687 
FXUS63 KIND 081131
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
631 AM EST Wed Nov 8 2023

...Updated Aviation Discussion...

.Short Term...(Today and tonight)
Issued at 301 AM EST Wed Nov 8 2023

* Near record high temperatures today in the upper 70s
* Last day of unseasonably warm air before more seasonal temps 
  arrives
* Potential for light showers tonight 

Current satellite imagery and surface analysis early this morning 
shows a warm front and associated stratus pushing northeast through 
Central Indiana. A large temperature gradient currently exists as 
the front is right on top of the region with Southwest Indiana 
already rising into the low to mid 60s while northeastern Indiana 
remains in the lower 40s. Expect temperatures to follow a non-
diurnal curve early this morning, with lows bottoming out a few 
hours before sunrise and temperatures quickly rising into the 50s 
and 60s with the passage of the front over the next several hours. 
Broad isentropic lift over the front will continue to result in 
cloudy skies in the vicinity of the front through the morning hours. 
Satellite imagery and soundings from around the region show very dry 
air behind the front with relatively clear skies already approaching 
southwestern Indiana. This will likely not be your typical cool 
season warm sector with mainly cloudy skies most of the time. 
Significant dry air through the column and the best forcing for 
ascent pushing north of the region with the front will likely lead 
to ample boundary layer heating today with the potential for record 
highs to be tied and/or broken. 

While there is no doubt it will be unseasonably warm today, the big 
question for today is how how well mixed will the boundary layer be? 
Some of the normally moisture biased models (i.e., NAM-based models) 
are extensive with deep moisture to the point where mixing is 
substantially limited, relative to the other extreme (i.e., GFS) 
that tend to over-mix. This will have implications for temperature 
and wind today and so forecast confidence is only low to moderate 
for those elements at this time. Current thinking is given the 
magnitude of the warm plume we would mix into, at least some mixing, 
and presence of fairly strong mass response-driven low-level jet 
attendant to the approaching trough/surface low, a blended model 
compromise should suffice. Nudged max temperatures in between the 
NBM 75th and 90th percentile for this afternoon. The past two days, 
highs have consistently been in this range and there really isn't 
any reason to believe we won't reach these levels again, even if 
there is lower confidence with how well mixed the boundary layer 
becomes. For winds, the forecast is not as windy as GFS Bufkit 
soundings would suggest due to concerns of over-mixing in that 
model, but it's worth noting there is a fairly high ceiling for wind 
gusts tomorrow. Adjusted wind gusts upwards of 25-30 kts for the 
afternoon hours, however would not be surprised to see sporadic wind 
gusts higher than that at or above 35 kts. 

Today's record high temperature for Indianapolis (for 11/8) is 79 
set in 2020. Records elsewhere across Central Indiana at other 
climate sites range from 79-82 degrees. Currently do not think 
record highs will be broken, even with the potential for deep 
mixing; however highs could come very close to that 79 degree mark 
for Indianapolis. Best chance for 80+ degrees is in far South 
Central and far Southwest Indiana where the strongest warm air 
advection is in addition to warmer low level temps aloft and less 
cloud cover. 

For tonight, a band of showers pushes in from northwest to southeast 
with the passing of the cold front. BUFKIT soundings continue to 
show a very dry column with limited low level moisture available for 
convective development. Even the overly moist biased models (NAM and 
NAM3K) show only scattered weak showers developing within a shallow 
saturated layer below a mid level inversion. Therefore, cutting back 
on PoPs for most areas to only have "chance" wording in the 
forecast. Keeping the highest chances for rainfall in the northeast 
quadrant of the forecast areas, an area closest to the surface low 
with slightly better forcing for ascent.

&&

.Long Term...(Thursday through Tuesday)
Issued at 301 AM EST Wed Nov 8 2023

- Seasonable and dry weather Thursday through Tuesday

Thursday through Saturday...

As we start Thursday, surface high pressure will be building across 
Illinois and Indiana in the wake of the departed cold front. Mainly 
a zonal flow will be in place aloft and this will protrude any polar 
continental air from arriving across the Ohio Valley. Moderate 
ridging in place over the Rockies will continue to allow for lee 
side subsidence across the plains, resulting in our area of surface 
high pressure.  This weak ridging remains west of Indiana through 
Saturday. This allows the surface high pressure to be the 
predominant weather feature, building across Central Indiana on 
Thursday and Friday, before passing across Indiana on Saturday. 
Forecast soundings show a very dry column through this period with 
subsidence in play. Thus partly cloudy skies can be expected for 
this period due to any passing high clouds within the flow aloft. 
Seasonable high in the 50s and lows in the 30s will be expected.

Sunday...

Models suggest a moderate upper trough along with a surface trough 
will push into the Great Lakes and Ohio Valley on Sunday. However 
with strong high pressure to the east and south, gulf moisture will 
be effectively blocked from reaching our area. Forecast soundings 
fail to show deep saturation as these features pass, showing 
saturation aloft due to some mid level clouds and plenty of dry air 
within the lower levels. Thus for now a dry forecast appears the way 
to go with just an increase in clouds as this wave passes.

Monday and Tuesday...

Even stronger upper ridging is expected to build across the plains 
states on Monday and Tuesday in the wake of the departed trough. 
This will once again promote lee side subsidence across the 
Mississippi and Ohio Valleys along with the Great Lakes. A strong 
area of surface high pressure will be pushing across Indiana on 
Monday and Tuesday. Again forecast soundings trend toward a dry 
column. No intrusions of warm  air from the south or cool air from 
the north appear present, thus continued seasonable temperatures 
with highs in the 50s and lows in the 30s under mostly clear skies.

&&

.Aviation...(12Z TAF Issuance)
Issued at 631 AM EST Wed Nov 8 2023

Impacts: 

* Easterly winds becoming southerly this morning with gusts of 20-
  30kts by the afternoon
* Winds shifting to the NW late tonight, then diminishing 


Discussion: 

Latest satellite imagery shows an area of lower clouds pushing 
northeast through North Central Indiana associated with the warm 
front. Observations indicate this cloud deck is around 3000-4000ft 
agl, with rising ceilings further to the southwest as the main 
forcing for ascent moves off to the north with the front. After the 
front moves northeast of the sites, winds will become southerly to 
southwesterly with gusts upwards of 30 kts mid morning through the 
evening hours. Before winds mix down after sunrise Wednesday, near 
LLWS conditions may develop briefly. Later this afternoon, potential 
is there for the boundary layer to mix out more than guidance 
suggests leading to gusts over 35 kts at times. Currently do not 
have that in the TAFs, but wanted to at least mention the potential 
for that within the 18-22z timeframe.

Showers move in from the northwest towards the end of the TAF 
period. Forecast soundings indicate an influx of low level moisture 
during this timeframe, potentially leading to MVFR or lower ceilings 
with passing showers. Winds during this time frame will also become 
more westerly, then northwesterly as a cold front pushes through the 
region late tonight.

&&

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

$$

Short Term...CM
Long Term...Puma
Aviation...CM