Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/25/23
Area Forecast Discussion
National Weather Service Indianapolis IN
1049 PM EST Tue Jan 24 2023
.Mesoscale Update...
Issued at 1049 PM EST Tue Jan 24 2023
The forecasted winter storm is on our doorstep as precipitation is
expected to begin from southwest to northeast within the next few
hours. This mesoscale update is going to focus on the
development/progression of the system currently in Arkansas,
Louisiana, and Tennessee and how models are handling the scenario
compared to observations.
As of 02z, the lowest pressure of 1004.3 mb was found in surface obs
was located just NE of Alexandria, LA. As of the writing of this
discussion, the surface low is still broad, but should tighten and
deepen over the next few hours. The broad surface low as of 10PM is
likely located in NE Louisiana near Winnsboro with a min pressure of
1004/1005mb. Comparing observations with 00z runs of short term hi-
res models shows that the low is right on track, possibly a county
or two further west. However, models struggle with developing lows
so this is not unexpected so early in the cyclogenesis stages. The
center of the low may also wobble around over the next few hours as
it gets more organized. Will have to watch the low later tonight as
it develops and follow its track as it compares to models. A storm
track deviation as small as 20 miles south or north could move the
axis of heavier snow in either direction resulting in significant
changes in the forecast for a few counties along the I-70 corridor
on the edge of the heaviest snowfall.
Looking at the radar, the dry slot associated with the expansive
precipitation shield northwest of the low has reached into northern
Arkansas. Both the NAM3K and the RAP have shown the dry slot getting
just up to Fort Smith, then the deformation band moves in and pivots
over that area. Radar observations show this happening very nicely,
increasing confidence that the models are initializing well and have
a good handle on precipitation. Further back towards Dallas, which
is getting the back edge of the deformation band, reports show
mostly snow with some pockets of rain mixed in. This matches well
with short term models, however looks like models may not be cold
enough on the backside of the low as observations show more snow in
areas where models suggest rain. Confidence is rising that P-type
tomorrow morning and early afternoon will be mainly snow on the
backside of the system, even for portions of Southern and South
Central Indiana. Strong forcing and high precipitation rates could
keep the column cooler resulting in mainly snow, rather than a mix.
However, still will have to watch surface temperatures as heavier
snow falling at 33-34 degrees will have to overcome melting
occurring in order to accumulate.
Ahead of the low in Tennessee this evening, ground observations show
surface temperatures in the upper 30s to near 40, but with mixed
precipitation falling. This area is associated with the first "wave"
of precipitation that will move northward into Indiana later
tonight. Short term models seem to be too warm ahead of the low as
they show mainly rain as a P-type while mixed rain and ice pellets
are reported throughout Western Tennessee and NE Arkansas. While we
fully expect precipitation to start as rain as it enters Indiana, we
do expect a transition within 1-2 hours of the onset of
precipitation. Paducah, KY transitioned to snow about an hour or two
ahead of what the RAP and NAM show, which is something to take into
account as that could potentially add another inch or two to final
snowfall totals.
ACARS soundings from across the south and Tennessee Valley line up
well with what short term models show, with a warm nose around 700mb
ahead of the system with a pronounced area of below freezing
temperatures below the warm nose supporting a brief period of sleet.
Due to heavier rates, think that evaporative cooling processes have
cooled down the column enough to support more wintry precip rather
than plain rain. Will have to watch P-type with the initial wave as
a brief period of sleet mixing in with rain and snow is possible
before a full transition to snow as observations show.
Overall, forecast is largely on track. Trending snowfall totals up
just slightly across Southern Indiana to account for more wintry
precipitation in downstream observations than what models depict.
Still a little early to determine if the low track will be a little
further north or south of what is currently forecasted. As the low
center becomes better defined, we may be able to tweak the forecast
a bit to account for where the deformation band will set up and
pivot. Confidence remains high for this winter storm event across
Indiana. Stay tuned for more updates throughout the night.
&&
.Short Term...(This evening through Wednesday)
Issued at 135 PM EST Tue Jan 24 2023
Key Points:
WINTER STORM WARNING across much of central Indiana from Late
Tuesday Night through Wednesday Afternoon
* Generally 6-9 inches with highest amounts north and west of
Indianapolis, and less amounts further south and east
* Significant impacts to travel expected Wednesday morning
Discussion:
A significant winter storm remains on track to impact central
Indiana Tuesday night through Wednesday afternoon. Finer grid spaced
models are continuing the idea of a two phased low pressure system,
with greater detail on the timing of each.
