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August 2018 & Summer 2018
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- Tulsa: No daily records were set or tied this month.
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- Using the radar-derived estimated observed precipitation from the RFCs, rainfall totals for August 2018 ranged from around 1.5” to isolated amounts around 15” across eastern OK and northwest AR. The highest rainfall totals of over 8” were primarily across far northeast OK, east central OK and west central AR, and Creek and Tulsa Counties in southeast OK. This corresponds to 50-400% of the normal August rainfall across the area, with around 600% of the August rainfall normal in northern Le Flore County.
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- An active weather pattern mid-month brought several rounds of heavy rain to portions of eastern OK and northwest AR, resulting in both flash flooding and river flooding.
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- Moderate flooding occurred along the Poteau River near Poteau and Panama and the Neosho River near Commerce rose to just below flood stage.
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- According to the Drought Monitor from August 28, 2018, Severe (D2) Drought conditions were impacting Osage, northern Pawnee, and southern Washington Counties in eastern OK. Moderate (D1) drought conditions were present across portions of Osage, Pawnee, eastern Kay, Washington, Tulsa, Nowata, Craig, Ottawa, Rogers, Mayes, and Choctaw Counties in eastern OK, and Benton and Carroll Counties in northwest Arkansas. Abnormally Dry (D0) but not in drought conditions encompassed portions of Pawnee, Osage, eastern Kay, Creek, Tulsa, Rogers, Mayes, Craig, Ottawa, Delaware, Cherokee, and Choctaw Counties in eastern Oklahoma and Benton, Carroll, and Madison Counties in northwest Arkansas.
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- According to the Oklahoma Climatological Survey, the 30-day period August 2-31, 2018 was the 23rd wettest for northeast Oklahoma, the 21st wettest for east central Oklahoma, and the 10th wettest for southeast Oklahoma. Records go back to 1921. For Summer 2018 (June-July-August), northeast Oklahoma ranked as the 44th driest, east central Oklahoma was the 37th wettest, and southeast Oklahoma was the 27th wettest period. For the Water Year-to-date, October 1, 2017-August 31, 2018, northeast Oklahoma ranked as the 34th driest, east central Oklahoma was the 40th wettest, and southeast Oklahoma was the 47th wettest period.
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- Showers and thunderstorms moved across northeast OK and northwest AR during the morning and early afternoon hours of the 7th. More intense convection developed during the afternoon along a cold front, bringing heavy rain and damaging winds to the Tulsa area before moving more quickly east across east central OK and northwest AR. Storms continued into the late night hours, with additional heavy rain across northern Franklin and southern Madison Counties. Rainfall totals ranged from around 0.25” to near 3” across the affected areas. Urban street flooding occurred in Tulsa.
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- An active northwest flow weather pattern set up over the region on the 13th-20th. Several waves moving through a strong upper-level low brought several rounds of rainfall to eastern OK and northwest AR. With precipitable water values around 2”, this resulted in significant heavy rain.
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- Showers and thunderstorms affected southeast OK during the morning of the 13th, expanding northward during the day. A second area of showers and thunderstorms moved into southeast OK during the evening and moved northeast into northwest AR. Rain continued over this region for much of the overnight hours. By 7am on the 14th, most of southeast OK and west central AR had received 2”-4” of rain. The showers and thunderstorms continued across this area until late afternoon, resulting in another 1”-2” of rain. Scattered convection then continued across all of eastern OK and northwest AR through the evening and overnight hours aided by the low-level jet. 24-hour rainfall totals were generally 0.50” to around 2” by 7am on the 15th, however an area of 3”-8” of rain fell over the Verdigris River basin in southeast KS just north of the OK state line. The rain lead to a rapid 20’ rise along the Verdigris River near Lenapah, but due to antecedent dry conditions, the river remained below flood stage.
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- Heavy rain continued primarily over east central OK and west central AR during the morning and early afternoon of the 15th as storms trained over the same area. To make matters worse, this heavy rain fell on areas which had already received high rainfall totals the previous two days. There was finally a break in the activity, with only isolated showers and thunderstorms across west central AR during the evening hours. Several locations across east central OK and west central AR received 3”-4” of additional rainfall, with 7.5” of rain measured near Panama in Le Flore County. Flash flooding occurred across east central OK and west central AR, including widespread closures of streets and state highways and stranded vehicles in Le Flore, Crawford, and Sebastian Counties.
