Wet & Cold Thursday...Winter Storm Potential Increasing...Cold Through Mardi Gras...

Wednesday, February 10, 2010

*Potential for Winter Storm Continues to Increase.* Snow/Sleet Likely down to I-10 late Thursday-Friday with little or no accumulations...North of I-10 several inches of snow is possible.*

SW Louisiana Forecast Discussion...This forecast is quite challenging to say the least. Don't hate the meteorologist if what he is about to say doesn't come to fruition. When forecasting winter weather, some will be disappointed, and some will be elated. That being said, let's get after it...

First, everything on right on track tonight so far based on the previous forecast. Clouds have increased across the area, and isentropic ascent is increasing little by little overnight as the factors necessary to produce our next weather maker come into place. The driving force behind this system is a cut off upper level low which is currently over SW Arizona. This will progress westward through the next couple of days, and keep overrunning in place across the forecast area. The overrunning has commenced tonight as minor disturbances embedded in the Subtropical Jet Stream will move across the area in advance of the main component. Also, the active Subtropical Jet Stream will ignite a surface low off the lower Texas coast in the vicinity of Brownsville Thursday. Light rain will move into the forecast area in the overnight hours, but much of it will evaporate as it falls to the ground because the air is very dry at the surface. This will create a process known as evaporative cooling or wet bulbing. That is, the dry air at the surface will gradually moisten up as the falling precipitation moistens the entire air column. The spread between the dew point and temperature will gradually decrease, and as you know the closer in relation temperature and dew point are the more moist (humid) the air is. Why is the mention of evaporative cooling important? It is because as the precip falls it will cool the surface temperature down into the 30s, and some of the light rain will mix with sleet or some very light snow towards morning. No accumulations are expected with any sleet or snow overnight, and rainfall amounts should be very light since much of it will evaporate initially. Temperatures will fall to near freezing in many locations across the area, but due to the very light nature of the precip no accumulations are expected even if the temperature is 32 or lower. The initial short wave has already produced several reports of sleet in and around the Houston area. The possibility of some sleet or snow mixing in overnight could really occur just about anywhere with the exception of coastal parishes. This light precip is a harbinger of things to come as the potential for a more significant winter weather event is shaping up for Thursday night and Friday. You can clearly see the players on the field on satellite imagery.

Rain chances are maxed out for Thursday with the formation of the Gulf low expected. This will throw copious amounts of moisture up and over the cold air at the surface, and sling it off to the NE towards our area. The end result will be persistent rain and brisk conditions as a tightening gradient will exist in response to the developing low in the Gulf, and a high situated over the Mid Mississippi Valley. Rains will gradually intensify through the day as overrunning increases in advance of the Gulf low, and the Desert SW upper low. 1-2" of rainfall will be expected. Sleet will be possible until mid-morning across the entire forecast area, before the atmospheric profile warms up just enough for all rain across the forecast area. Rain will be heavy at times in the afternoon. Colder air will hover just to our North across the Northern half of Louisiana, and they will likely see a true snowstorm with up to a half foot of snow possible through Friday. The low will continue to slowly trek ENE across the Gulf, and models still diverge on where cyclogenesis initialization will occur. The evolution of this low will foretell the winter weather possibilities across the area. The credentials are marginal at best along and South of I-10, with better chances of frozen precip across the Northern half of the area. I'll break it down specifically in a moment. There is no doubt that rain will occur Thursday, and it will likely occur all day. This is the same old song and dance for this winter season. At the same time as cyclogenesis is occurring, a strong Jet will be developing over the area, this in turn increase the necessary lift needed to produce widespread precipitation. As I stated, rain should be primary p-type across the forecast area during the day Thursday, however, some sleet or snow flurries could mix in from time to time, but still no accumulations are expected just yet. The worst of the weather comes in the afternoon as the low and better Jet dynamics come into play. The atmospheric profile suggests a sufficient warm layer above the surface at around 850 mb. (5,000 ft.)  By late afternoon, as some slightly colder air works into the Northern portion of the area, the rain will likely begin to mix in with more significant sleet and snow. Surface temperatures should be above freezing, so no accumulations are expected. Though, many areas won't get out of the 30s Thursday. The high in Lake Charles for example will occur at midnight somewhere in the mid 40s...44 or 45 perhaps. The daytime high, however, will barely make 40. Areas further north are in the 30s at this time, and will stay there after dropping below freezing for a few hours by sunrise. Rain will continue to be the p-type for much of the area until Thursday night. It will be quite raw as well with the winds increasing out of the NE to over 20 mph at times.

