Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 212349

Area Forecast Discussion
National Weather Service Indianapolis IN
749 PM EDT Mon May 21 2018

The AVIATION Section has been updated below.


Issued at 324 PM EDT Mon May 21 2018

Chances for rain and thunderstorms will continue into Tuesday as a
cold front moves slowly through the region. High pressure will bring
an extended period of dry weather beginning late Tuesday and
continuing through the end of the work week. A more unsettled
weather pattern will return for the holiday weekend as Gulf moisture
is drawn north into the Ohio Valley with a tropical system impacting
the southeast states.


.NEAR TERM /Rest of This Afternoon into Tonight/...
Issued at 324 PM EDT Mon May 21 2018

Sunshine has been increasing since midday over much of the forecast
area as high level cloud coverage has diminished. This has result in
rapid warming to the south of a warm front roughly draped across our
northern row of counties in a WNW-ESE direction. Showers have been
confined to primarily the northern Wabash Valley recently with new
convective development just recently commencing to the west of KBMG.
19Z temperatures ranged from the low 70s far north to mid 80s in the

Primary focus will be on the convective evolution and potential
impacts to the region over the next 6-8 hours through late evening.
Mesoanalysis showing that much of the region has been slow to
destabilize so far this afternoon with the cloud debris from earlier
in the day. As that has diminished over the last hour or two
however...instability and heating have increased and as mentioned
above...beginning to see scattered convective development to the
west of KBMG and across the lower Wabash Valley. As the airmass
continues to destabilize through the remainder of the afternoon...
expect a steady increase in convective coverage...especially as
storms move northeast and approach the higher BL shear levels
closer to the warm front.

The potential for locally severe storms remains something to monitor
going through the rest of the afternoon and into the early evening.
As mentioned...better BL shear and storm relative helicities are
focused near and north of the warm front over the northern half of
the state. Greatest concern for severe convection is likely to be
where the higher BL shear and storm relative helicities interact
with the deeper instability and at this point...that appears most
likely to take place over the northeast quadrant of the forecast
area. The close proximity to the warm front will add another element
of interest as an enhanced layer of shear will exist near the
boundary. The boundary should continue to retreat to the north out
of the forecast area by early evening in response to a surface wave
moving into western Illinois. This may end up taking the primary
area of severe storms northeast out of the area by 23-00Z...but the
presence of lingering instability and broad ascent will support
continued convection into the evening gradually shifting east. Could
see strong to pulse-type severe cells within this activity...but
overall suspect the more organized and stronger convection will be
northeast of the region after 00Z where shear and instability will be
better aligned and maximized.

There is likely to be a lull in convection from late evening into
the overnight as the deeper moisture and forcing shift easts...but
the aforementioned surface wave and boundary lingering back west will
warrant reintroducing low chance pops during the predawn hours. The
front should be moving into our northwest counties by daybreak

Temps...generally nudged lows closer to the warmer MAVMOS for much
of the area as lows remain in the low to mid 60s across central


.SHORT TERM /Tuesday through Thursday/...
Issued at 324 PM EDT Mon May 21 2018

Forecast challenges focus on lingering chances for rain Tuesday and
temperatures throughout the short term.

The aforementioned surface wave will drift across the lower Great
Lakes on Tuesday finally drawing the cold front across the forecast
area through the day. Instability will be weak at best on Tuesday
but the presence of steeper low level lapse rates warrants a
continued mention of chances for showers and storms into the early
afternoon before the front clears the area by late day.

Once the front moves off to the southeast Tuesday afternoon...high
pressure will build into the lower Great Lakes and Ohio Valley with
dry weather expected for the rest of the short term. Diurnal cu will
be possible each day as convective temps are approached but
overall...should be a spectacular couple of days with plenty of
sunshine and continued warmer than normal conditions. Potential
exists for a bit more presence of mid and high clouds on Thursday
as upper level moisture spills over a developing ridge aloft. There
will also be noticeably drier feel to the airmass with winds
predominantly from the E/NE through much of the period.

Temps...generally ran with a model blend for highs through the
period. After slightly cooler temperatures in the upper 70s and
lower 80s Tuesday and Wednesday...temps will recover into the mid
80s for Thursday as heights aloft rise in response to the
approaching ridge. Lows will fall into the 50s Tuesday night before
recovering back into the 60s later in the week.


.LONG TERM /Thursday night through Monday/...
Issued at 235 PM EDT Mon May 21 2018

The long term will begin with dry weather in place over central
Indiana under the influence of an upper ridge. Fairly high
confidence given model agreement on the larger upper pattern that
conditions will be dry with well above normal temperatures for
through early Saturday morning. Chances for showers and some
storms will return Saturday afternoon as upper ridging breaks down
and moves east. Then will see shower and thunderstorm chances
through the remainder of the holiday weekend. Confidence is low
from Saturday onward as a tropical system forming over the Gulf
will have an influence on the amount of moisture available over
the area and how far a frontal system might be able to move into
area. While its existence is a consistent feature within several
model runs, this system is still showing a good amount of
variability in position and movement (not unusual this far out)
and thus did not deviate from the blended initialization given the
low confidence. High confidence above normal temperatures remain
through the entire period.


.AVIATION /Discussion for the 22/00Z TAF Issuance/...

Issued at 731 PM EDT Mon May 21 2018

VFR conditions have returned to all TAF sites as showers and
thunderstorms move farther east/northeast this evening. However,
MVFR (or worse) conditions are expected late tonight along with
possible redevelopment of showers and thunderstorms with frontal
boundary. MVFR category will then persist through the morning
hours tomorrow before VFR returns for the remainder of the TAF
period. Meanwhile, winds will start out southwesterly, gradually
veering to the northwest with sustained speeds of 4 to 8 kts.





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