Huge trough provides a pleasant weekend, then summer arrives

An unusually cool few days culminated in a record low this morning and it appears the unseasonably cool weather will stick with us through the weekend before our first good spell of summer weather arrives next week. Unfortunately, cool weather also means unsettled weather and a few rain chances for Memphis in May BBQ Fest.

First, I'd like to share a few pics I received last night as showers passed over the area around 5-6pm.  The high-based showers (meaning the base of the clouds was fairly high) with sun peeking through the clouds and a stable layer of air beneath the clouds made for some interesting sky-watching and even a double rainbow!  The clouds with round "nobules" or "sacks" below them were mammatus clouds, which are more commonly associated with severe weather, but which also form when falling precipitation encounters a stable layer of air, thus making the cool formations on the base of the clouds.

Mike H sent us these pics of the mammatus clouds on Twitter.

Joey Sulipeck took this great pic of the rainbows over Barbecue Fest

 

Posted by the Memphis Redbirds Twitter account right before the first pitch last night!

Looking ahead to the next 72 hours, the huge trough of low pressure at the mid and upper levels of the atmosphere will  slowly break down and move east, but until it does, it means continued cool air over the area. Clear skies and light wind this morning allowed temps to fall into the mid 40s across the area. Officially, the airport dropped to 46, which breaks the record low for the date of 47 set last in 1967.

Besides cool temps, the trough also has upper-level disturbances rotating around it. As we are in the base of that trough, the disturbances pass over and bring us rounds of precip, one of which occurred last evening. The next fairly strong one is due in tonight and will bring a better chance of showers overnight into the early morning Saturday. Though a shower is possible this evening, most rain will hold off until after midnight and end by mid-morning Saturday if not a bit quicker. one more, slightly weaker, disturbance arrives Saturday night, bringing another chance of rain late Saturday night into early Sunday.

That should be the last chance of rain for some time as the trough moves east and a summer-like ridge of high pressure build in behind it for next week. The transition from trough to ridge is shown in the animation below, which depicts forecast atmospheric pressure and wind at about 18,000' up every 24 hours from this morning through next Wednesday. The yellows/red over the center of the country are this morning and that is the huge trough (it looks like a dip, or trough, in the pressure pattern). You can see that that area of yellows/reds weakens and shifts north, while a hill, or "ridge," or light browns moves east across the southern U.S. The south-central and southeast U.S. is under that ridge by Tuesday and Wednesday as it strengthens (light brown becomes pink). As that happens, the ridge warms temperatures and suppresses precipitation. In other words, a hot and dry week is ahead!

Loop of 500mb (18,000') pressure pattern and wind, showing a significant trough being replaced by a large ridge.

You can find our complete MWN Forecast, including temps that bottom out in the 50s this weekend and rise to near 90 by week's end, on our mobile apps and website. (A side note about the apps - new features are nearly complete and ready to release, so if you don't have the app yet, now is a great time to get it!)  Enjoy this fine weather this weekend, keep an umbrella handy in the mornings especially, then get ready for an early taste of summer as schools let out and we head towards Memorial Day weekend!

Erik Proseus
MWN Meteorologist

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Roller-coaster temps this week thanks to mainly dry cold fronts

Temperatures this week will mimic some of the best roller coasters around as multiple cold fronts move through the area.  Fortunately, the fronts will be moisture-starved, bringing little to no rain with them it appears.  The fronts will be noticeable to Mid-Southerners however, marked by cold weather and gusty north wind behind them and warmer days as wind shifts back to south ahead of the next front.  This is what we refer to as a "progressive pattern," meaning that systems do not stall out, but continue moving through every couple of days.  Much like a roller coaster car that doesn't stop in the valley or at the top of the hill, but heads straight for the next loop!

The image below is taken from this morning's GFS (American) computer model showing near-surface temperatures for the next 7 days.  High temperatures for each 6 hour period are in red and low temperatures for each 6 hour period in black.  The daily highs are labelled with the vertical axis on the left indicating the temperatures in degrees F.  Friday morning's low is also labelled as it will be the coldest morning this week.  I'll bet you can even pick out about when the fronts will come through!  Precipitation is represented by blue bars (scale to the right for amounts in inches).  You'll notice that after today's rain (the first 2 blue bars), there is no more precipitation expected from the GFS until early next week, despite the hills and valleys in the temperatures.

