114 



METEOROLOGY FORECASTING 



ill a series of clues tu be used as an aid to over-land 

 forecasting in Florida. Since the clues are closely 

 related to the topography and peninsular situation 

 of Florida and to the season of the year, they are not 

 directly applicable to other locations in their present 

 form. However, they suggest that investigation of 

 these points at other locations would quickly yield 

 useful correlations. Some examples of these relations 

 follow. 



1. Of the 600 ft low-level sounding standard curves, 

 90 per cent gave standard ranges. 



2. During early morning hours : 



a. Surface winds of 10 mph or more produced 

 standard propagation always; winds of 5 to 9 

 mph produced superrefraction 20 per cent of 

 the time; 2 to 4 mph showed superrefraction 

 60 per cent of the time ; and calm winds pro- 

 duced superrefraction almost always. 



b. Similarly, the 1,000-ft winds of 30 mph or 

 more produced standard, while 1,000-ft winds 

 of 10 mph or less almost always produced 

 superrefraction. 



c. Superrefraction occurred with clear skies ex- 

 cept on two occasions, one with broken high 

 clouds, the other with broken middle clouds, 

 never with low clouds. 



d. High-pressure centers within 700 miles and with 

 gradients of 1 mb per 100 miles or less pro- 

 duced superrefraction. 



e. Ground fog patches were obser\'ed during pe- 

 riods of class 4 propagation, with two excep- 

 tions. 



3. Simple surface ducts of TO ft and Ail/^o (refer- 

 ence level 50 ft) of 4 or more and elevated S curves 

 with ducts above 200 ft and Ail/-f, of 6 or more pro- 

 duced class 3 or 4 propagation with possibly one ex- 

 ception. 



4. Large Ail/'s observed by radiosonde between 

 1,000 and 3,000 ft showed no correlation with S-band 

 propagation but did show fair correlation with super- 

 refraction on P band. Superrefraction on both S and 

 P band showed good correlation with large Ail/'s ob- 

 served below 1,000 ft. 



5. The height of the temperature inversion in- 

 creased with increasing 1,000 ft wind speeds up to 

 10 or 13 mph, then decreased slowly with further in- 

 crease in wind. 



6. Substandard propagation conditions were never 

 observed over land, either on the radar or the sound- 

 ings. 



A series of low-level soundings taken at hourly in- 

 tervals throughout the night were related to corre- 

 sponding radar ranges. The soundings were made at 

 Leesburg; the radar data were taken at Tomato Hill 

 (2 miles west of the sounding site) and at Winter 

 Garden (25 miles southeast of the sounding site). 



The general weather situation for the night of 

 March 5 to 6 shows maritime tropical air pouring up 

 over Florida around the western end of the Bermuda 

 high, giving clear skies and southerly winds of 10 mph 

 at 1,000 ft and 3,000 ft at 3000 EWT,« increasing to 

 30 and 25 mph respectively by midnight, and to 23 

 and 35 mph by 0400. Figure 5 shows the PPI scopes 



Figure 5. SCR-588, Leesburg, night of March 5 to 6, 

 1945. 



of the P-baiid SCE-588. The arrows point north; the 

 small grid squares are 5 miles on a side. Before mid- 

 night, propagation was standard, as illustrated by the 

 0400 frame. The ranges built up rapidly, reaching 65 

 miles and decreased slowly between midnight and 

 0400. (Eadar shadows of surrounding topographical 

 features account for the uneven distribution of range 

 increase.) 



Figure 6 shows the progression on the S-band SCE- 

 584. The bold line points north, the range markers are 

 at 10,000-yd intervals. (The sounding site is roughly 

 315° at 45,000 yd.) From 1900 to 2300 propagation 



"All times to follow are Eastern ^^'ar Time. 



