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MOBILE DEVICE? Turn sideways. Weather conditions directly above are near Lakefront. Top tabs refer to O'Hare (official).

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.


Monday, July 15, 2024

SPC Jul 15, 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 Mon Jul 15 2024

Valid 151300Z - 161200Z



Severe thunderstorms are possible this afternoon and evening across
portions of the Midwest, central High Plains, lower Great Lakes, and
Arizona. The greatest potential for severe gusts is over eastern
Iowa into Illinois and Indiana.

Mid/upper-level pattern amplification in the northern stream will
contribute to weakening (but not dissipation) of the persistent
anticyclone over the Four Corners region. A 500-mb low over
northern MB will dig south-southeastward to northwesternmost parts
of ON through the period, combining with a series of small shortwave
perturbations in the cyclone's southern semicircle to increase both
cyclonic flow speeds and height curvature over upper parts of the
Midwest, Mississippi Valley and Great Lakes.

As this occurs, a shortwave trough -- evident in moisture-channel
imagery over the Black Hills and vicinity -- will accelerate
eastward to southern MN and northern/western IA by 00Z, then reach
Lake Huron, northwestern OH and northern IN by the end of the
period. That feature should be preceded by a smaller shortwave
trough and MCV -- now apparent over western MN -- and forecast to
move across northern WI and Upper MI through this evening. To its
southeast and well downstream from the Black Hills perturbation,
another MCV was quite evident in composite radar imagery over
southern Lower MI, with shortwave trough southwestward to parts of
central/eastern IL. This perturbation should move westward to
western parts of NY/PA by 00Z, then near-coastal areas of central/
southern New England and the northern Mid-Atlantic by 12Z tomorrow.

At the surface, 11Z analysis showed a low over northeastern SD with
cold front southwestward across western NE and northern CO. By 00Z,
the low should move/redevelop to a position near DBQ, with cold
front southwestward across northeastern to northwestern KS and
east-central/southeastern CO. By 12Z, the front should reach Lower
MI, northern/western IL (perhaps obscured by convective effects),
southern KS, and northeastern NM. Relevant prefrontal boundaries
are discussed below.

...IA to southern Lower Great Lakes...
The decaying remnants of the prior/overnight MCS responsible for the
southern Lower MI MCV also have left an outflow boundary over
southern portions of IN/IL, arching northwestward and becoming
quasistationary over western IL into southeastern/central IA.
Clouds/precip from the prior MCS, and shortwave subsidence/DNVA
immediately following its associated shortwave trough, should be
long gone by mid/late afternoon, when the airmass along the outflow
boundary will have had several hours to modify favorably from west
to east. The boundary itself also may drift northward amidst weak
but steady ambient warm advection, with the boundary layer favorably
destabilizing on both sides.

A combination of lift near the boundary, increasing large-scale
ascent ahead of the upstream mid/upper-level shortwave trough,
steepening low-level lapse rates from diurnal heating, and rich
moisture (surface dewpoints commonly upper 60s to low 70s F) are
expected to prepare the corridor in and near the "enhanced risk"
area for severe potential through the afternoon. Isolated to
scattered thunderstorms should develop near and north of the western
limb of the outflow boundary (mainly IA, but also possibly western
IL) from mid/late afternoon into early evening. Some of this
activity may be supercellular in the first few hours, with large
hail possible.

However, given the presence of a convergent, moisture-rich, broad
gradient of instability north of the boundary aligned strongly
parallel to favorably strong mid/upper winds, large low/middle-level
lapse rates, and a related reservoir of high buoyancy (MLCAPE of
3000-5000 J/kg) this activity should evolve quickly upscale to an
MCS with severe gusts (some over 75 mph) becoming the greatest
hazard. With a vorticity-laden boundary, and potential for backed
surface winds and vertical-shear/hodograph enhancement to its north,
a corridor of relatively maximized tornado potential (from
supercells and/or QLCS-embedded circulations) also exists -- likely
narrower than depicted here due to current boundary-position
uncertainty. Uncertainty exists also on how far the MCS will travel
(and whether far enough to qualify as a derecho) before weakening
tonight. This will be related to depth/breadth of the cold pool and
mesobeta-scale rear-inflow jet dynamics, and their ability to exert
forced ascent on a moist but gradually stabilizing inflow layer with
eastward extent.

