Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 170323
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1123 PM EDT Mon Apr 16 2018

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

&&

.SYNOPSIS...
Issued at 330 PM EDT Mon Apr 16 2018

Snow showers will end this evening as an upper low moves away from
the region. Widespread subfreezing temperatures are expected
overnight before a recovery to near normal temperatures by
Wednesday. A quick moving low pressure system will bring chances for
rain showers Wednesday and Wednesday night with dry and cooler
weather to follow for late week. Dry conditions will likely continue
into the weekend with slightly warmer temperatures.

&&

.NEAR TERM /Rest of Tonight/...
Issued at 939 PM EDT Mon Apr 16 2018

Radar trends show that the heavier snow showers have exited the
area, but flurries continue across the northeast half or so. Have
removed the snow shower wording and replaced with flurries. These
will diminish from southwest to northeast into the early overnight
hours.

Otherwise forecast is in good shape and only tweaked hourly numbers
to reflect current trends.

Previous discussion follows...

Miserable spring day in progress across central Indiana as a deep
upper low moving across the lower Great Lakes provides a mid winter
style day with snow bursts and squalls. Where snow have ripped for
short periods of time...elevated surfaces and grassy areas have
received a dusting in spots before melting shortly after once the
rates lighten up. Temperatures have been extremely sluggish to
respond with the cold pool overhead. Even at 20Z...most areas remain
in the low to mid 30s...a solid 25 to 30 degrees below normal. Gusty
W/NW winds have just added to the misery.

The focus through tonight is twofold.  The initial focus is on the
scattered snow showers which are already beginning to diminish in
coverage as the upper low shifts east and takes the more widespread
snow showers with it. Should see this trend continue into the
evening as more substantial forcing aloft is lost but presence of
shallow but steep lapse rates will likely enable flurries and/or a
few snow showers to linger through the evening over northeast
portions of the forecast area.

The second focus will be on the Freeze Warning already in place for
the southern half of central Indiana where vegetation growth has
progressed far enough. Considering the mid to possibly upper 30s
will be the best temperatures can do over the next few hours...there
should be no difficulty in temps dropping into the upper 20s and
lower 30s. This is a high confidence forecast.

The arrival of drier air and high pressure late tonight will allow
for some clearing to develop from the southwest and enable winds to
slacken...especially over the lower Wabash Valley which is most
susceptible to frost accrual. Winds remaining around 10mph should
mitigate most frost accrual further north and east towards the I-70
corridor. It should be noted that our northern counties have not
started the spring frost/freeze season yet due to vegetation growth
not being as far along as points further south in the forecast area.
That being said...will issue an SPS to highlight the subfreezing
temperatures for any sensitive plants/fruits that could be
susceptible.

Temps...felt comfortable trending temps towards the cooler end of
guidance overnight as lows will fall into the upper 20s and lower
30s.

&&

.SHORT TERM /Tuesday through Thursday/...
Issued at 330 PM EDT Mon Apr 16 2018

Forecast challenges focus on precip chances Wednesday and Wednesday
night...and temperatures throughout as a warming trend commences.

The Freeze Warning will continue Tuesday morning through 14Z as
surface temps should rise above 32F by that point. Much of the
forecast area will still be under the influence of cyclonic flow
aloft Tuesday morning even as a high pressure ridge builds into the
lower Ohio Valley. Potential for lake enhanced stratocu and maybe
even a stray flurry or two to still impact the northeast half of the
forecast area through midday Tuesday before the cyclonic flow breaks
down and the ridge builds in. Overall though...expect increasing
sunshine and warmer temperatures as warm advection finally begins.

Low pressure set to eject out into the central Plains Tuesday night
and into the mid Mississippi Valley by Wednesday morning. A warm
front extending east from the low will lift into the forecast area
from the south late Tuesday night. Model soundings are showing an
initially dry layer below 4kft and forcing aloft is not overly
impressive but as isentropic lift increases late...think some
potential exists in the predawn hours for sprinkles. More
substantial lift will arrive as the surface low moves across
northern Indiana Wednesday. The trailing cold front will sweep
across the region during the afternoon with scattered showers
expected along and behind the front Wednesday night as another deep
upper low trailing the surface wave tracks across the region. Not
entirely out of the question to have a few snowflakes mix in before
precip ends late Wednesday night but overall...rain should be the
primary precip type.

Dry and cooler weather once again returns for Thursday as cyclonic
flow aloft returns on the back side of the departing upper low.
Breezy conditions are expected Wednesday into Thursday as well.
Sustained Spring weather remains elusive.

Temps...the climb back out from the miserable weather will be
swift...with highs returning into the 50s for many on Tuesday and
60s ahead of the cold front on Wednesday. Took a model blend for
Tuesday and went over all temperature guidance fro Wednesday as good
warm advection exists out ahead of the late afternoon front. Trended
towards the warmer MAV for lows through the period.

&&

.LONG TERM /Thursday through Sunday/...
Issued at 240 PM EDT Mon Apr 16 2018

Main focus for the extended will be on whether or not there is
enough confidence that showers will make it far enough north for us
to include low weekend and or early next week PoPs.

Models and ensembles in reasonable agreement that high pressure will
dominate over the Great Lakes through at least Saturday. This leads
to high confidence in the forecast builder output of dry conditions
through the early weekend. Then, models are trending further south
with a potent southern Plains system. A blend has this system moving
slowly over the South this weekend and early next week. Forecast
Builder continues with a dry forecast, and that looks reasonable
with the trends. However, confidence is lower that all of our
southern counties will stay dry late weekend and early next week.

Confidence in temperature trends is high but confidence is not as
high on exact timing. Will accept the blend which has hear normal
highs in the 60s by next Monday with below normal temperatures
prior to Monday.

&&



.AVIATION (Discussion for the 170600Z TAF Issuance)...
Issued at 1123 PM EDT Mon Apr 16 2018

MVFR conditions expected early in the period for some sites, then
VFR.

Area of stratocumulus will gradually clear from the southwest
through the morning hours. Ceilings at KIND/KLAF will likely bounce
around between MVFR and VFR during the first several hours of the
TAF period before settling down to VFR.

Clouds will scatter out everywhere by 15-17Z. More mid and high
clouds move in later during the afternoon.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Freeze Warning through 10 AM EDT Tuesday for INZ045>048-051>057-
060>065-067>072.

&&

$$

SYNOPSIS...Ryan
NEAR TERM...Ryan/50
SHORT TERM...Ryan
LONG TERM....MK
AVIATION...50



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