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fxus63 kiwx 211925 

Area forecast discussion
National Weather Service northern Indiana
225 PM EST Tue Feb 21 2017

issued at 225 PM EST Tue Feb 21 2017

As winds becoming light tonight, residual moisture along with
cooling temps will lead to patchy dense fog development after
midnight. On Wednesday, fog will burn off leading to sunshine and
record warmth. Clouds will fill back in Thursday as a deep low
pressure system begins its trek towards the region out of the
plains. With increasing moisture, rain chances will increase
towards evening Thursday with some thunder possible at night and
especially Friday. Severe thunderstorms are possible Friday
afternoon as a strong cold front sweeps across the area.
Temperatures will be above normal for this forecast period with
highs around 70 Wednesday and in the 60s Thursday and Friday.
Behind the cold front Friday night, temperatures will return to
near normal and some back end snow showers are possible Saturday.


Short term...(this evening through wednesday)
issued at 225 PM EST Tue Feb 21 2017

Potent srn stream SW cutting off over the lower MS
valley will amplify sewd into the Gomex late tonight. Inverted sfc
trough extending north into the lakes in the process of washing out
aiding in rapid decay of prior rainband.

Primary near term challenge is erosion of cloud plume overhead and
extent of temp dropoff overnight. Developing light return flow along
with current unseasonably high dewpoints would suggest MOS implied
dense fog development late tonight...esp north half on track given
thinning cloud canopy NW and will add mention.

Morning fog will lift out and burn off quickly Wed morning as
renewed low level thermal troughing builds in out of the Central
Plains. Given expected insolation and modest mixing...most locations
will flirt with 70...setting new record highs as sbn and FWA.
Current records are 66/1922 & 67/1922 respectively.


Long term...(wednesday night through tuesday)
issued at 225 PM EST Tue Feb 21 2017

Unprecedented stretch of record warmth to continue through Fri as
deep layered cyclone develops across Iowa. Deep mixing within
unseasonably strong low level thermal trough should again promote
widespread mid to upper 60s both Thu and Fri which will again meet
or exceed prior records for the date at both sbn & FWA.

Primary uncertainty at this time range is ewd progression and timing
of strong/deep frontal zone. Robust downstream deep layer shear
impressive esp given the date yet severe threat will hinge on degree
of sfc based destabilization within the broad warm sector over the
Ohio Valley and srn Great Lakes. Will follow general uptick in blended
pop guidance esp Fri aftn-Fri evening given good Med range based

Otherwise brief cold advection Wing wraps east under remnant mid
level deformation zone Sat with a period of lake enhanced snowfall
likely. Daytime temps not particularly cold with any minimal
accumulations relegated to non-pavement surfaces and of little

Thereafter return flow develops in earnest Mon ahead of next
vigorous disturbance digging into the srn rockies. Temps expected to
moderate to well above normal again by dy8 (tue) if not sooner along
with substantial increase in rain chances as Gomex opens wide.


Aviation...(for the 18z tafs through 18z Wednesday afternoon)
issued at 1223 PM EST Tue Feb 21 2017

Cold front continues to push through the area this afternoon. Noting
some dryness in the low levels allowing for less precipitation
and VFR conditions across the area. Also, noting some IFR cigs and
MVFR visby in north IL, but feel the wind direction and slow movement
of the front will keep those west of the area. Winds will be able
to become more southerly at the taf sites as the front washes out
into the early overnight. Attention then turns to fog
possibilities for Wed morning as winds die out, nocturnal cooling
takes place and residual low level moisture gets trapped in
subsidence. FWA/sbn could reach into IFR and even LIFR fog as a
result. Clouds will then start clearing on Wednesday as drier air
works in.


Iwx watches/warnings/advisories...


short term...T
long term...T

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