Archive for the ‘Chase Potential’ Category

The latest from the NHC was very interesting on 97L….

SHOWERS AND THUNDERSTORMS ASSOCIATED WITH A LOW PRESSURE SYSTEM
LOCATED ABOUT 900 MILES EAST OF THE LESSER ANTILLES HAVE CHANGED
LITTLE IN ORGANIZATION DURING THE DAY.  HOWEVER...AIRCRAFT DATA
FROM A RESEARCH MISSION BEING CONDUCTED BY THE NATIONAL CENTER FOR
ATMOSPHERIC RESEARCH...AS WELL AS SATELLITE DATA...SUGGEST THAT
THIS SYSTEM IS ALREADY PRODUCING TROPICAL STORM FORCE WINDS IN A
SMALL AREA NORTH OF THE CENTER.  ONLY A SMALL INCREASE IN
ORGANIZATION OF THE SHOWER AND THUNDERSTORM ACTIVITY WOULD RESULT
IN THE FORMATION OF A TROPICAL STORM...AND ADVISORIES COULD BE
INITIATED LATER THIS AFTERNOON OR TONIGHT.  THERE IS A HIGH
CHANCE...90 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS AS IT MOVES GENERALLY WESTWARD AT ABOUT 20
MPH.

Earl is getting ready to pound the islands as he continues to intensify pretty rapidly this evening and has become a category two hurricane.  Hurricane warnings are in effect and hurricane conditions are expected for the islands over the next 12-24 hours.  Earl is now expected to become a dangerous hurricane while passing near the islands so please take the warnings seriously. 

97L is still showing a decent spin and we are looking for a n increase in convective development overtop the system this evening.  If this happens to occur….we could be dealing with a tropical depression on Monday and possibly tropical storm Fiona soon after/

Earl has became a hurricane today and developed a rather intense inner core over the last couple of hours.  The CDO or Earl is becoming well defined and he is on his way to become a major hurricane within the next 24-36 hours if not sooner than that.  The forward speed has slowed slightly and is allowing for the storm to become more organized and compact.  The northern Leeward Islands should have there hurricane preparations completed NOW!

Earl is showing a much better outflow signal today as Danielle has been pushed toward the north and sheared apart as the upper trough axis pushes toward the east north of Earl.  This should eventually be an influence in turning Earl more northerly within the next 72 hours and will hopefully keep it away from the east coast of the US.

Behind Earl…..we have 97L….future Fiona.  This system has the biggest potential to bring big trouble to the US in the form of some kind of landfall.  The latest 12z European shows a disaster situation for portions of the northern Gulf as a major hurricane barrels toward the coastline in about 10 days.

That is likely a Category 3-5 storm in the Gulf per this run of the European weather model.  Surface pressures of 939mb support winds in the 130+ mph range which would devastate the coast line.  We will continue to monitor this situation as the days go by and things begin to develop.  Keep in mind….Fiona isn’t even a storm yet but many of the weather models and ensembles to develop it into a large, major hurricane. 

This evening Tropical Storm Earl continues to get better organized east of the British and US Virgin Islands with maximum sustained winds of 60 mph once again.  The system has had a hard time becoming well organized due to its very fast motion over the last couple of days. 

The microwave imagery once again this evening shows that Earl is not very symmertrical in terms of a well defined inner core.  Over the next day or so he is expected to slow down a bit and be less influenced by Danielle’s outflow….therefore we expect him to become a major hurricane over the next 2 days.  Track is still very tricky at this point, but anyone along the east coast of Florida to the Carolinas should keep a close watch on the track and intensity forecasts of Earl.

Our Gulf low this afternoon is still trying to gain some organization, but it seems some northeasterly dry air and potentially some shear is hampering thunderstorm devleopment on the north and east side of the low level center of circulation.  This may be a limiting factor of development over the next day or so as this system moves westward now.  It won’t spend much time over water and should make landfall along coastal Louisiana by Wednesday.  The NHC gives it a 60% chance of development before making landfall……we believe that there is a 50/50 shot.  It is unlikely that we will pursue this system given its lack of organization.  We will save our dime for something better to come down the road…..hopefully. 

