*December Severe Weather Outbreak Wednesday.*
SW Louisiana Forecast Discussion...3 more days until Christmas! Today was the first official day of winter...The Winter Solstice!!! It's been so pretty here since Friday, and this is well-deserved after a dreary December overall. While it was beautiful here, a huge snowstorm occurred over the weekend along the East Coast. This is essentially the same system that affected us on Thursday. It felt like winter this morning with widespread frost across the area with actual temperatures near freezing. Clear skies greeted us once again, along with a few areas of patchy ground fog. The fog quickly burned off, and it was another Delightful December day with the weekend high pressure in control for one more day. After the cold start, temperatures warmed up rapidly underneath the clear skies and calm winds. Highs were in the 60s across the area, which is at or just above normal for this time of year. A quiet night is in store across the area. High pressure has moved Eastward into Dixie, and a subtle return flow has commenced. The return flow will result in increasing dew points overnight, and much warmer temperatures will result. Low to mid 40s should suffice for Tuesday minimums across the forecast area. Fog won't be a big issue tonight with relatively dry air still in place, but some ground fog could be present once again first thing Tuesday morning. Skies should remain clear overnight.
Tuesday will be a day of transition ahead of the vigorous mid-week storm system. This system is getting its act together out West, and will be moving East into the nation's mid-section at mid-week. Extensive details on this system are forthcoming, as it will have a huge impact on the nation's weather during a time of high traffic volume for Christmas. It will have a significant impact on our area. Tuesday should still be relatively nice day. The present Southerly flow will intensify and become more pronounced. The mid-week system will continue to strengthen as the associated trough deepens and digs Southward. The warming trend will continue with high temperatures nearing 70. Clouds will increase during the day as the return flow intensifies, and as sufficient low-level moisture moves into place by Tuesday evening rain chances will be returning to the forecast. Some scattered showers will begin to develop as the Subtropical Jet Stream strengthens and moves over the area. While a chance of showers is maintained in the return flow Tuesday night, the biggest issue for this portion of the forecast period will be advection fog. Ample amounts of low-level moisture will be place, and the continued onshore flow will bring humidity values back near 100% overnight, and winds will subside enough to allow for a perfect night for fog. Temperatures will be much more mild, and be well above December normals. I expect overnight minimums to be in the mid to upper 50s. The fog could be quite dense after midnight especially closer to the coast. Areas that don't see fog will likely see the formation of a return flow stratus deck generating Mostly Cloudy skies overnight. While it should generally just be a warm and humid night Tuesday night across the forecast area, it should still be quiet. However, while the fog and low clouds are setting in over our area, the major storm system will really be getting ramped up at this time. The trough will continue strengthening, and its associated cold front will be sliding out of the Rockies. Jet dynamics will create cyclogenesis in the lee of the Rockies overnight Tuesday, and this low will strengthen and move Eastward overnight. Precipitation will develop out ahead of the low, and a big snow storm is expected for the Great Plains and Mid West.
