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000 
FXUS63 KIND 210458
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1158 PM EST Wed Feb 20 2019

.UPDATE...
The AVIATION Section has been updated below.

&&

.SYNOPSIS...
Issued at 318 PM EST Wed Feb 20 2019

A frontal system will push off to the east early this evening. In 
the wake of this front, high pressure will move through the Ohio 
Valley on Thursday. A strong low pressure system is expected to 
affect the area over the upcoming weekend. High pressure is expected 
to build into the area for early next week.

&&

.NEAR TERM /Rest of This Afternoon and Tonight/...
Issued at 318 PM EST Wed Feb 20 2019

A weak broad occlusion currently arcing across eastern Illinois, 
with areas of rain and fog along and ahead of this feature. Short 
term models suggest this feature will drift across the area during 
the rest of the afternoon, passing off to the east around 210000Z. 
Will continue the PoPs into the early evening hours until frontal 
passage, and cut them after that. 

Short term model data suggests low cloud cover may begin to scatter 
out from the southwest late tonight, although it appears there will 
be quite a bit of high cloud cover lasting most of the night.

Low level thicknesses suggest the GFS MOS lows tonight are probably 
too cool. Will bump up the guidance lows tonight about 2-5 degrees.

&&

.SHORT TERM /Thursday through Saturday/...
Issued at 318 PM EST Wed Feb 20 2019

It appears the precipitation focus for Thursday and Thursday night 
will be south of the forecast area, closer to the Tennessee Valley. 
Some of the ensembles bring the northern fringes of the precipitation 
threat close to the southern border zones, so this may have to be 
watched in case things start to trend north. For now, will keep 
Thursday and Thursday night dry.

Warm advection begins to spread across the area by Friday, as the 
next upper trough moves into the Plains. Will bring in chance PoPs 
for rain to the southern zones by Friday afternoon, and all areas 
Friday night.

Stronger forcing is expected to arrive by Saturday, as models prog a 
low level jet, possibly in excess of 60 kts, will nose into the 
area, coupled with advection of precipitable waters near the top end 
of climatology. Will go with high PoPs for Saturday. The combination 
of a strong low level jet, very high precipitable waters, and some 
elevated instability, suggest potential for heavy rain and embedded 
thunderstorms on Saturday. Deep layer shear may also become very 
high by Saturday afternoon, with the approach of a 100-120 kt 500mb 
jet.

Progged low level thicknesses suggest the GFS MOS highs for Friday 
look too warm. Will cut about 5 degrees off of the guidance highs in 
that period. Other periods look OK for now.

&&

.LONG TERM /Saturday Night through Wednesday/...
Issued at 318 PM EST Wed Feb 20 2019

The beginning of the extended period will be the most active
portion of the forecast as a surface low rapidly deepens Saturday
night as it tracks northeast into the Great Lakes. The potential 
for severe storms will exist during the evening along and 
immediately ahead of the associated cold front. At this early 
stage...shear and helicity profiles are quite impressive with 
strong mid and upper level diffluence courtesy of a split jet 
regime aloft. 

A classic high shear/low CAPE environment would likely support a 
fast moving low topped squall line impacting parts of the region 
Saturday evening. With 60kt winds as low as 2-3kft...damaging 
winds will be the primary threat but the available helicity 
values in the lowest 1-3 km will support an isolated tornado risk 
too. The higher severe weather threat will likely be displaced to 
the southwest of the forecast area...but have seen these cool 
season setups too many times to discount potential here in central
Indiana. 

Any threat for severe convection will end as soon as the front 
passes Saturday evening. However...the primary impact will shift
to a prolonged period with strong winds that will likely last into
Sunday evening due to a combination of an extremely tight surface
pressure gradient between the intensifying surface low and strong
high pressure diving out of the Canadian prairies. With post
frontal cold advection and continued strong flow through the
boundary layer...growing concern that peak gusts will be well 
into Wind Advisory criteria and possibly higher. This will be
something to closely monitor in addition to the severe threat 
going forward in the coming days. But it is awfully impressive 
that sounding data already suggesting potential for peak gusts to 
push 50mph if not slightly higher at 3 1/2 to 4 days out.

The remainder of the extended will be largely quiet as opposed to
the first 24 hours. The aforementioned Canadian high will take
over for early week with dry and cool weather. A fast moving 
front and low will track into the region late Tuesday into 
Wednesday and enough cold air will be present for a rain/ snow 
mix. Beyond the seven day...hints continue to show that the
predominantly zonal flow regime aloft will transition to a
northwest flow with more substantial cold impacting the region for
the end of February into early March.

&&

.AVIATION /Discussion for the 21/06Z TAF Issuance/...

Issued at 1153 PM EST Wed Feb 20 2019

Conditions have improved more quickly than forecasted in previous
TAF period. VFR conditions have already returned to all TAF sites
with KIND be the outlying site, but VFR will also return there
within the next few hours. High pressure continues to strengthen
over the TAF sites, and conditions will stay at VFR levels through
the end of the TAF period. Meanwhile, winds will generally be
westerly at 5 to 11 kts except for some 13 kt sustained speeds at
KIND for a few more hours.

&&

.IND WATCHES/WARNINGS/ADVISORIES...NONE. 

&&

$$

SYNOPSIS...JAS

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