Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0109 AM CST Fri Dec 15 2017 Valid 171200Z - 181200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE LOWER MISSISSIPPI VALLEY...
...SUMMARY... Thunderstorms will likely develop on Sunday across parts of the central Gulf Coast region including the lower Mississippi Valley. A few damaging wind gusts and a marginal tornado threat will be possible.
...Lower Mississippi Valley... A shortwave trough will move quickly northeastward into the mid Mississippi Valley on Sunday as southwest mid-level flow remains in place across the Gulf Coast Region. At the surface, moisture advection will continue across the lower Mississippi Valley where surface dewpoints are forecast to reach the lower to mid 60s F across southeastern Louisiana and southern Mississippi by midday. Isolated to scattered thunderstorms are forecast to be ongoing in southwestern Louisiana at the beginning of the period with this convection spreading eastward into the lower Mississippi Valley by early afternoon. NAM and GFS forecast soundings at New Orleans, Louisiana and Mobile, Alabama at 21Z Sunday afternoon show weak instability with strong deep-layer shear. Although MLCAPE values are only forecast to be in the 250 to 500 J/kg range, 0-6 km shear values could be as high as 50 kt. This would be enough for a marginal severe threat making isolated damaging wind gusts possible with the stronger thunderstorms. 0-1 km shear of 25 to 30 kt will also make storm rotation possible and a marginal tornado threat can not be ruled out. As moisture advection continues and the shear environment is maintained during the evening and overnight period, a marginal severe threat could persist across the region.
AREA FORECAST DISCUSSION...CORRECTED National Weather Service New Orleans LA 357 AM CST Fri Dec 15 2017
.SHORT TERM... An upper trough will be swinging across the Mississippi Valley this morning. At the surface, observations show a cold front currently moving southward across the CWA. At the same time, the sub-tropical jet is carrying Pacific moisture across Mexico to the northern Gulf coast. Showers will develop over portions of the forecast area as a result of this overrunning moisture. The bulk of rain will be limited to areas from New Orleans southward. Exactly how far north the showers actually reach is quite challenging. Thinking it will be around I-12. In terms of temperatures, the combination of overcast skies and cold air advection will likely keep temps fairly steady throughout the day.
These showers will fade and shift south as the front continues towards the central Gulf of Mexico. Decreasing clouds and colder dry air mass moving in will bring down nighttime lows quite a bit. Expecting mid 30s for most locations with a few in Mississippi touching the freezing mark Saturday morning.
.LONG TERM... Models still show a cutoff low that is currently stuck over the Baja of California getting pickup by a Pacific trough and racing northeast to the mid Mississippi Valley this weekend. In response to this, a surface low and appendant frontal boundary will develop over east Texas, with the front stalling over the CWA Sunday. Numerous showers and a few thunderstorms are likely to develop as frontogenesis takes place. While rain will begin from west to east Saturday night, most of the higher pops shouldn`t come in until Sunday.
The boundary will likely remain stalled along the northern Gulf Coast through Tuesday as troughing is maintained west of the CWA. This will lead to bouts of rain moving across the area rather than constant downpours. Confidence in the forecast is normal through this period and below normal thereafter. The main difference is the the GFS clears out moisture Wed and Thu with the aforementioned Pacific trough, while the ECMWF is slower with the progression of this trough. Didn`t make too many changes from previous forecast and went with a blend of solutions for pops.
Last Edit: Dec 15, 2017 5:36:20 GMT -6 by Helicity
BULLETIN - IMMEDIATE BROADCAST REQUESTED Special Marine Warning National Weather Service New Orleans LA 741 AM CST SUN DEC 17 2017
The National Weather Service in New Orleans has issued a
* Special Marine Warning for... Lake Pontchartrain and Lake Maurepas...
* Until 915 AM CST
* At 741 AM CST, severe thunderstorms capable of producing waterspouts were located along a line extending from Manchac to 14 nm south of Lake Maurepas, moving northeast at 35 knots.
HAZARD...Waterspouts and wind gusts 34 knots or greater.
IMPACT...Waterspouts can quickly form and capsize boats...damage vessels and oil rigs...and create suddenly higher waves. Make sure all on board are in a secure location and wearing life jackets. Expect wind gusts in excess of 34 knots and suddenly higher waves. Boats could sustain damage or capsize. Make sure all on board are wearing life jackets. Return to safe harbor if possible.
* Locations impacted include... The Mid Point Of The Causeway Bridge, Lake Pontchartrain/Lake Maurepas, Orleans Marina, Eden Isle and Kenner.
Post by thibodauxwx on Dec 17, 2017 8:21:48 GMT -6
It looks like us folks here in Thibodaux and Houma are in a training effect with this line moving through right now, my yard never floods but we have standing water right now, it’s been pouring for a while and looks like there is still more to come. And if all days my weather station is down for some reason, I have an old fashion rain gauge out back , I’ll check it shortly
SKYSUMMIT President | Director of OperationsAdministrator
I'm in Galveston right now. When that line rolled through, it was friggin awesome with horizon rain, waves crashing on the seawall...very much like a tropical storm. There were even a few transformers that blew, but I believe it stayed below severe criteria.
Winter 2018/2019 Number of Freezes: 9 CWOP ID: DW2721, CoCoRaHs Station: LA-TG-11 NWS's Ponchatoula/Hammond Area's COOP Member, Station ID 16-7425-08, PONL1