Area Forecast Discussion
Issued by NWS Northern Indiana

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972
FXUS63 KIWX 221155
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
655 AM EST Thu Feb 22 2018

.SYNOPSIS...
Issued at 400 AM EST Thu Feb 22 2018

Widespread significant flooding will continue over northwest
Indiana and southwest lower Michigan with record crests expected
on several rivers. A wintry mix of precipitation over east central
Indiana and northwest ohio will gradually end this morning. Highs
today will reach the upper 30s to lower 40s. A brief break in
precipitation is expected this afternoon and this evening but
light rain will return overnight into Friday. A brief period of
mixed precipitation is possible over the Tri State region of
Indiana, Ohio and Michigan late tonight. Low temperatures in the
lower to middle 30s will occur in the evening with slowly rising
temperatures overnight.

&&

.SHORT TERM...(Today and Tonight)
Issued at 352 AM EST Thu Feb 22 2018

Difficult and fluid near term forecast with pcpn type and amount
challenges into mid morning. Radar showing pcpn extending through
eastern half of forecast area but very dry low level air has
hindered pcpn reaching the ground so far from Fort Wayne to points
east. Evaporative cooling of supercooled water drops through this
dry layer was leading to some sleet in spots mixed with the rain.

First issue is with current advisory. Sfc temps have remained in
the mid 30s over the far southern portions of advisory area and
pcpn type has been predominately rain. Last several runs of hires
guidance keeps sfc temps above freezing through the morning and
top down procedures yield mostly rain with warm air aloft. After
collaboration have followed IND and cancelled the advisory in far
south. Could see brief periods of sleet before pcpn ends but not
enough to warrant an advisory.

Further north pcpn type and amounts more difficult. Finally seeing
lower levels saturate as higher returns on radar move northeast.
This also generating some sleet and cooling processes helping sfc
temps and dew points slowly fall. Using hires consensus blends for
temps this morning yields mainly sleet with some freezing rain in
remainder of advisory area. Fort Wayne and Defiance remain problem
areas as they are right on the cusp of freezing/frozen pcpn with
temps expected to fall to around 31-32 but also as back edge of
pcpn shield nears per latest radar trends. Have opted to not
expand advisory for now as much of this pcpn could be rain, sleet
and snow mix with less impacts than freezing rain. Will be
monitoring conditions through the early morning.

HRRR and RAP showing some redevelopment of pcpn next few hours
upstream which raises some concerns for additional pcpn mid
morning in the south and east. Subtle mid level jet couplet noted
in models around 12z with a coupled upper level jet over the
area. Models are keeping a mid level FGEN band across the region
and thinking hires guidance is picking up on additional
development with this forcing. Have seen recent uptick in pcpn
trends over southwest IL and will have to see if this trend
continues and moves northeast this morning. Collaboration
thresholds keep us from higher pops for now but did leave chance
in through mid to late morning to account for this additional pcpn
possibility later this morning.

Break in pcpn this afternoon and evening but more light rain
expected to develop and move back across the area overnight.
Models have trended toward the warmer solutions with rising temps
overnight but still a concern in the far northeast of a brief
period of freezing pcpn at onset with any evap cooling processes.
This will be especially true if breaks in clouds develop and
temps fall during the evening. Will have to watch 12z model trends
closely.

&&

.LONG TERM...(Friday through Wednesday)
Issued at 352 AM EST Thu Feb 22 2018

Main focus in long term continues to be on heavy rain potential
with system during first half of weekend. 00z model suite
primarily in agreement with heavy pcpn axis over central Indiana
but extending northeast through our southeast counties. NAM12 was
farthest north over central and northeast area. Generally followed
WPC and Superblend QPF for now but this is a strong, dynamical
system which often pulls moisture farther north as negative tilt
develops. No changes planned to ESF as it has latest trends
covered. May actually see a few days of dry weather following this
system for Sunday into middle of next week with above normal temps
in the 40s and 50s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday Morning)
Issued at 654 AM EST Thu Feb 22 2018

A sheared upper level short wave is interacting with low level
front to produce some light precipitation this morning. Isentropic
upglide may allow some of this light precip to make it as far
north as KSBN for a brief time this morning, but confidence is
low. Thermal and moisture profiles are supportive of some light
sleet and snow and did include mix at KFWA through mid morning
before changing to light rain before ending. Lower end MVFR cigs
or possibly IFR cigs are expected at KFWA this morning while
confidence in lower cigs is lower at KSBN. Rain will overspread
terminals tonight as low level moisture advection ramps up again,
with perhaps some marginal LLWS conditions toward the end of the
period. Deteriorating cigs expected tonight with trend to IFR and
possibly LIFR toward end of period.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Winter Weather Advisory until 11 AM EST this morning for INZ026-
     027.

MI...Flash Flood Watch until 1 PM EST this afternoon for MIZ077.

OH...Winter Weather Advisory until 11 AM EST this morning for OHZ016-
     024-025.

LM...NONE.
&&

$$

SYNOPSIS...Lashley
SHORT TERM...Lashley
LONG TERM...Lashley
AVIATION...Marsili


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