Tonight, a closed surface low will approach from the southwest. To
its east, the combination of a strong high over the Atlantic will
create a robust LLJ, topping out around 75kts within its core. This
strong LLJ will provide intense WAA over the Ohio Valley, deepening
the surface pressure out ahead of the already developed surface
cyclone. This region of deepening low pressure, along with strong
vertical ascent will be the primary focus of the initial wave of
precipitation.
Temperatures this afternoon will get into the mid 40s over south
central Indiana, quickly cooling off around dusk. A rapidly
expanding cloud deck will act to limit diurnal cooling however,
creating some uncertainty on temperatures as precipitation enters
Indiana from the SW/S. The current expectation is for temperatures
to be around 36-38 degrees initially, leading to a rain/snow mix.
Temperatures should begin to fall towards freezing with wetbulb
temperatures around 34, aiding in the maintenance of snowflakes as
the fall to the surface. Soundings during this initial wave show a
near isothermal layer well above the ideal DGZ temperatures, of
which will lower SLRs significantly (3-5:1). This should result in a
very dense 1-3 inches south of I-70, with lesser amounts to the
northeast. Timing for this initial wave looks to be between 12am and
6am EST.
The second wave of precipitation will be more associated with the
aforementioned established surface cyclone. This system will be
dynamically aligned with the surface low just to the SE of the 850mb
and 750mb closed lows respectively. This should create an optimal
zone for vertical lift along and north of I-70 where high snowfall
rates are likely during the Wednesday morning hours. The 0C isotherm
should be just south I-70, and will create a rain snow mix,
decreasing SLRs and lowering totals for this region. In far SE
central Indiana, p-type will eventually transition to all rain in
the late morning to afternoon.
High resolution model input has added some clarity to the timing of
heaviest snowfall rates for central Indiana tomorrow. Around 8-9am,
deepening of the 700mb low along with intense isentropic lift out
ahead of the low will create very strong vertical lift, most of which
in a saturated DGZ. This should lead to a prolonged period of at
least 0.5"/hr snowfall rates, along with some locations reaching
1"/hr. This is expected to continue til around 12-1pm, with less
intense snow continuing through the afternoon. In total, the second
wave will proved an additional inch or two over south central
Indiana, with an additional 5-7" likely along and north of the I-70
corridor. Locally higher amounts are also likely within mesoscale
banding within north central Indiana. South central Indiana will
have some snow, but will compact quickly as rain becomes more
predominant. This area is expected to see 0.5"-2" with the second
wave.
Summary:
Snow will begin around midnight Wednesday morning / Late Tuesday
night. Snow ratios will be a bit lower with dense wet snow during
the night. Snow quickly accumulating on the road surfaces is
expected as higher rates / lack of solar radiation will overcome any
residual ground warmth. A couple of inches will likely already be on
the ground by sunrise Wednesday, leading to hazardous driving
conditions. Rain may mix in temporarily near and just south of the
surface low, which will most likely pass just south of I-70. Higher
snowfall rates are likely during the late morning hours on Wednesday
as deformation banding on the northwest side of the low begins to
take shape. Snow begins to wind down late in the afternoon, after 4-
6 PM or so. In totality, Snow totals of 6 to 9 inches are expected,
with the highest amounts north and west of Indianapolis. Lesser
amounts further to the southeast.
&&
.Long Term...(Wednesday night through Tuesday)
Issued at 135 PM EST Tue Jan 24 2023
*Lingering light snow Wednesday night through Friday.
*Next potential system Sunday.
Wednesday Night through Friday.
The bulk of the snow will have wrapped up by Wednesday night as the
surface low pressure moves into Ohio and continues to track to the
northeast. In the aftermath of the low, northwesterly flow aloft
associated with the broad upper level trough will persist through
Friday. Models have also been keying in on an embedded shortwave
that may locally enhance the forcing aloft and bring greater chances
for snow Friday into Friday night.
On Thursday, expect occasional light snow showers and flurries
through the daytime hours with lesser coverage during the overnight.
Over the course of the day around an inch of snow is possible. The
aforementioned shortwave then arrives Friday with the majority of
the snow falling across the northern counties, but confidence
remains low on this system and its impacts.
Saturday through Tuesday.
Flow will then shift to be more zonal and then southwesterly ahead
of the next system that is expected to arrive late Saturday night
into Sunday. Models have had a much more difficult time handling
how a weakening clipper system will interact with a developing
trough across the Gulf states which is leading to a low confidence
event with a lot of moving parts.
