SW Louisiana Forecast Discussion...It was another day of showers and thunderstorms across the area as an active Subtropical Jet Stream remained in place, and periodic disturbances rotated through the area this morning. This was ahead of a decaying frontal boundary that was pushing through East Texas. This boundary essentially washed out over our area. This is known as frontolysis. Some of the shower and thunderstorm activity this morning was quite strong with several reports of small hail mainly before dawn in Acadiana. No severe weather was reported. Rainfall amounts were generally 1/2" or less for the second day in a row. A warm front had moved through last night, and the entire forecast area was enveloped in the warm sector in its wake. The end result was mild temperatures throughout the day with morning lows in the upper 50s and afternoon highs in the upper 60s to lower 70s. An onshore flow persisted throughout the day. Most of the rain ended across the area by mid-afternoon, and it remains dry precipitation wise tonight. However, there is quite a lot of low-level moisture in place. Just look out the window, and you can see it! A very low stratus deck is in place, and it will remain through the overnight hours. Also, fog will likely be an issue especially South of I-10 overnight as the established WAA pattern transports sea fog inland from the coastal waters. This is created by the temperature differential of land vs. water. The fog should be the main issue tonight, but I wouldn't rule out some scattered showers especially after midnight as the potent Pacific system out West moves closer to the area, to generate some lift. Overnight temperatures will not drop much from the current readings. Expect minimums to bottom out around 60. That's right...lows around 60, how many days this winter did we have where the high didnt reach 60? A dense fog advisory has been issued for Calcasieu, Cameron, Jefferson Davis, Vermilion, Iberia, St. Mary, & Lower St. Martin Parishes in SW Louisiana, and Jefferson and Orange Counties in SE Texas. It lasts until 8a.m. Wednesday, but the fog will quickly burn off after this time, and it won't be dense in all locations.
One more day of subpar weather is on tap for Wednesday. The much advertised Pacific storm system will be advancing Eastward into Texas during the day Wednesday. It should start off a quiet night with just the areas of dense fog to contend with until about mid-morning otherwise Cloudy and mild conditions are anticipated. Rain chances during he morning hours will be limited as a decent cap will be in place. A renegade shower or two is possible during the morning mainly due to the extremely moist and unstable air that will be in place. Rain chances shoot up into the likely category Wednesday afternoon, as the advancing system heads towards our area. This will act as the necessary trigger to lead to the development of showers and thunderstorms across the area. A very strong Jet Stream is advancing NE towards the area from Old Mexico tonight in advance of this potent storm system. The Jet max or Jet Streak with winds approaching 200 mph at flight level will be directly overhead Wednesday. This will be the fuel (instability) to aid in development of shower and thunderstorm activity. The added effects of convective heating will also factor into the equation. There is more than enough surface-based moisture in place, and all we really need is the trigger mechanism to produce the shower and thunderstorm activity. Remember, here that there are many synoptic set ups that can occur, and each one acts differently in respect to severe weather. The incredibly strong Jet Stream overhead will always rise some eyebrows when discussing severe weather, and it certainly is very impressive. However, there's no sure thing that severe weather will occur based on this alone. There are other factors we need to discuss as well, before I give my final take on this situation.
