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000 
FXUS63 KIND 240451
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1151 PM EST Thu Feb 23 2017

.UPDATE...

The Aviation section has been updated below.

&&

.SYNOPSIS...
Issued at 307 PM EST Thu Feb 23 2017

.SYNOPSIS...
The unseasonably warm weather of the last week will come to an 
abrupt end Friday evening as a powerful cold front sweeps across the 
region.  Scattered thunderstorms and the threat for severe weather 
will accompany the passage of the front Friday afternoon and 
evening. Much colder conditions more typical of late February will 
return for the weekend along with the potential for snow showers 
late Friday night and Saturday. After a dry Sunday, wet and 
unsettled weather will continue through the first half of next week.

&&

.NEAR TERM /Tonight/...   
Issued at 931 PM EST Thu Feb 23 2017

Have slightly reduced pops and removed thunder for the night with
current convective development far less than short term models had
initially depicted. Front will make some progress north later
tonight and remove precipitation threat altogether for at least a
short time. Minor temp adjustments required in the vicinity of the
front over the far northwest. Previous discussion follows.

Issued at 307 PM EST Thu Feb 23 2017

Plenty of stratocu present across the region this afternoon as a 
warm front sets up over northern portions of the forecast area. Sun 
was peaking through the cloud deck sporadically...and the strong warm 
advection developing had enabled temps to surge into the mid and 
upper 60s over most areas despite the cloud cover.

Focus for the rest of the afternoon and evening is on potential for 
isolated to scattered convective development in the vicinity of the 
boundary and a wave traversing it moving into Ohio. Current 
mesoanalysis indicating an axis of MLCAPE values from 500-1000 J/KG 
extending east-west across the southern half of Ohio back into far 
eastern Indiana. These areas saw more sunshine and consequently 
better warming earlier. Despite the clouds over the area...appears 
further weak destabilization may develop back west into the forecast 
area beneath a subtle inversion. This is likely to be just enough to 
generate isolated convection for the rest of the afternoon...focused 
over the eastern half of central Indiana. Additional showers and 
perhaps a storm or two could extend back into the northern Wabash 
Valley into the evening with low level convergence in the vicinity 
of the warm front. 

Scattered showers and a few storms will focus over northern portions 
of central Indiana through the evening...gradually shifting north 
with the warm front overnight as the forecast area works solidly 
into the warm sector. Despite the presence of the nocturnal 
inversion...increasing flow through the boundary layer as a low 
level jet expands into the area will translate to increasing gusts 
at the surface late tonight into early Friday.

Temps...it will feel downright balmy tonight as the warm advection 
and increasing winds keep temps from falling much at all. MOS 
guidance looked reasonable as lows fall only into the upper 50s over 
much of the forecast area.  

&&

.SHORT TERM /Friday and Friday Night/...
Issued at 307 PM EST Thu Feb 23 2017

The primary focus for the period will be the threat for severe 
weather as storms impact the forecast area mainly during the 
afternoon and evening ahead of a strong cold front.

Friday morning will start windy and warm as the aforementioned warm 
front lifts into northern Indiana. Fair amount of moisture noted in 
the lower levels on both model soundings and RH progs and will 
likely see stratocu across the region.  With that being said...the 
moisture is shallow enough that some sunshine is anticipated into 
the early afternoon. Expect gusts to kick up rather fast during the 
morning as the initial surge of the low level jet noses into the 
area with the surface low tracking from northern Missouri into 
northern Illinois.

Focus then shifts to the severe weather threat which will begin to 
grown from 19-20Z into the evening. Model consensus has generally 
come into line on timing of the greatest threat for severe storms 
impacting the forecast area from mid afternoon through mid evening. 
Moisture return is a bit problematic and may serve as a mitigating 
factor on amount and intensity of storms. With that being said... 
overall dynamics associated with the system are strong enough to 
overcompensate for the limited moisture fetch. 

