Sunday, March 20, 2016

First week of spring - snow, then warmer!

After weeks of above normal temperatures, spring officially begins with - what else - snow and Freeze Warnings! After an unusually warm winter, astronomists deem it spring and "the lost winter" shows up!

Today - cold and "snow"?

What may be the last gasp of winter arrives with accumulating snow on the northeastern seaboard and cold temperatures across the eastern U.S. An upper level low diving south across the region is responsible for our clouds and scattered showers this afternoon, while cold surface high pressure over the Plains and low pressure off the Atlantic coast combine to bring a gusty north wind and chilly temps to the Mid-South today.

A deep (strong) upper level low pressure system at 500mb (about 18,000') is located over northwest TN this afternoon, which is driving the formation of showers in the region. The degree of upper level "energy" is shown by the colors with strong values over the metro early this afternoon according to the GFS model.
Some of these showers are producing a mix of snow and graupel ("soft hail" or "snow pellets," or as I sometimes reference them as - "dippin dots"). Even though the temperatures at the surface are in the mid 40s to near 50, the freezing level is dropping below 2,000 feet and the temperatures at 5,000 feet are between 15-20° F. This is supportive of freezing precipitation aloft that simply doesn't have enough time to completely melt as it falls to the ground. All of this will end with sunset tonight and skies will clear.

Temperatures at about 2,500' are below freezing (blues) as shown by the GFS model valid at 1pm today. This is contributing to the mixed precipitation that is occurring at the surface. All precipitation at this level is snow.

Temperatures at 18,000' are very cold around the upper level low, approaching -35°C, according to the GFS model valid at mid-day.

Tonight - protect outdoor plants

High pressure moves east and will be over the Mid-South Monday, meaning a slightly warmer day, but a very cold start to spring break week for many school kids. Freeze Warnings and Frost Advisories warn of air cold enough to cause damage to some of the young plants that have started to grow already in the previously-mild March air. Many places in the outer suburbs of the metro - indeed much of the region outside the Memphis heat island and the MS/AR Delta - will see temperatures fall below freezing for a few hours early Monday morning. If you're worried about outdoor vegetation, tonight is a good night to offer them some protection from the cold with a blanket or other cover, or bring them in the garage or covered patio if possible.

Later this week - warming with a chance of thunder

By Tuesday, we'll be back in a more springlike pattern as wind turns southerly and becomes gusty and temperatures respond by climbing towards 70° under abundant sunshine. Wednesday will be similar with the morning chill a thing of the past and more clouds overhead as our next weather-maker approaches. Rain and probably some thunderstorms will be a good bet Thursday. The latest computer models that go out that far are making this system more "progressive," which means it moves through a little more quickly. In fact, most of the rain could be done by noon if the current model solutions are correct. That would limit the instability that comes with daytime heating this time of year so hopefully storms remain at bay.

StormWatch+ Re-Energized!

Tomorrow marks the roll-out of version 3.0 of our StormWatch+ national weather app. In work for several months, this version marks a significant improvement in the "front end" of the app, which admittedly had been lacking. While the severe weather push notification alerts are not being changed, pretty much everything else is. The result is what I am hoping will become a weather app of choice for nationwide use to get day-to-day, reliable weather information, including local radar, current conditions, and the general forecast.

We've gone to great things to ensure a beautiful, fast-loading, smooth radar display with precipitation typing and multiple layer selections that cover the entire nation, but also can be zoomed to your neighborhood (sorry, no screenshots ahead of tomorrow's release!). The forecasts are driven by the professionals at the National Weather Service, not a computer model that flip-flops 4 times a day or more. You know me - no crap apps here! NWS "point forecasts" are quality controlled by meteorologists in the the area that you request the forecast for.  In sum, we are hoping that StormWatch+ becomes #yourNEWweatherapp, especially for those outside the Memphis area, or for use by Mid-Southerners that travel and want a reliable app that will work nationwide.

StormWatch+ does not replace your app for local use and you don't have to purchase StormWatch+ Alerts for push notifications from that app, as the MWN app has the same capability. However, it is free to download and removes the geographic boundaries that the MWN app applies. I hope many of our iPhone and iPad users will consider giving it a try! Unfortunately for Android users, it is currently only available for iOS, but we hope that its success will lead us to develop an Android version! You can download StormWatch+ here and then get the free upgrade to version 3.0 tomorrow when it is released. I think you'll like the great improvement you see! Check it out!

Erik Proseus
MWN Meteorologist

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