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January 1998 - Report and Summary

by Robert K. Peters, Ph.D. - National Weather Service Cooperating Observer

The month of January 1998 was much warmer and much wetter than normal. With the El Nino Southern Oscillation (ENSO) remaining in full force off the West Coast of the Americas, storms crossed frequently in the southern branch of the jet stream. The southern branch prevented Arctic air masses from penetrating the region. With mild air over the area much of the month, three severe weather events occurred--unusual this far northwest in January.

January 1998 was 5.9 degrees warmer and 4.28 inches wetter than January 1997. Indeed, January 1998 was the fourth wettest January in National Weather Service records for Tyler, which go back to 1896. The three wetter Januaries were: 1932 with 9.60 inches, 1949 with 8.91 inches, and 1946 with 7.99 inches. January 1998 was nowhere being the warmest January on record. That honor goes to January 1923 when the temperature averaged 57.0 degrees. January 1911 occupies second place with 56.0 degrees, and January 1907 third with 55.9 degrees. Within the past generation, two Januaries were warmer: 1990 with 54.3 degrees and 1989 with 52.9 degrees.

The season-to-date heating degree-day total dropped below normal in January. However, accumulated cold thusfar this cool season is still ahead of that for the 1996-1997 cool season. Through January 31, 1998, 1394 heating degree-days had accumulated, compared with 1344 for the same time last year. The thirty-day outlook had called for below normal temperatures and above normal precipitation.

The first week in January saw temperatures eleven degrees above normal and precipitation about 600 percent of normal. A powerful and slow-moving upper air storm was over the area from the 2nd through the 8th. Consisting of a closed-off low aloft over the Southwestern United States, a nearly stationary cold front after the 3rd just to the north of the region (which finally crossed on the 7th,) and a continuing stream of moist air from the Gulf of Mexico just above the surface, very heavy rains fell. Indeed, two daily precipitation records were set--on the 6th and the 7th. The 3.71 inches on the 6th was the second heaviest single- day rainfall total observed in Tyler since Weather Service records began.

In addition, an outbreak of severe weather occurred on the night of the 5th. An F-2 tornado struck in the Gresham community--about five miles southwest of Tyler--at 11:10 p.m. on the 5th, causing some property damage but no personal injuries. About an hour later, two tornado signatures were observed on radar in Upshur County. In addition, numerous primary and secondary roads were closed in various counties around the area because of very heavy rainfall. The situation was aggravated by the fact that in mid-Winter, the ground is substantially bare of green vegetation, and rainfall usually runs off causing localized flooding. This storm was unusual in its intensity and duration, and can probably be ascribed to ENSO 3.4 (the El Nino Southern Oscillation) which was particularly pronounced during the 1997-1998 cool season.

Temperatures during the second week in January were two degrees above normal and rainfall was 125 percent of normal. For most of the week, an upper air low pressure trough was to the west of the region. Disturbances rotating around the base of this trough triggered thunderstorm activity and rain in the moist air mass which was in place for much of the week. In addition, shallow cold air was trapped for much of the week beneath a layer of warm air a few thousand feet above ground level. The result was a nearly continuous overcast, with visibilities frequently restricted by dense fog.

Another severe weather event occurred on the 11th when a warm frontal boundary moved northward from the Gulf of Mexico and intersected with a passing disturbance. Large hail was reported in parts of the region along with gusty surface winds on the afternoon of the 11th.

The third week in January saw temperatures four degrees above normal and precipitation about one-tenth normal. One storm exited the region early in the week while another approached late in the week. The mid-week period saw a Polar Maritime air mass over the region, which brought fair and tranquil weather. Another severe weather event occurred on the afternoon of the 21st, with large hail reported in the southwestern part of Smith County.

The final ten days of the month saw temperatures four degrees above normal and rainfall near normal. Weak upper air storms crossed causing the period's rainfall. These were followed by Polar Maritime air masses, which lowered temperatures only slightly.

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.

January 1998



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