Yesterday this thing was centered over Alexander City, AL; however it is now back on track for a date with the Gulf of Mexico once again.  Ex-TD #5 could become a TD and even a tropical storm over the next 24-48 hours as it continues southward and re-emerges back over the open, warm waters.  Currently, the low level center is located near Dothan, Alabama with plenty of convection on the SW side of it.  Isolated thunderstorms are developing around the main circulation…..mainly due to daytime heating processes.  This is expected to continue through the afternoon and evening hours as it moves south.

Over the next day the sytsem  is expected to continue to oraganize and intensify potentially into a tropical cyclone.  The National Hurricane Center has already scheduled a RECON visit to this system during the day tomorrow….and many more if development does indeed occur. 

The main influence of the system continues to be the upper level ridge to the north over the Midwest and Tennessee Valley regions.  This will also give the low a favorable upper level environment for strengthening.  The determining factor will be how long this area of low presure is able to stay over the open waters. Remember….the waters in the northern Gulf are fairly shallow but they are hot.  The further south this thing is able to go….the higher probability it will have to become a substantial storm because of the deeper content of warm water.

Current expectations are for this system to become a moderate tropical storm with winds of 50-60 mph before making landfall once again along the coast of Louisiana.  Details still remain sketchy at this point due to some variation in guidance, but things will become more clear over the next day as we see how much the low can organize.  There is a slim possibility that this could become stronger than forecast and make a run at hurricane status depending on it’s life span over water.  As with most tropical cyclones….expect the unexpected as intensity forecasts are very low confidence.

There is a possibility that we could be making a run toward the Gulf Coast for this system if it looks to have a greater impact than we currently expect.  Stay tuned for further updates as our plans change and this system organizes.

Given the image above, I wouldn’t be shocked to see Alex form over the next day or so.  The system is beginning to get a nice CDO (central dense overcast) overtop a mid level and potential low level circulation.  The thunderstorm flare-up is more condensed than the last couple of days and conditions are becoming more favorable for organized tropical development.  The system has been labeled Invest-93L.

The latest forecast model tracks are scary….given the oil spill crisis in the Gulf of Mexico along with the boiling hot water and weak shear forecast ahead of this developing system.  We don’t see this becoming a "major" US hit, but that can certainly change in a hurry given the potential conditions.  Track models are varying big time so I won’t go into specifics at this point on a potential forecast path, but we will get more into those possibilities later this weekend.

A weather watch is now looking possible for portions of Central Alabama this afternoon as the environment is becoming very unstable with afternoon heating and sunshine.  The SPC will upgrade portions of the area to a convective slight risk on the 1630z update….or around 11:30am.  We will monitor the situation and keep you updated on the sitaution….the SPC text and statement of the MCD follows…

 AREAS AFFECTED...NRN MS...NRN AL...NWRN GA...ERN TN AND WRN NC

   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

   VALID 191530Z - 191630Z

   THREAT FOR MAINLY ISOLATED DAMAGING WIND WILL EXIST THIS AFTERNOON
   WITH STORMS DEVELOPING FROM NRN MS THROUGH NRN AND CNTRL AL...NWRN
   GA...ERN TN AND WRN NC. THIS AREA IS BEING UPGRADED TO A SLIGHT
   RISK...AND A WW IS POSSIBLE DEPENDING ON CONVECTIVE TRENDS.

   AT MID-DAY AN EXPANSIVE OUTFLOW BOUNDARY IS MOVING SOUTHEASTWARD
   THROUGH ERN KY AND ERN TN THEN WWD INTO NRN AL AND NRN MS. THE
   ATMOSPHERE SOUTH OF THIS FEATURE IS ALREADY MODERATELY UNSTABLE WITH
   2000-2500 J/KG MLCAPE. STRONG DIABATIC HEATING OF THE BOUNDARY LAYER
   WILL RESULT IN FURTHER DESTABILIZATION THIS AFTERNOON. FLOW ALOFT IS
   WEAK WNWLY ALONG NRN PERIPHERY OF UPPER RIDGE. HOWEVER...GIVEN THE
   PROPENSITY FOR STORMS TO ORGANIZE INTO MULTICELL LINES ALONG THE
   OUTFLOW BOUNDARY...A SLIGHTLY GREATER CONCENTRATION OF STRONG TO
   DAMAGING WIND GUSTS WILL BE POSSIBLE THAN IS USUALLY EXPECTED IN A
   PULSE STORM ENVIRONMENT.

