 Corri dor. P e a k 1-hour oz one c onc e nt ra t i ons ros e i nt o t he 87-99

ppbv ra nge i n t he W a s hi ngt on a re a

. T he bul k of t he m oni t ors e xc e e di ng t he 8-hour s t a nda rd

w e re i n t he 90-100 ppbv ra nge , re fl e c t i ng a ri s i ng re gi ona l oz one l oa d.

T he m orni ng IA D s oundi ng s how e d a l a ye r of s t rong s out hw e s t w i nds a nd t he F ort M e a de

, M D

profi l e r s how e d s t e a dy W S W w i nds t hrough t he da y. A s re fl e c t e d i n t he a ft e rnoon vi s i bl e

i m a ge

, t he re w a s s i gni fi c a nt bounda ry l a ye r ove rt urni ng produc i ng w i de s pre a d, t hough s ha l l ow

,

c um ul us be ne a t h a s ubs i de nc e i nve rs i on ba s e d a t

~ 770 m b. T he 0000 U T C IA D s oundi ng for

J ul y 2 s how s a re s i dua l m i xe d l a ye r t o ~ 800 m b c orrobora t i ng t ha t de e p bounda ry l a ye r m i xi ng

oc c urre d.

Ju l y 2 : T he m os t unus ua l a s pe c t of t hi s da y w a s t he a brupt de c re a s e i n vi s i bi l i t y be gi nni ng i n

t he l a t e m orni ng a nd c ont i nui ng t hrough t he a ft e rnoon a nd t he s pe e d w i t h w hi c h t he ha z e l a ye r

m ove d nort he a s t w a rd i nt o N e w E ngl a nd. T ypi c a l l y, vi s i bi l i t y re a c he s i t s m a xi m um w i t h m i xi ng

a nd i nc re a s e d w i nds i n t he a ft e rnoon a nd t he n re a c he s a m i ni m um j us t be fore s unri s e

. T hi s

oc c urre d i n t he c ont e xt of c ont i nui ng bri s k s out hw e s t w i nds w i t h 10-13 knot s re port e d by

a ft e rnoon. T he re gi ona l s urfa c e w i nd fi e l d w a s c ompl e x w i t h va ri a bl e w i nds t hrough t he e a rl y

a ft e rnoon be c om i ng s out he a s t

.

T he uppe r l e ve l a na l ys e s a t 850 m b a nd 500 m b a re ba re l y di s t i ngui s ha bl e from t he pre vi ous da y.

O f m os t i nt e re s t i s t he pos i t i on of hi gh pre s s ure a t 850 m b t ha t i s s l i ght l y furt he r nort h ove r IL a t

1200 U T C. U nl i ke t he s t a nda rd m i d-A t l a nt i c pol l ut i on c a s e

, how e ve r, t hi s c ont i ne nt a l hi gh ha s

not l i nke d up w i t h t he s e m i -pe rm a ne nt Be rm uda H i gh a s a l i nge ri ng t rough i s pre s e nt a l ong t he

E a s t e rn S e a

boa rd. A s a re s ul t

, 850 m b w i nds re port e d a t IA D w e re nort h t o nort h-nort hw e s t

e a rl y on J ul y 2, 2002. A t IA D

, t hi s fl ow pa t t e rn i s c ons i s t e nt t o t he ba s e of a s t rong c a ppi ng

i nve rs i on a t

~ 800 m b. T he IA D s oundi ng a t 0000 U T C on J ul y 3 s how e d t he bounda ry l a ye r

w a s furt he r s uppre s s e d duri ng t he da y w i t h m i xi ng onl y t o ~ 1500 m

. A s a re s ul t

, onl y s ha l l ow

c um ul us de ve l ops ove r t he m i d-A t l a nt i c duri ng t he a ft e rnoon w i t h t he e xc e pt i on of s c a t t e re d

s t rong c onve c t i ve a c t i vi t y a c ros s w e s t e rn P A s out h i nt o W V

.

Ba c k t ra j e c t ori e s

, a nd re gi ona l s urfa c e obs e rva t i ons

, s ugge s t t ra ns port of pol l ut a nt s froml oc a t i ons nort hw e s t of t he I-95 Corri dor. U ps t re a m oz one a t 1600 U T C a c ros s nort hw e s t e rn P A

w a s on t he orde r of 70-80 ppbv.

