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Table 2.2--Stoms important to determination of PMP for tbe CD-I OJ region (continued) Storm Lat. Lon~. Elev.# 1000 mi 2 10 mi2 Number Name Date (0) (') (0) (') (ft) 24 hr 6 hr 76. Plum Creek, CO 6/13-20/65 39 05 104 20 6700 9.5 11.5 114. Glen UIlin, ND 6/24/66 47 21 101 19 2000 11.1 77. Big Elk Meadow, CO 5/4-8/69 40 16 105 25 8000 5.5 4.0 78. Rapid City, SD 6/9/72 44 12 103 31 4800 79. Broomfield, CO 5/5-6/73 39 55 105 06 5700 4.7 2.9 81. Big Thompson, CO 7/31-8/1/76 40 25 105 26 8300 B 82. White Sands, NM 8/19/78 32 47 106 11 4600 B 116. Medina, TX 8/1-4/78 29 55 99 21 1800 15.0 17.0 # Elevation is from smoothed barrier/effective elevation analysis. "B" indicates barrier elevation. * Local storm elevation to nearest 100 ft. was then pulled counterclockwise around the two low centers and westward into North Dakota and Montana. As the warm air moved northward, northwestward, and then westward around the Lows, it was forced over the cooler air mass already present in the region north of the low centers. This forced lifting of the warm moist air resulted in precipitation starting on June 6 in Nortl1 Dakota and Montana. During the next 24 hr, the two low centers appeared to merge and deepen and the storm increased in intensity. The single low center remained almost stationary over western North Dakota, occluding as the cold front continued its eastward movement into Wisconsin, Illinois, and Missouri. The intensity of the Low caused high winds and strong convergence, as well as heavy precipitation over the region. During this time, winds at several locations in Montana and North Dakota exceeded 40 mph and rainfall at Warrick, MT reached its greatest intensity. Air flow was from the northeast to the northwest in the vicinity of the rainfall center during the time ,of maximum rain. By the morning of June 8, the Low began to weaken and started drifting toward the northeast, which brought a dry northwesterly flow from Canada into Montana. The cold front continued its eastward movement, resulting in an occluded front that stretched into east central Canada. Showers occurred along this front. Rainfall in Montana generally ceased by late morning of the 8th. The isohyetal map for the storm is given in figure 2.3. This map shows that rain fell primarily in the plains areas of eastern and northern Montana. However, the maximum rainfall occurred at Warrick and fell around an isolated orographic feature, the Bear Paw Mountains. These mountains rise about 1,500 ft above the surrounding terrain. Although rainfall was significant (greater than 2 in.) throughout northeastern Montana, the rainfall at Warrick greatly exceeded other recorded amounts. This suggests that the Warrick center was a result of a local orographic influence upon thunderstorms embedded within the general-storm rainfall. This suggestion is reinforced by a rapid decrease in rainfall amounts 19