Cold temperaturesMany of us woke up to frost this morning as temps fell into the mid to upper 30s. Now a Freeze Warning is in effect for areas northeast of Shelby County (including Tipton and Fayette Counties) and a Frost Advisory for the rest of the area Saturday morning. A repeat of these cold conditions can be expected Sunday morning until finally a bit of a pattern shift will mean some warmer temps return.
|Freeze Warning tonight for the counties in light blue. Frost Advisory for the darker blue counties including Memphis and Shelby County.|
But that's not all...However, cold is not all we're dealing with unfortunately. Yes, we're putting a chance of snow in the forecast for tomorrow - March 28th. I've been looking at the possibility all week actually, and doing my best to ignore it like a middle school pimple, in the hopes that it goes away. Alas, it hasn't. Kudos to the GFS model for not budging all week on the upper-level disturbance that brings the precip chance tomorrow.
|Our favorite response in Facebook comments to this story... :-)|
Atmospheric setupThe setup looks like this: the pattern that brought brutally cold air and rounds of ice and snow to the eastern U.S. over the past couple of months has re-appeared. It features a large trough of low pressure in the upper and mid-levels east of the Mississippi River and a ridge of high pressure over the western states. The Mid-South happens to be positioned in the "sweet spot" - northwest flow between the ridge and trough where the jet stream is setup and upper-level disturbances track like trains on an atmospheric train track (one such disturbance is responsible for our showers today in nearly the same setup).
|At 500mb (18,000') a large ridge (and warmer air) is to our west, while a trough (and cooler air) covers the Midwest and Northeast. The Mid-South is in "northwest flow" with wind blowing from the northwest. Graphic courtesy WxBell.|
|At 30,000' (300mb), the huge dip in the jet stream over the eastern U.S./Canada is evident with the Mid-South on the western periphery of that trough. The let stream overhead is the "train track" for upper level disturbances to move along.|
The flies in the ointmentThere are two main model discrepancies to consider: 1) the height of the freezing level above ground and 2) the exact track of the main axis of precip. In the colder solutions that promote a better chance of snow, the freezing level is closer to 500-1000' (low enough to get snow at the surface), while in the warmer models, it's closer to 2000' (more of a chance of the snow melting before reaching the ground). The exact track of the narrow band of precip that is expected is also hard to determine, but appears to be from northeast AR across the metro into north-central MS.
Bottom lineSo how do we think this plays out? The most likely scenario sees a light rain/snow mix beginning after 8am with temperatures in the mid 30s. As temps slowly rise to near 40, precip should change over to just rain by noon or so. Because rain is mixed with snow, precip is light, and temperatures are above freezing, no accumulation is expected, especially on roads. A low probability exists for a dusting on grass/mulch beds, etc. but this would mainly be to the northwest of the metro in northeast AR. Tomorrow afternoon sees a chance of rain showers continuing until about mid-afternoon with temperatures remaining in the 40s. It'll be a cold day.
Another word on near or below freezing tempsBesides the snow, for those who have tender vegetation already in the ground, frost (or a light freeze east of the Bluff City) is possible tonight and again Sunday morning. Make plans to cover those plants. By Sunday afternoon, we should be back in the 60s and hopefully FINALLY putting winter in the rearview mirror! By the way, the average last freeze at Memphis International Airport is March 19, but it's March 28 (tomorrow) at the Agricenter, which is also representative of most of the suburbs. The latest snow ever recorded in Memphis is April 25, so this is not unprecedented by any means. I personally am looking forward to 70s again next week!
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