678
FXUS63 KIWX 181913
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
313 PM EDT Sat May 18 2024

.KEY MESSAGES...

- Warm temperatures in the 80s through Tuesday. 70 degree
  temperatures take over for the late week.

- Strong to possibly severe thunderstorms still appear possible
  between Tuesday evening and Wednesday evening.

- One potentially dry day next week is Thursday.

&&

.DISCUSSION...
Issued at 310 PM EDT Sat May 18 2024

Forcing that helped Friday`s isolated to scattered showers and
thunderstorms form shifts to our south and east as mid level ridging
moves in this afternoon as further indicated by mid level height
rises during the day today. Perhaps a few lingering boundaries, like
the lake breeze, could force an isolated shower or thunderstorm this
afternoon with 1000 to 1500 J/kg of MUCAPE, but expect they will be
fewer and further between than Friday. For tonight, a few clouds
could be around, but not enough to impact radiational cooling,
especially east of the approaching cold front and its accompanying
cloud decks. Think the greatest chance of fog reforming tonight is
south of US-24/east of I-69 and so have continued the patchy fog
mention for these areas. The cold front slows up just to our
northwest on Sunday, but there may be enough low level moisture and
convergence around to force a few showers and thunderstorms across
the area Sunday afternoon. Will maintain the slight chance PoPs as a
result. Locally heavy rain and perhaps a strong downburst could be
have from these storms, but severe weather doesn`t look likely with
the lack of shear in place. For Monday, the close proximity of
forcing from a low pressure system pushes the stalled frontal
boundary back northward as a warm front. With lingering low level
moisture and reforming instability, could see a few showers and
storms pop again Monday afternoon. Have pulled back the chance PoPs
to more slight chance PoPs though with forcing being the main
lacking ingredient unless another lake breeze can get things going
or an outflow boundary moves in from the north or west. A shortwave
crosses into Southern Lower Michigan Monday night increasing PoPs to
slight chance for counties west of IN-15 and well as north of US-6.
Another shortwave takes a little bit more of northerly track perhaps
scraping our northeastern counties Tuesday morning, but only have a
slight chance as the warm sector gets set up and the column dries
out.

Later Tuesday night into Wednesday increases chances for strong to
severe weather. With an upper low to northwest in the Upper
Mississippi Valley/Northern Plains area pushing its cold front into
the area, we`ll have ample forcing and a moisture axis to work with
in addition to  an area of 7 C/km lapse rates. With this moisture
axis swinging through during the overnight, instability appears to
wane and effective shear drops out with the lowered instability. So,
the timing and diurnally influenced ingredients may be the limiting
factor for the Tuesday night time period. The front appears to stall
out over the forecast area as another vort max swings around the
upper low to our northwest. During the diurnal curve, instability
reloads (debris clouds-defendant) and there`s potentially some
shear to work with along with what remains of the 7 C/km mid
level lapse rates Wednesday afternoon. The main question with
this is where will the front be and can things get going quick
enough Wednesday afternoon for severe weather to occur east of
I-69 or potentially as far west as east of IN-15.

Deterministic model confluence still exists on retaining the dry day
on Thursday as surface high pressure noses in and mid level height
rises ensue.

Coupling between the Pacific and subtropical jets occurs Friday
allowing a low pressure system to form. The upper low from the
Tue/Wed event is situated over southeast Canada during this time
period and shunts the developing surface low to south of the
forecast area. As such, there`s some question about how far north
its moisture plume can get towards the area.

High temperatures during this forecast period start in the low 80s
for today, but attain the mid to upper 80s from Sunday through
Tuesday before stair-stepping down to the low to mid 70s for late
week next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1205 PM EDT Sat May 18 2024

VFR/dry with light winds through the period. The only exception
may be a period of brief shallow ground BR around daybreak
tomorrow.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Air Quality Alert until midnight EDT /11 PM CDT/ tonight for
     INZ005-012>015-022-023-103-104-116-203-204-216.
OH...None.
MI...Air Quality Alert until midnight EDT tonight for MIZ078-177-
     277.
MARINE...None.

&&

$$

DISCUSSION...Roller
AVIATION...Steinwedel