Friday, October 20, 2017

The fall weather roller coaster is leaving the station!

A gorgeous fall week is in the books and I know many of you are grateful for that! After a few "false starts" and a late end to the warm season, the pleasant days and cool mornings this week have been welcomed.

Friday Night

Now we're all ready for a beautiful fall weekend right? Well, perhaps Mother Nature can partially deliver... The weekend starts with Friday night though and it promises to be a nice one. Skies will be mainly overcast, but it will be dry with temperatures in the 70s and comfortable humidity levels for Friday Night Lights, the last free concert of the fall season at Levitt Shell (here's a plug for their awesome end-of-season benefit concerts in 2 weeks), and whatever else you might have planned.

Saturday

As we head into Saturday, I expect most of the day to be pretty decent, though clouds stick around and the south wind increases a bit ahead of our next weather-maker. Despite the chance of a few sprinkles or a brief light shower, it will be mainly dry with highs topping out near 80. Morning lows won't be as cool as this week - near 60 most likely, owing to increasing dewpoints on that south wind. Saturday evening should also be dry for most with a persistent south breeze at about 10 mph.

The surface map for Saturday evening shows a cold front across the Plains, with most active weather (some severe storms) well to our west. There will be a low chance of a couple showers in the Mid-South tomorrow evening. (NWS)

Sunday

Things change early Sunday as a cold front nears and a fairly deep upper level trough , which is currently along the west coast, slides into the Plains. Precipitation chances increase precipitously (which they are wont to do) Sunday morning with a few non-severe thunderstorms thrown in for good measure. It will be mild as you head to church or brunch with temperatures in the 60s as rain becomes occasionally heavy. Look for the trend to continue throughout the day Sunday with temps not rising much above the lower 70s and rain continuing, producing up to 1-2" totals on Sunday. Though models differ a bit on the details, and any potential lulls, if you have outdoor plans Sunday, you'd be best served by having an alternate arrangement made.

An upper level trough is shown over the Plains on Sunday morning just behind a cold front that will be advancing into the region. Rain will arrive early Sunday in the metro with a few thunderstorms also possible. (PivotalWx)

Predicted rainfall totals through Sunday evening from the NWS - between 1-2" is a likely amount for the metro. (WxBell)

Monday

The forecast Monday is a little murky and unclear, mostly because the trough overhead is apt to form a "cut-off low" over the lower Mississippi Valley. Basically, this means a piece of the trough "cuts off" from the rest of the upper level flow and forms its own low pressure. That looks to prolong rain chances, at least in scattered form, into the day Monday. Again, details are still TBD, but for now I"m going with scattered showers and cooler temperatures (60s) Monday, as well as a steady north wind behind Sunday's cold front.

By Monday morning, the upper level trough has lifted north and left behind a cut-off low pressure system (shown over the Mississippi Delta), which will keep showers in the forecast on Monday. (PivotalWx)

Predicted rainfall totals through Monday evening from the NWS. We'll probably end up with widespread 2" rainfall amounts from this system. (WxBell

Tuesday and beyond

By Tuesday, the low moves east, high pressure builds back in, and in fact, another large trough develops over the eastern U.S. driving much cooler air into the Mid-South for mid-week. While it will be sunny out, this will likely be the coolest air of this early fall season with highs (maybe struggling) into the 60s and a few outlying areas probably seeing frost on Wednesday morning.

A massive upper level trough will be in place over the eastern U.S. by mid-week (shown on Wednesday morning), bringing the coolest weather of the fall to areas under its influence. (PivotalWx)

Looking out a bit further, another large-scale system quickly transits into the region as the progressive upper level pattern continues and we're probably looking at another rain event a week from now. Hang on tight - the autumn roller coaster has left the station!

Erik Proseus
MWN Meteorologist

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Thursday, October 19, 2017

NOAA / NWS Winter Outlook released

The National Oceanic and Atmospheric Administration has released their 2017-2018 Winter Outlook, which is predicated on the emergence of a weak La Nina event in the eastern Pacific. NOAA indicates that La Nina is likely to be "weak and short-lived," but will still have an effect on the weather patterns over the United States. La Nina typically results in cool and wet conditions across the northern tier of the country and warm and dry conditions for the southern U.S. as compared to an average winter. The outlook graphics reflect that general thinking.

Temperature

The temperature outlook calls for a broad area across the southern United States with a high chance of above average temperatures. Specifically, the most likely areas for above average warmth are from the Four Corners region across Texas to the central Gulf Coast. North of those areas though, there is a good chance of seeing above normal temperatures across the rest of the southern U.S. and potentially the eastern U.S. Memphis and the Mid-South is also expected to average above normal this winter in the temperature department.



