Late Season Snow Still on Tap Overnight...
SW Louisiana Forecast Discussion...The much advertised short wave and upper level trough is affecting the region right on schedule tonight. Precipitation is predominantly rain at this time, but the changeover has occurred across the extreme NW portion of the forecast area with snow being reported from around Leesville-Fort Polk, but into East Texas. Temperatures will continue to fall, and reach the 30s area wide by midnight. The threat for precipitation will continue through the early morning hours of Wednesday, but as the cold core upper level low currently over Central Texas drops ESE into the forecast area, precipitation will be in the form of snow. The rain over the area at present is being caused by upper level forcing generated by the advancing short wave. The upper level low is the driving force behind this system, and is what will produce the snow across the area. There will be a break in the precipitation as the initial short wave heads off to the East quickly. The snow will spread into the area between midnight and 2a.m. and exit the region around sunrise Wednesday.While snowfall amounts will be generally an inch or less, the same can be said for rainfall totals due to the light nature of the precip, and the quick motion. One problem that has prevented much frozen precip so far is that the precip has outrun the colder air. That's why I always use the disclaimer...you just never know what you're going to get with frozen precip events in SW Louisiana, and this has been no exception.
The winter weather advisories remain in effect for all of SW Louisiana, and the only area still under a Winter Storm Warning remains over upper SE Texas. Accumulations for the entire area should be limited due to temperatures at the surface remaining above freezing for the majority of the area. The areas which have already changed over and those in the Winter Storm Warning area will likely reach freezing overnight, and there could be some icy travel up that way. Accumulations in this area could exceed 2", but average accumulations for the rest of the forecast area should be an inch or less. It won't take much snow to make this a historical event across SW Louisiana. Any accumulation of more than a trace would result in the latest accumulating snowfall in history for Lake Charles. This would break the record by one day...February 23, 1968 is the current record. 0.3" of snow fell on that late February day back in 1968. This would also be the third snowfall event of the season across the forecast area, and this is almost unprecedented.
The upper level low is currently over Central Texas and continues to dive SE towards the Bryan-College Station and Houston areas. Moisture amounts aren't overly impressive with the ULL, but it is generating its own moisture, and will likely feed off the Gulf as it approaches Houston in the next few hours, to produce a little more coverage of snow that what is currently ongoing. As the snow falls from the upper levels of the atmosphere, it will help pull down the colder air associated with the upper level low to the surface. This is a process known as dynamic cooling. It is the dynamic cooling that causes the snow to reach the ground. Temperatures at the surface don't have to be below freezing for snow to fall, if you remember my diagram of the atmosphere from last night. That is the case we have tonight. The snow will fall, but the majority of it will melt on contact. The minor accumulations will occur mainly on grassy and elevated surfaces, and all snow will melt very quickly once the precip ends after sunrise Wednesday. The most likely time frame for snow in the Lake Charles area will be between 1 and 6a.m. Snowflakes will likely be seen all the way down to the coast at some point early Wednesday morning, but with warmer air hugging the coastal areas a rain/snow mix may be the mode of precipitation with no accumulation. Unlike, the last event across the area, all accumulations will be light, and no one should see snowfall approaching 4-5" that occurred in parts of the area last time. Precipitation chances are in the likely category especially for the rain that is ongoing, but the chances of snow will be fairly high as well as this upper level comes across. This will be very similar to the event of December 11, 2008, although snow amounts will likely be more uniform this time around. There could be just as much snow in Lake Charles as there will be in Alexandria, or there could be more in Lake Charles than there will be in Alexandria, or vice versa....there's really no skill in pinpointing who exactly will get the heavier amounts with this type of set up. The upper level low supports some convective banding somewhere in the forecast area, and where this occurs amounts could exceed 1". It is just a wait and see deal at this point. Models are irrelevant at this point, although they do get credit because they depicted this chance of snow as early as about a week ago, especially the GFS. If you want to see the snow you will have to either stay up late, or get up early, because as quickly as it comes in, it will be gone. Conditions will drastically improve on Wednesday with high pressure moving in behind the departing snow. The morning low will be in the low to mid 30s across the area with the early morning snow, but with the sun quickly appearing by noon, temperatures should warm up close to 50. Brisk Northerly winds will be an issue as well with a strong pressure gradient in place in response to the advancing ULL coming across Texas, and the strong Mid West high that will be settling Southward on Wednesday. The Winter Weather Advisory is in effect for the entire area with the exception of the coastal parishes and lower Acadiana until 9a.m. (15Z) Wednesday. The counties in upper SE Texas will remain under the Winter Storm Warning until the same expiration time.
