Late Season Winter Storm to Bring Accumulating Snow to Much of the Forecast Area Tuesday Night...
Get your cameras out, I want your snow pictures! If you get snow, and can get some good pictures please feel free to send them to me at BestWxMan1980@yahoo.com
SW Louisiana Forecast Discussion...The following discussion may get a bit technical at times, but I feel it is prudent to do so to justify forecast reasoning ahead of this snow event. Again, I use my usual disclaimer when it comes to forecasting snow.."Some will be disappointed, and some will be ecstatic" with what transpires. There's little skill in specifying who is going to get the most snow, and the following forecast and logic behind it can change at the last minute, so without further adieu...
Did you enjoy the free preview of spring this weekend? I hope so because it is going away in a hurry this Monday night. We will quickly be zapped back into the reality of late winter. It was a breezy and cooler day today in the wake of a Pacific front which came through last night. This front brought widely scattered showers and thunderstorms to the area Sunday afternoon and evening. Most of the area came through virtually unscathed, but one severe thunderstorm in St. Mary Parish near Franklin caused destructive hail to the size of tennis balls. The taste of spring across the area this weekend resulted in temperatures reaching the 70s area wide on Sunday. Today was a bit cooler with a sun and cloud mix. Monday maximums reached the mid 60s along I-10. It was much cooler across the Northern half of the forecast area where colder air was filtering in. This was as a result of a secondary, stronger cold front with Arctic origination. This boundary was slow to ooze through the remainder of the forecast area, but it has since done so. As a result temperatures are steadily falling tonight, and many areas are already in the 40s. A low stratus deck envelops the area at this time, and this will continue as a temperature inversion remains in place across the area. Surface CAA will continue resulting in a continued decrease in temps overnight. By morning, expect temperatures to range from the upper 30s to mid 40s across the forecast area with overcast conditions. Boundary layer moisture is at a minimum tonight, so no rainfall is expected. However, the dry stint will be short-lived as our next weather maker is already on the map. This will be heading our way Tuesday afternoon through Wednesday morning, and this is where the fun ensues...
This next weather system, a potent upper level low and associated trough of low pressure is located over the Desert SW stretching into West Texas tonight. It will trek ESEward overnight and approach the area Tuesday. This is a very similar system to many of its predecessors this winter. The big difference this time is the ample amounts of cold air in the atmosphere that will be transported downward as the lift associated with the aforementioned feature. The lift will generate precipitation across the forecast area with commencement expected between 18Z and 22Z (noon-4p.m.) The precipitation will overspread the area from W to E as the potent upper air system dives SE. The Arctic air will be trickling into the region during the day Tuesday with temperatures struggling to warm up much. Initial light rain and/or drizzle is possible Tuesday morning, but the more significant rainfall will hold off until afternoon when isentropic lift increases. Temperatures will be in the low to mid 40s in the morning, but once the precip begins in the afternoon, temperatures will drop back into the upper 30s. Dry and colder air is filtering into the area tonight, and this will continue with dew points continuing to drop into the 30s overnight. The drier air at the surface and in the boundary layer will slowly erode, and some evaporative cooling will occur. This evaporative cooling is what will help to moisten the lowest levels of the atmosphere, and by late afternoon the entire atmospheric column should be sufficiently moist to support precipitation reaching the ground. It is certain that precip will begin as rain across the forecast area, but now I'll get to the uncertainty. Snow will be ongoing across a large portion of Texas by Tuesday afternoon as temperatures continue to drop across this area with the SE advancing disturbance. The light rain over the forecast area will begin to transition to snow after 5p.m. from NW to SE across the forecast area. There will be a rain/snow mix for several hours from late afternoon through the evening before a complete transition to snow occurs closer to midnight for just about the entire area. All but the immediate coast and portions of Lower Acadiana will see a complete transition as the potent upper level low makes its way into the forecast area. I will give a specific time line for Lake Charles momentarily. A series of graphics follows to help illustrate the situation.
First, here's a look at model data from the NAM and GFS just as I did back in December.
This is the 00Z Tuesday run of the GFS model valid from 00Z Wednesday (6p.m. Tuesday). It depicts snow across the entire forecast area. The 0 C isotherm runs from near Birmingham, AL to Baton Rouge to offshore of Sabine Pass. If this is right then the complete changeover will occur a bit sooner than I currently expect it to. I do believe this run of the GFS is a bit fast, so we'll look at the NAM in just a minute.
Now, here's the GFS on the same model run 6 hours later. Remember, these images come in 6 hour intervals.
Now, let's switch gears and look at the NAM.