Ju l y 3 : A l t hough t e mpe ra t

ure s c ont i nue d ve ry w a rm i n t he uppe r 90’s ○ F

, t he c ha ra c t e ri s t i c s of

t he a i r m a s s a ppe a r t o c ha nge ra pi dl y ye t a ga i n. O z one c onc e nt ra t i ons fe l l a c ros s t he re gi on w i t h

pe a ks re a c hi ng t he Code O ra nge ra nge

.

F ore c a s t ba c k t ra

j e c t ori e s for J ul y 3 w e re qui t e s i m i l a r t o t he pre c e di ng da y a nd ve ri fy w e l l w i t h

a na l ys i s t ra

j e c t ori e s

. O z one c onc e nt ra t i ons ups t re a m

, how e ve r, ra n ~ 10 ppbv l ow e r t ha n on t he

pre c e di ng da y. T he m orni ng s oundi ng for J ul y 3 w a s m ore uns t a bl e w i t h a m uc h re duc e d c a p

from t he pre vi ous da y a l t hough onl y s ha l l ow c um ul us form e d duri ng t he a ft e rnoon hours

.

T he A L T

, w hi c h w a s a na l yz e d a l ong t he I-95 Corri dor for m uc h of J ul y 2, s l i ps s l ow l y e a s t w a rd

a nd t he re gi on of hi ghe s t oz one c onc e nt ra t i ons i s roughl y a l i gne d w i t h i t s l a t e r a ft e rnoon

pos i t i on.

E pi s ode of J ul y 31-A ugus t 5

Ju l y 31 : S c a t t e re d Code O ra nge re port e d i n t he s out he rn m i d-A t l a nt i c

. G e ne ra l l y m ode ra t e

oz one i s re port e d a l ong t he I-95 Corri dor. F ore c a s t ba c k t ra j e c t ori e s s ugge s t fa i rl y fa s t bounda ry

l a ye r fl ow w i t h t he a i r m a s s ori gi na t i on i n s out he rn O nt a ri o. O z one c onc e nt ra t i ons a t 1600 U T C

on J ul y 30t h i n t ha t re gi on w e re a bout a ve ra ge (45-50 ppbv). T he c ol d front

, l oc a t e d ne a r

N orfol k, V A a t 0000 U T C, dri ft s a bi t furt he r s out h by 1200 U T C a nd t he n di s s i pa t e s by 1800

U T C.

Au gu s t 1 : O z one c onc e nt ra t i ons ri s e re gi on-w i de

. F ore c a s t ba c k t ra j e c t ori e s s how a s t rong

a nt i -c yc l oni c c urva t

ure from ne a r L a ke O nt a ri o t hrough nort he rn N J

. A ga i n, ups t re a m oz one i s

re l a t i ve l y l ow (40-50 ppbv) i n s out he rn Ca na da a nd nort he rn P A but e m i s s i ons a l ong t he pa t h a re

l i ke l y qui t e hi gh a s t he a i r pa rc e l s c ros s t he m e t ropol i t a n N e w Y ork a re a

. A n A L T i s a na l yz e d

ove rni ght a l ong a nd e a s t of t he I-95 Corri dor. By 1200 U T C, hi gh pre s s ure i s c e nt e re d ove r W V

a c l i m a t ol ogi c a l l y fa vore d l oc a t i on for hi gh oz one i n t he I-95 Corri dor. A ve ry s t rong l ow -l e ve l

i nve rs i on i s obs e rve d w i t h nort he a s t w i nds i n t he l a ye r be ne a t h 800 m b.

Au gu s t 2 : H i ghe s t O 3 c onc e nt ra t i ons a re re port e d ri ght a l ong t he I-95 Corri dor w i t h s c a t t e re d

Code Re d obs e rva t i ons i n t he W a s hi ngt on a re a

. T he hi ghe s t oz one c onc e nt ra t i ons a re found

s out h a nd w e s t of W a s hi ngt on D C. F ore c a s t ba c k t ra j e c t ori e s s how a good de a l of va ri a bi l i t y.

A t 1200 U T C, a ba c k door front i s a na l yz e d ne a r N Y C w i t h s urfa c e hi gh pre s s ure s t i l l c e nt e re d

ne a r W V

. A s on A ugus t 1, t he s oundi ng a t IA D s how s a s t rong l ow -l e ve l i nve rs i on. E a rl y

m orni ng obs e rva t i ons s how ha z e a l ong t he I-95 Corri dor w i t h t he m os t num e rous obs e rva t i ons i n

V A a nd N C. A s a ft e rnoon m i xi ng oc c urs , onl y w i de l y s c a t t e re d ha z e re port s by a ft e rnoon.

