900 
FXUS63 KIND 242003
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
303 PM EST Wed Jan 24 2024

.Key Messages...

- Dense Fog Advisory 4PM this evening to 10 AM Thursday North 
Central Indiana 

- Dense Fog Advisory 7 PM this evening to 10 AM Thursday along and 
south of I-70 corridor 

- Isolated rain showers tonight, then steadier, heavier rain 
  during the day Thursday

- Ice Jam and river flooding threat continues in Wabash River Valley

&&

.Short Term...(This evening through Thursday)
Issued at 303 PM EST Wed Jan 24 2024

.This evening and Tonight...

DENSE FOG EXPECTED AGAIN TONIGHT FOR MUCH OF CENTRAL INDIANA

Observations indicate a deep frozen ground layer 6 to 9 inches in 
depth across Central Indiana. Continued warm air advection on top of 
cold surface will promote fog development this evening into the 
overnight hours. Elongated area of low pressure, stretching from 
Illinois southwestward to Texas, will slowly push eastward over the 
state tonight resulting in a weakening pressure gradient and 
decreasing winds. With a saturated boundary layer already, expect 
dense fog to rapidly develop later this evening and into the 
overnight hours. Will go ahead and issue a Dense Fog Advisory for 
North Central Indiana from 4 PM this evening to 10 AM Thursday as 
observations in that area already show rapidly dropping visibility 
down to 1/4 mile at times. Starting the advisory a few hours later 
along and south of the I-70 corridor as visibility in this area has 
been slowly to drop. Expect visibility to bounce around through the 
evening and overnight hours between 1/4 mile and mile, likely 
improving some from south to north Thursday morning as rain pushes 
back in. Near 100 percent saturation of the boundary layer should 
also prevent temperatures from falling too much overnight, so have 
increased lows to the low 40s in the north and mid to upper 40s 
further south. With the elongated area of low pressure coming right 
over the region, expect a good NW to SE temperature gradient across 
the state. 

.Thursday...

The next wave moves northeastward into Central Indiana by tomorrow 
evening with widespread rainfall out ahead of it. Rainfall should 
increase from south to north late tomorrow morning into the 
afternoon hours. Increased low level mixing during the day Thursday 
should result in slightly improving visibility, however expect very 
similar conditions to Wednesday with persistent low clouds and rain.

Guidance suggest an additional 0.30 to 0.60 inches of rain for the 
region with this next round of rainfall. Saturated and frozen 
grounds will promote runoff of additional rainfall. Will continue to 
keep an eye on area rivers and streams as additional rainfall along 
with warmer temperatures will increase the ice jam and flooding 
threat, especially in the Wabash River Valley. 

Temperatures will also be similar Thursday to Wednesday with a NW to 
SE gradient across the state. Expect highs in the low 50s ahead and 
east of the low track in Eastern and Southern Indiana and 
temperatures in the mid 40s along and northwest of the low.

&&

.Long Term...(Thursday night through Wednesday)
Issued at 303 PM EST Wed Jan 24 2024

The possibility for additional rounds of rain, ice jams, and 
flooding are the main concerns late this week into the weekend as a 
few disturbances are expected to move through within southwest flow 
aloft.

Thursday night through Friday night...

A low pressure system associated with an upper shortwave will be 
directly overhead at the start of the period. Favorable dynamics 
combined with anomalous moisture will support widespread 
precipitation. QPF amounts will remain light, generally around a few 
tenths of an inch due to how fast the system is moving. However, 
both rain and warm advection will lead to more ice melt with the 
potential for additional ice jams and flooding. The aforementioned 
low will quickly depart by late Thursday night. Forecast soundings 
then show increasing subsidence aloft behind the disturbance as 
subtle upper ridging builds in. This will trap abundant moisture in 
the low levels, promoting low stratus and fog development.

Surface high pressure and upper ridging will provide quiet weather 
conditions on Friday. Clouds will stick around due to abundant low-
level moisture beneath subsidence aloft. Temperatures begin to cool 
down slightly heading into the weekend due to weak cold air 
advection, but will still remain above normal. Expect limited 
diurnal temperature swings from increased cloud cover with highs in 
the 40s and lows in the 30s

Saturday through Sunday...

Another low pressure system associated with a deeper trough may move 
across the region over the weekend bringing additional chances for 
precipitation. Latest ensemble guidance has trended noticeably 
slower suggesting precipitation could linger into Sunday. Some 
uncertainty remains regarding the track of this system, but 
generally the favored location is just south of the Ohio River. This 
supports the best chance for rainfall across southern portions of 
the area where greater moisture return is expected. Rain will likely 
begin to overspread central Indiana Saturday afternoon. By Saturday 
night, some guidance suggest snow will mix in due to weak cold air 
advection and dynamic cooling northwest of the surface low. Forecast 
soundings show if any snow mixes in SLRs will be fairly low as low-
level thermal profiles are marginal. This will limit the potential 
for snowfall accumulations. Minor accumulations are however still 
possible, especially if snowfall rates are heavy enough. Clouds 
should linger through the day Sunday with the potential for some 
lingering light precipitation.

Sunday night onward...

Quiet weather conditions are expected next week as upper ridging 
builds across the western CONUS with northwest flow aloft across the 
Midwest. A few subtle impulses may approach the area from the north 
supporting a few minor chances for light rain, but confidence is low 
at this time. Southwesterly flow returning will warm temperatures 
next week.

&&

.Aviation...(18Z TAF Issuance)
Issued at 1240 PM EST Wed Jan 24 2024

Impacts:

- LIFR to IFR cigs and vis generally expected through the TAF period 
- Dense fog expected to redevelop overnight tonight

Discussion:

Low visibility and cigs persist across all of Central Indiana this 
afternoon. With the weather pattern remaining largely the same over 
the next 24 hours, expect these conditions to continue into the 
overnight hours and through tomorrow. 

Rainfall will become more sporadic this afternoon and evening, 
tapering off to areas of drizzle this evening into the overnight 
hours. Warm air advection over a frozen ground in addition to a 
saturated boundary layer supports IFR to LIFR cigs and vis due to 
low clouds and fog the rest of this evening and overnight. Expect 
visibility to fall back towards 1/4sm to 1sm overnight at most 
locations. Rainfall moves back into the region from the south late 
Thursday morning, which may work to slightly increase visibility. 
Have a slight improving trend at all TAF sites towards the end of 
the TAF period, however still expect sub MVFR conditions through 
Thursday.  

 
Southeast winds this afternoon will gradually shift and become 
southwesterly this evening then more easterly and northeasterly 
overnight as an elongated area of low pressure pushes northward 
toward the region. Speeds should remain under 10 kts through the 
period though.


&&

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

$$

Short Term...CM
Long Term...Melo
Aviation...CM