by Robert K. Peters, Ph.D. - National Weather Service Cooperating Observer
The month of January 2000 saw above normal temperatures and slightly below normal precipitation. For most of the month, the area was under upper atmospheric high pressure. This blocking pattern kept storm features away from the area, and also resulted in the above-normal temperatures. The one exception to this pattern was during the last week of the month, when a powerful upper air storm and Arctic air mass brought widespread sleet.
Compared with January 1999, last month was 1.5 deg. cooler and 5.58 inches drier. Precipitation over the past twelve months was 79.9 percent of normal. This reflects the dry weather which commenced in July 1999. The thirty-day outlook for January 2000 had called for above normal temperatures and below normal precipitation.
Temperatures during the week December 26, 1999-January 1, 2000 were five degrees warmer than normal, and there was no rainfall. For most of the week, upper air high pressure was over Western North America. Though this feature began a westward shift late in the week, it still prevented major storm systems from reaching the area. In actuality, minima were near normal. It was daytime maxima which were so high. This was because of a very dry air mass which permitted maximum sunshine, and compressional heating caused by the upper air high. Weak cold fronts did cross, but their only effect was on nighttime low readings.
The week January 2-8 saw temperatures average four degrees warmer than normal, and rainfall about 150 percent of normal. The week began very mild, with a brief and sharp cool-down on the 4th. Warmer air returned on the 6th, in time for an upper air storm which crossed slowly on the 7th/8th. It was this storm which brought the bulk of the rainfall. In fact, general rains of around one inch were common in the area. Temperatures during the week January 9-15 averaged about eleven degrees above normal, and rainfall was minimal. In fact, the only rain actually occurred on the early-morning of the 8th, but was reported on the 9th since it fell after 6 a.m. on the previous day.
Upper atmospheric high pressure over Western North America during the week built eastward. This kept the storm track along the U.S.-Canadian border. Only minor intrustions of cooler air reached East Texas, which lowered temperatures briefly before they again rose. The record high maximum was equalled on the 11th, and approached on the 12th. Temperatures quickly recovered after the cold fronts of the 9th and 13th.
The week January 16-22 saw temperatures ten degrees above normal and there was no rainfall. A modified Polar Continental air mass moved inot the region on the evening of the 19th. This lowered temperatures on the 20th. Otherwise, the area was under Tropical Maritime air for the remainder of the week. An upper air disturbance crossed overnight on the 21st/22nd, causing a few light sprinkles. There was, however, no measurable rainfall in Tyler
The week January 23-29 saw temperatures nine degrees colder than normal, and precipitation about 150 percent of normal. On the 27th, a sharp upper air disturbance crossed. This, in combination with an Arctic high pressure ridge which brought a shallow layer of cold air, and overrunning moisture brought widespread sleet, snow, and freezing rain. There was a 2.5 inch coating of sleet and snow on the ground by the time the sleet stopped at late-afternoon. This was the first significant accumulation of ice since February 1, 1996. the precipitation on the 27th established a new record for that date, replacing the 0.70 which had occurred on that date in 1990.
Thundersleet fell about 1 p.m. on the 27th. The bulk of the frozen/freezing precipitation occurred between noon and 2 p.m,. on that day. Another modified Polar Continental air mass had moved into the area earlier in the week--on the 23rd. Following the cold front of the 27th, temperatures held below freezing for seventy-six consecutive hours from 6 a.m. on the 27th through 10 a.m. on the 30th. In addition, skies were overcast during the days of the 26th, 27th, 28th, and 29th. Clearing finally occurred on the night of the 29th-30th.
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
January 2000, RECORDS AND SUMMARY: