October 21: Looking Ahead To Winter, Daily Links

WEATHER

Still some lingering light showers in eastern Middle Tennessee today, but the rest of us will see decreasing clouds by midday and this afternoon.  The HRRR model’s radar simulation is thoroughly unimpressed with our rain chances today:
hrrr_2016102111_ref_nashville
Temperatures will remain cool all day, with highs only reaching the low 60s, even once the sun emerges:
friday-highs
Breezy throughout the day as well, which is why temperatures will remain so cool, but the wind will relax after sunset this evening.  Skies will be mostly clear overnight, which means conditions will be much better if you want to catch a glimpse of the Orionid meteor shower.

A very pleasant weekend in store for us…chilly in the mornings, especially tomorrow — temperatures will start off in the upper 30s to low 40s:
saturday-lows
Maybe even some frost in the very chilliest spots?  It won’t be widespread, but think about covering up the plants or bringing them inside if you live in a spot that tends to be colder than surrounding communities.  We’ll warm up nicely each afternoon this weekend, though — highs Saturday will reach the mid 60s:
saturday-highs

Up to the mid 70s Sunday, and high temperatures will stay in the 70s most of next week:
wsmv-7-day-am
That 20% rain chance Wednesday and Thursday isn’t anything to worry about — the rain will likely miss us to the north, but it’s far enough down the line that I’m hedging my bets for now.

 

WINTER OUTLOOK

Since the weather is looking calm for the next several days, let’s talk about the upcoming winter.  A word of caution as we start, though — long-range seasonal outlooks are just baaaaaaarely on the “science” side of the dividing line between science and witchcraft.  So take all of this with a grain of salt roughly the size of Nebraska.

Last winter’s weather was affected to a large degree by El Niño conditions in the Pacific Ocean — the warm water temperatures there helped to re-arrange the overall flow of air around the world.  But El Niño is over, and its counterpart, La Niña, is now taking shape.  That means cooler-than-normal sea-surface temperatures in eastern Pacific Ocean:
la-nina

The downstream effect of La Niña generally yields these conditions around the country during the winter months:
la-nina-winter

This year’s La Niña is forecast to be relatively weak — a weak La Niña typically doesn’t yield a strong signal toward either warmer-than-normal or cooler-than-normal temperatures in the Midstate.  I crunched the numbers, and it’s literally 50-50…half of the weak La Niña winters have brought us slightly below-average temperatures, with the other half slightly above-average.  In terms of precipitation, there is a slight signal toward wetter-than-normal conditions for the Midstate…but there are plenty of weak La Niña winters that yielded below-average precipitation as well.  (I’m not going to bore you to tears with the charts and regression analyses for the data — if you’re interested in the specific methodology, drop me and email and I can bore you that way.)  The bottom line is this: in general, the strongest effects of both El Niño and La Niña are felt elsewhere in the country.

The Climate Prediction Center’s outlook for December-January-February (“meteorological winter”) reflects their belief that even a weak La Nina will have a significant impact on weather patterns this winter.  They estimate a slight chance (33%) that temperatures will run slightly above average in the Midstate this winter, with a stronger signal toward warmer-than-normal conditions farther to our southwest:
winter-outlook
The precipitation outlook puts us squarely in the “equal chances” region — that is, there isn’t a strong climate signal toward either above-normal or below-normal precipitation:
winter-outlook-precip

But the El Niño/La Niña cycle is NOT the only large-scale factor that helps guide the winter weather patterns over North America.  There’s the Pacific/North Atlantic Oscillation (PNA), the Arctic Oscillation (AO), the North Atlantic Oscillation (NAO) — and they’re all tricky to predict.  Some private forecasters place a greater emphasis on those atmospheric seesaws, which leads them to predict a colder-than-normal winter for the eastern half of the country.  The Washington Post’s Capital Weather Gang does a nice job of summarizing those forecasts and the uncertainties inherent in such long-range predictions.

Of the private forecasting companies, I’m personally partial to the methodology used by WeatherBell.  Their winter outlook calls for a mild start to winter, followed by slightly below-average temperatures after the first of the year.  They also estimate near-average snowfall for this part of the country.  (Scroll down to the bottom of the linked article for the “bottom line” summary of the forecast.)

Keep in mind, we’re talking about long-term forecasts of long-term temperatures and precipitation, which tend to obscure the day-to-day details.  For instance, we could have near-average temperatures most of the winter, with just one good cold snap to skew the numbers downward…or wild up-and-down swings in temperatures that even to out to near-average once the data is smoothed out.  The same goes for precipitation/snowfall — last year was snowier than average, even though we just had one significant snow storm.

As with all long-range forecasts, it’s easier to just sum things up in GIF form:
raw

 

LINKS

Still more nerdiness!

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About paulheggen33

Morning meteorologist for WSMV-TV in Nashville.
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One Response to October 21: Looking Ahead To Winter, Daily Links

  1. Pingback: November 11: Pleasant Veterans Day, Daily Links | 4WARN Weather Blog

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