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Office: IND

FXUS63 KIND 190923
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
523 AM EDT Fri Oct 19 2018

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

&&

.SYNOPSIS...
Issued at 341 AM EDT Fri Oct 19 2018

A cold front passing through the region tonight followed by a
strong upper level disturbance and surface front Saturday will
bring unsettled and at times windy weather to central Indiana.
High pressure will then build in with dry and cool weather for
much of next week.

&&

.NEAR TERM /Today/...
Issued at 341 AM EDT Fri Oct 19 2018

High pressure centered over the central Appalachians early this
morning remains the primary influence across the Ohio Valley with
mainly clear skies early this morning. 07Z temperatures were
generally in the 30s.

With temperatures already in the lower and middle 30s throughout
much of the southern portions of the forecast area where the growing
season remains active...will continue with the frost advisory as
is through 13Z.

Mid and high level clouds beginning to increase from the west as
moisture aloft ahead of a frontal boundary moving through the Plains
gradually advects into the area. Residual subsidence and drier
air through the lowest 10-15kft will be slower to erode...possibly
taking much of the afternoon until better lift develops
immediately ahead of the front and in tandem with a surge of
stronger flow through the boundary layer. Some of the CAMs
guidance appears too fast in developing light rain showers into
the area by midday with model soundings still showing a fairly
deep area of subsidence present below 10kft. Prefer continuing
with the previous forecast trend of ramping up pops from the west
after 18Z as the stronger forcing arrives with the front.

While overall rainfall amounts should be less than a tenth of an
inch in most areas...the expected coverage warrants going with a
short period of high pops during the late afternoon and early
evening as the deeper moisture plume shifts through the area.
Potential for gusty southwest flow this afternoon with increasing
winds slipping down as low as 2-3kft. Could see peak gusts briefly
push 20-25 mph.

Temps...Bit of compressional heating ahead of the front even with
increasing clouds should push temperatures warmer than the last
few days. Nudged temps closer to the warmer MAVMOS with highs
topping out in the mid and upper 50s. A few spots warming into the
lower 60s over far southern counties is possible.

&&

.SHORT TERM /Tonight through Sunday Night/...
Issued at 341 AM EDT Fri Oct 19 2018

Forecast challenges focus primarily on the arrival and passage of a
secondary cold front and sharp wave aloft on Saturday...bringing
precip and strong winds Saturday afternoon and evening followed by
colder and drier weather to wrap up the weekend.

Light rain will be in the process of shifting east of the area with
the deeper moisture plume. this evening. Most of the rain should
be out of the forecast area prior to midnight but the front itself
will hang back and not fully move across central Indiana until
predawn Saturday. Will hold onto a low chance for light rain
through about 06-07Z to account for any isolated showers lingering
with the front...then go dry thereafter as subtle surface ridging
builds in immediately behind the front Saturday morning.

The focus turns to the northwest as the first strong upper level
system of the fall dives out of the Canadian prairies and across
the Great Lakes Saturday. A secondary cold front will accompany
the upper low and its associated energy diving into the region
Saturday afternoon. A pleasant start to the day should transition
rather quickly into a cloudy...windy afternoon with scattered
showers developing over the northeast half of the forecast area.
Model soundings show weak instability and very strong lapse rates
through 750 mb during the afternoon. This will likely not be
enough to generate any thunder considering the nature of the
airmass...but this setup with freezing levels below 5kft and
dropping could support some graupel mixing in with showers.

The bigger story for the area is likely to be the wind as momentum
transfer techniques suggest peak gusts to near 40mph in the
afternoon. While the gusts are expected to remain below advisory
criteria...will highlight this potential in the HWO as it is the
first big wind maker system of the fall. Winds will remain gusty
Saturday evening before dropping off overnight.

Precipitation will focus over the far northeast counties before
ending Saturday evening as the upper wave quickly moves away to the
east. Critical thicknesses could 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
Saturday night. Skies will clear late Saturday night as high
pressure builds into the mid Mississippi Valley. The high will
expand across the Ohio and Tennessee Valleys Sunday with dry and
cool weather. With the exception of a subtle increase in high
clouds as a weak front drifts into the lower Great Lakes early
Monday...expect mainly clear skies for Sunday and Sunday night.

Temps...trended closer to the MAV over northern counties Saturday
while undercutting the MAV in southern counties. Undercut all
guidance Sunday with highs in the upper 40s and lower 50s.
Utilized a model blend for overnight lows. Lows in the upper 20s
and lower 30s Sunday morning will likely warrant a headline for
freezing temperatures over southern portions of the forecast area
where the growing season has not ended yet. While lingering winds
will minimize frost accrual...expected temperatures may very well
put a merciful end to the growing season across south central
Indiana Sunday morning.

&&

.LONG TERM /Monday through Thursday Night/...

Issued at 341 AM EDT Fri Oct 19 2018

Dry but below normal temperatures can be expected for most of the
extended period with high pressure in place. A cold front is
progged to move through on Tuesday, but no moisture is associated
with it. So, will not deviate from the dry forecast that the
latest blended initialization is trending toward. The dry
conditions will then persist through mid-week as an upper ridge
strengthens over Canada and the north-central U.S. It won't be
until late in the period when low chances for rain enter the
forecast as moisture increases slightly ahead of the next upper
trough. Confidence is low though in the rain chances from
Wednesday night through Thursday night, there might not be enough
moisture.