Determining which model has the timing of the precip correct is a tough call. The NAM is a bit slower and wetter than the GFS on this run, and who knows they could be flip-flopped on the next run. Again, the main reason for showing this is to throw out all possibilities in regards to the snow potential. This look shows the 0 C isotherm running from near Baton Rouge to offshore the Texas coast. On this run, snow would be falling at midnight Wednesday along and W of this line. This would mean that all of the forecast area will have switched over to snow.
6 hours later, the NAM shows snow continuing across the forecast area. At this time, snow is tapering off over the Lakes Area of SE Texas. The timing of the precip on the NAM seems more reasonable. The total QPF for the NAM and the GFS seems fairly close. In forecasting snow, you have to remember that the models depict precip values in the liquid equivalent. The conversion rate for snow varies depending on location, and generally along the Gulf coast is 10:1....that means 1" of rain equals 10" of snow. So, based on the depicted QPF amounts total accumulations between 1-2" are possible. Although, accumulations will be largely limited across the forecast area based on the following parameters: warm soil temperatures, relatively warm surface temperatures for much of the event. Surface temperatures in the 40s on Tuesday afternoon with rain will drop into the 30s, but as the atmospheric column moistens up the temperature will level off in the mid 30s, and only slowly fall closer to freezing as the heavier snow falls. Also, the soil temperatures are well above freezing, therefore, most of the snow that falls will melt shortly after it makes contact with the ground. These factors should preclude significant accumulations across the area, but 1-3" of snow will be possible across the forecast area. The highest totals based on the current model trends should be across the Northern half of the forecast area, with up to an inch possible for the Lake Charles area. Along the coast, snow will likely fall but accumulations should be just a bit more than a dusting.
Nearly the entire air column is below freezing. The exception is the temperature from around 800 mb. to the surface. This would indicate that a rain/snow mix is likely at this time, with rain still the most likely p-type as snow falls into this above freezing layer, but melts before reaching the surface.
Let's take it out a bit further, even though precip could be over by this time...it's a tough call. For now, I believe precip will continue after daylight Wednesday. So, based on that here's the projected atmospheric profile at 6a.m. Wednesday at Lake Charles.
It is very similar the profile at 6Z except some drier air is beginning to set in at the lower levels as depicted by the spread between the dew point and temperature line. Temperatures are just above freezing at the surface, but any precip at this time would be in the form of snow.
I'll take another look at sounding data tomorrow morning, but it is getting down to time now where it's just a matter of looking out the window, and not relying on models to see what will transpire. When forecasting snow, things can change right up to the last minute, and I would expect further revisions to the accumulation forecast and possibly further revisions to the watches and warnings already set forth by the National Weather Service. Based on the data above, the National Weather Service in Lake Charles has issued the following:
*A Winter Storm Warning is in effect from 6p.m. Tuesday until 9a.m. Wednesday for Vernon, Rapides, and Avoyelles Parishes in Louisiana, and Tyler, Jasper, and Newton Counties in SE Texas.
*A Winter Weather Advisory is in effect south of this area for the same time frameand includes a large portion of the forecast area. In SE Texas, it includes Jefferson, Hardin, and Orange Counties, and in SW Louisiana it includes Beauregard, Allen, Evangeline, St. Landry, St. Martin, Lafayette, Acadia, Jefferson Davis, and Calcasieu Parishes.
What is the difference in these? A Winter Storm Warning means that significant amounts of snow, sleet, or ice are occurring (in this case, snow) or will occur. Travel will likely become treacherous. Generally, a Winter Storm Warning is issued when 2" or more of snow is expected. A Winter Weather Advisory means that periods of snow, sleet, or ice will occur and cause travel difficulties, slippery roads, and limited visibilities. Use caution when driving. A Winter Weather Advisory is typically issued when snow amounts are forecasted to be less than 2". This criteria varies depending on location.
These warnings/advisories encompasses nearly the entire forecast area. The only parishes not included in any sort of winter weather advisory or winter storm warning is Cameron and Vermilion Parishes. Though, even these areas will see some snow. Little to no accumulation is expected in these areas as the precip should predominantly be a rain/snow mix for the duration of the event.
As I stated earlier, rain is the likely p-type for the afternoon hours on Tuesday. It should mostly be light with total amounts of a quarter inch or less. Snow will start mixing in across the Northern half of the forecast area after 4p.m. The same holds true for SE Texas. Snow should start to mix in with the rain in Lake Charles after sunset, and it may take a few more hours for the complete transition to all snow to occur. However, there is the possibility that the air could be a couple of degrees colder than forecast, and if so the transition would occur sooner. By the same token, if the temperature is a couple of degrees warmer, than the transition would take longer. There's a really fine line in determining this, and there's very little skill in pinpointing exactly when the changeover will occur. All model data suggests that snow will occur in SW Louisiana, and I see no reason to believe otherwise. Snow should fall much of the night Tuesday night through the early morning hours of Wednesday before ending between sunrise and mid-morning across the area. Here is my official time line for the city of Lake Charles. It'll be a 24 hour time line from noon Tuesday to noon Wednesday for purposes of this event. Precip type and temperatures are indicated in this time line.
Noon
Light Rain/Drizzle- 42
4p.m.
Light Rain- 39
8p.m.
Rain/Snow Mix- 37
Midnight Wednesday
Snow- 35
4a.m. Wednesday
Snow- 34
8a.m. Wednesday
Snow Ending- 35
Noon
Sunny- 43
*While not indicated here, a transition period may begin the 4p.m. and 8p.m. window at Lake Charles. If transition occurs a little later, it could be between 8p.m. and midnight, but it is likely to be all snow by midnight. This is the way I see things at the moment. I will update this in the morning once we see how the system is progressing over Texas.
Precipitation amounts should be light, but there has been some hint at a surface reflection forming over the Gulf as the potent system moves into SE Texas. This solution is discounted for now, as models have been inconsistent with this idea, but if this were to occur then precip would likely be enhanced across the forecast area. Rainfall amounts will be light as I've previously stated, and while significant by SW Louisiana standards, the actual snow amounts will be light as well basically because of reasons stated above. Snow will potentially be heavy at times. The set up favors convective banding (deformation zone) as most snow events typically do, and wherever this deformation zone sets up is where the heaviest snow will likely occur. At this time, this looks to be in the Winter Storm Warning area, but other heavier bands could possibly set up further South, it just remains to be seen. I say it every time we have the potential for snow in SW Louisiana, but it really is a situation where we won't know who is going to get the heaviest snow until the snow bands materialize. Precip chances will be minimal in the morning hours on Tuesday, but will quickly leap into the likely category by the evening. Precip chances will max out overnight Tuesday through early Wednesday before the system pushes East during the morning hours Wednesday. A chance of snow is maintained until mid-morning Wednesday, but conditions will rapidly improve as the potent upper level system pulls away on Wednesday with sunshine returning by the afternoon hours. Temperatures will be challenging as well. Tuesday temperatures will likely be confused with falling temperatures with the onset of the rain in the afternoon. Temperatures will approach freezing during the snow Tuesday night/Wednesday morning, and be below freezing North of I-10. This is where the difficulty comes into play. The surface temperatures North of I-10 will likely lead to some ice formation on bridges and elevated roadways, which will make for difficult travel Wednesday morning. Any snow that melts while temperatures are above freezing will re-freeze towards sunrise creating black ice. Some snow could stick to the roads and bridges if temperatures cool off quicker than expected in these areas, and make Wednesday morning travel quite dangerous. Further south, along I-10 not many travel problems are expected, though there could be some icing on elevated surfaces, however, temperatures are forecast to bottom out right at or just above freezing, thus limiting icing potential in these areas. Depending on how long the moisture hangs over the area, SW Louisiana could wake up to a world of white on Wednesday with some snow on the ground, and snow still falling for a little while longer. However, as stated previously, the snow will quickly end after sunrise Wednesday, and skies will clear rapidly behind the snow. All snow will melt away by noon Wednesday. The sun comes out, but it will remain cold with highs in the mid to upper 40s. A brisk North wind will be present as well, not only for the winter storm but into Wednesday. A wind chill factor in the 20s will be present during the precipitation, so bundle up if you head out to play in the snow. The clear skies, and continued CAA will set the stage for another cold night on Wednesday night into Thursday morning with an area wide freeze. Temperatures will range from the upper 20s to lower 30s across the forecast area.
I need to be brief with the rest of this discussion, because all focus is on the winter storm. Here goes...the active pattern that we are accustomed to this winter will continue as we head into March. Thursday should be a nice day after a cold start. Lots of sunshine is expected with high pressure overhead. Temperatures should easily top the 50 degree mark, and probably end up near 55. Unfortunately, the nice weather doesn't last long as we'll have another El Nino type system in the offing for Friday into Saturday. The timing of this second system is still a bit uncertain, but we'll hone in on that come Wednesday. Models depict a Gulf low forming, so this could enhance the expected cold rain across the area. Rain should begin late day Friday, and be in the likely category for Friday night into Saturday morning. Rain should be the predominant p-type, and probably the only p-type with this event for this area, however, a snow event could occur up across North Louisiana. There is a chance of some frozen precip on the backside of this system across our neck of the woods, but again, I'll re-evaluate that later. Conditions improve quickly again Saturday, but it remains cold with highs in he 40s and 50s and lows in the 30s, and we'll stay dry with not a whole lot of sunshine into Sunday, before another Gulf low forms in response to yet another potent Pacific short wave. This one could usher in March like a lion on Monday. It, too, may provide a chance for some frozen precip on its backside late Sunday into Monday. Insult will be added to injury during this time, as the cold temperatures remain in place. We don't anymore rain either, in what has been an incredibly wet winter. As we get into March next week, you would figure Spring isn't too far way, but in this pattern all bets are off. I certainly believe the wet pattern will continue for March, but Spring should make a more permanent appearance before too long. This has been an incredible winter. Multiple frozen precipitation events in South Louisiana, who would've guessed that? I can't recall an instance where we've ever had 3 snows in one season, but that is indeed what may happen if it snows tomorrow night into Wednesday. In closing, here's a brief aside...if it snows more a trace at Lake Charles on Wednesday (2/24), it would be the latest accumulating snowfall of more than a trace on record at that location. It's very interesting indeed because we have already established a record for our earliest snowfall on record this season. As it stands right now, the record for latest snowfall is 0.3" on February 23, 1968. There have been many occurrences of trace snow amounts in March, and even in April. Stay tuned for more on this winter storm!
