by Robert K. Peters, Ph.D. - National Weather Service Cooperating Observer
The month of July 2000 was slightly warmer and much drier than normal. The month's weather featured upper air high pressure oscillating back and forth over Southern North America. When the center was to the west of the region, weak cold fronts moved through lowering temperatures. When the center was overhead or to the east, temperatures went above normal.
This past month was 1.1 degrees warmer than July 1999, and 2.48 inches drier. Year-to-date rainfall through July 31, 2000 was 0.05 inch less than one year ago. Precipitation over the twelve months ending July 31, 2000 was 92.1 percent of normal. The thirty-day outlook for July 2000 had called for near normal temperatures and near normal precipitation.
The week June 25-July 1 saw temperatures near normal and rainfall about 200 percent of normal. The northwest flow event, which commenced in mid-June, continued. As a result, disturbances crossed along with weak frontal boundaries. These interacted with the moist air mass in place over the area to bring scattered to numerous showers and thunderstorms during the week. The moist air, and the presence of clouds and rain, held temperatures down.
The week July 2-8 saw temperatures about one degree above normal and no rainfall. Upper air high pressure built into the area during the week. This suppressed rainfall. As the ground began drying towards the end of the week, temperatures warmed into the middle 90s. There were isolated showers on the afternoon of the 8th because of a moisture axis, though no rain fell in Tyler.
The week July 9-15 saw temperatures three degrees warmer than normal and no rainfall. Upper air high pressure was over the area. The subsiding air beneath this feature warmed temperatures and suppressed precipitation.
The week July 16-22 saw temperatures four degrees warmer than normal, and no rainfall. Upper air high pressure continued over the area, though northwest flow aloft set up on the 22nd. There were thunderstorms over the northern counties on the 22nd, but no rain fell in Tyler. Temperatures and humidities began lowering on the 22nd. The week July 23-29 saw temperatures two degrees below normal, and no rainfall. The front of the 22nd introduced surface high pressure, whose air mass originated in Canada. This kept temperatures below normal through the 28th, with readings warming to near normal on the 29th when yet another front came through.
Rain fell on the evening of the 29th, and there were scattered showers on the 30th and 31st.
The reporting period for temperatures and phenomenon on each day is for the twenty-four hours ending at midnight hours GMT--6 p.m. CST and 7 p.m. CDT. The reporting period for precipitation is for the twenty-four hours ending at noon GMT--6 a.m. CST and 7 a.m. CDT. All times are given using the twenty-four hour clock, and are expressed in Greenwich Mean Time.
Observations are from NWS Station 41/9207/4 in Tyler, Texas. The term "normal" refers to averages from the standard climatic period 1971-2000.
MX MN OBS PCPN REMARKS
July 2000, RECORDS AND SUMMARY: