Thursday, December 01, 2005

Heading to Demopolis!

* This will have to be a short update, I am running quite low on time today. We are doing our Live at Five and Newscenter 11 at 6pm broadcasts live from Demopolis. The folks over in Demopolis are preparing for Christmas on the River, one of the most unique and enjoyable Christmas celebrations in the Southeast. Tune in, or if you are in the neighborhood, stop by! We'll be broadcasting live from Lyon Hall in Demopolis at 5 and 6 o'clock. We'd love to hear from you.

* Not a lot of change in our forecast thinking. The rest of the work week looks dry. A few showers are possible as early as late Friday night (after midnight) or early Saturday. But, the best rain chances hold off until late Sunday into Monday.

* Still looks very cold around the late Monday-Wednesday time frame. Highs Tuesday and Wednesday will likely struggle to make the 40's, with stiff northerly winds. Definitely not a good day for a walk in the park. I have received a few notes about how our forecast temperatures are much lower than other forecast outlets like the Weather Channel, etc.

The Weather Channel's forecast products are based heavily, if not exclusively, on computer model output. They have to cover the entire country. Here, we cover this area alone - so we have a lot more time and effort invested in getting the forecast correct here. Not saying we'll always be correct, but we'll spend more time on it. I suppose that's a post for another day...

* Snow? Of course, the GFS has changed its tune for next week's potential wintry weather. The 12z run is too warm for any of the white stuff. That's a great example of why you can't base a forecast on one model run. That being said, the pattern is favorable, so we don't completely discount the possibility of some winter weather late next week. In fact, I would be surprised if somewhere south of I-40 did not receive at least the threat of some wintry weather in the next 7-10 days. However, while the pattern is favorable, but climatology is not. December winter weather events are very rare. But, so is reaching the Greek alphabet during hurricane season (which, of course, we did). That's the beauty of meteorology - anything is possible, however rare it may be.

* Got to run, it's time to put together our forecast graphics and hit the road for Demopolis!

Wednesday, November 30, 2005

Winter Thoughts...

* Forgive the lack of posts, I have been very sick for most of this week - probably as sick as I've been in years. If you watched the weather segments this week, I'm sure you noticed my voice being off. But, I'm improving, and there are a lot of weather issues to discuss. The forecast between now and the weekend is fairly dull. Temperatures will be just below normal, with dry weather continuing. The fun really begins this weekend, as overrunning moisture will likely lead to some showers and thunderstorms. While we could see an isolated shower as early as the predawn hours Saturday morning, but the best chance of rain will hold off until late Sunday into Monday.

* Winter weather fans, here is where your fun begins. The coldest air of the season will likely rush into the Deep South by Monday. Monday will likely feature morning temperatures in the 50's, with readings falling into the 40's by afternoon. Tuesday and Wednesday will likely be cold, with highs in the 40's. Morning lows Wednesday will fall into the upper teens.

* HMMMMMM...I notice that the 0z GFS hints at the potential for a winter storm somewhere in northern Mississippi/Alabama around Dec. 7/8. Let me say up front that I am not forecasting snow for us - it's simply too far out to try and get specific. But, I will also say that the pattern is favorable for SOME part of the Deep South to have at least the threat of a winter storm. And, should the next few model runs show this potential threat, I will amend our forecast. In my mind, the threat of snow is not based only on one model run, but rather several factors:

The North Atlantic Oscillation and Arctic Oscillation are both negative, which usually correlates to a cold airmass in the eastern U.S. Also, the SOI has been running negative for much of the last month, which means we will have a larger than normal influence from the subtropical jet. Not to oversimplify, but cold air + moisture can often lead to some fun around here.

We'll continue to eye the latest data, and will update this space...

Monday, November 28, 2005

Severe T-Storm Warning Marengo County

* Just when I think things are winding down...

THE NATIONAL WEATHER SERVICE IN BIRMINGHAM HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
EAST CENTRAL MARENGO COUNTY IN SOUTHWEST ALABAMA

* UNTIL 430 PM CST

* AT 358 PM CST...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
SEVERE THUNDERSTORM CAPABLE OF PRODUCING NICKEL SIZE HAIL. THIS
STORM WAS LOCATED NEAR THOMASTON...OR ABOUT 8 MILES SOUTHEAST OF
LINDEN...AND MOVING NORTHEAST AT 30 MPH.

* OTHER LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO
DAYTON AND FAUNSDALE.

DOPPLER RADAR HAS INDICATED SOME WEAK ROTATION WITHIN THIS STORM.
WHILE NOT IMMEDIATELY LIKELY...A TORNADO MAY STILL DEVELOP. IF A
TORNADO IS SPOTTED...ACT QUICKLY AND MOVE TO A PLACE OF SAFETY IN A
STURDY STRUCTURE...SUCH AS A BASEMENT OR SMALL INTERIOR ROOM.

TO REPORT SEVERE WEATHER...
CALL 1-800-856-0758.

* We're watching the radar closely with this storm. The core of this storm is over eastern Marengo County...As the NWS stated, there has been some weak rotation aloft in this storm. Should a tornado warning be issued, we will interrupt programming to bring you an update. Keep an eye here and on our FirstWarn crawl system to stay up to date.

Threat Winding Down

* The boundary is pushing through central Alabama now. I'm sure you can feel the much cooler and drier airmass across most of east Mississippi and west Alabama. The exception comes across portions of Greene County, where thunderstorms are in progress at the moment. But, for everyone along and west of U.S. Highway 43, the threat of severe weather has ended. Even east of Hwy 43, this has not been a big event. Instability is simply insufficient for a major outbreak of severe weather.

* Now our attention can begin to focus on what should be a very interesting December. The Arctic Oscillation swings negative by early December, as does the North Atlantic Oscillation (NAO). Both of these oscillations being negative leads us to believe that December will likely feature at least a few bouts of chilly air. Coupled with an active southern branch, that could make for lots of fun later this month!

Progress Report

* Radar seems to show our line pulsing back up a bit. It had weakened quite a bit, but a few storms are firing in southern Mississippi. We expect this to continue.

* It seems like the original squall line has almost completely washed out north of I-20. This will likely leave a boundary, which could serve as a focus for thunderstorm development later this morning.

* Still trying to shake the sinus problems...Will continue watching things closely from home...Charles Daniel is at WTOK and will break in should things deteriorate. I will be in later this morning if the situation warrants.


The 13z (7 AM) update from the Storm Prediction Center has extended the Moderate risk much further west, to include most of west Alabama. This is in line with our thinking that the worst of the weather will come along and east of US Highway 45. Posted by Picasa

Quiet Right Now

* Radar is showing that the line of thunderstorms is fairly weak at this point. The broken band of thunderstorms seems to be strongest from roughly Forest back towards McComb.

* I notice some sun breaking through the clouds at times. This increase in surface heating will mean greater instability. Because of this, we expect thunderstorms to intensify through the next few hours. There is still a chance that we'll see some supercells develop ahead of the line, but it is more likely that the line itself will intensify and become a band of supercells. In fact, radar seems to hint at this cellular mode in the thunderstorms already.

* Model data (6z=midnight) suggests that the best upper level dynamics may lag behind the line as it moves over us. If that verifies, the greatest threat would come east of our area. We'll stick with our idea that the worst of the weather today will be along and east of Highway 45.

* I'm watching things closely from home, while Charles Daniel mans the weather office...Will write another entry near or before 9 AM...

Squall line moves forward

* Be sure to check out Josh's post below...some great information on our thinking. I just wanted to point out a couple of things I am seeing

* The wind profiler at Okolona is showing 60 kn0t (near 70mph) winds barely off the surface. When storms interact with this environment and mix out the air, that wind will have an easy time getting to the surface. I expect we will see a good share of wind reports today.

* Storms are trying to fire up along Hwy 45 near Starkville ahead of the squall line. There is a fairly decent midlevel cap in place, and these storms are fightning like heck to punch through. With highly impressive shear values, any prefrontal supercells will likely rotate and have a high likelihood of tornadoes. In fact, the shear values match the threshold values for strong/violent tornadoes, but as Josh pointed out, timing and instability are the key.