Au gu s t 3 : H i gh oz one l e ve l s a re c onc e nt ra t e d a l ong t he I-95 Corri dor a ga i n on A ugus t 3. T he

fore c a s t ba c k t ra

j e c t ori e s a re t he s t a nda rd w e s t -nort hw e s t fl ow a l t hough m i d-da y oz one a c ros s

nort he rn O H on t he pre c e di ng da y w a s not e xt re m e (47-56 ppbv). T hi s l i ke l y re fl e c t s di ffi c ul t i e s

i n t he t ra j e c t ory m ode l i n t he vi c i ni t y of a front a l bounda ry w hi c h re a c he s c e nt ra l P A by 0000

U T C a nd t he n j us t N of P H L by 1200 U T C w he re i t s t a l l s

. S c a t t e re d ha z e i s re port e d a c ros s P A

,

M D a nd V A l i nge ri ng i nt o t he e a rl y a ft e rnoon hours

.Au

gu s t 4 : O z one i nc re a s e s a l ong a ba nd from j us t nort h of W a s hi ngt on, D C t o j us t nort h of

N e w Y ork Ci t y w i t h w i de s pre a d Code Re d c onc e nt ra t i ons i n a pa t t e rn c ha ra c t e ri z e d by re

c i rc ul a t i on a nd s t a gna t i on. T he c ol d front t ha t re a c he d i nt o e a s t e rn P A on t he pre vi ous da y

be c om e s s t a t i ona ry a l ong a l i ne from P ort l a nd, M E t o j us t nort h of N e w Y ork Ci t y a nd t he n

a c ros s c e nt ra l P A t o ne a r P i t t s burgh. T hi s bounda ry w a s he s out by 1200 U T C w i t h s urfa c e hi gh

pre s s ure re m a i ni ng i n pl a c e ove r W V a nd a n A L T a na l yz e d a l ong t he I-95 Corri dor a t 1800

U T C.

Au gu s t 5 : S c a t t e re d Code Re d oz one c onc e nt ra t i ons ne a r W a s hi ngt on D C. T he pre s e nc e of

s i gni fi c a nt c l oud c ove r nort h of t he M a s on D i xon L i ne re duc e s pe a k oz one i n t ha t re gi on. T he

front a l bounda ry ha s w a s he d out ove r N e w E ngl a nd w i t h re m na nt s s t i l l qua s i -s t a t i ona ry ove r

nort he rn P A

. T he ne xt c ol d front re a c he s nort hw e s t e rn P A by 1200 U T C. A ga i n t he re i s

c ons i de ra bl e ve rt i c a l s he a r not e d by t he fore c a s t ba c k t ra j e c t ori e s w i t h s out he rl y fl ow a t t he

l ow e s t (500 m ) l a ye r.

E pi s ode of A ugus t 10-14

Au gu s t 10 : H i gh pre s s ure i s di re c t l y ove r t he m i d-A t l a nt i c w i t h de w poi nt s i n t he m i d-50’s ○ F

,

a nd c l e a r s ki e s . T e mpe ra t ure s a re ge ne ra l l y i n t he uppe r 80s a c ros s t he W a s hi ngt on, D .C. re gi on.

W i t h hi gh pre s s ure ove rhe a d, t he fore c a s t ba c k t ra j e c t ori e s i ndi c a t e ve ry l i ght w i nds a nd

re c i rc ul a t i on. H i ghl y va ri a bl e oz one fi e l d w i t h c onc e nt ra t i ons a re pre s e nt on A ugus t 10 t h i n t he

W a s hi ngt on, D .C a re a

. S c a t t e re d Code O ra nge pe a ks w e re re port e d a l ong t he I-95 Corri dor.

W hi l e t he D ul l e s

, V i rgi ni a (IA D ) s oundi ng a t 1200 U T C di d not s how a ve ry s t rong l ow -l e ve l

i nve rs i on, w i t h 950 m b t e mpe ra t ure s onl y 21 ○ C, t he re w a s a ve ry s t rong c a p a t 805 m b w i t h

a bs ol ut e l y s t a

bl e c ondi t i ons a

bove t hi s l e ve l

. T he pre s e nc e of a de e p re s i dua l l a ye r (975-805

m b) s ugge s t s t he pre s e nc e of s t a gna t i on. P e a k e i ght -hour a ve ra ge oz one e xc e e da nc e s i n t he

W a s hi ngt on, D C re gi on ra nge d from 87 ppbv (A rl i ngt on a nd L oudoun Count i e s

, V A ) t o 93 ppbv

(F a i rfa x Count y, A nna nda l e , V A ).

