IWX issues Area Forecast Discussion (AFD) at Jan 29, 3:24 PM EST124
FXUS63 KIWX 292024
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
324 PM EST Wed Jan 29 2025
.KEY MESSAGES...
- Gusty west winds will diminish early this evening.
- Mild conditions are expected Thursday with highs well into the 40s.
- Widespread rain is expected late Thursday into Friday.
Rainfall amounts in the quarter of an inch to three quarters
of an inch range are expected.
- Some snow may mix in toward end of precipitation Friday north
of US 24, but confidence in any snow accumulation remains
low.
&&
.DISCUSSION...
Issued at 324 PM EST Wed Jan 29 2025
The short term period will begin quietly, but rain chances increase
Thursday afternoon and particularly Thursday night into Friday as
a storm system across southwest CONUS slowly ejects eastward
into the southern Great Lakes and Ohio Valley through Friday.
Low level baroclinic zone has shown best southeast progress across
south central/southeast Lower Michigan today with a tendency toward
neutral temperature advection back across the western Great Lakes
into west central Indiana. This cold advection has supported a few
flurries/light snow showers across southeast Lower Michigan. This
cold advection weakens late this afternoon which should lead to
continued diminishment in stratocu.
The departure of broad southeast Canada/northeast CONUS negative
upper height anomaly late tonight into early Thursday will allow
backing of low level winds and onset of low level theta-e
advection. A couple axes of moisture convergence are expected
to develop in response to increasing southerly flow downstream
of primary upper level disturbance of interest across the Four
Corners region. The primary low level jet on Thursday is
expected to nose into western KY/western TN/southern IL later in
the day Thursday, but a secondary area of weaker low level
moisture convergence is expected to develop across northern
Indiana in the afternoon in response to the developing upstream
low level thermal anomaly. Moisture quality with this northern
forcing will be more limited however, and still feel that we will
have to wait until later Thursday night into Friday for deeper
moisture advection and stronger mid/upper level support for more
appreciable rain.
A stronger thermal/moisture advection forcing push should occur late
Thursday night into early Friday. It still appears as though best
frontal convergence forcing will be confined well south of the
local area across the Lower OH Valley into the Lower MS Valley
where the greatest concern for heavy rainfall will be. An item
of greater uncertainty is how the precip shield will evolve
toward tail end of this event later Friday in association with
deformation forcing. A low level diabatic PV anomaly across
MO/IA should get affected by this deformation flow arising from
a separate and stronger northern stream flow across the western
Great Lakes creating a strong shear zone. This should really
elongate this diabatic PV anomaly in a west-east fashion keeping
precip chances into Friday evening. Profiles could briefly
support a changeover to snow before precip tapers in this
deformation forcing zone, but confidence in any snow
accumulation still is quite low. Still concur with previous
forecast in general 0.5 inch plus rainfall amount potential,
with some locally higher amounts possible if deformation forced
precip can materialize. However, much of the storm total will
depend on the wave of precip Thursday evening and whether best
mass/moisture convergence remains shunted just south/southeast
of the area. Have also continued to omit any thunder mention,
but some modest mid level lapse rates and best upper forcing
late Thu into early Fri may lead to very low end potential of an
isolated rumble of thunder far south/southeast.
Weak low level cold advection builds in for late Friday night into
early Saturday, but deamplification of the flow and strong eastern
Pacific jet nosing into Pacific northwest will induce lee troughing
for Sunday and quick transition back to low level southwesterlies.
Favored northern stream track and strongest resulting isentropic
upglide across Great Lakes still suggests greater precip
chances late weekend north of the local area. A trailing cold
frontal boundary late Sunday night into Monday could induce some
precip chances, but moisture availability may be limited. Temps
should shoot back above normal (mid 40s to low-mid 50s) for
Sunday, but then fall behind cold front early next week (but
likely still at or above normal for early February). Upper
pattern should remain progressive and of low amplitude behind
this early week system which makes predictability with
additional eastern Pacific systems difficult at this forecast
distance.
&&
.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1125 AM EST Wed Jan 29 2025
VFR this period as sfc ridging transects the terminals. Gusty nw
winds this aftn will quickly subside and back swrly overnight.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Small Craft Advisory until 10 PM EST this evening for LMZ043-
046.
&&
$$251
DISCUSSION...Marsili
AVIATION...T
Source:
IWX issues Area Forecast Discussion (AFD) at Jan 29, 3:24 PM EST---------------
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