115 
FXUS63 KIND 280157
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
957 PM EDT Fri Oct 27 2023

.Forecast Update...
Issued at 957 PM EDT Fri Oct 27 2023

Convection continued to overspread the Wabash Valley late this 
evening with a couple embedded stronger, yet well below severe 
limit cells, that were moving ENE around 35 knots. CAMs were 
showing that and upstream activity spreading east across central 
Indiana through the night. Continued 305K Isentropic lift and a 
saturating column supports post frontal convection. The cold front
currently was extending from around Danville, Illinois to 
Farmington, Missouri and it will sweep quickly southeast across 
central Indiana late this evening and overnight and be clear of 
all of central Indiana before daybreak. 

MRMS, dual Pol and legacy precipitation products suggest the 
isolated heavy cells could leave a corridor of 0.50+ inches of QPF 
with most areas seeing below a quarter inch.

Lightning data and weakening instability suggests lightning strikes 
will likely be few and far between.  

Temperatures behind the front have dropped by some 15 to 20 degrees, 
which supports the current forecasted overnight lows in the mid 40s 
northwest to mid 50s southeast.

&&

.Short Term...(This evening through Saturday)
Issued at 300 PM EDT Fri Oct 27 2023

Clouds have been been slow to clear out, but at least some clearing 
is expected later this afternoon as drier air aloft mixes down. A 
cold front will move in from the west this evening with numerous 
showers overspreading the area. Long-skinny CAPE profiles with less 
than 1000 J/kg of instability could support isolated thunderstorms 
at times. Convection will dissipate towards daybreak Saturday as 
drier air filters in behind the departing surface cold front. Winds 
will become northerly overnight and eventually northeasterly on 
Saturday.  

Guidance shows mean flow becoming parallel to the elevated 
850-700mb cold front once it moves into central Indiana. This will 
keep the baroclinic zone over the region providing more chances for 
rain. Much of the day Saturday looks quiet due to subsidence behind 
the aforementioned surface cold front. Forecast soundings show a 
developing subsidence inversion above a saturated lower troposphere. 
This will likely keep much of the area mostly cloudy. Showers are 
then expected to begin moving in towards the end of the period as a 
wave tracks along the baroclinic zone. CLouds and N/NE will keep 
temperatures in the mid 50s to low 60s.

&&

.Long Term...(Saturday night through Friday)
Issued at 312 PM EDT Fri Oct 27 2023

* Heavy Rainfall Totals Likely From Saturday Night-Sunday Night
* Halloween Unseasonably Cold + Blustery...Snow Showers Possible
* Widespread Hard Freezes, Near Record Cold Begins Monday Night

Saturday Night through Sunday Night...

Middle to late portions of the weekend will bring three periods of 
much-needed rain to central Indiana, with increasing confidence in a 
1.00 to 1.75 inch storm total across most central and southern 
counties.  Synoptically, an elongated but stalled frontal boundary 
will extend from Texas to Pennsylvania, with a large corresponding 
anafrontal zone draped over the region.  The lack of any potent 
surface low will be complemented by broad approaching mid-level 
forcing from a deep upper trough...as well as strengthening 
isentropic lift as potent Canadian high pressure plunges southward 
through the Plains.

Rainfall amounts should be greater during the two overnight periods 
...first from moist flow off of the western Gulf Saturday night... 
and then from more dynamic lift as the changing pattern pushes 
through Sunday night.  Rainfall during both 12-hr period should be 
0.20-0.80 inches for most locations...with only moderate confidence 
due to some lingering model inconsistencies...that Saturday night 
should overall produce more rain.  Rainfall is still expected during 
the day Sunday, in what should be a lull in heavier/steadier 
precipitation...totaling closer to 0.10-0.25 inches for most 
locations.  Storm total rainfall will exhibit the usual north-south 
gradient...following during of precipitable water over 1.20 
inch...which will be briefly over the upper Wabash Valley, and 
throughout much of the weekend south of the I-70 corridor.  The 
potential for storm totals exceeding 2.00 inches does exist 
south/west of Bloomington...this possibility will be refined over 
future updates.  High confidence in no river flooding as the region 
will need twice of this weekend's potential to leave drought 
intensity...although low-lying areas and small creeks/urban drainage 
could briefly flood if caught under a heavier rain band.

Temperatures will continue the near normal trend established during 
the day Saturday with mainly light northerly breezes and cloudy 
skies within the frontal zone allowing only modest diurnal 
variations.

Monday and Tuesday...

Mainly dry conditions will return to central Indiana for the early 
work-week...yet significantly colder conditions will be the main 
story as a broad and deep H500 trough, occupying most of North 
America...advances into the Midwest.  Corresponding surface high 
pressure will be delivered from western Canada in two doses...the 
first ridge following the departing rain, building in from the 
southern Plains...before a rather potent reinforcing shot slams 
across the Plains, reaching Indiana just in time for trick-or-
treating late Tuesday.

This part 2 will be following a more potent 
H500 short wave embedded in the broad upper trough, which may well 
work with the warm and wide open Lake Michigan to bring flurries and 
at least isolated lake-enhanced snow showers within a 12 hour period 
that may well match with the late Tuesday Halloween festivities. 
Location and scope of potential flurries would be favored along/ 
north of I-74...although even southern counties could see flakes 
should the short wave dig far enough south before swinging through. 
No impacts are expected from any snow per rather warm ground and 
antecedent air temperatures likely rebounding well above freezing 
earlier on Tuesday.

The record lows for the Indianapolis Area on both Monday night and 
Tuesday night are 24F...current forecasted minimums are 3 degrees 
higher each night.

Wednesday through Friday...

The rest of the mid-week will more closely resemble early winter 
than early November...as the very broad surface high pressure dome 
shifts steadily progresses from the southern Plains to the Mid-
Atlantic coastline.  The surface ridge will tilt clockwise with the 
southern half buried over the southern CONUS while northern portions 
twist eastward amid the faster zonal flow to our north.  The 
resultant southwest to northeast alignment while the ridge slides to 
our south...will block any Gulf moisture from returning to the 
Midwest. Meanwhile lowered mid-level heights and NW/W breezes will 
maintain readings 10-15 degrees below normal through Wednesday night.

Return flow, at times robust, will be then be the rule for Thursday-
Friday...courtesy of the gradient between the 1030 mb surface ridge 
to our east-southeast and a modest open wave low crossing the 
northern Plains.  WAA and ample sunshine will slowly moderate 
temperatures back to to near seasonable levels by the end of the 
work week.  The normal max/min at Indianapolis through the long term 
is 59/40.

&&

.Aviation...(00Z TAF Issuance)
Issued at 656 PM EDT Fri Oct 27 2023

Impacts:

- MVFR and briefly IFR ceilings possible in showers, mainly 
  after 02z tonight, starting earliest at KLAF and KHUF

- MVFR ceilings remaining and showers ending toward 12z

- More showers possible at KHUF and KBMg after 21z Saturday 

Discussion: 

Deteriorating flying conditions and showers are expected by late 
evening as a cold front drops southeast across the terminals. The 
showers will be ending toward daybreak. There is a very low 
possiblilty of thunder. There will be a break in the cloud cover 
Saturday morning in the wake of the front. However, more showers 
will move in from the southwest late Saturday afternoon and evening, 
due to warm air overrunning the front and a wave lifting northeast 
along the front. 

Winds will be 10 knots or less and switch from southwest to 
northwest and north late this evening and early overnight, in the 
wake of the front.


&&

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

$$

Update...MK
Short Term...Melo
Long Term...AGM
Aviation...MK