The potency of the Pacific system will interact with the energetic Subtropical Jet Stream, and the resultant surface low will form (cyclogenesis) over the Red River Valley of the Texas & Oklahoma Panhandle. This low will form Wednesday morning and travel ESE across the aforementioned area towards the ARK-LA-TEX Wednesday afternoon. The backside upper level low over the Great Plains tonight will eject NE as the system progresses Eastward. A secondary cold front will extend SW from the low through Central Texas by Wednesday afternoon, and this front will begin to make steady progress to the SE at that time. This is when the shower and thunderstorm activity will begin to initiate across the area as the cap is busted, and the encroaching system feeds off the dynamics in place. Any storm that fires up Wednesday afternoon will have the potential to exceed the severe threshold, but this seems more likely to the N and E of the immediate area. Areas to the North i.e. the Shreveport-Monroe area will be in closer proximity to the advancing surface low, and to our East towards SE Louisiana a bit better dynamics and low-level energy will be in place to elevate the severe weather just a bit. However, the environment locally is favorable for a few severe storms. The set up favors a few supercells likely developing from 'streamer' showers that move inland off the Gulf, and intensify, before transitioning to a linear set up (MCS). I expect an MCS to develop along the frontal boundary in Texas, and strengthen as it moves our way Wednesday evening. All modes of severe weather will be possible across the forecast area, but the main threat should be damaging winds and large hail. The greatest risk for tornadoes should be displaced to the N of the forecast area in the areas closest to the deepening surface low. The scattered showers are possible really any time starting after noon, but the chances for shower and thunderstorm activity ramp up to likely by late afternoon through the evening hours. It doesn't appear that Wednesday will be a wash out, but most of us will see some rain likely around evening drive time. The timing of the expected arrival of the storms isn't exactly great, but this system is still evolving, so there's still some uncertainty with respect to timing of when the worst weather will occur. It is certainly near impossible to pinpoint exactly who will get some severe weather, and what mode. All of these are factors that will go unbeknownst to us until the storms initiate. The storms should push through rather swiftly with vast improvement noted Wednesday night. I'd anticipate the severe threat to end before midnight Thursday morning with rain ending by that time as well or just a bit after. As with almost every severe weather event around these parts, there are limiting factors as well, and it is just a matter of seeing which way this system evolves...whether or not it feeds off of the energy in place or if our close proximity to the Gulf once again shields us from severe weather. Temperatures on Wednesday will be above normal with afternoon highs exceeding 70. A steady onshore flow will remain in place as well, although the pressure gradient will tighten some as the very strong Jet moves overhead. Rainfall totals should average an inch or less. Some severe weather graphics are included below along with the expected 5 day QPF chart. I would expect that some sort of watch box for severe weather will be issued during the afternoon hours on Wednesday. Stay tuned!
Rapid improvement occurs in the wake of the storms, and the weak cool front pushes through as we head into Thursday. Skies should clear rather quickly behind the storms as the forecast area is dry slotted from the SW on the backside of the advancing ULL. There will be sufficient residual moisture in place after 3 days of rain, therefore fog is expected to be an issue once again late Wednesday night and Thursday. The fog will scour out shortly after sunrise Thursday, and high pressure will build into the area providing for the first day of a prolonged stretch of dry weather. Thursday will also likely be the warmest day of 2010 so far with high temperatures expected to reach the mid 70s, this comes after a morning low in the lower 50s. This illustrates that there won't be much cooling behind the Wednesday evening cold front. However, that being said, a series of re-enforcing fronts and high pressures will dominate the forecast beyond Wednesday. Therefore, it will get progressively cooler through the period. Fog should not be an issue for awhile after Thursday morning. The first in the series of weak, dry re-enforcements arrives Thursday night. Low temperatures will cool to the mid to upper 40s for Friday morning. Perfect weather is in the offing for Friday afternoon with beaucoup sunshine and a high just below seasonal norms in the mid 60s. This March weekend looks fantastic with near perfect weather. Get outside and enjoy it! Wall to wall sunshine is expected both Saturday and Sunday with low humidity values. Low temperatures will drop well down into the 40s Friday night into Saturday morning...ditto for Sunday morning. Sunday morning should be a tad cooler with a noticeable nip in the air expected. The dry air will have no problem radiating at night, therefore, even though the air mass residing over the area won't be terribly cold, it will still be quite cool simply because of the effects of radiational cooling. Many locations will see some 30s on Sunday morning, and this is reflected in the 7 day forecast with mid 30s to lower 40s expected across the forecast area. The controlling high in place for the end of the week and the weekend will slowly shift Eastward by Sunday afternoon allowing for a subtle return flow at that time, but you will hardly notice it since the 'gunk' will be well offshore.
This return flow will come into play for the latter stages of the forecast period on Monday. Another cold front is expected to develop in the lee of the Rockies over the weekend, and dive into the forecast area Monday It is a question of moisture return across the area that at this time negates any mention of rain chances for the day 6 period. I note that a few showers are certainly possible ahead of this next front, but this could strictly be because of the forcing associated with the approaching front itself, and not so much the brief low-level moisture that will be available ahead of the boundary. The time frame of sufficient moisture return will be limited due to the orientation of the high, and the fast moving Pacific front. Further revisions to this portion of the forecast will be made as needed in the coming in days. The temperature forecast Monday does offer a continuation of the pleasant temperatures will enjoy over the weekend with 40s for lows and 60s for highs. This front on Monday seems quite strong by March standards. Dry and cool weather is in the offing at the end of the forecast period. A period of unseasonably cool temperatures could set up if the current forecast model projections are correct. I still believe we'll have some more frosty weather, and it could very well come next week. Low temperatures cool into the 30s while highs drop to right around the 60 degree threshold for the day 7 day period in the wake of the next front on Monday. Another large ridge of high pressure will dominate the weather next week, and keep a NW flow at the surface ongoing thus providing pleasant weather. Most of next week just beyond this forecast period looks like a winner as well, with a moderation of temperatures occurring. A sure sign that Spring isn't too far away now! Finally, here's a friendly reminder to be sure to remember to change your clocks Saturday night/Sunday morning as the bi-annual occurrence of daylight savings time takes effect. This is the bad one, in my opinion beings as we'll lose an hour of sleep when we spring forward Sunday morning.
