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The Dexes / Heavy Rain / 837642

Eventdex · Heavy Rain

POLK

837642 · 41.280, -97.550

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Event typeevent_typeHeavy Rain
NOAA NCEI event IDncei_event_id837,642
Episode IDepisode_id138,394
Begin UTCbegin_utc2019-06-25T12:00:00+00:00
End UTCend_utc2019-06-26T12:00:00+00:00
StatestateNEBRASKA
County/zone typecz_typeC
County/zone namecz_namePOLK
Latitudelat41.280
Longitudelon-97.550
End latitudeend_lat41.280
End longitudeend_lon-97.550
Deaths directdeaths_direct0
Deaths indirectdeaths_indirect0
Injuries directinjuries_direct0
Injuries indirectinjuries_indirect0
Damage propertydamage_property0.00K
Damage cropsdamage_crops0.00K
Weather forecast office sourcewfo_sourceCoCoRaHS
Episode narrativeepisode_narrativeBetween the mid-afternoon of Tuesday the 25th and early morning of Wednesday the 26th, mainly the eastern half of South Central Nebraska endured two rounds of severe thunderstorms and heavy rainfall, with the first round by far the most impactful as it produced some of the largest hail of 2019 within the area (up to 3 diameter). Examining Round 1 in more detail, it unfolded from 4-8 p.m. CDT within several counties south of Interstate 80 and east of Highway 183, but with the majority of action focused within Adams, Webster and Nuckolls counties. The primary player here was an initially isolated, high-precipitation supercell that developed over western Adams County, gradually growing upscale into more of a supercell cluster as it surged southeastward before departing into northern Kansas. This storm was a prolific hail-producer, particularly within southwestern Adams County where there were numerous reports of stones ranging from quarter to larger than baseball size. The area in and near Holstein was particularly hard-hit, as hail as large as 3 was documented there by an NWS employee (although the vast majority of stones were smaller than this). As this massive storm sank farther south it became increasingly outflow-dominant and more of a wind-producer, with several gusts of 55-70 MPH reported in the Guide Rock and Superior areas. Independent of this storm of the day, other severe storms flared up during the afternoon and early evening within counties such as Clay/Fillmore/Franklin, producing hail of 2 diameter near Ong and golf ball size in Naponee. Rainfall-wise, though not extreme, amounts of 1.50-2.50 fell within much of Adams/Webster counties. This led to minor flooding on the Little Blue River, with the gauge near Deweese cresting at 10.3 feet on the afternoon of the 26th (flood stage 10 ft.). ||After Round 1 departed into Kansas, all was quiet on the local front for several hours. However, Round 2 got underway after 1 a.m. CDT on the 26th and persisted until past sunrise. This round of convection was not as intense, mainly producing heavy rainfall, sub-severe wind gusts and small hail within northeastern portions of the area (mainly northeast of an Ord-York line). However, there were a few severe-criteria reports including quarter size hail in York and a 61 MPH wind gust near Waco. Technically, Round 2 consisted of a few separate areas of storms: one small cluster that blew up over York County along the nose of a nocturnal low level jet and another larger complex that expanded across several northeastern counties between 3-7 a.m. CDT before finally weakening and departing the vast majority of South Central Nebraska by 9 a.m. CDT. Rainfall totals of 1.50-3.00 were fairly common with this early-AM activity, highlighted by NeRAIN totals of 3.60 near York and 3.33 north of Osceola. Resultant flooding was relatively minor, including along the Clear Creek in northern Polk County, which crested at 8.3 feet on the morning of the 27th (flood stage 8 ft.).||For yielding so many severe weather reports, this was actually a fairly weakly-forced event in the mid-upper levels, with Nebraska positioned along the southern periphery of broad westerly flow and no significant shortwave troughs of note. However, the intense afternoon-early evening convection was clearly tied to low-level convergence along a west-east oriented, quasi-stationary surface front. As afternoon temperatures climbed into the upper 80s F, the mesoscale environment became quite supportive of severe storms (including supercells), featuring 2000-3000 J/kg mixed-layer CAPE and 30-40 knots of deep-layer wind shear. Later in the night, Round 2 was fueled by a classic increase in convergence/moisture transport within the exit region of a 30-40 knot southwesterly low-level jet.
Event narrativeevent_narrativeAn NERAIN observer recorded a 24-hour rainfall of 3.33 inches 7 miles north of Osceola. Another NERAIN observer recorded a 24-hour rainfall of 3.25 inches 4 miles west northwest of Shelby. Most rain fell early morning of the 26th.
Yearyear2,019

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POLK — Heavy Rain — TerraPulse