20 TOR BERGERON 
Distribution of maximum precipitation 
intensity at orographically conditioned 
convergence with w =l 
[w I Iw 
m/, —movh mm/h 
/s 10?m,Im/ 107m m/s at 0.7 km 
height 
lo 
i) 
Oa 
= 00 Q) Oz C3 Os Os Oe 07 Os Oo | 
z la lz ls lakm 
10° 75 
TAY Pi 
| 0° -6 
Fre. 14—/w diagram of orographically condi- 
tioned precipitation 
Figure 14 is an Jw diagram for this case with 
two alternative temperatures at the cloud base, 
+10°C and 0°C, the latter applying to our case. 
The curve J represents the specific intensity 
of condensation and w the assumption made as 
2— Isohyetal 2 in. 
--—— \Isohypse 150m ab. s-l. 
is 300" "8 
‘Divide 
9 Region of max. rain 
i g! 
Be 
a 
to the vertical motion, being zero at the ground 
and at a front surface, 1.4 km above sea level, 
and 1 m/see halfway in between. We then get 
an Zw curve that corresponds to a precipitation 
of 5 mm/hr or double the amount needed, since 
there are 180 mm in three days to be explained 
if the other assumptions are correct. Thus, the 
updraft would have been of the order 0.5 m/sec 
instead of 1 m/see (as assumed in Fig. 14), a 
value that goes well with the surface convergence 
observed. 
Figure 15 illustrates about 50% of the rain in 
January, 1937, that produced the famous Ohio- 
Mississippi flood, which began in the Ohio River 
drainage basin. This isohyetal map only renders 
the rainfall during the period January 20-25, 
reaching 10-14 inches along the river; the maxi- 
mum total sum for the month was about 24 
inches. This is a terrific amount, and the flood 
was, as you know, one of the biggest on record, 
rising more than 25 m, or 85 ft, above normal 
"__[U.S. DEPT. OF AGRICULTURE 
WEATHER BUREAU 
OHIO RIVER 
DRAINAGE BASIN 
PRECIPITATION 
JAN. 20- 25,1937 
Fic. 15—Rainfall in the Ohio-Mississippi Basin, Jan. 20-25, 1937 