Preliminary Numbers & Zone Forecast:
LCH 63/71 52/74 46/64 30 70 30 0 0 0
LFT 62/72 54/75 47/65 30 70 30 0 0 0
BPT 63/73 53/75 45/64 30 70 20 0 0 0
AEX 61/72 50/75 42/63 30 70 30 0 0 0
POE 61/72 50/75 43/63 30 70 30 0 0 0
ARA 63/72 56/75 48/66 30 70 30 0 0 0
*Dense Fog Advisory until 8a.m. Wednesday.*
Tonight...Cloudy with areas of Dense Fog after midnight with a 30% chance of showers. Low 63. SE wind 5-10 mph.
Wednesday...Morning Fog dissipating by mid-morning otherwise Mostly Cloudy with showers and thunderstorms in the afternoon and evening. Locally heavy rainfall possible and severe weather possible. High 71. South wind 15-20 mph and gusty. Chance of rain 70%.
Wednesday Night...Showers and Thunderstorms likely in the evening with conditions drastically improvement overnight. Skies clearing after midnight. Areas of fog developing after midnight Cooler. Low 52. SW wind 5-10 mph. Chance of rain 30% in the evening.
Thursday...Areas of fog early, otherwise Sunny. High 74. SW wind 10-15 mph.
Thursday Night...Clear and Cooler. Low 46. NNW wind 10 mph.
Friday...Sunny. High 64. NW wind 10 mph.
Wednesday 3/10/10 Daily Planner
7a.m.
Weather: Fog
Temp: 63
Precip: 20%
Wind: SSE 6
Noon
Weather: Cloudy
Temp: 69
Precip: 40%
Wind: SSE 17
5p.m.
Weather: T-Storms
Temp: 70
Precip: 80%
Wind: SSW 15
Drew's 7 Day Outlook
Wednesday
3-10-10
Low: 63
High: 71
Precip: 70%
Wind: SSE 15-20
Thursday
3-11-10
Low: 52
High: 74
Precip: 0%
Wind: SSW 10-15
Friday
3-12-10
Low: 46
High: 64
Precip: 0%
Wind: NW 10
Saturday
3-13-10
Low: 42
High: 64
Precip: 0%
Wind: N 5-10
Sunday
3-14-10
Daylight Savings Time Begins
Low: 38
High: 65
Precip: 0%
Wind: NE/SE 5-10
Monday
3-15-10
Low: 45
High: 68
Precip: 0%
Wind: SSE 10-15
Tuesday
3-16-10
Low: 37
High: 61
Precip: 0%
Wind: NNW 10-15
...Marine Forecast....
*Dense Fog Advisory*.
Tonight...South winds 10 to 15 knots. Seas 2 to 3 feet. Areas of dense fog developing with visibility 1 nm or less after midnight.
Wednesday...South winds 10 to 15 knots. Seas 2 to 3 feet. Areas of fog in the morning...then patchy fog in the afternoon. A chance of showers and thunderstorms in the morning...then numerous showers and thunderstorms in the afternoon.
Wednesday Night...South winds 10 to 15 knots becoming southwest after midnight. Seas 2 to 3 feet subsiding to 1 to 3 feet after midnight. Numerous thunderstorms and isolated showers in the evening. Patchy fog in the evening...then areas of fog after midnight.
Thursday...West winds 5 to 10 knots. Seas 1 to 2 feet. Areas of fog in the morning.
Thursday Night...West winds 5 to 10 knots becoming northwest 10 to 15 knots after midnight. Seas 1 to 2 feet building to 1 to 3 feet after midnight.
Friday...West winds 15 to 20 knots. Seas 1 to 3 feet.
Good night and God bless!
-DM-
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