While the severe weather threat is present over the entire forecast 
area...the greatest risk will likely set up over the eastern half of 
central Indiana east into western Ohio. Potential exists in this 
area for an initial round of potentially discrete convection 
developing in the vicinity of the prefrontal trough followed by the 
squall line anticipated to organize along the cold front. The low 
level jet will transition across the region into the afternoon hours 
with the back side of the jet aligned over eastern Indiana and 
western Ohio.  Mid and upper level diffluence is pronounced with the 
exit regions of both jets over the Ohio Valley.  The upper jet 
structure in particular favors a splitting of the northern and 
southern jets over the Ohio and Tennessee Valleys...further 
accentuating the diffluence aloft. Wind analysis showing best 
potential for directional shear through the column will develop from 
Indy east around 21Z...maximizing over eastern Indiana and western 
Ohio into the early evening. The instability axis will align in this 
area too immediately along and ahead of the trough...with MLCAPEs 
around 1000 J/KG which is impressive for late February.

Taking all of this into consideration...plausible scenario 
developing where local and brief backing of the near surface layer 
along and immediately ahead of the prefrontal trough will present a 
brief enhanced threat for rotating storms and possibly tornadoes. 
Again...this looks to be focused over the eastern half of the 
forecast area in the 21Z to 00Z time period. The cold front itself 
will arrive during the evening and provide another round of severe 
weather in the mode of a thin...low topped and fast moving squall 
line with damaging winds as the primary threat. There will exist a 
small tornado potential as weak and short lived couplets develop 
along the line...a typical occurrence with Ohio Valley QLCSs. The 
presence of the stronger dynamics over eastern Indiana may allow for 
a strengthening of the convective line as it moves east across the 
forecast area.

The cold front and squall line will be east of the forecast area by 
03-04Z. Passage of the front will bring an abrupt end to the 
unseasonably warm weather enjoyed over the last week or so. Much 
colder air will spill into the region immediately behind the front 
Friday night with light precipitation redeveloping as wraparound 
moisture rotates into the area predawn Saturday. The boundary layer 
will become sufficiently cold enough to support rain mixing with or 
completely changing over to light snow by Saturday morning. 

Temps...generally took a split of the MOS guidance for highs Friday. 
Should the sun appear for an extended period of time...could easily 
see highs approach MAVMOS levels in the 70-75 degree range. Went 
slightly cooler than this in the upper 60s and lower 70s with the 
potential for the stratocu. Record high watch once again for Indy as 
the high of 71 from 2000 definitely could be threatened. 
Temperatures will tumble behind the front Friday night...falling 
into the 30s. Continued gusty winds will make it feel even colder. 

&&

.LONG TERM /Saturday through Thursday/...
Issued at 235 PM EST Thu Feb 23 2017

Temperatures tumble back to seasonal on Saturday in the wake of
the strong frontal system. With cyclonic flow and a little upper wave
moving through, could see enough forcing to produce brief snow
showers (or a mix of rain and snow in the south) across the area
during the morning hours. With the dry air also advecting in think
the initialization slight chance pops work well. By afternoon
enough dry air should be in place and the trough axis will be east
of the area so should see dry weather. Would not rule out a stray
sprinkle or flurry, but low enough chance to leave out at this
time. Brief ridging should allow for dry weather through Sunday
afternoon. For Saturday night this could mean mostly clear skies
and lows down into the low to mid 20s. Some return flow develops
on Sunday allowing highs to climb back into the mid 40s and Sunday
night lows should be near or just above the freezing mark with
increasing clouds and chances for snow or a rain snow mix as a
warm front forms south of the area and overrunning develops.

After that expect rain chances to continue until late Wednesday
night with the upper ridge off to the east and upper waves moving
through a more progressive upper flow with a trough to the west
and a ridge to the east. Model differences with temperatures and
precipitation chances past Monday night are pretty large and thus
fairly low confidence forecast from Tuesday on. For that reason
did not add any thunder Tuesday/Wednesday, as GFS and ECM differ
on availability and timing of instability. There is a signal that
the warmup will continue though, so should see warmer than normal
temperatures from Monday on.

&&

.AVIATION /Discussion for the 24/06z TAFs/...
Issued at 1150 PM EST Thu Feb 23 2017

Mainly VFR conditions expected.

Winds will be a significant impact, with gusts approaching 30KT
out of the southwest (190 to 210 degrees) in advance of a strong
cold front tomorrow.

Convection, perhaps strong to severe, will be a threat very late
in the period but is too uncertain in timing and impact for more 
than a VCTS mention at this time. Fluctuating conditions will be
likely within thunderstorms.

Expect some low level wind shear around 2kft as the low level jet
approaches overnight into Friday morning.

&&

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

&&

$$

SYNOPSIS...Ryan

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