Thursday, October 30, 2014

First fall freeze on tap this weekend, maybe the second as well

As promised, a big time chill is on deck, and is slated to move in behind tonight's cold front. The only good news is that it won't last long, but the magnitude of the cold will be quite a shock after a couple of 70 degree days and last weekend's 80s.

We'll first feel the effects of the front tomorrow during the day. Despite temperatures only falling to 50 overnight, a brisk north wind will pick up by mid-morning under cold air advection stratus clouds, gusting at times to near 30 mph during the day. Coupled with the clouds (which depart by late afternoon), temperatures will remain in the 50s all day. It could be our coldest high temperature since April.

For trick-or-treating, Tiger football, and Friday Night Lights, "layer up" will be the action plan as temperatures fall through the 40s in the evening with wind chills near 40. Doesn't sound bad until you get out and walk a few blocks with Elsa, who will discover she isn't as prepared for Frozen as the real princess! By dawn, temperatures will reach the freezing mark for nearly everyone in the metro with wind chills early Saturday morning in the 20s. A Freeze Watch  Warning (as of early Fri AM) is in effect and will be upgraded to a Freeze Warning tomorrow. (The average date of first freeze at Memphis International Airport is November 12, while it is November 5 at the Agricenter, which is representative of the suburbs.)

Overnight lows Friday night will be below freezing across a huge portion of the eastern U.S.

Saturday will be downright cold for November 1. Though it won't set a cool record, temps in the 40s nearly all afternoon (the high will be just above 50) with a north wind at 10-15 mph will feel more like mid-December than the day after Halloween. Sunny skies will be little comfort. Saturday night will again see temperatures plummet to near freezing. The is a little more uncertainty with regard to reaching 32 in the city, but with calm wind, most areas outside the city will fall to freezing and outlying areas have the potential for upper 20s early Sunday morning. A Freeze Watch has been issued for early Sunday morning.

Another very cold night Saturday night with low temperatures Sunday morning shown above.

Temperatures start to moderate Sunday with highs nearing 60.  Another 10 degrees of warmth can be expected on Monday as we return to a more normal pattern.

If you have outdoor plants or other vegetation that could succumb to frost or a freeze, plan to have them covered Friday and Saturday nights, especially if they are not within a couple of feet of a heated structure like a home. There is not a lot of concern over water or pipes freezing as the duration of freezing temperatures will be a couple of hours or less. Also, bring in your outdoor pets or provide a warm spot for them each night. Finally, keep space heaters away from any flammable items, such as drapes or upholstery that could cause a fire.

Now to get back to inciting panic...


Erik Proseus
MWN Meteorologist

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Tuesday, October 28, 2014

Two cold fronts result in a cool Halloween and chilly start to November!

Autumn weather can be fickle and this week is proving to be exhibit A, at least in the temperature department. This past weekend, Mid-South air conditioners cranked back up as highs reach the 80s with more humidity than we have been accustomed to the past couple of weeks. For the first weekend of November though, it appears there will be more shivering than sweating!

A cold front moves through the Mid-South today, bringing with it scattered showers and a chance of afternoon thunderstorms. The showers will linger through the evening hours, but clouds and precipitation will hold temps down in the 70s, which is still a bit above average. The Storm Prediction Center has placed the metro under its first-ever "Marginal" (category 1 of 5) risk of severe weather today ahead of the cold front, but we're rather skeptical that any storms will get anywhere near severe limits. (For a review of the new SPC outlook categories, click here.)

SPC places areas ahead of the cold front in a Marginal risk of severe storms this afternoon. We think the threat of anything approaching severe will be very isolated.
Tonight, rain moves out and by early Wednesday morning clouds follow suit, leaving a mostly sunny day with cooler but not unpleasant temperatures near average for late October - 70 degrees. Thursday will be similar to Wednesday with highs near 70, though a reinforcing (dry) cold front will approach the area. This front moves through early Friday, resulting in a cooler and breezy day on Halloween Friday. Trick-or-treaters those heading to the Liberty Bowl for Memphis Tiger football will need to plan on cool conditions (50s) with a noticeable north breeze on Friday night.

A reinforcing cold front moves through early Friday, with cold Canadian-origin high pressure building in at the surface behind it. This will result in cool temperatures for the weekend.
Behind the secondary cold front, a large upper-level trough forms over the eastern U.S., promising below normal temperatures throughout this first weekend in November. In fact, some areas outside the urban core could see their first frost Saturday and/or Sunday mornings as lows look like they'll drop into the 30s! (For those curious, we're well past the earliest recorded fall freeze dates. The average first freeze in Memphis is November 12. It's a week earlier - November 5 - at the Agricenter which is reflective of conditions in the suburbs. Today is the average first freeze date in Jackson, TN.)

Saturday's high with full sunshine will remain in the 50s before temperatures start to rebound a bit Sunday into early next week. For those who dislike cold weather, this weekend's cool spell looks to be brief as warmer air moves back in next week, along with more rain chances by mid-week. Click here for the complete MWN Forecast.

