ILLUSTRATIONS 
135 
Feb. 13,1936 6an 38 29°00 on Hots 
Fic. 10. A somewhat complicated situation 
sccompanied by widespread precipitation. The 
three occluded lows resulted from a series of 
minor wave disturbances that came in from 
the Pacific. The southern low deepened fur- 
ther and occluded off Hatteras, causing heavy 
snow in Boston on the 14th. 
Dec. 31, 1937 Bax 
Fic. 11. A large occluding Pacific low 
moving eastward along the western Pc front 
eventually drew Te into its circulation caus- 
ing intensification and a new wave which was 
occluding the next day over New England. 
Note the upper cold front (warm-front occlu- 
sion) in the west where the Pp-Pc occluded 
front (Nec occluded) is moving aloft over 
the Pc. The Ta will soon enter into this 
upper occlusion by rising over the Nec and 
displacing it. 
HI 
35 
April 12, 1933-8am 
Fic. 12. The deep occlusion in Canada had 
been formed by TG intensifying an older occlu- 
sion that had advanced from the Pacific along 
a Pc front to near Omaha. The Pc spread 
south behind the low to California and by 
the 12th was as shown here modified to Nrc 
with a fresh Pc outbreak in the NW. A sec- 
ondary low, in the southeast, formed at the 
base of the occlusion. It moved NE between 
rising pressure at Bermuda and the PA cur- 
rent flowing down from the N, occluding off the 
New England coast where it caused Nly gales 
and snow. The northern low is one of the 
spring type that sometimes develop into deep 
cold vortices without fronts—‘“‘dynamic lows’’. 
April 9,1935-8anm 
PES 00 ores 
Fic. 13. This shows a typical situation for 
Pa invasion of the northeastern seaboard, in- 
duced by a slow moving high to the north and 
an occluding wave disturbance from the south- 
east. As the low moves NE, the PA may con- 
tinue for days on the seaboard. 
