Merry Christmas everyone!
SIGNIFICANT SEVERE WEATHER EVENT EXPECTED FOR CHRISTMAS DAY OVER PARTS OF THE GULF COAST STATES
The main body of this synopsis will be regarding the current DAY 2 Convective Outlook in which a portion of the SLIGHT risk area has been upgraded to a MODERATE risk area.
The SPC has issued a SLIGHT risk of Severe Thunderstorms overnight for portions of CENTRAL-E TX AND WRN LA…
The current developing storm system is forecast to strengthen tonight as it progresses eastward. From the SPC message text:
TX/LA AREA OVERNIGHT…CONVECTIVE POTENTIAL WILL INCREASE OVERNIGHT…FIRST N OF SFC FRONT LATE EVENING THROUGH PRE-DAWN HOURS WITH MOST INTENSE CELLS POSING HAIL THREAT. ACTIVITY MAY DEVELOP PROGRESSIVELY CLOSER TO FRONT THROUGH END OF PERIOD…EVENTUALLY BECOMING SFC-BASED WITH SUPERCELLS AND BOW/LEWP FEATURES POSSIBLE. AS SUCH…THREAT EXISTS DURING LAST FEW HOURS OF PERIOD FOR SVR HAIL/GUSTS. TORNADO RISK EXISTS FROM ANY SFC-BASED AND RELATIVELY DISCRETE CELLS IN WHAT SHOULD BE VERY FAVORABLE SHEAR ENVIRONMENT…BUT COVERAGE OF SFC-BASED TSTMS IS TOO UNCERTAIN ATTM FOR MORE THAN 5% UNCONDITIONAL TORNADO RISK.
DEEP SHEAR AND LOW-LEVEL HODOGRAPHS EACH ARE EXPECTED TO STRENGTHEN OVER RETURNING WARM SECTOR TONIGHT…AS 60S F SFC DEW POINTS CONTRIBUTE TO 1000-1500 J/KG MLCAPE BY 12Z ALONG AND S OF FRONT OVER SE TX. LARGEST LOW-LEVEL HODOGRAPHS WILL BE ALONG FRONT…WHERE BACKED SFC WINDS WILL CONTRIBUTE TO EFFECTIVE SRH 300-500 J/KG. SRH ALSO WILL BE FAVORABLE FARTHER S OVER COASTAL AREAS IN WARM SECTOR…HOWEVER FCST SOUNDINGS SUGGEST PRONOUNCED EML-BASE INVERSION BETWEEN 850-700 MB THAT MAY RESTRICT TSTM COVERAGE AWAY FROM BOUNDARIES.
Put plainly, any tornado activity may be limited close to the frontal feature given the presence of a 850-700 mb inversion which should limit Tstm activity away from boundaries.
During my analysis, various parameters suggest to me, that there could be an increase of the current 5% tornado probability as this system continues to strengthen later into the evening. Analysis of SRH and 2 tornado parameter models indicate this may be a possibility, although the main threat based on soundings are damaging straight line Tstm winds and hail associated with any elevated supercell storms and bow echoes.
Residents should monitor local NWS statements, watches and warnings as issued, and tune to NOAA Weather Radio. I will have interactive maps posted at the end of this discussion, so you may stay up to date on any significant severe weather for your area.
The SPC has issued an upgraded Day 2 Convective Outlook, to include a MODERATE risk area.
Probability of severe weather within 25 miles of a point.
Hatched Area: 10% or greater probability of significant severe weather within 25 miles of a point.
The aforementioned system is forecast to continue to strengthen. Analysis of the 500 mb and 200 mb level maps today indicate a pretty potent jet at both levels, with the exit region situating itself over the SLIGHT risk area. Albeit most of the forecast parameters which have not been updated since earlier today, do not correlate with the SPC text. However, careful analysis of F5 Data severe weather forecast software, combined with the forecast parameters provided in the SPC outlook, indicate the potential for a significant severe weather event. Based on Significant Tornado Parameters, Helicity, Moisture, Shear, and projected CAPE values of 1000-1250 J/KG near the coast, there will be sufficient energy and rotation within the atmosphere for some STRONG TORNADOES within the MODERATE risk area. These could become long tracked in nature. Again, since some of the data posted has not exactly matched up, I believe to gather a better idea of the strength of severity, I will be reviewing soundings in the a.m. from around the risk area, which will yield better information as to the various forecast parameters. I will be monitoring to see if this has the potential to become a PDS (Potentially Dangerous Situation) based on what the forecast parameters indicate tomorrow. Should this occur, this office will issue a statement to that effect. Sometimes these situations will prompt SPC to issue a Tornado Watch tagged with a statement PDS if conditions warrant. If your area SHOULD come under one of thee POSSIBLE watches, PLEASE…pay particular attention to your surroundings and be prepared to take IMMEDIATE action if a Tornado Warning is issued. Also based on some parameters, I am not ruling out the possible extension northward to the borders of MS/AL of a possible tornado threat…Soundings in the a.m. will determine this.
There is another SLIGHT risk issued in the Day 3 Outlook, and will be included in tomorrow’s synopsis
I will have an update tomorrow.
SPC CONVECTIVE WATCH DISPLAY
SPC MESOSCALE DISCUSSIONS DISPLAY
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST
MEMBER WEST CENTRAL FL AMS
CERTIFIED SKYWARN OFFICIAL STORM SPOTTER (advanced)