SW Louisiana Forecast Discussion...After a stretch of nice & dry weather that lasted through the weekend, the string of dry days ended today at 6. Widespread mainly light to moderate rainfall occurred across the majority of the forecast area for a good portion of the day as an overrunning situation developed. The culprit was an advancing Pacific storm system which is going to take its own sweet time pushing through the forecast area. At the same time a weak warm front was advancing NE through the Gulf coastal waters into the forecast area. Widespread stratiform precipitation formed as the warm front advanced, and as mid-level and upper-level support enhanced the moisture content across the forecast area. An embedded disturbance in the active Subtropical Jet Stream also factored into the equation. This perturbation was poorly diagnosed by all global forecast models. While rainfall persisted for several hours from mid-morning to mid-afternoon, rainfall totals were on the light side with generally a 1/2" or less. Temperatures remained on the cool side with a small diurnal range in the cool sector this Monday afternoon. High temperatures reached the lower 60s, but with the rain and wind it felt a bit cooler than that. Quieter weather is over the forecast area at present as the warm front has traversed the entire forecast area as of 3Z (9p.m.). However, a moist, unstable air mass has taken over, and will remain in place through the short-term period.
Although we're dry for the time being, rain chances remain in the forecast, and will for the next couple of days. Here's what I make of a very complex situation. The cold front associated with the strong Pacific system advancing out of the Rockies currently stretches from the Great Plains to the Rio Grande. It's forward progress is slowing as it advances ESE through Texas. Along and ahead of this boundary a large area of showers and thunderstorms exist (MCS) as the front lifts the unstable air mass, and Jet Stream energy comes into the fray. However, this complex will weaken as it continues to push further to the ESE overnight. The associated cold front will also weaken, and eventually fizzle out on Tuesday over East Texas. The air mass over our area has stabilized significantly in the wake of today's rain and the advancement of the warm front. The atmosphere is generally capped at this time, therefore, not much rain is expected overnight. However, some scattered showers are possible after midnight as the decaying MCS moves closer to the area, and erodes the temporary cap. The best chances for additional rain tonight will be North of I-10, though it can't be ruled out at any location across the forecast area. Temperatures won't change much either, now that a very humid air mass is in place. Current readings are in the upper 50s, and minimums should not be lower than the middle 50s by sunrise Tuesday. A steady onshore flow has commenced, and this will continue to be the story into Tuesday. Some dry slotting is occurring as well, and this will allow for clear periods overnight, so patchy fog may become an issue if a prolonged clearing occurs.
Tuesday will likely be a better day than today, but not entirely dry. The air mass will remain moist and unstable across the forecast area, and at the same time frontylsis (dissipating front) will occur over East Texas. A WAA regime will persist over the region in advance of the slow moving Pacific system. The main lobe of this Pacific system is currently near Las Vegas. Certainly rain chances will remain in the forecast, but that being said, shower/thunderstorm activity should be on a scattered basis. The STJ will reside in our general vicinity as well, thus embedded perturbations out ahead of the Desert SW trough will rotate through, and each one will likely spark off some scattered showers or perhaps a thunderstorm across the area. Some periods of sunshine are expected as well, and the effects of daytime heating with the moist, unstable air mass in place will also aid in scattered development. Temperatures should be at or just above the seasonal norm around 70...give it take a couple degrees depending upon how much the sun breaks through. While some Jet Stream energy will be in place Tuesday, the best dynamics will be off to our W and NW over Texas in closer proximity to the decaying cold front and dry line. No severe weather is expected, though I wouldn't be surprised to see a thunderstorm or two with sufficient instability in place. Rain chances should be in the 30-40% range, and it is hard to pinpoint exactly what time it will rain. Generally rain could occur at any point of time during the day, though the best chance will be between noon and 6p.m. The best chance for rain will likely be North of I-10 and over the East Texas Lakes region in the vicinity of leftover outflow boundaries from the decaying boundary. Low-level convergence and upper level divergence will come into play later in the day to engender other shower or thunderstorm activity. The persistent onshore flow will continue as the Desert SW trough digs and deepens as it ejects into West Texas. A chance of rain is maintained for the Tuesday night period as the system approaches. I would anticipate a bit better chance for showers and thunderstorms by late Tuesday into Tuesday night as some better dynamics and a stronger short wave moves into the forecast area in advance of the deepening and diving Pacific trough. Temperatures will remain quite mild as we remain entrenched in the warm sector. Lows will be close to 60. No severe threat weather is expected through Tuesday night, and rainfall should be on a scattered basis.