The snow is all gone Wednesday after sunrise, and the aforementioned quick improvement will be noted. The period of benign weather will be short-lived, however. Wednesday should turn out to be quite a beautiful late February day, albeit on the cool side. Highs will reach the upper 40s for much of the area, but some lower 50s are possible as well in places where the sun comes out sooner. This will quickly melt any snow that does happen to accumulate quickly, and it will be a fast, fading memory before noon. A cold night is in store Wednesday night as the Canadian high settles in right over the forecast area. This will provide for a night of maximum radiational cooling, and set the stage for an area wide freeze. Under clear skies and calm winds, temperatures will fall into the upper 20s to lower 30s. The coast should avoid a freeze, but it'll still be plenty cold with readings in the mid 30s by Thursday morning. Thursday will be a quiet weather day with plenty of sunshine to start the day, but clouds will be on the increase late in the day as our next El Nino storm system approaches. The controlling high will slide into Dixie early Thursday, and the anti-cyclonic flow will result in a return flow off the Gulf by the afternoon. This will increase low-level moisture in response to the continued fast flow at the surface with the next short wave over the Desert SW. The advanced guard of cloud cover out ahead of this system will move into the region late Thursday and Thursday night, but this period should remain dry. A warming trend will result as well with highs reaching the upper 50s. No threat of freezing temperatures Thursday night in response to the increased cloud cover and moist low-level flow. Lows should be in the mid 40s. This next disturbance will be weaker than its predecessor, and a bit moisture starved despite the low-level return flow. However, there will be enough lift and forcing to generate some showers on Friday. It doesn't appear that there will be a threat for a changeover to snow on the backside of this system in the forecast area , although Northern portions of the state could see some snow with this event. This doesn't look like a major rain event, and it should also move through fairly quickly. This should set the stage for a fairly nice weekend.
A renewed area of high pressure follows the Friday short wave just in time for the weekend. It will remain on the cool side as drier air filters into the region Friday night. Lows should be in the mid to upper 30s. Saturday looks beautiful with lots of sunshine, low humidity, and pleasantly cool temperatures for late February. Maximums should remain below normal in the mid 50s. Dry weather continues for Saturday night into Sunday, the timing was just right! Saturday night's low will be similar to that of Friday night's. Sunday will be another day of fast transition as a return flow off the Gulf is established once again. This is ahead of a more vigorous system which is in the offing for Monday. Clouds increase after church Sunday, and I wouldn't rule out a shower or two Sunday night. Some modification occurs with highs reaching the upper 50s at best. A much stronger system moves into the region for Monday, and it looks like March will come in like a lion in 2010. A potent Pacific trough will be digging into the Rockies, and this will carve out more short waves that will be embedded in the Jet Stream. The active Subtropcial Jet will come into play, and help to energize the system further. The Jet Stream energy will engender a surface low in the Western Gulf Monday. Have we heard that before this winter? Widespread rain is expected, and it could be heavy at times. No severe weather is anticipated, but locally heavy rainfall could lead to some flooding. There will be plenty of lift and forcing could be maximized as well. Upper level dynamics could generate some elevated convection, and a few rumbles of thunder are possible. There is still some uncertainty in regards to the evolution of this system, but we'll focus on it over the weekend. Rain appears likely for most of the day Monday with rain ending Monday night as the low pushes further East through the Gulf. There is somewhat of an increasing likelihood of frozen precip on the backside of this low as colder air will be looming up North. As the low pushes on by, it will pull down this colder air. Models indicate that there will be a good deal of post-frontal precip, and some of this could changeover to sleet/snow before the precip ends late Monday night or early Tuesday. For now, this possibility will continue to be watched, but it will not be included in any forecast. At this point, rain seems inevitable for Monday, and I believe rain chances will max out by week's end. Rainfall totals Monday could exceed 2", but for now I'll say 1-2" is expected. A colder and drier air mass takes over Tuesday behind this latest system, and temperatures will remain below normal for early March with lows in the 30s and highs in the low to mid 50s. The active pattern should continue through the first half of March, but a progression towards Spring should occur before too long.
