081 
FXUS63 KIND 270838
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
338 AM EST Sun Dec 27 2020

.UPDATE...
The SYNOPSIS...NEAR TERM...SHORT TERM
and LONG TERM Sections have been updated below.

&&

.SYNOPSIS...
Issued at 333 AM EST Sun Dec 27 2020

Dry and seasonably warm conditions today with winds occasionally
gusting upwards of 30 mph. A quick moving system will pass through
during the early overnight hours with a quick tenth of an inch of
rain expected for much of central Indiana. Dry weather then
briefly returns Monday and Tuesday before a much stronger system
brings widespread rain Wednesday into Thursday followed by
accumulating snow Thursday night and Friday. Snow amounts remain
quite uncertain with higher confidence in the widespread rain.


&&

.NEAR TERM /Today/...

Issued at 333 AM EST Sun Dec 27 2020

Strong surface southerly flow will advect warm, moist air into 
central Indiana through the day today as a surface low pressure 
tracks across the Central Plains. Indiana will remain smashed 
between this low pressure and a broad area of high pressure across
the Eastern United States. As the low nears, pressure gradients 
will increase along with a strengthening LLJ at 850mb. By late 
today, winds at 5000ft will be nearly 60kts, but conditions do not
look favorable for mixing down of these winds with a strong 
inversion just off the surface. With that in mind, do think there 
will be frequent gusts up to 30 mph, but gusts above that will be 
infrequent and isolated. This strong southerly warm air advection 
should be enough to counteract the increasing clouds by mid 
afternoon, so increased highs above model guidance with temps 
ranging from the mid 40s in the north to the low 50s in the south.


&&

.SHORT TERM /Tonight through Tuesday night/...

Issued at 333 AM EST Sun Dec 27 2020

The aforementioned low pressure system will be moving from the 
Central Plains into the Upper Midwest during the overnight hours 
tonight with a surface cold front nearing the area at the start of
the period. Current expectations are that the cold front passes 
through shortly after midnight with light rain out ahead of the 
front and then briefly after the passage. Even with the ample 
southerly flow today, the fast motion of the system will keep QPF 
amounts fairly minimal with around a tenth of an inch of rain
expected with highest amounts across the northern counties where 
the forcing will be to be strongest.

High pressure will then quickly build in the aftermath of the 
frontal passage with colder air moving in as flow switches from 
the south to the northwest. Quiet and seasonable weather is then 
expected Monday and Tuesday with the high pressure and upper level
ridging in place.

The pattern will begin to shift Tuesday night as a much stronger 
low pressure system builds in the lee of the Rockies and begins to
track to the northeast. During the overnight hours on Tuesday, 
flow will again shift to be more southerly with a very similar 
pattern to the weather that is expected today with high pressure 
in the east and a surface low tracking across the Plains. There 
may be a brief period of precipitation across the northwestern 
counties late Tuesday night as the system nears, but confidence 
remains low. Confidence in precipitation type is even lower with 
a combination of rain, snow, and freezing rain possible.

Highs will climb into the low to mid 30s on Monday and Tuesday.
Lows will fall into the upper 20s and low 30s tonight and Tuesday
night. Lows will dip into the upper teens to low 20s on Monday
night.

&&

.LONG TERM /Wednesday through Saturday/...

Issued at 333 AM EST Sun Dec 27 2020

Complex systems may make quite a splash rounding out the old year 
and bring in the new one. 

Models in slightly closer in agreement in timing at the onset. 
Northern stream wave will start off the more active one. This system 
will dart off to the eastern great lakes and Quebec on Thursday. 
Associated warm front will lift north across central Indiana 
Wednesday as a 60 knot low level jet moves overhead. That combined 
with deep moisture, an approaching cold front and a 150 plus low 
level jet over the upper Midwest (central Indiana in favorable 
right rear quadrant) supports increasing chances of rain Wednesday. 
The cold front will move through Wednesday night with models hinting 
around that a wave or two may develop along the front in response to 
deepening Texas upper low. This would suggest widespread rain 
Wednesday per the blend. Could see the rain briefly mix with snow 
over northwestern sections early Thursday, otherwise, thermals 
support rain and models having some differences whether or not the 
activity will briefly end from northwest to southeast Thursday 
afternoon behind the front. 

Strong warm advection supports the well above normal temperatures in 
the 50s on Wednesday despite increased cloud cover and rain.  

Could see over an inch of rain through Thursday. This could cause 
some minor water issues. 

More precipitation will return Thursday night and Friday as the 
southern upper low ejects northeast over the Ohio Valley/Great 
Lakes. Models having issues with the track of that feature with the 
00z GFS much further south than the 00z ECMWF. The 00z Canadian was 
a compromise and took the upper low across the heart of central 
Indiana late Friday. The actual track of this system will determine 
precipitation type and where the highest amounts of any snow will 
be. For now, with confidence in the eventual correct track lacking, 
too soon for any pseudo snowfall accumulation forecast. All models 
quickly move the second system well northeast and move high pressure 
to the Ohio Valley Friday night and Saturday. This will allow for 
dry and seasonable remainder to next weekend.


&&

.AVIATION (Discussion for the 270600Z TAF Issuance)...
Issued at 1131 PM EST Sat Dec 26 2020

IMPACTS: VFR through about 23Z...then MVFR conditions
         Gusty winds develop Sunday afternoon
         LLWS also develops Sunday afternoon
         Rain is possible Sunday evening

DISCUSSION: A low level jet will develop ahead of an 
            approaching cold front Sunday afternoon, providing
            wind gusts over 20kt along with LLWS. MVFR 
            conditions and some rain will accompany the front.

CONFIDENCE: High confidence in VFR through much of the day Sun.
            High confidence in winds and LLWS.


&&

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

$$

SYNOPSIS...White
NEAR TERM...White
SHORT TERM...White
LONG TERM....Koch
AVIATION...50