&&

.AVIATION /Discussion for the 19/09Z TAF Update/...

Issued at 521 AM EDT Fri Oct 19 2018

Update...
No changes.

Previous Discussion...
VFR through the night and much of Friday, with increasing clouds
through the day on Friday as a front approaches from the
southwest. Will see MVFR clouds moving in before around 0z. There
is some potential for showers but think the dry air could pose a
problem for the northward development of the rain. As a result
will continue to leave rain mention out of the TAFs for now. Winds
will be light and variable through the overnight but then increase
in speed and veer to the southwest around 9 to 14 kts. May see
some wind gusts Friday afternoon but not confident enough to
include.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Frost Advisory until 10 AM EDT this morning for INZ062>065-
070>072.

&&

$$

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



Office: IWX FXUS63 KIWX 191003 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 603 AM EDT Fri Oct 19 2018 .SYNOPSIS... Issued at 428 AM EDT Fri Oct 19 2018 Cool and dry conditions will continue this morning but the chance for light showers will increase this afternoon ahead of a cold front. This front will pass through the region tonight followed by a second cold front with rain showers and falling temperatures on Saturday. Lake effect rain showers will continue Saturday afternoon and likely into the evening, possibly mixing with wet snowflakes well inland before ending. The extended forecast for Sunday and most of next week looks dry with temperatures near or slightly below normal for late October. && .SHORT TERM...(Today and Tonight) Issued at 428 AM EDT Fri Oct 19 2018 Return flow underway this morning as water vapor shows GOMEX moisture being pulled northward ahead of approaching short wave and sfc cold front. IR showing cirrus already spreading into western Indiana early this morning and clouds should gradually thicken and lower later this morning and especially this afternoon. Bulk of deeper Gulf moisture will be shunted east and stay south of our area while better dynamics associated with short wave pass across the north. Just enough moisture advection and saturation coupled with frontal forcing to support rain chances this afternoon with highest PoPs across the north closer to short wave forcing. GFS and ECMWF develop a 300mb jet streak this afternoon that may aid in large scale lift across the north as well. Amounts should remain light as it will take some time to saturate lower levels keeping pcpn duration short. Lingering chance PoPs into first half of tonight as initial cold front passes through. Brief period of drier air behind this front should keep overnight hours dry prior to arrival of more potent short wave on Saturday. && .LONG TERM...(Saturday through Thursday) Issued at 428 AM EDT Fri Oct 19 2018 Sharp trough dropping through the Canadian Northwest Territories will intensify and move across our area Saturday as impressive 110+kt 500mb jet streak dives into the Ohio Valley region. Associated cold front will bring very cold airmass into the area originating over the above normal Canadian snowpack. Result will be falling afternoon temps Saturday along with rain showers spreading south and east. Lake instability will increase as deeper cold air arrives with a period of extreme lake induced instability in the afternoon as Lake CAPE increases to over 1000 J/kg and equilibrium levels to near 18kft. Trajectories also favorable for short period of upstream conditioning off of Lake Superior. All signs point to a very good lake response in wake of short wave leading to corridor of moderate rain showers and perhaps some thunder and even waterspout potential over the lake. Still the usual uncertainty with exactly where showers will move inland but rather good run to run and model consistency to warrant a bump to categorical pops in typical northwest flow locations Sat afternoon. Big question remains how long lake effect will continue and if any snow will mix with the rain Sat night. Models indicate inversion heights falling rapidly during the evening but typical model bias is to overwhelm mesoscale forcing with synoptic drying and subsidence too quickly, especially early in season when lakes are warmest. Inversion height looks to remain above 5kft through at least 03-06z with moderate instability still in place along with favorable longer NW fetch. Soundings suggest lower levels remaining saturated with lift through at least mid evening and have bumped pops into likely category. Again could see this area shift a bit but used consensus of NAM12, NAM3K, GFS and Canadian models for placement. Could also see a few light showers linger overnight but low level thermal trough does begin to move east with anticyclonic flow and subsidence increasing, eventually shutting off lake response. Remainder of long term looks quiet, mainly dry with slightly below normal temperatures with ridge across the region. A weak front may drop into the area Monday night/Tuesday with northern stream short wave but lack of moisture and forcing suggest this will be a dry passage. && .AVIATION...(For the 12Z TAFS through 12Z Saturday Morning) Issued at 600 AM EDT Fri Oct 19 2018 Southwesterly winds will increase with gusts 20-25 knots possible late morning and afternoon. Clouds will lower/thicken with time today, possibly yielding scattered showers 19-23z at KSBN and 21-01z at KFWA as a pre-frontal trough moves in. CIGS likely lower into low VFR or MVFR along this feature for a time this evening into the early overnight. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...Gale Watch from Saturday morning through Saturday evening for LMZ043-046. Small Craft Advisory until 11 AM EDT Saturday for LMZ043-046. && $$ SYNOPSIS...Lashley SHORT TERM...Lashley LONG TERM...Lashley AVIATION...Steinwedel Visit us at www.weather.gov/iwx Follow us on Facebook...Twitter...and YouTube at: www.facebook.com/NWSNorthernIndiana www.twitter.com/nwsiwx www.youtube.com/NWSNorthernIndiana