National Weather Service Raw Text Product

661 
FXUS63 KIND 091034
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
534 AM EST Sat Mar 9 2019

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

&&

.SYNOPSIS...
Issued at 340 AM EST Sat Mar 9 2019

Low pressure will strengthen as it tracks from the central Plains 
this morning to the Great Lakes tonight. Rain and embedded 
thunderstorms will impact central Indiana this afternoon and evening 
with a few strong to severe storms possible ahead of a strong cold 
front this evening. Windy conditions will follow the frontal passage 
tonight and Sunday with high pressure ushering in a dry and cool 
start to the work week. Temperatures will turn much warmer by 
midweek ahead of a cold front that will bring another round of rain 
and storms for Wednesday and Thursday.

&&

.NEAR TERM /Today through This Evening/...
Issued at 340 AM EST Sat Mar 9 2019

Storm system poised to impact the region with heavy rainfall and 
thunderstorms later today already getting its act together over the 
southern Plains early this morning. Ridging aloft over the Ohio 
Valley maintaining quiet weather with stratus encompassing much of 
the forecast area. 08Z temperatures were in the 30s.

Upper level trough currently tracking through the Rockies early this 
morning will kick northeast today and strengthen as energy dives 
into trough and carves out an increasing negative tilt to the upper 
level system. At the surface...low pressure over the High Plains 
currently will steadily deepen as it tracks into the western Great 
Lakes by this evening. The approach of the low pressure with an 
associated cold front tracking into the area early this evening will 
bring locally heavy rainfall and thunderstorms with a narrow window 
for storms to reach severe levels over southern counties late 
afternoon and early evening.

Much of the first half of the day will remain quiet with cloudy 
skies. Developing convection over the southern Plains into the 
Ozarks this morning will expand rapidly into the lower Ohio Valley 
by late morning courtesy of a strengthening low level jet which will 
efficiently transport moisture north into the region from the Gulf 
of Mexico. Rain will reach the lower Wabash Valley by late morning 
and expand across the rest of the forecast area into the early 
afternoon. The most active part of the near term will come from mid 
afternoon into the early evening over about a 6 hour period as first 
a warm front lifts north into the forecast area then is followed by 
a strong cold front during the evening as the surface low tracks 
into northern Illinois. Precip water values will surge above 1 inch 
during the mid and late afternoon as the low level jet focuses over 
the region. Expect widespread and locally heavy rainfall with an 
increasing risk of embedded convection through the late afternoon. 
Potential for much of the forecast area to see an inch of rain by 
the time precip ends late this evening.

By late afternoon...northern fringes of a dry slot in between the 
warm front and cold front will expand into southern counties with 
the threat for severe weather existing between 21Z and 01Z along and 
immediately ahead of the front. Main focus for severe storms will 
extend from the lower Ohio Valley south into the western Tennessee 
Valley where appreciable instability will exist with ample amounts 
of moisture and shear. In addition...this area will reside between 
splitting upper jets that will maximize diffluence aloft. BL shear 
and 0-1km helicities will increase substantially during this time 
period as far north as central Indiana but as is common with these 
early season severe weather setups...the mitigating factor to a more 
significant threat will be the lack of greater instability this far 
north. In addition...model soundings show the presence of an 
inversion between 2-3kft over much of the area which will further 
limit the ability for convection to tap into the stronger 70kt low 
level jet present at 850mb. That being said...still expect gusts to 
around 30mph by late day into the evening outside of storms.

At this point...most plausible scenario is that the northern part of 
a narrow low topped convective line will track rapidly across the 
forecast area during the early evening. Any potential for storms to 
briefly pull damaging winds to the surface will focus over far 
southern portions of the forecast area where the inversion may 
briefly diminish immediately ahead of the front. Cannot rule out an 
isolated tornado over southern counties either considering the high 
amounts of BL shear and helicities but it remains a much more 
conditional threat than the wind. 

Temps...tricky temperature forecast as much warmer air will not 
arrive into the region until late afternoon and early evening once 
the warm front lifts north. Potential for areas near and south of I-
70 to warm into the 50s by early evening.