According to modeled temperatures from the GFS model for the coming couple of weeks (this is NOT forecast data), trends favor a return to warmer weather after this weekend's cool conditions. Other sources agree with this general trend. 

P.S. Don't forget that it's also the end of Daylight Saving Time this Saturday night! "Fall back" to Standard Time when low sun angles occur during rush hour and evenings are dark. Not my favorite time of year...

Erik Proseus
MWN Meteorologist

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Thursday, October 23, 2014

A warm weekend in store; rain chances hold off until next week

A rather cool afternoon is underway with temps in the mid to lower 60's as a partial solar eclipse will hopefully be visible in the Mid-South. The only issue at this time is some high clouds over the area, but these are showing some signs of breaking up and we're hoping we'll be lucky enough to catch a break for the eclipse beginning at 4:52 PM (more info in our previous blog post). (If we aren't able to view it locally, you can always tune into the Slooh Observatory live broadcast.) However, our main story concerns the fairly drastic change in temperatures for this weekend and into next week.

GFS model valid Friday night showing temperatures (in °C) about 5000' feet above the surface
Warmer temperatures will begin streaming into the Mid-South starting tomorrow mainly due to a shift in the upper-level atmospheric pattern. A ridge (area of higher pressure) to our west will bring northwesterly flow aloft which will advect warmer air into the Mid-South from the lower plains. This may seem like a bit of an unusual pattern, but warmer air is often brought into the plains earlier then the south after several rounds of cold fronts. The ridge to our west and trough to our east promote this atmospheric pattern.

GFS model Friday night showing temperatures (in °F) at the surface
At the surface the pattern is more of what you would expect, with winds shifting towards the south with a weakening surface high over the area (which was responsible for the cooler air). Expect temps to begin increasing tomorrow with highs in the mid 70's. Warming continues into Saturday and Sunday with temps getting all the way into the lower 80's. It will feel quite warm during the day, but by Saturday night temps will only get into the 60's at night, making it relatively mild even in the mornings to end the weekend.

GFS model Tuesday afternoon showing Precipitable Water Values
Rain chances will return early next week as the next cold front moves through. Models are indicating a strengthening low pressure system to our north with a developed cold front sweeping through the Mid-South. The band of high precipitable water values along the cold front represent deep moisture which could bring thunderstorms along with it. We'll keep an eye on this threat and will let you know if we expect anything significant. As always you can check out the full MWN Forecast here.

William Churchill
MWN Social Media Intern

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Wednesday, October 22, 2014

Partial solar eclipse visible to Mid-Southerners on Thursday

In an event that won't be seen again for nearly 3 years, a partial solar eclipse will grace the sky over North America on Thursday, October 23. Partial solar eclipses happen when a new moon comes between the sun and the Earth, but they don't align in a perfectly straight line. Therefore, the moon only partially covers the sun's disc. 

Diagram of how a solar eclipse occurs, as a new moon passes between viewers on Earth and the sun.
Graphic credit: EarthSky.org.
In the Memphis metro, the partial eclipse will begin at 4:52pm Thursday afternoon as a small shadow on the right side of the sun. As the shadow moves across the top of the sun, a maximum eclipse (shown below) will occur at 5:53pm low on the western horizon. The sun will slip below the horizon at 6:14pm, thus ending the viewing opportunity prior to the end of the eclipse.

How the sun will appear at maximum eclipse (5:53pm Thursday) just prior to setting. For an animation of the complete eclipse cycle, see TimeandDate.com.

The next solar eclipse opportunity won't be until August 21, 2017 when a total eclipse takes place. While we look forward to that opportunity, don't miss the chance to see this partial eclipse or you'll have to wait another 3 years to see it again!

As to viewing an eclipse, remember the #1 rule is to NEVER look directly at the sun, eclipsed or otherwise, without protective eyewear! The sun’s UV radiation can burn the retinas in the eyes leading to permanent damage or even blindness. The only way to safely see a solar eclipse is to wear protective eclipse glasses, look through welder's goggles with a rating of 14 or higher, or to project an image of the eclipsed sun using a pinhole camera. Here's info on making a simple camera from Mr Eclipse.com:
One safe way of enjoying the Sun during a partial eclipse--or anytime--is a "pinhole camera," which allows you to view a projected image of the Sun. There are fancy pinhole cameras you can make out of cardboard boxes, but a perfectly adequate (and portable) version can be made out of two thin but stiff pieces of white cardboard. Punch a small clean pinhole in one piece of cardboard and let the sunlight fall through that hole onto the second piece of cardboard, which serves as a screen, held below it. An inverted image of the Sun is formed. To make the image larger, move the screen farther from the pinhole. To make the image brighter, move the screen closer to the pinhole. Do not make the pinhole wide or you will only have a shaft of sunlight rather than an image of the crescent Sun. Remember, this instrument is used with your back to the Sun. The sunlight passes over your shoulder, through the pinhole, and forms an image on the cardboard screen beneath it. Do not look through the pinhole at the Sun.
Be safe and have fun watching the eclipse on Thursday!

Erik Proseus
MWN Meteorologist

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Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!