Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 140942

Area Forecast Discussion
National Weather Service Northern Indiana
442 AM EST Sun Jan 14 2018

Issued at 432 AM EST Sun Jan 14 2018

Quiet but cold weather is expected today with high temperatures
near 20 degrees. A clipper system will bring a widespread 2 to 3
inches of snow late tonight into Monday, with areas closer to Lake
Michigan seeing amounts around 4 inches. Another lake effect snow
event will develop Tuesday into Wednesday with the possibility of
several inches of additional snowfall in the favored snowbelt
region. Warmer weather is expected by the weekend.


.SHORT TERM...(Today and Tonight)
Issued at 431 AM EST Sun Jan 14 2018

Quiet but cold start to the day. Lake effect clouds drifting east
and north and mainly confined to Michigan and Ohio counties early
this morning. Clear skies and light winds outside of cloud plume has
led to temperatures falling into single digits. Expecting a
continued slow drop through daybreak with west to southwest areas
seeing temps in single digits below zero. High pressure will drift
across the area today with plenty of sunshine and light winds. Highs
will reach near 20.

Clipper system will quickly drop out of southern Canada today and
into the upper Midwest tonight. Weak system relative isentropic lift
will develop but flow remains light through the period leading to
sustained weak lift from mid evening tonight through Monday morning
ahead of main trough. Mixing ratios remain between 1 and 2 g/kg
through entire event. Light snow will develop and spread east this
evening and overnight. Strong 100-110kt cyclonically curved jet
streak to round base of upper trough late tonight with left front
exit region over our area providing ideal diffluence aloft and aiding
in increased synoptic lift through Monday morning. Bufkit soundings
show deep DGZ but also still indicating best vertical velocities
remaining near the upper portion of snow growth zone and
saturation remaining below 100 percent. Both of these factors
should limit dendritic growth and help keep snow ratios near or
just above 15:1. Soundings do suggest a period Monday morning
where lift and DGZ become better aligned and this likely around
time of jet streak passage and brief intensification leading to
some better snow rates. Moisture does remain quite limited with
this system with no GOMEX moisture influx. Above parameters along
with deep PVU intrusion should help overall efficiency of snowfall
despite lack of moisture. Models have been quite consistent with
QPF values around 0.2" on average for the event. This still looks
like general 2 to 3 inches across the area with some slightly
higher amounts in the northwest where lake enhancement aids
moisture influx.

No advisory being issued with this package since this is a marginal
event but also in middle of what has been an active winter season
in most locations. Intensity of snowfall looks to be light through
the event and accums will be spread over 10-12 hours so road crews
should be able to keep up and limit impacts outside of those going
too fast for conditions.


.LONG TERM...(Monday through Saturday)
Issued at 431 AM EST Sun Jan 14 2018

Light snow should be diminishing late Monday into Monday night.
Exception will be in the far north where residual trough in wake of
synoptic sfc low will lay out west to east. Approach of upper low in
addition to weak convergence along boundary and lake enhancement
should keep snow showers going through the night. Models have
shifted location of this trough southward from previous runs but
still think Type VI mesolow formation over south central Lake
Michigan will occur followed by intense single band. Impressive
925mb wind trajectories perfectly aligned with cyclonically curved
lake late Monday night leading to near ideal fetch length and
moisture influx into single band. Flow then backs on Tuesday with
Lake Superior connection providing pre-conditioning and keeping snow
showers going. Sfc-850mb Delta Ts should be well into 20s and 0-2km
ThetaE lapse rates between -1 and -2 K/km. Only negative is a fair
amount of shear in the cloud layer which could disrupt vertical
development. Models also differ on location of surface trough and
trajectories coming onshore. This will have to be watched closely
with possibility of headlines being needed for Tue and Tue night.

Remainder of forecast rather quiet with warming trend still on track
for late week and next weekend. A lot of model differences
concerning storm system in middle of country for next weekend so
just some very low pops for now in day 7.


.AVIATION...(For the 06Z TAFS through 06Z Sunday Night)
Issued at 1228 AM EST Sun Jan 14 2018

VFR with mainly clear skies and light winds today as brief
shortwave ridging works through. Conditions do deteriorate with
light snow toward the end of the TAF cycle at KSBN and likely just
after the 24 hour period at KFWA as elevated warm advection wing
overspreads in advance of a clipper system.




SHORT TERM...Lashley
LONG TERM...Lashley

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