Au gu s t 11 : S urfa c e hi gh pre s s ure drops s l ow l y s out he a s t w a rd a c ros s t he m i d-A t l a nt i c w i t h t he

c e nt e r a na l yz e d i n w e s t e rn N C a t 1200 U T C dri ft i ng t o c oa s t a l S C by 1800 U T C. T he uppe r

l e ve l ri dge ha s a l s o m ove d e a s t a nd i s l oc a t e d ove r t he m i d-A t l a nt i c a t 1200 U T C. T he oz one

m a p for t he W a s hi ngt on a re a s how s a not he r da y of hi ghl y va ri a bl e pe a k oz one

. A pe a k

c onc e nt ra t i on of 120 ppbv oc c urre d a l ong t he I-95 Corri dor nort he a s t of W a s hi ngt on D C. A ga i n,

a ve ry c l e a r da y i n t he m i d-A t l a nt i c . W i nds a re ge ne ra l l y s out h t o s out hw e s t a s i s re fl e c t e d i n t he

bounda ry l a ye r ba c k t ra

j e c t ori e s

. T he ke y fa c t or dri vi ng l oc a l oz one produc t i on a ppe a rs t o be a

ve ry s t a bl e bounda ry l a ye r. T he 1200 U T C s oundi ng a t IA D s how s a ve ry s t rong l ow -l e ve l

i nve rs i on from 950-900 m b w i t h a de e p re s i dua l l a ye r be ne a t h a c ont i nui ng s t rong s ubs i de nc e

i nve rs i on, now ba s e d a t 760 m b. P e a k e i ght -hour a ve ra ge e xc e e da nc e s ra nge d from 88 ppbv

(P ri nc e G e orge s Count y, M D ) t o 106 ppbv (W a s hi ngt on, D .C., M c M i l l a n).

Au gu s t 12 : T he uppe r l e ve l ri dge re m a i ns qua s i -s t a t i ona ry w i t h i t s a xi s ove r t he m i d-A t l a nt i c

.

T he c e nt e r of hi gh pre s s ure a t 850 m b i s ove r N C/ G A

. A t t he s urfa c e

, t he c ha ra c t e ri s t i c

A ppa l a c hi a n l e e t rough (A L T ) i s a na l yz e d a t 0000 U T C a nd re m a i ns i n pl a c e t hrough 1800 U T C,

c ont i nui ng i nt o A ugus t 13. Cl e a r s ki e s re m a i n, a l t hough ha z e i s s e e n i n t he 1600 U T C vi s i bl ei m a ge

. T he s urfa c e obs e rva t i ons s how a ra pi d a nd w i de s pre a d de c re a s e i n vi s i bi l i t y w e s t a nd

nort hw e s t of t he I-95 Corri dor, s hi ft i ng furt he r e a s t by e a rl y a ft e rnoon. T he 1200 U T C IA D

s oundi ng i s s i m i l a r t o t he pre c e di ng i n s e ve ra l re s pe c t s : a s l i ght l y de e pe r a nd c ont i nui ng s t rong

l ow l e ve l i nve rs i on, now from 975-925 m b w i t h a s t rong c a p a t

~ 770 m b. W i nds a re fa i rl y

s t rong from t he N W

. T hi s i s re fl e c t e d i n t he fore c a s t ba c k t ra j e c t ori e s t ha t s how a s hi ft t o

w e s t e rl y t ra ns port

. T he upw i nd O 3 c onc e nt ra t i ons a t 1600 U T C on A ugus t 11 i n t he vi c i ni t y of

t he ori gi n of t he fore c a s t ba c k t ra j e c t ori e s i s e nha nc e d, on t he orde r of 78-86 ppbv. O z one

c onc e nt ra t i ons fa l l t hi s da y w e s t of t he A ppa l a c hi a ns but i nc re a s e m a rke dl y a c ros s t he m i dA t l a nt i c w i t h w i de s pre a d Code Re d obs e rva t i ons from N C t o Bos t on. W i de s pre a d e xc e e da nc e s

a re found i n t he W a s hi ngt on a re a , ra ngi ng from 85 ppbv (Roc kvi l l e , M D ) t o 114 ppbv (A rl i ngt on

Count y, V A ).

