ILLUSTRATIONS 
129 
A Succession of Polar Air Masses: Weather Maps and Cross-Sections for 
Nov. 30-Dec. 2, 1938 
The charts below are from an ar- 
ticle by George and Elliot in the Bull. 
Amer. Met. Soc. for March 1939. The 
period was featured by an outbreak 
of Pc air over the Great Lakes region, 
and a series of rapidly moving in- 
vasions of NPP air across the western 
states. Npc is stagnating in the 
Scutheast, and a tongue of TA begins 
to move cver Texas from the Gulf. 
The cross-sections from Oakland to 
Washington show the considerable 
depth of the PP compared to the Pc 
air and the tendency for warm-front- 
type occlusions and upper cold-fronts 
to form from PP invasions. (Cold 
fronts are drawn solid black, warm 
fronts double lined, occluded fronts 
dashed, upper fronts dotted; tempera- 
ture in °F and winds are entered for 
a few stations) —R. G. S. 
Fic. 1. Synoptic Chart, Nov. 30, 1938, 7:10 a.m., E. S. T. 
VA 
Nee ca oy PP (3) 
os 
7 
6 
- Ss 
y, : 
—-35 
J Bees 
7 ’ 
Pew 
—waamne TOR 
Nov 50 1538 
Fic. 2. Cross-section, Oakland to Washing- 
ton, 4 a.m., E. S. T., Nov. 30, 1938. 
Dec 1, 1938 
Fic. 4. Cross-section, 4:00 a.m., Dec. 1, 1938. 
