Sunday, February 5, 2017

Another round of spring-like warmth, wind, and storms

Warm weather more suitable for March/April returns early this week as a storm system moves out of the Rockies and across the mid-section of the country into the Mississippi Valley by early Tuesday. Southerly wind has already set up across the region, returning a bit of moisture from the western Gulf as dewpoints climb through the 40s as we end the weekend. A dichotomy in sky conditions exists across the metro with clouds over north MS but sunshine over the northern half of the metro.

Clouds are prevalent over the southern half of the area this afternoon, while sunshine abounds north of the TN/MS line.
As high pressure over the Gulf of Mexico shifts east, clouds increase over the northern metro tonight and by morning we'll see southwest flow bringing in greater amounts of moisture on a strengthening low-level (2000-5000') jet stream. The increasing wind and moisture will trigger the development of scattered showers in the wee hours of the morning as a quasi-warm front moves north through the region. A few cracks of thunder are also possible though severe weather is not expected.

A round of scattered showers and a few thunderstorms is expected early Monday as this model simulation of radar echoes shows. The model depicted is the newest high resolution NAM valid from midnight to noon Monday. (PivotalWx)
By mid-morning, that round of precipitation will lift north and the atmosphere will become "capped" by a layer of warm air aloft throughout much of the rest of the day, putting an effective lid on anything but a few stray showers. With warm Gulf air being pumped into the region Monday on southerly wind of 15-20 mph, a lack of widespread precipitation, and dewpoints climbing towards 60°, high temperatures will likely reach 70°.

Very warm air will be in place Monday afternoon, as shown by the forecast temps at 3pm from the high-resolution NAM model. Highs in Memphis could reach 70° with a warm southerly wind. (PivotalWx)
Late Monday afternoon, the primary upper-level energy will begin moving across the nation's mid-section, resulting in thunderstorms well to our west. On Monday night, those storms continue rolling east with the upper-level shortwave, reaching the Mid-South in the wee hours of the morning Tuesday.

This loop of upper-level energy (yellows/oranges) from the GFS model shows a shortwave trough and its attendant lift moving across the southern Plains Monday and into the Mid-South very early Tuesday. (PivotalWx)
Activity should weaken a bit during those overnight hours due to a lowering of instability under the cover of darkness, but strong south wind pulled north by a low pressure system moving into the midwest, plenty of atmospheric moisture, and the lift generated by the shortwave will result in thunderstorms from very early Tuesday morning through perhaps mid-day. There is currently a Slight Risk (category 2 on the 5-point scale) of severe weather for the metro during that timeframe. Damaging wind and hail are the primary threats, with an isolated tornado not out of the realm of possibility. A greater threat of strong storms will likely exist to our east as areas from the Ohio to Tennessee Valley get more unstable due to storms arriving later in the day.

The early day storms will far out-run a cold front, which means after the storms, a few showers will be possible Tuesday but temperatures should again reach the 70° mark (perhaps warmer than Monday) as wind remains southwesterly and dewpoints still at least in the 50s.

Another warm day is expected Tuesday behind the morning storms and ahead of Wednesday's cold front. The high-res NAM model predicts widespread 70s along and west of the Mississippi River at 3pm. (PivotalWx)
The cold front finally moves through early Wednesday it appears, as weak low pressure forms over the southern U.S. and pulls it south. Previous forecasts had Wednesday dry with moderate temperatures, but it appears that there could be a few more showers, and maybe a thunderstorm, as the low moves quickly by to our south and the front drops through the metro. The end of the week appears much cooler again, but dry, leading to our next chance of rain next weekend.

We encourage everyone to stay tuned to the latest forecast information, particularly with regards to Tuesday morning, in case severe weather chances increase. As it stands, you still need to plan on having a way of getting severe weather information via a wake-me-up source like NOAA Weather Radio or StormWatch+ in the mobile app overnight Monday.

Erik Proseus
MWN Meteorologist

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