IWX issues Area Forecast Discussion (AFD) at Jan 5, 8:57 PM EST692
FXUS63 KIWX 060157
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
857 PM EST Sun Jan 5 2025
.KEY MESSAGES...
- A winter weather advisory remains in effect for snow along and
south of the SR 18 corridor tonight.
- Remaining cold for the week ahead with highs in the 20s and
lows approaching single-digits at times.
- Lake effect snow showers spread well inland Wednesday.
&&
.UPDATE...
Issued at 840 PM EST Sun Jan 5 2025
Just some minor tweaks made to the going forecast, but overall
very little difference in forecast thinking this evening. Main
isentropic forcing push has largely bypassed the the local area
to the south and southeast as a stout easterly low level flow
component has kept low level theta-e gradient anchored just
south of the local area. This effect also appears to be
amplifiedby an elongated west-east low level diabatic PV
anomaly from SE Missouri into southern IN. This PV anomaly has
been enhanced from upstream precip shield over past 18 hours,
with tendency for maintenance of stronger easterly component to
the north of this diabatic anomaly across northern Indiana.
This induced low level flow is also frontogenetic in nature
which is enhancing the low level easterlies preventing good
northward moisture transport into the local area.
Over the next few hours, expecting to see a transition to some
banded snow as mid/upper level baroclinicity strengthens
downstream of an an approaching upper level trough with slight
negative tilt. Model time/height sections do indicate most of
the lift during the overnight hours being tied to axis of
700-500 mb frontogenesis forcing that should maximize from west
to east across the area in the 03Z-09Z timeframe. Guidance cross
sections do indicate some reduction in static stability co-
located with this forcing, but highly elevated nature of the
forcing, and little northward movement in low level moisture
gradient, suggests that this should result in just a few tenths
of an inch of accumulation where these mid/upper level fgen
bands are induced. Given this forcing, did add just some low
PoPs to the north of the Winter Weather Advisory area overnight.
Did consider removing winter weather advisory headlines across
Jay, Blackford, Grant Counties, but given a few more hours of
isentropic forcing this evening followed by weak deformation
precip in the overnight, cannot rule out a few inches of snow
accumulation across these areas. Light snow accumulations
coupled with cold overnight lows around 20, could create some
hazardous travel conditions for the Monday morning commute.
Thus, previous headline has been maintained with just a
continuation of the trend in snow amount reductions with the
evening update.
&&
.DISCUSSION...
Issued at 104 PM EST Sun Jan 5 2025
Potent winter storm over KS will eject ewd into MO tonight and
shear out through the mid Atlantic by late Mon. Sharp and dry
mid lvl confluence zone across the srn lakes swd of blocking
upper low over ern Canada will steer this sys well south of the
area near term. That said still some signs that very dry
boundary layer will saturate before intensifying mid lvl forcing
breaks down to afford a period of accumulating snow far south
late tonight. Prior update addressed this and that thinking
still holds.
Cold advection in wake of this sys and long axis fetch over lake
Michigan looks to support a vigorous band of lake snow early Mon
toward the wrn shoreline which then transitions slowly ewd
reaching far nw zones late Mon and diminishing quickly there
after as lake based thermal trough shuts down.
Next following nrn stream disturbance sharpens swd out of wrn ON
early Wed and through the OH valley early Thu. Expect a band of
light snow to accompany this sys late Wed followed by spirited
lake effect Wed night into Thu morning along with a renewed
push of cold air.
Complex upper pattern presents late period as large amplitude
trough develops through the central plains ahead of competing
nrn/srn stream disturbances. High spread in how this evolves
late week into next weekend and see little reason to stray from
blended guidance at this range.
&&
.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 650 PM EST Sun Jan 5 2025
A potent upper level low across Missouri will continue to
migrate eastward tonight and will becoming increasing influenced
by upper level deformation flow across the Ohio Valley.
Northward moisture transport downstream of this feature has been
limited in its northward extent, in part due to broad west-east
elongated low level diabatic PV anomaly from upstream precip
shield keeping easterly flow locked in place. Perhaps best
chance of some light snow for terminals will be in the 05Z-10Z
time frame with an uptick in mid-upper level frontogenesis.
Some question as to the efficiency of this forcing given its
highly elevated nature and marginal low level moisture. However,
cannot rule a few bands of light snow from this forcing that
could produce some light snow accums of a half inch or less. The
inherited PROB30 group at KFWA still seems appropriate during
the overnight hours. By 12Z, this mid/upper forcing will shift
into Ohio ending measurable precip threat. Light winds to begin
the period will become gusty out of the northeast into the 15 to
20 knot range late tonight into Monday. Lake effect show
showers on backside of this system should remain well west of
KSBN through this forecast valid period.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Winter Weather Advisory until 10 AM EST Monday for INZ032>034.
OH...None.
MI...None.
MARINE...Small Craft Advisory from 4 AM Monday to 4 PM EST Tuesday for
LMZ043-046.
&&
$$
UPDATE...Marsili
DISCUSSION...T
AVIATION...Marsili
Source:
IWX issues Area Forecast Discussion (AFD) at Jan 5, 8:57 PM EST---------------
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