IND issues Area Forecast Discussion (AFD) at Nov 12, 9:57 PM EST609
FXUS63 KIND 130257
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
957 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
&&
.FORECAST UPDATE...
Issued at 957 PM EST Tue Nov 12 2024
No significant changes are required for this evening's update.
High clouds are streaming into the region on a southwesterly jet
streak, and made minor sky cover increases to account more fully for
this. Despite the increasing cloud cover, temperatures should still
drop well into the 30s across most if not all of the area tonight,
and latest high resolution numerical guidance is in good agreement
with the going forecast.
Cloud cover will continue to gradually increase and lower through
the day on Wednesday before rain arrives from the southwest in the
afternoon hours.
&&
.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 (00Z TAF Issuance)...
Issued at 620 PM EST Tue Nov 12 2024
Impacts:
- Rain arrives mid afternoon Wednesday
- Ceilings to rapidly deteriorate to IFR and visibilities to
MVFR near or just beyond the end of the TAF period
- Wind gusts to around 18KT late tomorrow afternoon
Discussion:
High pressure will keep conditions quiet much of the period, though
winds will stay up in the 6-9KT range out of the east overnight as
the pressure gradient strengthens ahead of an approaching low late
in the period. Winds will become more southeasterly on Wednesday
morning.
A gradual increase in mid and high cloud is expected late tonight
into Wednesday, before rain pushes into the area late in the day,
along with some gusty winds to about 18KT out of the southeast.
Ceilings will rapidly deteriorate to IFR within a few hours of rain
onset as the rain becomes more widespread and a bit heavier.
Visibilities will also likely become MVFR with a few periods of IFR
possible in the heaviest showers.
Depending upon persistence of gusts, there may be potential for
modest low level wind shear tomorrow evening/overnight, but this
remains uncertain.
&&
.IND WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
UPDATE...Nield
SHORT TERM...Eckhoff
LONG TERM...Eckhoff
AVIATION...Nield
Source:
IND issues Area Forecast Discussion (AFD) at Nov 12, 9:57 PM EST---------------
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