SW Louisiana Forecast Discussion...Everything fell into place nicely on this last Wednesday of 2010. The widespread rain event unfolded right on cue as we got into the afternoon hours. The upper level feature out ahead of the main Pacific system has rolled across the area, and the advancing warm front is in transit as well. Thankfully, the severe weather aspect of things never materialized at least for most of the forecast area. The prospects of severe weather were an iffy proposition to begin with. Better dynamics and instability slowly worked their way into the area as forcing increased late this evening. Some severe weather occurred in the SE portion of the forecast area mainly in coastal areas from near Rockefeller Wildlife Refuge over towards New Iberia. The elongated troughiness is pulling East of the area, and rainfall is coming to an end from West to East tonight. Much needed rainfall has occurred across the area with many locations receiving a nice soaking in excess of 2". Isolated higher amounts near 4" have occurred in heavier clusters near the coast. It was almost strange to hear thunder and see the lightning since it has been many weeks since such an occurrence happened around these parts. Temperatures won't really drop much overnight, in fact they may rise slightly after midnight as warmer air works into the region behind the departed disturbance. Expect minimums to range from the mid 50s to lower 60s across the area. In the wake of the rain, fog may become an issue by Thursday morning with areas of dense fog possible with plenty of residual moisture in place. This is quite common in a warm frontal environment. The already persistent onshore flow will continue.Today's rains will at least take away any thought of enduring the driest December on record, but we are still mired in an extreme drought situation.
There is not much change in the forecast philosophy from 24 hours ago. We will still endure a lull on Thursday as we will be in between weather systems. Today's rain maker will continue lifting out to our E and NE and weaken as it does so. However, we will turn our attention to the West. A rather potent Pacific storm will be coming down the pipe. A warm air advection regime will be in place Thursday. We will be dry slotted at the surface, and drier air will temporarily reside in the mid and upper levels. This will keep rain chances on the slim side with no presence of a trigger mechanism to generate more widespread rain. I certainly can't totally eliminate rain chances with the presence of the deep low level moisture over the area. Only scattered activity is expected mainly due to the effects of daytime heating and later in the day as moisture begins to pool over the region, and convergence starts to increase ahead of the advancing storm system. It will be much warmer on Thursday afternoon with high temperatures easily surpassing the 70 degree threshold. It could ultimately get as warm as the mid 70s across the area, and it won't feel much like the end of December. It will be on the breezy side as well due to the pressure anomalies driven by the orientation of the two weather systems. Expect a long fetch Southerly flow to remain in place across the area with gusts over 20 mph at times. Skies will generally be Mostly Cloudy, but certainly a few peeks of sun are expected in the dry slot. Very similar conditions will be in place for Thursday night, but the rain chances will increase a bit with convergence increasing ahead of the Pacific storm. Overnight lows will be on the mild side, and will more or less be what the normal high should be for this time of year. Overnight minimums will be in the lower 60s heading into Friday.
That takes us to Friday, New Year's Eve...The second round of rain and storms will affect the area at this time. There is not much change in the forecast reasoning for this period either. The day will start relatively calm with perhaps some patchy fog and the unseasonable warmth. Skies will generally be Partly to Mostly Cloudy to start the day. The strong storm system and its associated cold front, and surface low will progress Eastward. There will also be a dry line feature associated with this front. This will develop over Texas Friday morning as the Jet Stream becomes active. The very potent upper trough will send the combination dry line, cold front towards the area. Moisture will pool over the area, and low level convergence will increase in earnest. The imposing synoptic features will cause weakening of the mid and upper level cap. Showers and thunderstorms will develop as the day progresses. Most of the morning will be dry, but during the afternoon convection will develop and work its way into the area. It should generally be of a scattered nature at first, but by mid to late afternoon activity should become more widespread. The Jet Stream dynamics will stream right over the area, and the forecast area is likely to be in the favorable right front quadrant of the Jet Stream by Friday evening. The strong onshore flow at the surface, and strong SW winds aloft will generate windy conditions ahead of the boundary. The chances for showers & storms will ramp up into the likely category yet again likely after about 3p.m. on New Years Eve, and remain high into the overnight hours.
