Wednesday, March 23, 2016

Early spring cold front brings a chance of strong storms

Warm and windy conditions precede the next big frontal system to move through the region. The parent low pressure system has already dumped inches of snow, accompanies by very strong wind, in Colorado, which has prompted Blizzard Warnings in the northeastern portion of the state and the closure of the the Denver Airport this afternoon!

That low will move from the Front Range into the Midwest and Great Lakes regions as it drags a cold front across the Plains tonight and into the Mississippi River Valley by early Thursday. A line of strong storms is expected to form this evening in far eastern OK south toward the Dallas metroplex, then move east across AR overnight.

Locally: thunderstorms early Thursday

With respect to the Mid-South, and specifically the Memphis metro, the best thing we have going for us as this system approaches is timing. Fortunately, the strongest forcing, or lift, associated with the approach of the cold front arrives around our diurnal minimum - meaning at the coolest part of the day, in the early morning hours. A round of showers and thunderstorms is still expected early Thursday morning, but the severity should be on the low end.

The upper level trough that is driving the front and its associated mid and upper level wind pattern is strong, but without the aid of very buoyant air (meaning it is very warm and will rise quickly once forced upwards by a cold front), the strength of the storms should be kept in check. A few strong storms with straight-line wind of 50+ mph is possible, but the tornado and hail threat will be very low with these storms. Plus, as quickly as it moves through (perhaps in just a few hours), downpours could be heavy but a prolonged heavy rain event that produces flooding is also not expected. Rainfall totals from this system, which exits the metro by late morning, should be generally under an inch.

The Storm Prediction Center places the majority of the metro in a "Marginal Risk" (category 1 of 5) of severe storms for late tonight and early Thursday morning. (The reason we are outlooked in a Marginal Risk in both the Day 1 and Day 2 outlooks, as shown below, is because the SPC "day" starts and ends at 6am. Thus, there is a low-end severe risk west of the Mississippi River before 6am and a similar risk east of the river after 6am.)

A Marginal (category 1/5) Risk of severe storms is forecast generally from the metro westward for late tonight (early Thursday) as a few scattered strong storms are possible towards daybreak. A higher risk is indicated to our west as storms in AR lose strength during the early morning hours Thursday.

A Marginal (category 1/5) Risk of severe storms is forecast generally from the metro eastward for Thursday morning after 6am as a few scattered strong storms are possible during the morning hours. A higher is indicated to the east of the metro as the storms move into a more favorable environment.
You'll notice that higher risk categories are "outlooked" for areas west and east of the metro. This isn't because we have bluffs or a Pyramid! It simply reflects the timing of the storms' arrival. Late tonight, the storms will be stronger to our west and diminishing in strength after midnight as they get closer and lose the heating of the day that contributes to their strength. Later, after the storms move east of us Thursday afternoon, they will again gain strength as they arrive in an atmosphere that has benefited from Thursday's heating of the day. It's all about the timing in this case!

Bottom line it for me!

What: Showers and thunderstorms ahead of an early spring cold front
Where: The entire Memphis metro
When: Between 5-11am Thursday
How strong: A few storms could have strong wind and localized downpours

Expect wind to shift to the west by late morning and remain gusty Thursday with temperatures in the mid 50s to lower 60s and partly sunny skies by afternoon. Temperatures will drop back down into the mid to upper 30s Friday morning outside the urban core. Friday and Saturday will be seasonal with good weather expected for Saturday morning egg hunts.

Easter Sunday brings a return of southerly moisture and warmth with warm temperatures but increasing chances of showers and thunderstorms again by afternoon and evening. Early morning worship services or egg hunts should see dry and mild conditions.

Erik Proseus
MWN Meteorologist

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