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000 
FXUS63 KIND 201714
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
114 PM EDT Sat Oct 20 2018 

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

&&

.SYNOPSIS...
Issued at 334 AM EDT Sat Oct 20 2018

A strong upper level disturbance and surface front will bring
unsettled and at times windy weather to central Indiana this
afternoon and evening. High pressure will then build in with dry
and cool weather for much of the upcoming week. Rain chances will
return by late week as an upper level disturbance tracks across
the Ohio Valley.

&&

.NEAR TERM /Rest of Today/... 
Issued at 1109 AM EDT Sat Oct 20 2018

Latest model guidance continues to show wind gusts near Wind
Advisory criteria this afternoon, but overall it looks like a
borderline situation. However, after collaboration with
surrounding offices, have decided to go ahead and issue a Wind
Advisory this afternoon and evening. Wind gusts around 45 mph will
be the primary threat. 

Otherwise, forecast is in pretty good shape. Tweaked sky cover as
skies have become mostly clear across most areas this morning.
With more sunshine this morning, bumped up highs a bit some areas. 
Adjusted some timing of the PoPs, but the overall trend and 
location of highest PoPs still looks good. 

Previous discussion follows...

Clearing skies slowly expanding south into the northern forecast 
area early this morning. Much of the rest of central Indiana
remains under low stratus with moisture trapped beneath a shallow
inversion. 07Z temperatures remained largely in the upper 40s and
lower 50s.

Interesting day setting up that will become more unsettled this 
afternoon as a vigorous upper level wave dives through the Great 
Lakes with a secondary surface front. Expect increasingly 
windy...raw and showery conditions as a result this afternoon and 
into the evening.

The low clouds will continue to shift southeast this morning as 
drier air and deeper subsidence eventually overwhelms the shallow 
inversion in the near surface layer. This will result in a 
relatively pleasant start to the day for most with sunshine and 
light winds for much of the morning. The focus will shift to the 
upper wave diving out of the Canadian prairies later this morning 
and pinwheeling through the Great Lakes later today. Stronger winds 
through the boundary layer will accompany the wave aloft and 
overspread the forecast area from the northwest by early afternoon. 
The surface front will drop through the area between 18 and 21Z with 
cold advection commencing immediately behind the front. The cold 
advection will combine with dry adiabatic flow up through about 
750mb to start pulling the stronger boundary level flow to the 
surface through the afternoon with peak gusts increasing to 40-45 
mph across much of the region. These values fall just shy of wind 
advisory criteria and considering that the strongest gusts will 
likely be confined to a narrow time window and within scattered 
convection during the late afternoon...will continue with an SPS for 
the gusts.

Weak instability and steep lapse rates will produce a low level 
environment conducive for scattered convection to develop and spread 
southeast with the upper wave after 18Z. Expect convection to be 
focused over the northeast half of the forecast area most 
predominantly this afternoon in closer proximity to the strongest 
forcing aloft associated with the upper wave. Low freezing and wet 
bulb zero levels beginning between 3-4kft and dropping thereafter 
support a potential for small hail and/or graupel to accompany any 
stronger convective cell later this afternoon. Will continue with no 
mention of thunder as overall instability levels look too weak to 
support. As mentioned above...not out of the question to see a few 
higher gusts within stronger convection as well considering strength 
of winds in the 925-850mb layer. Finally as we get into late day and 
the airmass cools...may begin to see a few snowflakes mix in with 
rain over northeast counties.

Temps...highs will come by midday with temps falling this afternoon 
once cold advection commences. Overall trended towards the warmer 
MAV guidance as highs should make it into the mid and upper 50s most 
areas. Temperatures will fall back into the 40s by sunset.

&&

.SHORT TERM /Tonight through Monday Night/...
Issued at 334 AM EDT Sat Oct 20 2018

Forecast challenges focus on any lingering precipitation this 
evening as the upper wave quickly departs...followed by the 
potential for freezing temperatures within areas where the growing 
season continues over southern counties Sunday morning. 

Precipitation will focus over the far northeast counties before 
ending this evening as the upper wave quickly moves away to the 
east. Critical thicknesses likely drop low enough for a few 
snowflakes to mix in with the rain...especially as a lake effect 
fetch briefly establishes for a few hours before winds back later 
tonight. Gustier winds will linger this evening then relax overnight 
as the upper wave departs and the surface pressure gradient relaxes. 
Skies will clear overnight as high pressure builds into the mid 
Mississippi Valley. The remainder of the short term will be quiet as 
the surface high drifts across the Ohio and Tennessee Valleys and 
eventually into the southeast states by Monday. Northwest flow will 
remain in the upper levels with the trough parked over the Great 
Lakes amplifying late in the period courtesy of another piece of 
energy aloft dropping out of Canada. This feature may spread some 
higher clouds into the region from the north Monday and Monday 
night...otherwise expect mainly clear skies from late Saturday night 
through the end of the period. 

While frost accrual will be minimized Sunday morning with 5-10mph 
winds lingering...expected temperatures falling into the upper 20s 
and lower 30s will warrant introducing a freeze warning over the 
southern two rows of counties where the growing season continues. If 
these temperatures are realized...likely to see a merciful end to 
the fall frost/freeze headline season over south central Indiana.

Temps...lows continue to trend colder for Saturday night and with 
clearing expected across most of the area by the predawn 
hours...upper 20s and lower 30s seem reasonable. Winds however will 
likely keep temps from fully bottoming out. Generally utilized a 
model blend through the rest of the short term supported by low 
level thermals.
After a cool day Sunday in the upper 40s and lower 50s...return flow 
on the back side of the high will bring temps up close to ten 
degrees on Monday. 

&&

.LONG TERM /Tuesday through Friday Night/...

Issued at 346 AM EDT Sat Oct 20 2018

Latest blended initialization was accepted for the forecast period 
with decent model consensus. Dry and below normal temperatures can 
be still be expected for most of the long term period. A cold front 
is progged to move through on Tuesday, but little moisture will 
result in no rainfall. The first chance for any rain showers will 
come on Thursday and Friday as a couple weak upper waves traverse 
the area. Confidence remains low though in those chances, too, due 
to limited moisture. Meanwhile, high temperatures through the period 
will generally be in the 50s and 60s with lows in the 30s.

&&


.AVIATION (Discussion for the 201800Z TAF Issuance)...
Issued at 114 PM EDT Sat Oct 20 2018 

VFR conditions expected through the period. Windy conditions 
expected into this evening.

Scattered to broken cumulus will continue through the afternoon. 
Clouds will diminish this evening, with mostly clear across the TAF 
sites for Sunday.

Main issue will be the winds this afternoon and evening. Sustained 
winds of 20-30kt along with gusts near 40kt will be common this 
afternoon into early evening. Winds will then quickly diminish into 
the overnight.

Winds will veer to the northwest early this afternoon as a cold 
front passes.

Can't rule out an isolated shower this afternoon with the front, but 
coverage will be too low to mention for the TAF sites.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 10 PM EDT this evening for INZ021-028>031-
035>049-051>057-060>065-067>072.

Freeze Warning from 3 AM to 10 AM EDT Sunday for INZ060>065-
067>072.

&&

$$

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