Au gu s t 13 : P e ri ods of c a l m w i nds a re re port e d ove rni ght

. S i gni fi c a nt ha z e ha s now s pre a d a l l

a l ong t he I-95 Corri dor a nd re m a i ns i nt o t he a ft e rnoon hours

. T he re gi ona l oz one m a p s how s a n

e xt e ns i ve e pi s ode

. S ki e s a re a ga i n c l e a r w i t h s ha l l ow c onve c t i on de ve l opi ng l a t e r i n t he

a ft e rnoon. T he 1200 U T C IA D s oundi ng s how e d a c ont i nui ng s t rong l ow l e ve l i nve rs i on w i t h a

re s i dua l m i xe d l a ye r t o 850 m b e ndi ng j us t be ne a t h a w e a k s e c onda ry i nve rs i on. T he c a p a l oft

ha s l i ft e d t o ~ 630 m b a nd t he s oundi ng i s m ore uns t a bl e c ompa re d t o pre vi ous da y’s be t w e e n

t he t w o i nve rs i on l a ye rs

. In a ddi t i on t o a ve ry s t a bl e

, a nd ha z y, bounda ry l a ye r, t he s urfa c e

a na l ys e s s how t ha t t he A L T c ont i nue s i n pl a c e from l a t e on A ugus t 12, t o a pos i t i on s l i ght l y

furt he r e a s t a t 1200 U T C a nd t he n ba c ki ng w e s t a t 1800 U T C. A s i s t ypi c a l l y t he c a s e

, t he

hi ghe s t oz one c onc e nt ra t i ons a re found i n proxi m i t y t o t hi s bounda ry. E i ght -hour e xc e e da nc e s

ra nge d from 87 ppbv (L oudoun Count y, V A ) t o 125 ppbv (F a i rfa x Count y, M t . V e rnon, V A ).

Au gu s t 14 : Ba c k t ra

j e c t ori e s fore c a s t fa i rl y fa s t fl ow a l ong t he I-95 Corri dor. T he i nc re a s e i n

s out he rl y w i nd c ompone nt re s ul t s a s t he uppe r l e ve l ri dge a xi s fi na l l y m ove s offs hore

. O n t he

ba c k s i de of t he uppe r l e ve l ri dge

, l ow l e ve l s out he rl y w i nds i nc re a s e a s t he Be rm uda H i gh

c i rc ul a t i on pus he s m a ri t i m e a i r nort hw a rd. T he ha z e re port s c orrobora t e a s l ow c l e a n out from

s out h t o nort h w i t h m orni ng ha z e re port e d nort h of W a s hi ngt on, D .C. T hi s e pi s ode e nds i n a

ve ry di ffe re nt m a nne r t ha n t he s t a nda rd hi gh oz one e pi s ode

. Ins t e a d of t he pa s s a ge of a s ha rp

c ol d front

, t hi s e pi s ode e nds gra dua l l y a s c l e a ne r a i r s w e e ps nort h, w i nds i nc re a s e a nd t he

a t m os phe re s t e a di l y de s t a bi l i z e s

. O n A ugus t 15, c onc e nt ra t i ons fa l l a c ros s t he re gi on a s l ow

l e ve l fl ow be c om e s m ore s out he a s t a nd t he Be rm uda

hi gh fi l l s i n w e s t w a rd. Cl oud c ove r s pre a ds

ove r t he re gi on on A ugus t 16 w i t h oz one c onc e nt ra t i on c ont i nui ng t o de c re a s e

. P e a k e i ght -hour

e xc e e da nc e s ra nge d from 87 ppbv (A rl i ngt on Count y, V A ) t o 101 ppbv (F ort M e a de , M D ).

E pi s ode of S e pt e m be r 9-10

S u m m ar y : A t w o-da y oz one e pi s ode w i t h nort he a s t e rl y fl ow due t o hi gh pre s s ure t o t he nort h

a nd w e s t a nd T ropi c a l S t orm G us t a v t o t he s out he a s t

. S t rong s ubs i de nc e oc c urs ove r t he re gi on

a s G us t a v a

pproa c he d a nd m ove s a l ong t he N ort h Ca rol i na c oa s t

. N ort he a s t e rl y w i nds oc c urs

due t o c l oc kw i s e fl ow a round hi gh pre s s ure ove r t he O hi o V a l l e y a nd c ount e r-c l oc kw i s e fl ow

a round G us t a v a s i t ne a re d t he O ut e r Ba nks

. H i ghe s t oz one c onc e nt ra t i ons on S e pt e m be r 9 t h

oc c ur i n c e nt ra l P e nns yl va ni a

, nort he a s t of Ba l t i m ore

, ne a r A nna pol i s

, M D a nd w e s t of F a i rfa x

Count y, V A

. A s ha rp oz one gra di e nt w a s e vi de nt on t he 10 t h w i t h l ow c onc e nt ra t i ons e a s t of aBa l t i m ore -Roc kvi l l e