Your New Year's Eve plans may need to be altered as it stands right now. The most likely time frame to see showers & thunderstorms will likely be between 4p.m. and midnight. Given better dynamics and instability, a greater chance of severe weather will exist with the main system on Friday. All modes of severe weather will be possible, but damaging winds seem like the most likely form. Isolated tornadoes certainly can't be ruled out given the favorable set up for wind shear over the area. Large hail is also in the mix. I am certainly more concerned about the prospects of severe weather during this time since many will be away from their TV or radio and out celebrating for New Years. I strongly suggest having a way to keep yourself informed of any threatening weather conditions. Being able to have your own fireworks display, looks like an iffy proposition at this time given the timing of this rain event. This will certainly be another widespread rain event, and another 1-2" of rain is expected area wide. Isolated higher amounts closer to 3" are possible. We are close enough to the event now that narrowing down a time of arrival is within reason. I will stick with a frontal passage before midnight, with the worst of the weather in the previously mentioned 8 hour window from 4p.m. Friday afternoon to around midnight Saturday New Year's Day. Of course, further revisions are expected tomorrow as new model data becomes available. The unseasonable warmth will be with us to close out 2010 as highs reach the mid 70s on Friday. It will turn sharply colder in the wake of the front overnight Friday. A storng CAA regime will establish itself as we start the new year, and waking up on New Year's Day it will be much cooler with morning lows generally in the mid 40s to around 50 or so. This cold front will not be nearly as strong as the predecessor was over Christmas weekend, but we will certainly chill down once again. The threat for strong to severe storms will come to an end in the overnight hours with the frontal working into the coastal waters.
Clouds and the chance for showers will linger in the post-frontal environment on New Year's Day. The colder and more stable air will filter into the region at the surface, but moisture will remain trapped in the boundary layer due to the shallow nature of the surface cold front. We will also have wrap-around moisture associated with the backside upper level low to deal with across the area. This means that a chance for rain will continue well into the day on New Year's Day before much improvement is noted. Expect the cloudiness and periodic shower activity to be in place with CAA continuing. Temperatures will not rise all that much at all on New Year's Day given continued CAA and the continued cloud cover and chance for post-frontal rains. A very small diurnal range is to be expected with highs only topping out in the mid 50s or so. A strong offshore flow will be locked in place over the area. Conditions improve further into the afternoon hours as high pressure sliding down the front range of the Rockies begins to build into the forecast area. This will clean out the moisture in the mid and upper levels as the cold front drives further into the Gulf of Mexico. Thus, the chances of lingering rain will cease and desist by mid and late afternoon. Cloud cover will slowly begin to exit stage right as well. Clear skies will take over by New Year's Night with the high pressure firmly entrenched over the NW Gulf Coastal Plain. Seasonably cold temperatures are on tap with morning lows by Sunday back down into the 30s once again. The offshore flow will slowly decrease in intensity overnight as the high builds in.
Quiet weather is on tap for Sunday and Monday with the high pressure in control. Once again, this air mass is not terribly cold so nothing out of the ordinary is expected. Overnight lows will fall into the mid 30s on average with clear skies and lighter winds in place. Plentiful sunshine is expected for the second half of New Year's weekend with high pressure in control. It will be seasonably cool even in the afternoon with highs falling short of the normal 60 degree threshold. More of the same is expected for Monday with the high pressure essentially anchored very near SW Louisiana. Monday morning looks to be the coldest one of this forecast period with lows close to freezing along I-10. Many locations north of the interstate will likely endure a light freeze, but this is nothing drastic compared to the hard freezes we've dealt with this month. The high pressure will only slowly work its way Eastward, so while CAA ceases, a very light Easterly flow will set up due to the orientation of the surface high. Afternoon highs may be a tick or two cooler than that of Sunday, but they won't be far off given the seasonably cool air mass in place, and the low sun angle during the month of January. There will also more than likely be a bout of frost on Monday morning, so an early word to the wise here to protect your pets and your tender vegetation. I certainly don't see any hard freezes in the near future, so pipes will not be an issue this go around.
Cloud cover may begin to return on Monday night. The New Year's cold front will likely stall out and hover over the coastal waters. This front may begin to lift back Northward as warm front beginning Tuesday. An advance of cloudiness will stream over the area Monday night. This cloud mass will likely keep us more insulated than a normal early January night would be in this situation. Thus, air mass modification should begin even though there won't be a classic return flow set up in place yet. It should remain dry as the high pressure keeps its grip over the area for a little while longer. Clouds will increase more significantly on Tuesday. Deeper moisture may quickly return on Tuesday afternoon as the slow moving warm front evacuates the coastal waters and moves back towards land. This could allow for a slight chance of showers & thunderstorms by the afternoon hours, but a major rain event appears unlikely at this time for Tuesday. I should pause just a moment to say that some of the forecast models still suggest the development of a prolonged overrunning event behind the front. I am still not totally convinced on this perception. It seems certain that our next temperature modification trend will be up at this time more than likely. Morning lows will continue to be seasonably cold with readings generally in the mid to upper 30s over the area. Tuesday afternoon highs should be very close to 60 degree norm. I fully expect the return flow to establish itself during the day. Better rain chances come at the end of this forecast period on Wednesday. The combination of the lifting warm front, and a system with Pacific origins pulls to the East overrunning seems be a more likely scenario. If the trends continue, rain chances could ultimately wind up in the likely category, but since this is at the end of the forecast period just chance pops will suffice for now. It is also too early to suggest whether or not thunderstorms will even be a possibility at this juncture. Given the look shown by models suggesting overrunning, thunder seems like a localized entity at best. Temperature modification will be likely with highs reaching the mid 60s easily. This will swing us back towards above normal. This period will have the potential to see a prolonged rain event, but a lot of uncertainties are in existence. Models show the best chance for showers & some thunderstorms coming just beyond the scope of this forecast package. Another cold front is advertised around the end of next week with rain chances continuing until then. Expect there to be many revisions in the coming days.
