Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 170403
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1203 AM EDT Sun Mar 17 2024

.KEY MESSAGES...

- Becoming Partly Cloudy Tonight
- Colder Tonight and Sunday
- Hard freeze likely Sunday Night and Monday night
- Isolated rain/snow showers possible Monday, mainly in the
  afternoon

&&

.SHORT TERM (This evening through Sunday)...
Issued at 259 PM EDT Sat Mar 16 2024

Synopsis:

Surface analysis early this afternoon shows high pressure centered
over KS/OK/AR with a ridge axis stretching east to KY. Low pressure
was found north of the Great Lakes with a moderate pressure gradient
in place across WI and MI. These two systems were resulting in
southwest flow across Central Indiana. A cold front was found across
Lake Michigan, southern WI and west into IA. GOES16 showed mostly
clear skies across Indiana, however an area of clouds was found in
the wake of the front over WI, IA and MI within the cyclonic flow
and an associated upper level disturbance. Radar mosaics show only
some some very light rain fall with this front over SW MI. Aloft,
water vapor showed a deep low over Ontario, with northwest flow
spilling south across the northern plains to Indiana and the Ohio
Valley.

Tonight...

Overall expect increasing clouds this evening and cooler
temperatures associated with passage of the cold front.

Models suggest the cold front to the north will push southeast
across Central Indiana this evening. An upper level disturbance
embedded within the cyclonic flow aloft will also accompany the cold
front. This will provide enough lift along with cold air advection
in the wake of the front to result in some mid level saturation
passing in the wake of the front. This effect can already be seen on
GOES16 as previously discussed. Time heights and forecast soundings
both depict mid level saturation as these features pass. Best
saturation will be found across the northeast parts of the forecast
area, closest to the cyclonic flow, with lesser moisture and fewer
clouds to the southwest. Thus overall, increasing clouds late this
evening, and then clearing late overnight as the clouds are expected
to depart.

Strong cold air advection will remain in play in the wake of the
front.  850MB temps are suggested to fall toward -6C by 12Z, and
this cold air advection pattern will persist into Sunday. Thus lows
in the middle 30s will be expected.

Sunday...

Dry but colder weather is expected on Sunday. The deep low
pressure system over Ontario is expected to move to Quebec, while a
strong area of Canadian high pressure sets up over Saskatchewan.
This strong high will extend its influence south along the high
plains and east through the Mississippi valley. This will set up a
classic northerly transport of cold Canadian air across the upper
midwest to the Ohio Valley for Sunday. Forecast soundings suggest a
dry column through day, however some afternoon CU will be possible
as convective temperatures in the 40s are reached. This should be
rather minimal during the late afternoon hours. Thus Partly Cloudy
should work for the day. The moderate pressure gradient will remain
in place across Central Indiana also. This will result in gusty
northwest winds up to 25 mph through the daytime heating hours.

As cold air advection continues through the afternoon, 850mb temps
are suggested to fall toward -8C to -9C. Thus highs only in the
middle to upper 40s will be expected.

&&

.LONG TERM (Sunday night through Saturday)...
Issued at 259 PM EDT Sat Mar 16 2024

Sunday night through Monday night...

The long term period begins with a deep upper trough moving into the
region from the northwest bringing much colder air. Cold air
advection will lead to below normal temperatures through Monday
night. Early onset to greenup will likely be impacted by sub-
freezing temperatures and probable hard freeze Sunday night/Monday
morning and again Monday night/Tuesday morning. Widespread mid-upper
20s are expected for minimums across central Indiana both nights.
Breezy conditions are likely going to make it feel even colder. Wind
chills could fall into the teens both nights. Forecast confidence in
temperatures is high since guidance is in great agreement showing
little variability.

Dry conditions are likely Sunday night as surface ridging is in
place. By Monday morning, it appears there is at least a low chance
for an isolated snow shower or flurries. Low-level dry air and lack
of forcing limit confidence in precipitation chances during the
morning, but steepening low-level lapse rates within the cold air
advection regime should promote isolated light rain/snow showers
during the afternoon. RAP soundings show impressive 0-3km lapse
rates near 9 c/km and sufficient low-level instability for at least
isolated coverage. Only slight POPs were added at this time, mainly
across N/NE counties, due to some uncertainty with low-level dry
air/limited moisture over the area. Snowfall accumulations or
impacts are unlikely due to warm ground temperatures.

Tuesday onward...

As western high-latitude ridging and blocking pattern break down mid-
week, a quasi-zonal split flow regime will develop. The most
uncertain part of the forecast in the long term period is onset of
warming, which in some ensemble clusters is more rapid than others
(i.e., non-EPS weighted clusters). Regardless of specific
temperatures in the Tuesday-Wednesday time period, a warming trend
will be ongoing by then.

These split flow patterns are notorious for confining the deepest
moisture to low latitudes and it appears only modest moisture will
return with warm advection late week. Ensemble clusters are split
into the EPS-weighted drier pattern with dominate southern stream
wave, and GEFS-weighted wetter more amplified northern stream wave.
Thus, mid-range/chance probabilities are assigned for late Thursday
into Friday. Regardless, this will be a light precipitation event
per even the wettest outlier ensemble members.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 1203 AM EDT Sun Mar 17 2024

Impacts:

- Gusty winds again Sunday

Discussion:

Post-frontal winds will gradually subside through early morning
before becoming gusty again with the diurnal mixing cycle tomorrow.
VFR conditions will prevail. Forecast confidence is high.

&&

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

$$

SHORT TERM...Puma
LONG TERM...Melo
AVIATION...BRB


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