Wednesday, April 11, 2018

One big fly in the spring ointment - weekend rain

With the return of southerly wind today, we're finally starting to get a good taste of spring despite a cool start. With abundant sunshine in place, we are topping out near 70 degrees this afternoon. That trend continues as we head into the end of the week!

Thursday - Friday

The warming continues as high temperatures reach the upper 70s each day with mild lows in the 50s Thursday and 60s Friday. We'll still see a good deal of sunshine Thursday, but the clouds increase and thicken heading into Friday. The biggest issue will be the wind. That south wind gets mildly ferocious as gusts reach 30 mph each day. Trade-off for the nice temps I guess!

Friday Night - Saturday

Note the title of the blog. Here comes the fly (and it's a big one, like the kind that can scare large toddlers), just in time for a bunch of springtime outdoor activities across the city.

A slow-moving cold front pushes towards the Mid-South by Friday evening. With it, we can expect frog-stranglers and gully-washers, as well as some thunderstorms, to arrive Friday night. In fact, during the day Friday, severe weather is likely to our west (while we stay dry). The ETA for our rain is starting to narrow in on the late evening hours Friday. While a few showers are possible early in the evening (6-9pm), rain chances ramp up quickly as we get later into the evening (9-11pm), to the point that by the time we hit midnight, it's almost a certainty. Storms are also expected overnight Friday night. We're hopeful that the rain holds off for the Memphis Tiger football #FridayNightLights event at the Liberty Bowl Friday evening!

Forecast radar loop from mid-day Friday through Saturday evening from the Wednesday morning run of the NAM model. It thinks we'll get rain Friday night, a lull Saturday morning, then additional showers Saturday PM. (PivotalWx)
As for severe weather, I mentioned storms to our west Friday. As the system gets closer, the threat of severe storms declines. However, as of Wednesday morning, the Storm Prediction Center includes the Memphis metro in a Marginal Risk (level 1/5) of severe weather, mainly for damaging wind, Friday night. Areas west of the river are under a Slight Risk (level 2/5). We'll be watching this the next couple days for the potential of a shift in that risk, up or down.

By Saturday, there are a couple of trains of thought in the model data. The front will move through very slowly due to upper level wind basically paralleling the front, thus not providing much of a "push" for it to move east. There appears to be a secondary low pressure system that develops to our south and moves north up the front on Saturday. That low would provide the threat for either additional, or continuing, rainfall for at least parts of the day. I don't expect a completely dry day.

If you believe the GFS and NAM models ("Made in America," NAM shown above), we'll see a lull in the rain Saturday morning with an additional chance of afternoon and early evening showers as the low moves by to our east. If you believe the European model, which may or may not come with tariffs now, it is a little slower with its eastward push of moisture and lends itself to a wetter Saturday, though not deluges. Either way, it will probably be mild (upper 50s-60s) and damp.

Total rainfall will really depend on the speed of the front and the coverage of thunderstorms Friday night. As of early this morning, the NWS was fairly bullish with 3-5" over the area. More recent data suggests perhaps 1-3". Still time to figure that one out, but expect periods of heavy rain, especially overnight Friday night. The severe weather threat Saturday will have shifted to our southeast.

NWS forecast for rainfall Friday-Saturday. Later data will likely result in a downward trend from the NWS in the next forecast update. (NWS/WxBell)

SPC severe weather outlook for Saturday, as the threat of severe storms moves to our southeast.

Sunday and beyond

As this big weather system shifts to the east coast, Sunday will likely feature wrap-around clouds and gusty north wind, meaning a chilly day. Look for temperatures ranging from the mid 40s in the morning to mid 50s in the afternoon, plus that wind. Sun returns as we head back to work next week (because... Monday) and temperatures start to moderate once again. Highs rebound into the 70s by Tuesday with a slight chance of rain on Wednesday, but nothing like the weekend system. In other words, spring warmth is interrupted for a couple days by a rainmaker - typical for this time of year!

Erik Proseus
MWN Meteorologist

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