Now, here comes the most challenging part of the forecast...Thursday night and Friday...A complete transition from rain to snow will occur North of I-10 overnight as the low slowly pushes East off our coastline, probably roughly 100 miles south of Cameron to Vermilion Bay. The upper level low will be moving into Texas at this time, and this will help bring in some colder air along with it just simply being nighttime to help cool the atmosphere. Temperatures won't need to drop much in the aforementioned areas for the changeover to occur, so it should occur fairly quick between 7p.m. and 10p.m. Accumulations will become possible as this happens as the precipitation (snow) will be heavy at times with plenty of moisture availability and continued lift in response to the progressing weather features. I will get into specifics of accumulations here in a minute. I haven't forgotten to talk about snow possibilities for the Lake Charles area. Our precip should continue to be rain until after sunset, but even here it won't take too much cooling for a mix to begin occurring. This should happen after 9p.m. It will most likely be rain and snow mix along the I-10 corridor with some warmer air trapped in the 850 mb. levels since we are in closer proximity to the Gulf. This is also based on the current prognostication of the low. No accumulation of snow is expected along the I-10 corridor for a while. After midnight will bring about the best chance of snow for the forecast area. The p-type should be all snow for parishes North of I-10, while the rain/snow mix continues along I-10 with cold rain for the coast. Model data continues to increase the possibility and confidence of significant accumulations across the Northern half of the area. There are some indications that 3-6" of snow will occur across Central Louisiana roughly from near Toledo Bend to Alexandria to Natchez, MS from Thursday night through noon Friday. For now, I will suggest that the Northern part of the forecast area will see around 2"...certainly further revisions are expected on Thursday. Further South, since a rain/snow mix is expected, accumulations will be limited. Perhaps, the region between I-10 and Hwy. 190 will see 1-2", and further South including Lake Charles less than inch is possible. (Similar amounts to December 4, 2009). However, whether or not the southern half of the forecast area sees snow is a 'close call.' This is a very challenging forecast to say the least, and there isn't really any skill in specifically pinpointing who will get the most snow, or even exactly where the rain/snow line will set up. It could be a case where the snow is just a mile or two north of I-10, or just a few miles south of I-10...it is that close. Friday morning from around 4a.m. to 10a.m. will bring about the best chance for seeing real snow (more than flurries) along the Southern portions of the forecast area, while the Northern portion will continue to see decent snow through the morning hours on Friday. I am certain there will be revisions to the forecast, and I believe that if the current model trends continue then the chances of seeing snow in Lake Charles and Lafayette will increase. I will try my best to post during the day Thursday after a morning analysis. Significant snow will be possible across a large portion of the South including the possibility of 2-4" from Baton Rouge to Slidell. There could even be accumulating snow on the beaches of Mississippi and Alabama. The snow amounts that occur just North of the forecast area and into Central Mississippi will be noteworthy with places like Monroe seeing 4-6" with some higher amounts possible in the hills of North Louisiana near Ruston. One thing, I would like to touch on again, as I did last night, is to mention the deformation zone. The set up we are facing here (Gulf low and ULL) often generates a deformation zone. This is basically like a pseudo-cold front if you will. Upper level winds cause the precipitation to stretch, and this often conglomerates into a band of heavy snow. These deformation zones are often where the heaviest snow amounts will occur, and this is likely to happen somewhere in the forecast area, but pinpointing exactly where is near impossible at this time because meteorology is an imperfect science. We won't know how the deformation zone evolves until the snow is occurring. However, the areas underneath the heavy snow could see amounts higher than currently forecast. Surface temperatures will be at or just above freezing for much of the area, therefore, accumulations should mainly be on grassy and elevated surfaces such as roofs and cars. Roads could become a bit slushy, but a major icing problem is not anticipated at this time with the marginal surface temperatures. Bridges and overpasses will have to be watched mainly North of I-10. There could be some travel issues on Friday morning, but again this is something to be fine tuned on Thursday. With the impinging winter weather threat, the National Weather Service has issued a Winter Weather Advisory for the Northern 1/2 of the forecast area. This includes Beauregard, Allen, Evangeline, St. Landry, Avoyelles, Rapides, and Vernon Parishes in Louisiana, and Hardin, Tyler, Jasper, and Newton Counties in SE Texas. This includes such cities as Lumberton, Jasper, Newton, and Woodville in SE Texas, and DeRidder, Oakdale, Ville Platte, Opelousas, Eunice, Marksville, Alexandria-Pineville, and Leesville-Fort Polk in SW Louisiana. The rest of the forecast area is not currently under any winter weather advisory, but further revisions to the forecast could lead to additional advisories, so stay tuned. Further North, the entire Northern half of Louisiana is under a Winter Storm Watch. The Winter Weather Advisory is in effect from 6p.m. Thursday until 6p.m. Friday. Precipitation tapers off around noon Friday, and comes to an end during the afternoon as the ULL and surface low exit stage right in tandem. While it is difficult to predict snow amounts at this time, rain totals will be in the 1-2" range with higher amounts near 3" through Friday. Temperatures will continue to be cold whether it's snowing or not. Highs will likely remain in the 30s to lower 40s at best for maxes through Friday. Wind chills will be a factor as well with the strong N-NE winds over 20 mph at times. The strong winds will create rough conditions in the offshore waters once again with another "Cajun Nor'Easter." Expect readings to be in the 10s at times through Friday. After the precipitation gets deported Eastward, cloud cover will remain in place through the day Friday as wrap-around moisture suggests a pesky low cloud deck hanging around. Any residual moisture will result in some snow flurries, but the major precip threat will be over at this time. Some graphical representation follows.

