Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 241731

Area Forecast Discussion
National Weather Service Northern Indiana
1230 PM EST Fri Feb 24 2017

Issued at 420 AM EST Fri Feb 24 2017

It will remain unseasonable warm today. Severe weather remains a
possibility from mid to late afternoon into the evening hours as
storms develop ahead of a cold front moving through the area.
Highs today will be in the middle to upper 60s and even lower 70s
possible in northwest Ohio into east central Indiana.
Temperatures will then plummet back to seasonable levels late
tonight and continue through the weekend along with a chance for
snow showers.


Issued at 1125 AM EST Fri Feb 24 2017

Mesoscale Update...Initial showers/isol storms have either pushed
NE of the area or weakened as main warm front was now residing
across southern Lower Michigan. South of the front, much of the
forecast area was in a capped warm sector with temperatures in the
lower to middle 60s and dewpoints in the middle 50s (FWA already
shattered their record, now sitting at 68). Sufficient mixing has
been occuring of the higher low level wind fields to bring gusts
to 30 knots in several locations. Near the lake shore, combination
of lake shadow and proximity to front yields a much colder setup
with readings only in the mid 40s to near 50. Effective warm front
could pose a severe threat for locations mainly north of the toll
road with strongest shear expected to reside there. However, may
push just far enough north to push most impacts just north of the
forecast area.

Pre frontal trough has been agitated over the past few hours as
suggested by HRRR but capping in place has generally limited
development. Steepening mid level lapse rates may help to allow
more robust updrafts to punch what should be a slowly weakening
cap this afternoon (lightning strike now showing in Cass Co
Indiana). Can`t justify more than slgt chance to chance pops until
more expanded development occurs. 15Z HRRR suggests expansion of
convection along this trough and even more robust development
along the cold front, currently across Central Illinois as it
moves east. Effective shear in excess of 60 kts and expanding EML
should still make for pockets of damaging wind potential as well
as tornadic threat with any discrete cells. Situation will be
monitored closely. Only minor changes to SWODY1.


.SHORT TERM...(Today and Tonight)
Issued at 420 AM EST Fri Feb 24 2017

Difficult forecast wrt thunderstorm chances/coverage/severity
today. At present scattered showers and a few/isolated weak storms
along/north of warm frontal boundary. Cold Lake Erie marine layer
continues to drive westward into far nern IN and undercut
elevated mixed layer. Suspect scattered showers/storms to continue
to slowly lift northward and weaken as capped prefrontal warm
sector finally begins to overtake marine influence beyond 12 UTC.
Then afford a lull in precip chances as remain largely capped
until mid to late afternoon with culmination of strong eml 8.5-9
c/km with modest low level moisture pooled as only mid to upper
50s dewpoints expected. Will likely have to wait for strong forced
frontal ascent which lags upstream until about 21-22 UTC...once
the surface frontal wave now into northeast MO reaches southern
Lake Michigan/extreme sw MI. Scattered convection develops ahead
of southward trailing cold front amid strong 50 to 60 kts deep
layer shear across western cwa initially and likely merging into
linear segments/squall line with time and eastward progression.
Leading edge of increasingly strong mid level height rises and
divergent upper jet region to allow longevity/sustenance until
east/southeast cwa exit around 03-04 UTC. Low wet bulb zero for
potential large amounts of small hailstones associated with
updraft cores. But loading/melt/evaporative cooling amid already
strong mid level winds to present with heightened/primarily isold-
sct damaging wind risk, especially across eastern half of cwa in
latter part of event. Initial storms however may present with
supercellular aspects and low tornado risk across far northern cwa
in closer proximity to triple point/frontal boundary...especially
if aforementioned Lake Erie marine layer proves difficult to


.LONG TERM...(Saturday through Thursday)
Issued at 420 AM EST Fri Feb 24 2017

Continued with similar rapid transition to snow potential late
tonight/early Saturday. Otherwise little change to blended
approach with another similar/weaker tracked system with best
rain chances about Tue/Tue night. This system appears bounded in
time by much weaker/clipper systems before and afterwards and
nudged downward the sometimes overzealous blended pops.


.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
Issued at 1230 PM EST Thu Feb 23 2017

Low pres over ne IL will shift into sw MI by late aftn as trailing
cold front surges east this evening. Grungy warm sector wwd of
prefrontal trough bisecting cwa sw-ne slowing sfc based
destabilization underneath as yet formidable mid level capping
inversion. However approach of upper trough out of IA will lead to
erosion of this feature as better height falls spread east and
still expect convection to initiate over nw IN twd 20Z.

Otherwise current prefrontal convection continues to struggle yet
likely to serve as a focus point for sfc based storms as cold front
approaches this evening...east of KSBN terminal but west of KFWA.
Quick upscale growth expected with brief near severe potential twd
00Z at KFWA. Strong low level cold advection follows with widespread
mvfr conditions thereafter tonight along with likely snow showers
invof KSBN late.




LONG TERM...Murphy

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