Severe Weather outlook

Storm Prediction Center

SPC Sep 19, 2024 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0751 AM CDT Thu Sep 19 2024

Valid 191300Z - 201200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM
MINNESOTA...IOWA AND WESTERN WISCONSIN SOUTHWARD INTO EASTERN KANSAS
AND WESTERN MISSOURI...

...SUMMARY...
Scattered severe thunderstorms are possible across central/eastern
Minnesota, Iowa, and western Wisconsin. A couple tornadoes, isolated
large hail, and damaging winds may occur. An area of locally severe
gusts and hail may also develop over parts of eastern Kansas,
southwest Missouri, and into northeast Oklahoma.

...Synopsis...
Early morning water-vapor imagery shows a slow-moving mid- to
upper-level low near the SK/MB/Dakotas border.  A negatively tilted
shortwave trough will move across the Dakotas and MN through the
day.  A belt of strong (40-50 kt) 500mb flow will extend through the
base of the trough from NE wrapping cyclonically through the Upper
MS Valley into western ON and to the northwest of a flattening ridge
over the mid MS Valley/southwest Great Lakes.  Farther south, weaker
west to northwest winds will encompass an area around a southern
Plains upper high from KS/OK into MO and AR.  In the high levels,
flow will be strongest across the central Plains, with weakening
winds over the northern Plains/upper MS Valley.

In the low levels, a cyclone will develop northeastward from
southeast SK into central MB by early Friday morning, while a cold
front moves into MN/western IA by mid afternoon, with frontolysis
expected during the latter part of the period.  A wind shift/surface
trough will also extend southward across eastern KS and into
northern OK.  Ahead of the aforementioned boundaries, southerly flow
will maintain a plume of mid to upper 60s F dewpoints.

...MN/IA/WI...
Scattered weak, elevated storms from the lower MO Valley northward
into MN/WI will gradually move east this morning and likely
dissipate by midday.  Cloud breaks and clearing in their wake will
contribute to appreciable heating and moderate to strong buoyancy
developing from near the MO River in western IA northward into MN. 
Forecast soundings show 2500-3000 J/kg MLCAPE with a veering and
strengthening wind profile into the mid levels.  A broken band of
quasi-discrete storms (including supercells) is forecast to develop
from MN southward into at least northern IA.  The risk for a couple
of tornadoes may be highest from MN into northern IA where effective
SRH may exceed 200 m2/s2.  A couple of stronger supercells may also
develop into western/southwest IA per recent HRRR model trends. 
Given the northward lifting of the shortwave trough, and increasing
inhibition east of the MS River, the primary threat should remain
relatively narrow.

...Eastern KS into western MO and into OK...
Widely scattered thunderstorms are ongoing this morning from
south-central into northeast KS.  Much of this activity will likely
dissipate but a few residual storms may continue or regenerate on
outflow over parts of western MO later this afternoon.  Strong
heating and the steepening of 0-3 km lapse rates will favor the
development of other isolated to widely scattered storms later this
afternoon near the wind shift.  12 UTC regional raobs sampled warm
mid-level temperatures (around -1 deg C at 525 mb at Norman, OK). 
These warm midlevel temperatures will limit the overall magnitude of
instability.  However, lengthy mid to upper level hodographs will
support storm organization with any robust/established updraft.  The
stronger storms will potentially be capable of a risk for severe
gusts and perhaps large hail.

..Smith/Mosier.. 09/19/2024

SPC Sep 19, 2024 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1126 AM CDT Thu Sep 19 2024

Valid 191630Z - 201200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE UPPER MIDWEST INTO EASTERN KANSAS...WESTERN MISSOURI...AND FAR
NORTHEAST OKLAHOMA...

...SUMMARY...
Scattered severe thunderstorms are possible this afternoon and
evening across central/eastern Minnesota, Iowa, and western
Wisconsin. A couple of tornadoes, large hail, and damaging winds may
occur across this region. Farther south, an area of locally severe
wind gusts and hail may also develop over parts of eastern Kansas,
southwest Missouri, and northeast Oklahoma.

...Minnesota/Wisconsin/Iowa...
Widely spaced and mainly elevated thunderstorms ongoing late this
morning across parts of IA into eastern MN and western WI should
continue to diminish in coverage over the next couple of hours. In
their wake, daytime heating of a seasonably moist low-level airmass
(surface dewpoints generally in the 60s) and somewhat steep
mid-level lapse rates will contribute to at least moderate
instability by mid afternoon along/ahead of a cold front extending
north to south from western MN into eastern NE and western IA. An
upper low over northern ND and southeast SK/southwest MB will
continue to advance slowly northeastward across south-central Canada
through the period. A belt of 35-50 kt mid-level west-southwesterly
winds on the southern periphery of the upper low will spread
eastward from the northern Plains into the Upper Midwest through
this evening. A veering/strengthening wind profile with height
through mid levels will support around 30-40 kt of deep-layer shear
across the warm sector. This shear will be sufficient for organized
thunderstorms, including the potential for a few supercells.

Current expectations are that scattered thunderstorms will develop
by mid to late afternoon across central/eastern MN into
northern/central IA along or just ahead of the eastward-advancing
cold front. A rather favorable thermodynamic environment will foster
robust updrafts, and any initial supercells should pose a threat for
large to very large hail (around 1.5-2.5 inches in diameter). But, a
fairly quick transition to more linear structures should occur given
the presence of the cold front, with a potentially greater damaging
wind threat evolving with eastward extent through the evening before
convection eventually weakens. South-southwesterly low-level flow
and related shear ahead of the front is not forecast to be overly
strong by most guidance this afternoon. But, some threat for a
couple of tornadoes remains apparent, especially with any sustained
supercells across east-central/southern MN into northern IA late
this afternoon/early evening.

...Eastern Kansas into Missouri and Northeast Oklahoma...
An upper ridge, with rather warm mid-level temperatures, will remain
centered over the southern Plains today. The surface cold front is
forecast to continue moving east-southeastward across the mid MO
Valley and central Plains through late this afternoon. A surface
trough extending southward from this front across the southern High
Plains should also mix eastward through peak daytime heating. Given
weak large-scale ascent and rather warm mid-level temperatures
across this area, there is still a fair amount of uncertainty
regarding how many additional thunderstorms will develop later
today, notwithstanding the ongoing (mainly elevated) convection over
eastern KS and far northwest MO. Still, other surface-based
thunderstorms may develop later this afternoon along/near the
front/dryline intersection in south-central KS/north-central OK, and
along the cold front in eastern KS. While low/mid-level flow should
remain fairly modest, steepened low-level lapse rates and moderate
instability should support a risk for mainly severe/damaging
downdrafts as convection spreads east-southeastward into western MO
and northeast OK through this evening.

..Gleason/Moore.. 09/19/2024