308 MONTHLY WEATEER REVlEW.
NOTES ON THE APPIZCATION OF UPPER-AIB OBSERVA!CXOHB TO WEATHHlB FORZCASTWB, P’BBRUARY, 3812.
By Prof. ALFRED J. HSNBY, Mount Weather, Va.
In the notes for Jemrrry, 1912, it was pointed out that the wind on the M e r n border of an anticyclone, pos- sibly coupled with the temperature conditions, mmed to foreshadow the course of cyclonic movement when the center of the cyclone is situated in the southwest. The u per-air conditions durin February, 1912, were watched c f osely for additional evi f ence on the point in question, whether favorable or unfavorable. An ap roxhation to the pmsaure distribution which
1912, with this important difference, viz, while the pasition and intensit of the eastern anticyclone was quite similar to the $anuary cases and the same high
winds and relatively hqgh temperatures were observed aloft as in the previous cases, the osition of the cyclonic depression was about 1,500 dometers (932 miles), farther west than on previous occasions. The conditions were still further involved by the presence in the Gulf States and the middle and lower Mississippi Valley of a .region of falling pressure and precipitation, that is, pressure was falling and precipitation was occurring at the time of the kite fight at Mount Weather. The latter sbowed at 3,326 meterr, (10,912 feet) above sea level the preivalence of southwest winds having a velocity of 57 The temperature at the miles per hour (2s meters same altitude was 1’ C. ower than at the surface. In
other words, tem erature was relatively high aloft. In these two partic uf ~m , viz, high southwest winds and high temperatures aloft, the case of February 24, 1912, agrees with those already reported on. It seems from the evidence thus far adduced that under like conditions of prewure distribution similar phenomena, especiallL-i wind recur; thus the
clearly the Tesult of the ressure distri ution in time and
over the ooean to the eastward. Frequently a pressure distribution of this oharacter includes a cyclonic dis- turbance to the southwest, but in the case of Februaiy
24 the center of the cylolone was so far removed from Mount Weather as to exert no influence on the wmther experiehced at the latter station. Instead of a c clonic
a fall of reasure in the Gulf States sild the lower Missis-
over Mount Weather. These ppwsure falls-the isallo- bars of Dr. Ekholm-sometimes advance from west to east without greatly distorting the existing isobam or
roducing a s stem of dosed isobars and the wind circu- fation which z elonga thereto . The u per air, as well as the surface observations, on the 24tB clearly indicated the coming of falling weather at Mount Weather. The upper-eir chservations of the next day, February 25, are full of interest. During the preceding 24 hours ths
prevaile a in the January case appeared on February 24,
f)* s.).
h winds and relatively
%
temperatures of which we Y ave been s eaking.seem to be
s ace. More precisely, t g ey occur when this station is on t 1 e western border of an anticyclone that is retreating
disturbmce to the west or southweat we have to x o with
sippi V a8 ey which advanced during the ensuing 24 hours
wave of falling pressure before referred to assed over
distribution that instead of southwest winds now west- northwest winds prevailed up to an altitude of 23 miles (4,000 meters). In the meantime the cyclonic depression of the 24th had advanced from Arizona to withm whet we m y oaIl
“striking)) distance of Mount Weather, that is to say, under favorable conditions of movement Mount Weather would be within its sphere of influence in 24 houm, d this fact makes the upper-air observations of the greater interest. Fortunately, as Mom stated, the kites reached an altitude on the 25th of 23 miles (4,000 meters) at which level the winds were from the west-northwest and the velocity was 68 miles per hour (30 meters p. s.).
There was no tern erature invemion, the vertical decrease per 100 meters ieing 0.43’ C. On the theory that storms are carried along in the general drift of the atmos- phere, much as eddies in a stream of water, it is a fair inference that, did the upper wind observed at Mount Weather prevail to the westward, say to the margin of the ridge of high pressure in which it was observed, then the course of the cyclone would have been diverted to the eastward. On the contrary, the latter increased in inten- sity and traveled almost due northeast, a direction practicall athwart the course of the strcl west-Muth-
Weather. Coincidently with the northeastwrrrd move- ment of the cyclone, so far as we can tell, the winds in the free air above Mount Weather went to south, the Q h t
on the 26th showing winds from that directioh u to 1,863 meters (6,112 feet), the top of the flight. &on- case here reported, it would seem station cangive little information air currents, and, second, that such currents, at least under 3 miles (5 kilometers), are exceedingly fleeting in character, rarely holding true in both direction and speed for more than 24 hours. The upper winds at Mount WeBther during February, 1912, were not conducive to kiteflying,. since on only 10 days was a flight of a mile or more above the station obtained, and ody two o€ these came on consecutive days. Another peculiarity of the month was the ve small velocities of the easterly arid southerly winds i n x n t of c clones approaching from the west and southwed. !&his peculiarity is well illustrated by the conditions which obtained on the 21st. On that date there was a
cyclone centered over western Eentucky, with l o m t pressure 29.15 inches (740 millimeters), and the ststion at Mount Weather was well within the system of circu- lating winds and closed isobars, yet there was not enough surface wind to get the kites into the air. On four &her days sufficient winds to fly kites were not present, and on three additional days the winds were BO strong that the kites broke away.
Mount Weather and evidently 80 altered & e preseufe
west win c9 s in the 24-mile level above sea an T over &unt