Area Forecast Discussion
Issued by NWS Indianapolis, IN

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482
FXUS63 KIND 172005
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
305 PM EST Fri Jan 17 2020

.UPDATE...
The LONG TERM and AVIATION Sections have been updated below.

&&

.SYNOPSIS...
Issued at 320 AM EST Fri Jan 17 2020

High pressure overhead will steadily move east of the region, as a
strengthening area of low pressure lifts northeast from the
Southern Plains reaching Southern Wisconsin saturday morning. This
low pressure system will then quickly lift northeast with a
frontal boundary pushing east across Central Indiana, allowing
another surface ridge of high pressure to approach the Western
Ohio River Valley late in the weekend with much cooler
temperatures.

&&

.NEAR TERM /Rest of Today/...

Issued at 912 AM EST Fri Jan 17 2020

Forecast is evolving as expected. Current thoughts remain that
precipitation will begin late this afternoon as mix of rain and
snow with brief periods of freezing rain tonight before all rain
by late tonight and tomorrow. No changes made to snow and ice
accumulations. Previous discussion follows...

Early this morning a steady feed of dry northeast flow has kept
clouds out of the area, but temperatures have radiated into the
upper teens to lower 20s with dewpoints several degrees lower due
to the drying in the lower levels of the atmosphere. Given the
expected progressive flow, the anticipation is that the departing
surface ridge will loosens it`s influence on Central Indiana, and
likely allow steady moistening in the lower levels late this
afternoon/evening ahead of the next system. That being said, there
is some indications that the further downstream ridge may be
slightly delayed from pushing east, and thus allow some subsidence
to linger into the evening and perhaps delay the onset of precip
by a few hours. This could be key in lowering snowfall totals,
which presently is around an inch for the northern counties. Any
delay in precip may also impact the potential for freezing rain to
occur as well.

Forecast soundings continue to indicate a warm layer aloft lifting
overhead after 6pm this evening, setting the stage for a slow but
steady transition from the moist dendrites towards a full melt of
falling dendrites towards freezing rain due to a sub-freezing
surface. Guidance has backed off marginally with ice accums, with
less than one tenth for the overnight hours. Have adjusted the
current headline to include two row of counties further south, but
expect the timing to be a short period and by 9z Sat any precip
that will be falling will likely be just rain. Further north
soundings still support some sub-freezing conditions, but expect
this to be transitioning to all rain by daybreak Sat and will
maintain the ending of the headlines at 12Z sat further north.

Temperatures will be slowly rising overnight, so the low temps
will occur prior to midnight in the upper 20s to around 30 range,
pushing into the lower to middle 30s by 9-12z Sat.

&&

.SHORT TERM /Saturday through Sunday night/...
Issued at 320 AM EST Fri Jan 17 2020

Warm/Moist conveyor will be ushering in a mild slug of air Sat
with temps quickly pushing into the 40s to perhaps lower 50s in
the southern forecast area. Otherwise the main concern will be on
the QPF totals given the remaining saturated soils across Central
Indiana. Expect steady rain to arrive shortly after daybreak and
linger through late morning, coupled with moderate forcing, and
precip totals could easily be between .5 to .75 inches before
noon. A dry wedge is progged to quickly lift northeast as the
mid-level trough axis arrives between 15-18Z Sat, which should
bring a brief end to the precip. But with cold air advection then
kicking in and wrap-around moisture bringing precip chances
quickly back to the region by early afternoon and transitioning
any precip to all snow. Given the northwest flow and cold air
advection behind the frontal passage, the depth of the moisture is
not substantial. Thus not anticipating much in the way of
accumulations on the back end of the shortwave Sat afternoon. But
temperatures will be falling through the afternoon into the 30s.

Quick push towards more typical winter like pattern for Sat ngt
into Sun, with a potent thermal trough arriving and allowing temps
Sat ngt to radiate into the single digits to lower teens.
Northwest cold air advection will persist, but expected to be dry
given strong subsidence from a surface ridge displaced to the
northwest of the region. Broad mid-level trough will then arrive
over the Great Lakes/Ohio River Valley regions, holding Sun high
temps in the teens to lower 20s. There is some indications of a
weak clipper like system traversing the region later in the day
Sun/early Mon, but this looks to remain further north.

&&

.LONG TERM /Sunday through Friday/...

Issued at 300 PM EST Fri Jan 17 2020

Dry weather is expected across the period with some of the
coldest temperatures of the season so far. The upper level low
pressure system that will bring precipitation to the area tonight
and tomorrow will have exited by Sunday morning with high pressure
building during the day. Morning lows will be in the single
digits to low teens Sunday and Monday morning with wind chills
near 0.

Temperatures will gradually warm back towards more seasonable
temperatures by the middle of the week with southerly winds
brining warmer air to the area by Thursday. An upper level low
pressure system will move through late this week bringing
precipitation to the area. Confidence on timing and strength of
the system is low, so plan on keeping POPs fairly low and
broadbrushed at this time.

Temperatures are expected to be well below average early next week
with more seasonable temperatures by the middle of the week. Temps
will be above average Friday and into the weekend.

&&

.AVIATION /Discussion for 17/21Z TAF Update/...

Issued at 300 PM EST Fri Jan 17 2020

No changes needed to IND TAF with forecast progressing as expected.
Previous discussion follows...


VFR conditions will deteriorate to MVFR/IFR conditions tonight and
tomorrow.

Wintry precipitation will move into central Indiana generally
after 0Z tonight. Current thoughts are a mix of sleet and snow are
likely for a couple of hours before transitioning to fzra by
around midnight. Fzra will then be the dominant precip type for a
few hours before a transition to rain by later tonight as
temperatures warm. Confidence on the timing of precipitation is
fairly high with lower confidence on the precip type at any time.
In addition to the precip, winds will be fairly gusty with winds
generally out of the south at 15 to 20kts and gusts to 30kts. LLWS
will be a concern with winds at 020 around 70 kts. Clouds will
stay overcast through the period with ceilings falling to MVFR
after 0Z tonight and IFR by tomorrow morning.



&&

.IND WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 7 PM this evening to 4 AM EST
Saturday for INZ043>049-051>057.

Winter Weather Advisory from 7 PM this evening to 7 AM EST
Saturday for INZ021-028>031-035>042.

&&

$$

SYNOPSIS...Beach
NEAR TERM...Beach/White
SHORT TERM...Beach
LONG TERM....White
AVIATION...White



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