December 21, 11 PM Weather Forecast Update

Looks like only the 4th time since 1879 that Christmas will be warmer than both Halloween & Thanksgiving! Here is your latest forecast update.

Posted: Dec 21, 2019 4:53 PM
Updated: Dec 21, 2019 11:23 PM

It has been a snowy October-December so far.  In our southern areas, snowfall is triple what is normal for the time of year!

Snowfall totals since October are running 3.5-11.7" as of December 21.  The Peru site looks like it may be missing a couple of days with some snow, bringing the total down to 3.5".  So, that total may not be be accurate.  Take that away & the totals are 4.2-11.7"

November was colder than normal after a warm October until late month.  December so far has been warmer than normal overall.

It is similarly mild & drier compared to last December:

December 2018 vs. 2019 at WLFI ob site:

Fall (September 1-November 30) averaged a bit colder than normal overall.

We were the buffer zone between the unusually cold Fall northwest of our area & the unusually warm Fall southeast of our area.

December temperature mean temperature anomalies are 1 to 2 degrees above normal currently.

It has been much colder than north in the Dakotas to New England.

It has been a drier than normal December with 50 to 70% of the normal precipitation as of December 20.

Note areas east & southeast & also northwest of us that have seen 4x thier normal precipitation for the month so far!

This is reminiscent of last December when farmers actually did field work mid-month after a soaking rain at the start.  A big rain occurred on the last day of the month with 1.41" measured, too.

FWIW, we have averaged 1 to 6 degrees below normal for our mean temperature over the past year (December to December).

We have been in a buffer zone between the very cold pattern north of us & the hot pattern southeast of us.

Since January 1, our totals precipitation is running 95-115% of normal.  Why not more after such a wet winter & spring?

We had a lot of significantly dry weather in late summer which brought the numbers down.  Here at WLFI, July, August, October & December have all seen below normal precipitation.  Between June 20 & August 26, no significant rains occurred.  The heaviest was a 0.75" quick downpour on July 21 in a thunderstorm after the 5th consecutive day with a high in the 90s.

Most of the rainfall in August occurred in one single day in a torrential thunderstorm with 1.90".  1.27" of that fell in 30 minutes.

Highs Friday ran 38-42.

Highs today ran 41-48.

We had a few patches of light freezing drizzle, then clearing skies with light freezing fog in places with black ice.

However, today saw any patches of low clouds remaining south of our area under the deepest melting snow pack.

So, we saw a mostly sunny day.  It was not completely sunny due to a few clouds early this morning.

This is a split flow pattern with phasing of the polar & subtropical jets occurring along the West Coast & in the Gulf of Mexico.

This is sort of an Omega Block pattern that will lock in for many days.

Deep upper troughs are gound in the Far West & sort of inverted into the Gulf of Mexico & Deep South.

At the surface, strong rising air motion on the right side of the troughs is inducing low pressure.

Just to the right of the crest of the upper ridge is a surface high.

Usually in this pattern, this time of year, this is a "Dirty High" in our area with lots of fog & low clouds (especially when snow pack melts).

We saw a similar scenario in January 2010 & we were overcast & foggy for days as snow melted & the high was overhead.  We were stuck in the 40s, while it was 50s in the Northern Plains.  It was also cool & rainy in the South.  It was warmer in the Northern Plains than the South at that time.

Such was the case today.

It was warmer at Milwaukee, Wisconsin today than it was at Atlanta, Georgia or Columbia, South Carolina or even Macon, Georgia.  Des Moines, Iowa was warmer than Hattiesburg, Mississippi.  Cody, Wyoming & Great Falls, Montana were warmer than DeFuniak Springs, Florida.

Denver, Colorado was warmer than Jacksonville, Florida.

The same will apply to tomorrow.  Great Falls & Billings, Montana will have the same temperature as the Dallas-Fort Worth area.

The "Dirty High" today was not so dirty.  We mixed things up enough for a mostly sunny sky.

Patchy to areas of freezing fog are possible tonight (visibility less than 2 miles in places) with lows in the 20s.

The most-widespread, really dense fog is setting up southwest, northwest & south of our area.

After a frosty morning, skies will trend partly cloudy to mostly sunny tomorrow with highs 44-51 with a south-southwest wind at 7-13 mph.

The warmest readings should be in the north.

This also shows up on a projected IR satellite loop via the North American Mesoscale model:

Projected cross-section through the troposphere near Lafayette shows much stronger inversion Sunday night-Monday morning.

This lid of warm, dry air with low-level moisture trapped from melting snow (& lack of much mixing at all in the lower levels) will increase the odds of dense freezing fog deck to be widespread over part of area.

The past several mornings, any fog has had visibility to 2 miles, but not below that.

This may have visibility less than 0.25 mile in parts of the area should this trend hold.

Model paints widespread fog deck with visibility 0.25 mile or less for part of the area.

This fog & low cloud deck may get trapped in the area in what may become a truly "Dirty High" Monday.

This may keep part of the area gloomy & foggy.

Given higher confidence, I did go ahead & drop the highs Monday to 37-45 as a result.

IR satellite trends show fog & some low clouds Monday night-Tuesday morning.  Before this burns off much, high & mid clouds already begin to overspread the area.

So, I went for mostly cloudy wording with highs of 44-50 after 27-34 in the morning.

With a mostly cloudy sky & breezy conditions from the south-southwest, Christmas Day looks mild with highs 47-53.

Looks like only the 4th time since 1879 that Christmas will be warmer than Halloween & Thanksgiving!  The last time we did it at West Lafayette was 1982.

Thursday looks mostly cloudy to cloudy with a couple morning showers are weak cold front continues to push eastward with highs 41-48.

Friday should be mostly cloudy to cloudy with a couple showers (mainly in the morning) as front tries to slowly migrate back north as a warm front.  Highs of 43-53 are likely.

Then...............widespread rainfall comes in late Saturday with breezy to windy conditions & highs 49-54.

Severe weather event to outbreak is possible across the southern U.S.

Colder air bleeds in Saturday night to Sunday with a change-over to mix & snow possible.

Should occur northwest first & slowly work southeastward.

Winds may gust to 40 mph from the north to northwest as the temperatures fall.

If near-bombogenesis occurs with this system over Michigan & Ontario, then our gusts may be much higher than that (+50 mph).

We will monitor. 

It will all depend on strength of upper jet streak that pivots south & southeast of the surface low.

A clipper & a couple of Texas storm systems will need to be monitored in the first 10 days of January as much colder air takes hold of the area.

Mix & snow are possible.

Above normal snowfall & some shots of bitter cold with lows to -20 are likely in January.  Given the extreme nature of the pattern & significant gradient in temperature (like last January) from Minnesota to Georgia, we will be caught in the middle.

Certainly, cold will dominate more than mild weather, but a couple random, very impressive warm-ups are possible suddenly with massive temperature rises, then drops.

One of these could bring a sudden severe weather outbreak to the southern U.S. with MARGINAL RISK up to Indiana with 60, then snow & below 0.

Issue would be ice jams & flash freezing in those situations with high winds & rapid change in precipitation types.

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Snow showers......
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