Greenfield, Indiana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

644
FXUS63 KIND 180506
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1206 AM EST Sat Jan 18 2025

.KEY MESSAGES...

- Rain will move in and mix with or change to snow mainly near and
  north of I-70 with minor wet snow accumulation up to an inch
  possible

- Bitterly cold air is expected Sunday through Tuesday Night. Nights
  with subzero lows likely and single digit highs expected on
  Monday and Tuesday.

- Wind Chills values of -10 to -20 will be possible Monday and
  Tuesday mornings.

&&

.FORECAST UPDATE...
Issued at 1000 PM EST Fri Jan 17 2025

Next system approaching from our southwest has induced a rather
impressive rainfall shield extending from Alabama to the Middle
Mississippi Valley...with less organized/lighter echoes within the
system`s northern extent over Illinois` southeastern half and so far
into portions of the Wabash Valley.  Rain coverage and intensity
will continue to increase over the local region from SW to NE
through the overnight.  Wet bulb temperatures in the mid-30s to
around 40F and warm advective south-southwesterly breezes gusting to
20-25KT will promote widespread rain precipitation-type through 09Z.
 Isolated/ patchy slick spots in lingering cold spots that were able
to avoid Friday`s ample sun are possible, yet no impacts are
expected through 400A on treated surfaces.

The system`s cold front will cross the CWA through pre-dawn hours.
P-type is expected to mix with snow from west to east north of I-70
as daybreak approaches.  Cannot rule out a thin coating of slush
across the region`s northern tier very late tonight...especially
along the Upper Wabash Valley.  Winds will shift from SSW to NW
prior to dawn, bringing temperatures to near freezing over central
Indiana`s northwest corner...elsewhere lows in the mid to upper 30s
can be expected.  Patchy fog cannot be ruled out in areas with a
thicker remnant snow pack, but winds and rain should prevent drastic
reductions in visibility.  Rainfall through dawn should total 0.20
to 0.40 inches for most locations.

&&

.SHORT TERM (This evening through Saturday)...
Updated at 425 PM EST Fri Jan 17 2025

The warming temperatures and resultant snow melt and then rain and a
potential a mix of rain and snow will be the big highlights to the
short term.

Rest of the Afternoon...

A low amplitude ridge is passing overhead this afternoon as seen on
H20 vapor imagery and models. Meanwhile, a surface high pressure
ridge, across the southeastern coast, has allowed for gusty south
winds to draw in slightly above normal temperatures to central
Indiana. Finally, a very dry column per Hi-Res soundings, GOES-16
satellite data and surface observations has manifested as sunny
skies. The sunny skies and above freezing temperatures will work to
start melting the snow pack in addition to raise temperatures, the
remainder of the afternoon. That said, visible satellite is not
currently hinting much as melted.

1 PM temperatures have climbed all the way to the upper 30s and
lower 40s and should top out at least a few degrees warmer as the
breezy southerly flow continues around the departed surface ridge.
Satellite and sounding trends suggest high clouds will start moving
in from the southwest ahead of a developing southern Plains system,
in the fast southwest flow aloft.

Tonight and Saturday...

An upper system, seen on H20 vapor imagery, over the Texas Panhandle
will move into the Ohio Valley overnight and Saturday morning as an
upper vortex spins across northern Ontario. Meanwhile, moisture will
surge northward on the back of the southeastern surface ridge and
ahead of a cold front, that is expected to push through central
Indiana Saturday morning. 60+ low level jet will bring in well above
normal PWATs from 0.7 to 0.8 inches which is nearing the max moving
average of the SPS ILX sounding climatology. Meanwhile, 295K
isentropic data was showing nice upglide tonight. Condensation
pressure deficits and Hi-Res soundings support the column saturated
down enough for rain to reach the ground across the Wabash Valley
shortly after 00z Saturday and over all of central Indiana by 06z.
Central Indiana will be in between a 250 millibar jet streaks across
northern Canada and also the southern states. The stronger southern
one /160+ knots/ will place central Indiana within the left exit
region. This could help enhance any precipitation. The soundings
suggest the precip should at least start out as rain but could mix
with or change to snow after 09z and mainly over areas near and
north of I-70. Very low snow ratios due to above freezing
temperatures lend good confidence that any snow accumulation will be
below an inch. Would not rule out a few slick spots on the roads
based on current frozen ground, but with air temperatures to
likely stay mainly above freezing, do not think this will be a huge
impact.

