MWN Blog: April (heavy) showers in the forecast

The rainfall deficit in Memphis so far this year is about 6" with about half of that since March 1. A wet system this weekend looks to put a dent in that deficit with the potential for heavy rain and some thunderstorms affecting springtime outdoor activities. Let's dig into the details.

Wednesday and Thursday

A front earlier this week is basically a non-factor now as we head into the middle of the week and start making plans for the weekend. A few pop-up showers are possible this afternoon and again Thursday afternoon, but coverage should be minimal with temperatures well into the 80s (10°+ warmer than average for this time of year).

By Thursday night, a cold front drops south into the metro and brings a chance of showers and thunderstorms. I expect the evening hours to only have small chances, but they'll increase overnight as the front stalls along I-40 like rush hour traffic with multiple accidents in progress. If you're headed to FedExForum to cheer Fizz and the Grizz and chide the refs, you should be in pretty good shape, though some rain might start to fall in sync with the streamers from the rafters about 11pm (#TakeThatForData)!

Friday

The front will likely stall along the I-40 corridor all day (because that's why I-40 exists - for fronts to know where to stop). Building instability to its south over north MS and energy in the mid levels of the atmosphere going by to its north will result in scattered showers and thunderstorms during the day and into Friday evening. There could be a few strong storms during the PM hours, especially over north MS.

The North American Model (NAM) shows the front roughly along I-40 Friday afternoon with instability ("storm fuel," measured by CAPE) along and south of the front where the best chance of storms will exist.

The entire area is currently outlooked under a Marginal Risk (category 1/5) of severe weather, which means a few severe storms are possible, but chances are low. Where the front stalls will be key as the best chance of strong storms, as well as potentially some heavy rain, will be along and south of it. Temperatures will remain in the 70s most of the day.

A Marginal Risk (category 1/5) of severe weather exists Friday across the area. A couple storms could contain strong wind.

On Friday night, low pressure over OK will move east into AR and start to pull that front back to the north, putting the metro in the "warm sector" of the approaching low by Saturday morning. Expect more thunder as it does so, as well as some downpours and breezy southerly wind. Friday and Friday night activities need to have a rain plan if you're risk tolerance is low.

Saturday

The low pressure system in AR looks like it'll also take I-40 eastbound and move just about over Memphis by mid-day. Models differ some on placement of the low, the warm front pulling north, and timing of a cold front that the low drags across the area. However, without trying to nail down exact details, expect Saturday to be a wet day, and potentially a washout for at least a portion of the day. As the low draws near, thunderstorm chances increase markedly, as does the likelihood of heavy rain. Right now, the morning and early afternoon hours are most "under the gun," with conditions improving steadily as we head towards Game 4 Saturday night.

The NAM model expects low pressure to be nearing the metro, dragging a cold front (blue line) towards the MS River by early afternoon Saturday. The red line is a warm front that had previously stalled along I-40 on Friday.

The Storm Prediction Center has the equivalent of a Slight Risk (category 2/5) of severe weather forecast for Saturday and I can't argue that. Instability should be sufficient, wind energy is expected, and a potent low will move right over us. That could be the recipe for a few strong storms with wind and hail threats. The tornado threat doesn't look too high right now, but where there's a low and a warm front, we have to consider that a possibility.

The day 4 (Saturday) outlook places the metro in a 15% risk of severe storms, equivalent to a Slight Risk. Areas ahead of the low and south of the warm front will have a risk of strong wind, hail, and an isolated tornado. Our threat ends with the frontal passage Saturday afternoon.

I believe the threat of flash flooding is more widespread than any of those threats right now though. Most areas in the Mid-South will likely see 2-3" of rain between Thursday night and Saturday evening with a good deal of that Saturday. Some spots could see 3-4" or more if storms train along the front. My concern is actually for spots that see heavy rain prior to Saturday, as that could set the stage for Saturday's rain being all run-off due to wet ground. Fortunately, this month has been fairly dry so far.

Total rainfall forecast through Monday morning. Widespread 2-3" totals are likely over the next 4-5 days. (NOAA/WPC)

Sunday into next week

Withe the low to the east and northwest wind wrapping around it, Sunday will be cooler and likely start off cloudy with clouds diminishing by afternoon or evening. A stray shower is possible as temperatures that start near 50 get no higher than the mid 60s on gusty northwest wind. It'll feel more like early spring than the early summer we have started to notice lately!

Early next week promises a return to nice spring-like conditions with abundant sunshine and highs in the 70s, rising to 80 by Wednesday. Sounds like something to look forward to!

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!