Details on possible severe weather Saturday night – #memstorm

OK maybe so, but if April showers DO have some thing to do with springtime flora, then we must be angling for a colorful May! Officially, we’ve already had nearly 4″ of rain this month, and my mid-month paycheck hasn’t even arrived yet. It’s possible we’ll pass the (entire month) April average rainfall this weekend. Let’s get into it.

Friday

A cold front snuck through the area while you were sleeping last night. You already know that because multiple days of 80s has been rudely replaced by the 60s today. I expected we’d see more sunshine, but the upper level jetstream has continued to pour high clouds over us, limiting warming a bit. While not unpleasant, it is a bit cool after getting used to the warm temperatures.

A southwest flow aloft has continued to funnel upper level clouds over areas east of the Mississippi River during the day today. (COD)

Early Saturday morning, that front starts to retreat north again as another front drops south, bringing the first of potentially several rounds of showers in a 24-hour window, just in time for your morning gardening or sports activities. Morning plans need an “in case of rain” backup.

Saturday daytime

As the fronts both have influence over our weather Saturday, upper level disturbances moving through a strong southwest jet stream set the stage for additional rain chances. Timing of these is near impossible, so we’re going to call it “scattered showers” for the majority of the day. We’ll give a slight edge to the morning hours over the afternoon for which period is wettest. It won’t be any warmer tomorrow either, thanks to the rain chances and plenty of cloud cover. In addition, a gusty east wind picks up in the afternoon that could sustain itself near 20 mph and gust to 30+ mph. An east wind is also not conducive to much warming. Look for maybe 3/4″ to 1″ of rain prior to dinnertime Saturday.

Saturday night

This is when things get more interesting. Strengthening low pressure moves out of Texas and makes a beeline for the Memphis metro. Rain chances increase into the evening as that wind remains strong. Some rain will be heavy Saturday night. We could see some urban flooding in those typical low-lying areas after dark. Remember: turn around, don’t drown!

The surface map for Saturday evening shows the low in northeast TX moving our way with a warm front pushing north across AR/MS. South of that front, and to the southeast of the low, is where the severe weather risk is highest. (NWS)

In addition, the approach of the low will drag the warm front that resides to our south back northward. At least portions of the greater metro enter the “warm sector” of the low, which means the severe weather risk goes up as instability climbs (yes, even after dark). There will also be plenty of wind energy with this system to enhance storm activity. Thunderstorms are a good bet for the metro area, but north Mississippi stands the best chance of severe weather. The most likely timing for any severe storms is 8pm until 3am Saturday night.

Risks include damaging straight-line wind, some hail, and a few tornadoes.  Currently, the Storm Prediction Center, the NWS severe weather experts, provides a range of severe weather probabilities for the metro: from a category 1 Marginal Risk (Tipton County) to a category 2 Slight Risk (the heart of the metro, including Memphis/Shelby), to a category 3 Enhanced Risk (southern Tunica, Tate, and southern Marshall Co.). See the maps below for the overall risk area across the southern U.S., as well as a zoomed view around Memphis.

A large area has the potential for severe weather Saturday PM with the highest risk of widespread severe storms, including possible strong tornadoes, southwest of Memphis in southern AR and northern LA. (NWS/SPC)

The highest risk of tornadoes will be south and west of the metro in the category 4 Moderate Risk area, though a tornado can’t be ruled out near and south of I-40 in eastern AR, northwest MS and southwest TN. You should prepare for the possibility of all modes of severe weather after dark tomorrow night. Consider where you’ll be and where you can take shelter if necessary, but particularly south of Memphis.

Note also that this risk area can, and likely will, be adjusted Saturday multiple times as more detail becomes available on how the storm is progressing. If the low tracks a bit further north, that warm sector could lift further north into the metro, raising our severe weather chances. If it is suppressed south a bit, our severe weather risk diminishes a bit. You MUST remain weather aware tomorrow as the situation is dynamic and the potential is real.

The Weather Prediction Center has a large portion of AR in a Moderate Risk (20-50% chance) that rainfall amounts Saturday into Saturday night could exceed flash flood thresholds. The metro is in a Slight Risk, meaning there is a 10-20% chance of seeing flash flooding nearby. Urban areas are likely to be the first affected as rainfall could top 2″. (NOAA/WPC)

Sunday

After about 2-3am Sunday morning, the weather looks to settle down quite a bit, with lingering showers possible into Sunday morning. Have Sunday morning plans outdoors? Consider a rain alternate, though heavy downpours are not expected. Total rainfall from this events will likely be well over an inch, and could fall in the 2-3″ range in spots. That would likely push us over the normal April rainfall total of 5.5″ as we head towards the second half of the month (which I am certain will not be dry).

NOAA’s Weather Prediction Center forecasts widespread 1.5″-2.5″ rainfall totals with this weekend’s event.

The next round of showers and thunderstorms arrives Wednesday-Thursday with a possible risk of severe weather once again. We’ll have more as we draw closer to the event, but for now, plan to enjoy the sunshine Monday and Tuesday and remain alert on Saturday!

Erik Proseus
MWN Meteorologist

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