90 again? When is REAL fall coming??

We've had a few tastes of fall in the past month, but between those, warm days have left many of you wondering "when is fall here to stay?"

We'll have another shot at it with a large-scale cold front that will move quickly through the region Thursday night. Prior to then, the Mid-South will be toasty the next couple of days. In addition, with southerly wind returning, humidity will also increase. Today's high of 90 could be matched tomorrow with enough sunshine, which I think is a good possibility. With increasing clouds and southerly wind Wednesday night, lows will remain above 70, but those clouds and a chance of thunderstorms Thursday afternoon will hold temperatures in the upper 80s.

On Thursday night, a cold front will sweep through the region, bringing showers and thunderstorms area-wide. The severe weather threat is low with this system, but not non-existent, particularly in Arkansas. This time of year, instability is typically the wild card in potential severe weather scenarios. The dynamics (for instance, upper level wind energy) associated with these systems tend to get stronger as the fronts get stronger in the transitional seasons. However, without instability (the gasoline that causes the fire to explode), strong storms have a harder time becoming severe.

Forecast instability, as measured by CAPE, at 1am Friday morning as the probability of storms increases. Values are more than sufficient for thunderstorms, but the severe weather threat is fairly low. Graphic courtesy WeatherBell.

The timing of Thursday's storms will be during the overnight hours when instability (brought about by heating of the atmosphere) will be lower than during the afternoon hours when the sun is high (but still at moderate levels). Therefore, while a marginal damaging wind threat is possible, the best scenario for severe storms will be to our west where the storms will be during peak heating. Rainfall amounts could reach an inch or more Thursday night, but widespread flooding is not expected either.

"Forecast radar" from the mid-day run of the NAM model valid at times indicated. This is an early indication of timing and is NOT a forecast of exactly what will occur. Note the general decrease in line strength between the two images. Graphic courtesy WeatherBell.

The storm system will likely be gone by the time you head to work or take the kids to school on Friday morning. Behind it, a much cooler airmass overtakes the Mid-South. Skies will quickly clear and, even with lows in the mid to upper 60s Friday morning, mid 70s may be as high as we go in the afternoon. The weekend looks simply stunning! Some outlying areas may see lows in the 40s with highs in the 70s across the board. A great weekend to get out and enjoy fall in the Mid-South!

Erik Proseus, MWN Meteorologist

----
Follow MWN on Facebook, Twitter, and Google+
Visit MemphisWeather.net on the web or m.memphisweather.net on your mobile phone.
Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!

MWN Lightning Round: weekend forecast, holes in the clouds, and NWS on Twitter

The MWN Lightning Round is back with three topics for this fabulous fall Friday!

1. First, and most important, the weekend forecast! Lots of activities again going on around town this weekend as fall gets into full swing. The weather will cooperate for most of them, but it will be warm with slightly increased humidity levels. For today, high clouds will stream overhead but no rain is expected and temps will reach the mid 80s, similar to yesterday. Friday night football looks great with temps near 80 at sunset and a light northeast breeze.

For Saturday, another day not unlike the last couple. Clouds will be a bit thicker, but the rain chance is still very low and not worth worrying about. Temps will once again reach the mid 80s, but morning lows will be a bit higher (mid 60s) as humidity increases. If you're headed to Oxford for the Memphis-Ole Miss football game, expect cloudy skies, a slight rain chance, and temps near 80 at kickoff.

A developing trough to our south is responsible for the clouds this weekend. As it moves northeast into the southeastern U.S., rain chances also go up a bit for us, mainly Sunday. Earlier this week, some models were hinting at a Sunday washout but that does not appear to be the case now. Scattered showers are expected though and will be more numerous to our southeast, over northeast MS into AL. Temps will be a few degrees cooler Sunday due to the showers in the area. A warm and dry pattern sets up for next week until another true fall cold front moves in by week's end.

Weekend rainfall forecast from the NWS. Precip (mainly Sunday) could average 0.10" in the metro with heavier amounts to the southeast. Graphic courtesy NOAA/NWS/WPC.

2. A unique cloud formation was observed over the Tuscaloosa, AL region this morning. A "hole punch" cloud, or fallstreak hole, caught the eye of a bunch of smartphone-toting folks, who captured pictures of the event. An example, from the Twitter feed of James Spann, is shown below. Hole punch clouds are typically formed when aircraft fly through an area of supercooled water droplets. In the aircraft's wake, rapid cooling takes place and introduces ice crystals into the air, causing the water droplets to evaporate. This leaves a hole in the cloud and ice crystals below it! For more on hole punch clouds, including some cool pics, see articles from the Cloud Appreciation Society and Wikipedia.

Fallstreak cloud over Tuscaloosa, courtesy James Spann on Twitter (@spann).

3. The National Weather Service is officially joining Twitter! OK, so many NWS offices have been there for some time, but as with any new product or service from the NWS, there is an "experimental" phase in which they test the waters and solicit feedback. As of October 31, their use of the service becomes "operational," meaning NWS offices are expected to utilize the medium for information sharing.

There literally is no faster way to share and receive information than Twitter. Breaking news almost always breaks there first these days. While the use of Twitter will be a "complementary" service at the NWS, they expect to "disseminate important information about hazardous weather conditions" and Twitter "will also be used for public outreach and education and to direct users to official NWS Web sites." The NWS stresses that users should not rely on their Twitter feeds for warning information. To this point, the NWS has not indicated if or when their experimental use of Facebook will become operational.

You already know that you can follow MemphisWeather.net on Twitter and Facebook (links below), but did you know that we have automated feeds of severe weather watches and warnings for each metro county on Twitter? Learn more and find your county's feed here.

Hope everyone has a great weekend! We'll be watching for our next big fall front late next week.

Erik Proseus, MWN Meteorologist

----
Follow MWN on Facebook, Twitter, and Google+
Visit MemphisWeather.net on the web or m.memphisweather.net on your mobile phone.
Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!