Scattered thunderstorms are expected to move eastward across this
area this afternoon into early evening -- some of which may initiate
late morning into midday back in ON closer to the MCV. Activity
should aggregate into clusters and/or a short QLCS, yielding
damaging to severe gusts. Isolated discrete or line-embedded
supercells also are possible, with some attendant severe-hail

As the MCV crosses southernmost parts of ON and also Lake Erie
today, the foregoing boundary layer over parts of NY/PA will
destabilize diurnally, while remaining favorably moist (with lower-
elevation surface dewpoints commonly in the mid 60s to near 70 F).
This will support a buildup of preconvective MLCAPE into the 1500-
2000 J/kg range (locally higher). Note that models with RAP physics
(RAP, HRRR) may be over-mixing higher elevations and
underforecasting buoyancy as a result (a common bias). Increase and
slight veering of winds with height will contribute to around 30-40
kt effective-shear magnitudes, which may be locally greater in any
channels of gradient-flow enhancement from the MCV that extend to or
past the zone of convective forcing. Meanwhile, a well-mixed
subcloud layer will supports damaging-downdraft potential.

...Central High Plains...
Isolate to scattered, high-based thunderstorms are expected to form
this afternoon over a broad area from central WY to the Front Range
and foothills of CO, with the most concentrated convection still
progged for portions of southeastern WY, western NE and northeastern
CO. Steep low/middle-level lapse rates (8.5-9 deg C/km) are
expected by midafternoon over this region, with enough easterly
component of flow behind the front (and relate moist advection) to
offset mixing and maintain mid 40s to low 50s surface dewpoints in
the "slight risk" area. These should contribute to a field of
peak/preconvective MLCAPE ranging from around 300 J/kg just east of
the mountains to around 1500 J/kg over parts of west-central/
southwestern NE. The post-frontal boundary-layer flow also will
enhance both storm-relative low-level winds and deep shear
(effective-shear magnitudes in the 35-45-kt range). This, along
with potential for cold-pool clustering, favors some organization
and maintenance of convection across the outlook this evening before
diminishing in a more strongly capped, nocturnal boundary layer over
lower Plains elevations.

Widely scattered thunderstorms are expected to form again this
afternoon over portions of the Mogollon Rim and smaller terrain
maxima to its south, offering locally strong-severe downbursts.
Although the synoptic anticyclone will be weakening through the
period, associated flow still will support motion toward the west or
southwest, atop deep/well-mixed boundary layers of the desert floor.
Airmass recovery from the prior day's convection by afternoon will
be aided by warm/moist advection and strong diurnal heating. Large
dewpoint depressions and deep subcloud layers in lower elevations --
beneath about 1000-1500 J/kg MLCAPE -- will support the gust
potential, especially wherever activity can become clustered and
maximize regenerative potential through cold-pool-aided lift.

..Edwards/Broyles.. 07/15/2024


SPC Jul 15, 2024 0600 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1250 AM CDT Mon Jul 15 2024

Valid 151200Z - 161200Z



Severe thunderstorms are expected this afternoon and evening across
portions of the Midwest, central High Plains, and the lower Great
Lakes. The greatest potential for severe/damaging winds appears to
be across eastern Iowa into Illinois and Indiana. More isolated
strong to severe thunderstorms are possible across southeast Arizona
and the New England region.

A complex severe-weather setup is anticipated for today across the
Midwest with the potential for one or more severe MCSs. The details
of how the severe threat will evolve this afternoon/evening will be
conditional on convective evolution of ongoing MCSs across ND and
IL/IN through 12 UTC, which introduces considerable uncertainty into
the forecast. In general, a broad surface cyclone is forecast to
deepen slightly over the upper Great Lakes over the next 12-24 hours
as a low-amplitude mid-level wave traverses the northern CONUS. As
this occurs, a weak cold front (noted in surface obs across MT and
the western Dakotas as of 05 UTC) will migrate south into the
Midwest and central Plains by late afternoon. Thunderstorm
development and/or re-intensification is anticipated along this
boundary and on the northern periphery of a reservoir of a high
theta-e air mass in place over the central Plains.

