IND issues Area Forecast Discussion (AFD) at Jan 18, 5:44 PM EST229
FXUS63 KIND 182244
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
544 PM EST Sat Jan 18 2025
.KEY MESSAGES...
- Light snow accumulations Sunday, highest chances across eastern
Indiana.
- Extreme Cold Watch converted to a Cold Weather Advisory and
extended through Wednesay morning.
- 10 below wind chills, possibly as low as 20 below for northern
portions of central Indiana.
&&
.SHORT TERM (This evening through Sunday)...
Issued at 147 PM EST Sat Jan 18 2025
Tonight.
High pressure will continue to build across the Ohio Valley tonight
as the surface low that brought the rain and snow moves off the East
Coast. Mostly cloudy to cloudy skies are expected through the
overnight hours with temperatures continuing to slowly fall as
strong northwesterly flow near the surface persists. Surface
pressure gradients will remain fairly tight through the night which
will allow for winds to remain in the 10-15 mph range as no near
surface inversion forms due to the cold temperatures aloft.
A broad vort max associated with a 120kt jet is expected to move
across Kentucky and Tennessee with weak lift as far north as southern
Indiana. This may bring a few light snow showers/flurries to south
central Indiana late tonight and towards daybreak but any
accumulating snow should remain along to south of the Ohio River.
Across northern Indiana a fetch from Lake Michigan may bring
additional light snow/flurries to north central Indiana towards
daybreak, but there remains some uncertainty as to how far south the
snow will make it.
Sunday.
During the mid morning through early afternoon the near surface flow
will begin to become more northwesterly again which will shift the
focus to any potential lake enhanced snow to the northeastern
counties. Overall accumulations look low, but non-zero with most
spots to see between a dusting and a half inch with isolated amounts
that could be as high as an inch. Another non-diurnal temperature
curve is expected for tomorrow with the daytime highs likely in the
morning before they continue to fall through the day ahead of the
much colder temperatures to begin the work-week.
&&
.LONG TERM (Sunday night through Saturday)...
Issued at 250 PM EST Sat Jan 18 2025
The long term portion of the forecast remains valid with high
confidence on dangerous cold Sunday night through Tuesday night. The
only changes we made after further collaboration with surrounding
offices was to convert the Extreme Cold Watch to a Cold Weather
Advisory, and extend through Wednesday morning.
It is worth noting that while blended model probabilistic guidance
shows high probability of sub-zero temperatures, there may be some
warm bias from less realistic model inputs that temper probabilities
some. Even without an optimal radiative component, the magnitude of
cold advection given its origin should bring most of the area below
zero Sunday night. Given that we're on the periphery of the MSLP
high center, could have clouds for a period, and have decreasing
snow cover, the opportunity for significant temperature variances
due to optimal/strong radiative process is less likely.
Previous discussion sent at 321 AM EST Saturday:
EXTREME COLD POTENTIAL
How cold we actually get depends on how efficiently we can
radiatively cool at night. This, in turn, depends on how much cloud
cover and wind are present. Additionally, how much of a snow pack is
remaining after today's warmth and rain. Ideal conditions do not
appear until Tuesday night. Before then, enough of a MSLP gradient
is present to promote a 10 to 15kt wind which will limit cooling
potential. It will still be very cold, simply due to the magnitude
of the arctic air mass overhead. Lows Monday morning may dip into
the negatives regardless of the wind...which may allow for extremely
cold apparent temperatures / wind chills (see next paragraph). While
the wind dies down by Monday night, cloud cover may be present at
times which could limit how cold overnight lows get. Tuesday night
looks to have the most ideal conditions for cold overnight lows with
clear skies, light winds still within the core of the cold air mass.
We will issue an Extreme Cold Watch with this forecast update, as
winds Sunday night into Monday along with single digit and negative
ambient air temps lead to wind chill values between -15 and -25
degrees. This watch could then be upgraded to a Cold Weather
Advisory (values of -10 to -19) or an Extreme Cold Warning (values
of -20 or lower) depending on which side of that spectrum we
eventually end up on. As of right now there is high confidence in
apparent temperatures of at least -10, with lower confidence in -20
degree values. Our watch will span from 06Z Sunday night to 18z
Monday, since this is when the lowest wind chills are anticipated.
Apparent temperatures rise above criteria thereafter for at least 12
hours. Tuesday and Wednesday should have lighter winds as mentioned
above, which despite colder low temps could lead to wind chills not
reaching the -20 criteria. The watch may need to be expanded if this
changes, however.
By mid week, ensemble guidance shows the trough de-amplifying
somewhat with troughing still present to some extent through next
weekend. Slight moderation in temps is likely from Wednesday onward,
though values will still be below normal for January.
&&
.AVIATION (00Z TAF Issuance)...
Issued at 544 PM EST Sat Jan 18 2025
Impacts:
- MVFR cigs through much of the TAF period
- Snow Flurries possible Sunday morning
Discussion:
GOES16 continues to show extensive cloud cover across the Taf sites.
The cloud cover was due to strong cold air advection resulting in
stratocu and lake cloud steaming off of Lake Michigan, pushing south
into Central Indiana within the flow aloft.
Time heights and forecast soundings continue to suggest mostly
cloudy to cloudy skies expected through the TAF period. Cigs will
remain generally MVFR with brief VFR periods.
Isolated to scattered snow flurries off of Lake Michigan is possible
towards the morning hours tomorrow with uncertainty as to exact
timing and coverage. Vsbys should remain VFR as any precipitation
will be very light.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
Cold Weather Advisory from 7 PM Sunday to 10 AM EST Wednesday
for INZ021-028>031-035>049-051>057-060>065-067>072.
&&
$$
SHORT TERM...White
LONG TERM...BRB
AVIATION...Puma
Source:
IND issues Area Forecast Discussion (AFD) at Jan 18, 5:44 PM EST---------------
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