Area Forecast Discussion
Issued by NWS Indianapolis, IN
FXUS63 KIND 231951
Area Forecast Discussion
National Weather Service Indianapolis IN
251 PM EST Thu Feb 23 2017
The LONG TERM Section has been updated below.
Issued at 258 AM EST Thu Feb 23 2017
A series of frontal systems will move through central Indiana during
the next week, creating occasional chances for precipitation. The
warm streak will come to an end after Friday as closer to normal
temperatures return for the weekend behind a strong cold front. This
front could bring severe thunderstorms Friday.
.NEAR TERM /Rest of Today/...
Issued at 1007 AM EST Thu Feb 23 2017
Stratus expanding in coverage this morning with fog lingering in
some locations. Temperatures at 15Z had risen quickly in the 60s
where the sun was or had been out already this morning. Locations
under stratus and/or fog remained in the 50s.
Axis of thickest stratus appeared to be in the vicinity of a
frontal boundary which will transition into a warm front this
afternoon as low pressure gets its act together over the High
Plains. Hi-res guidance continues to highlight isolated convective
development in the vicinity of the boundary and a weak wave riding
along it over the northern half of the forecast area this
afternoon. Model soundings favor subtle instability present with a
capping inversion limiting more substantial levels of available
CAPE. Will continue with chance pops and an isolated thunder
mention focused over the northern half of central Indiana.
Greatest potential coverage likely to be from Indy and points
northeast where MLCAPE expected to be in greatest abundance and
near the location of the subtle surface wave traversing the front.
Other issue for the rest of the day is how expansive low clouds
become and what impacts that might have on temps. As mentioned
above...temps have shot up quickly this morning where some
sunshine has been realized. Despite the presence of stratus into
the afternoon in many locations and an otherwise limited amount of
sunshine...have chosen to bump up highs a degree or two from I-70
south based on where current temps are at 15Z. Think potential
exists for Indy to make a run at 70 even with a fair amount of
Zone and grid updates already out.
.SHORT TERM.../Tonight through Saturday night/
Issued at 258 AM EST Thu Feb 23 2017
Models are close enough that the SuperBlend initialization
was accepted for most items.
A similar setup to this afternoon will continue across the area this
evening, with flow aloft over the surface front. Forcing looks a
little better so went with higher PoPs than this afternoon but still
no higher than the chance category. Highest PoPs will be across the
north, closer to the surface front.
As the front moves north as a warm front overnight, forcing weakens
and PoPs will lower from south to north during the night.
On Friday morning, there won`t be much forcing with the area in the
warm sector. Kept some low PoPs north to account for any lingering
rain from the exiting warm front.
As the upper trough and a cold front approach the area during the
afternoon, PoPs will increase once again. Instability builds in the
warm sector and shear increases. A couple of lines of showers and
storms could develop across the area, one with a pre-frontal trough
and one with the front itself.
Will go with chance PoPs most areas during the afternoon, with some
likely PoPs far northwest close to the surface front. Severe storms
will be possible with decent instability and good shear. The Storm
Prediction Center`s Day 2 Convective Outlook covers this well and
should be read for details.
The NAM allows for clearing and temperatures into the low and mid
70s (The MET MOS for Indy has a high of 75, 1 degree shy of the all
time record high for the month of February). Feel this is too
optimistic as cloud cover should keep readings down.
As the upper trough and cold front move through Friday evening, went
likely or higher PoPs most areas. The threat for severe storms will
continue for areas ahead of the front. Overnight, have some low PoPs
to account for any wrap-around precipitation.
These low PoPs will continue into Saturday north. Otherwise dry and
much colder conditions will be the rule.
.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 231800Z TAF Issuance/...
Issued at 1215 PM EST Thu Feb 23 2017
MVFR stratus will continue to impact the area at times this
afternoon and again Friday morning.
Frontal boundary draped across the area this afternoon with
stratus in the vicinity of the boundary and cu developing further
south. Ceilings have generally been below 2kft on the stratus with
the cu developing at a higher level between 3 and 4kft. The
boundary will transition to a warm front this afternoon and begin
to lift north...with the lower stratus likely maintaining over
northern portions of central Indiana. Further south...expect
continued cu development within a weakly unstable airmass.
Potential for isolated convective development during the second
half of the afternoon as well...especially at KIND and KLAF.
Confidence levels in convective impacts are too low to consider
any more than a VCSH mention at KLAF but will continue to monitor.
Scattered showers or perhaps a few rumbles of thunder remain
possible this evening over northern portions of central Indiana
before the front shifts north of the region late tonight. Model
soundings indicate potential for a reestablishment of MVFR
ceilings during the predawn hours and into Friday morning. Winds
will begin to increase substantially Friday morning as an intense
low pressure system tracks into the mid Mississippi Valley and
eventually the Great Lakes. Expect southwest winds to become gusty
early Friday morning and continue for much of the day...with max
gusts in excess of 30-35kts becoming likely.
Threat for stronger convection ahead of the cold front will impact
the terminals late afternoon into the evening Friday.