Area Forecast Discussion
Issued by NWS Indianapolis, IN

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074
FXUS63 KIND 212306
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
608 PM EST Sat Jan 21 2017

.UPDATE...
Aviation Section has been updated below.

&&

.SYNOPSIS...
Issued at 242 PM EST Sat Jan 21 2017

Mild and unsettled weather will continue across the Ohio Valley
through the early part of the week with potential for rain and a few
thunderstorms. After a brief break from the wet weather...another
storm system will track through the region the middle of next week
with progressively colder weather more typical of late January
arriving for late week into next weekend.

&&

.NEAR TERM /Tonight/...
Issued at 242 PM EST Sat Jan 21 2017

Sunshine increasing across central Indiana from the west this
afternoon serving as a reminder that yes...it does still exist. The
sunshine presents an added bonus to the unusually mild temperatures
being enjoyed over the area this afternoon. With weather conditions
that would be more typical of early April...19Z temps had surged
into the lower and mid 60s across the area.

The warm temperatures and the increasing sunshine currently come
partly as a result of the region residing in between three
systems...the first causing convection and severe weather over the
deep South and southeast states and providing the high clouds
drifting east from the area...the second a low pressure spinning
over the Dakotas and northern Plains...and the third an amplifying
upper low ejecting out of the Four Corners region of the southwest U
S. This third system will bring a return to the unsettled pattern
experienced of late...but not until Sunday. Clouds though in advance
of this system will arrive across western counties this evening and
gradually spread across the rest of the area.

A surface wave associated with the upper low will develop over the
Texas panhandle this evening then kick out east towards the lower
Mississippi Valley by daybreak Sunday. As it does so...a boundary in
the form of an inverted trough will extend out from the low into the
region then pinwheel back and attach to the northern surface low
over the Dakotas. The 3/4/12km NAM all highlighting the potential
for isolated convective development along the boundary later this
evening into the early overnight impacting the northern Wabash
Valley with subtle hints even present from the HRRR and WRF.
Considering deeper moisture and general forcing aloft is
limited...remain somewhat skeptical at this solution coming to
fruition. With that being said...the inverted trough and presence of
weak elevated instability may be enough to generate a few showers
and will carry low chance pops west of a Kokomo-Crawfordsville-
Vincennes line through the early overnight. Showers and a few storms
will then expand into the area from the south towards daybreak as
deeper moisture arrives.

One other issue to contend with tonight will be areas of fog as
model soundings showing a shallow inversion developing once again in
the near surface layer. HRRR guidance in particular has been rather
bullish in expanding areas of fog north of I-70 overnight and
considering dewpoints have risen into the 50s...skies will be mostly
clear at least initially this evening and wind flow should be
generally light...fog development is likely. Will need to monitor
through the evening for potential for locally dense fog to develop.

Temps...trended much closer to the warmer MET guidance for lows
tonight ranging from the mid 40s to lower 50s. Lows most places
tonight will be 10 to 15 degrees warmer than the average highs for
this time of year.

&&

.SHORT TERM /Sunday through Tuesday/...
Issued at 242 PM EST Sat Jan 21 2017

Forecast challenges focus on precip chances Sunday and Monday.

Aforementioned upper low and the strong surface wave accompanying it
will continue an E/NE trek across the Tennessee Valley on Sunday
with a secondary low developing over the southeast states and
becoming the primary wave by early Monday over the Carolinas. The
NAM as it has done the last several runs since Thursday continues to
pull the initial surface wave further to the northwest than most
other model guidance and linger it over the lower Ohio Valley
longer...all the way into Monday morning. While it remains somewhat
apart along with its 3/4km solutions...hard to discount as it
remains consistent with its earlier runs.

Expect heavier rainfall potential spreading north into the southern
half of the forecast area on Sunday as an axis of deformation in the
mid levels rotates north and interacts with deeper low level
convergence and precip water values approaching 1 inch. Elevated
instability will lift into areas south of I-70 with any thunder
mention likely being confined to southern counties on Sunday. Will
be carrying higher pops for Sunday and Sunday night as the system
moves by to the south of the region slowly. Still feel NAM models
may be a bit overzealous with precip totals through early Monday but
the idea...but potential for an additional 0.50 to 1 inch over the
southern half of central Indiana by Monday seems quite reasonable
with locally higher amounts under any convection. This could
exacerbate existing flooding on area streams and rivers and bring a
renewed period of lowland and field flooding as the ground is
saturated. Will highlight in the HWO.

Scattered showers will gradually diminish in coverage from west to
east Monday afternoon and night as central Indiana remains within a
cyclonic flow on the back side of the departing storm system.
Conditions will finally improve for Tuesday as ridging aloft quickly
replaces the upper level cyclonic flow within the continued
amplified upper pattern across the country.

Temps...Mild conditions are expected again Sunday but presence of
clouds and rain along with easterly flow will keep it cooler than
today in the 50s to around 60. Cooler weather for Monday as low
level flow shifts to northerly with highs in the mid and upper 40s.
Remains in the 40s on Tuesday. Overall ended up near MAVMOS for
highs through much of the period.

&&

.LONG TERM /Tuesday night through Saturday/...
Issued at 207 PM EST Sat Jan 21 2017

An upper trough will move into the area from the west during the
long term. This will keep small chances for precipitation in the
forecast off and on as upper waves eject out of the trough and
provide lift, mainly across northern parts of the forecast area.
Tuesday night an initial cold front will move through, followed by
a secondary cold front Wednesday night, and this second front will
usher in a return to normal temperatures for this time of year.
Small chances for snow or a mix of rain and snow will move in with
the passage of the cold front and remain through the rest of the
extended. Fairly good model agreement on the main upper pattern, so
confidence on temperature trends is high, while confidence on timing
of precip chances is low.

&&

.AVIATION /Discussion for 220000Z TAF Issuance/...
Issued at 608 PM EST Sat Jan 21 2017

VFR conditions through 06Z to 08Z then MVFR or IFR that.

A light to moderate southerly flow was occurring across the area
with mainly thin high clouds at best.   Areas of low pressure were
over northern Wisconsin with another low pressure centered over the
Texas panhandle.  The Texas low pressure system will move to the
middle Mississippi valley by midday Sunday and to eastern Kentucky
by end of the forecast period.   Areas of fog will be a concern
late tonight as dewpoints are high.  Model soundings indicate low
ceilings may spread into KLAF after midnight...but most other areas
will see increasing mid/high clouds overnight followed by lowering
ceilings after 12Z Sunday as rain spreads our way.  Rain from the
southern low pressure system will overspread most areas by mid to
late morning Saturday.

Winds will be light overnight becoming northeast 5 to 8 knots Sunday
and north 10 to 15 knots Sunday evening.

&&

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

&&

$$

SYNOPSIS...RYAN
NEAR TERM...RYAN
SHORT TERM...RYAN
LONG TERM....CP
AVIATION...JH



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