Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

FXUS63 KIND 151717

Area Forecast Discussion
National Weather Service Indianapolis IN
1212 PM EST Sat Dec 15 2018


The Aviation section has been updated below.


Issued at 228 AM EST Sat Dec 15 2018

Low pressure over Tennessee is expected to push across Kentucky 
to the Virginias by Sunday Morning. Rain is expected across 
Southern Indiana today as the low passes to the south. Rain will 
come to an end tonight as the low exits the area tonight. This 
will bring an end to the precipitation.

Dry weather is then expected for the end of the weekend and the
start of the next work week as high pressure across the Plains
states builds through the Ohio valley. Dry weather is expected to
last at least into the middle of the next work week with above
normal temperatures. 


.NEAR TERM /Today/...
Issued at 228 AM EST Sat Dec 15 2018

Surface analysis shows low pressure in place across western
Tennessee early this morning. Cyclonic NE surface flow was in 
place across central Indiana. Radar shows bands of showers
associated with the low to the southwest passing across the
southern parts of the forecast area. Water Vapor imagery shows the
upper low over Mississippi with dry air intruding in to the system
across Central Kentucky. GOES16 show much of the warm and moist flow
ahead of the flowing north across the appalachians...but there
remained some wrap around moisture across southern Indiana and
southern Illinois. 

Models suggest the low will make a slow progression across 
Kentucky today. Cyclonic wrap-around flow is expected to continue
across Central Indiana...with best moisture across the southern 
parts of the forecast area. Forecast soundings and Time heights 
show saturated lower levels this morning and afternoon as the low 
passes...again with best forcing across the southern parts of the 
forecast area. Thus with a favorable set-up again for rain 
today...will trend toward categorical pops across the southern 
parts of the forecast area. With a sharp cut-off expected tonight 
north...will not stray far from the forecast builder blends on 
pops north of I-70. Given the expected clouds and rain 
today...will trend highs at or below the forecast builder blends.


.SHORT TERM /Tonight through Monday Night/...
Issued at 228 AM EST Sat Dec 15 2018

Low pressure departing the area tonight is expected to lead to a
strong high pressure system building across the forecast area for
Sunday through Monday night and into the middle of the next work

GFS and NAM suggest best forcing and moisture will be exiting the
area near 00Z or shortly there after as the surface low is
expected to reach West Virgina. Time heights show best lift is 
low by 00Z but lower level moisture continues to linger. HRRR 
suggests some lingering precip may still be found across the 
southeastern parts of the forecast area after 00Z. This seems 
reasonable given the expected position of the departing low. 
Forecast soundings after 06Z Sunday suggest subsidence and drying
within the column as surface high pressure and ridging begins to 
build across the area from the plains states. Thus will keep some 
pops across the southeast during the first third of the evening 
tonight...but trend toward a dry forecast overnight. Will stick 
close to a blend of the forecast builder blends on Lows.

GFS and NAM then suggest a very large area of high pressure over 
the plains states slowly building across the Indiana through 
Monday night. Aloft...strong ridging is indicated across the 
Rockies...resulting in NW flow across the plains and lee side 
subsidence...generating the large surface high. Forecast soundings
indicate a very dry column starting Sunday Night and persisting 
through Monday night. The NAM suggests the surface high pressure 
center finally reaches Indiana toward 12Z Tues. Thus from Sunday 
through Monday night a dry forecast will be used with mainly clear
skies. Only a few passing high cirrus clouds will be expected. 
Furthermore...with the northern jet really passing to the 
northeast...temperatures will remain at or above seasonal normals.


.LONG TERM /Tuesday through Saturday/...
Issued at 238 AM EST Sat Dec 15 2018

The long term period will start dry with high pressure in control
across the area. A large scale trough will swing into the area mid
to late week, and models are significantly more wrapped up and
slower with this system than in previous runs, so will have pops
from as early as Wednesday morning through Friday evening. Vast
majority of this precipitation will fall as rain per low level
thermal progs, but cannot rule out some snowflakes at times,
mainly overnights.

Blended initialization handled things reasonably well and required
only minor adjustment.


.AVIATION /Discussion for the 15/18Z TAF Issuance/...
Issued at 1212 PM EST Sat Dec 15 2018

Good confidence in dry conditions and VFR conditions at LAF through 
the TAF period.

Otherwise, the rain will be ending at HUF after 22z, but hang out 
until 00z Sunday or so at IND and BMG. Flying conditions will likely 
vary mostly between MVFR and VFR but generally improve after the 
rain ends per the SREF and GFS LAMP.

Winds will be northeast around 10 knots with gusts to 18 knots 
through 00z. Then winds will switch to north less than 10 knots. 





National Weather Service Glossary of Abbreviations