SW Louisiana Forecast Discussion...The string of wet Thursdays was broken today as high pressure continued to rule the roost. The only proverbial fly in the ointment was some streaming high clouds from time to time with an active Subtropical Jet Stream over the NW Gulf. The slowly progressing warming trend continued today as highs topped out right around 60 after another light morning freeze. In the short term, much of the same is expected across the forecast area. A strong Canadian high is slowly pushing Eastward into Dixie tonight, and its orientation has allowed for a subtle return flow to commence across the forecast area this evening. This will slowly bring back low-level moisture across the area, but overall it will still be very comfortable with the dry air in place. The high clouds will continue to stream in from time to time overnight, perhaps scouring the moonlight at times. The air mass modification will continue in response to the subtle Southerly flow with overnight lows in the mid to upper 30s for most with exception of the coldest locations which should be near freezing once again, and the immediate coast which should hold in the low to mid 40s. Some patchy frost and fog is possible towards morning. Fog will be more likely in areas nearest the coast, and frost will be more likely North of I-10.
Friday will be another dry day as the benign pattern continues. The active STJ will continue to stream cloudiness into the area, and this will filter the sunshine at times. Rain will tease the area as a disturbance has formed in response to the active Jet. The upper level flow is zonal (W to E) across the forecast area, and this should keep all the rainfall with this system over the Gulf waters. It is feasible that some sprinkles could reach the coastal parishes, but there will be no mention of measurable rainfall in the forecast. The aforementioned cirrus shield will be the only influential weather across the forecast area Friday. Low-level moisture will continue to slowly increase as the Gulf flow becomes more established across the forecast area. Temperature moderation will continue with low to mid 60s expected across the area. Quiet weather will persist into the weekend with the high clouds holding firm across the area with the persistent STJ in place. The southerly flow will continue to strengthen, and sufficient Gulf moisture will be place by late Saturday. Normal temperatures are expected for the Friday night/Saturday morning period with lows in the mid 40s. Afternoon highs on Saturday will be at or above normal in the mid to upper 60s. No rain is expected through Saturday despite the sufficient cloud cover.
Significant changes will be occurring over the weekend. Our next cold front will be taking shape in the lee of the Rockies. A surface low will also initiate in the Panhandles of Oklahoma and Texas. This front will form on Saturday and displace (overtake) a weaker boundary that is currently in place across the Red River Valley. As this boundary approaches Sunday, rain chances will return to the forecast at this time. Sunday should start dry, and temperatures will continue the moderation reaching above normal levels in the lower 50s. Instability and lift gradually increases through the day as the sharp boundary approaches, thus some thunderstorms will be possible. Showers could break out as early as noon Sunday, but I believe models may be too quick with this idea since the necessary lifting mechanism will still be back in Texas. Temperatures could very well reach 70 for the first time all month on Sunday. It will certainly be breezy as there will be a sufficient pressure differential across the area in response to the approaching front. Rain chances will be highest in the Sunday night/early Monday morning periods, as this will be the time of greatest lift and instability. Rain chances are certain at this time, and will be in the likely category. However, models differ to a degree on the possibility of severe weather. This will be fine tuned over the weekend, and I will have special blog entries on the severe possibilities as the event draws closer. Here's what I see as of now. Thunderstorms are likely to occur, but it's a borderline situation in regards to severe weather. There will certainly be added energy and support from the persistent STJ, this should be more than enough to produce convective (cumuliform) activity across the area. However, many of the dynamics needed to produce severe weather will be lacking despite the placement of the surface low shown by the 0Z run of the GFS). The front should be a fast mover as well, and this will limit rainfall totals likely to an inch or less. This will minimize the flood threat across the area. The fast moving nature of the front could result in some strong downbursts which would realize a damaging wind threat across the area. I believe this will be the main issue with the storms on Sunday at this point, though the placement of the surface low on the GFS could signal a tornado threat if it comes to fruition. The depicted placement of the low would suggest some presence of wind shear at this time. The front should quickly push through the area, and clear the forecast area by mid-morning Monday. The 0Z Friday GFS (6p.m. Thursday) and 0Z NAM at 72 hours (6p.m. Sunday) are included. The QPF chart is included as well.
The GFS depicts a surface low over Central Arkansas, with the cold front trailing from the low near LZK (Little Rock) to SHV (Shreveport) to BPT (Beaumont) at 6p.m. Sunday. This seems a bit fast to me, but it should be slicing into Northern portions of the forecast area at this time, nonetheless. If the position of the low on this run is correct, then the severe weather potential across the forecast area will increase. Tornadoes and strong winds would be the main threat.
The NAM model output at this time depicts a double-barreled low with a stronger low further North over SW Missouri, and a secondary low along the front near Paris, TX. If this comes to fruition then the best dynamics and instability would be displaced to our North, thus lessening the severe weather threat across our area. The better chance for severe weather would be in the ARK-LA-TEX region up into the Ozarks. Certainly some thunderstorms would be still possible here, but the severe threat is lessened based on the placement of the low on the NAM. The NAM is a bit slower with the evolution of the front as well. Rain continues back to between Houston and San Antonio. Rainfall totals should be 1-2" for the event, and some heavy downpours will be possible at times.
