Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 181737
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
137 PM EDT Tue Apr 18 2017

.SYNOPSIS...
Issued at 122 PM EDT Tue Apr 18 2017

Dry weather will continue the rest of the day today. However, as a
cold front approaches from the west and then stalls nearby,
clouds will be on the increase overnight and chances for showers
and thunderstorms will occur Wednesday and Thursday. The front
will finally push through on Thursday cooling things off for
Friday and the weekend. Temperatures falling back into the mid to
upper 50s tonight will be able to rise back into the upper 60s to
mid 70s for Wednesday.



&&

.SHORT TERM...(Today and Tonight)
Issued at 356 AM EDT Tue Apr 18 2017

Quiet weather for the short term today and tonight with low chances
of showers and storms across the far north and northwest late
tonight.

Easterly low level flow will gradually very today as broad low
level anticyclone across the eastern Great Lakes begins to shift
eastward. Significant moisture transport will not arrive until
later tonight, and a dry air mass will persist across the region
today. The combination of a decent amount of mixing today,
strengthening low level height gradient, and dry nature of air
mass should allow temps to rise well into the 70s again today for
most locations. Sfc winds veering to the southeast with gusts up
around 20 mph will suppress any lake breeze and allow this warming
to affect locations closer to the Lake Michigan shoreline.

For tonight, attention will turn to short wave evident on morning
water vapor imagery across the western Dakotas. This wave will reach
the northern Great Lakes by this evening allowing modest low level
jet across the mid MS Valley to work its way across the southern
Great Lakes/Ohio Valley region. Dampening nature of this trough
across the northern Great Lakes tonight will allow for only slow
eastward migration to low level cold frontal zone and have continued
trend from previous forecast in slowing down the onset of low
chance shower/iso thunder PoPs across the north and west
overnight tonight.

&&

.LONG TERM...(Wednesday through Monday)
Issued at 356 AM EDT Tue Apr 18 2017

Frontal boundary will likely stall across the local area on
Wednesday due to dampening nature of Great Lakes short wave.
Confidence in appreciable coverage of these showers in the morning
is on the low side, mostly of the isolated to widely scattered
variety. By afternoon, low level winds will likely exhibit some
subtle backing which could increase advective forcing, but hard to
latch onto much in terms of mid/upper forcing for the Wednesday
period as stronger forcing refocuses well west of the forecast
area as next more amplified eastern Pacific wave ejects out of the
northern Rockies. The stalling frontal boundary and cold Lake
Michigan waters should set up a classic very strong April thermal
gradient across the region with temps likely dropping into the 50s
near the lakeshore in the afternoon, with highs in the far south
possibly reaching into the upper 70s.

Forecast picture for Wednesday night/Thursday now becoming bit more
muddled and of lower confidence in terms of precip chances as slight
northward trend in aforementioned upstream wave and low level mass
features should keep heavier precip potential north of the forecast
area. Entire forecast area will be entrenched in warm sector by
later Wednesday night as warm front surges north, which will
complicate precip forecast. Remnant effects of elevated mixed
layer advecting northeastward also may cut down instability
magnitudes from previous indications for Wednesday night. Fairly
warm mid level profiles will limit any potential for sfc based
convection, except for possibly Wednesday afternoon across the
south but shear/forcing much less impressive at this time. Thus,
confidence in severe weather risk for Wednesday night has
diminished somewhat. Cannot completely rule out some isold hail
with elevated instability and if steeper mid level lapse rates
with EML can be realized however. Of higher confidence for
Wednesday night will be very mild conditions/high dew points
persisting through the night.

Mid level warm layer will get eroded on Thursday as mid/upper trough
translates eastward which will likely set up a narrow window of sfc
based instability. This may result in some convective wind
concern for eastern portions of the forecast area in narrow window
Thursday given much stronger wind profiles but confidence in this
risk is very low at this time given dependencies on timing short
wave track, uncertainties in instability magnitudes, and lack of
real sharp low level frontal convergence. Other story for Thursday
will be gusty synoptic winds and potential of some afternoon wind
gusts in excess of 30 mph.

No major changes made to the post-Thursday forecast with trend to
below normal temps looking reasonable. Medium range model
consensus still suggests portions of the area become affected by
deformation forcing with next southern stream cut-off system for
next weekend, but given sharp nature to low/mid level moisture
gradient, the Sat-Sun period will be prone to forecast deviations
over the next several cycles.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
Issued at 122 PM EDT Tue Apr 18 2017

With our region in an area between high pressure to the northeast
and low pressure to the northwest, this allows a low level jet to
approach later in the day today. VFR conditions coupled with
diurnal heating, should allow gusts between 17 and 22 kts to
reach the surface. Heading into the overnight tonight, a cold
front will stall just north of the region allowing warm-moist
advection and decreasing CIGs into Wednesday morning. Overnight
precipitation is a possibility, but don`t have enough confidence
in an exact location at this time and with so much driness in the
low levels, left it out. SREF probs and TAF MOS show chances of
CIGs making it into MVFR range at FWA and with increasing column
RH in the low levels, there is increasing confidence in this.

&&

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

$$

SYNOPSIS...Roller
SHORT TERM...Marsili
LONG TERM...Marsili
AVIATION...Roller


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