July 2009

Report and Summary

Tyler, Texas
July 2009
by Robert K. Peters, Ph.D.
National Weather Service Cooperating Observer

The month of July 2009 saw near normal temperatures and much above normal precipitation. The month neatly divided meteorologically into its two halves and on the 16th. The first half of the month saw much above normal temperatures, and below normal rainfall. The last half saw much below normal temperatures and much above normal rainfall. The reason was the development of an upper air trough over Eastern and Central North America, and the retreat of the upper air Sub-Tropical High Pressure Ridge into the Western United States. Compared with July 2008, the month was 1.0 deg. Cooler and 6.58 inches drier.

Year-to-date rainfall through months' end was 3.83 inches less in 2009 than in 2008. The thirty-day outlook had called for near normal temperatures and near normal precipitation.

The week June 28-July 4 saw temperatures about 4 degrees above normal, and no rainfall. A weak cold front moved into the region on the 28th, lowering temperatures slightly for early in the week. At mid-week, the upper air high pressure ridge returned, again sending temperatures to above normal levels, and requiring a heat advisory for the 3rd and 4th. There were a few isolated afternoon showers on the 3rd and 4th. The week's average temperature was 86.0 deg., which was 0.9 deg. Cooler than the previous week. Compared with the same week in 2008, the week was 6.5 deg. Warmer, and 2.21 inches drier.

The week July 5-11 saw temperatures about 2 degrees above normal, and rainfall nearly 200 percent of normal. A cold front moved into the area on the morning of the 5th, which lowered temperatures for a few days as the upper air high pressure ridge retreated westward. The front, and its accompanying upper air disturbances, brought scattered showers and thunderstorms on the 5th and 6th. The upper air ridge returned on the 7th, again warming temperatures and ending showers. The week's average temperature was 84.5 deg., which was 1.5 deg. Cooler than the previous week. Rainfall was 1.39 inches. Compared with the same week in 2008, the week was 0.1 deg. Warmer, and there was no rain in 2008.

The week July 12-18 saw temperatures about 2 degrees above normal, and rainfall about one- third normal. The upper air ridge persisted until the 17th, when it was shunted westward by an upper air trough and its associated cold front. As a result, temperatures were well above normal through the 16th, but lowered to below normal and with scattered showers on the 17th and 18th. The week's average temperature was 85.9 deg., which was 1.4 deg. Warmer than the previous week. Rainfall was 0.24 inch. Compared with the same week in 2008, the week was 2.3 deg. Warmer, and 0.22 inch wetter. The week July 19-25 was dramatically different: temperatures about 3 degrees below normal and rainfall about 300 percent of normal.

The northwest flow event which set up on the 17th, continued through the 24th. Upper air high pressure made a brief re-appearance late in the week. Two cold fronts on the 20th and 23rd set off showers and held down temperatures. Disturbances in the northwest flow contributed to the shower formation. Severe thunderstorms developed on the night of the 21st, with power outages and wind damage in Tyler. Measurable rain fell on four days during the week, and normal temperatures were only observed on one day the 25th. The week's average temperature was 80.9 deg., which was 5.0 deg. Cooler than the previous week. Rainfall was 2.07 inches. Compared with the same week in 2008, the week was 5.3 deg. Cooler, and 1.97 inches wetter.

The final six days of the month saw two occurrences of heavy rain in the area: the first on the 28th-29th, and the second on the 30th-31st. Cold fronts moved into the area on the first day of each event, along with severe thunderstorms. In the first event, heavier rains were over the north; in the second, over the central and south. Temperatures ran below normal for the six days.

• KEY TO SYMBOLS:
• A = HAIL
• B = BLOWING
• D = DUST
• F = FOG
• H = HAZE
• IP = SLEET
• K = SMOKE
• L = DRIZZLE
• R = RAIN
• S = SNOW
• T = THUNDERSTORM
• Z = GREENWICH MEAN TIME
• ZL = FREEZING DRIZZLE
• ZR = FREEZING RAIN
• - = LIGHT
• + = HEAVY

R FOLLOWING A TEMPERATURE OR PRECIPITATION VALUE = RECORD

The reporting period for temperatures, precipitation, 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. 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.