Current thoughts are that precipitation is likely Sunday, but
confidence in the precipitation type is very low. Snow is probable
in spots, but think that rain is the more likely precipitation type
for much of the area.
The active pattern we`ve been in looks to continue early next week
with yet another system late Monday through Wednesday. This system
is even more uncertain than the late weekend system, but will
continue to monitor the model ensemble trends.
&&
.Aviation...(00Z TAF Issuance)
Issued at 614 PM EST Tue Jan 24 2023
Impacts:
- MVFR ceilings possible at KLAF this evening
- Rapidly deteriorating conditions overnight as precipitation
spreads in
- Widespread sub-LIFR conditions predawn hours through late
Wednesday with moderate to heavy snow at times
- Gusty winds at times Wednesday
- Mixing with rain expected at KBMG and possible at times at both
KHUF and KIND
Discussion:
...IMPENDING WINTER STORM WILL CAUSE HIGH IMPACT TO AVIATORS...
High level clouds have quickly expanded across central
Indiana late this afternoon and early this evening ahead of the
impending winter storm. Clouds will thicken through the evening and
gradually lower overnight as precipitation approaches. Light
precipitation will first impact KBMG and KHUF near midnight...KIND
shortly after and KLAF later in the overnight. Expect rain to mix
with snow initially with the snow but as deeper forcing combines
with low level temps dropping to near freezing...snow will become
the main precip type from the predawn hours into Wednesday morning.
The heaviest snowfall is expected Wednesday morning into the early
afternoon with lighter precipitation rates thereafter. During the
period of heaviest snowfall...visibilities will likely dip to 1/4 to
1/2SM. Rain will likely mix back in at KBMG as the morning
progresses and may sporadically mix in at KHUF and KIND as well.
Winds will become gusty first from the northeast Wednesday
morning...backing to N/NW into the afternoon as low pressure passes
by to the southeast of the terminals. Ceilings will largely be at
500ft and lower for much of the day with visibilities remaining at 2-
3SM into Wednesday evening as snow becomes more scattered.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 7 PM EST Wednesday for INZ021-028>031-
035>049-051>057-060>065-067.
Winter Weather Advisory until 7 PM EST Wednesday for INZ068>072.
&&
$$
Mesoscale...CM
Short Term...Updike
Long Term...White
Aviation...Ryan
mentioned in the previous forecast discussion, a local "minima" in
snow totals may materialize near I-80 or the Kankakee River Valley
between both bands of snow.
While snow will continue to fall after noon on Wednesday surface
temperatures are expected to inch upward toward and eventually above
the freezing mark decreasing the efficiency at which snow
accumulates on roadways. Indeed, many roads may simply become wet by
mid-Wednesday afternoon leading to the primary impact of the snow
being reduced visibility. Snow should begin to taper late Wednesday
afternoon as the surface low and associated upper-level forcing
shift eastward. However, increasing northwesterly to northerly winds
and cooling 925-850mb temperatures will support lake effect snow
showers along the Lake Michigan shoreline. With winds quickly
turning northeasterly by Wednesday evening, all lake effect snow
should quickly shift into northwestern Indiana with the longest
residence time in Porter county overnight into Thursday. For
additional details on the lake effect snow, please see the Long
Term Discussion below.
Borchardt
&&
.LONG TERM...
Issued at 319 PM CST Tue Jan 24 2023
Wednesday night through Tuesday...
Forecast concerns for the long term period...
*Active pattern continues with periods of snow through early next
week
*Colder temperatures look to arrive this weekend and linger into
next week
The shortwave trough that caused the accumulating snow on Wednesday
(see short term discussion for details) will be exiting the area at
the start of the period, but a second shortwave is expected to be
moving into the area on the heels of the first. While this second
shortwave will be weaker than the first one it will still provide
sufficient ascent to help maintain snow showers through the day on
Thursday. While snowfall rates will be light with these snow
showers, the below freezing surface temperatures will allow for some
accumulation which could lead to some slick travel conditions
through Thursday afternoon.
Additionally, as winds become northwesterly behind the departing
surface low a convergence axis is expected to develop along the
western portion of Lake Michigan which will support the development
of lake effect snow showers on Thursday as well. Forecast soundings
indicate that lake induced equilibrium levels would increase upwards
of 7000 ft by Thursday morning which would create nearly 100 J/kg of
CAPE into the base of the DGZ. Couple these lake effect parameters
with the saturated DGZ and the steep low-level lapse rates and we
could be looking at a period of decent snow rates for a period. Low-
level winds are expected to gradually become westerly Thursday
afternoon which should push the lake effect band farther eastward
into northern Indiana and far southwestern Michigan before snow
starts to taper off.
