Thursday, January 21, 2016

Thursday afternoon update on Friday's winter storm

It's the day before a major winter storm and it's been chaotic. But enough about Kroger...
Here's the latest information you need to know.

Overview - what you need to know

Watches/Warnings/Advisories: Winter Storm Warnings are now in effect for tonight through Friday.
What/when: Rain changing to sleet or freezing rain after 4am, then snow by 8am and lasting into the afternoon. Strong wind and bitter wind chills Friday and Friday night.
Where: The entire Memphis metropolitan area
How much: Minor ice accumulation (less than 1/4") as rain transitions to snow, then periods of heavy snow possible into early afternoon. Widespread 3-6" snow amounts.
Possible Impacts: Significant. Possibly heavy snow coupled with north wind gusts to 30-40 mph and temperatures near 30° on Friday could result in areas with power outages and near-whiteout conditions, resulting in hazardous to impossible travel conditions. Wind chills in the teens Friday and Friday night.
Confidence: High. Snow amounts will differ from point to point depending on mesoscale banding features and possible convection (thunder) that may occur, either of which would enhance snow amounts. However, confidence in a significant winter storm occurring is high.
NWS-Memphis snowfall projections as of early Thursday afternoon. We are in agreement with these totals.
Models continue to have slight variations that produce differing snow and ice amounts, but that is the nature of the south - forecasting a winter storm is never straight forward. As always, we encourage you to pay most attention to the IMPACTS of the storm and not the exact snow totals, though we have provided the most likely outcome above.  Impacts from this storm will require preparation, so below you'll find out winter weather preparedness tips, which include tips to prepare for power outages, which are possible due to heavy snow and high wind.

MWN Winter Weather Tips. Click for larger image.
As with yesterday's blog post and thinking, the setup location and intensity of the deformation zone will be the biggest driver of heavy snow. We also have a trailing upper level low pressure system that will move just to the south of the city which will also have an effect on snow totals, as mentioned on last night's video chat. Atmospheric lift associated with the upper low could drive totals to the higher end of our guidance, especially if we get some thundersnow, which is not impossible.

We'll have more details in another video chat tonight, scheduled for 9pm, as well as on our social media channels. In the meantime, tonight is the time to wrap up all preparations for yourself, those you care for including pets, and alternate plans for tomorrow should (perhaps when) they need to be enacted.

Links to watch tonight's video chat
YouTube: http://www.youtube.com/watch?v=a7bp_UWBr0Y
Google+: https://plus.google.com/events/chslv292nn495avh3cuo7bhcrf4
MWN Hangout page with chat: http://www.memphisweather.net/hangout.shtml

Erik Proseus
MWN Meteorologist

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6 comments:

Anonymous said...

Erik,
Thanks for the update. As always, your blog is the best source for realistic info available.

Kevin Yancy said...

Always great coverage! Thanks so much!

Anonymous said...

info without the hype

Anonymous said...

Thanks for the info, but what a bust! Any chance you will cover the how's and why's of the wide margin of error between the forecast and what actually happened? How does the NWS learn from these events to create more accurate forecasts in the future?

Meteorologist Erik Proseus said...

it was not quite the bust that you think, given the state of the science, the capabilities of the models, and the nature of snow which can vary a lot within a few short miles. Yes, we'll have some comments later but in this case, 3" of snow was recorded in far northern Shelby County and throughout Tipton County with more north of that. Granted south of that totals were generally an inch or less. But the fact that there were 3" totals within the area we outlined for 3-6" yesterday provides some legitimacy to the forecast. In general, the event was over-forecast. The zone of heaviest snowfall, as I mentioned on both video session the last 2 nights, is very hard to pinpoint, as well as exactly how much snow it will produce. It stayed (mainly) just north of Shelby County and under-performed the models even in the areas that did get heavier snow. We learn from every event. Thanks for your questions.

-Erik

Anonymous said...

Let me first say thank you for what you and your profession does on a dialy basis for me, the city and civilization as a whole.
I hope this response was not to entirely based on my comment that started with “Thanks for the info, but what a bust”. My questions regarding the how’s and why’s of the margin of error were not meant as a personal accusation of any nature. Blaming an individual for the impacts or severity of a storm is ridiculous. I genuinely would be interested in reading your thoughts and analysis regarding what information and model consensus created a forecast for “near blizzard conditions” throughout most of the metropolitan area and what variables within the atmosphere did not align with the forecast to yield the actual outcome. Also, regarding my question about learning from this storm (or from winter storm to winter storm), I actually would like to know how this experience is incorporated into future winter storm forecasts. Is it broken down into base components and raw numbers that factor into future model runs, is it absorbed into a less defined meteorological “collective conscious”, does it add to a personal “gut instinct” for each forecaster and provide counterweight to future model consensus, is it all of the above or some totally different process? Is there a method by which uncertainty regarding an outcome can be communicated to the public (or at least those of us that are interested) in a way that is not confused with probability?