Preliminary Numbers & Zone Forecast:
LCH 35/50 30/56 40/55 80 30 0 0 0 60
LFT 36/51 29/55 39/55 80 30 0 0 0 50
BPT 34/52 31/57 42/55 70 20 0 0 0 60
AEX 33/48 27/53 37/50 90 30 0 0 0 60
POE 33/49 28/53 38/51 70 20 0 0 0 60
ARA 38/51 30/57 41/55 80 30 0 0 0 40
*Winter Weather Advisory in effect until 9a.m. Wednesday.*
Tonight...Cloudy, Cold, & Windy with rain likely before midnight, transitioning to all snow after midnight. Light snow accumulations possible up to 1". Low 35. NNW wind 15-20 mph and gusty. Chance of precipitation 80%. Wind chill in the 20s.
Wednesday...Cloudy with a 30% chance of snow ending by 8a.m., then quickly clearing with skies becoming Sunny by noon. High 50. NNW wind 10-15 mph.
Wednesday Night...Clear and Cold. Low 30. Light North wind.
Thursday...Mostly Sunny. High 56. NE wind 5-10 mph in the morning, becoming SE in the afternoon.
Thursday Night..Becoming Mostly Cloudy & Not as Cold. Low 40. SE wind 5-10 mph.
Friday...Cloudy with rain likely. High 55. SE wind 10-15 mph becoming NNW at 15-20 mph and gusty in the afternoon. Chance of rain 60%.
Wednesday 2/24/10 Daily Planner
7a.m.
Weather: Snow Ending
Temp: 35
Precip: 30%
Wind: NNW 12
W.C.: 27
Noon
Weather: Sunny
Temp: 46
Precip: 0%
Wind: North 10
W.C.: 42
5p.m.
Weather: Sunny
Temp: 49
Precip: 0%
Wind: N 6
Drew's 7 Day Outlook
Wednesday
2-24-10
Low: 35
High: 50
High: 50
Precip: 30% AM
Snow Ending by 8a.m.
Wind: NNW 10-15
W.C.: 25-40
Thursday
2-25-10
Low: 30
High: 56
Precip: 0%
Wind: NE/SE 5-10
W.C.: 20-35
Friday
2-26-10
Low: 40
High: 54
Precip: 60%
Wind: SE/NNW 15-20
Saturday
2-27-10
Low: 38
High: 54
Precip: 0%
Wind: NNW 5-10
Sunday
2-28-10
Low: 38
High: 58
Precip: 20% after dark
Wind: SE 15-20
Monday
3-1-10
Low: 42
High: 50
Precip: 70%
Wind: SSE 15-20/NNW 20
Tuesday
3-2-10
Low: 35
High: 45
Precip: 20%
Wind: NNW 15-20
W.C.: 25-35
...Marine Forecast...
*Small Craft Advisory.*
Wednesday...North winds 20 knots. Seas 4 to 5 feet subsiding to 3 to 4 feet in the afternoon. A slight chance of rain in the morning.
Wednesday Night...North winds 10 to 15 knots. Seas 2 to 3 feet subsiding to 1 to 2 feet after midnight.
Thursday...East winds 5 to 10 knots becoming southeast 10 to 15 knots in the afternoon. Seas 1 to 3 feet.
Thursday Night...South winds 10 to 15 knots. Seas 2 to 3 feet.
Friday...North winds 15 to 25 knots. Seas 4 to 6 feet. A chance of showers.
Good night and God blesss!
-DM-
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