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Archives for the SPC Convective Outlook are updated daily (approximately) with a live map at the beginning of each article. Follow the link at the end of the article to check for current updates on the NOAA/NWS Storm Prediction Center website. Also, see Archives for Chicago's hourly weather data on CARDINAL NEWS Magazine.


Wednesday, April 17, 2024

SPC Apr 17, 2024 1300 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0752 AM CDT Wed Apr 17 2024

Valid 171300Z - 181200Z


Scattered thunderstorms capable of producing damaging winds, large
hail, and a few tornadoes should develop across parts of the Ohio
Valley and Lower Great Lakes this afternoon. Thunderstorms with
mainly a large hail threat may occur tonight over parts of the
central Plains.

An upper trough/low over the Upper Midwest this morning will
continue to move east-northeastward across the Great Lakes and OH
Valley today while gradually de-amplifying/weakening. An associated
40-60 kt mid-level jet will accompany this trough and overspread
much of the OH/TN Valleys. At the surface, a low over southeastern
MN/western WI should continue to gradually occlude through the day
in tandem with the weakening upper cyclone. An attendant cold front
will sweep eastward over the Lower Great Lakes/OH Valley through
this evening, while a warm front advances as far north as parts of
Lower MI and perhaps far western NY.

...Lower Michigan into the Ohio/Tennessee Valleys and
Upper 50s to low 60s surface dewpoints are expected to be in place
ahead of the cold front late this morning/early afternoon. A
pronounced mid-level dry slot evident on water vapor satellite
imagery should aid in diurnal destabilization via a general lack of
mid/upper-level cloud cover across parts of the OH Valley. As the
boundary layer gradually warms/moistens, around 1000-1500 J/kg of
MLCAPE should develop across southern Lower MI, eastern IN, and OH.
Sufficiently strong low/mid-level winds will support 40-50 kt of
deep-layer shear and updraft organization. Current expectations are
for convection to develop along or just ahead of the cold front by
early afternoon, and subsequently spread quickly east-northeastward
across Lower MI, OH, and western PA through this evening. Tendency
may be for thunderstorms to quickly organize into a line, especially
across Lower MI which will be in closer proximity to the large-scale
ascent attendant to the upper trough/low. If this evolution occurs,
then severe/damaging winds would be the main threat with this
activity. Have expanded the Marginal and Slight Risks northward
across Lower MI to account for this potential.

Farther south across eastern IN and OH, forcing will gradually
become more limited, which may allow for somewhat lower thunderstorm
coverage initially. Even so, deep-layer shear will be strong enough
to support supercells, with large hail, damaging wind, and a few
tornadoes all possible. The best tornado potential may be focused
across parts of southeastern Lower MI and northern OH, in closer
proximity to the warm front and greater low-level shear. Some
upscale growth may also occur with this activity as it moves into
eastern OH and western PA, with a potentially greater threat for
damaging winds through the early evening before convection
eventually weakens.

Overall convective coverage should be lower across the TN Valley
into the Southeast, with weaker large-scale ascent present over
these regions. Still, isolated strong thunderstorms may occur this
afternoon and early evening in a weakly unstable but strong
deep-layer shear environment. Occasional hail and gusty winds appear
possible with the more robust cores. Based on latest guidance
trends, have trimmed the western extent of the Marginal Risk over
western KY/TN and northern MS.

Across the eastern Mid-Atlantic (northern VA/MD/DC/DE/south-central
PA), a well-mixed boundary layer and steep low-level lapse rates
forecast by some guidance may support occasional strong to damaging
winds with convection spreading eastward off the higher terrain of
the Appalachians and Blue Ridge Mountains. With limited instability,
the overall severe wind threat will likely remain isolated.

...Nebraska/Kansas into Iowa/Missouri...
An upper-level trough will move eastward across the north-central
CONUS tonight. A 40-45 kt southerly low-level jet will develop this
evening across parts of the southern/central Plains in response.
Thunderstorms should eventually initiate near the northern edge of
the low-level jet late this evening from central KS into far
southeast NE. Ample MUCAPE, steep mid-level lapse rates, and strong
shear in the cloud-bearing layer should support some threat for
large hail with this mainly elevated convection. The large hail
threat should to be greatest in the 04Z to 08Z time window with
initial development, but it may persist through the end of the
period. If convection can grow upscale into a small bowing cluster,
then isolated damaging winds may also occur.

A conditional threat for a supercell or two will exist farther south
across south-central/southeastern KS into far northeastern OK. Here,
modest low-level convergence along the intersection of a developing
warm front and dryline may be sufficient to initiate isolated
convection early this evening as the low-level jet strengthens. If
this occurs, then all severe hazards appear possible.

Very isolated thunderstorms may develop late this afternoon and
early evening across parts of south-central into central TX along a
surface dryline. If any convection can be sustained, it could
produce severe winds and hail. But, this threat currently appears
too conditional and uncertain to add low severe probabilities.

..Gleason/Bentley.. 04/17/2024

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CHICAGO UTC-5 during CDT (Daylight Savings Time, e.g., summer)