Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 140917
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
417 AM EST Sat Jan 14 2017

.SYNOPSIS...
Issued at 407 AM EST Sat Jan 14 2017

There is potential for a wintry mix of snow, sleet, and freezing
rain this morning, mainly south of US 24/US 224. Light ice
accumulations may occur. Otherwise, expect mostly cloudy skies
this afternoon with highs in the 30`s. 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.

&&

.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 shieldof
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 06Z TAFS through 06Z Saturday Night)
Issued at 1223 AM EST Sat Jan 14 2017

Subtle upr level trof movg through nrn stream flow across the upr
grtlks inducing inverted sfc trof movg along stalled frontal
boundary over the Oh valley. Low level theta-e advection/isent
lift associated with this system causing sct shower from central
IN wsw across MO. Bulk of this activity should remain south of FWA
but close enough to add a vcsh mention this morning. If precip
does reach FWA, prbly would be sleet initially and psbly freezing
rain later. Contd low level moisture advection should cause mvfr
cigs over central IL to spread into nrn IN by daybreak. With the
trof passage midday, low cloud deck should slowly move e-se out of
the area as dry nw flow develops allowing vfr conditions to
develop by eve.


&&

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

$$

SYNOPSIS...MCD
SHORT TERM...MCD
LONG TERM...MCD
AVIATION...JT


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