Wednesday will be far be the day of interest this week. The advancing Pacific system will continue to deepen as it advances Eastward, and this strengthening low will combine with the strengthening Jet Stream to create cyclogenesis across North Texas. At the same time, an almost unprecedented amount of Jet Stream energy will be streaming across the Northern Gulf. Winds at flight level (30-35,000 feet) will be close to 200 mph. This is literally almost off the charts for Jet Stream energy, and it is very rare to see this kind of Jet energy in SW Louisiana. The associated upper level low will follow in tandem with the surface low and undergo a strengthening or deepening phase. The washed out cold front over Texas will be replaced by a second, stronger cold front trailing from the North Texas surface low. The amounts of low-level moisture present Wednesday morning will likely help generate some scattered showers and thunderstorms, but the main event will come during the afternoon as the front bears down on the forecast area. The very impressive Jet dynamics in place could possibly set the stage for some severe weather. Certainly strong thunderstorms with gusty winds and small hail will be expected. This system has the set up to be the focus of our first severe weather outbreak of the season and of the month. Even more specifics will be given on Tuesday. As of right now, the main threat from any severe thunderstorms will be damaging winds with the very fast Jet Stream overhead, although isolated tornadoes and large hail can't be ruled out. The environment is one that will support supercells at first from the late morning through mid-afternoon hours on Wednesday, before it transitions to an MCS (squall line) environment right along and just ahead of the front. Rainfall will be heavy at times, but no widespread flooding is expected at this time. The current severe weather outlook from the Storm Predicition Center indicates a slight risk of severe weather to the North of the I-10 corridor, however, it is noted that it may very well be shifted further South in later outlooks. Based on the data which I have perused, I would suggest that this will occur, so stay tuned. Bottom line is to expect some rough and tumble weather on Wednesday. Severe weather in March is not unusual and I would figure that it will be even more enhanced in 2010 via the El Nino pattern. While there are still some uncertainties in regards to the strength of the system, the timing is becoming a little more certain. The ETA is of right now is expected to be around 6p.m. Wednesday. The system should start speeding up a bit once it feels the effects of the strong Jet Stream, and this will limit rainfall totals, and result in quick improvements overnight. I would also expect that the greatest risk area for the aforementioned severe weather will be just to the North of the 170 kt. Jet Streak, basically in the ARK-LA-TEX region. The severe weather potential will come to an end with frontal passage Wednesday evening, and the stage will be set for an extended period of great weather for the remainder of the forecast period. Afternoon temperatures should be near normal values, after a mild morning as well.
Clearing skies will occur overnight late Wednesday into Thursday morning as high pressure displaces the departing low. Modest CAA takes over at this juncture. This will set the stage for a nice, extended period to dry out and to enjoy the best of what Mother Nature has to offer. Mild weather will continue initially as there won't be much cooling behind the front Wednesday night, but re-enforcing cold fronts are on tap for Thursday and then again later in the period over the weekend. Lows should be near 50, really about seasonable for early March on Thursday while afternoon highs reach close to the warmest readings we've seen this year are on tap for Thursday afternoon with mid 70s expected. High pressure strengthens its grip, and will have a stranglehold over the area by Friday through the weekend. A dry re-enforcing front makes its way through with a surface NW flow aloft in place. The end result here will be a continuation of speculate spring sunshine while temperatures slowly decrease, and drop to below normal levels. Although, that being said, the temperatures in store for the weekend will not be anywhere near comparable to what we've had this winter. This translates to lows in the upper 30s to lower 40s and highs in the lower to middle 60s...just about perfect for the weekend! The string of nice weather will continue into early next week with Monday, the Ides of March, seeing lots of sunshine and temperatures warming up only slightly with upper 60s for the high. Dry and pleasant weather is expected for much of next week with possibly our next wet weather maker in the offing towards the latter half of next week.
