Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 230903

Area Forecast Discussion
National Weather Service Northern Indiana
403 AM EST Thu Feb 23 2017

Issued at 400 AM EST Thu Feb 23 2017

It will remain unseasonable warm today into Friday. A frontal
boundary will cool the lakeshore area today where highs will only
reach the upper 40s. Well inland highs today will push well into
the 50s with even lower to middle 60s south of route 24 expected.
There will be a chance for showers late in the day today as the
frontal boundary becomes increasingly active as low pressure
approaches. Chances of rain Thursday will have increasing chances
for rain late as a low pressure system moves eastward from the
Plains. Severe weather is possible Friday afternoon and evening as
a cold front moves through the area. High on Friday will be in
the middle 60s to the lower 70s in spots, then plummet back to
seasonable temperatures for the weekend along with a chance for
snow showers.


.SHORT TERM...(Today and Tonight)
Issued at 355 AM EST Thu Feb 23 2017

The southern portion/trailing weak frontal boundary to sag
southeast through the cwa in near term/today as open/northern
Upper Great Lakes shortwave moves quickly into western Quebec by
this afternoon. Expect little more than wind shift/slightly cooler
yet still well above normal temps. Max temps rather tricky with
wide mos spread noted. Combination of far inland reach of lake
shadow/deeper colder air northwest cwa to a significantly more
shallow thermal wedge southeast though with greater coverage of
cu/stratocu expected. Surface front stalls along to just south of
cwa by evening and to provide focus for showers and provide focus
for developing showers late afternoon/more widespread with time
into overnight hours and perhaps a few thunderstorms as well as
initial zone of 1000-1500 j/kg MUCAPE lifts northward/weakening
with time though offset by increased forced ascent as low level
jet focus shifts into eastern IL 09-12 UTC Fri.


.LONG TERM...(Friday through Wednesday)
Issued at 355 AM EST Thu Feb 23 2017

Primary focus remains on first severe potential for the year this
Friday afternoon/evening. Multi-lobed/digging shortwaves over
intermountain region to congeal into single/strong/deepening mid
level low pressure that moves eastward through the plains/I80
corridor Friday and into western Upper Great Lakes by daybreak
Saturday. Meanwhile southeast Colorado surface low ejects through
central plains to southern Lake Michigan by 00 UTC Sat. Open tap
of GOMEX moisture surges n/ne with mid/upper 50s surface dewpoints
reaching cwa by midday Friday. Overspread of steepening mid level
lapse rates to 8 c/km should provide midday/afternoon MLCAPE on
order of 1000 to perhaps as high as 1500 j/kg. Strong helical flow
in lowest km appears relegated to north of cwa along retreating
warm frontal boundary. Still 150-200 m2/s2 values across CWA amid
45 to 60 kts deep layer shear. Initial early afternoon risk
appears to be a few damaging wind gusts, potential for prolific
amounts of sub to low end severe hailstones associated with
strongest updrafts in 8500ft wet bulb zero heights and low end
tornadic risk for any prefrontal supercells. Transition to
damaging wind potential event late afternoon/evening as 60-70 kt
mid level wswly flow impinges frontal boundary/squall line.

Thereafter...transition to ra/sn mix western third before daybreak
Saturday, then to all snow through the day on Saturday as
temperatures steady west/fall through the 30s east as 8H temps
plummet 20-22C/24 hours and have dropped temps several degrees on
Sat below optimistically warm blend. Lake enhanced/wraparound
moisture should be short-lived as system sweeps rapidly
northeastward and mixed layer/inversion heights dwindle through
Sat aftn/night. Thereafter low chance pops associated with mixed
ra/sn Sunday night into Monday. GFS strongest with system into
OH/TN Valleys, though do not anticipate more than nominal qpf in
this timeframe amid low amplitude broad mid level trofing across
CONUS. Higher chances for rainfall Tue/Tue night as western trof
sharpens and progresses into Upper Midwest/Western Great Lakes by


.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
Issued at 1245 AM EST Thu Feb 23 2017

Some significant changes to TAF`s to reflect drier low levels as
seen in observational evidence and latest hi-res guidance. NAM and
GFS still indicate potential for MVFR/fuel alternate conditions to
develop later this morning. Left in some high MVFR but confidence
is low and could remain VFR. Same story for much of the day. NAM
and GFS seem too aggressive with low level moisture profiles
based on current conditions and lack of any substantive moisture
advection. Will go with VFR and adjust later this morning if
necessary. Warm front crosses the area at the end of the period
with increasing chances for rain and lower flight categories.




LONG TERM...Murphy

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