Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 141724
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
1224 PM EST Sat Jan 14 2017

.SYNOPSIS...
Issued at 1034 AM EST Sat Jan 14 2017

Periods of freezing rain, freezing drizzle, and sleet will
continue through early afternoon roughly along and south of a line
from Monticello to Marion to Portland Indiana. Light ice
accumulations may occur. Otherwise, expect mostly cloudy skies
this afternoon with highs around the 30 degree mark. Lows tonight
will be in the 20`s. After a brief break in precipitation tonight
and Sunday, expect another chance for a wintry mix and light icing
late Sunday night and early Monday morning. Rain will move in
Monday afternoon and continue through Tuesday night. Rainfall will
lead to additional rises and possible flooding on area rivers.

&&

.UPDATE...
Issued at 1032 AM EST Sat Jan 14 2017

Not much change to previous forecast with the only tweak to
previous grids to slightly expand duration of higher PoPs across
the extreme south through early afternoon. A weak upstream short
wave across central Illinois interacting with strong pre-existing
baroclinic zone, should allow for period of precip to be
maintained through early afternoon across the far south. Flow has
veered more westerly with weak thermal advections at current time,
but weak warm layer will persist through the day which will
continue to support freezing rain potential. Precip should
diminish after 19Z or 20Z as weak low level trough shifts east of
the area allowing drier low level air to be advected across the
south. With ice accumulations expected to be minor, and
confidence in impacts on the low side for local area will continue
with SPS for now to highlight light ice potential through about
19Z.

&&

.SHORT TERM...(Today and Tonight)
Issued at 407 AM EST Sat Jan 14 2017

The biggest question for the short term forecast is chances for
light icing this morning as another wave passes south of us. We
had a bit of inconsequential light snow/sleet/freezing rain mix
along the southern border of our CWA earlier with the initial
passing shortwave. IND was observing light freezing drizzle around
330 AM EST. Guidance is still conflicted as to what will happen as
this second wave moves in...but most of them have trended slightly
southward. For now, kept slight chance to low chance pops over our
southern CWA through the early afternoon, but I`m not feeling
really confident about it. The pop/qpf gradient was pretty tight,
so it wouldn`t take much of a shift to send the forecast awry.
Additionally, since we saw the mix of snow/sleet with the freezing
rain this morning, and Max TW`s aloft only climb to around 2-3C at
their warmest today, I wonder how much of an impact the precip
will really have on driving conditions. At the moment, there are
freezing rain advisories along our southern borders, but did not
feel confident enough to issue one for our area. If it looks like
the precipitation shield is lifting further northward than
expected and freezing rain is observed, dayshift can consider
whether an advisory is appropriate. At this point, the best
chances for any light icing this morning would be south of US
24/US-224.

Otherwise, surface high pressure builds into the area late this
afternoon and tonight, ending all precipitation chances for our
CWA. High temperatures will rise into the 30`s. Lows will drop
into the 20`s overnight.

&&

.LONG TERM...(Sunday through Friday)
Issued at 407 AM EST Sat Jan 14 2017

After the quick break in precipitation Saturday night into
Sunday, the next active weather period begins. The next low
pressure system will begin to impact our area Sunday evening
through Wednesday.

Both the ECMWF and GFS are consistent with the overall synoptic
pattern associated with this system through Monday morning as the
closed upper level low lifts into the desert southwest. From there,
the GFS takes both the upper low and the associated surface low on a
track that is further eastward than the ECMWF. Both models have the
low being absorbed into the northern stream trough near IA (or IL
per GFS) by 06Z Tuesday. The main difference is through Wednesday
morning...where the ECMWF lifts the trough/upper low over the UP of
MI with a secondary trough in it`s wake....and the GFS takes it over
Lower MI...with a building ridge in it`s wake. These differences
will lead to variances in the timing/amounts of precipitation in the
forecast for the Sunday night into Wednesday time frame. As a result-
left the consensus pops in for now...except for the highest chances
for precipitation that I increased Monday night into Tuesday.

As far as what this means for sensible weather, it looks like both
the ECMWF/GFS have backed off on precipitation chances late Sunday
afternoon...keeping them just south of our CWA border once again.
The only exception may be the far southwest/White County, IN. If
precipitation manages to develop Sun afternoon/early evening it
would be in the form of snow or sleet.

Sunday night into Monday morning will be the time frame to watch for
mixed precipitation again as weak isentropic ascent on 290K sfc
develops over the region. As mentioned in earlier
discussion...limitation is initial dry air...with deeper moisture
not arriving until after 6Z-9z. From forecast soundings...it
appears that we`ll see another wintry mix of snow/sleet/freezing
rain initially before it quickly transitions to rain from
southwest to northeast. The Monday morning commute could be
hazardous due to icy conditions.

Attention then turns to Monday afternoon into Wednesday...our best
chances for precip. Plenty of warm air and moisture is lifted straight
into the CWA from the Gulf of Mexico...so we`ll see a broad shield
of rain spread across the CWA. With additional rainfall
expected...flooding potential remains along area rivers.

Wednesday afternoon into Thursday should remain dry as a building
ridge aloft moves overhead. We see high temperatures climb from the
40`s Thursday to the 50`s and even maybe low 60`s on Friday/Saturday-
which is well above normal for this time of year. A few passing
waves bring additional chances for rain showers Friday and Friday
night.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
Issued at 1217 PM EST Sat Jan 14 2017

The combination of a weak upper level disturbance progressing
through the region and a weak inverted surface trough lingering
across northeast Indiana has allowed for some deterioration in
cigs over past hour or two at KFWA. Not expecting IFR conditions
to be of very long duration as eventual eastward progression of
sfc trough through 20Z will allow drier air to begin to advect
southeastward. Any precip in the form of freezing drizzle would be
very light and limited to the 18Z-20Z timeframe, and still
expecting the bulk of freezing rain/freezing drizzle to remain
south of KFWA. Otherwise for the remainder of the day winds will
be generally light and variable, but beginning to favor light
northwest later this afternoon/early evening. Surface high
pressure will build into the region today which could allow for
some patchy fog formation at KFWA, in closer proximity to slightly
better near sfc moisture trapped beneath the inversion.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

UPDATE...Marsili
SYNOPSIS...Marsili/MCD
SHORT TERM...MCD
LONG TERM...MCD
AVIATION...Marsili


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