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064
FXUS63 KIWX 191729
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
129 PM EDT Sat May 19 2018

.SYNOPSIS...
Issued at 259 AM EDT Sat May 19 2018

Showers and thunderstorms are expected today into the early part
of next week. Some storms could become strong to marginally
severe Sunday evening. The combination of cloud cover and a weak
cold front will result in slightly below average daily high
temperatures both Sunday and Monday.

&&

.SHORT TERM...(Today and Tonight)
Issued at 259 AM EDT Sat May 19 2018

Upper trough ejects northeastward across the Ohio Valley today.
This will result in showers across the area through the late
morning hours. By noon, the the trough axis will start to move
east of the area. The result will be a gradual decrease in rain
chances from west to east. Embedded thunderstorms can`t be ruled
out today due to increasing instability (roughly 1000 - 1500 J/kg
of SBCAPE by this afternoon) and the proximity to the upper
trough. The environment remains poorly sheared so while a storm
may pulse, organized potential should be limited. PWATs remain
briefly heavy rain are possible with storms.

Clearing cloud coverage throughout the day will make high
temperatures tricky. Generally lower 70s across the north and west
to mid 70s across the south and east.

Weak cold front pushes into the Upper Great Lakes region to enter
into our northern zones late Saturday night.

&&

.LONG TERM...(Sunday through Friday)
Issued at 259 AM EDT Sat May 19 2018

Sunday/Sunday night remains the target of opportunity in the
forecast and has the greatest uncertainty due to model
variations.

An upper low anchored over the Plains is forecast to have a pair
of shortwaves break off and move over the area during the day
Sunday. The cold front which pushed into the Upper Great Lakes
Region late Saturday night will play a significant role in our
strong/severe chances on Sunday. Models generally agree the front
will be near I-70 by Sunday morning before retreating northward
throughout the day. The morning shortwave could initiate
convection along the front near I-70. The majority of this
convection should should remain south of our area, but the far
western counties may get clipped by the northern edge.

A brief lull in activity is possible for the mid-day/early
afternoon timeframe before the second shortwave moves in. The
location of the front at this point is in question and will
delineate which areas will be impacted by the late evening round
of convection. The most aggressive models push the front far
enough north that the entire area is in play while the less
aggressive ones favor the southern half of the CWA. Given the
trends in the models, would lean towards the better part of the
area being impacted by thunderstorms; generally south of HWY 30 in
IN and OH. South of this line, afternoon MLCAPE is forecast to
rise to 1000 J/kg on the low end to 2000 J/kg on the high end.
Deep layer shear is also expected to be between 40kt and 50kt.
Curved BUFR hodographs hint at initially discrete development
before quickly forming into a linear structure. Damaging wind
gusts and hail would be the primary threats with organized
convection. Locally heavy rain will also be possible with
convection Sunday evening. Forecast PWATs remain climatologically
high in the 1.6" to 1.75" range Sunday evening. With all that
being said, there is still sizable uncertainty concerning this
threat due influences on frontal position from earlier
convection, and the relatively weak synoptic forcing.

Another round of showers and thunderstorms are possible on Monday
across the area. A few strong storms aren`t out of the question
as deep layer shear of 40kt is forecast, but influences from early
convection may hinder some development. Slight differences with
respect to the timing of the end of precipitation for early next
week. Some linger rain chances into Wednesday while others clear
them out late Tuesday. Mid-week looks dry before precipitation
chances return as the weekend nears.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
Issued at 117 PM EDT Sat May 19 2018

A smattering of sites upstream of SBN are reporting LIFR ceilings.
However, satellite indicates the back edge of these ceilings are
rotating over the western shore of the lake. As such, I will offer
a TEMPO period of possible LIFR with otherwise MVFR ceilings
expected this afternoon.

Over at FWA, a TEMPO is in play for rain showers developing off to
the west and south. These appear to be developing behind the cold
front, perhaps aided by an upper-level disturbance. MVFR ceilings
will exit FWA later this afternoon as the surface low departs the
area.

At both sites, winds will be weak overnight but becoming north-
northeasterly. Beyond 12Z Sunday, there is the opportunity for
showers and thunderstorms, but confidence leaves something to be
desired at this time.


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

SYNOPSIS...CM
SHORT TERM...CM
LONG TERM...CM
AVIATION...Brown


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