, M D -F a i rfa x Ci t y, V A l i ne w hi l e e i ght -hour e xc e e da nc e s oc c urre d i n

c ount i e s i m m e di a t e l y w e s t a nd s out h of F a i rfa x.

S e pt e m be r 9: A t 1200 U T C, T ropi c a l S t orm G us t a v i s s out he a s t of Ca pe H a t t e ra s

, N C w i t h hi gh

pre s s ure w a s ove r O hi o a nd Indi a na

. W i de s pre a d s urfa c e ha z e obs e rve d i n O hi o, M i c hi ga n,

Indi a na

, a nd Il l i noi s

. V e ry w a rm a i r a l oft ove r P e nns yl va ni a a nd W e s t V i rgi ni a e nha nc e d s t a bl e

a t m os phe ri c di s pe rs i on c ondi t i ons

. T he uppe r a i r pa t t e rn i ndi c a t e s a l a rge ri dge ove r t he e a s t e rn

ha l f of t he U S

, w i t h a c l os e d l ow a s s oc i a t e d w i t h G us t a v off t he s out he a s t c oa s t

. S t rong

s ubs i de nc e oc c urs ove r M i d-A t l a nt i c re gi on, c e nt e re d ove r s out h-c e nt ra l P e nns yl va ni a

. F ore c a s t

ba c k t ra j e c t ori e s i ndi c a t e fl ow from t he nort he a s t m e ga l opol i s (P hi l a de l phi a t o N e w Y ork Ci t y).

Code O ra nge c onc e nt ra t i ons a re obs e rve d t hroughout m uc h of N e w J e rs e y, nort he a s t M a ryl a nd,

a nd t he w e s t e rn V i rgi ni a s uburbs of W a s hi ngt on, D C. Code Re d w a s re a c he d nort he a s t of

Ba l t i m ore

. Code G re e n c ondi t i ons oc c urre d i n c oa s t a l s out he rn D e l a w a re a nd M a ryl a nd due t o

t he i nfl ue nc e of c l e a n a i r from G us t a v.

S e pt e m be r 10: T ropi c a l S t orm G us t a v ne a re r Ca pe H a t t e ra s w i t h he a vy pre c i pi t a t i on a l ong t he

O ut e r Ba nks

. W i de s pre a d s urfa c e ha z e w a s a ga i n obs e rve d t hroughout t he O hi o V a l l e y i nt o

Indi a na

, Il l i noi s

, a nd M i c hi ga n. A s G us t a v m ove s c l os e r t o t he N ort h Ca rol i na c oa s t

, t he re gi on

of s t rong s ubs i de nc e m ove s furt he r w e s t

, a l ong a nd t o t he w e s t of t he A ppa l a c hi a ns

. F ore c a s t

ba c k t ra j e c t ori e s i ndi c a t e t he i nfl ue nc e from G us t a v a s t he fl ow w a s ge ne ra l l y from t he e a s t

. T he

m a ri t i m e t ropi c a l a i r from G us t a v re a c he s a s fa r i nl a nd a s W a s hi ngt on, D .C. but s t a bl e

,

c ont i ne nt a l a i r i s qui t e c l os e t o t he w e s t a s i ndi c a t e d by t he 8-hour oz one pe a k c onc e nt ra t i on

m a p. A ve ry s ha rp oz one gra di e nt i s e vi de nt

. Condi t i ons ra nge from Code G re e n t o Code Re d

j us t s e ve ra l m i l e s a pa rt i n F a i rfa x Count y, V A

. Code O ra nge c ondi t i ons oc c ur w e s t of Ba l t i m ore

a nd i n t he w e s t e rn V i rgi ni a s uburbs of D C w hi l e Code G re e n c ondi t i ons oc c ur a l ong I-95 a nd

e a s t w a rd. Code Re d c ondi t i ons oc c ur j us t w e s t of I-95 a t t hre e V i rgi ni a l oc a t i ons i n t he

W a s hi ngt on, D .C. re gi on.