Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 141527
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
1127 AM EDT Mon Aug 14 2017

.SYNOPSIS...
Issued at 406 AM EDT Mon Aug 14 2017

One more day of fair weather is expected in our area today as
high pressure moves slowly east from the Great Lakes. Low
pressure over southern Minnesota this morning will move east
across southern Michigan on Tuesday with a trailing frontal
boundary dropping south into Indiana and Ohio, possibly causing a
few showers or thunderstorms. Shower and thunderstorm chances
increase Wednesday and Thursday as a low pressure system moves
northeast from the Plains. High pressure will build in behind this
system on Friday, providing dry weather. Temperatures will be a
bit above normal through Thursday, with highs in 80s and lows in
the 60s, then cool off to around normal on Friday.

&&

.UPDATE...
Issued at 1111 AM EDT Mon Aug 14 2017

Previous forecast appears to be in good shape with only minimal
tweaks to sky cover to account for current trends. A weakening
area of showers and thunderstorms across eastern Iowa downstream
of an approaching upper level wave should continue to weaken
through the morning with some high clouds overspreading northern
Indiana. Several hours of good diurnal heating in advance of this
wave may support some weak sfc based instability in the 500-1000
J/kg range, and feel that compromise between NAM/RAP instability
progs probably the wisest course of action at this time. Given
potential weak surface based instability cannot completely rule
out an isolated shower with approach of this wave, mainly north of
US Route 6 this afternoon which should be in better proximity to
weak upper forcing with this short wave. With low confidence in
occurrence and very limited coverage, will keep some silent 10-14
PoPs going across the north this afternoon and may need to
eventually add an isolated shower mention. Weak lake breeze
formation could also serve as focusing mechanism for an isolated
shower. Otherwise, highs today should reach into the lower 80s,
with decent mixing heights and weak low level warm advection.

&&

.SHORT TERM...(Today and Tonight)
Issued at 406 AM EDT Mon Aug 14 2017

Shearing out upr low over MN will move east across the upr Grtlks
today and tonight. In advance of this system, a wk shrtwv was
evident on water vapor movg across srn WI with radar/sfc obs
suggesting a few sprinkles associated with this feature. GFS conts
to indicate some showers will develop over our cwa today in
response to this system and wk low level waa and has a little
support from latest hires models. However, given very wk
instability in fcst soundings, believe we`ll have a few sprinkles
at worst this aftn and thus have kept fcst for today dry. Wk waa
should result in high temps a little warmer than yday, generally
in the lower 80s. Sheared out upr low will move ese across the wrn
Grtlks tonight as flow across the U.S./Canada begins to amplify.
This system may cause iso-sct showers/tstms to spread into nw
portion of the cwa late tonight.

&&

.LONG TERM...(Tuesday through Sunday)
Issued at 406 AM EDT Mon Aug 14 2017

Shrtwv will cont to move ese from MI to NY/PA Tue with a trailing
wk sfc cdfnt in its wake dropping south into nrn IN/OH and
stalling out as ridging aloft builds into the wrn Grtlks. Models
in decent agreement that moderate instability of 1000-1500j/kg
will develop along the wk sfc boundary over IN/OH in the aftn
psbly allowing iso-sct tstms to develop. This sfc boundary should
grdly strengthen as trof aloft and accompanying sfc low move e-ne
to the plains by tue ngt and Wed resulting in slow increase in
shower/tstm chances across our area in this timeframe. Better
chances for showers/storms Wed ngt-Thu as this system lifts ne
into the upr Grtlks with associated warm front lifting ne across
our area Wed ngt followed by a cdfnt movg from west to east across
the area on Thu. High pressure will build into the Midwest behind
this system providing dry weather Friday. Temps should be a bit
above normal through Thu and it will become more humid. A modest
cool down is expected behind Thu`s cdfnt with near normal temps
Friday.

Medium range models have large differences by next weekend with
ECMWF/GEM suggesting Thu`s shrtwv movg through the Grtlks will
transition to a deep trof over the ern U.S. by Sat while GFS is
much more progressive with this system and indicates another
rather strong shrtwv will move across the Midwest next weekend.
Given such large discrepancies at this time range, followed a
model blend which is close to climatology with a 20% chc of
showers and near normal temps.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday Morning)
Issued at 639 AM EDT Mon Aug 14 2017

Weak return flow will begin today as a high pressure area remains
over the region. For now, kept fog out as any fog should be very
brief and should not be operationally significant. There is an
outside chance for a shower or storm after 06Z at SBN, but have
kept activity out given only a small chance and low confidence.

&&

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

$$

UPDATE...Marsili
SYNOPSIS...JT
SHORT TERM...JT
LONG TERM...JT
AVIATION...Skipper


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