Wednesday will be an eventful day across the forecast area. Convergence ahead of the approaching front and trough will strengthen. The atmosphere will be very buoyant, and the energy created by the Jet Stream will generate sufficient dynamics. Fog will dissipate by mid-morning Wednesday as winds strengthen in response to the deepening low and increasingly negatively tilted trough. A warm and humid air mass will reside across the forecast area with highs reaching the lower 70s. Dew points will be in the lower 60s, this is certainly high enough to support severe weather in December. Showers and thunderstorms will become likely during the day as lifting and forcing along and ahead of the front increase. Areal coverage of shower and thunderstorm activity will overspread the forecast are from the SW as moisture converges in the offshore waters, and works inland. The cold front will likely push into East Texas Wednesday evening, and shower and thunderstorm activity will likely congeal into a strong squall line (MCS) along the front as forcing maxes out. A surface low will track into the ARK-LA-TEX region, and this is a position that places the forecast area in a favorable spot for severe weather. The greatest severe weather will evolve in the overnight hours Wednesday as the strong cold front works through the forecast area from West to East. A low-level Jet of 60-70 kts. will be translating across the area in the Wednesday evening time frame as the squall line generates to our West. Instability will be present across the entire forecast area, and all modes of severe weather will be possible. A tornado threat seems more likely Wednesday afternoon into early Wednesday night with any supercells that develop out ahead of the squall line. The environment will favor supercellular development somewhere across the forecast area. Sufficient low level shear will be present during this time, and this will aid in the possible tornado outbreak. Another factor contributing to the severe weather therat will be the orientation of the Jet Stream. The forecast area will lie under what is known as the LFQ (left-front quadrant), and this is where the majority of severe weather occurs. The severe weather threat will evolve a hail and damaging wind event overnight with the squall line. Isolated tornadoes will be possible with the squall line as well, but the highest tornado threat typically resides with the individual thunderstorms out ahead of an MCS. On top of the potential severe weather threat, a heavy rain threat exists. Even though we've had a nice 5 day break from the rain, we haven't dried out much, as drying rates are lower this time of year as compared to summer. The ground is still very saturated, and we simply do not need any rain. However, 2-3" of rain seems likely as heavy rains are expected with this system. I will fine tune this forecast as necessary on Tuesday. I think it is more prudent to elaborate on the severe weather threat at this time. Wednesday will be a busy travel day with many people heading out of town for Christmas, so the timing of everything here is essential. Rain chances will be in the likely category for Wednesday, and be highest for the Wednesday night period, perhaps maxing out.
I expect the greatest threat for severe weather to occur between 4p.m. Wednesday and 4 a.m. Thursday. Storms will certainly be possible before this time, and extend for a time afterwards as well. My analysis of the synoptic situation leads me to believe that the greatest threat for severe weather will occur during this 12 hr. window. There are still some timing discrepancies with the forecast models, so this will likely be adjusted as the event gets near. The dynamics associated with the impinging system are very impressive for this time of year. Another question is what portion of the forecast area will be in the greatest threat area for severe weather. The Gulf is always a mitigating factor (which is a plus when it comes to severe weather possibilities) especially this time of year. The greatest threat is often removed from the coastline, and resides north of the I-10 corridor, and I think this is a classic set up for that. That doesn't mean Southern portions of the area will escape severe weather. The set up for severe weather across the area is so favorable, that I will be surprised if the forecast area gets off unscathed. Wednesday will likely be a day with several watches and warnings across the country. It has the potential to be a very significant Christmas week severe weather outbreak. This system is so dynamic that while we're dealing with severe weather on the Southern end, our neighbors to the North in the Mid West will be reeling as well from blizzard conditions. This will make for travel nightmares during this period. I would expect a Tornado Watch or two across the forecast area Wednesday, and also the possibility of a Flash Flood Watch due to the extremely saturated grounds. The Storm Prediction Center has the entire area highlighted for a slight risk of severe weather for the Day 3 period (Wednesday). A graphical representation follows, as well as the expected QPF---Qualitative Precipitation Forecasts (Forecasted Rainfall Amounts). We'll take another shot at forecast specifics on Tuesday, but the bottom line I want to stress here is that you need to be alert of rapidly changing weather conditions on Wednesday, and understand the forecast possibilities, and have a severe weather plan of action in place should it become necessary.