Recent CAM guidance depicts a range of possible scenarios for the
next 24 hour period. The most probable scenario involves the cluster
of thunderstorms ongoing across the Dakotas as of 05 UTC, which will
likely weaken by 12 UTC as it approaches the mid-MS River Valley.
The remnants of this complex may act as foci for re-development by
mid to late afternoon on the northeastern periphery of a reservoir
of high theta-e air (denoted by dewpoints in the low to mid 70s)
across IA, southern WI, and northern IL. Thunderstorms emerging from
this zone will likely organize and intensify into an organized MCS
as it propagates southeast into eastern IA and northern IL.

If the ND cluster weakens substantially by late morning, convective
initiation will likely be focused along the cold front as it
migrates south and/or along a residual outflow boundary from ongoing
storms. The location of initiation varies in latest model solutions,
which introduces uncertainty on where the corridors of relatively
higher severe-wind potential will be established. Higher wind
probabilities were placed based on where ensemble guidance shows the
best QPF signal, which likely correlates to where deep convection
will most likely occur. Additionally, forecast soundings suggest
sufficient low-level SRH may be in place to support a tornado threat
across eastern IA into northern IL; however, this threat will likely
be conditional on realizing a predominantly discrete storm mode
prior to upscale growth and/or embedded circulations with an
organized MCS.

05 UTC regional radar imagery reveals a mature MCS ongoing across
northern IL/IN. A vorticity maximum associated with this system is
apparent over lower Lake Michigan, and is expected to migrate east,
reaching the lower Great Lakes by around 18 UTC. Mid-level lapse
rates are fairly modest across New England per 00 UTC soundings, but
dewpoints in the upper 60s/lower 70s should support around 500-1000
J/kg MLCAPE by peak heating. Thunderstorm development ahead of the
MCV appears likely based on latest CAM guidance, and slightly
augmented flow in the vicinity of the vorticity maximum should
result in around 25-30 knots of effective bulk shear. These
environmental conditions will likely be sufficient to support
organized convective clusters within a somewhat focused corridor
across parts of PA and NY.

...Central High Plains...
Steep mid-level lapse rates and mid-level moisture across the
central Rockies will foster another day of widely scattered
thunderstorms across CO and WY. Storms will migrate into the central
High Plains by late afternoon amid a mean easterly flow regime. Weak
low-level storm-relative winds and a deeply mixed boundary layer
should yield outflow-dominant storms, but stronger mid-level flow
compared to previous days may favor some thunderstorm
clustering/cold pool amalgamation. Consequently, a more focused
corridor of severe-wind potential may emerge across the central High
Plains. While the exact location of where such clusters may emerge
remains uncertain, ensemble guidance suggests this is most probable
across the NE Panhandle into northeast CO/northwest KS.

...Southeast Arizona...
Thunderstorm development is expected again along the eastern
portions of the Mongollon Rim and out of the Gila region of
southwest NM. Southwesterly flow out of Gulf of California will
maintain dewpoints in the upper 50s to low 60s that should support
MLCAPE values above 1000 J/kg. Warm temperatures in the upper 90s to
low 100s should support another day of 40-50 F dewpoint depressions
amid deep boundary-layer mixing. Storms moving off the terrain will
be capable of strong to severe downburst winds as they migrate into
the buoyant, but deeply mixed environment at lower elevations.

..Moore/Darrow.. 07/15/2024


Sunday, July 14, 2024

SPC Jul 14, 2024 0600 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1234 AM CDT Sun Jul 14 2024

Valid 141200Z - 151200Z


Strong to severe thunderstorms are expected from the northern Plains
into the Upper Midwest.

...Northern Plains to Upper Midwest...

Large-scale pattern is not expected to change appreciably during the
day1 period, though some amplification is possible later in the
week. Upper high is forecast to remain anchored in the Four Corners
vicinity while seasonally strong mid-level flow will hold along a
corridor near the US/Canadian border. Negligible height changes are
expected during the first half of the period, though a few notable
short waves will track east-southeast from southern AB/SK into the
Great Lakes. Each short-wave trough should encourage convective
development -- some of it will likely be severe.

