IND issues Area Forecast Discussion (AFD) at Feb 11, 5:36 AM EST733
FXUS63 KIND 111036
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
536 AM EST Tue Feb 11 2025
.KEY MESSAGES...
- An inch or less snowfall over areas mainly south of Bloomington
and Rushville Today
- Another wintry system Wednesday and Wednesday night with potential
for greater impacts due to a combination of freezing rain and snow
&&
.SHORT TERM (Today and tonight)...
Issued at 233 AM EST Tue Feb 11 2025
Rest of the Overnight and Today...
GOES-16 RGB Nighttime Microphysics loop and obs were indicating a
thick cloud deck with ceilings above 6K feet and mostly near 10K
feet streaming northeast across central Indiana in the fast
southwest flow aloft. Meanwhile, the MRMS reflectivity loop and obs
were showing an area of rain from eastern Oklahoma into the Missouri
Bootheel and into eastern Kentucky and northeastern Tennessee. This
area was make little northeasterly progress. Meanwhile, temperatures
across central Indiana were stationary or only slowly falling due to
the cloud cover with upper 20s to around 30 degrees over northern
sections to the middle 30s over south central sections. Dew points
were only in the teens to lower 20s in the very dry deep boundary
layer.
295K isentropic analysis was showing upglide that will continue
through today. However, Hi-Res soundings are indicating very dry low
levels that will be reinforced by the northeasterly boundary layer
winds and should make it difficult for any snow accumulation from
making it as far north as the I-70 corridor. The bulk of the precip
should stay south of central Indiana but wouldn't rule out areas
south of Bloomington and Rushville getting possibly a half an inch
to an inch from near daybreak through the early evening. Areas
further north could see a few flurries but no impacts.
The thick cloud cover and northeasterly winds will keep temperatures
from rising much with highs mostly in the middle and upper 30s.
Tonight...
More mid and high clouds will be rolling in tonight in the continued
fast southwest flow aloft, ahead of the next system. This will keep
temperatures from falling below the middle 20s north to lower 30s
south despite the northeast winds increasing to around 10 knots.
&&
.LONG TERM (Wednesday through Monday)...
Issued at 233 AM EST Tue Feb 11 2025
Wednesday and Wednesday Night:
System #2 still looks on track to pass through the Ohio Valley
Wednesday through Wednesday night providing a mix of different
precipitation types for central Indiana. Lets take a closer look.
This system is being set up by shrinking the available baroclinic
zone and creating tight pressure gradients over the CONUS. In return
the subtropical and polar jets will merge creating inhabitable zones
for pressure depletion, especially within the mid-Mississippi
Valley. The alignment of the jet streaks isn't quite ideal for deep
, but as the subtropical jet streak becomes prominent late Tuesday,
a corridor of negative height tendency develops leading to a gradual
deepening of the upper level trough.
What will fuel this winter storm is actually more focused further
down in the troposphere, in the 700-850mb layers. Once again, high
pressure over the SE coast will act as a blocking mechanism,
tightening the pressure gradient as the upper level trough deepens.
By Wednesday, this LLJ becomes strong and orients towards the SW,
pushing very moist air northward into the Great Lakes and Ohio
Valley. These diabatic effects along with supper of upper level
diffluence will likely lead to a low level low deepening with a
surface low developing over the mid Ohio Valley late Wednesday
through Wednesday night.
As typical with winter storms the 850mb low will be a marker for
where greatest snowfall rates are expected with this system.
Currently this generally progged to pass through central IL,
northwest IN and southern MI. The next corridor of interest will be
where the surface low will track and the subsequent warm nose
attached with the LLJ. Just N/NE of the surface-to-925mb low will be
a corridor of freezing rain, where the warm nose is warm enough to
melt any falling snowfall before reaching the surface, but the
surface remains below freezing allowing for rain to freeze upon
contact. This corridor is currently progged to pass through southern
IL, and central IN. The greatest ice accumulation rates are likely
to occur Wednesday evening as both diurnal cooling near the
surface, and nocturnal LLJ increases lead to greater QPF rates and a
wider zone of potential FRAM.
