591 
FXUS63 KIWX 131828 CCA
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
226 PM EDT Mon Sep 13 2021

.SYNOPSIS...
Issued at 226 PM EDT Mon Sep 13 2021

Thunderstorms become likely late Tuesday afternoon into Tuesday 
night as a cold front approaches. Some of these storms may be 
strong to severe with damaging winds. Isolated large hail and 
torrential downpours are also possible. A chance of showers and 
storms will linger Wednesday, primarily southeast of US 24. It will 
be a bit cooler Wednesday, but the unseasonable heat will return by 
the weekend. 


&&

.SHORT TERM...(This Evening through Tuesday)
Issued at 226 PM EDT Mon Sep 13 2021

Steep mid level lapse rates and associated capping inversion to 
quell convection over northernmost CWA through most, if not all of 
tonight into Tuesday morning. Otherwise, anticipate ongoing upstream 
convection through MN/IA at daybreak. This in advance of a robust 
shortwave trough, presently from the northern part of Manitoba into 
eastern Montana. Primary focus on increased strong to severe risk 
later Tuesday evening into the early night, roughly 5 pm to 
midnight. Both prefrontal initiation with steep low/mid layer lapse 
rates and near 70F surface dewpoints contributing to around 2000-
2500 J/kg environment by late afternoon. Prefrontal region 
instability to be collocated with uptick in deep layer shear on 
order of 30-35 knots as southern periphery of mid level jetlet 
approaches. Primary speed shear with concerns centered around wind 
threat as primary. Moisture laden downdrafts and storm motion should 
yield a few isolated strong to low end severe reports. Initial 
convection could also produce large hail to one inch in diameter in 
initial/more discreet storm mode. Additional storm risk tied to 
frontal zone and lagged upper level support, though expect this to 
be on relative quick downturn through late evening as boundary layer 
instability decreases. Torrential downpours with a non-zero risk for 
urban/small stream flooding with warm cloud depths to 12-13kft and 
precipitable water values touching 2.0 inches in narrow corridor. 

&&

.LONG TERM...(Tuesday Night through Monday)
Issued at 226 PM EDT Mon Sep 13 2021

Second strong upstream shortwave trough over Gulf of Alaska to 
central Canada by Thursday. This feature is higher belted than Day
2 system. Concern here is to what extent subtropical ridging and 
weak surface ridge can hold convection at bay to the northwest 
through north of CWA, as intervening ridge may retrograde west in 
deference to potential western Atlantic tropical depression 
formation. This would tend toward dry and quite warm this weekend 
into early next week. Will temper blends slight chance pops in 
preference for dry/no mention this timeframe. 

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday Afternoon)
Issued at 100 PM EDT Mon Sep 13 2021

VFR conditions to prevail throughout the 18z TAF issuance. Models
do hint at the potential for shallow ground fog around 11z to 13z
Tuesday morning given increasing low level moisture. At this point
have decided not to include in prevailing conditions given low
confidence of occurrence. Gusty winds develop around midday 
Tuesday as stronger 850mb winds start to mix to the surface. Any 
convective concerns look to develop beyond this forecast window. 


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...Small Craft Advisory from 6 AM to 5 PM EDT Tuesday for LMZ043-
     046.

&&

$$

SYNOPSIS...Murphy
SHORT TERM...Murphy
LONG TERM...Murphy
AVIATION...CM


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