Early this morning, a weak MCS was propagating southeast across
northern IL/southern Lake MI. This activity is supported by a weak
disturbance and should progress into the southern Great Lakes/OH
Valley later today. Diurnal heating will contribute to strong
buoyancy, and robust updrafts may evolve along the leading debris
field by mid day. Locally severe winds may develop if convection

Of more concern will be convection that develops across the northern
Plains later in the afternoon. A strong short-wave trough will dig
southeast across southern AB by 15/00z before translating into
MB/eastern Dakotas by the end of the period. It appears a weak
surface low should evolve ahead of this feature over eastern MT
early, then shift into central SD by peak heating. A
northwest-southeast corridor of low-level warm advection will extend
across the Dakotas north of a synoptic boundary that will be draped
from southern MN-central SD-northeast MT. Strong boundary-layer
heating will negate CINH across the High Plains such that isolated
convection should develop by 22z. This activity will mature and grow
upscale through the evening. Early storm mode should be
supercellular, then clustering will lead to an MCS that is expected
to track southeast toward the mid MO Valley. Very steep lapse rates
will lead to strong buoyancy, and potentially very large hail
(possibly in excess of 2 inches). Very strong winds (>70mph) may
also be noted along the leading edge of the surging MCS.

..Darrow/Moore.. 07/14/2024


Saturday, July 13, 2024

SPC Jul 13, 2024 2000 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 2000Z Day 1 Outlook

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0244 PM CDT Sat Jul 13 2024

Valid 132000Z - 141200Z


Multiple clusters of strong to severe thunderstorms are possible
across portions of the Northern Plains into the Upper Mississippi
Valley through tonight. Other more isolated strong storms are
possible in northern New England, and portions of Nevada.

...20z Update...

The previous outlook remains on track, and no changes are needed
with the 20z update.

For short term information on severe potential across portions of
NV/AZ/UT, as well as across the northern High Plains, see MCDs 1593
and 1594. Otherwise, see previous discussion below for more forecast

..Leitman.. 07/13/2024

.PREV DISCUSSION... /ISSUED 1128 AM CDT Sat Jul 13 2024/

...Northern High Plains...
Relatively fast westerly mid-level flow is present today across the
northern Rockies/Plains. Several weak shortwave troughs are
tracking across southern Canada and parts of MT/ND today, including
one with an associated cluster of thunderstorms over southwest SK.
Persistent east-southeasterly low level winds ahead of this system
across eastern MT will likely allow it to persist through the day
and intensify with afternoon heating. A combination of supercells
and bowing structures are suggested by morning CAM guidance, with a
risk of large hail and damaging winds tracking across northeast MT
into western ND during the late afternoon and evening. Given the
consistent signal in guidance for fast-moving storms, and the
favorable CAPE/shear environment, have upgraded parts of this
corridor to ENH risk.

...MN/WI and Vicinity...
Remnant MCS and associated MCV is currently located over southeast
MN. This system will track southeastward across central/southern WI
through the afternoon, where strong daytime heating and dewpoints in
the upper 60s to lower 70s will yield strong instability.
Re-development of storms is possible, with a few severe/supercell
storms possible - capable of hail and damaging wind gusts.

Later this evening, thunderstorms are expected to intensify along a
weak cold front sagging into northeast ND and northern MN. These
storms are depicted by most morning CAM solutions to organize into a
linear MCS and spread southeastward across much of MN and northern
WI overnight. This scenario would pose a risk of damaging winds and
some hail in this area as well.

...Northern New England...
Scattered thunderstorms have begun to form this afternoon across
southern Quebec and parts of northern VT/NH/ME. Relatively strong
westerly flow aloft and moderate CAPE values will promote a risk of
locally gusty/damaging winds in the stronger cells through the

...NV and Vicinity...
Similar to the last couple of days, ample mid-level moisture is
present today across parts of NV, western UT, and northwest AZ. Hot
surface conditions and steep mid-level lapse rates will yield
widespread inverted-v profiles. Model guidance suggests scattered
coverage of high-based thunderstorms, with sufficient winds aloft to
promote locally damaging wind gusts in the stronger downdrafts.

SUNRISE AND SUNSET TIMES IN UTC (if you're not logged in to Google)
CHICAGO UTC-6 during CST (Central Standard Time, e.g., winter)
CHICAGO UTC-5 during CDT (Daylight Savings Time, e.g., summer)