Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 150444

Area Forecast Discussion
National Weather Service Northern Indiana
1244 AM EDT Fri Sep 15 2017

Issued at 816 PM EDT Thu Sep 14 2017

Mostly clear skies are expected overnight as an upper level
disturbance continues to pull away from the region. Areas of fog
will likely develop once again tonight, with some patchy dense
fog a possibility early Friday morning. Friday morning low
temperatures will be in the middle 50s, warming into the upper 70s
to lower 80s by afternoon. The warming trend will continue into
the weekend with highs in the lower to mid 80s for Saturday and
Sunday. The next chance of showers and thunderstorms will arrive
for Sunday afternoon through Monday.


.SHORT TERM...(This Evening through Friday)
Issued at 346 PM EDT Thu Sep 14 2017

Quiet weather to continue in the short term with the primary near
term concern on fog potential once again later tonight into early
Friday morning.

Widespread dense fog earlier this morning has mixed out to low
cloud deck and has scattered across much of western half of the
forecast area. Low clouds will maintain longer duration across far
northeast Indiana and northwest Ohio in closer proximity to
remnant low level cyclonic circulation. Expecting gradual
decreasing coverage of these low clouds across the east but have
some lower confidence in low cloud coverage duration across these
locations this evening as some near term model guidance hangs
onto higher low level RH into the evening.

Overall stagnant/stable wave pattern will lead to some potential of
patchy fog formation once again tonight. Some favorable factors
for fog potential tonight include continued dry mid level air,
relatively high crossover temps, and continued weak wind field.
Some weak return southerly flow is expected late tonight however
as low level anticyclone slowly nudges eastward. Given above
factors did add fog mention again tonight, with greatest coverage
expected across eastern half of the forecast area where crossover
temps may hold up a bit higher this afternoon due to longer
duration of low clouds/weaker mixing. Some patchy dense fog is
possible once again, although currently not expecting dense fog to
be as widespread as this morning.

Upstream upper level ridge will build into the region on Friday as
it amplifies, with mostly sunny/partly cloudy skies. Thermal
advective pattern remains weak through Friday in this stagnant
pattern, but good deal of insolation on Friday should allow high
temperatures into the 75 to 80 degree range.


.LONG TERM...(Friday Night through Thursday)
Issued at 346 PM EDT Thu Sep 14 2017

For Friday night through the weekend, main synoptic feature of
interest will be evolution of large scale upper trough across the
Pacific Northwest this afternoon. Stronger low level moisture
transport and frontal convergence will remain well west of the
local area through Saturday night across the Plains. The next
chance of rain showers should hold off until Sunday afternoon/night
when the strong upper level trough lifts northeast across south
central Canada, eventually dragging weak cool front southward
across the southern Great Lakes. Did maintain low-mid chance PoPs
across the northwest ahead of this front on Sunday due to some
expected pooled pre-frontal moisture. Did maintain an isolated
thunder mention Sunday/Sunday evening, but upper ridge in place
across the area will not be fully dampened by this wave, and wind
shear will remain quite weak. Not expecting any severe threat at
this time due to the combination of weak instability axis with
prefrontal moisture axis and weak shear.

Cold frontal boundary will not progress significantly southward on
Monday as forcing lifts across Hudson Bay area, but additional
weak short waves in southwest upper flow may result in periodic
stronger warm advection episodes and had to broadbrush chance PoPs
for Monday night/Tuesday. Also have introduced chance PoPs for
midweek with some indications in medium range models of stronger
short wave lifting across Mid MS Valley, resulting in eastward
translation of stronger low level jet into the region. Confidence
remains on the high side in terms of a return to above normal
temps by midweek after weak early week fropa.


.AVIATION...(For the 06Z TAFS through 06Z Friday Night)
Issued at 1240 AM EDT Fri Sep 15 2017

Main concern conts to be vsbys this morning. Wk pressure gradient
over the area combined with shallow low level moisture should
result in fg/br developing early this morning. Latest model
guidance conts to suggest low level moisture a little more
plentiful and pressure gradient a little weaker at fwa than sbn,
so previous tafs of lower visibilities at fwa still seem
reasonable and no sgfnt changes planned with tempo ifr at sbn and
lifr at fwa expected. Given shallow moisture over the area,
fog should burn off quickly after sunrise, followed by just sct
diurnal cu later today. Southerly pressure gradient expected to be
a little stronger tonight which should keep vsbys from dropping
as low as this morning, though at least some mvfr restrictions
still psbl after 06z.




SHORT TERM...Marsili
LONG TERM...Marsili

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