IND issues Area Forecast Discussion (AFD) at Dec 18, 2:46 AM EST818
FXUS63 KIND 180746
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
246 AM EST Wed Dec 18 2024
.KEY MESSAGES...
- Rain ending this morning, leading to a cloudy and cooler
afternoon
- Cooler than normal temperatures will return Thursday through the
weekend
- Light snow possible Thursday night into Friday. The snow could
impact the Friday morning commute.
- Rain for Christmas Eve into Christmas Day
&&
.SHORT TERM (Today and tonight)...
Issued at 245 AM EST Wed Dec 18 2024
Low level moisture will continue to increase over the next few
hours, as low level WSW flow strengthens. This has lead to a
widespread 5-7kft stratus deck across most of central Indiana.
Within this cloud deck, precipitation processes have begun, leading
to further low level saturation, and eventually rain. This process
will work eastward throughout the night and into the morning, with
numerous showers across the the I-70 corridor and southward after
09Z. A majority of the QPF will be south of the I-70 corridor (0.2-
0.4"), with 0.05-0.1" expected north of I-70. A stationary boundary
is currently located along the Ohio River, of which is expected to
lead to greater low level vertical motion and higher precipitation
rates for far southern IN. The current expectation is for these
higher rates to remain south of Knox/Daviess/Martin counties, but
with the margin of error only being in the tens of miles, this is
something that will need to be monitored this morning.
The lift in this initial precipitation will be mostly due to a
strong area of 900-750mb WAA and isentropic lift. This area of WAA
is expected to create a robust warm nose, of which should keep all
precipitation as rain despite wetbulb surface temperatures nearing
freezing early this morning. With that said, there will be a push of
colder 850-700mb temperatures along the mid level trough post 12Z
this morning. If precipitation does occur within this cooler
corridor, snow will likely mix with rain. HREF members currently are
varied in coverage of precipitation with this mid level wave
leading to low confidence in occurrence. Either way, snow
accumulations would be confined to generally Crawfordsville to
Muncie and areas north, and would be less that 0.2", with no impact
expected on warm roadways.
The rest of the day will be rather quiet, with high pressure
building underneath modest CAA. This will lead to much cooler
temperatures today with afternoon highs in the upper 30s to low 40s.
Guidance is suggesting some clearing in cloud cover this afternoon,
but given how quickly high pressure builds in, there is likely to be
a remnant suppressed saturated layer though most of the day and
tonight. This should also buoy overnight temperatures a little,
keeping lows in the upper 20s to low 30s. If breaks/cooler overnight
lows due occur, they would be most likely over W/SW portions of
central IN.
&&
.LONG TERM (Thursday through Tuesday)...
Issued at 245 AM EST Wed Dec 18 2024
Focus in the long term is on a couple of precipitation events. One
is a clipper system around Friday and the other is rain for
Christmas Eve/Christmas Day.
Thursday will be quiet ahead of an approaching upper trough and
surface low. Thursday night into Friday, the upper trough will move
in, and an area of low pressure will move through northern Indiana.
Good isentropic lift will accompany the system, and an upper jet
will provide additional forcing. Best moisture though will be
confined to near and north of the surface low.
Some model forecast soundings do show limited moisture in the ice
formation zone, so there is some concern for some freezing drizzle
with precipitation onset Thursday night. However, given the
uncertainty, will leave mention of that out for now.
Will go with likely PoPs across north and northeast portions of the
area Thursday night into Friday morning, with snow as the
precipitation type. As cold advection continues behind the system
Friday afternoon, additional scattered snow showers will be around.
Will keep chance PoPs going then.
Snowfall amounts have come up with the southward trend of the low,
but amounts will still be relatively light. Highest amounts near an
inch would be across the northeast forecast area with lighter
amounts to the southwest. The Friday morning commute could be
affected by this light snowfall.
Saturday through much of the day Monday look to be quiet and
cold with surface high pressure in control.
For Christmas Eve into Christmas Day, an upper trough will move into
the area. At the surface, an initial front will stall nearby, and a
surface wave will ride along it. Plentiful moisture will be brought
into the system from the south and southwest. Temperatures will be
warm enough for all rain.
Questions remain though on timing of forcing, where the front will
hang up, and the surface low tracks. These will have impacts on when
the highest PoPs will occur and where the heaviest rain will fall.
00Z GFS has 48 hour rainfall amounts over 2 inches in the south, but
the GEFS and other models place this axis south of the area. This
will be something to keep an eye on.
High temperatures will warm into the mid 40s by Christmas Day.
&&
.AVIATION (06Z TAF Issuance)...
Issued at 1150 PM EST Tue Dec 17 2024
Impacts:
- MVFR ceilings will move in overnight south and during the
day Wed elsewhere
- Rain will be around overnight into Wed morning. MVFR visibility
possible with it
- Some light snow might mix in with leftover rain at KLAF after
13Z
Discussion:
Ceilings will continue to lower overnight, with KBMG moving into
MVFR along with potentially KHUF. KIND/KLAF will lower to low VFR.
During the Wednesday, all sites will see MVFR ceilings by early
afternoon. These will improve Wednesday evening.
Rain will increase in coverage overnight, especially for the
southern sites. Rain will end by early afternoon Wednesday.
Northeast winds will back to northwest by Wednesday afternoon.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...Updike
LONG TERM...50
AVIATION...50
Source:
IND issues Area Forecast Discussion (AFD) at Dec 18, 2:46 AM EST---------------
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