Drier air is expected to begin filtering in aloft as the the
shortwave begins to exit the area Thursday afternoon. While it will
take some time to fully dry out the the DGZ, snow showers are
expected to gradually taper off from west to east with most areas
looking to be precipitation free by Thursday evening. However, there
is a chance that a few flurries may linger through Thursday evening,
but moisture depth looks rather shallow so I opted to forego a
formal mention for now. These snow showers on Thursday are expected
to only cause minor accumulations upwards of a few hundredths with
higher amounts near an inch under the lake effect in northwest
Indiana.
The active pattern is expected to continue through the rest of the
long term period with additional chances for snow Friday with
another chance possible over the weekend. The Friday system looks to
be a rather quick hit of snow caused by a clipper system that looks
to dive southward across the upper Midwest ahead of an arctic front.
Depending on how far south this front will get looks to determine
where a baroclinic zone will establish which looks to be the main
focus for a snow potential towards the middle part of the weekend.
As of right now, guidance establishes this baroclinic zone across
the Ohio River valley which would allow for some accumulating snow
to be seen across northeastern Illinois and northwest Indiana, but
things could shift as time gets closer.
Colder temperatures are look to move in behind the arctic front on
Friday with highs forecast to be in the upper teens to mid 20s with
lows in the teens and single digits heading into next week. While
there has been a slight warmer trend with recent forecast runs,
there still looks to be a period of more typical winter temperatures
to start off the month of February.
Yack
&&
.AVIATION...
For the 00Z TAFs...
Aviation Forecast Concerns:
* Gradually lowering MVFR ceilings tonight.
* Snow develops during the pre-dawn hours, with conditions
deteriorating to IFR and the potential for a period of moderate
snow and LIFR conditions possible Wednesday morning.
* Snow intensity diminishes late morning, though IFR conditions
expected to persist. Improvement to low-MVFR toward evening.
Total accumulation during the morning of 1-3 inches RFD and 2-4
inches for Chicago terminals.
* Winds become light southeast early this evening, then eventually
northeast with gusts near 20 kt by mid/late Wednesday morning.
Winds eventually back north-northwest late afternoon/evening.
Surface low pressure over southwest Louisiana this evening will
track northeast into the lower Ohio Valley by Wednesday morning
and to the lower Great Lakes by Wednesday evening. As this occurs,
an area of snow on the north/northwest flank of the low will
spread across the terminals during the pre-dawn hours of early
Wednesday. While the heaviest snow is expected to remain south of
the terminals from southern IL into central/northeast IN, a period
of favorable dynamics and instability aloft will likely support a
period of moderate snow and LIFR conditions over northeast
IL/northwest IN including the Chicago metro TAF sites during the
morning hours of Wednesday. Visibility as low as 1/2SM and
snowfall rates of 1/2-1 inch per hour will be possible with total
accumulations of 2-4 inches expected. Though IFR conditions will
persist, snow should decrease in intensity by late morning, which
along with temperatures rising slightly above freezing should
limit additional accumulations during the afternoon to less than
an inch. Snow will decrease further by early evening with
improvement to MVFR expected. Some light snow or flurries will
likely linger into the night however. KRFD, farther north of the
track of the system, will likely have better conditions and lower
snow amounts than the Chicago terminals.
Wind wise, winds will become light (5 kts or less) from the
southeast early this evening, then gradually increase and back to
the east-northeast overnight as the low moves into the lower OH
valley. Winds turn northeast by mid-morning Wednesday, with gusts
approaching 20 kts at times. Winds further back to north-northwest
by late Wednesday afternoon as the low continues to move east of
the region.
Ratzer
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Winter Weather Advisory...ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-
ILZ033-ILZ039-ILZ105-ILZ106-ILZ107-ILZ108 until 6 PM
Wednesday.
Winter Weather Advisory...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-
ILZ011-ILZ012...3 AM Wednesday to 3 PM Wednesday.
Winter Weather Advisory...ILZ006-ILZ013-ILZ103-ILZ104...3 AM
Wednesday to 9 PM Wednesday.
IN...Winter Weather Advisory...INZ001-INZ002 until midnight Thursday.
Winter Weather Advisory...INZ010-INZ011-INZ019 until 6 PM
Wednesday.
LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742-LMZ743...9 AM
Wednesday to 3 PM Thursday.
Small Craft Advisory...LMZ744-LMZ745...9 AM Wednesday to 10 PM
Thursday.
&&
$$
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