Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 170146

Area Forecast Discussion
National Weather Service Northern Indiana
946 PM EDT Fri Mar 16 2018

Issued at 210 PM EDT Fri Mar 16 2018

A wintry mix will move into areas along and south of the highway 24
corridor late tonight into Saturday morning before ending. Light
snow and ice accumulations are possible. Temperatures will warm into
the 40s by afternoon with clearing skies. Pleasant weather is
expected on Sunday, with temperatures rising into the lower 50s
under bountiful sunshine.


Issued at 945 PM EDT Fri Mar 16 2018

Mixed precipitation along with a few isolated thunderstorms
continue to affect much of western Illinois and eastern Iowa this
evening. This precipitation shield has developed downstream of
large scale upper level low across the Central Plains in a zone
of strong low level moisture convergence. Local area remains on
the dry side of this intense moisture gradient this evening, but
low level moisture convergence axis will gradually overspread
especially southwest half of the forecast area overnight. This
will also be accompanied by approach of lead short wave associated
with mid/upper level speed max, and axis of modest 850-750 mb
fgen forcing. Above factors will support a band of mixed
precipitation overspreading the area from west to east overnight,
particularly across southwest half or southwest two thirds of the
area due to aforementioned moisture gradient. Precip rates along
this band of strongest forcing may also be augmented by fairly
steep elevated lapse rates moving in later tonight.

Current thinking is that shearing nature of upper level wave late
tonight into early Saturday and initially very dry low levels
will make it difficult for any significant elevated warm layer and
freezing rain threat to reach that far northward across the area,
with best potential of freezing rain/ice accumulation across the
current winter weather advisory area. A mix of snow and sleet is
expected immediately north of this area, with a slushy snow/sleet
accumulation of an inch or less. Will hold off on expanding
advisory at time time with lesser confidence in notable impacts
where snow/sleet mix is expected. May need to watch for some
northward adjustment to freezing rain mention late tonight as some
mid level drying lifts northward, but precip rates should also
begin to diminish as this occurs. Have made just some minor
modifications to ice/snow accumulations, but general theme of
previous forecast will be left intact.


.SHORT TERM...(Tonight and Saturday)
Issued at 210 PM EDT Fri Mar 16 2018

Intense/deep cyclone over nw KS will open and shear ewd into the wrn
OH valley late tonight. Leading arc of warm advection driven
precipitation expected to overlap sw zones generally in the 06-12Z
timeframe which coincides closely with prior issued WW.Y. 12Z
guidance as a whole fairly agreeable although troubling detail
differences exist with extent/newd spread of measurable QPF owing to
various model progged intensity differences/timing of warm conveyor
belt shutdown locally. However doubt penetration of precip shield
north of the highway 30 corridor feasible given current dryness noted
within sfc ridge axis (ref 12Z DTX raob). However could see an
argument to spread WW.Y to include Marshall through Allen counties
in nodded agreement with RAP/HRRR trends especially in context of
much colder sfc temps invof highway 30 corridor versus highway 24
corridor. Nonetheless without a wider consensus will hold pat and
defer to evening shift.

Precip shunts rapidly sewd Sat morning with aftn clearing west-east
in the aftn. Late insolation should equate to similar max temps as


.LONG TERM...(Sunday through Thursday)
Issued at 210 PM EDT Fri Mar 16 2018

Short amplitude ridging spreads east into the Great Lakes Sunday
ahead of nearly identical deep cyclone winding up across Kansas
again Mon night.

A substantial amount of height suppression aloft within the nrn
stream through ern Canada exits to favor this sys tracking further
south invof the OH river Mon night-Tue. However nrn extent of
significant precip shield likely to clip far srn zones with another
bout of mixed precip potential south of the highway 24 corridor, if
not further north based on a bit faster newd trending ejection and
slower intensity decline and bears close watching.

Quite thereafter through DY7 Thu as cold nrly flow redevelops
through the ern US within deep ern NOAM upper trough.


.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
Issued at 749 PM EDT Fri Mar 16 2018

An expansive mid/high level cloud shield has overspread northern
Indiana this evening downstream of large upper level system
spinning across the central Plains. Easterly low level flow
continues and this will continue to promote a very dry air low
level air mass through the early parts of the overnight hours.
Low level winds will begin to veer late this evening with
increasing low level warm advection forcing, but warm front is not
expected to make significant northward progress. Strong moisture
convergence and increasing upper level forcing overnight should
allow precip to overspread northern Indiana, mainly south of US
Route 30. Better chance of freezing rain is expected to remain
south and west of the terminals, with confidence in any measurable
precip at KSBN on the lower side. Confidence remains somewhat
higher for some light snow accumulations of an inch or less at
KFWA late tonight into very early Saturday morning. Precip will
diminish Saturday morning as upstream wave shears rapidly. With a
strong south-north moisture gradient developing tonight-early
Saturday, terminals are expected to remain with VFR low cloud


IN...Winter Weather Advisory from 4 AM EDT /3 AM CDT/ to 9 AM EDT /8
     AM CDT/ Saturday for INZ013-015-020-022>027-032>034.




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