DISCUSSION 383 
tropospheric wind patterns over the west fre- 
quently are different during spring (broken 
lines of Fig. 13). This upper-level pattern, of 
course, depends on circulations in other parts 
of the hemisphere. The combination of surface 
and upper-level patterns results in differential 
advection over a broad area (especially shaded 
area). In the low layers we get warm moist air 
flowing into the Great Plains in the form of 
great warm moist tongues. At upper levels, 500 
mb or so, the air is frequently very cold, having 
arrived from the eastern Pacifie or even the 
Gulf of Alaska. The lower warm moist air is 
shielded by the Rockies, so the cold air over- 
runs. This cold air has low specific humidity, 
and it is relatively dry; so that over a large 
area where this differential flow pattern ob- 
tains, there is increasing instability, both con- 
ditional and convective. The lapse rate increases 
because of the cold air overrunning the warm, 
and also convective instability increases because 
moist air from below is being overrun by rela- 
tively dry air. Also, one of the most favored 
storm tracks in spring when the polar front 
moves north is the ‘Colorado Low,’ so that 
synoptic-seale disturbances which have the vigor 
to release the energy of this instability are fre- 
quent. The synoptic activity is favored by geo- 
graphical considerations. The presence of the 
Gulf, the cold air from Alaska and the Pacific, 
and the Continental Divide all fit into the dy- 
namic climatology of hail and tornadoes. In the 
East we rarely have such meteorological condi- 
tions, since this type of differential advection 
rarely takes place. The rain situations are of a 
quite different character, and by the time the 
moist air and trough arrive, there has been a 
warming, and the conditional and convective 
instability have been released. There are many 
factors which make the East climatologically 
quite different from the standpoint of stability. 
Occasionally, tornadoes occur when the flow 
pattern at upper levels stalls so as to permit a 
moist current from the Gulf to enter below an 
eastern jet stream and into confluent pattern. 
After a period with very warm lower air and 
high troposphere, some storm may rip through 
and do the job of releasing the pent-up insta- 
bility. But this is a very infrequent case and 
most of the time the pattern I earlier described 
is present. 
Mr. Blackmer—Recently when looking at var- 
lations in hail occurrence across the state of 
Kansas, I plotted a cross section using ten-year 
mean June soundings for Columbia, Mo., Dodge 
City, Kan., and Grand Junction, Colo. On this 
cross section I marked the height of the con- 
vective condensation level and the height of the 
freezing level. At Grand Junction, where hail is 
quite frequent, the low humidity at low levels 
resulted in a convective condensation level at 
sub-freezing temperatures. At Columbia the 
convective condensation level was at a tempera- 
ture considerably warmer than freezing. Thus 
the cross section showed considerable change in 
the thickness of the layer between the cloud base 
and the freezing level. 
I believe that the temperature and thickness 
of the layer between the cloud base and the 
freezing level is very important in the forma- 
tion of hail. In humid regions where there is 
a thick layer of cloud beneath the freezing level, 
the cloud water will be quite warm. To freeze 
any of this water it must be lifted considerably 
and the cloud drops could possibly grow to 
fallout size before being lifted to the freezing 
level. In a cloud with a base near the freezing 
level the cloud water will be cold and will not 
have to be cooled much more to freeze. 
The cross section showed that the thickness 
of the cloud layer between the cloud base and 
the freezing level varied from zero in western 
Kansas to 35000 ft in eastern Kansas. Long- 
period insurance company records show an 
average crop loss of ten per cent in western 
Kansas while in the eastern part of the state 
the loss is about one per cent. 
Obviously, much more work needs to be done 
before any definite conclusions can be reached. 
One very important step would be to obtain 
long-period average sounding using data only 
on days with hail. These soundings would pro- 
vide data which could be compared with in- 
surance company records of hail loss to learn 
more about just what conditions are most favor- 
able for hail. 
Dr. G. D. Kinzer—In bringing the session to 
a close, I would like to read to you from to- 
day’s newspaper, “Eighteen inches of hail falls 
in Kansas.” “A hail storm battered this small 
prairie town of Seldon in northwest Kansas for 
two hours last night covering the town with 18 
inches of ice.” I think that is a very remarkable 
event, and yet in the light of what we have dis- 
cussed tomight it does not seem unusual. (A re- 
port on this spectacular hailfall can be found in 
the Monthly Weather Review, 87, 301-303, 
1959, by A. D. Robb, entitled “Severe Hail, 
Seldon, Kansas, June 3, 1959.”—Ed.) 