Even with all of these known commodities, there are still many
uncertainties that are present within this forecast. Ensemble
members as of the 00Z runs still have a 50-75 mile spread in system
track, of which could shift the greatest snowfall and ice amounts by
a similar magnitude. With that said, there is a cluster of
solutions, leading to a greater probability that the surface low
passes near/along the Ohio River, with subsequent lows aloft passing
generally NW of this. The amounts within the summary below are
generally represented by expectations if this cluster of solutions
is correct
Even though location of greatest accumulation has some remaining
uncertainty, magnitude/amounts have begun a decline in variance,
with a general agreement that the greatest FZRA axis will have have
greater than 0.15" of FRAM. The current uncertainty is if the high
end will get to 0.25" or higher, of which could lead to greater
impacts. Snowfall amounts very a bit more, as this will have a high
dependence on SLRs and the width of the transition zone between rain
and snow. There is high confidence in far NW central Indiana
receiving the most snow within central Indiana, but these high end
amounts could be anywhere from 1-4" as of this issuance. Generally,
any snow accumulations above an inch should remain N/W of a
Rockville to Lebanon to Tipton line, leaving Indianapolis and the
surrounding suburbs primarily in the threat for either ice or rain.
Sleet looks to be less of a factor for this storm, as the near
surface airmass is likely not cold or deep enough to refreeze any
melted snow; that said, there could be brief period of sleet mixing
into snowfall on the northern edge of the transition line.
Timing also has had a greater consensus as of the 00z runs, with
most ensemble members placing greatest precipitation rates Wednesday
evening, and most areas out of the precipitation shield sometime
shortly after midnight. That said, there could be some lingering
snow showers on the backside due to wraparound moisture along with
building high pressure.
*********************************************************************
Storm Summary:
This summary correlates with the current expectated low track. As
stated above, there is still some variance in ensemble track, and
specific location's amounts could shift.
Current expectation is for generally 1-4" of snowfall over NW
portions of central Indiana, with lesser amounts the closer you get
towards a Rockville, to Lebanon to Tipton line. Greatest ice
accumulations are expected to be generally just north of I-70 (west
of Indy) west/north of I-69 (east of Indy). Total ice accumulations
could be 0.2" or greater in some areas. Further south/east all rain
is currently expected with total rain amounts around 0.25 to 0.5
inches
*********************************************************************
Thursday Through Monday.
High pressure will quickly move in during the daytime hours Thursday
with single digit temperatures are likely for at least portions of
central Indiana Thursday night into early Friday as cold air rapidly
moves in as the aforementioned low pressure exits. The pattern will
remain active into the weekend with yet another two part low
pressure system expected Friday night through Sunday. Ensemble
spread is even higher for this system, but the general consensus is
that rain is the most likely precipitation type for the first
portion of the low passage, and then increasingly drier as the
primary low passes to the south. Another surge of anomalously cold
air will move into central Indiana Monday into Tuesday with the
potential for temperatures 15-25 degrees below normal.
&&
.AVIATION (12Z TAF Issuance)...
Issued at 535 AM EST Tue Feb 11 2025
Impacts:
- MVFR ceilings and visibilities in light snow possible at KBMG
through 24z
- MVFR ceilings possible at all but KLAF after 02z-08z Wednesday
Discussion:
MVFR ceilings and visibilities in light snow are expected at KBMG
today. Further north, there will be a big cutoff in the snow with
with a few flurries possible at KIND and KHUF and perhaps a brief
period of MVFR at KHUF. MVFR ceilings will then roll in tonight
ahead of the next wintry system.
Winds will be northeast near and less than 10 knots.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...MK
LONG TERM...Updike
AVIATION...MK
Source:
IND issues Area Forecast Discussion (AFD) at Feb 11, 5:36 AM EST---------------
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