Alert archive / Iowa / Mesoscale Discussions in 2017
Mesoscale Discussion 521
The Storm Prediction Center issued this mesoscale discussion at Apr 19, 2017, 6:55 PM CDT for 21 counties in Iowa. It was in force for 95 min.
The area
The outline as issued.
The facts
- Issued
- Apr 19, 2017, 6:55 PM CDT (23:55 UTC)
- Expired
- Apr 19, 2017, 8:30 PM CDT
- In force
- 95 min
- Issued by
- the Storm Prediction Center
- Chance of a watch
- 40%
All 21 counties
Boone County, IA, Calhoun County, IA, Carroll County, IA, Cerro Gordo County, IA, Crawford County, IA, Floyd County, IA, Franklin County, IA, Greene County, IA, Hamilton County, IA, Hancock County, IA, Hardin County, IA, Humboldt County, IA, Kossuth County, IA, Palo Alto County, IA, Pocahontas County, IA, Sac County, IA, Story County, IA, Webster County, IA, Winnebago County, IA, Worth County, IA, Wright County, IA
The radar
The Des Moines radar (KDMX), 108 km from the middle of the area, began a volume at 23:56 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 watches that followed
Watches SPC issued over any of the same counties within four hours of this discussion.
The nearest sounding before it
Omaha, NE (KOAX), launched 12:00Z, 11.9 hours before the alert went out and 232 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
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 1072 m above ground
- 0-6 km bulk shear
- 42 kt
- 0-1 km storm-relative helicity
- 194 m²/s²
- 0-3 km storm-relative helicity
- 314 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.5
The text
As transmitted.
968 ACUS11 KWNS 192356 SWOMCD SPC MCD 192355 MNZ000-IAZ000-200130- Mesoscale Discussion 0521 NWS Storm Prediction Center Norman OK 0655 PM CDT Wed Apr 19 2017 Areas affected...Northern/Central Iowa Concerning...Severe potential...Watch possible Valid 192355Z - 200130Z Probability of Watch Issuance...40 percent SUMMARY...Thunderstorms are expected to increase in areal coverage across much of central and northern Iowa over the next few hours. Marginally severe hail is the primary risk with convection north of the warm front. DISCUSSION...Low-level warm advection should aid areal expansion of convection across much of central and northern IA over the next few hours. Latest surface analysis suggests the primary warm front has advanced into southern Crawford/Carroll counties, just north of current Tornado Watch 148. A marked increase in thunderstorm activity has been noted along the cold front extending from northwest IA into southeast NE. Activity north of I-80 has yet to exhibit very large hail, possibly due to unfavorable storm mode and significant clustering. Unless discrete supercells evolve near the warm front it appears much of the elevated convection may struggle to generate large hail. For these reasons will continue to monitor for possible ww. ..Darrow/Edwards.. 04/19/2017 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...ARX...MPX...DMX...FSD...OAX... LAT...LON 41959583 43379452 43549296 43019257 41999348 41959583
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 19, 2:29 PM CDT | Mesoscale Discussion | SPC | Crawford, Fremont, Harrison, Ida, Mills, Monona and 4 more | 3 hr |
| Apr 19, 3:23 PM CDT | Tornado Watch | SPC | Adair, Adams, Audubon, Carroll, Cass, Crawford and 11 more | 7 hr |
| Apr 19, 5:30 PM CDT | Mesoscale Discussion | SPC | Audubon, Cass, Fremont, Harrison, Mills, Montgomery and 3 more | 60 min |
Nearby
Mesoscale Discussions in Iowa, 2017Every mesoscale discussion in 2017
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.