IND issues Area Forecast Discussion (AFD) at Dec 17, 6:03 PM EST289
FXUS63 KIND 172303
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
603 PM EST Tue Dec 17 2024
.KEY MESSAGES...
- Dry this evening; Rain arrives overnight, especially southern
Central Indiana
- Rain ends Wednesday morning, leading to a cloudy and cooler
afternoon
- Cooler than normal temperatures will be around later in the week
through the weekend
- Light snow possible Thursday night into Friday; low potential for
some light freezing drizzle - this may impact the Friday morning
commute
&&
.SHORT TERM (This evening through Wednesday)...
Issued at 304 PM EST Tue Dec 17 2024
Surface analysis this afternoon shows high pressure in place over
western KY. This high was providing westerly surface flow to Central
Indiana. The high was also providing subsidence and mostly clear
skies across Central Indiana. Looking aloft, a mainly zonal flow was
in place across Central Indiana, extending west to the high plains.
An upper level disturbance was pushing across the plains providing
cloud cover across KS/NB. IA and MN. This wave has shown signs of
deepening over the past few hours.
Tonight -
The surface high pressure system to the south is expected to slowly
exit east this evening. This will lead to dry weather through the
evening hours as forecast soundings show a dry column continuing.
However the effects of the subsidence will be lessening through the
evening. The approaching upper level wave over the plains is
expected to deepen and advance toward Indiana. This will allow for a
gradual increase in cloud cover through the late evening and into
the overnight hours.
Overnight, forecast soundings trend toward a saturated column after
09Z. The 290K GFS isentropic surface shows isentropic lift arriving
after 09Z with favorable specific humidities. Best forcing will be
found across the southern half of Central Indiana, and we will use
highest pops at that location. Lesser, probably only chance pops
will be found to the north. Forecast soundings are in good
agreement, showing saturation within the low and mid levels by 12Z,
in a warm air advection type pattern. So confidence is high for some
light precipitation across the southern parts of the forecast area,
with less confidence for places like LAF-OKK-MIE.
As the associated surface low passes well to the south across TN and
KY, cold air advection will begin on northerly winds late tonight.
This will allow for temperatures to fall to the lower to middle 30s.
Wednesday -
Lingering rain showers from the departing upper wave and surface
low are expected to be present for Wednesday morning, through the
morning rush hours, before tapering off by midday. Best isentropic
lift departs to the southeast by early Wednesday morning. HRRR also
trends toward a dry forecast in the 15Z-17Z window and forecast
soundings show a dry column as subsidence returns. Lower levels
remain saturated although, showing trapped cold air advection
stratocu. Thus will keep chances for morning rain, especially
across the southeastern parts of the forecast area and trend toward
a dry forecast everywhere by mid day. The expected clouds and cold
air advection in the wake of the low and trough will lead to minimal
rises in temperatures. Look for cooler high temperatures in the
upper 30s and lower 40s.
&&
.LONG TERM (Wednesday night through Tuesday)...
Issued at 304 PM EST Tue Dec 17 2024
Primary focus during the long term period is on a weak clipper
system that pushes through the region Thursday night into Friday,
followed by a brief weekend cool spell.
High pressure will keep the area dry Wednesday night into Thursday.
Thursday night into Friday a weak clipper system will drop southeast
across the area, with solid potential for wintry precipitation.
Light measurable snow appears possible, with anywhere from a few
tenths to perhaps an inch or two possible, assuming deep enough
saturation.
Some forecast soundings show an airmass that is fairly dry in the
mid and upper levels, including well into the dendritic growth zone,
though the most recent runs have improved slightly in this respect.
That said, this does lend to at least low concern that shallow
moisture could lead to freezing drizzle or a mix of snow and
freezing drizzle, which would be poorly timed with respect to the
Friday morning commute. This will require monitoring over the next
few days. Regardless, light snow and/or freezing drizzle
accumulation will be a concern late Thursday night into Friday
morning.
The GFS has consistently shown a second weak wave on Saturday that
could produce a few additional light snowflakes, but it appears to
be a bit of an outlier for the time being.
The weekend will be cool, with highs a few degrees either side of
freezing and lows a few degrees either side of 20 degrees, but this
will be brief, with heights rising early next week but another weak
wave necessitating low precipitation chances Monday night into
Tuesday. Temperatures will moderate a good bit, but may be cool
enough overnight for a mix or a few snowflakes.
&&
.AVIATION (00Z TAF Issuance)...
Issued at 603 PM EST Tue Dec 17 2024
Impacts:
- MVFR through at least 08z
- MVFR with rain showers possible after 09Z, continuing through
14z-15z
Discussion:
VFR conditions will continue through the early overnight under the
influence of a ridge of surface high pressure. There is only
expected to be an increase in cirrus and AC ahead of a Missouri
Valley to central Plains upper trough
Isentropic lift and the approaching trough combined with moisture
building down in the column will then lead to some MVFR ceilings and
rain showers. In addition, some snow could mix in at KLAF 12z-15z
before the precipitation ends.
Cold air advection in the wake of the departing system will lead to
more MVFR ceilings for a time Wednesday afternoon.
Winds will be light and variable to calm tonight and north and
northwest to around 10 knots Wednesday.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...Puma
LONG TERM...Nield
AVIATION...MK
Source:
IND issues Area Forecast Discussion (AFD) at Dec 17, 6:03 PM EST---------------
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