• 01 100 74 97 F
• 02 101 73 96
• 03 99 77 96
• 04 99 77 96
• 05 91 74 75 0.82 T, F, PCPN 2200-2400 MN 0000-1200 79
• 06 85 73 82 0.57 F, T, PCPN 0900-1200
• 07 90 71 87 F
• 08 94 74 84 F, T
• 09 98 74 93
• 10 97 78 96
• 11 97 76 95
• 12 98 77 96
• 13 99 78 97
• 14 99 77 96
• 15 99 76 97
• 16 101 76 97 MN 0000-1200 78
• 17 92 68 90 0.24 T, F, PCPN 1000-1300
• 18 89 73 85 MN 0000-1200 74
• 19 94 68 88 0.06 T, F, PCPN 2000-2100
• 20 87 71 83 0.14 T, F, PCPN 1800-1900 MN 0000-1200 74
• 21 92 70 89 0.23 T, F, PCPN 1400-1600 MN 0000-1200 75
• 22 91 69 85 1.64 F, PCPN 0300-0500
• 23 90 72 84
• 24 90 71 88 0.02 PCPN 1800-1900
• 25 96 72 93 H
• 26 85 74 85 0.13 T, F, PCPN 1400-1600 MN 0000-1200 76
• 27 85 74 79 0.21 T, F, PCPN 0800-1100 MN 0000-1200 75
• 28 90 75 89 0.14 PCPN 1400-1500
• 29 91 74 88 MN 0000-1200 77
• 30 87 70 85 2.52R T, F, PCPN 0600-1500, MN 0000-1200 75
• 31 91 70 87

JULY 2009, RECORDS AND SUMMARY:

• 30TH RECORD RAINFALL 2.52 INCHES., PREVIOUS RECORD 2.00 INCHES IN 1938;
• HIGHEST TEMPERATURE 101 ON THE 2ND AND 16TH,
• LOWEST TEMPERATURE 68 ON THE 17TH, 19TH, AND AND 22ND,
• AVERAGE MAXIMUM 93.5 F.,
• AVERAGE MINIMUM 73.4 F.,
• AVERAGE TEMPERATURE 83.5 F.,
• 0.1 DEG. WARMER THAN NORMAL.
• 0 HEATING DEGREE DAYS,
• 0 PERCENT OF NORMAL HEATING DEGREE DAYS.
• 579 COOLING DEGREE DAYS,
• 101.9 PERCENT OF NORMAL COOLING DEGREE-DAYS;
• TOTAL PRECIPITATION 6.72 IN.,
• 4.56 IN. GREATER THAN MONTHLY NORMAL.
• 311.1 PERCENT OF NORMAL MONTHLY PRECIPITATION.
• YEAR-TO-DATE PRECIPITATION 24.48 IN., 0.52 IN. LESS THAN THAN NORMAL YEAR-TO-DATE PRECIPITATION,
• 97.9 PERCENT OF NORMAL YEAR-TO-DATE PRECIPITATION;
• 10 DAYS ON WHICH THUNDERSTORMS OCCURRED;
• 14 DAYS ON WHICH THE VISIBILITY WAS RESTRICTED TO BETWEEN 1 AND 7 MILES BY FOG, SMOKE, OR HAZE;
• 0 DAYS ON WHICH THE VISIBILITY WAS RESTRICTED TO 1 MILE OR LESS BY FOG;
• 0 DAYS ON WHICH THE VISIBILITY WAS RESTRICTED BY DUST OR BLOWING DUST;
• 0 DAYS ON WHICH FROZEN PRECIPITATION WAS OBSERVED;
• 0 IN. TOTAL SNOWFALL.
• 11 DAYS ON WHICH MEASURABLE PRECIPITATION OCCURRED.
• 25 DAYS ON WHICH THE MAXIMUM TEMPERATURE REACHED OR EXCEEDED 90 DEG.;
• 3 DAYS ON WHICH THE MAXIMUM TEMPERATURE REACHED OR EXCEEDED 100 DEG.;
• 0 DAYS ON WHICH THE TEMPERATURE FAILED TO RISE ABOVE 32 DEG.
• 0 DAYS ON WHICH THE MINIMUM TEMPERATURE REACHED OR FELL BELOW 32 DEG.
• 0 SEASON-TO-DATE HEATING DEGREE DAYS,
• PERCENTAGE OF NORMAL SEASON-TO-DATE HEATING DEGREE DAYS: 0;
• 1468 YEAR-TO-DATE COOLING DEGREE DAYS.
• PERCENTAGE OF NORMAL YEAR-TO-DATE COOLING DEGREE DAYS: 102.7.
• PRECIPITATION DURING THE PREVIOUS TWELVE MONTHS 53.82 IN.,
• TWELVE-MONTH PRECIPITATION PERCENTAGE 118.9.

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