218 
FXUS63 KIND 221617
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1117 AM EST Wed Dec 22 2021

...Updated Aviation Discussion...

.Forecast Update...
Issued at 950 AM EST Wed Dec 22 2021

Surface analysis this morning shows high pressure in place over the 
mid Mississippi valley with a surface ridge axis extending north to 
western WI. This was resulting in continued NW surface flow to 
central Indiana of cool and dry air. GOES16 shows clear skies across 
the state. Some mid cloud over MN/W WI/NW IL was advancing SE toward 
Indiana within the flow aloft.  

Forecast soundings and time heights tonight show a dry column across 
the area this afternoon as the surface high pressure system advances 
eastward into the Ohio Valley. Forecast soundings also show a 
strong inversion in place aloft that will keep cooler air trapped 
near the surface and prevent any CU development. Thus will continue 
with a mostly sunny sky this afternoon with chilly highs in the low 
to mid 30s. Overall...the forecast remains in good shape.

&&

.Short Term...(Today through Thursday)
Issued at 249 AM EST Wed Dec 22 2021

A cold front had quickly moved across the region late Tuesday 
evening and was now off to the southeast of the area. Colder air was 
rushing into the region behind the front with gusty northwest winds. 
07Z temperatures had fallen into the upper 20s and lower 30s over 
the forecast area with gusts occasionally up to 30-35mph.

The weather will remain quiet through late Thursday but with a brief 
backward slide to temperatures today before we resume the warming 
trend set to peak at the end of the week. An amplified upper trough 
trailing the cold front will track across the lower Great Lakes 
early this morning with a quasi-zonal regime in its wake for later 
today gradually transitioning to a broad upper level ridge over much 
of the country on Thursday.

At the surface...high pressure already in the process of resuming 
its hold across the region in the wake of the Tuesday evening 
frontal passage. The high will track across the Ohio and Tennessee 
Valleys later today into tonight maintaining a cold northwest flow 
across the region for much of today before winds back late. The 
gusty winds immediately behind the frontal passage will linger for 
the next few hours before dropping back later this morning as the 
strongest cold advection diminishes and surface pressure gradient 
relaxes. Periodic mid and high clouds will drift across the area 
through the afternoon in what otherwise should be a day filled with 
abundant sunshine.

Skies will remain mostly clear tonight with low level flow backing 
to a return southerly flow on the back side of the departing high 
pressure. Winds will steadily increase on Thursday in response to a 
sharpening of the pressure gradient between the retreating high and 
low pressure moving out of the upper Midwest. Increasing warm 
advection will aid in increasing clouds within the boundary layer as 
an inversion likely organizes. Some uncertainty with respect to how 
widespread the cloud coverage becomes...but the increase in moisture 
underneath the inversion supports at least partly cloudy skies 
focused especially across the northern half of the forecast area 
Thursday afternoon. 

Temps...chilly day in store today with cold advection well 
established across the region. Even despite sunshine...low level 
thermals support only low to mid 30s for highs for much of central 
Indiana. The arrival of warm advection and brisk S/SW flow on 
Thursday will bring a nice bump in temperatures on the order of 10-
15 degrees over today. Lows tonight will fall largely into the lower 
and mid 20s.

&&

.Long Term...(Thursday Night through Tuesday)
Issued at 249 AM EST Wed Dec 22 2021

The long term period will largely be characterized by fast 
quasizonal to weakly anticyclonic flow over the CONUS, becoming more 
amplified with time to a western trough/eastern ridge pattern, 
placing central Indiana under the influence of southwest flow aloft.

Weak disturbances in this fast upper level flow will keep multiple 
chances for precipitation in the forecast, with most if not all of 
it falling as rain thanks to the above normal temperatures expected 
throughout the period.

Introduced some slight chances for rain on Christmas day that was 
not in the NBM given models the last couple of nights have continued 
to depict some QPF with a weak surface wave moving through the area. 
Otherwise, stuck fairly close to initialized PoPs.

&&

.Aviation...(18Z TAF Issuance)
Issued at 1117 AM EST Wed Dec 22 2021

IMPACTS:
- VFR conditions are expected this TAF period.
- No impacts expected throughout the forecast period

Discussion: 

Surface high pressure over the middle Mississippi valley will build 
east across Indiana this evening before moving east of Indiana 
overnight. GOES16 shows clear skies arriving through the period as 
forecast soundings continue to show a steep inversion aloft 
preventing any diurnal CU.

Overnight as the surface ridge builds east...a weak upper level 
disturbance is expected to push east from the upper midwest. This 
may result in some mid and high cloud arriving overnight...but any 
CIGS will remain VFR.

NW winds are expected this afternoon ahead of the passing high but 
are expected to become southerly overnight as the High passes to the 
east of Indiana.

&&

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

$$

Update...Puma
Short Term...Ryan
Long Term...Nield
Aviation...Puma