Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 191442
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
940 AM EST Mon Feb 19 2018

.UPDATE...
The Near Term Section has been updated below.

&&

.SYNOPSIS...
Issued at 345 AM EST Mon Feb 19 2018

A highly amplified flow pattern across the country for much of the
upcoming week will maintain a moist southwest flow into the Ohio
Valley with multiple opportunities for heavy rain and eventually a
growing threat for flooding as the week progresses. Temperatures
will be above normal for much of the next seven days...including
well above normal levels today and Tuesday.

&&

.NEAR TERM /Rest of Today/...
Issued at 940 AM EST Mon Feb 19 2018

Radar and short term model guidance suggests most of the organized
lift and rainfall will be near or north of the northwest border
zones for the rest of the day. It does appear intermittent shower
activity will linger over the area at least into the early to mid
afternoon hours based on radars upstream.

Highs today over the south may be on the warm side based on this
morning`s upper air, but will leave them alone for now and monitor
temperature trends over the next several hours.

Previous discussion follows.

Scattered showers with a few rumbles of thunder continue to expand
rapidly across the northwest half of the forecast area early this
morning at the nose of a strong low level jet moving into the area.
08Z temperatures were generally in the 40s across central Indiana.

The onset of the wet and active regime that has been discussed the
last few days is ramping up as a combination of the strong low level
jet and increasing warm advection is contributing to a steadily
expanding area of showers with a few rumbles of thunder since late
last evening. Expect continued precipitation expansion through
daybreak focused along and north of I-70.

A warm front will extend east into the northern half of the forecast
area by daybreak then gradually shift north through the course of
the day. The front will serve as a focusing mechanism for the axis
of steadiest rainfall across the northwest half of the forecast area
into the afternoon with rain showers remaining much more isolated
further south across central Indiana. There may be a brief lull in
rainfall coverage during the early afternoon before a secondary wave
brings a renewed surge of rain showers into the northwest half of
the forecast area for the second half of the afternoon. The low
level jet will persist across the region into the afternoon with
precip water values surging up to 1.3 to 1.4 inches. The combination
of the deep moisture and low level forcing will promote locally
heavy rainfall and the potential for a few thunderstorms into the
afternoon. Categorical pops are warranted over much of the northern
half of the forecast area...dropping off to low chances further
south.

CAMs guidance overnight has come in more aggressive with
precipitation amounts near and north of I-70 today...suggesting 1 to
1.5 inches are possible by this evening. Considering much of the
northern half of the forecast area was not impacted as substantially
by the heavier rainfall last Thursday...and there is not a snowmelt
component to address unlike locations over northern Illinois and
Indiana...plan on holding off on issuing a Flood Watch this morning.
That being said...these rainfall amounts will likely prime flooding
potential as the week goes on...with a more enhanced flood threat
developing Tuesday into Wednesday.

Temps...much warmer air will surge into the region today with entire
area rising to well above normal levels. Felt the MAV guidance was a
bit aggressive with its temperatures and have trended a few degrees
cooler. Still...highs well into the 60s will be common today.

&&

.SHORT TERM /Tonight through Wednesday Night/...
Issued at 345 AM EST Mon Feb 19 2018

Forecast challenges focus on continued chances for heavy rain and a
growing threat for flooding as moisture continues to surge across
central Indiana along and ahead of a cold front.

The well advertised highly amplified upper level flow pattern will
set up through much of the period as an exceptionally strong
ridge develops off the Carolina coast and an upper trough develops
from the Rockies west. In between...southwest flow and an
enhanced subtropical jet will advect moisture from the equatorial
Pacific while the presence of a strong low level jet on the
eastern flank of an approaching cold front supplies a surge of
rich Gulf moisture. This will result in an axis of steady to
occasionally heavy rain in the vicinity of the front through much
of the short term.

The initial focus tonight and through much of Tuesday for the heavy
rain impacts to the forecast area will be over the northern Wabash
Valley which will be in closest proximity to the low level jet and
deep plume of moisture stretching from Texas northeast into the mid
Mississippi Valley and Great Lakes. Will continue to carry high pops
over the northwest half of the forecast area as a result. Further to
the southeast across central indiana...the strengthening ridge off
the southeast coast will raise mid level heights as far north as the
Ohio Valley. This will result in just isolated to scattered showers
over the southeast half of the area through Tuesday with the
potential for temperatures to rise into the 70s as 850mb temps climb
above 10C.

The front will finally begin to move east Tuesday night in response
to a broad high pressure building into the central Plains with solid
model agreement on the boundary slowly tracking through the forecast
area late Tuesday night into Wednesday. The deep plume of moisture
and strong low level forcing will shift into the region in tandem
with the front...with widespread rain and embedded thunderstorms
encompassing the entire forecast area. Precip water values will
remain at or above climatological maxes for mid-late February...
peaking near 1.5 inches early Wednesday. The front will shift to a
position from the Tennessee Valley into the central Appalachians
Wednesday night before stalling against the flank of the strong
upper ridge. The boundary will remain close enough to continue with
precipitation chances through Wednesday night...with most widespread
precipitation focusing over southern counties closest to the front.

