Area Forecast Discussion
Issued by NWS Indianapolis, IN

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120
FXUS63 KIND 231858
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
258 PM EDT Tue May 23 2017

.UPDATE...
The LONG TERM Section has been updated below.

&&

.SYNOPSIS...
Issued at 403 AM AM EDT Tue May 23 2017

Low pressure will deepen across Indiana late today...tonight and
Wednesday as an upper trough over the upper midwest moves southeast
and develops into a closed upper low over the Ohio valley by
Wednesday.

This system will bring showers and a few thunderstorms Wednesday
and a chance of showers along with quite cool temperatures
through Thursday.    The area of low pressure will move to the
New England coast and high pressure will move east across Indiana
late Thursday night and Friday.   Another area of low pressure and
a frontal system will affect us over the upcoming weekend.

&&

.NEAR TERM /Rest of Today and Tonight/...
Issued at 955 AM AM EDT Tue May 23 2017

Going forecast is right on track and no changes made for the morning
update. Previous discussion follows...

Radar indicated very light widely scattered light showers were across
northern Indiana to west Central Illinois.  An area of low pressure
will develop over Illinois later today as another system brings
showers across Tennessee and parts of Kentucky later today.  Central
Indiana which is in between these systems will be mostly dry.
Will mention a slight chance of showers over far west and northwest
sections today and go dry elsewhere.

Shower chances will increase overnight as low pressure moves towards
central Indiana and deepens.  Models have trended a little slower
in developing showers and will go with chance POPS most areas
tonight but with likely POPS far west.

Highs today will be in the lower to middle 70s which is close to a
MOS blend.   Lows tonight will be in the middle 50s northwest to
near 60 southeast.   Went slightly warmer than MOS numbers tonight
as clouds thicken across the area.

&&

.SHORT TERM /Wednesday through Thursday Night/...
Issued at 403 AM AM EDT Tue May 23 2017

Models indicate low pressure will deepen across central Indiana
Wednesday and move slowly northeast Wednesday night and Thursday.
Numerous showers and a few thunderstorms will occur Wednesday as
strong upward forcing occurs across the area.  Most Unstable cape
only around 500 J/KG but with good UVV...this should be enough for
at least a chance of thunderstorms mainly Wednesday afternoon as a
strong upper low moves into the Ohio valley.

Showers will slowly diminish Wednesday night and Thursday as the
deep area of low pressure moves slowly northeast.  It will be dry
Thursday night as a week ridge of high pressure moves our way.

Lowered high temperatures slightly Wednesday with clouds precip
and increasing cold advection.   For most other periods went close
to a MOS blend concerning temperatures.   Highs will be in the
lower to middle 60s Wednesday and middle to upper 60s Thursday...
while lows will be in the lower 50s.

&&

.LONG TERM /Friday Night through Tuesday/...
Issued at 258 PM EDT Tue May 23 2017

Unsettled and active weather is the headline for the upcoming
holiday weekend as a frontal boundary and wave aloft combine to
bring the potential for scattered convection to impact central
Indiana at times through Sunday.

A broad upper low will set up over the Canadian prairies with
pieces of energy ejecting from the base of the parent low east
into the Mississippi and Ohio Valleys within a wavy southwest flow
aloft regime. Aforementioned frontal boundary will align across
the Ohio Valley beginning Friday night and remain over the area
before shifting southeast by late weekend as the upper low drops
southeast.

While model differences in timing remain...some clarity starting
to develop in terms of timing higher impacts to the area and
potential for heavy rainfall and severe weather. An initial wave
tracking through the area and along the boundary Friday night and
early Saturday showing hints of a potential MCS. Additional
impacts appear likely Saturday afternoon and evening with
possibility for robust convection in the vicinity of the frontal
boundary to develop in a warm and modestly unstable airmass. CIPS
analogs strongly suggestive that highest severe weather threat may
exist across central Indiana on Saturday.

Convective threats diminish through the day Sunday as the front
shifts south and region comes under the influence of cyclonic flow
associated with the upper low sagging into the Great Lakes. At
this point...dry and cooler weather is expected for early next
week although a lingering presence of northwest flow aloft as the
week progresses is suggestive of a continued convective threat.

&&

.AVIATION /Discussion for 231800z TAF issuance/...

Issued at 1257 PM EDT Tue May 23 2017

VFR through the rest of the day with light southeasterly winds.
KLAF will have light showers nearby but they are widely scattered
and unlikely to impact flight category so just included a VCSH.
Ceilings will develop overnight as low pressure system gets closer
and brings initially scattered showers and then more widespread
rain to the sites. MAV/MET showing IFR/low IFR ceilings developing
at the sites mid morning Wednesday for at least a brief period,
but SREFS show only low probabilities of even MVFR. Thus for now
will go with MVFR ceilings overspreading the area after around
9-12z and leave IFR out for this issuance. Winds should be light
and pretty variable with surface low meandering across the area
Wednesday.

&&

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

&&

$$

SYNOPSIS...JH
NEAR TERM...JH/CP
SHORT TERM...JH
LONG TERM....Ryan
AVIATION...CP



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