NWS Indianapolis, IN wrote its last area forecast discussion before the first event at Nov 30, 9:49 PM EST, 2 hours 11 minutes earlier. Its key messages:
Area forecast discussion, Nov 30, 9:49 PM EST, 2 hours 11 minutes before
Area Forecast Discussion
National Weather Service Indianapolis IN
949 PM EST Sat Nov 30 2024
.KEY MESSAGES...
- Winter Weather Advisory for far south central Indiana; 1 to 3
inches of snow is expected by the time the snow ends tonight
- Well below normal temperatures with wind chills in the single
digits Sunday, Monday and Tuesday nights.
&&
.FORECAST UPDATE...
Issued at 948 PM EST Sat Nov 30 2024
Snow is now confined to the far southern forecast area, where
forcing lingers. The heaviest snow remains not too far south of
central Indiana, associated with frontogenetical forcing and some
slightly negative EPV.
This enhanced forcing should remain just south of the area, but the
extreme southwest forecast area could be clipped on the northern
fringe of the heavier bands (briefly moderate snowfall). Have
adjusted PoPs to reflect these trends, lowering them significantly
north and keeping higher PoPs going in the southwest.
Reports of actual accumulations have been sparse, with 1.3 inches of
snow reported in Vincennes at around 815 PM. The additional expected
snow should keep the area within the expected 1 to 3 inch totals.
INDOT cameras do show some snow on the roads across the south, with
some slowdowns noted. Given the impacts, and the potential for snow
to linger in the southwest, will continue the Advisory as is. For
just north of the Advisory where some travel impacts have been
noted, have updated the Special Weather Statement to focus on travel
impacts. As temperatures fall tonight, some of the water on roads
could freeze. This has been noted as well.
Otherwise, lower clouds will linger across the south into the
overnight with higher clouds north. These will keep temperatures
from bottoming out. Ongoing forecast lows look reasonable and only
made some tweaks. Wind chills by sunrise will be in the single
digits north to teens south.
&&
.SHORT TERM (This evening through Sunday)...
Issued at 234 PM EST Sat Nov 30 2024
Primary concern for the short term portion of the forecast is a
quick hit of light accumulating snowfall late this afternoon into
tonight across southern portions of central Indiana.
The forecast remains on track as deterministic and ensemble guidance
suites have largely come into good agreement on overall details.
The primary change from a meteorological standpoint this afternoon
is that forecast soundings now show a substantial low level dry
layer that never fully saturates on the northward fringe of the
snowband area - roughly coincident with Indy metro. As a result,
have tightened the PoP gradient slightly and focused accumulations
just slightly southward of prior forecast.
The additional dry air, though it is not quite as substantial in the
advisory area south as it is in central zones, may cut into amounts
slightly, cause snow to end a bit earlier than previously expected
late tonight as the column dries out aloft as well, and result in
quite a sharp gradient between little to no accumulation and
slightly more substantial amounts.
Despite a fairly cold column, and a dendritic growth zone of solid
depth, large scale forcing for ascent is only briefly collocated
with the DGZ this evening, and is never terribly impressive. A lack
of any real frontogenetic component effectively eliminates any real
mesoscale banding concerns, and all of these factors should limit
ratios to no more than near or only slightly above climo
(approximately 12 to 1).
This all results in a zone of trace to a few tenths east-west from
north of Terre Haute to Indy metro and Rushville, amounts around an
inch from Terre Haute to Bloomington and Greensburg, 1-2 inch
amounts along a zone from Sullivan to Bedford and North Vernon, and
2-3 inches in the original advisory area far southwest, including
Vincennes/Washington/Shoals.
As previously mentioned, the column will begin to dry out aloft
quickly after about 06Z tonight, and will quickly taper off PoPs
after this time, though with a mention of flurries continuing
through about 10Z in the far southeast.
Given the holiday weekend is ongoing and additional travel may be
occurring, did decide to add a tier of counties in the
aforementioned 1-2 inch zone to the advisory.
Decent guidance agreement suggests another night with lows down into
the teens across much of the area, save for perhaps the far south
where cloud cover will be most persistent and dewpoints will be
highest - these areas will likely only drop to around 20.