&&

.SHORT TERM /Midnight Tonight through Monday Night/...
Issued at 340 AM EST Sat Mar 9 2019

Forecast challenges focus on post frontal winds late tonight and 
Sunday.

All rain and convection will be east of the forecast area by late 
evening as the cold front rapidly shifts into Ohio. May see clouds 
briefly scatter in wake of the frontal passage before the cold pool 
stratus expands back across much of the area after midnight. May see 
a few light showers over northern counties late but the main focus 
for the overnight will shift to stronger wind gusts as a tight 
pressure gradient lingers behind the cold front. Model soundings 
show the inversion weakening with dry adiabatic flow and steepening 
lapse rates establishing through much of the boundary layer for 
several hours late tonight into Sunday morning. With continued 
strong flow in the 3-4kft layer overnight being pulled more easily 
to the surface...potential exists for peak gusts to exceed 40-45mph 
over parts of the area. Will highlight the higher winds in the HWO 
at this time but possible that a Wind Advisory may eventually be 
needed late tonight and early Sunday...especially near and north of 
I-70. Stay tuned.

Gusty winds will linger Sunday but should gradually weaken by the 
afternoon as the surface low departs off into Quebec and the 
pressure gradient relaxes. Model soundings and RH progs hint at low 
level moisture remaining trapped with stratus likely lingering over 
the area for much of the day Sunday. Clouds should finally scatter 
Sunday night into Monday as high pressure expands across the region. 
Will trend towards mostly clear skies late Monday into Monday night 
as subsidence increases with the center of the high drifting over 
the area.  

Temps...quasi-zonal flow behind the storm system later today will 
keep a seasonably cool airmass present over the Ohio Valley for 
Sunday into early next week. Low level thermals supported a model 
blend for temperatures from Sunday on...with highs mainly in the 40s 
and lows in the 20s. 

&&

.LONG TERM /Tuesday through Friday/...
Issued at 233 AM EST Sat Mar 9 2019

Ensembles in good agreement on the upcoming weather pattern during
this period. A significant short wave trough is expected to eject
across the Plains into the western Great Lakes towards the middle
of next week. The remnant upper trough will drift east into the
Midwest by late next week.

Will keep PoPs going from Tuesday night into Thursday to cover the
passage of the associated surface system. At this point it 
appears the highest precipitation threat will be Wednesday 
night, when the majority of the ensembles suggest the surface
front will passing through the local area. There continues to be a
potential for some mixed precipitation near the beginning of the
event Tuesday night into Wednesday morning, particularly over the
northern zones, but accumulations appear unlikely.

Will also keep some chance PoPs for light showers going into
Friday over parts of the area, due to the passage of the lagging
upper trough.

&&

.AVIATION /Discussion for the 091200Z TAFS/...
Issued at 531 AM EST Sat Mar 9 2019

Short term model data suggest organized lift will begin moving
over the terminals after 091800Z, so should see widespread rain
impacting the terminals from the southwest after that time. IFR
visibility restrictions probable in the heavier precipitation
areas. Potential for embedded lightning strikes looks rather 
high by mid to late afternoon as a 60-65 kt low level jet 
interacts with steeping mid level lapse rates ahead of a dry slot.

Low ceilings generally 004-008 AGL expected at the terminals
today. May see low ceilings scatter out at times this afternoon 
as the strong lift and precipitation may help mix up the air mass.
May also see the low ceilings lift over the southern terminals
towards 100000Z, as a warm front drifts north.

Threat for low level wind shear should increase by mid afternoon
in the pre warm front zone as the strong low level jet noses into
the area. Forecast soundings suggest the top of the frontal
inversion this afternoon around 008 AGL-012.

Should see surface gusts in excess of 20 kts from 100-120 degrees 
increase in frequency as the morning goes by, with some gusts
in excess of 30 kts possible this afternoon. Surface winds will 
veer around to 170-200 degrees over the southern terminals towards
100000Z with the passage of the warm front.

&&

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

$$

SYNOPSIS...Ryan
NEAR TERM...Ryan
SHORT TERM...Ryan
LONG TERM....JAS
AVIATION...JAS