Preliminary Numbers & Zone Forecast:
LCH 57/69 59/70 51/73 30 40 40 80 30 0
LFT 54/71 58/71 52/74 30 30 40 80 40 0
BPT 59/70 61/69 53/75 40 50 60 80 30 0
AEX 56/70 55/72 49/72 40 60 60 80 30 0
POE 56/70 55/72 50/72 40 60 70 80 30 0
ARA 53/71 58/71 54/74 30 40 40 80 40 0
Tonight...Mostly Cloudy with a 30% chance of showers and thunderstorms after midnight. Patchy Fog possible towards morning. Warmer. Low 57. SSE wind 5-10 mph.
Tuesday...Mostly Cloudy with a 40% chance of showers and thunderstorms. High 69. SSE wind 10-15 mph.
Tuesday Night...Mostly Cloudy with a 40% chance of showers and thunderstorms. Low 59. SSE wind 10-15 mph.
Wednesday...Cloudy and Windy with showers and thunderstorms likely. Locally heavy rainfall & severe weather possible with damaging winds, isolated tornadoes, & large hail. High 70. SSE wind 20-30 mph and gusty. Chance of rain 80%.
Wednesday Night...Cloudy with a 30% chance of showers and thunderstorms early. Rain ending before midnight with Decreasing Cloudiness after midnight. Cooler. Low 51. SSW wind 10-15 mph.
Thursday...Sunny. High 73. SW wind 10 mph becoming NNW at 10-15 mph in he afternoon.
Tuesday 3/9/10 Daily Planner
7a.m.
Weather: Cloudy, Patchy Fog
Temp: 57
Precip: 30%
Wind: SE 5
Noon
Weather: Mostly Cloudy, Scattered Rain
Temp: 66
Precip: 40%
Wind: SE 12
5p.m.
Weather: Cloudy, Scattered Showers/T-Storms
Temp: 68
Precip: 40%
Wind: SE 14
Drew's 7 Day Outlook
Tuesday
3-9-10
Low: 57
High: 69
Precip: 40%
Wind: SSE 10-15
Wednesday
3-10-10
Low: 59
High: 70
Precip: 80%
Wind: SSE 20-30
Thursday
3-11-10
Low: 51
High: 73
Precip: 0%
Wind: SSW/NNW 10-15
Friday
3-12-10
Low: 45
High: 65
Precip: 0%
Wind: NNW 10-15
Saturday
3-13-10
Low: 42
High: 64
Precip: 0%
Wind: N 10
Sunday
3-14-10
Low: 41
High: 66
Precip: 0%
Wind: N 5-10
Monday
3-15-10
Low: 39
High: 64
Precip: 0%
Wind: N 5-10
...Marine Forecast...
Tonight...Southeast winds around 15 knots becoming 10 to 15 knots after midnight. Seas 4 to 5 feet subsiding to 3 to 4 feet after midnight. A chance of showers.
Tuesday...South winds 10 to 15 knots. Seas 3 to 4 feet. A chance of showers and thunderstorms.
Tuesday Night...South winds 10 to 15 knots. Seas 3 to 4 feet. A chance of showers and thunderstorms.
Wednesday...South winds 10 to 15 knots. Seas 3 to 4 feet subsiding to 2 to 3 feet in the afternoon. A chance of showers and thunderstorms.
Wednesday Night...Southwest winds 10 to 15 knots becoming west 5 to 10 knots after midnight. Seas 2 to 3 feet.
Thursday...West winds 10 to 15 knots. Seas 2 to 3 feet.
Good night and God bless!
-DM-
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