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< 
NORTHERN GREAT PLAINS FIELD STATION, 1913-1922 3 
last frost in the spring was May 13 and of the first in the fall Sep- 
tember 24. The average number of frost-free days for the 48-year 
period from 1875 to 1922, inclusive, was 130. The average date of 
the last frost in the spring for this period was May 12 and of the 
first in the fall September 19. | 
TABLE 1.—Frost-free period at the Northern Great Plains Field Station for the 10-year 
period, 1913-1922, inclusive 
Killing frosts 
Last inspring | First in fall Frost- 
free 
Year | period 
| Tem- | | Tem- | (days) 
pera- pera- | 
Date care | Date care 
CF) | (CF) 
PS She a as a es a ae se Se eI os Oe May 6 32 | Sept. 21 32 138 
bbnah. a eS sehen dD sel pat cere nee eine oe Gn ee = May 13 | 32 | Aug. 25 32 104 
LOU). 2 ae 2 a Rs ee ae ee, SE alee eae tee eee May 18 31 | Oct 3 32 138 
DIG as 2 Se ee re ee May 15 | 32 | Sept. 14. 23 122 
UGG 2 Be aa aR Ee ee ee a May 26 | 28 | Sept. 25 32 122 
PAUISS 2s 2 i ps Sa eee i eee ee = May 11 23 | Sept. 19 22 131 
it ej ears ee eeeeen eee ee Re St a June 2 32 | Oct 3 28 123 
a) gee Rens Ween eT Ae ee ee | Apr. 27 18 | Sept. 28 28 154 
Si) Dy ements ee = one es Re ee ee May 14 | 32 | Sept. 30 | ola 139 
UD Sass sles aie) i ape ae al ie eS Sa oe i Apr. 25 | 29) | Ochs a7 26 | 165 
Kecreces Pee eee ers Pere Ow Wray 13) |) aoc Sept. 24 |_-______ Pore 
The wind movement at the station is measured by an anemometer 
placed 2 feet above the surface of the ground. The average wind 
velocity for the 9-year period from 1914 to 1922, was 6 miles an hour. 
The average for the months from April to September was the same. 
April and May are the months of highest wind velocity and July and 
August of lowest wind velocity. The highest velocity for any 24-hour 
period in the nine years was 24.2 miles an hour. 
The evaporation from a free water surface during the warm season 
is shown in Table 2. Evaporation is highest in July and August and 
lowest in April and September. 
TaBLE 2.—EHvaporation from a free water surface at the Northern Great Plains 
Field Station for the 9-year period, 1914-1922, inclusive 
{ 
| 
Evaporation (inches) 
| l | 
Year | 5 | Sea : 
April | May June | July | August | ,°°P | to Sep- 
tember | tember, 
| inclusive) 
(awe ig ae ee ee 2 eed a | 
| | 
SUE be Spe ese Sle SG OS Eee 4. 030 | 5. 680 | 5. 998 | 7. 550 5. 636 | 5. 055 | 33. 949 
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3. 647 | 28. 616 
LNs a Sa ie tee alte eee | 3. 489 | 5. 505 | 4.745 | 7. 411 5. 727 4. 400 | 31. 277 
GS ee a eee 2. 183 | 6. 437 | 7.175 8. 695 7. 021 4.171 | 35. 682 
LTR Booed 2 ees eee ee ee 3. 793 | 5. 510 7. 264 | 7. 226 7. 272 4. 434 | 305. 499 
it! 32 et Se ee 3. 739 | 6. 022 | 7. 258 | 9. 168 8. 057 5. 347 | 39. 591 
a LER SS 2a ee 3. 155 | 5. 543 6. 297 7. 157 8. 452 | 4. 647 | 30. 251 
Le 3. 638 | 5. 147 7. 324 | 8. 899 8. 524 | 5. 730 39. 262 
3 YE Si ee ee ee 3. 379 | 5. 337 5. 638 | 6. 740 7. 935 4. 826 33. 855 
iverapes test) ffir 3.584 5,448 6.342 | 7.585 7.121} 4.695| 34.775 
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