IWX issues Area Forecast Discussion (AFD) at May 19, 7:30 PM EDT818
FXUS63 KIWX 192330
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
730 PM EDT Sun May 19 2024
.KEY MESSAGES...
- Strong to possibly severe thunderstorms still appear possible
late Tuesday night and possibly again Wednesday afternoon.
Both of these periods are marked by low confidence in severe
weather.
- Chance of storms for Monday and Monday night. Widespread
severe weather is not expected, but an isolated storm may have
a hail or wind threat.
- Warm temperatures in the 80s through Tuesday. 70 degree
temperatures take over for the late week.
- Lull in precip chances for Thursday, but additional chances of
showers and thunderstorms next weekend.
&&
.DISCUSSION...
Issued at 239 PM EDT Sun May 19 2024
A cold front, divorced from any mid level vorticity, stalls just to
our northwest today. A moisture axis glides into the forecast area
and short term guidance indicates low level convergence will be
present in an environment with strong low level lapse rates and CAPE
values exceeding 2500 J/kg. Forecast soundings indicate there's
quite a bit of dry air below 850 and above 700 mb that might make it
a little bit more difficult to form storms, but should they overcome
it say with a few outflow boundaries, DCAPE values exceed 900 to
1000 J/kg making downbursts possible. Additionally, the low level
dryness and mid level lapse rates between 6.5 and 7 C/km could make
hail a possibility with limited melting in the dry low level layer.
PWATs do actually exceed climatology by 1 SD making locally
heavy rain possible with the 60F degree dew points and 10C 850
mb dew points. Slow storm motions also contribute to the heavy
rain possibility, which could be exacerbated over a more urban
area. There is also some indication that these storms continue
beyond sunset with the 500 to 1000 J/kg of MUCAPE remaining
along with 6.5 C/km mid level lapse rates and as a front lifts
northward into MI Monday morning.
Monday morning, the area is once again devoid of forcing, but we'll
be watching for the arrival of a likely convectively enhanced
shortwave from the Central Plains to arrive in the evening. Short
range guidance indicates this could die on our doorstep, which could
happen as the shortwave appears to move towards Lower Michigan, but
lingering diurnally enhanced instability may be able to help before
sunset. Forecast soundings look a little bit similar to today's
soundings, but CAPE appears weaker. Similar DCAPE and mid level
lapse rate magnitudes contribute to wind and hail potential, but
shear appears more limited providing some ceiling for strong to
severe potential. SPC's marginal risk of severe weather appears
warranted for Monday, but would want a little bit more shear and
turning in the low levels to make a tornado threat a little bit more
believable.
With some remnant shortwaves nearby Tuesday, we may start with some
clouds around, but models indicate some clearing may be possible
during the afternoon allowing models to generate 1500 J/kg of CAPE.
The low level jet is around Tuesday, which may help to remove
cloudiness, but it won't be strong enough for severe storms until
later Tuesday night. By that point, 500 J/kg of MUCAPE and 6 to 6.5
C/km mid level lapse rates will be available, with shear finally
around after midnight. Effective helicity values do surpass 200
m2/s2 during this time as well, but modeled surface LCLs appear too
high for a tornado unless those are incorrect. DCAPE doesn't appear
to stay as high overnight, but gusty to damaging winds and some hail
still appear possible. SPC's slight risk appears warranted for
Tuesday into 12z Wednesday. Then, with the cold front bisecting the
area into east and west halves, the eastern area has the greatest
chance to see afternoon thunderstorms refire, Wednesday afternoon,
but this will depend on the eventual placement of the front. Too far
east and storms develop east of our area. Storms are modeled to have
1500 J/kg of CAPE to tap into along with some shear and 6 to 6.5
C/km mid level lapse rates. Helicity appears to be weaker for this
setup, though. SPC's slight risk also appears warranted for
Wednesday afternoon.
A break in the action is indicated for Thursday as surface high
pressure moves in behind the front. There is a chance the dry
weather continues for Friday as well with an upper low in southeast
Canada and the strength of a shortwave through the Tennessee Valley
likely determining how far north the precip shield gets. There is a
chance our area could get clipped Friday from that low to our south.
Our next chance for showers and perhaps thunderstorms appears to be
Saturday night/Sunday as an upper low in south-central Canada drags
a cold front through the area.
&&
.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 730 PM EDT Sun May 19 2024
Weak cold front currently supporting isolated storms west of
KFWA will continue to slowly sag east this evening. However,
with very weak shear and forcing, storms will likely diminish
with the loss of daytime heating and confidence remains low that
one will actually impact KFWA. Will therefore hold with just
VCSH mention. Otherwise VFR conditions will persist through the
period given relatively dry low levels. The next chance of
convection arrives Monday evening just outside this forecast
window.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Roller
AVIATION...AGD
Source:
IWX issues Area Forecast Discussion (AFD) at May 19, 7:30 PM EDT---------------
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