* Squall line is moving across the MS delta and crossing the river near Vicksburg at this time. Several tornado warning have come across the wire, but no reports of tornadoes, not a suprise considering its 2am and not many people are awake to see any confirmed sightings.

* Time for a catnap before more radar/analysis.

Back in the Saddle

* I hope you all had a nice holiday weekend. I was fortunate enough to see some family and eat some great food this weekend. However, I was unfortunate enough to come down with some kind of sinus crud. With the help of plenty of orange juice, I'm better by the minute. But, enough with the weekend wrap and medical report, we have some real weather issues to confront this Monday morning.

* Be sure to scroll down and read Renny's excellent discussion. His appraisal of the situation is spot on, so I'll only add a few details...

We expect supercells to form across eastern Mississippi later this morning. These will likely be rotating supercells, with the potential for some tornadoes. The highest tornado threat will come across west Alabama.

After the supercells move out, a squall line will sweep from west to east across MS and AL. Damaging winds will be possible within this line, with an isolated tornado also not out of the question.

This potential event is all about TIMING. Exactly when the best upper level support moves overhead will play a huge role in the evolution of this event. Another timing issue will be exactly when the forcing arrives. If it arrives during daylight hours (and we are seeing some sunshine), then things could go from bad to worse in a hurry.

* The new SPC Day 1 Outlook shows a MDT risk for much of central Alabama. The guys at SPC do great work, but the opinion of our weather office is that this MDT risk should be extended further west and include much of our area - especially along and east of U.S. Highway 45. That's not a knock on the SPC, we just happen to disagree. And, we do not think today is a day to lessen our attention on the severe weather potential.

* The bottom line is that today is a day you should stay close to a good source of weather information. I'm going to get a quick power nap, but will update the weblog later this morning with more information...

Sunday, November 27, 2005

Evening Forecast Update

* Our thinking has not changed too much with the forecast analysis. A strong squall line is moving across Arkansas at the current moment and we anticipate it moving into far northwestern Mississippi after midnight. This squall line has a history of tornadoes, damaging straight line winds, and hail including one fatality in Arkansas.

* The squall line really doesn't have too much in its way to slow it down or weaken it. Shear profiles are very impressive across our region. It appears that the squall line could become broken with individual supercells within the line. This would enhance the tornado threat across our region. Also, a few discrete supercells may form in advance of the squall line. These storms would also pose a threat for tornadic development.

* I will be watching the situation overnight and will be joined by Josh Johnson and Charles Daniel in the morning as we see how things evolve. This has the potential to be a significant outbreak and takes on similar characteristics to previous November tornado outbreaks. Keep it tuned to Newscenter 11 for further information!

Early Afternoon Analysis

* I will be posting a few discussions this afternoon and evening regarding severe weather potential across our area. This one is from the 12z model guidance...

* A strong shortwave trough is ejecting out of the Rockies and into the Great Plains ahead of a strong embedded jet max pivoting through the longwave trough. The main energy moves northward through the central MS valley towards the Great Lakes, but another piece of energy extendeds southward and will lead to differential positive vorticity advection in our area (PVA). PVA is one type of uplift we look for in determining thunderstorm potential.

* We have fairly good confidence that a squall line will form across Kansas, Missouri, Arkansas, and portions of Louisiana that will work its way into Mississippi overnight. Within this squall line we expect embedded supercells due in part to the extremelly high value of wind shear (or changing of wind speed and direction with height). Damaging wind and isolated tornadoes are possible within this squall line, especially in portions of northern Mississippi.

* The challenge is determining how much instability will form ahead of the approaching squall line/frontal system. If enough instability forms ahead of the squall line, discrete supercell thunderstorms with the capability to produce tornadoes could form, and we think at least one or two discrete storms will form. If storms do fire, there is a high likelihood that they will rotate into supercells with a threat of tornadoes. Also, 0-3km CAPE is sufficient. 0-3km CAPE is a measurement of instability in the lowest level of the atmosphere. This is important because instability near the surface allows a greater likelihood of a storm to be both surface based and ingest the shear into the storm (one of the processes of supercell and tornadogenesis).

* Regardless, the threat is certainly present and will require a lot of analysis and nowcasting as a few uncertainties are present. Keep checking this blog frequently for more updates to our forecast!

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