We’ve been a little slack on the blog so I figure we better get something out here ahead of time so we aren’t beaten to the punch. After the events of this past weekend, it certainly looks like another major severe weather threat could be on tap for parts of the Ozarks/Mid South this coming weekend. On to the maps…

By 21z on Friday….a large positively tilted trough axis with a coupled upper jet structure will begin to eject eastward out of the Plains states and affect the Mid-South.  Of most concern is that the Mid-South will be in the left exit region of the subtropical jet streak.  Given this coupled structure, divergence will be remarkable over the region by early afternoon as wind profiles also become increasingly supportive of supercells and the potential for long track tornadoes given the kinematic environment coming into place. 

Step two in this game will be the potential energy available at the surface.  Each model run is consistently raising these numbers from Central LA into AR and W MS.  CAPE values of over 2000J/kg are likely.  Given that the model is projecting temperatures in the 70′s for most of the day, these could even be a little on the low side.  Very little forcing and a EML (elevated mixed layer), otherwise known as a capping inversion, across the area should keep junk convection at bay.  If this were to occur….the model could be low on temperatures and some areas could reach the lower 80′s across portions of LA/AR/W MS.  This would provide a “loaded gun” environment and be more like a time bomb waiting to go off.

The lifted index values by the afternoon tell me that initiation is about ready to occur as some frontal forcing begins to arrive from the west.  By this time….the atmosphere is extremely unstable and ready for the rapid formation of supercells and tornadoes.  There is plenty of fuel for the storms to go well after dark as well. 

Low level shear…..which is on the order of 40 knots will allow for rapid development of storm rotation as supercell thunderstorms initiate.  These storms will likely move between 25-35kts which is not to bad in terms of speed….so these storms should be much more chase-able for us than the system this past weekend. 

So, what does this mean for the Mid-South?  Get ready for a possible severe weather outbreak with the potential for long track tornadoes to be involved.   Some of these tornadoes could be strong to violent given the thermodynamic and kinematic environments in place.  Damaging winds and large hail will also be a threat in any supercell thunderstorms that can develop.  We will be moving our chase status to high.  Stay Tuned….

This evening we have began looking at a few prospects for the potential for a couple of severe storms on Thursday afternoon across portions of the state…..particularly west of I-65.  The factors are not very impressive at this point, but if more low level moisture can become established ahead of the cold front we might deal with a few issues.  To the maps….

This map is valid at 7PM on Friday evening.  You can see the main shear is exiting the area ahead of the cold front where some surface based instability has developed along the Alabama/Mississippi state line.  This is due to a tongue of 60° dewpoints that try to nose northward ahead of the cold frontal boundary from about Reform to Tuscaloosa on southward. 

This chart notes where the best low level moisture corresponds with the cooler temps aloft advecting in ahead of the upper trof axis.  0-3KM CAPE values in excess of 200+ J/kg are considered very high.  This would lead me to believe that we could have some surface based storm development into Thursday evening.  Given the ejecting shear I believe that we could have a couple of supercells with the potential for damaging winds and large hail along with some developing line segments along the frontal boundary.  Surface flow will veer ahead of the front really killing low level shear values.  However, if the shear lags behind what is currently projected we could deal with a couple of tornadoes.  We will need to monitor low level moisture closely….because any increase would allow for higher instability values over a larger area and potentially lead to a more enhanced threat of severe storms. 

The Storm Prediction Center in Norman has outlined much of Mississippi, West Alabama, and West Tennessee in a Slight Risk of severe storms for Thursday.  Stay tuned for further updates on this impending situation.  We will be changing the chase status to slight at this time.