Alert archive / Iowa / Mesoscale Discussions in 2021

Mesoscale Discussion 20

January 15, 20218 counties in Iowa; Atchison County, Nodaway County, Missouri; 5 counties in Nebraska

The Storm Prediction Center issued this mesoscale discussion at Jan 15, 2021, 3:37 AM CST for 8 counties in Iowa; Atchison County, Nodaway County, Missouri; 5 counties in Nebraska. It was in force for 3 hr.

The area

The outline as issued.

The facts

Issued
Jan 15, 2021, 3:37 AM CST (09:37 UTC)
Expired
Jan 15, 2021, 6:30 AM CST
In force
3 hr
Issued by
the Storm Prediction Center
Concerning
Blizzard

Counties Fremont County, IA, Harrison County, IA, Mills County, IA, Monona County, IA, Montgomery County, IA, Page County, IA, Pottawattamie County, IA, Taylor County, IA, Atchison County, MO, Nodaway County, MO, Burt County, NE, Douglas County, NE, Sarpy County, NE, Thurston County, NE, Washington County, NE

The radar

The Omaha radar (KOAX), 67 km from the middle of the area, began a volume at 09:38 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, 9.6 hours before the alert went out and 67 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.

Skew-T log-pSkew-T log-p diagram, Omaha, NE at 00:00Z on 2021-01-15Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Omaha, NE at 00:00Z on 2021-01-15The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 83 square meters per square second.19395878Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.
Mixed-layer CAPE
0 J/kg
Mixed-layer CIN
No buoyant parcel
Mixed-layer LCL
1841 m above ground
0-6 km bulk shear
16 kt
0-1 km storm-relative helicity
83 m²/s²
0-3 km storm-relative helicity
136 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

857 
ACUS11 KWNS 150937
SWOMCD
SPC MCD 150937 
IAZ000-MOZ000-NEZ000-151230-

Mesoscale Discussion 0020
NWS Storm Prediction Center Norman OK
0337 AM CST Fri Jan 15 2021

Areas affected...Parts of eastern Nebraska and western Iowa into
northwestern Missouri

Concerning...Blizzard 

Valid 150937Z - 151230Z

SUMMARY...Moderate to occasionally heavy snow and strengthening
surface gusts are expected to contribute to periods of blizzard or
near blizzard conditions, with sharply reduced visibilities, through
6-9 AM CST.

DISCUSSION...A short wave impulse pivoting around the northwestern
and western periphery of the deepening mid-level low appears to be
contributing to increasing mid-level forcing for ascent
overspreading the Missouri Valley, including within the favorably
cold mid-level layers supportive of dendritic ice crystal growth. 
Snowfall rates have recently been increasing along the Iowa/Nebraska
border vicinity, and latest model output suggests that this may
persist at least another several hours, with heavier snow gradually
developing southeastward into areas near/northwest of St. Joseph,
MO.  

It also appears that this will coincide with a strengthening
pressure gradient on the southwestern periphery of the surface
cyclone, which is expected to migrate southward toward the eastern
Missouri/Iowa border through mid morning.  Beneath a strengthening
north-northwesterly low-level jet (to near 70 kt at 850 mb), it
appears that surface gusts may increase to 40-50 kts.  Although snow
rates may mostly be on the order of 1/2 inch per hour or less, brief
heavier rates approaching 1 inch per hour appear possible,
contributing to periods of sharply reduced visibilities when coupled
with considerable blowing of snow.

..Kerr.. 01/15/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...DMX...EAX...FSD...OAX...

LAT...LON   42359599 41289510 40919463 39959466 40469578 42239681
            42359599

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Jan 14, 8:44 PM CSTMesoscale DiscussionSPCCherokee, Ida, Lyon, Monona, O'Brien, Osceola and 3 more5 hr

Nearby

Mesoscale Discussions in Iowa, 2021Mesoscale Discussions in Nebraska, 2021Mesoscale Discussions in Missouri, 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.