IWX issues Area Forecast Discussion (AFD) at Feb 13, 2:37 AM EST231
FXUS63 KIWX 130737
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
237 AM EST Thu Feb 13 2025
.KEY MESSAGES...
- Snow will continue into the early overnight from northwest
Indiana into south central Lower Michigan, while a wintry mix
eventually changes to all snow across far northeast Indiana
and northwest Ohio. Hazardous travel conditions will likely
persist into the Thursday morning commute.
- The greatest total snow accumulations are expected from
northwest Indiana into southwest Lower Michigan while the
greater ice accumulations up to one quarter of an inch are
expected east of Interstate 69 and south of the Toll Road.
- There is the potential for another round of wintry
precipitation and hazardous travel late Friday through Sunday
and again Wednesday night/Thu.
&&
.UPDATE...
Issued at 839 PM EST Wed Feb 12 2025
Previous forecast thinking remains intact this evening, with no
major changes to messaging.
Surface obs/radar data indicate delineation of snow vs wintry
mix precip types extending roughly from just southeast of
Logansport to near Fort Wayne to near Wauseon Ohio. The
strongest axis of isentropic upglide will be exiting east to the
eastern Great Lakes over the next few hours, but this forcing is
being replaced by a fairly strong low-mid level frontogenesis
axis from south central Lower Michigan into west central
Indiana. Cross sections from near term guidance progs suggest
reduced instability atop this frontogenesis forcing, although
some indications of weak convective instability as opposed to
slantwise instability which would be more conducive for longer
sustained snowbands. From reports received so far, snow to
liquid ratios have been on low side in the 10-12:1 ballpark. A
special evening sounding from Valparaiso Univ depicts a very
deep layer up to 10k feet supportive of supercooled water
droplets that would be conducive for riming and lower ratios.
The DGZ from this sounding is also based very high (~ 4km).
These above factors still support snow to liquid ratios on the
low side, although may be higher for the shorter spurts of more
convectively driven cellular/small band features where vertical
motions are maximized. Based on some reports trickling in this
evening, it appears 2 to 4 inches of snow has fallen from far NW
Indiana into SW Lower Michigan, with a potential of an inch or
two additional before mid level dry slot becomes more dominant.
Meanwhile to the east, a wintry mix will continue and precip
rates associated with sleet/freezing rain will be augmented by
the eastward progressing 850-700 mb fgen axis. Best ice
accumulation potential appears to be in place through 06 or 07Z.
Have received reports of around one tenth of an inch of ice
accumulation across portions of NW Ohio through 02Z, with
another tenth to locally two tenths of an inch possible. This
may take total ice accretion near warning criteria across
portions of NW Ohio, but a few factors still support lower ice
to liquid ratios including relatively weak winds during time of
ice accumulation and sfc wet bulbs a little higher than would be
optimal for more efficient accretion. With really no change in
messaging at this point with general expectation of up to 0.25
inch ice accumulation, will stay the course for now with Winter
Weather advisories.
&&
.DISCUSSION...
Issued at 153 PM EST Wed Feb 12 2025
A PV hook approaches the area from the west during the afternoon
hours. Td depressions lower and reach 3 to 5 degrees this afternoon
and evening allowing precipitation to get underway. Some question on
how early this happens though with the RAP showing saturation around
18z where as the the NAM is closer to 21z. The later saturation
occurs, the higher the ceiling for road temperatures to get. This
plays a roll in when rain can begin accreting to roadways as
freezing rain. Indications are freezing rain begins between 20z and
3z this evening from northwest to southeast. Snow begins in the
northwest as early as early this afternoon and then begins pushing
southeastward. There still exists some uncertainty on where the
highest icing totals reside with one camp being from southern Henry
county southwestward to southeast Grant county and another camp
residing north of that. These totals reach around or just above 0.25
inch accretion of ice, but these will depend on that afternoon
window of how quickly accretion can get started. Models
indicate the better f-gen banding and perhaps some CSI towards
the 21z to 3z time where the stronger precipitation would
arrive. The HREF has a quick 21z to 00z timeframe when the
strongest snow pushes through just southwest of Lake MI. Gusty
winds around midday today are expected to relax some from around
25 mph once precipitation starts and any mixing layer that
might form collapses and then could reinvigorate early Thursday.
Given some of these uncertainties, had flirted with the idea of
an ice storm warning in the US-24 corridor, especially in NW
OH, but just don't have enough confidence on where the thin
swath resides and if it even gets to 0.25 inch. Additionally,
could see some power outages due to the weight of the ice
accretion, especially if it does reach the 0.25 inch total, but
think the relaxing winds will help to limit that this afternoon.
Will also continue the winter weather advisories for areas
where snow is the main ptype, generally north of US-6, where 3
to 6 inches of snow is likely. Still think this is enough to
affect the evening commute in those northern areas where precip
starts early enough. Lake effect snow begins moving down the
tear drop of the lake to affect areas just adjacent during the
wee hours of the morning on Thursday. Residence time isn't that
long and the low levels appear dry enough to limit
precipitation. Away from lake effect snow, could also see some
freezing drizzle work in as the DGZ begins to dry out after 03z
or so. This probably ends up with some light snow and moreso
just lake effect clouds. We will be colder on Thursday with
highs in the mid 20s to around 30 degrees and this may allow the
ice accretion to linger unless roads are treated.
Winds turn out of the south on Friday with surface high pressure now
to our east and this should shut off cloud cover and allow for
sunshine. Highs are not too far from where they end up on Thursday,
once again, in the mid 20s to low 30s. The area of warm advection at
the onset Friday night may be enough to set off snow if it gets
going early enough, warm air appears unencumbered enough to
potentially cause some mixing of sleet and freezing rain in the US-
30 corridor with a better chance of rain south of that. The
transition to the low pressure system being the main forcing takes
over Saturday night and a transition to lake effect snow happens on
Saturday. Given the path of the low pressure system to our south,
any initial rain is expected to change to snow, especially overnight
into Sunday with the deformation zone overhead and cool air wrapping
in. It may also occur earlier than that as the GFS shows a more
isothermal layer that may keep it snow. One issue that we've been
having all winter long has been getting systems to phase in time to
produce a good amount of snow in the area as opposed to just being
piecemeal and reducing output as a result. That may be an issue for
this storm too. So far, it looks like 2 to 5 inches of snow north of
US-30 Friday night into Saturday.
Yet another wave ejects off the Rockies for Monday night/Tuesday.
This one appears to dissipate before it arrives. It really lacks any
warm advection area. Still another wave may get its act together
between Tuesday night and Wednesday, but how wound up and phased it
gets is still question for that time period. Expect below normal
temperatures for the next work week.
&&
.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 147 AM EST Thu Feb 13 2025
Much colder and drier air will spread over northern Indiana
today behind the cold front. Conditions should become VFR near
or before 00Z.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Winter Weather Advisory until 7 AM EST /6 AM CST/ this morning
for INZ005>009-012>015-017-018-020-022>027-032>034-103-
104-116-203-204-216.
OH...Winter Weather Advisory until 7 AM EST this morning for OHZ001-
002-004-005-015-016-024-025.
MI...Winter Weather Advisory until 7 AM EST this morning for
MIZ078>081-177-277.
MARINE...Small Craft Advisory until 4 AM EST Friday for LMZ043-046.
&&
$$
UPDATE...Marsili
DISCUSSION...Roller
AVIATION...Skipper
Source:
IWX issues Area Forecast Discussion (AFD) at Feb 13, 2:37 AM EST---------------
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