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- The 3-day rainfall total ending at 7am CDT 8/16/18 at Panama 2E, OK was 14.47”. This is approximately a 500-year recurrence interval (or 0.2% annual chance of occurrence) for a 3-day rainfall. Widespread 6”-12” occurred within a 3.5-day period. The 3.5-day heavy rainfall impacted the Poteau, Lower Arkansas, and Upper Kiamichi River basins. Moderate river flooding occurred along the Poteau River.
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- A subtle boundary was located near Highway 412, as noted by moisture pooling and high heat index values to its south. As an mesoscale convective vortex (MCV) from High Plains convection the night before approached the area, thunderstorms developed along the boundary from Tulsa westward during the afternoon of the 16th. These storms brought heavy rain to Tulsa before expanding in area across northeast OK and northwest AR during the evening. Shortly after midnight on the 17th, an area of showers and thunderstorms moved south out of KS into northeast OK, affecting the area through the pre-dawn hours. By 7am on the 17th, northern Creek, western Tulsa, northern Craig, and northwestern Ottawa Counties had received 2”-5” of rain. One site, Tulsa 5SSW, OK, measured 4.66” of rain. The showers and thunderstorms continued to the southeast through the morning, primarily affecting northeast OK through northwest AR before shifting southeast of the area. This activity brought 0.5” to 2.5” of rain. Flash flooding resulted in high water over roadways and led to stranded cars near Sand Springs, urban street flooding in the Tulsa metro area, numerous side roads flooded in Craig County, water in a business and encroaching on a home both near Sapulpa, and street and state highway flooding across portions of Creek, Benton, and Franklin Counties. Storms redeveloped during the late evening hours of the 17th near I-40 where an outflow boundary left from the morning convection was located, and they continued into the pre-dawn hours of the 18th. Training storms across northern Le Flore and Sebastian Counties resulted in 1.5” to around 4” of rain. The heaviest of this rain was centered near Panama in Le Flore County, the same area that had just received heavy rain from the previous storm activity. The rain gauge at Panama 2E, OK measured another high 24-hour rainfall total of 4.07” by 7am CDT 8/18/2018. The 6-day total rainfall ending at 7am CDT 8/18/2018 at Panama 2E, OK was 19.14”. This amount is greater than a 1,000 year recurrence interval (or less than a 0.1% annual chance of occurrence) for a 7-day rainfall! The Poteau River near Panama had been receding from the previous heavy rain, but this additional water resulted in another rise to minor flooding.
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- In the pre-dawn hours of the 19th, a large complex of thunderstorms moved into northeast OK. This activity continued to progress to the northeast, affecting northeast OK north of I-40 and far northwest AR during the morning and early afternoon hours. Additional scattered thunderstorms developed during the afternoon and evening across far eastern OK and western AR. Several of these were low-topped, mini supercells. Two of these supercells produced EF-1 tornadoes in Mayes and Rogers Counties (see https://arcg.is/1f5Ob4 for details). Rainfall totals were 1.5” to 5” along the I-44 corridor from Creek to Ottawa Counties. The 24-hour rainfall total ending at 7am 8/20/2018 at Quapaw 3SE, OK was 4.82”. Flash flooding affecting urban roadways was reported across the Tulsa metro area. Figures 22-24 illustrate the heavy rain received across eastern OK and northwest AR for the week ending at 7am CDT 8/20/2018.
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- Thunderstorms developed across eastern Kay, Pawnee, Osage, Washington, and Nowata Counties during the early morning hours of the 25th within an area of favorable isentropic lift and warm air advection. This activity continued through the morning and finally dissipated in the early afternoon. While most of the affected area received around 0.50” or less of rain, eastern Kay, western Osage, and northwestern Pawnee Counties, just south of the Ponca City area, received 0.75” to around 3” of rain.
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- Two rounds of showers and thunderstorms affected southeast KS and northeast OK both during the morning and afternoon hours of the 30th. The afternoon activity moved southeast and also affected northwest AR. While rainfall totals in far northeast OK and northwest AR ranged from around 0.50” to around 2.5”, heavier rainfall of 1.5” to 4” fell in the Neosho River basin in southeast KS. This resulted in the Neosho River near Commerce rising to just below flood stage.
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| Summer (June-July-August) 2018 |
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