This first graphic is one you are used to seeing here, the QPF chart:

This next map shows the snow possibilities across the forecast area. I stress that this is not an official forecast, this is just one models prediction.

This is basically right in line with my current forecast philosophy. It shows the potential for several inches across Central Louisiana, and lighter amounts around a dusting near Lake Charles.


The forecast improves at least precip wise as we get into Friday night and the weekend. Though, it will still be cold, and stay cold through Mardi Gras. The extended offers another Arctic blast next week. First off though, the weekend...skies clear Friday night as high pressure nudges into the region from the Ozarks. It will be cold and precip free for all the Mardi Gras parades. Some areas have some parades on Thursday, and all I can say in regards to that is...yikes! There will be much better luck with the Friday and weekend parades. Bundle up though as temperatures Friday night will fall into the upper 20s to right around freezing by morning. Clearing will be a slow, gradual process after sunset Friday, but it will happen. This will set the stage for a gorgeous February day on Saturday, but still cold. Highs should rebound somewhat, but I'll tell you it will be a tricky temperature forecast if there is snow still on the ground in some areas. Snow cover would keep those areas insulated, and result in less warming during the day, but nevertheless, all areas will get above freezing after the cold start. Thus, any remaining snow should melt quickly after sunrise until about noon. Highs should reach the lower 50s Saturday. A noticeable decrease in wind will have occurred too, thanks to the high pressure moving in behind the low. The fast pattern will continue with clouds returning, and likely a Gulf flow as well, Saturday night. A fast moving system (an Alberta Clipper) will move from the NW on Sunday, and while moisture will be limited due to a short duration return flow, there will be a rather robust short wave associated with the Alberta Clipper that will produce enough lift to produce a few showers Sunday afternoon. This will certainly not be enough to throw a wrench into any Mardi Gras parades, but it will be on the cold side. Winds will pick up behind the fast moving system as it brings its cold front through the area. Winds will return to offshore once again and be in excess of 20 mph at times. Temperatures will reach the mid 50s ahead of the front, before a reduction occurs.

The new week starts off very cold. Mardi Gras celebrations will continue regardless. On President's Day or Lundi Gras, skies should clear out nicely behind the quick moving front. This front will usher in another shot of Arctic air, but will also signal a drier pattern for more than just a day or two. Monday should be a sunny day, but cold and windy with morning lows below freezing with upper 20s to lower 30s expected. The strong winds will keep strong CAA ongoing across the area, thus temperatures will struggle to warm up much as they try to offset the sunshine. I would only expect highs to reach the mid 40s at best. The models are simply too warm for maximums at this time due to the climatology errors. Heading into the culmination of Mardi Gras on Tuesday, it looks even colder in the morning with the potential for a hard freeze north of I-10 and a freeze expected to the coastline. Temperatures should be in the 20s for Lake Charles and Lafayette. However, with a strong high pressure nearly overhead by Monday night winds should be not much of an issue, though, it is going to be one of the coldest Mardi Gras's in recent memory as highs struggle to reach 50. CAA will cease with the light winds in place. All systems are go for the beaucoup number of parades and festivities...see y'all at the big parade in Lake Charles Tuesday night!!! Rounding out the forecast period on Ash Wednesday...bundle up heading to church! Another morning freeze is expected, but clear and quiet weather should continue with a large high pressure ridge in control. Air mass modification will occur as the high slowly weakens and drifts East. Highs should have no problem exceeding 50, but it will still be chilly with readings staying below normal. Briefly, looking at the extended...dry and quiet weather continues for the short work week with moderating temperatures. A welcomed chance to dry out some will occur as well. The progressive pattern looks to only take a brief hiatus as it looks to return next weekend with another El Nino type system, and some more chilly air to follow after some warmer days. Stay tuned for more on the winter weather potential!