The severe weather threat will end overnight Wednesday into Christmas Eve morning on Thursday as the cold front pushes through and flushes everything out to sea. Strong CAA will become established, as a large area of high pressure builds in behind the departing front. The upper flow will be predominantly from the NW at this point. Clouds will linger through much of the day on Christmas Eve as wrap-around moisture remains present. The departing low will be over the Mid-Mississippi Valley, and the big snowstorm will be pushing Eastward towards the East coast. The severe weather threat will be lesser points to our East. The flow at the surface and aloft will usher in a more stable, much colder air mass. The air behind this front will have Arctic origins, though the thrust of it will be shunted further East. Afternoon experiencing a couple days of above normal temperatures, we'll be back to the reality of winter on Christmas Eve as temperatures will likely fall throughout the day. Residual moisture in place with the orientation of the low will also keep a chance of mainly light rain and/or drizzle in place for much of the day on Christmas Eve. A chance of showers and thunderstorms will be necessary for the morning hours as some post-frontal convection is possible, but we'll transition to the light rain and drizzle for the afternoon hours. Temperatures will be working their way downward from the low 60s around midnight into the 40s by evening church service time. It will quite windy as well with a strong pressure differential in place thanks to the departing system. NNW winds over 20 mph at times will be likely for much of the day Thursday. Winds will subside late Thursday as high pressure settles closer to the forecast area. Santa Claus should feel right at home with a chilly arrival into SW Louisiana. Skies will clear overnight, so Santa should have good visibility over the skies of SW Louisiana. Seasonably cold temperatures are expected with overnight lows heading into Christmas morning expected to be in the low to mid 30s across the forecast area.
Christmas Day through the remainder of Christmas weekend offers benign weather, and good presents from Mother Nature. As everyone awakes on Friday to see what's under the tree, it will be a beautiful morning with clear skies and cold temperatures. It will be much better than last Christmas when it was pushing 80 degrees in many places. It will still on the cold side throughout the day with highs only warming up to near 50 as CAA continues in response to a polar vortex over the Great Lakes and a series of Canadian highs rotating through the NW flow aloft. Aside from a few high clouds, Friday should be a sunny day, and it'll be a nice Louisiana Christmas...if you can't have the snow, at least it'll be cold. The coldest weather will come over the remainder of Christmas weekend as high pressure strengthens and a re-enforcing front moves through Christmas night into early Saturday. Clear skies are expected through Sunday while temperatures gradually cool through Sunday. Saturday morning temperatures should be below freezing for much of the forecast area with the exception being the coast. Upper 20s to lower 30s are expected across the area, while afternoon highs top out between 45-50. The coldest morning of this forecast period, and perhaps of the season will come on Sunday with 20s expected area wide. A hard freeze is likely North of I-10 with a light freeze for the coastal marshes. CAA ceases during the day Sunday as the strong high moves nearly overhead. It will be chilly for the entire Christmas weekend with Sunday highs as many people head home in the upper 40s to lower 50s. At this time Christmas weekend looks precipitation free. For the end of the forecast period on Monday, changes will begin to occur as a Southerly fetch is re-established with the latest high exiting Eastward. It will be another cold morning with lows near freezing once again, but significant modification will occur for the afternoon with highs approaching the 60 degree threshold. No rain is expected at the end of the forecast period. At present, it appears there will be one more rain event before we close out 2009, and that looks to come just beyond this forecast period around Tuesday/Wednesday (29-30). How strong that system is, and how much rain it brings remains to be seen. The overall pattern seems cold and unsettled around New Years into the first week of 2010. Stay tuned for the latest on the severe weather threat looming for Wednesday.
This Date in Weather History...December 21: The first day of winter definitely lived up to the billing on this date in 1929 with a big snow across the Deep South. An exceptional storm produced snow from the Middle Rio Grande Valley of Texas to southern Arkansas. The storm produced 26 inches of snow at Hillsboro TX, 18 inches at El Dorado AR, and 14 inches at Bossier City, LA. Snow fell across portions of SE Texas and SW Louisiana as well. Only trace amounts occurred at Lake Charles, Lafayette, and New Iberia, but 5" fell at Alexandria, and 2" was reported at Beaumont.