Temperatures on Sunday will struggle to recover much, both as a
result of early morning lingering cloud, light snowpack in the
south, and a reinforcing shot of modest cold advection in the wake
of tonight's disturbance. Most areas will likely struggle to make it
out of the mid to upper 20s Sunday, despite afternoon sunshine.
&&
.LONG TERM (Sunday night through Saturday)...
Issued at 234 PM EST Sat Nov 30 2024
Sunday Night through Tuesday night...
The beginning of the long term is expected to remain well below
normal as central Indiana will remain in northwest flow aloft. Given
the amplified pattern, super geostrophic flow over the northern
Rockies will induce weak upper level waves within the NW flow. None
of these waves will be within strong baroclinicity and are expected
remain weak as they reach central Indiana, however given the
abnormally cold air mass, only weak lift will be needed in any
saturated layer to produce scattered flurries. There will be surface
high pressure attempting to push into Indiana from the west beneath
CAA, of which would reduce chances of a saturated layer from
forming. Due to low confidence in location/timing, and minimal
impacts, these have not been included in the forecast, but it's
something to monitor nonetheless. with some weak waves moving
through the flow.
Outside of low chances for scattered flurries, the main point of
emphasis will be the abnormally cold weather. Given the departure
from early December climatology, model guidance is expected to be a
touch too warm, especially within more conducive radiational cooling
environments. For this reason, temperature forecasts have been
lowered into the 25-50th percentile ranges with lows in the teens
Sunday through Tuesday night. If there is any area that could
further drop in overnight lows (upper single digits) it would be
over the SW portions of central Indiana where a continuous 1" or
greater snow pack could lead to lower daytime highs and more
efficient cooling.
Wednesday and Thursday...
The pattern begins to shift slightly over the middle of next week as
one of the waves induced by supergeostrophic flow interacts with
stronger baroclinicity over the Northern Plains and moves north of
Indiana. With the center of the low moving well north of central
Indiana, winds will shift towards southerly pushing our temperatures
back towards seasonal. There will be a moderate amount of lift out
ahead of this low, but moisture convergence will likely be confined
to near the low center keeping relatively dry air over central
Indiana. Still, pockets of precipitation will be possible late
Wednesday into Thursday. With temperatures increasing prior to
precip arrival, rain should be the predominant p-type. However, some
wet-bulb cooling could lead to p-type changes Wednesday night.
Friday and beyond...
A return to much colder air is in store as high pressure builds in
from Canada again. Lows in the teens to around 20 and highs around
30 can be expected Friday into Saturday. Cold advection may be able
to squeeze out a few snow showers/flurries, especially Friday.
&&
.AVIATION (00Z TAF Issuance)...
Issued at 607 PM EST Sat Nov 30 2024
Impacts:
- MVFR or worse at HUF/BMG in light snow this evening
Discussion:
Light snow will continue at KBMG into mid-evening but may end early
at KHUF. KBMG will see IFR conditions at times, with MVFR more
likely early. KIND may see some flurries with no restrictions, while
KLAF remains quiet.
After the snow exits, VFR conditions will return. Some low end VFR
clouds may develop Sunday morning before moving east out of the
area.
Winds will become northwest tonight and remain there for Sunday.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 1 AM EST Sunday for INZ060-061-
067>072.
&&
UPDATE...50
SHORT TERM...Nield
LONG TERM...Updike
AVIATION...50
Special weather statement, Nov 30, 9:31 PM EST, 2 hours 29 minutes before
Special Weather Statement
National Weather Service Indianapolis IN
931 PM EST Sat Nov 30 2024
INZ051>053-062>065-010600-
Vigo-Clay-Owen-Monroe-Brown-Bartholomew-Decatur-
Including the cities of Terre Haute, Brazil, Spencer, Gosport,
Bloomington, Nashville, Columbus, and Greensburg
931 PM EST Sat Nov 30 2024
...SLICK AREAS ON ROADS INTO THE OVERNIGHT...
Although much of the light snow has ended across the area, slick
spots on roads from the earlier snow will continue. In addition,
as temperatures fall overnight, some of the water on the roads may
freeze, adding to the slick areas.
If traveling, slow down, drive carefully, and allow extra time to
reach your destination.