Preliminary Numbers & Zone Forecast:
LCH 59/74 62/75 45/58 80 20 30 70 80 30
LFT 57/74 61/76 46/59 90 30 20 70 80 30
BPT 61/75 64/75 44/61 80 20 30 70 80 30
AEX 55/73 59/73 40/55 90 30 20 80 80 30
POE 55/73 59/74 41/56 80 20 30 80 80 30
ARA 58/74 60/75 48/60 90 30 20 70 80 30
Tonight...Mostly Cloudy w/ Showers & Thunderstorms likely early, but ending from West to East as the nigh progresses. Warmer. Low 59. Fog developing after midnight. SSE wind 10-15 mph. Chance of rain 80% early, but dropping to 20% towards morning.
Thursday...Areas of fog early, otherwise Mostly Cloudy w/ a 20% chance of scattered Showers & Thunderstorms. High 74. SSE wind 15-20 mph and gusty.
Thursday Night...Partly to Mostly Cloudy w/ some Patchy Fog development after midnight. A 20% chance of scattered showers & thunderstorms especially after midnight. Low 62. SSE wind 10-15 mph.
New Year's Eve Day...Mostly Cloudy, Unseasonably Warm, Windy, & Humid with showers & thunderstorms developing & becoming likely as the day wears on. Locally heavy rainfall & some strong to severe thunderstorms are expected. Damaging winds and isolated tornadoes will be the main threats late in the day. High 75. SSE wind 15-20 mph and gusty. Chance of rain 80%.
New Year's Eve Night...Cloudy & Continued Windy w/ showers & thunderstorms likely. Some locally heavy rainfall & severe storms possible with damaging winds & isolated tornadoes the main threat. Rains tapering off after midnight & turning much cooler. Low 45. SSW wind around 20 mph becoming NNW at 20-25 mph and gusty overnight. Chance of rain 80%.
New Year's Day...Mostly Cloudy & Much Cooler w/ a 30% chance of rain mainly in the morning. Windy. Clouds beginning to decrease in the afternoon. High 58. NNW wind 15-20 mph and gusty.
Thursday 12/30/10 Daily Planner
6a.m.
Weather: Mostly Cloudy w/ Areas of Fog
Temp: 59
Rain: 20%
Wind: SSE 8
9a.m.
Weather: Mostly Cloudy
Temp: 66
Rain: 20%
Wind: SSE 13
Noon
Weather: Cloudy
Rain: 20%
Wind: SSE 16
3p.m.
Weather: Mostly Cloudy
Rain: 20%
Wind: SSE 20
6p.m.
Weather: Mostly Cloudy
Temp: 70
Rain: 20%
Wind: SSE 17
9p.m.
Weather: Mostly Cloudy
Temp: 67
Rain: 20%
Wind: SSE 13
Drew's 7 Day Outlook
Thursday
12-30-10
Low: 59
High: 74
Rain: 20%
Wind: SSE 15-20
Friday
12-31-10
New Year's Eve
Low: 62
High: 75
Rain: 80%
Wind: SSE 15-20
Saturday
1-1-11
New Year's Day
Low: 45
High: 58
Rain: 30%
Wind: NNW 15-20
Sunday
1-2-11
Low: 36
High: 56
Rain: 0%
Wind: N 10
Monday
1-3-11
Low: 33
High: 55
Rain: 0%
Wind: NE 5-10
Tuesday
1-4-11
Low: 38
High: 60
Rain: 20%
Wind: ESE 5-10
Wednesday
1-5-11
Low: 49
High: 67
Rain: 40%
Wind: SSE 10
...Marine Forecast...
Tonight...South winds 15 to 20 knots. Seas 3 to 5 feet. Showers and thunderstorms late in the evening...then a chance of showers and thunderstorms after midnight. Patchy fog after midnight.
Thursday...South winds around 15 knots. Seas 3 to 5 feet subsiding to 2 to 4 feet in the afternoon. Patchy fog in the morning. A slight chance of showers in the late morning and afternoon.
Thursday Night...Southeast winds 15 to 20 knots. Seas 2 to 4 feet. A slight chance of showers.
New Year's Eve Day...South winds 15 to 20 knots. Seas 2 to 4 feet. A chance of showers and thunderstorms in the morning...then showers and thunderstorms likely in the afternoon.
New Year's Eve Night...West winds 15 to 20 knots becoming north after midnight. Seas 2 to 4 feet. A chance of showers and thunderstorms.
New Year's Day...North winds 15 to 20 knots. Seas 2 to 3 feet. A slight chance of showers and thunderstorms in the morning.
Have a great Thursday & God Bless!
-DM-
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