947 
FXUS63 KIND 180907
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
407 AM EST Thu Feb 18 2021

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

&&

.SYNOPSIS...
Issued at 253 AM EST Thu Feb 18 2021

Light snow will impact central Indiana through this morning with 1
to 2 inches expected. Subseasonal temperatures are expected to
continue through Saturday with below zero wind chills tomorrow and
Saturday morning. The next chance for precipitation will be Sunday
into to Monday with chances for a rain/snow mix at times
overnight. More seasonal temperatures are on the horizon with high
projected to be in the low 40s early next week. 

&&

.NEAR TERM /Today/...

Issued at 253 AM EST Thu Feb 18 2021

Central Indiana is slowing becoming enveloped with light snow this 
morning. Heaviest snow fall rates are to the SW/S where visibilities 
are less than 2 miles. This will progress ENE along the mean 500mb 
flow. 0.25" an hour rates are likely at times. An area of dynamic 
alignment between vertical lift (WAA/CVA) and upper level diffluence 
is expected to induce moderate, low to mid level height falls this 
morning, enough to assemble an organized cyclonic field and pressure 
center. In return, the enhanced E/NE flow north of the pressure 
center will create a zone of deformation and enhanced lift for a few 
hours over eastern central Indiana later this morning. As this 
occurs, snowfall rates should increase leading to slightly higher 
snowfall totals over this area. Overall, around an inch is expect 
over most of central Indiana, with areas to the far south and east 
receiving closer to 2 inches. A few isolated locations could seed 
totals between 2-3 inches toward the SE, depending on where 
snowbands pass over. 

Snow fall should begin to decrease late this morning with only a few 
lingering light snow showers around this afternoon. Areas to the NE 
may experience a lightly longer snow duration depending on where the 
deformation zone propagates. Mostly cloudy to overcast skies are 
expected through most of the day with central Indiana influenced by 
a strong upper level jet and cyclonic flow aloft.  

Temperatures are expected to remain fairly stagnant due to a 
constant snow pack and decoupled PBL. Temperatures rises of 5-10 
degrees are still likely within inefficient diurnal warming leading 
to highs in the mid 20s. Temperatures below zero and thick cloud 
cover will limit road temperatures and therefor slick road 
conditions are expect for most of the day, but this will be 
especially true during the morning commute with light snowfall 
expected through 10am.

&&

.SHORT TERM /Tonight and Friday/...

Issued at 253 AM EST Thu Feb 18 2021

Snow should be well east of central Indiana by nightfall as high 
pressure moves in at the surface. CAA will further enforce surface 
height rises leading to dry conditions and breaks in the cloud 
cover. This CAA will also impact temperatures overnight, with lows 
expected to be back into the single digits. 

Central Indiana will start to experience influence from an 
approaching upper level ridge friday, and large scale subsidence 
inhibits cloud growth and dries out the PBL. With this in mind, 
mostly clear skies are expected by Friday afternoon. Enhanced 
incoming SW radiation will increase temperatures and reduce the snow 
depth slightly; high temperatures should reach the low to mid 20s 
even with a cold air mass overhead. 

&&

.LONG TERM /Friday Night through Thursday/...

Issued at 253 AM EST Thu Feb 18 2021

Friday night will be quiet with high pressure in control. Skies 
won't be clear with some warm advection beginning aloft, but there 
should be enough clearing for some radiational cooling off the snow 
cover. Winds will lessen too, so another cold night is expected. 
Will cut guidance some and up with lows below zero north to low 
positive single digits south.

Warm air advection will continue aloft on Saturday, but any forcing 
from this will be weak and moisture lacking. Will continue a dry 
forecast. 

Brief upper ridging ahead of an approaching system will keep the area 
dry into early Sunday.

A large upper trough, good upper and lower level jets, and a surface 
low pressure system will bring forcing to the area Sunday afternoon 
and night. The low level jet will bring plentiful moisture as well. 
Thus expect precipitation across the area, especially Sunday 
evening. Will up guidance PoPs.

Precipitation type still remains in question. Models try to warm 
things up quickly on Sunday, but still feel this might be overdone 
some at the surface given the snow cover. Cut guidance highs a bit, 
which leads to mainly snow north and a rain/snow mix south. As noted 
previously, will have to watch ground temperatures where rain falls. 
Lows Saturday morning will be in the single digits and in the teens 
Sunday morning. If the ground doesn't warm fast enough, some 
freezing precipitation may be possible even with warmer air 
temperatures.

Quiet weather returns for the remainder of the forecast. More zonal 
flow aloft will lead to warmer temperatures (maybe even above 
normal). Quick moving pieces of upper energy moving through will 
bring clouds at times, but moisture doesn't look adequate for 
precipitation.

&&

.AVIATION /Discussion for 18/09Z TAF Update/...

Issued at 404 AM EST Thu Feb 18 2021


Widespread light snow ongoing and should continue through 12Z.
Mainly 2-3 mile visibilities with isolated snow bands at 1-2 mile
visibilities. MVFR ceilings becoming more likely with most snow
bands having around 2500ft ceilings. 

Previous discussion as follows...

IMPACTS: Ceilings, and at times visibilities, will deteriorate to 
MVFR and worse in light snow 08z-11z.   

Winds will back from northeast to north 10 knots or less 12z-18z. 

DISCUSSION: A low pressure system will lift from the the southern 
Plains and Ozarks to the Ohio Valley today. This will bring 
deteriorating sky cover and visibility in light snow overnight and 
today. 


&&

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

$$

SYNOPSIS...Updike
NEAR TERM...Updike
SHORT TERM...Updike
LONG TERM....50
AVIATION...Updike