Preliminary Numbers & Zone Forecast:

LCH  35/40  33/38  31/52  40 100 100 100 0 0
LFT   34/41  33/38  30/53  30 100 100 100 0 0
BPT   35/42  34/40  32/54  60 100 100 100 0 0
AEX  30/38  30/35  27/48  30 100 100 100 0 0
POE  31/39  30/36  27/48  30 100 100 100 0 0
ARA  35/42  34/39  30/53  30 100 100 100 0 0


*Winter Weather Advisory in effect from 6p.m. Thursday through 6p.m. Friday for all parishes and counties  North of I-10.*

Tonight...Cloudy and Cold with light rain spreading into the area overnight from West to East. Rain may be mixed with light sleet or light snow at times. No accumulation expected. Low 35. NE 10 mph. Chance of rain 40%.

Thursday...Cloudy, Cold, & Windy with rain likely. Rain heavy at times in the afternoon. Rain possibly mixed with sleet or snow until mid-morning and then again late in the afternoon. No snow or sleet accumulation. High 40. NNE wind 15-20 mph and gusty. Wind chill 20-25. Chance of precipitation 100%.

Thursday Night...Continued Cloudy, Cold,  & Windy with rain likely. Rain heavy at times. Rain mixed with sleet and/or snow at times during the evening, and possibly changing over to snow overnight. Some snow accumulations possible. Accumulations if any, should be less than an inch. Low 33. North wind 15-20 mph and gusty. Wind chill 15-25. Chance of precipitation 100%.

Friday...Cloudy, Windy, & Cold with ran and snow likely in the morning. Snow accumulations from a dusting to near an inch possible. Precipitation ending in the afternoon. High 38. North wind 15-20 mph and gusty. Wind chills 15-25. Chance of precipitation 100%. Total rainfall amounts from Thursday morning through Friday morning 1-2" with isolated amounts to 3" possible.

Friday Night...Clearing and Cold. Low 31. North wind 10-15 mph. Wind chill 20-25.

Saturday...Sunny. High 52. NE wind 5-10 mph.


Drew's 7 Day Outlook

*Graphics Unavailable Tonight due to Technical Difficulties...My apologies. I am working to fix the problem.

Thursday
2-11-10

Weather: Rain mixed w/ Sleet & Snow at times...No accumulation
Low: 35
High: 40
Precip: 100%
Wind: NE 15-20
W.C.: 20-25

Friday
2-12-10

Weather: Rain/Snow Mix...Dusting to 1" of accumulation possible
 Low: 33
High: 38
Precip: 100%
Wind: NNE 20-25
W.C.: 15-25

Saturday
2-13-10

Weather: Sunny, AM Freeze
Low: 31
High: 52
Precip: 0%
Wind: NE 5-10
W.C.: 25-30

Sunday
2-14-10
Valentine's Day

Weather: Partly to Mostly Cloudy, Chance of Afternoon Rain
Low: 36
High: 54
Precip: 30%
Wind: SE/NNW 10-20
W.C.: 40s

Monday
2-15-10
President's Day
Lundi Gras

Weather: Sunny & Cold
Low: 30
High: 45
Precip: 0%
Wind: NNW 15-20
W.C.: 20-30

Tuesday
2-16-10
Mardi Gras

Weather: Sunny, Cold
Low: 27
High: 51
Precip: 0%
Wind: N 5-10
W.C.: 20-35

Wednesday
2-17-10
Ash Wednesday

Weather: Sunny, Another Cold Start
Low: 30
High: 55
Precip: 0%
Wind: NE 5-10
W.C.: 25-40


...Marine Forecast...

Tonight...Northeast winds 10 to 15 knots. Seas 2 feet or less. A chance of rain.

Thursday...East winds 15 to 20 knots becoming 15 to 25 knots in the afternoon. Seas 1 to 3 feet building to 2 to 4 feet in the afternoon. Rain likely in the morning...then rain in the afternoon.

Thursday Night...Northeast winds 20 to 25 knots. Seas 2 to 4 feet. Rain.

Friday...North winds 15 to 25 knots becoming 15 to 20 knots in the afternoon. Seas 2 to 4 feet building to 3 to 4 feet in the afternoon. Rain likely in the morning...then a chance of rain in the afternoon.

Friday Night...North winds 15 to 20 knots decreasing to 10 to 15 knots after midnight. Seas 3 to 4 feet subsiding to 2 to 3 feet after midnight.

Saturday...South winds 10 to 15 knots. Seas 2 feet or less.

Good night and God bless!
-DM-