Friday, December 30, 2011

12/30 - 3:30pm - A Good Day to Fly a Kite in Kentucky

Gusty winds will continue through this afternoon in Louisville and most of Central Kentucky as a storm system in the Midwest creates quite the pressure gradient for strong winds. Winds at 5,000 feet (850 mb in weather geek speak) are high right now, surpassing 50 kts or 60 mph as you'll see in the orange shade on the left image. The peeks of sunshine we're seeing are allowing these winds to mix down to the surface due to heating, and that's why we're having the higher wind gusts.

The National Weather Service has issued a Wind Advisory for areas just south of Louisville since wind gusts have been hitting the criteria for this down that way. Even without the Wind Advisory, Louisville could see gusts surpassing 30 mph this afternoon as a cold front continues to approach from the west.

Check out some of the wind speeds and gusts from around the region as of 3pm. I've highlighted the wind gusts that are close to Wind Advisory criteria in orange and the ones that exceed the criteria (40 mph) in red:

Louisville Airport:   SW 17 mph, gusting to 24 mph
Bowman Field:         SW 18 mph, gusting to 29 mph
SE Louisville:          SW  9 mph,  gusting to 26 mph
Fort Knox:               SW 23 mph, gusting to 33 mph
Lexington:                SW 21 mph, gusting to 39 mph
Frankfort:                 SW 23 mph, gusting to 44 mph
Bowling Green:        SW 17 mph, gusting to 29 mph

More cities and observations are available hourly on the NWS's State Weather Roundup. A few light showers will be possible this evening in Louisville and surrounding areas as this front moves through.

Monday, December 26, 2011

12/26 - 12:30pm - Post-Christmas Snow Chance?

While many did not have a white Christmas yesterday, it certainly was a nice day across much of the East US with warm temperatures. We now turn our attention to a system that will be bringing much of the Southeast rain and possibly some snow as you head northward. This system is brewing in the Gulf Coast states right now and will bring West Tennessee rain this afternoon through tomorrow and the Louisville area rain tonight through tomorrow. While West Tennessee will likely stay all rain throughout the duration of this system due to warmer temperatures, Kentuckiana may have to deal with some snowfall during the afternoon tomorrow. The track of this storm from Tennessee to Eastern Kentucky is usually one that gives us our bigger snow events during the winter, but this time that won't be the case because of the lack of cold air we'll have to work with.

The forecast for snow is a tough one because we'll be dealing with colder air coming in on the backside of this system to give us our snow. This means that the atmosphere will cool from top to bottom and while snow will be falling it will likely not accumulate much, if any, because the air at the surface will still be warm while the upper atmosphere cools down. Nevertheless, a switchover to snow in the Louisville area will likely happen sometime tomorrow during the early to mid afternoon hours as cold air penetrates enough of the atmosphere to keep snow falling all the way to the surface. The NAM (left) seems to be the most aggressive on this switchover right now due to the surge of cold air it brings in early on in the afternoon in Louisville but the forecast sounding, or a vertical snapshot of the atmosphere at a given time, still indicates that we'll have temperatures just above freezing near the surface. This means that snow will be making it to the ground, but will likely melt on contact or accumulate lightly on the grass and elevated areas in heavier snow bands. Speaking of banding, that's another issue we could face. Snow banding is when you get a thin strips of heavy snow falling that look like bands due to winds coming together in these areas. These bands can produce snow accumulations even when temperatures are above freezing, just like in Jackson, Tennessee earlier this month when over an inch of snow accumulated with temperatures just above freezing.

Overall, I think areas in and close to Louisville can expect a dusting and maybe up to an inch of snow on grassy and elevated surfaces at some point tomorrow evening. If cooler air does not come in as quickly as expected this will remain a rain/snow mix or even just plain rain. Areas north and west of the Ohio River have the best shot for a light accumulating snow as they'll be slightly cooler and have an earlier switchover during the late morning hours. Most of the models are agreeing that we'll stay above freezing during most of this event, but we will be dipping down below that mark late Tuesday evening. This may create slick spots if any roads are wet from the snowfall during the afternoon. The 12z NAM (top left) is indeed the most aggressive on snowfall totals around here by looking at the snowfall output map, which you can see a larger view of by clicking. The 0z GFS (bottom left) is less aggressive, which is typical for it lately, and the Euro (which I cannot post here to copyright policies) keeps the snowfall along and north of the Ohio River. There are still a lot of small variables like exactly how fast the precipitation will move out of here and how much cold air will actually work into this process, so little details like these can drastically alter who gets snow and how much.

