IWX issues Area Forecast Discussion (AFD) at Oct 17, 2:35 PM EDT343
FXUS63 KIWX 171835
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
235 PM EDT Sat Oct 17 2026
.KEY MESSAGES...
- Widespread frost is expected tonight into early Sunday
morning. Low temperatures for locations along and east of
Interstate 69 are expected to reach near freezing. Patchy
frost is possible Sunday night and Monday night.
- An extended period of dry weather is expected to continue
through this work week as temperatures moderate to near normal
or just above normal.
&&
.DISCUSSION...
Issued at 230 PM EDT Sat Oct 17 2026
Clear skies and deep layer subsidence are expected to continue
tonight as Great Lakes/Ohio Valley remain positioned between
longwave ridging across central CONUS. An expansive low level
anticyclone from MO to the western PA will allow for winds to
quickly decouple this evening. The extent of temperatures drops
tonight is still a bit uncertain as low level thermal trough is
departing to the east this evening and will continue to
moderate. This should be overcome by ideal radiational cooling
condition this evening. Some weak southwest flow on back side
of the sfc high is possible across western Great Lakes later
tonight, but this should not have a dramatic impact on
temperatures. Previous forecast still appears on track with best
chance of mins at or just below freezing roughly along and east
of Interstate 69, with generally mid 30s elsewhere. Frost
advisories and freeze warnings remain in effect for tonight into
early Sunday morning.
The primary storm track Sunday into Monday will remain across
central Canada as broad longwave trough remains anchored across
northern tier of CONUS. Some upstream height rises across Upper
Midwest following departure of central Canadian short wave will
allow for sfc anticyclone to be reinforced across
southern/western Great Lakes early week. This could result in a
lower end patchy frost potential Sunday night and Monday night
as strong decoupling should compensate for slightly modifying
low level/near sfc thermal profiles. For the middle of the week,
a tendency for negative eastern Pacific upper height anomaly
should develop which will allow for downstream maintenance of
mean upper level ridging and little change in position of low
level anticyclone. A slow day to day temperature moderation is
expected in this pattern. The much drier airmass will maintain
its grip across the region given stagnant longwave pattern much
of this week, but given temperatures only slightly above normal
and weak winds through the period, significant fire weather
concerns are not expected.
Some lower forecast confidence exists for the Day 7 to 9 timeframe
with deterministic/ensemble guidance showing larger spread in
eventual eastward ejection of eastern Pacific negative height
anomaly. Some indications another fropa could be possible late next
weekend/early the following week, but this will depend on how the
eastern Pacific energy phases with broader northern stream trough.
A dry forecast has been preserved through this forecast valid
period.
&&
.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1239 PM EDT Sat Oct 17 2026
High pressure in place for the next few days will promote VFR
conditions, wind less than 10 knots and mainly clear skies.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Frost Advisory from 3 AM EDT /2 AM CDT/ to 9 AM EDT /8 AM CDT/
Sunday for INZ005-012>015-020-022-103-104-203-204.
Freeze Warning from 3 AM to 9 AM EDT Sunday for INZ006>009-017-
018-023>027-032>034-116-216.
OH...Freeze Warning from 3 AM to 9 AM EDT Sunday for OHZ001-002-004-
005-015-016-024-025.
MI...Frost Advisory from 3 AM to 9 AM EDT Sunday for MIZ078>081-177-
277.
MARINE...Small Craft Advisory until 4 PM EDT this afternoon for LMZ046.
&&
$$
DISCUSSION...Marsili
AVIATION...Brown
Source:
IWX issues Area Forecast Discussion (AFD) at Oct 17, 2:35 PM EDT---------------
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