Likely to be an axis with mixed precipitation developing Wednesday
night over the northwest counties as temperatures in the near
surface layer slip to near/just below freezing. Model soundings show
a broad warm layer present from 2000-5000ft which will bring
freezing rain and possibly even a band with sleet and light snow
mixing in. The warm temperatures from today and Tuesday combined
with the saturated ground should mitigate any substantial icing/snow
threat...and overall precip rates do not look particularly heavy at
this point. Certainly will be something to monitor going forward as
the shallow layer of colder air advects south into northern counties
Wednesday night.

Overall rainfall amounts by Thursday morning will range from 1 to 2
inches over southeast counties...to 3 to 4 inches over the northwest
half of the forecast area. More rain is expected for late week into
the weekend and will be addressed in the long term section below.

Temps...an overall model blend works well through much of the period
with a wide variation in temperatures anticipated. As stated
above...highs will be on the verge of records on Tuesday as many
locations rise into the 70s. The passage of the front early
Wednesday will cause a non diurnal trend with temperatures likely
falling back through the 50s and into the 40s during the day. Lows
in the vicinity of 60 tonight...which will shatter the warmest low
record at Indy...will fall back into the 30s by Wednesday night with
the forecast area on the north side of the front.

Indianapolis Record Watch -
High Today: 69 (1930)
Warmest Low Tonight: 52 (1930)
High Tuesday: 72 (2016)

&&

.LONG TERM /Thursday through Sunday/...
Issued at 315 AM EST Mon Feb 19 2018

The long term will continue with the active pattern of the short
term, with an upper trough over the western U.S. and a ridge over
the east. As the long term begins high pressure will be sliding
through the Great Lakes and will push precipitation on Thursday
southeast out of the forecast area by the afternoon. During the
overnight hours Thursday night the high will be off to the
northwest, and this will allow an upper wave to bring in forcing
from the southwest and will see an increase in PoPs then. A surface
front will set up near southern portions of the forecast area and
this will serve as a focusing mechanism for rain through the rest of
the long term as upper waves move along and interact with it.

Gulf moisture will be prevalent and precipitable water values high
throughout, so moderate to heavy rain will be the expectation. At
this time models are focusing the heaviest rainfall across the
southern counties during the long term. Current forecast using the
blended initialization has storm total amounts from Thursday through
Sunday around an inch or less in the northwestern counties to around
3.5 to 4 inches in the southeast. These amounts will cause flooding.

Temperatures throughout the long term will run above normal even
with relatively little sunshine. At this time initialization is not
producing enough instability for thunder and as such this was not
included, but cannot rule it out during this period either.

&&

.AVIATION /Discussion for the 191500Z KIND TAF UPDATE/...
Issued at 921 AM EST Mon Feb 19 2018

Radar loop and short term model guidance suggests the main area of
lift/rain has moved off to the north of the KIND terminal, so
rainfall for the rest of the morning and afternoon looks to be more
intermittent in nature.

Low level wind shear threat near the 015 level expected to continue
into the early to mid afternoon hours, with short term model
guidances suggesting the low level inversion may break after that.

Surface winds should become 190-210 degrees with frequent gusts 24-
28 kts within the next hour or so.

Previous discussion follows.

MVFR with rain showers moving through central Indiana at 6 am. Rain
will continue through the morning and then will see the main axis of
rain shift north a little so that it will be less likely at KBMG,
possible at KHUF and KIND, and remain at KLAF through the period for
the most part. Expect ceilings to drop to IFR over the next few
hours based on hi res models and upstream obs in Illinois. Wind
shear is likely to last through the period as well with a low level
jet in place over the area. This could also result in wind gusts of
20 to 30 kts out of 190 to 210. Isolated thunderstorms will be
possible, but the likelihood of one occurring at one of the sites at
a specific time is low enough to leave out.

Ceilings could return to VFR for a brief period this evening into
the overnight, but expect MVFR conditions to return during the
overnight with another wave of rain arriving.

&&

.HYDROLOGY...
Issued at 345 PM EST Sun Feb 18 2018

Potential for significant flooding continues across the area this
week.

Precipitable water values will be near the climatological maximum
into mid-week as the strong low level jet continues to pump in
moisture from the Gulf of Mexico. This will be briefly pushed south,
but then the values will return late week.

At this time...4 to 6 inches with locally higher amounts appear
likely across all of central Indiana through next Sunday. Exactly
where the main band sets up is still in question and will
fluctuate...with the potential for the heavier rain to be in the
northwest early this week and then across the south later this
week.

The northwest forecast area...where the first round of rain will
be heaviest has been relatively dry of late and can handle more
rainfall initially. Additionally...these areas are not dealing
with a snowmelt component unlike locations over northern Illinois
and Indiana. With this in mind...have chosen to hold off on a
Flood Watch at this time. Will continue to mention flooding
potential in the ESF...HWO and social media products.

If trends continue will likely have to issue a Flood Watch by
Tuesday into midweek as the front moves into the area. If the
front should slow down or stall over the forecast area...rainfall
amounts could be enhanced further. Stay tuned for additional
updates on this developing threat for heavy rain.

&&

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

&&

$$

SYNOPSIS...Ryan
NEAR TERM...Ryan/JAS
SHORT TERM...Ryan
LONG TERM...CP
AVIATION...CP/JAS
HYDROLOGY...50/Ryan


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