IND issues Area Forecast Discussion (AFD) at Feb 8, 4:53 AM EST389
FXUS63 KIND 080953
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
453 AM EST Sat Feb 8 2025
.KEY MESSAGES...
- Rain arriving this morning, with a brief period of freezing rain
possible mainly over the northern half of central Indiana
- Active weather pattern with additional chances for wintry
precipitation next week
&&
.SHORT TERM (Today and tonight)...
Issued at 306 AM EST Sat Feb 8 2025
Currently, a large temperature gradient is present across
central Indiana, as a low level wave helps develop a frontogenetical
region. This has already created weak lift over southern portions of
the state, and in combination with moderate 850-700mb moisture
advection has already led to patches of light rain. As this frontal
region strengthens over the next 4 to 6 hours, this patchy rain and
drizzle will push northward, eventually encompassing the I-70
corridor and points southward. As stated, the temperature variance
over central Indiana is large, of which could create precip type
issues on the northern extend of the rainfall. In areas that remain
near to below freezing, very light ice accumulation will be
possible. This is currently expected to remain along the I-70
corridor and eventually points northward this morning as the
moisture advection continues its progression. Luckily, the
saturation along this frontal boundary is vary shallow, keeping
light precipitation rates, and therefor any morning ice accumulation
minimal. With that said, a few hundreths of an inch of ice could
lead to isolated slick spots on low traffic roads, bridges and
overpasses.
As we reach midday on Saturday, a surface low is expected to develop
increasing the overall lift in the atmosphere. This should also
strengthen the temperature and low level wind gradient over the
state pushing surface temperatures above freezing in most locations,
even nearing 50 degrees in far southern central Indiana. This
greater source of low level lift is expected to lead to showers with
periods of moderate rainfall rates at times Saturday afternoon and
evening; greatest coverage would be along and south of I-70. Model
soundings are also picking up on some elevated instability just
north of the warm front, of which could lead to thunder and isolated
small hail in the heaviest showers.
In the previous section, there was a mention of "most areas should
push above freezing". This is due to some uncertainty in far
northern portions of central Indiana struggling to increase in
temperature this morning. The primary factor in curtailing
temperature gains will be due to a greater easterly wind component
mitigating a northward push of warm air. The current expectation is
for this area of near to below freezing temperatures to remain north
of a Delphi to Kokomo line late this morning afternoon. Although,
there is still high uncertainty, and this freezing line could shift
north or south by 10-25 miles. If there is any widespread adverse
hazards due to ice accumulation (slick roads, weighed down branches)
it would likely be in these areas that stay at or below freezing
late this morning and early afternoon as rain rates increase leading
to greater amounts of ice. For now, uncertainty is too high for any
headlines, but this will be a close area to watch throughout the
morning.
By Saturday evening, all rain is expected to be east of central
Indiana, with a shift back towards NW winds and a subsequent drop in
temperatures. Given a lingering low level cloud layer and strong
subsidence aloft, patchy drizzle is possible this evening and early
tonight. Greatest coverage of drizzle is likely to be over far
northern and northeastern central Indiana. Overnight low temperature
forecasting will be tricky tonight due to competing factors of CAA
and IR warming of lingering cloud cover. Current expectation is for
lows in the upper 20s, but this could be raised by a few degrees if
cloud cover leads to a warmer trend.
&&
.LONG TERM (Sunday through Friday)...
Issued at 306 AM EST Sat Feb 8 2025
A transition to a colder and more active pattern is expected this
weekend and into next week. On the global scale, guidance is in good
agreement showing the Arctic Oscillation (AO) turning negative.
During negative phase AO, the polar jet typically weakens and
becomes more amplified. Such jet configurations can lead to arctic
air moving more freely southward, as may be the case next week.
Another large-scale teleconnections, the North Atlantic Oscillation
(NAO), is shown by guidance to be generally neutral with perhaps a
slight trends towards negative. Negative NAO tends to bring about a
blocking pattern which can also lead to a more amplified jet pattern
and thus colder temperatures over the Midwest / Eastern US. However,
the AO turns sharply negative well before the NAO reaches neutral so
our long term weather should be more influenced by the AO. We'll
likely see the trend towards cooler temperatures but with a more
progressive and active pattern. That is, more storm systems moving
quickly eastward within a wavy jet stream.
The first substantial upper level system within the long term looks
to impact the Ohio Valley late Monday through Tuesday night with
models continuing to show agreement in the overall synoptic pattern.
Trends have pushed this system further south, leading to greatest
impacts with this system likely south of central Indiana. With that
said, there is still 96 hours until arrival and track changes are
still possible. This pattern consists of a relatively deep surface
low moving somewhere across the Tennessee Valley with central
Indiana remaining in the cold sector of the system, including modest
northeasterly surface flow. Although greatest FGEN and deformation
is likely to remain south of central Indiana. Moderate mid level
lift within the cold conveyor belt could lead to periods of snowfall
Tuesday if enough moisture is available. The greatest threat for 1
inch or more is along and south of a Bloomington to Columbus line.
Keep monitoring forecast updates in the coming days as details
become more apparent, and plan on the potential for Tuesday travel
hazards in the event snowfall comes to fruition.
The next upper level wave is expected to arrive late Wednesday into
Thursday. At this time, ensemble variance is too high to resolve
much more than chances for precipitation, but this will be another
system to keep an eye on in the coming days. Latest trends are
keeping this system further north, leading to increasing potential
for some level of impact to central Indiana. However, this would
also likely lead to greater temperature variance and uncertainties
related to precipitation type. Once again, as of this forecast
update, the recommendation is to stay up to date on latest forecast
trends, and prepare in the event travel impacts happen Wednesday
night into Thursday.
&&
.AVIATION (12Z TAF Issuance)...
Issued at 453 AM EST Sat Feb 8 2025
Impacts:
- Freezing drizzle possible at KIND through 15z and KLAF through
14z and possibly into the afternoon
- Ceilings to deteriorate to MVFR and then IFR after 12z-15z
starting first at KBMG
- Thunder possible at all but KLAF 15z-21z
- Winds will shift from ESE to NW after 21z and gust to near 20
knots after 01z Sunday
Discussion:
A warm front will approach from the south and overrunning
precipitation and deteriorating flying conditions will ensue. A
brief period of freezing rain will be possible, mainly at KLAF and
KIND this morning. Thunder and perhaps small hail are possible over
all but KLAF late this morning and afternoon as the surface low
moves over southern Indiana. Confidence in lightning coverage is not
high enough to include thunder, however.
As the frontal system moves off to the east tonight, winds will
shift to the northwest and light gusty winds will be possible.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...Updike
LONG TERM...Updike/Eckhoff
AVIATION...MK
Source:
IND issues Area Forecast Discussion (AFD) at Feb 8, 4:53 AM EST---------------
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