IND issues Area Forecast Discussion (AFD) at Nov 12, 2:32 PM EST539
FXUS63 KIND 121932
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
232 PM EST Tue Nov 12 2024
.KEY MESSAGES...
- Rain arrives late Wednesday and continues into Thursday, possibly
heavy at times.
- More rain chances late weekend into early next week
- Above normal temperatures expected Wednesday through early next
week
&&
.SHORT TERM (This evening through Wednesday)...
Issued at 232 PM EST Tue Nov 12 2024
Low-level stratus continues to drift in from the northeast. Model
soundings show a deep and pronounced inversion a few thousand feet
off the surface. Strong subsidence above this inversion should keep
any cloud cover confined to the boundary layer for most of today.
Guidance tends to dissipate the stratus rather quickly, which may be
a bit too optimistic. We will maintain some cloud cover for most of
the afternoon gradually lowering coverage through about 00z. After
that, high cirrus begins to build in as a trough ejects into the
Plains later today.
The aforementioned trough will be our next weather-maker. At the
same time a tropical moisture plume, associated with the remains of
Hurricane Rafael, lifts northward out of the Gulf of Mexico. These
two features begin interacting just to our southwest, leading to a
widespread area of moderate to heavy rainfall. There remains some
uncertainty in the models in terms of amounts and placement. One
possible reason is that models are still coming into agreement on
how amplified the parent trough will be, and in turn how strong and
far north the resulting low-level jet ends up. The placement of this
jet will largely determine where the greatest low-level convergence
lies, and therefore where the heaviest rainfall occurs. Based on
current guidance the most likely placement is closer to the Ohio
River into our southern counties. There has been a slight shift
northward in recent guidance in the past 12 to 24 hours.
In terms of amounts, we're looking at between 0.5 to 1.0 inches
where the axis of heavy rainfall sets up, with lower amounts outside
of that region. Amounts may end up a bit lower than guidance
suggests, except in areas of convection, because the preceding air
mass is quite dry and evaporation may eat into the rainfall totals
somewhat. Will likely need to adjust temperatures downward
coincident with the rain's arrival due to evaporational cooling
effects.
The system should weaken as it departs, which will limit how much of
an air mass change we see. Temperatures should largely be the same
before and after the system's passage with highs in the 50s. Still,
some weak cold air advection is anticipated from the northwest.
Stratus and stratocumulus may persist well after the system departs.
&&
.LONG TERM (Wednesday night through Tuesday)...
Issued at 232 PM EST Tue Nov 12 2024
Rather quiet weather to start the long range as the
Wednesday/Thursday system departs. The system is expected to weaken
as it exits to the east with little in the way of an air mass change
behind it. Temperatures should largely remain about the same before
and after the system departs with highs in the 50s. Lingering
boundary layer moisture combined with light winds and clearing skies
may lead to some fog Thursday and Friday nights. Fog will be highly
dependent on how much clearing occurs.
By the weekend, another trough begins digging southward through the
western states. This feature should then gradually work its way
eastward, potentially bringing active weather to Indiana as early as
Sunday. However, a lot of uncertainty exists within the models for
this timeframe. Model uncertainty likely stems from large-scale
blocking over the North Atlantic. Blocking may potentially intensify
this weekend and into early next week as the NAO dips deeply
negative. Guidance can struggle in these patterns, so uncertainty in
the long range may be greater than normal for longer than normal.
Despite the uncertainty, a few things can be said about the pattern
going forward. First, above-average temperatures are likely to
continue. The overall signal is for troughing to remain to our west
for the most part, and there are few indications of substantial
arctic air dropping southward in the majority of guidance (at least
through early next week). Second, near to above-average
precipitation is the more likely outcome given troughing to our
west. We will maintain chance PoPs from Sunday onward, since a storm
system of some kind looks to be taking shape to our west around that
time.
&&
.AVIATION (18Z TAF Issuance)...
Issued at 1236 PM EST Tue Nov 12 2024
Impacts:
- MVFR conditions persist this afternoon, mainly IND and LAF.
- Rain arrives late in the TAF period, around 20-23z Wednesday, with
associated MVFR conditions.
Discussion:
Stratus resides across the northern half of Indiana, with LAF and
IND under a 2500 ft overcast deck. These clouds should gradually
diminish late in the day. Cirrus arrives overnight ahead of the next
storm system.
Winds maintain an easterly component overnight, becoming
southeasterly tomorrow morning. Speeds 5 to 10 kt are expected
overnight, rising to 10-15 kt after sunrise Wednesday.
Ceilings lower on Wednesday with rain arriving between 20-23z. MVFR,
or lower, conditions are possible once the rain arrives.
&&
.IND WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
SHORT TERM...Eckhoff
LONG TERM...Eckhoff
AVIATION...Eckhoff
Source:
IND issues Area Forecast Discussion (AFD) at Nov 12, 2:32 PM EST---------------
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