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FXUS63 KIND 232121
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
521 PM EDT Sat Jun 23 2018

.UPDATE...
The AVIATION Section has been updated below.

&&

.SYNOPSIS...
Issued at 321 PM EDT Sat Jun 23 2018

Weak high pressure will build into the region and provide mainly dry
weather for central Indiana for the rest of the weekend along with a
less humid airmass. The approach and passage of a warm front for
early week will bring an increase in thunderstorms. The
development of a strong upper level ridge by late this upcoming
week supports a return to hot and humid conditions with daytime
temperatures soaring into the 90s.

&&

.NEAR TERM /Tonight/...
Issued at 321 PM EDT Sat Jun 23 2018

Mainly cloudy and quiet afternoon ongoing across central Indiana as
the region resides in the backwash of the departing upper low over
the eastern Great Lakes. Plenty of lingering low level moisture
present maintaining a blanket of stratocu with a few light showers
as well. 19Z temperatures were generally in the 70s.

Overall...not particularly excited about an uptick in rainfall and
convective coverage through the evening as too many factors are
present to mitigate more substantial development. Weak ridging aloft
has developed behind the upper low and forcing is largely non-
existent through the boundary layer. Deeper moisture has shifted
east of the region as well with precip water values now progged
below 1.5 inches in most areas. Diurnal heating has been largely
mitigated by the lower clouds and further analysis indicating strong
convective inhibition across the area as well. Hence the reason much
of the day so far has seen little in the way of rain and likely will
continue to do so through the rest of the afternoon.

While the rain threat is low...it is non-zero through the evening.
Sounding analysis suggests the convective inhibition will weaken
over the next few hours and at least allow for a minimal amount of
instability to develop. The approach of a broad...weak upper wave
from the west may present a narrow window during the late afternoon
and evening where we see a slight increase in shower coverage...
enough to warrant a low chance pop through the evening. Available
instability even at its peak will likely not be enough to generate a
thunderstorm later today and will continue with just showers
mentioned. Beyond that into the overnight however...subtle
instability is lost and better forcing aloft associated with the
wave focuses north into the Great Lakes. Feel comfortable rolling
with a dry forecast after midnight.

Temps...slightly cooler air will spill into the region overnight
with lows likely to fall into the lower to middle 60s from south to
north. An overall model blend handled this well.

&&

.SHORT TERM /Sunday through Tuesday/...
Issued at 321 PM EDT Sat Jun 23 2018

Forecast challenges focus on precip chances...especially Monday and
Tuesday as a warm front followed by an upper low impact the lower
Great Lakes and Ohio Valley.

The second half of the weekend will see a brief break from the
recent unsettled regime as ridging aloft amplifies and surface high
pressure builds in from the north. Low level flow will transition to
northerly for Sunday...ensuring a drier surge of air into the region
and providing a break from the higher humidity levels of late. Model
soundings show limited instability aloft with a capping inversion
and considering the lack of any available forcing...expect dry
weather to persist into Sunday evening.

A warm front lifting north out of the Ozarks and Tennessee Valley on
Sunday will be a focus for convective development during the
afternoon and evening as it lifts into the lower Ohio Valley. Could
see the northern edge of the convection clip the lower Wabash Valley
during the evening...but overall expect the evening to remain dry.
The northward progression of the front into the area during the
predawn hours Monday will warrant an introduction of low chance
pops in southwest counties before expanding into the forecast area
on Monday as the warm front parks from central Iowa southeast
into southern Indiana and northern Kentucky.

Strong high pressure over the eastern Great Lakes with deep
subsidence will limit the front from pushing further north through
Monday night. Deeper moisture and instability will be capped near
and southwest of the location of the front...with convective
potential largely confined to the southwest half of the forecast
area. Presence of stronger boundary layer shear and helicity in the
0-3km level near and just SW of the front supports potential for a
few severe storms Monday afternoon and evening again focused over
the southwest half of the forecast area.

Surface high pressure will shift east to the New England coast on
Tuesday which will enable the warm front to finally progress north
through most if not all of the forecast area. An upper low will
track from the northern Plains on Monday into the western Great
Lakes Tuesday with an attendant surface wave. Forcing aloft will
increase over the region as a result...aided by the presence of an
upper jetlet lifting north and overall diffluent flow in the mid and
upper levels. Low level flow will increase as well from the
southwest and transport rich moisture into the region as precip
water values peak near 2 inches and dewpoints likely climb to 70
degrees or warmer. All of these factors support the best potential
for widespread convective impacts for central Indiana on Tuesday and
will carry high chance pops as a result. Moderate instability and an
overall increase in boundary layer shear over the region will once
again support a potential for severe storms throughout the day.

Temps...the short term will serve as a reprieve from the hotter
temperatures from this past week as more substantial heat is noted
on the horizon for later this upcoming week. Low level thermals are
supportive of high temperatures generally at or just above the
warmest guidance from the MAV. Expect mid 80s Sunday followed by
slightly cooler temps Monday before warmer and more humid weather
returns Tuesday as the warm front lifts north. Lows will be largely
in the 60s through the period.

&&

.LONG TERM /Tuesday night to Saturday/...
Issued at 321 PM EDT Sat Jun 23 2018

The extended timeframe begins with an upper level trough pushing
into the Great Lakes region from the west. Continued with chances
for showers and thunderstorms across the forecast area as the
upper trough presses eastward...sending a weak frontal boundary
into the area from the northwest on Wednesday. Shower and storm
chances clear Wednesday evening as the weak front passes the area
and the upper trough continues its trek toward the New England
states. An upper level ridge then builds northeast across the Ohio
River Valley Thursday into Friday. A weak upper wave passing
through the top of the ridge as it builds northeast may produce
some showers and thunderstorms on Thursday morning and early
afternoon. Then the heat is on. There looks to be no shortage of
90 degree temps starting Thursday afternoon through the remainder
of the period. Friday and Saturday appear to be the warmest days
of the extended as the upper ridge builds further over the
forecast area...with low to mid 90s on Friday and did increase
max temps slightly from the regional initialization blend to lower
90s across much of the area on Saturday. Though under the upper
ridging...convective temps may be reached in some areas on Friday
and Saturday. Current model forecasted instability is quite high.
Will be interesting to keep an eye on this as we head into next
week.

&&

.AVIATION /Discussion for the 23/21Z TAF Update/...

Issued at 423 PM EDT Sat Jun 23 2018

Update...
Shifted winds from the west to southwest and increased the winds
to 12 kts.

Previous Discussion...
Both MVFR and VFR conditions persist at the beginning of the
timeframe. Currently expect IND to be the next to scatter its MVFR
ceilings by 1900Z or so based on upstream trends. LAF is expected
to hold their MVFR conditions longer than the rest of the sites.
I would not be surprised if they hold ceilings under 3000 feet
past the forecasted 2000Z scattering of the deck. Removed the VCSH
as any remaining showers are few and far between and not
confident that any impactful convection will occur. VFR
conditions are then expected overnight tonight into tomorrow.
Expect westerly winds to become light overnight...remaining light
and veering to the northwest to north tomorrow.


&&

.IND WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SYNOPSIS...Ryan
NEAR TERM...Ryan
SHORT TERM...Ryan
LONG TERM....MRD
AVIATION...TDUD
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