The cold front will sweep through from northwest to southeast on
Saturday morning with most areas seeing the high at 12z and then
dropping during the day into the 30s and 20s. The precip should be
east of the area by Noon. Model soundings hold on to some shallow m
moisture below 5K while also showing very dry air moving in the mid
levels. This feels like a trick to introduce more clearing then
will probably actually occur due to the difficulty in stratocu
breaking up this time of year under a subsidence inversion and
considering the low sun angle.

&&

.LONG TERM (Saturday night through Friday)...
Issued at 226 PM EST Fri Jan 17 2025

Saturday Night through Sunday Night -

The cold onset begins Saturday night. Aloft the pattern is expected
to be dominated by a deep area of arctic low pressure settling over
Hudson Bay. The broad and deep cyclonic flow aloft is expected to
engulf much of the United States east of the Rockies. This pattern
aloft is expected to continue through Tuesday. Due to this flow, a
continued flow of arctic air is expected to begin spilling southward
into the Ohio Valley. The onset of this cold air advection will
begin on Saturday night in the wake of the earlier departing system.
Northwest flow at 850mb suggests temps of -16C arriving by Sunday
morning. The surge of cold air will continue with 850mb temps
reaching near -25 by Sunday night. Thus from Saturday Night through
Sunday Night, temperatures will struggle to rise. Highs on Sunday
may only reach the teens. This dry cold air mass will have little
moisture to work with and precipitation will not be expected as
there will be a lack of forcing within the broad cyclonic flow
aloft. However forecast soundings through the weekend show the
arrival of lower level saturation with a typical trapping inversion
aloft. This will lead to mostly cloudy skies for Saturday night
through Sunday Night,

Monday through Tuesday Night -

This will be the coldest part of this forecast period, if not the
coldest part of the year thus far. The continued broad cyclonic flow
aloft will remain in place allowing a continue flow of cold, arctic
air to spill across Indiana and much of the eastern half of the
United States. By Monday and Tuesday, strong surface high pressure
will have settled across the Central Plains. This will keep a cool
northwest flow across Indiana, but its influence will allow for a
clearing of skies. Forecast soundings on Monday through Tuesday
night show a dry column, which will lead to ideal radiational
cooling conditions. By this time, the core of the cold air, near -
25C will be in place over Central Indiana. This should allow
temperatures to only reach the single digits to near 10 for highs on
both Monday and Tuesday. A moderate pressure gradient will remain
across the area on Monday and Tuesday. This will allow for winds to
remain near 5-10 mph, resulting in possible morning wind chill
values of -10C to -20C. Again this will likely result in advisory
criteria at that time, approaching extreme cold criteria of
-20F apparent temperature. This will likely result in risks to those
outdoors, especially for the unsheltered population.

Wednesday through Friday -

By Wednesday, models show the upper pattern starting to moderate,
becoming a bit more zonal across the CONUS. This will allow core of
cold air to continue to moderate and slide east. Strong warm air
advection is noted on Wednesday as 850mb temps begin to climb,
reaching the negative single digits by Thursday. Aloft on Wednesday
and Thursday, little to no upper forcing appears present, thus more
dry weather will be expected with partly cloudy days and nights as
some moisture passing aloft within the quick flow will be possible.
Given our warm air advection, temperatures will moderate through
Thursday, reaching the 20s on Wednesday and the lower 30s by
Thursday.

By Friday, models suggest a broad, elongated through approaching
Indiana from the upper midwest and plains states. Ample forcing
appears to be approaching along with an associated cold front. At
this point arrival for any precipitation looks to be contained to
the afternoon hours, although as this is a week way, certainly
timing adjustments will come into play.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 1206 AM EST Sat Jan 18 2025

Impacts:

- IFR conditions developing overnight with rain
- Rain at least mixing with snow by 10Z-12Z...before ending 12Z-15Z
- Wind gusts around 20kt
- Winds shifting quickly from SW to NNW within 09Z-15Z

Discussion:

Rain will continue to overspread the sites early in the period.
Ceilings are likely to fall into the IFR category as the atmosphere
saturates. Ceilings will improve to MVFR by around 15Z.

A cold front will move in, allowing rain to mix with or change to
snow from northwest to southeast 09-14Z or so. This will also shift
the winds to northwest. Winds will gust to around 20kt pre and post
front. Isolated higher gusts are possible.

Strong winds aloft will create near non-convective LLWS conditions
overnight.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...AGM
SHORT TERM...MK
LONG TERM...Puma
AVIATION...50