GFS Monday morning model data showing temperatures in pink and black (highs and lows for each 6 hour interval, respectively) and precip (blue bars).  Warm temps are expected Tue, Thu, and this weekend, while cold days will be Wed and Fri when highs will probably stay in the 30s!

The official MWN Forecast calls for pleasant days on Tuesday (with a very small chance of a shower as the first front moves through) and Thursday with cold, windy days on Wednesday and Friday.  A moderating trend is expected this weekend.  It looks like another cold snap will arrive early next week.  Overall, a not-unexpected pattern for the middle of winter and thankfully not as cold as the start of last week!

Follow us on Facebook, Twitter, or Google+ for multiple updates each day (links below)!

--Erik Proseus
MWN Meteorologist

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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!

Moderating temps on the horizon

Finally, after some brutally cold days this week (in which no records have been broken but should have been), a massive Arctic high pressure system responsible for the mid teens lows and highs in the 20s will be moving to our east. For those that know a little about weather, high pressure to our east means southerly wind and a better than average chance of some warming. That will be the case this time as well.

After one more cold day today (near 30) and cold night tonight (near 20), things start to improve and the "feels like" temperatures gradually improve from "Minnesota" to "Memphis." By this weekend, we'll be seeing low temperatures near today's high and afternoons reaching well into the 40s and perhaps low 50s. Another weather system moves in Monday with showers possible by late Sunday, but at least it will be rain. We'll be watching the tail end of the system carefully as temperatures could fall Tuesday while precipitation ends.

A note on Mid-South winter temperatures so far: December ended up much below average (3 degrees) and January is beginning worse (-4 degrees to this point). Besides high heating costs, at the almost half-way point of meteorological winter, I'm beginning to believe that we could have a hard time ending up "above normal" for the season as generally expected in La Nina winters. If we do, there will haev to be some serious warming in the next 6 weeks. At this time of year, that can only mean one thing - severe weather. I think I'll stick with below normal, thank you very much!

Where do you think we fall on the "Feels Like" scale above?

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When will Memphis get its last freeze of the spring?

The last freeze at Memphis International Airport was March 5, 2010, when the temperature briefly touched 32 degrees. It's now March 15th. Our typical "last freeze" date in the city is March 22nd, though in the suburbs and outlying areas it averages a few days later. (The last freeze for most suburban areas was March 6th, when the airport bottomed out at 33.) Of course, a frost is likely even later than these dates as temps in the 30s are still possible until the first of April on average.

Over the last decade, the lastest occurrence of 32 degrees or less (and hence, the start of the agricultural "growing season") was:

2009: March 3 (25 deg.)

2008: March 9 (30 deg.)

2007: April 8 (28 deg.) (remember that Easter Sunday morning?)

2006: March 26 (30 deg.)

2005: March 2 (28 deg.)

2004: March 10 (32 deg.)

2003: March 10 (30 deg.)

2002: March 23 (28 deg.)

2001: March 29 (31 deg.)

2000: April 9 (32 deg.)

This averages out to March 19th , slightly earlier than the 30-year climatological average.

So, are freezing temps over for the Memphis area until later this fall? The latest MWN Forecast does not show any freezing temps through March 29, however a system this weekend could pack a cold punch behind it. Depending on the exact track of the system and the strength of the cold air behind it, cold temperatures are not out of the question Sunday or Monday morning.

Here's a chance for you to be the forecaster! Vote in MWN's unscientific webpoll! When will we have our last freeze?

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Nowhere to go but up!

It is somewhat unusual, though not as much in the wintertime as in other seasons, for the temperature to rise during the overnight hours, but how about doing it for three nights straight? That may be exactly what we see, as a warm front pushing up from our south and abundant cloud cover are working in tandem to cause temperatures to hold steady or rise for almost 72 hours!

At Memphis Int'l Airport, beginning last night (Tuesday) at 11 pm local time, temps have been steady or rising each hour. I expect that trend to continue overnight tonight as abundant cloud cover has helped keep the lid on temperatures today and a warm front pushes a little closer to the area overnight. They will continue rising tomorrow, to a high at least in the upper 40s. Thursday night, the warm front should make it all the way through Memphis, so I expect that temps will again hold steady in the evening before rising overnight as a stiff south wind kicks in. By Friday, a little sun might peek through and highs should reach well into the 60s. This would make a stretch of almost 3 days (Tuesday night to Friday afternoon) that temps will have held steady or risen every hour.