Alert archive / Iowa / Mesoscale Discussions in 2021
Mesoscale Discussion 1449
The Storm Prediction Center issued this mesoscale discussion at Aug 8, 2021, 11:58 PM CDT for 4 counties in Iowa. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 8, 2021, 11:58 PM CDT (04:58 UTC)
- Expired
- Aug 9, 2021, 2:00 AM CDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
Counties Boone County, IA, Hamilton County, IA, Polk County, IA, Story County, IA
The radar
The Des Moines radar (KDMX), 40 km from the middle of the area, began a volume at 05:01 UTC, the scan nearest the moment this went out.
Open the radar archive at this moment
The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.
The nearest sounding before it
Omaha, NE (KOAX), launched 00:00Z, 5.0 hours before the alert went out and 242 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.
- Mixed-layer CAPE
- 1733 J/kg
- Mixed-layer CIN
- -130 J/kg
- Mixed-layer LCL
- 1356 m above ground
- 0-6 km bulk shear
- 36 kt
- 0-1 km storm-relative helicity
- 104 m²/s²
- 0-3 km storm-relative helicity
- 137 m²/s²
- Significant tornado parameter
- 0.2
- Supercell composite
- 6.0
The text
As transmitted.
801 ACUS11 KWNS 090458 SWOMCD SPC MCD 090458 IAZ000-090700- Mesoscale Discussion 1449 NWS Storm Prediction Center Norman OK 1158 PM CDT Sun Aug 08 2021 Areas affected...Parts of central Iowa Concerning...Severe potential...Watch unlikely Valid 090458Z - 090700Z Probability of Watch Issuance...20 percent SUMMARY...Isolated supercell development may continue between Fort Dodge and Des Moines into the 1-2 AM CDT time frame. Beyond that it remains unclear. Until activity finally diminishes, it may continue to pose a risk for locally strong surface gusts, with perhaps some potential for a tornado. DISCUSSION...Models suggest that a digging jet in the 700-500 mb layer may have contributed to forcing for ascent along a persistent zone of lower/mid tropospheric warm to the southwest of a mid-level low centered near southeastern Minnesota. Guidance also suggests that this jet may begin to redevelop eastward around base of the low during the next few hours, and large-scale ascent supporting persistent isolated supercell development may begin to weaken by the 05-07Z time frame. However, at least weak low/mid-level warm advection will persist in a rough northwest-southeast corridor across central Iowa, where it appears that a seasonably moist boundary-layer remains characterized by CAPE in excess of 2000 J/kg. So it remains unclear how soon vigorous convective development will diminish. While potential for substantive upscale convective growth appears low, deep-layer shear remains strong and supportive of the continuing evolution of supercell structures capable of producing localized strong surface gusts and perhaps some risk for a tornado. However, while thermodynamic profiles are supportive of tornadic potential, low-level hodographs are more uncertain, with a weakness evident around the 850 mb level. ..Kerr/Hart.. 08/09/2021 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...DMX... LAT...LON 42479346 41989297 41589342 41739402 42289449 42479346
Nearby
Mesoscale Discussions in Iowa, 2021Every mesoscale discussion in 2021
Sources
The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.