IWX issues Area Forecast Discussion (AFD) at May 26, 5:20 PM EDT909
FXUS63 KIWX 262120
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
520 PM EDT Sun May 26 2024
.KEY MESSAGES...
- Scattered showers and storms will remain possible into
tonight. A few strong to locally severe storms cannot be ruled
out, though the overall severe threat has diminished.
- Lingering showers and thunderstorms may impact activities
Memorial Day through Wednesday.
- Hazardous swimming conditions for Lake Michigan beaches in La
Porte County in Indiana and Berrien County in Michigan
Memorial Day through Wednesday.
&&
.UPDATE...
Issued at 520 PM EDT Sun May 26 2024
Line of sub-severe convection along a fgen/MCS outflow should
exit our eastern zones by 22/23z with a lull in activity for
most locations in its wake. Second round of convection for this
evening/overnight continues to look diminished/limited with most
of the area now worked over, with a more robust MCS on target
to pass south of the area during this time. Incoming trough on
the leading edge of an incoming vort max and weak sfc
reflection (now near WI/IL border), and some added convergence
from outflow bubble on the northern fringe of the maturing OH
Valley MCS, will bring renewed chances for widely scattered
showers/storms tonight. Cannot rule out an isolated strong-
severe cell into areas mainly west of IN-15 9p,-midnight EDT as
there will be adequate shear along the incoming sfc trough.
Buoyancy will be somewhat limited however with the bulk of the
energy going to what should be a dangerous MCS tracking east
along the OH River. Only minor adjustments made to PoPs/Sky
cover trends into tonight.
&&
.DISCUSSION...
Issued at 1220 PM EDT Sun May 26 2024
A deepening area of low pressure approaches the Western Great Lakes
today and moves into the Northern Great Lakes by Monday morning. As
it does so, a warm front pushes into Michigan by this evening.
Models expect low lapse rates to be the highest in the I-69 on
eastward where the greatest amount of sunlight and least amount of
thunderstorm overturning resides into the afternoon ahead of the
approaching storm-filled warm front. Much of the shear lags behind
this warm front so the most likely hazards out of a line like this
include strong to damaging wind gusts up to 60 mph with heavy rain
that could lead to flooding. There is some progressive nature to
this initial line so that will likely limit the residence time of
the rather moist ingredients including surface (into the 60sF) and
low level dew points (above 10C in many southern locations).
There has been some question about what happens behind this line. Do
we get clearing or does a potential cold pool keep cloud cover
around enough to restrict recovery of instability for an evening
batch of severe thunderstorms? Additionally, what time do storms
initiate? As late as the the 00z models, there were still a few
models that hang onto a possibility of pop storms after the line,
but it appears 12z guidance has since backed off that possibility.
The 6z RAP seemed keen on initiating around 5pm, but that seems less
likely than some of the other models bringing a line through our
southern zones or just to our south around 8pm. By this point, shear
would be better established with the low level jet overhead and
helicity would be present as well allowing the introduction of the
hazard of a few tornadoes. The mid level lapse rates are shown to be
replenished behind the initial warm front line that had 8C/km mid
lapse rates to work with this morning. This will also make large
hail a possibility with the potential afternoon resurgence. If
storms do initiate behind the line, storm motion will also be in
question as the continued moist environment could allow any slower
moving storms to produce quite of rain in a short time frame. The
NAM40 also seems keen on keeping some storms southeast of US-24 into
the overnight with strong to damaging wind and large hail being the
main threats along with heavy rain that could lead to flooding.
Aside from the lower res NAM, the HREF suite brings a midnight or
1am end time to this second batch of strong to severe storms with
potentially a few isolated cells thereafter as the EML and lingering
instability could keep a few cells going after dark. Again, 12z
guidance appears to back off this second batch possibility
altogether.
The cold front moves southeast vacating the area Monday morning
allowing surface dew points to drop back into the 50s indicating the
dry air mass behind the front. But it's a quick reprieve as another
wave approaches the area for Monday night. Even the NAM only has 100
to 500 J/kg of MUCAPE around for this episode which indicates weak
thunderstorms would be the expected outcome at strongest outcome.
Highs Monday will also be cooler, in the upper 60s and low 70s with
the negative theta-e advection behind the previous departed
cold front. Still not much cooler for highs on Tuesday with
upper 60s to low 70s, but models want to generate some more
instability to the tune of 500 to 1000 J/kg, which would
indicate more thunderstorms are possible during the afternoon,
especially as another broad area of vorticity approaches Tuesday
afternoon/night.
Behind this area of vorticity, surface high pressure comes in and is
expected to provide dry weather from mid to late week as a large
ridge stations itself over the Central CONUS. Some lingering
moisture may be able to sprout a few showers Wednesday morning, but
that should be east of I-69. Expect 60s for Wednesday that trend
warmer, reaching the 80s on Sunday. Our next chance for rain likely
holds off until late Saturday.
&&
.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1220 PM EDT Sun May 26 2024
A line of elevated convection on track to lift through both
terminals in the 1830-2030z window. Brief period of LIFR/IFR vis
restrictions, frequent lightning and perhaps some small hail
the primary threats with this activity. A lull late afternoon
may then give way to additional chances for scattered convection
this evening into the early overnight as the upper system and
sfc cold front follow through. Post-frontal IFR-MVFR cigs then
settle in within a 10-15 kt westerly wind late tonight into
Monday morning.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...Beach Hazards Statement from Monday morning through Monday
evening for MIZ177-277.
MARINE...Small Craft Advisory from 8 AM to 8 PM EDT Monday for LMZ043.
&&
$$
UPDATE...Steinwedel
DISCUSSION...Roller
AVIATION...Steinwedel
Source:
IWX issues Area Forecast Discussion (AFD) at May 26, 5:20 PM EDT---------------
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