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Severe Threat May 15-16, 2025

Don't know too much about the experimental MPAS models (mainly how reliable they are compared to the other CAMS), but 0Z runs of both the MPAS-HN and MPAS-HT have a midday MCS blasting across southern WI/northern IL that other guidance hasn't really indicated (but would be more in keeping with how severe weather days historically go in this region), and both develop another round behind this which includes supercells in either southern WI or northern IL.

0Z MPAS-RT, which goes to 84 hours, hasn't quite come in for the timeframe of greatest interest yet.
 
IWX is not confident in severe weather occuring, as apparent in their public graphics. Don't think I've seen an ENH risk have a "low confidence" mark next to it before.

AFD:

"The primary item of concern in this forecast period remains very hot
conditions Thursday followed by a slight risk (and enhanced risk per
SPC) of severe thunderstorms. A primarily dry day, partly cloudy
skies, and a 576dm ridge nosing in are all setting the stage for
highs Thursday to be well into the 80s. Compared to a few days ago,
the guidance has formed a concensus of highs in the mid-to-upper
80s; good for 75th percentile of model guidance (it was previously a
99th percentile forecast closer to 90 degrees). Cannot completely
rule our far southwestern areas (Monticello, Logansport) cracking 90
degrees, which would appear to be among the top 10 earliest 90-
degree days on record.

Thursday`s severe thunderstorm forecast remains murky. We face a
conundrum of a powder-keg environment capped by an elevated mixed
layer with mismatched forcing mechanisms. The daytime hours Thursday
appear primarily dry and we`re not completely out of the woods yet
for an evening/overnight severe risk, but the forecast remains
uncertain.

There are two forcing mechanisms at play for storms Thursday. The
first is a warm front arriving from southwest to northeast during
the midday hours. Forecast soundings ahead of the front depict a
capped low-level environment. In the wake of this front, the low-
level profile warms by about 5C which further strengthens the
capping inversion. CAMs generally have an unassuming QPF footprint
associated with this front. The environment otherwise has copious
CAPE values and 40 knots of shear. By late-afternoon, forecast
soundings depict an elevated mixed layer, further complicating the
chance of storms.

The second forcing mechanism, a cold front, arrives to northwest
Indiana near 00z Friday (7CT Thursday). Even so, soundings still
depict a subtle cap in place locally. The parent low of this cold
front is incredibly wrapped up over Minnesota, focusing the best jet
dynamics across southern WI and northern IL. Instead, a secondary
500-mb jet is focused across central IL and IN, but this jet would
enhance convection south of US 24. Overall, have stayed close to the
existing POP forecast and will focus this morning`s messaging on
continued uncertainty for how this evolves. The advertised enhanced
will be incredibly dependent on if we can break the cap."

1000080315.jpg
 
US_Highway15 said:
IWX is not confident in severe weather occuring, as apparent in their public graphics. Don't think I've seen an ENH risk have a "low confidence" mark next to it before.

AFD:

"The primary item of concern in this forecast period remains very hot
conditions Thursday followed by a slight risk (and enhanced risk per
SPC) of severe thunderstorms. A primarily dry day, partly cloudy
skies, and a 576dm ridge nosing in are all setting the stage for
highs Thursday to be well into the 80s. Compared to a few days ago,
the guidance has formed a concensus of highs in the mid-to-upper
80s; good for 75th percentile of model guidance (it was previously a
99th percentile forecast closer to 90 degrees). Cannot completely
rule our far southwestern areas (Monticello, Logansport) cracking 90
degrees, which would appear to be among the top 10 earliest 90-
degree days on record.

Thursday`s severe thunderstorm forecast remains murky. We face a
conundrum of a powder-keg environment capped by an elevated mixed
layer with mismatched forcing mechanisms. The daytime hours Thursday
appear primarily dry and we`re not completely out of the woods yet
for an evening/overnight severe risk, but the forecast remains
uncertain.

There are two forcing mechanisms at play for storms Thursday. The
first is a warm front arriving from southwest to northeast during
the midday hours. Forecast soundings ahead of the front depict a
capped low-level environment. In the wake of this front, the low-
level profile warms by about 5C which further strengthens the
capping inversion. CAMs generally have an unassuming QPF footprint
associated with this front. The environment otherwise has copious
CAPE values and 40 knots of shear. By late-afternoon, forecast
soundings depict an elevated mixed layer, further complicating the
chance of storms.

The second forcing mechanism, a cold front, arrives to northwest
Indiana near 00z Friday (7CT Thursday). Even so, soundings still
depict a subtle cap in place locally. The parent low of this cold
front is incredibly wrapped up over Minnesota, focusing the best jet
dynamics across southern WI and northern IL. Instead, a secondary
500-mb jet is focused across central IL and IN, but this jet would
enhance convection south of US 24. Overall, have stayed close to the
existing POP forecast and will focus this morning`s messaging on
continued uncertainty for how this evolves. The advertised enhanced
will be incredibly dependent on if we can break the cap."

View attachment 41452
Click to expand...
Dang. Not often you see an enhanced risk issued and a NWS mentions they are not confident in severe weather occurring.
 
AJS said:
Dang. Not often you see an enhanced risk issued and a NWS mentions they are not confident in severe weather occurring.
Click to expand...
I honestly don't disagree with them. More times than not in these setups around the IWX area where you need a cap to break in order to get severe storms, it does not happen. In fact, I cannot recall a single setup around here (besides Palm Sunday of course) in my lifetime (23 years) where we have actually gotten severe storms in a cap erosion or bu$t enviornment. So while I do badly want to dog on them for having this kind of messaging, I can't blame them.
 
200.gif
youtube.com

Post from Convective Chronicles

Broyles interview on the April 2 outbreak will be out tomorrow! Be there!
youtube.com youtube.com
 
Last edited:
US_Highway15 said:
I honestly don't disagree with them. More times than not in these setups around the IWX area where you need a cap to break in order to get severe storms, it does not happen. In fact, I cannot recall a single setup around here (besides Palm Sunday of course) in my lifetime (23 years) where we have actually gotten severe storms in a cap erosion or bu$t enviornment. So while I do badly want to dog on them for having this kind of messaging, I can't blame them.
Click to expand...
Wow, rare..
 
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