Preliminary Numbers & Zone Forecast:
LCH 48/36 33/47 30/54 0 60 100 40 0 0
LFT 48/37 34/46 31/54 0 40 100 50 0 0
BPT 46/36 33/48 32/55 0 70 100 30 0 0
AEX 43/32 29/44 26/50 0 40 100 40 0 0
POE 43/32 29/45 26/51 0 50 100 40 0 0
ARA 50/38 35/49 32/55 0 30 100 60 0 0
*Winter Weather Advisory in effect for Jefferson, Orange, & Hardin Counties in SE Texas, & Calcasieu, Beauregard, Jefferson Davis, Allen, Evangeline, Acadia, Lafayette, St. Landry, & St. Martin Parishes in SW Louisiana from 6p.m. Tuesday until 9a.m. Wednesday.*
*Winter Storm Warning from 6p.m. Tuesday until 9a.m. Wednesday for Tyler, Jasper, and Newton Counties in SE Texas and Vernon, Rapides, and Avoyelles Parishes in Louisiana.*
Tonight...Cloudy and Colder. Low 43. North wind 10-15 mph.
Tuesday...Cloudy, Cold, & Windy with rain developing in the afternoon. Intermittent light rain and/or drizzle in the morning. Rain becoming likely late afternoon. Rain becoming mixed with snow in the evening. No snow accumulation. High 46 with temperatures falling into the 30s in the afternoon. North wind 15-20 mph and gusty. Chance of precipitation 60%.
Tuesday Night...Rain and Snow likely in the evening, then becoming all Snow by midnight. Snow after midnight. Snow accumulations up to 1". Low 33. North wind 15-20 mph and gusty. Chance of precipitation 100%. Wind chill in the 20s.
Wednesday...Cloudy & Cold w/ a chance of snow until mid-morning. No additional snow accumulation expected. Snow totals 1-3" across the forecast area. Snow ending in the morning with skies become Sunny around noon. High 47. North wind 10-15 mph. Chance of snow 40% in the morning.
Wednesday Night...Clear and Cold. Low 30. Light North wind.
Thursday...Sunny and Warmer. High 54. North wind 5-10 mph.
Drew's 7 Day Outlook
Tuesday
2-23-10
Low: 36
High: 48
Precip: 60% PM
Mostly Rain until after Sunset
Wind: N 15-20
W.C.: 30s
Wednesday
2-24-10
Low: 33
High: 47
Precip: 40% AM Snow
Wind: N 10-15
W.C.: 25-40
Thursday
2-25-10
Low: 30
High: 54
Precip: 0%
Wind: N 5-10
W.C.: 25-40
Friday
2-26-10
Low: 37
High: 52
Precip: 60%
Wind: NE 10-15
W.C.: 40s
Saturday
2-27-10
Low: 38
High: 46
Precip: 40% AM
Wind: NNW 15-20
W.C.: 30s
Sunday
2-28-10
Low: 42
High: 54
Precip: 30% PM
Wind: NE 10-15
W.C.: 40s
Monday
3-1-10
Low: 43
High: 51
Precip: 70%
Wind: SE/NNW 15-20
W.C: 40s
...Marine Forecast...
Tuesday...Northeast winds 10 to 15 knots. Seas 2 to 3 feet. A slight chance of rain in the afternoon.
Tuesday Night...North winds 15 to 20 knots. Seas 3 to 5 feet building to 4 to 6 feet after midnight. Rain likely in the evening... Then a chance of rain after midnight.
Wednesday...North winds 15 to 20 knots. Seas 4 to 6 feet subsiding to 4 to 5 feet in the afternoon. A chance of rain in the morning.
Wednesday Night...North winds 10 to 15 knots. Seas 3 to 5 feet subsiding to 2 to 4 feet after midnight.
Thursday...Southeast winds 5 to 10 knots. Seas 2 to 4 feet.
Good night and God bless!
-DM-
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