685
FXUS63 KIWX 211752
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
152 PM EDT Wed Jun 21 2017

.SYNOPSIS...
Issued at 345 AM EDT Wed Jun 21 2017

Dry conditions will continue through this evening. Showers and
thunderstorms are possible late tonight into early Thursday
afternoon as a warm front lifts northward through the region. The
best chance for storms will be late Thursday afternoon into the
overnight timeframe. There is a slight risk for strong to severe
storms during that time.


&&

.SHORT TERM...(Today and Tonight)
Issued at 345 AM EDT Wed Jun 21 2017

Mainly quiet weather today will give way to chances of showers and
thunderstorms tonight, particularly across far northern
Indiana/southern Lower Michigan.

An upper vort max will continue to exit the region across the
eastern Great Lakes early this morning. An associated sfc boundary
has slowed its southward progression and will become stationary
across central Indiana today. Some rising mid/upper level height
tendencies anticipated today behind this departing short wave. Focus
for any isolated shower/storm activity is expected to remain south
of the forecast area in closer proximity to this boundary where
modest narrow instability axis is expected to reside. Warmest temps
this afternoon in lower 80s expected across west/southwest portions
of the area as low level baroclinic begins to shift northeast late
in the day in response to subtle backing of low level winds with
approach of mid level ridging. Weak lake breeze development today
should result in slightly cooler mins near Lake Michigan in the
mid 70s.

For tonight, primary short wave track will remain well to the north
across Upper Midwest to the northern Great Lakes, but low level west-
southwest flow will begin to increase across the southern Great
Lakes, with an accompanying increase in warm advection/isentropic
forcing. Low level theta-e gradient will quickly lift across Lower
Michigan by late this evening. Have not made much change to
inherited chance thunder PoPs (highest across the north) given above
factors and associated weak low level moisture convergence at
leading edge of the swrly LLJ. Coverage should remain limited due to
lack of cohesive mid/upper level trigger.

&&

.LONG TERM...(Thursday through Tuesday)
Issued at 345 AM EDT Wed Jun 21 2017

By Thursday morning, LLJ axis will shift north/northeast of the area
with focus for showers/storms also likely migrating to the north.
Thursday looks to be the hottest day of the period as low level
thermal ridging overspreads the region. Continued to trend grids few
degrees above blended solution given decent afternoon mixing and
favorable positioning of low level thermal ridge, along with at
least some filtered afternoon isolation. Decent mixing Thursday
should tend to limit dew points into the mid-upper 60s, limiting
forecast peak afternoon heat indices to the lower to mid 90s.

Convective redevelopment Thursday afternoon remains of quite low
confidence with some weak capping concerns likely to take shape
along with stronger forcing remaining well to the north and west.
Will have to watch for the possibility of some afternoon thunder
development along residual outflows/differential heating
boundaries from Great Lakes convection, but confidence as far
south as local area not high to go more than slight to low chance
for PoPs.

Best chance for more organized showers/thunderstorms still appears
to be Thursday night into Friday as a more substantial mid level
wave reaches the western Great Lakes along with the best period of
low level moisture transport. Potential will exist for scattered
thunderstorms along pre-frontal trough type feature Thursday
evening/early Friday, followed by stronger frontal forcing with
the cold front. Deep layer shear will increase Thursday night as
this short wave approaches, but what appears to be somewhat
unfavorable diurnal timing may tend to preclude a more significant
severe risk. However, hard to discount at least an isolated
severe threat given increasing forcing/shear by Thursday evening,
mainly across northern half of the forecast area where mid level
lapse rates should tend to be steeper. Friday severe potential
also of low confidence given destabilization uncertainty at this
forecast distance, but southeast half or southeast third of the
area may be prone to some isold severe risk with gusty winds as
potential main threat.

Frontal passage later Friday will set the stage for much cooler
conditions for the weekend with perhaps a few periods of
isolated- scattered showers/storms as several upper waves rotate
across the Great Lakes region. With difficulty timing any of these
waves at this forecast distance and more limited moisture
availability this weekend, will keep PoPs for any period on the
low side.

Flow deamplification expected by the middle of next week which
will result in a warming trend along with at least a more
favorable pattern for additional shower/thunderstorm chances in
the Day 7-8 period.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday Morning)
Issued at 647 AM EDT Wed Jun 21 2017

VFR conditions are expected throughout the TAF period. Low level
wind shear is a possibility tonight at KSBN, as a warm front surges
northward through the area and a LLJ develops over WI/IL/Far NW IN.
There are some low chances for showers and thunderstorms later
tonight along the warm front-however most models show precipitation
developing to the north and east of the TAF Sites. Given the low
confidence, left it out of the TAF for now. Winds will veer around
to the south-southwest through Thursday, and begin gusting into the
upper teens and low to mid 20s. Better chances for storms will be
late Thursday afternoon and evening.

&&

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

$$

SYNOPSIS...Marsili
SHORT TERM...Marsili
LONG TERM...Marsili
AVIATION...Skipper


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