Preliminary Numbers & Zone Forecast:
LCH 43/68 59/72 61/46 0 0 20 70 90 60
LFT 44/68 58/72 63/47 0 0 20 70 80 70
BPT 47/70 60/73 60/44 0 0 30 80 80 60
AEX 39/66 51/70 56/42 0 0 20 90 80 60
POE 40/67 52/71 57/43 0 0 30 90 80 60
ARA 40/69 58/72 64/48 0 0 20 70 80 70
Tonight...Clear and Not as Cold. Patchy Fog after Midnight. Low 43. Light SE wind.
Tuesday...Partly Cloudy and Warmer. High 68. SE wind 10-15 mph.
Tuesday Night...Mostly Cloudy with a 20% chance of rain. Areas of fog developing overnight. Much warmer. Low 58. SE wind 5-10 mph.
Wednesday...Areas of fog early. Cloudy, Warm, and Windy with a 70% chance of showers and thunderstorms becoming likely by afternoon. Heavy rainfall and severe weather possible. High 72. SSE wind 15-20 mph and gusty.
Wednesday Night...Cloudy, Windy, and Warm with showers and thunderstorms likely. Heavy rain and severe weather possible. Turning Cooler after midnight. Low 61. SSW wind 15-20 mph and gusty, becoming NNW at 20-25 mph and gusty after midnight. Chance of rain 90%.
Christmas Eve...Cloudy, Windy, and Cooler with a chance of showers and thunderstorms in the morning. Light rain and drizzle likely from late morning through mid afternoon before ending. High around 61 in the morning, then temperatures falling throughout the day to 46 by evening. NNW wind 20-25 mph and gusty. Chance of rain 60%.
Drew's 7 Day Outlook
Tuesday
12-22-09
Low: 43
High: 68
Rain: 0%
Wind: SE 10-15
Wednesday
12-23-09
Low: 58
High: 72
Rain: 70%
Wind: SSE 15-20
Thursday
12-24-09
Christmas Eve
Low: 61
High: 46
Rain: 60%
Wind: NNW 20-25
Friday
12-25-09
Christmas Day
Low: 36
High: 48
Rain: 0%
Wind: NNW 15-20
Saturday
12-26-09
Low: 31
High: 47
Rain: 0%
Wind: N 10-15
Sunday
12-27-09
Low: 28
High: 50
Rain: 0%
Wind: NE 5-10
Monday
12-28-09
Low: 32
High: 56
Rain: 0%
Wind: SE 5-10
...Marine Forecast...
Tuesday...Southeast winds 10 to 15 knots. Seas 2 to 4 feet.
Tuesday Night...Southeast winds 15 to 20 knots. Seas 2 to 4 feet building to 3 to 5 feet after midnight. Patchy fog. A chance of showers. Isolated thunderstorms after midnight.
Wednesday...Southeast winds 15 to 20 knots. Seas 3 to 5 feet. Patchy fog in the morning. A chance of showers and thunderstorms.
Wednesday Night...South winds 15 to 20 knots. Seas 3 to 5 feet. A chance of showers and thunderstorms.
Thursday...Northwest winds 15 to 20 knots. Seas 3 to 5 feet. Thunderstorms likely and a chance of showers.
...Tide Data...
Tuesday Tides @ Calcasieu Pass
Low: 11:38a.m.
High: 7:11p.m.
...Toledo Bend Pool Level...
170.18'
...Lake Charles Climate Summary...
Monday, December 21, 2009
Low: 35
Normal Low: 42
Record Low: 22-1901
High: 66
Normal High: 62
Record High: 78-1998
Precipitation
Today: 0.00"
Month to Date: 7.63"
Normal Month to Date: 3.02"
Year to Date: 72.17"
Normal Year to Date: 55.61"
Record: 4.45"-1923
Sunrise Tuesday: 7:05a.m.
Sunset Tuesday: 5:18p.m.
Tuesday Hunting Times: 6:35a.m.-5:48p.m.
...Lunar Table...
First Quarter- Thursday December 24
Full Moon- Thursday December 31
Last Quarter- Thursday January 7
New Moon- Friday January 15
Good night and God bless!
-DM-
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