A blend of the two models seems logical at this point until the event gets closer and we have a better idea of how things will evolve. That being said, I would expect the ETA of the front at LCH at this time should be between 3 and 6a.m. Monday morning. For now, I will forgo mention of any severe weather, but re-assessment tomorrow may suggest otherwise. El Nino often enhances these type of systems across the Gulf coast, however, a negating factor is the lack of upper level support with the system. This is why I'm forecasting no severe weather at this time. The front will quickly move through the area with a fast flow in place helping to push it along. Conditions quickly improve Monday with a drier and cooler air mass returning to the area. Mild temperatures will continue until the frontal passage with the maximum near 70 Sunday and 60s for Sunday evening. However, temperatures will quickly fall behind the front with 40s expected by Monday morning. A strong offshore flow will develop in the wake of the front. Skies quickly clear out Monday with high pressure building in, but temperatures will struggle as CAA offsets afternoon sunshine with highs only reaching the mid 50s at best.
Much uncertainty is abound for the latter part of the forecast. Models are all over the place at this time. However, Tuesday will be on the chilly side and with cloud cover as the STJ continues to be a disturbed individual. This will result in a short clearing on Monday into Monday night before the clouds begin to stream over the area again on Tuesday. Below normal temperatures are introduced behind this front once again as the CAA pulls down some colder Canadian/Arctic air over the Great Plains. The clouds and continued CAA will limit warming with highs only in the mid 40s. The STJ will eject out another disturbance from West Texas beginning on Tuesday, and this will increase isentropic lift over the area. Thus, a short reprieve from rain chances is expected. This is the same song, different verse for the winter of 2009-2010. As the West Texas disturbance emanates Eastward toward the Texas coast, another Gulf low is progged to form by some models. This seems logical based on what has happened repeatedly so far this season. This will only enhance moisture across the area, resulting in a further increase of rain chances on Wednesday. The misery will continue as the flow around the low keeps cold air filtering into the region with lows in the mid 30s and highs only in the low 40s at best. I have undercut guidance for this period because of the model uncertainty. Models historically have a hard time with these cold air masses this far out. The major discrepancy with the models lies with the prospects of rain chances. Some limit rain chances as they keep the majority of the activity over the Gulf waters with just cloudy skies and very light rain from time to time across the forecast area, while other models suggest that the Gulf low will track closer to the coast engendering a heavy rain event in the Tuesday/Wednesday time frame. There is enough confidence to introduce rain chances for Tuesday, and increase them for Wednesday as this energy moves through. Further fine tuning is forthcoming. Models will hopefully have a better handle on this situation by the weekend. Temperatures will certainly be cold at this time, but it appears it will be too warm for anything other than liquid precipitation. Dry weather should return at the end of the forecast period on Thursday as this latest customer in the El Nino winter moves away. Temperaturewise it will remain below normal with more freezing temperatures expected for lows as skies clear out behind the ejecting short wave at mid-week. Many of you are ready for spring to arrive, so enjoy the taste of it that we'll receive this weekend, because winter isn't over yet. Cold and dry weather will continue into the final weekend of February before a warming trend takes us into March, and transition into meteorological Spring. It's still a few more weeks until astrological Spring.
Preliminary Numbers & Zone Forecast:
LCH 36/63 45/67 54/70 0 0 0 0 0 40
LFT 35/63 44/68 53/71 0 0 0 0 0 30
BPT 38/64 48/70 55/72 0 0 0 0 0 40
AEX 31/62 42/66 50/68 0 0 0 0 0 30
POE 31/62 43/66 51/68 0 0 0 0 0 30
ARA 35/63 44/67 55/71 0 0 0 0 0 30
Tonight...Mostly Clear to Partly Cloudy and Not Quite as Cold. Low 36. Light SE wind.
Friday...Partly Cloudy and Warmer. High 63. SE wind 10 mph.
Friday Night...Partly to Mostly Cloudy and Warmer. Low 45. Light SE wind.
Saturday...Mostly Cloudy. High 67. SE wind 10 mph.
Saturday Night...Mostly Cloudy. Low 54. SE wind 10 mph.
Sunday...Mostly Cloudy & Windy with a 40% chance of showers and thunderstorms in the afternoon. High 70. SSE wind 15-20 mph and gusty.
Friday 2/19/10 Daily Planner
7a.m.
Weather: Mostly Sunny
Temp: 36
Precip: 0%
Wind: SE 3
Noon
Weather: Partly Cloudy
Temp: 59
Precip: 0%
Wind: SE 8
5p.m.
Weather: Mostly Cloudy
Temp: 60
Precip: 0%
Wind: SE 10
Drew's 7 Day Outlook
Friday
2-19-10
Low: 36
High: 63
Precip: 0%
Wind: SE 5-10
Saturday
2-20-10
Low: 45
High: 67
Precip: 0%
Wind: SE 10
Sunday
2-21-10
Low: 54
High: 70
Precip: 40%...70% Night
Wind: SSE 15-20
2-22-10
Low: 48
High: 53
Precip: 30% AM
Wind: NNW 15-20
Tuesday
2-23-10
Low: 36
High: 42
High: 42
Precip: 30%
Wind: NNW 15-20
W.C.: 20-30
Wednesday
2-24-10
Low: 35
High: 41
Precip: 60%
Wind: NNE 15-20
W.C.: 20-30
Thursday
2-25-10
Low: 29
High: 47
Precip: 0%
Wind: N 10-15
W.C.: 20-35
...Marine Forecast...
Friday...East winds 10 to 15 knots. Seas 1 to 2 feet. A slight chance of showers.
Friday Night...Southeast winds 10 to 15 knots decreasing to 5 to 10 knots after midnight. Seas 2 feet. A slight chance of showers.
Saturday...East winds 5 to 10 knots. Seas 1 to 2 feet building to 1 to 3 feet in the afternoon.
Saturday Night...Southeast winds around 10 knots. Seas 2 to 3 feet.
Sunday...Southwest winds 10 to 15 knots. Seas 2 to 4 feet. A chance of showers and thunderstorms.
Good night and God bless!
-DM-
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