IND issues Area Forecast Discussion (AFD) at Dec 31, 2:40 PM EST456
FXUS63 KIND 311940
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
240 PM EST Tue Dec 31 2024
.KEY MESSAGES...
- Flurries with isolated snow showers tonight; little to no snow
accumulation expected
- Much colder temperatures will usher in the New Year.
- Light snow accumulation are expected Thursday night into early
Friday morning with impacts possible to the morning commute.
- A significant Winter system will likely effect the Ohio Valley
late this weekend and early next week.
&&
.SHORT TERM (This evening through Wednesday)...
Issued at 240 PM EST Tue Dec 31 2024
A 994mb low continues to track across central IN into OH, providing
widespread showers for a majority of the Ohio Valley. This low has
started to fill some as it nears upstream ridging, but should still
provide a strong enough pressure gradient for continued 10-15kt
sustained winds and gusts of 20-25kts tonight and tomorrow.
The CCB will continue to develop during the afternoon and evening;
along with diurnal cooling, will likely allow for wet-bulb
temperatures and surface temperatures to approach freezing within
saturation this evening. This could lead to some snow to mix-in
after 23Z, before showers exit central IN; no accumulation is
expected at this time. After the main bulk of showers push through
with the passing deformation zone late the afternoon into the
evening, isolated showers, drizzle and sprinkles will fill in behind
the low. This is expected to continue through the evening into the
early overnight hours until cold, dry air is advected into central
Indiana overnight.
Overnight, weak low level instability in conjunction with a shallow
saturated layer will likely lead to scattered flurries. There is a
low chance for these to become isolated snow showers as well with
light accumulations, but this has not been included at this time due
to low confidence. Low level instability with shallow saturation
looks to continue over N/NE central Indiana tomorrow, thus will
continue flurries over this area through tomorrow afternoon.
Temperatures will plateau some late tonight through tomorrow as
diurnal warming, CAA and extended cloud cover cancel each other out.
Current expectation is for highs near freezing.
&&
.LONG TERM (Wednesday night through Tuesday)...
Issued at 240 PM EST Tue Dec 31 2024
Much colder temperatures are in store for the long term as a broad
trough sets up over the Ohio Valley, Great Lakes and eastern parts
of Canada and the United States while a ridge amplifies over the
West and Rockies. On a smaller scale, an Alberta Clipper will bring
the threat for light snow to central Indiana Thursday and a northern
Pacific system will track into the southern Plains and Ohio Valley
late this weekend and early next week with the potential into
developing into a major Winter storm.
New Year's Day night through Thursday...
Broad surface low pressure will lift northeast from the Gulf to the
Ohio Valley. Subsidence related to the high along with a dry column
per BUFKIT soundings will lead to breaks in the cloud cover until
Thursday afternoon, when mid and high clouds will increase ahead of
the Clipper.
The cold advection and breaks in the cloud cover will lead to below
average temperatures with afternoon highs in the 30s on Thursday.
Thursday night and Friday...
Models in reasonable agreement that a Clipper system will drop
southeast across central Indiana late Thursday night. Limited
moisture with the Gulf cutoff but high liquid to snow ratio amounts
of 15:1 to 18:1 support light snow amounts around an inch with
locally higher amounts north of Noblesville by Friday morning.
Raised PoPs to likely, after adjacent office coordination. Despite
small snow amounts, impacts from these amounts would likely effect
untreated roads during the morning commute, so future headlines will
be possible.
In the wake of the Clipper, Arctic high pressure from Saskatchewan
to the Gulf of Mexico will draw breezy northwest winds into central
Indiana. The cold advection despite soundings support partly cloudy
skies, will mean well below temperatures with afternoon highs mostly
only in the 20s and wind chills in the single digits to the teens.
Friday night and Saturday...
Arctic high pressure combined with a mostly dry column and gusty
northwest winds will keep it cold but dry through at least Saturday.
Wind chills are expected to be around zero degrees at times,
early Saturday, north of I-70.
Saturday night through Tuesday...
All eyes will remain on the potential for the first big Winter storm
as a potent northern Pacific jet spins up a low pressure system that
will move to somewhere over the southern Plains Saturday night and
the Ohio and or Tennessee Valleys Sunday night into Monday. With the
strong kinematics associated with this system, copious amounts of
moisture will be ingested off the Gulf of Mexico. The combination of
synoptic and mesoscale forcing, isentropic lift and deep moisture
will lead to widespread precipitation over the region. There is good
confidence that this system will produce the gamut of precipitation
type. What it comes down to will be the exact track of the deepening
low and models and ensembles have had run to run and model to model
consistence issues. Confidence should increase on the evolution of
the low track when the system actually reaches the west coast and
becomes better sampled. In other words, confidence is good regarding
high QPF with this system but is low on where across the region, the
biggest impacts will be regarding snow, ice and rain. Just for sun
and for what it is worth, DESI LREF 10% (high end) total snow
accumulation through Monday night was showing 8 to 11 inches over
central Indiana with the 90% (low end) showing only an inch.
Meanwhile, the same quartiles were only showing minor freezing rain
accumulation over our far southern tier. However, just to reiterate,
the precise track of the low will be key to precip type, timing and
amounts and this system as yet to reach the west coast.
Confidence is high that temperatures will remain below normal
through the long term but confidence is low on zoning in on more
precise temperatures next week. Temperatures will depend a lot on
how much snow the area gets but below zero wind chills sure look
reasonable even in a best case scenario.
&&
.AVIATION (18Z TAF Issuance)...
Issued at 1216 PM EST Tue Dec 31 2024
Impacts:
- IFR ceilings through 22Z, slow improvement to MVFR after
- Visibility mainly MVFR in periods of rain this afternoon into the
evening
- Generally W/NW winds at 15kt with gusts to 25kt but direction will
vary this afternoon
Discussion:
An area of banding has developed across the I-70 corridor that has
lead to steadier rain rates and IFR VIS & CIGs. Outside of this band
VIS increases to MVFR. Rain should become more sporadic this
evening, with continued low MVFR cigs. There is a low chance for
these ceilings to remain IFR, but the current expectation is for
slight improvement. Overnight, scattered flurries may develop,
leading to brief VIS reductions, but otherwise minimal impacts.
Wind direction will be chaotic this afternoon as the system's
surface low tracks east-northeastward up the I-70 corridor, with but
most areas will generally be W/NW. Robust breezes from 300-340
degrees will gust up to 23-30KT through most of the night.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...AGM
LONG TERM...MK
AVIATION...Updike
Source:
IND issues Area Forecast Discussion (AFD) at Dec 31, 2:40 PM EST---------------
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