Area Forecast Discussion
Issued by NWS Northern Indiana

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS63 KIWX 181706

Area Forecast Discussion
National Weather Service Northern Indiana
106 PM EDT Tue Jul 18 2017

Issued at 105 PM EDT Tue Jul 18 2017

High pressure will keep conditions quiet through the rest of this
afternoon and tonight. Warm and humid overnight, with lows only
dipping into the upper 60`s to near 70. A weak disturbance will
bring a slight chance of showers and thunderstorms to the region
early Wednesday, mainly across the north and west. Highs will be in
the mid to upper 80`s. Heat indices will be in the upper 80`s and
low 90`s.


.SHORT TERM...(Today and Tonight)
Issued at 232 AM EDT Tue Jul 18 2017

Transition to mid-week warm-up underway as upper ridge begins to
expand eastward into the region. Resulting height rises along with
surface ridge shifting eastward bringing light SW flow into the
area will have temps well into the mid 80s today. First round of
upstream convection ongoing early this morning with downstream
diffluence influencing a back-building/regenerative nature to the
MCSs. Favored location for next round of convection appears to be
directed toward the northern plains/upper MS valley in vicinity of
right rear quadrant of 100kt upper jet and short wave impulse
that will have 50-55kt mid level speed max. As this MCS propagates
eastward along W/NW cloud bearing wind during the
afternoon...enhanced low level flow in the form of a decent
30-40kt nocturnal LLJ will feed up into it tonight and allow for a
slight SE forward propagating turn. CAMs trend has this a
decaying complex as it approaches our area after midnight as it
becomes orphaned from the better forcing.


.LONG TERM...(Wednesday through Monday)
Issued at 232 AM EDT Tue Jul 18 2017

Blended POPs yielding a slight chance in the far NW CWA Wednesday
morning which seems reasonable in light of short term discussion
of potential decaying MCS arriving. Renewed Pacific energy coming
onshore into northern California on Tuesday will ride up top of
plains ridge and provide ingredients for replay of convection
igniting in the northern plains/upper MS valley again on
Wednesday. Models indicating even more enhanced forcing as short
wave disturbance riding along upper ridge will have 60-70kts of
mid-level flow. Resulting nocturnal MCS will once again take SE
track toward our area bringing chance for storms to NW/N CWA after
midnight Wednesday night. Quasi-stationary surface boundary sags
slowly south into our area leading to multiple rounds of
convection possible toward the end of the week. Low predictability
of this pattern however once again warrants eliminating likely
POPs this far out in the forecast. Very warm and muggy Wed-Fri
with highs 85-90 and dewpoints in the lower 70s. Medium range
models indicating break in this pattern to occur toward the end of
the weekend. Upper low in eastern Pacific just off British
Columbia coast will come onshore as Aleutian low drops south. This
will suppress upper ridge and break down eastern extent as it
reaches great lakes region on Sunday. This should allow front to
clear the area and trend toward a dry start to beginning of next


.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
Issued at 105 PM EDT Tue Jul 18 2017

VFR conditions are expected at the TAF sites through Wednesday
afternoon. High pressure over the forecast area will remain anchored
in place for the most part, keeping winds light and variable
overnight. A weakening trough will move in from the west, and could
even kick off a few showers and thunderstorms after 12Z near KSBN.
Given the present weakening trends, left out of the TAF for now.
Expect mainly a wind shift to the west and maybe some SCT/BKN
afternoon cloud cover. KFWA could see some BR between 8Z-13Z, but
it`s likely to be brief and only drop down to MVFR. Winds should be
high enough at KSBN to preclude any BR/FG development tonight.





Visit us at

Follow us on Facebook...Twitter...and YouTube at: is the U.S. government's official web portal to all federal, state and local government web resources and services.