Its Beginning to Look All Winter-like

Colder Temperatures Coming in Along with Rain and Snow Chances

The mild month that we knew is now fading away. This mild air is going on vacation and cooler air will be coming in. We'll begin to start seeing some of our coldest temperatures since January and February. This includes highs in the 20s and lows in the teens. This month has produced an avg of 11° above normal per day. When you combine the months highs and lows it averages out to a temperature of 44.3°. If the month had ended today this would end as the 3rd warmest December on record. Even with the cold end expected for the month, I think this should atleast keep us within the top 10 list. Here is the current top ten list of warmest Decembers:

1889: 46.2°
1877: 45.5°
1923: 42.4°
1931: 41.2°
1918: 41.2°
1875: 40.8°
1891: 40.6°
1881: 40.6°
1982: 40.2°
1994: 38.9°


The weather is undergoing some changes and winter might be starting to get settled in now just in time for astronomical winter to begin. The winter solstice occurs on Friday at 6:12AM EST. This is the shortest day, in terms of daylight hours. On Friday, the sun rises at 8:03AM in Indianapolis while the sun sets at 5:24PM. This means we will have 9 hours and 21 minutes of daylight. This will also be the same for the 22nd. Starting on the 23rd we begin to gain daylight back. The sun will rise at 8:03AM and the sun setting at 5:25PM, this adds 1 minute of daylight. We will gain a few more minutes for the remainder of the month.



One thing that plays a role into colder weather is increasing snowpack. Take a look at the snow depth for December 19, 2012 from the National Oceanic and Atmospheric Administration.


Currently 35.6% of the nation is covered in snow. This up from 9.1% last month and even up from 20.9% from last year. In 2011, Indianapolis received 2.30" of snow and finished with an average temperature of 37.8°. I talked a little bout it last month, snow reflects heat and keeps temperatures down. When there is no snow, then the pavement retains heat and that keeps temperatures up. Meteorologists look at several weather indices. These are weather indicators which helps meteorologists make their forecast. During the winter months, we look at what's called the North Atlantic Oscillation (NAO), Arctic Oscillation (AO), and Pacific North American pattern (PNA). The NAO and AO needs to be negative, and the PNA needs to be positive and hold in order to stir up the right combination for a cold and snowy winter.
Looking below at one of the last model runs, the NAO (top left) remains negative up until atleast the first week of the New Year. The AO (top right) remains negative til atleast New Years Day then trends positive. Both teleconnectors show a dip on the 20th (tomorrow) and later around Christmas Day. This is an indication that a storm is stirring up for these two time periods. This means cold temperatures and yes, SNOW! Also, the PNA (bottom left) spikes towards the positive. This reinforces this theory.



Based on these images, I am leaning towards a Cooler End to 2012 and sort of a warmer open to 2013 (not a very mild open though).


Tonight, as a warm front creeps North, rain and maybe some thunderstorms will move into the area. Also temperatures will actually either remain steady overnight or increase. Temperatures are forecasted to be in the 50s early tomorrow. We may hit a high in the mid 50s before a cold passes. This looks to pass after lunchtime. This will puts an end to the rain and temperatures will plummet. Could see a time period that is dry but this will be very brief. We expect some leftover moisture thus turning on the snow machine (starting sometime AFTER sunset). This will continue into the overnight hours ending Friday morning or early afternoon. Snow accumulations looks to total to an inch or less South of Indy, 1-2" in Central and Northern Indiana and there could be some pockets of 3-5" in extreme northern counties of the state. Due to the storm system coming in, this has prompted the NWS to place counties in Central and Northern Indiana under a winter weather advisory from 1PM Thursday until 10AM Friday. Also, we turn on the wind machine. Winds will be in excess of 40mph. A wind advisory will also be in effect from 1pm Thursday to 10AM Friday. Watch those holiday decorations!!!!!!!
By Friday Morning temperatures will have dropped into the 20s. Wind chills will be in the single digits. Temperatures go even lower into the upper teens for Saturday Morning as skies clear. We should see some sunshine for Saturday and Sunday before the next storm system comes in for Christmas Day. More Details on this in the days to come.



***7 DAY EXTENDED OUTLOOK***

DEC. 20	DEC. 21	DEC. 22	DEC. 23	DEC. 24	DEC. 25	DEC. 26
THURSDAY	FRIDAY	SATURDAY	SUNDAY	XMAS EVE	XMAS DAY	WEDNESDAY
T'STORMS PM SNOW	AM SNOW	PARTLY SUNNY	PARTLY SUNNY	CLOUDY	PM RAIN?	WINTRY MIX?
BREEZY
55↓	29	35	39	40	40	36
26	18	24	33	37	30	25