Precipitation

On the precipitation side, La Nina is well known for dry conditions across the southern tier of the U.S. and that is exactly what we see in the outlook graphic. The desert southwest, southern plains, Gulf Coast, and Mid-Atlantic are all forecast to end up drier than average. Areas that are likely to see above average precipitation include the norther Rockies, Ohio Valley, and central Great Lakes. The Mid-South is in an "equal chances" area, meaning there are no clear signals to indicate above or below precipitation.


Commentary

It should be noted that above average temperatures for a season do not necessarily mean a lack of winter precipitation in the Mid-South. The Memphis area averages about four inches of sleet and snow each year, though it tends to vary each winter around that average, from an inch of two to 5-6" or more during the snowiest winters. Of course, one or two storms can produce those amounts, so it really comes down to having the right mix of moisture and cold air simultaneously. In addition, ice storms can also occur when a rain event runs into a shallow layer of cold air, either behind a cold front, or when high pressure north of the region filters cold air south into the region.

It's been several years since the area has seen "good" snowfall. The past six years have yielded a total of 7.1". The two previous years, 2009-10 and 2010-11, recorded 6.8" and 9.7" respectively, with big storms dumping even higher totals that affected portions of the metro but missed the airport. Maybe this will be our year for another heavy snow! As an aside, it should be noted that La Nina can sometimes produce severe weather episodes in the late wintertime as well, so we'll need to keep an eye out for that potential as well.


Erik Proseus
MWN Meteorologist

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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Friday, October 13, 2017

Trending towards fall... after one more hot day

The past couple of day have provided some evidence that fall is indeed here, while the warmth this afternoon and Saturday remind us that "fall" is relative and includes peaks and valleys.

As opposed to last weekend when hot temperatures (90°+) were coupled with very muggy air, the hottest day (Saturday) before the next fall front arrives (Sunday) will feature dewpoints in the mid 60s instead of the low to mid 70s. So while it'll be quite warm for the Tigers tilt against a formidable-and-respected Navy opponent (forecast highs of 89° are within a degree of the record), a southerly breeze and only-somewhat-uncomfortable humidity levels should make for a bit more tolerable day. Just ignore the calendar and pretend it's early September! [As an aside, I suffered through the weather to revel in a win over UCLA and expect the level of suffering, at least from a weather perspective, to be a bit more muted. As for the outcome of the game... we can only hope that the heat of the day translates to a hot hand on the end of the right arm of one Riley Ferguson.]

The surface map for Saturday shows high pressure to our east ushering in warm air from the south, but a frontal system over the Plains is poised to dive south as a cold front by Sunday morning, bringing relief from the heat. (NWS)
Back to weather... As for what comes next - a return to the fall weather we expect in mid-October! A cold front moves through the Mid-South early Sunday. A warm start turns to off-and-on showers, a gusty north wind, and temperatures that don't move a lot from the morning lows in the upper 60s. Humidity falls on that north wind as temps only peak in the mid 70s. Don't expect a lot of sun, but I also don't expect prolonged rain.

Rainfall amounts associated with Sunday's front taper off from north to south with very small rain amounts expected in the Memphis area. (WxBell)

Precipitation earlier this week helped the dry ground that had developed, but don't expect enough Sunday to continue the trend. No drought indications are currently showing up in west TN or east AR, but parts of north MS have moved into the "abnormally dry" category on the most recent Drought Monitor.
The Drought Monitor shows D0 (abnormally dry) conditions over parts of north MS.
Looking ahead to next week, the first few days post-front look stunning, and the rest of the week doesn't look half bad! Sunny skies pervade as cooler high pressure builds in. Highs for most of the week will be in the 70s (though we might not quite make it there on Monday). Evenings will be cool with low humidity allowing temperatures to drop quickly once the sun sets - which is now getting closer to 6:00 than 7. Mornings will be crisp (I've been waiting to use that word!) with lows near 50° in the city and into the 40s in rural areas. Now THAT is fall!

The American GFS model forecasts temperatures to drop to autumnal levels next week behind Sunday's front. (WxBell)

A slow warming trend takes place  by week's end, though clouds will also start to increase as the next system approaches about a week from now. The good news is that the warmest days behind this weekend's front will be closer to 80° than 90°. Yet another sign that we're nearing Halloween. Enjoy this time of year - before you know it, we'll be complaining about it being too cold!


Keep tabs on the temperature swings and precipitation chances with the MWN mobile app and our social media feeds! Links are provided below.

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 is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder