Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 050005

Area Forecast Discussion
National Weather Service Northern Indiana
705 PM EST Sun Dec 4 2016

Issued at 700 PM EST Sun Dec 4 2016

An area of snow will move through the region this evening and then
taper to light snow or perhaps some light drizzle before ending
overnight. snow totals will likely range from 2 to 4 inches over
northwest Indiana into far southwest Lower Michigan, with lesser
amounts elsewhere. More wet snow is likely Tuesday before much
colder air and lake effect snow arrive late this week.


.SHORT TERM...(This Evening through Monday)
Issued at 240 PM EST Sun Dec 4 2016

Water vapor shows strong short wave approaching with impressive
moisture feed originating from eastern Pacific. Closed upper low
over Mexico helping tap the Pacific moisture and throw it into the
southern CONUS while northern stream short wave is tapping this
influx. Result is widespread precipitation across the Midwest with
hourly liquid rates of 0.5 to 0.10 in per hour being reported.

Lower levels finally beginning to saturate locally this afternoon
with mixed precipitation occurring. Primarily rain south and snow
north as expected. Will see rain/snow line remain stationary for a
period but should slowly sink south this evening with subtle
cooling as weak sun angle diminishes further. Period of strong
system relative isentropic lift ahead of short wave to generate
good UVM for a 3 to 5 hour window and support moderate
precipitation rates with brief bursts of heavier rates possible.
Still looking at accums mainly on grassy and elevated surfaces of
1 to locally 4 inches with compaction and melting hampering
overall accums. Road temps this afternoon running in the mid to
upper 30s but expect some cooling this evening. Surface wet bulb
temps per RAP/HRRR/NAM hover around 33-34F this evening which may
help keep roads mainly wet. the higher snow rates
develop this evening will likely see a period where some snow
begins to develop on roads...especially on secondary and those
less traveled. No plans to issue advisory right now with no rush
hour to contend with and low relative impacts. Caution is urged as
bridges and overapasses will likely be slick as well. Evening
shift will be monitoring road temps and conditions in event
deterioration is more severe than currently expected.

A period of drizzle is possible on back side of pcpn shield as
mid layers dry quickly and low stratus is left trapped under
strong inversion. Have kept late tonight and early Monday dry but
soundings show a decent amount of trapped moisture lingering so
some freezing drizzle is not out of question. Otherwise stayed
pessimistic with cloud cover on Monday per 1000-925mb RH fields
but some breaks possible south in afternoon. Lowered temps several
degrees with more clouds and possible snow still on grassy


.LONG TERM...(Monday Night through Sunday)
Issued at 240 PM EST Sun Dec 4 2016

...Wet snow possible Tuesday then much colder with lake effect
snow still on track for later this week...

The NAM remains the western most solution on Tuesday with
ejection of upper low out of Mexico and through the Ohio Valley.
While models agree on opening this wave up and accelerating it
northeast...NAM is strongest and therefore further northwest while
GFS and ECMWF open wave faster and allow it to become absorbed in
southwest flow quicker. The question will be how far west pcpn
shield extends Tuesday morning and precipitation type on northwest
periphery. GFS has trended cooler with evap cooling as pcpn moves
into drier air. Have stayed with primarily light snow at onset
except for far southeast...then transition to primarily rain mid
day. Some small accums are possible before turning over to rain.

Arctic intrusion still on tap mid to late week. Few changes to
temps and lake effect snow grids for later periods with broad area
of likely to categorical pops downwind of the lake. If moisture
and trajectories remain favorable...significant accumulations
still possible with extreme instability as sfc-700mb delta Ts
approach 30 and upper trough over lakes provides favorable
synoptic background conditions.


.AVIATION...(For the 00Z TAFS through 00Z Monday Evening)
Issued at 700 PM EST Sun Dec 4 2016

More pessimistic with respect to IFR/LIFR ceilings overnight into
Monday morning as trapped low level moisture beneath strengthening
subsidence inversion fails to thin. Some midday/early afternoon
improvement as condensation levels lift with diurnal heating,
though maintain fueling/alternate criteria through the end of the
forecast period as concern that latest models/guidance a bit
overzealous in improvement/scattering out too soon.




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

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