THE USE OF CLOUDS IN FORECASTING 
Martin [65]. Whittier [101, p. 4] urges that more re- 
liance be placed on halos as prognostics of precipita- 
tion when they end owing to the thickening of the Cs 
into As. Reeder [79] cites the brilliant halo of Sept. 27, 
1906, at Columbia, Mo., as the first indication of a trop- 
ical cyclone moving northward in the Gulf of Mexico. 
Dole [89] has cited colored sunsets at a coastal station 
as a valuable clue to the existence of a tropical storm. 
According to Neuberger [73, 74], the prognostic value 
of noncircular halos is greater than that of circular ones, 
being 85 vs. 77 per cent in Pennsylvania and 73 vs. 68 
per cent in northwest Germany; bright halos are better 
than moderate or weak ones: 72 vs. 66 or 61 per cent in 
Pennsylvania but the reverse in Germany, 65 vs. 68 
1169 
slightly higher than Palmer’s 69 per cent for Cs carry- 
ing solar halos. The small difference is probably not 
significant. We cannot say the halo has no value of its 
own, however, for the presence of a halo identifies C's 
as a thin ice cloud and is one of the chief criteria for 
differentiating C's from the thicker As. 
Double Cirrus. String [95, pp. 24-25], following 
Mylius’ lead that bad weather, especially precipitation, 
is preceded a short time by multilayered clouds, found 
that double-layered Ci (usually the feathery type) and 
vertebratus are followed by warm-front precipitation, 
mostly of thunderstorm or squall characteristics, in 
90 per cent of the 37 cases observed. These are char- 
acteristic of secondaries, particularly on the right front 
Tasue II. Frequency or ANy PREcIPITATION WITHIN A Given NumBeEr or Hours arrerR HALo 
Freq. of precip: 
ee oe No, o No. of Interval after halo general average ‘ 
12 hr 18 hr 24 hr 36 hr 48 hr | Average| 24 hr 48 hr 
(%) (%) (%) (%) (%) (hr) (%) (%) 
Fort Worth, Tex. Martin [66] 168 6 — 26 36 48 59 24. — — 
Columbia, Mo. Reeder [79] 40 2 — — 24 _ 49 — — _ 
Wauseon, Ohio Mikesell [57] | 2918 40 — — 58 — — — — — 
Columbus, Ohio Martin [65] 185 12 — 54 65 75 86 26 — — 
State College, Pa. Neuberger [73] 497 6 37 50 58 69 77 15 — 50t 
Blue Hill, Milton, Mass. Palmer [75] 569 10 — — <57 67 — 16 50t 704 
York, N. Y. Stewart [91] 317 7 — a 64 — 83 20 — — 
London, England Russell [83] 977 7 _ — 68 — — — — -— 
NW Germany Neuberger [74] 316 — 58* — 68 — — 8 44F -- 
* Frequency of halos followed by precipitation on the same day. 
t Nonhalo days. 
{ Hight-year average. 
or 69 per cent, and short-lived (<15 min) are better 
than long-lived (>120 min) halos: 80 vs. 60 per cent 
in Germany, by the end of the following day. These are 
to be compared with the chance of precipitation within 
forty-eight hours when no halo is observed, which is 
50 per cent at State College. Brooks [17] found pre- 
cipitation within thirty-six hours after each of seven 
complex halos, and after a 46-degree halo Reeder [79] 
said that precipitation [always] occurred in from twenty- 
four to thirty-six hours in Missouri, while Neuberger 
found a 78 per cent probability in Germany. 
TasiE III. Hanos, Pressure, AnD PRECIPITATION 
Per cent of halos 
Pressure and tendency Cases followed by precipi- 
tation within 24 hr 
Below normal and falling.... 334 83 
Near the lowest point........ 205 66 
High but falling ,...7....... 893 64 
Aboutmonmallinn weelrc ss. 572 58 
Irony [ORG TMM. Loh enous oen 199 53 
At about highest point....... 495 42 
Above normal and rising..... 220 37 
In evaluating the halo as a prognostic, in comparison 
with Cs without halo, it is of interest to note that 
Clayton’s tabulation of all daytime Cs, whether halo- 
producing or not, shows a rain probability of 73 per 
cent (interpolated) within thirty-six hours, which is 
of a general cyclone. Sometimes these clouds are seen 
after the end of the warm-front precipitation. Double- 
layered Cz occur in 16 per cent of all cases of C7. 
Undulated Sheet Clouds. Sweetland [98, p. 39] found 
that, at Blue Hill, undulated sheet clouds at all levels 
are more likely to be forerunners of warmer weather 
and rain than the more indefinite cloud types (Table 
IV). Sharp contrasts between over- and under-running 
Taste IV. UNpuLATED CLoUuDS AND PRECIPITATION AT 
Buivur Hizx [98] 
Ci, Cs Ce Ac, As Sc St 
Gases mtecme cor tensity anee 42 16 24 36 6 
Precipitation within 24 hr 
(MDEeTACent)Ri ee 2k. to: 50 66 67 53 67 
winds usually result in sharp cloud markings and strik- 
ing wave formations and produce a maximum tendency 
toward forced ascent. Martin [67] has presented records 
of a “mackerel sky”’ at Columbus, Ohio, which may be 
compared with Sweetland’s undulated Ac (Table V). 
Mammatus Clouds. According to Sweetland [98], these 
are followed by some precipitation within twenty-four 
hours in 51 per cent of 51 cases. Angot [2] remarks that 
Cu mam mean rain without wind in cold air masses below 
a warm front surface in the lowlands of Lancashire, 
but indicate a gale in the exposed Orkneys. Whittier 