Saturday, December 17, 2011

12/17 - 11:50pm - A Not So White Christmas

Positive NAO -
Christmas is just a week away and snow chances for many in the eastern half of the nation look pretty bleak. The next major system to pull through on Tuesday and Wednesday will produce snow in the Plains, but to the east it's expected to be all rain. A second low moving through the Deep South on Friday will bring more rain, but most of that will stay south of Kentucky and the heaviest south of Tennessee. After that point it looks pretty dry right through Christmas. Why so rainy and relatively warm lately? It has to do with the North Atlantic Oscillation, or NAO for short. When the NAO is negative, storms tend to ride up the East Coast or just west of the Appalachian Mountains. This is a recipe for snow for many across the East since these storms have cold air streaming in just to the north of their track. When the NAO is positive, storms begin deflecting northward to Canada before they reach the Mississippi River. This means that the cold air and snow with these storms stays out in the Plains. The NAO is in this positive phase right now and isn't forecast to go neutral or even negative until around the new year (see forecast and history chart to the right). Until we can get the NAO negative, I wouldn't bet on a winter storm for Kentucky, Tennessee, or much of anywhere else in the East.

23% of the United States is covered by snow at the moment, which is quite a bit lower than the 47.3% covered by snow at this time last year. Aside from Lake Effect snowcover in Pennsylvania and New York and snowcover in northern Maine, the East is snow-less.

A big winter storm is forecast to hit New Mexico, the Texas/Oklahoma Panhandles, and Kansas on Monday and Tuesday as an area of low pressure cuts northeastward (because of the positive NAO as explained above) through the Plains. A Blizzard Warning (green color on right image) has been issued for Northeast New Mexico while the other areas are under a Winter Storm Watch. Areas in the core of the snowfall north of Amarillo, TX up through Dodge City, KS could get well over a foot of snow.

Monday, December 12, 2011

12/12 - 7pm - A Few Bits About Snow

While things have since quieted down snow-wise, it has been a very snowy start to the season in West Tennessee. Jackson, TN has had 3.3 inches of snow so far this season, which is an astounding figure given that only about 0.1 inches falls on average by this time of year. This total beats out the season totals in many northern cities, some of which are known for their heavy snowfall including Buffalo, New York and Bismarck, North Dakota. Check out the graphic on the left to see a full list of some of the cities that Jackson is beating out. The rain to snow chance on the 21st isn't showing up on the models right now because they're dissolving the upper-level low before it makes it past NW Arkansas, but it's something to keep an eye on. A few flakes may fly further north near Louisville, but even that's not going to be a big deal according to the models. Another system packing precipitation and cold air may try to roll through a couple days before Christmas too, but that's way to far down the road to make guesses for any location at this point.

Speaking of snow, did you know that the Grand Canyon in Arizona gets more snow than Minneapolis, Minnesota? It's true! You may think of Arizona as a dry and hot state, but the higher elevations in the northern regions near Flagstaff get quite a bit of snow. Grand Canyon Village, AZ at the top of the canyon is expected to get 4 to 10 inches of snow by Wednesday morning while Flagstaff could get 12 to 16 inches. These areas are under a Winter Weather Advisory and Winter Storm Warning respectively.

Saturday, December 10, 2011

12/10 - 2:30pm - A Cool Weekend Before the Rain

The sunshine and drier air moving in helped us get into the lower 40's this afternoon in Jackson. This is a welcome surprise since all indications this morning were pointing to a high only in the upper 30's. Tomorrow will be a day like today again in the 40's with plenty of sunshine. By the middle of next week we'll be talking warmer temperatures in the 50's and 60's, but rain chances will be on the increase. Thursday looks to be the best shot at rain in West Tennessee as a cold front generates a line of thunderstorms that will move though ahead of the front. Some of these could be on the strong side, so this is something we'll have to keep an eye on. Be sure to click on your Hokey Weather Fact of the day on the left, which relates to the movie A Christmas Story, and check out your full forecast from this morning's edition of Good Morning West Tennessee on WBBJ below:

Saturday, December 3, 2011

12/3 - 2:45pm - Batten Down the Hatches, Heavy Rain is Coming!

West Tennessee and North Mississippi are going to be inundated with heavy rainfall starting tomorrow and lasting through Tuesday. The HPC's latest 12z rainfall forecast (right) has over 5 inches of precipitation in portions of Northwest Tennessee by the time this is all said and done, but amounts of 2 inches and over will be quite common across the area. Flooding will no doubt be a concern since this rain will fall on already saturated ground in a relatively short period of time (mostly Sunday and Monday), so the National Weather Service has issued a Flood Watch for the entirety of West Tennessee for Sunday morning through Monday night. The Tennessee and Mississippi Rivers will have to be watched during this, along with those low-lying areas that usually flood during these kinds of heavy rainfall events. After the rain and accompanying cold front move through, cooler temperatures and dry weather will be the rule for Wednesday and the remainder of the week. Check out my complete forecast on WBBJ this morning below for all the details: