…GULF COAST STATES TO SERN ATLANTIC COAST…

AS MENTIONED IN THE SYNOPSIS…SEVERAL MIDLEVEL IMPULSES ARE EVIDENT IN MORNING WATER VAPOR IMAGERY TRANSLATING GENERALLY EWD ALONG LOW-LEVEL BAROCLINIC ZONE. VISIBLE SATELLITE IMAGERY SHOWS MORE EXTENSIVE CLOUD COVER THIS MORNING ACROSS THE TN VALLEY INTO THE CNTRL/SRN APPALACHIANS. HOWEVER…AREAS TO THE S WILL LIKELY EXPERIENCE STRONG DAYTIME HEATING. WHEN COUPLED WITH LOWER/MID 70S DEWPOINTS…ENVIRONMENT WILL BECOME MODERATE TO STRONGLY UNSTABLE BY AFTERNOON. ALSO OF NOTE…12Z OBSERVED SOUNDINGS AND CURRENT VWP DATA SUGGEST A BELT OF 30-35 KT FLOW PRESENT IN THE 3-6 KM AGL LAYER…WHICH WHEN COMBINED WITH THE STRONG INSTABILITY WILL LIKELY FOSTER CORRIDORS OF MORE INTENSE STORMS…PRIMARY IN ADVANCE OF THE MORE PERSISTENT MIDLEVEL IMPULSES. THE PRIMARY HAZARD WITH THESE STORMS WILL BE DAMAGING WIND GUSTS.

The clouds preventing heating have, for the most part, dissipated. All that remains are lower level cumulous pockets and those wont affect how the atmosphere heats. Now that the atmosphere is heating, we will gain some fairly strong CAPE values, but mainly by evening. These storms look like they will show up mainly at or after 7 PM, with 2-3 j/kg CAPE and some pretty nice Helicity values. I haven’t seen helicity like this over Tennessee in a while, so it could be nice. This helicity will also allow for the possibility for tornadoes, with the EHI model showing values ranging from 1-3 over a large area, mainly over western portions of the mid state.

So, in summary…

Thunderstorms will be widespread across the state, mainly this evening but a scattered thunderstorm cannot be ruled out before then. There will be large amounts of instability and shear, allowing for thunderstorms with threats mainly being damaging winds/hail. Tornadoes cannot be ruled out as well.

I am hoping to catch one of the earlier storms, and maybe even tonight’s storms. Check back for updates!

Update: all of Middle Tennessee is under a Flash Flood Watch

DISCUSSION AND 48-HOUR OUTLOOK

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AT 100 PM CDT…1800 UTC…THE CENTER OF TROPICAL STORM ALEX WAS LOCATED NEAR LATITUDE 22.9 NORTH…LONGITUDE 93.6 WEST. ALEX IS NOW MOVING TOWARD THE NORTHWEST NEAR 13 MPH…21 KM/HR. A GRADUAL TURN TOWARD THE WEST-NORTHWEST IS EXPECTED ON WEDNESDAY. ON THE FORECAST TRACK…THE CENTER OF ALEX WILL APPROACH THE COAST OF NORTHEASTERN MEXICO AND SOUTHERN TEXAS ON WEDNESDAY AND MAKE LANDFALL WEDNESDAY NIGHT. MAXIMUM SUSTAINED WINDS ARE NEAR 70 MPH…110 KM/HR…WITH HIGHER GUSTS. STRENGTHENING IS FORECAST DURING THE NEXT 36 HR OR SO BEFORE LANDFALL…AND ALEX IS LIKELY TO BECOME A HURRICANE LATER TODAY. TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 140 MILES…220 KM FROM THE CENTER. NOAA BUOY 42055…LOCATED ABOUT 65 MILES SOUTHWEST OF THE CENTER…RECENTLY REPORTED 1-MINUTE MEAN WINDS OF 38 MPH… 61 KM/HR…AND A WIND GUST OF 45 MPH…72 KM/HR. THE MINIMUM CENTRAL PRESSURE REPORTED BY AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT IS 981 MB…28.97 INCHES.

The storm surge forecast is showing heights ranging anywhere from 3 ft to 6 ft as the hurricane moves in over southern Tx/Mexico. This is not a good thing because of how close to sea level most of the gulf is. If you are at 3 ft or below, I would recommend taking some precaution before this storm moves in. At one point this hurricane was forecast to reach Category 2 strength, but the latest observations indicate that it will remain a Category 1 hurricane until it makes landfall, where it will weaken. Again, the center will make landfall on the Tx/Mex border, but the rest of the storm will impact the majority of the gulf. Take action as needed, but thankfully this wont be too serious. However, please take local National Weather Service advisories seriously. Be safe.

This outflow boundary that is surging ahead of this line can do one of two things. On one side, it can act as a lifting mechanism, creating more thunderstorms. Or, on the other side, it can cut off and kill these current thunderstorm’s updrafts, causing it all to die. With the current speed and trajectory of the outflow boundary (also known as a gust front), I am guessing it will do the latter. I will keep monitoring things and radar and update as things happen.

The SPC has placed all of Middle Tennessee under a Slight Risk for severe storms today. We have FINALLY picked up some wind shear, so now it looks more favorable for longer living and more severe storms as opposed to the pulse storms we have been having all week. Here is what the SPC says about today…

…TN VLY/SRN APPALACHIANS INTO ERN KY…NC…SRN VA…

MODERATE TO STRONG INSTABILITY WILL DEVELOP WITH DAYTIME HEATING ALONG PORTION OF COLD FRONT CROSSING PARTS OF KY/TN…AND ALONG PREFRONTAL TROUGH OVER VA/NC. MID/UPR LVL FLOW AND ASCENT WILL INCREASE OVER THESE AREAS AS REGION IS GLANCED BY SRN FRINGE OF GRT LKS TROUGH. 35-40 KT WNWLY 700 MB WINDS COULD SUPPORT ORGANIZED STORMS WITH DMGG WIND/HAIL…ESPECIALLY OVER NRN PARTS OF THE REGION. THE SVR THREAT COULD PERSIST INTO MID EVE IN VA/NC.

The SPC even dared to include us in todays tornado risk. At the moment it is a very low risk, but I could honestly care less. Even a small risk gives me hope for something! The models do agree with the possibility of a weak tornado, thanks to the wind shear we have today. However, if a tornado were to develop I would imagine it would be brief. Still, a tornado is a tornado and there is a chance (albeit extremely small) for one today.

So, at the moment a cold front is digging southeast towards us. This will be the mechanism to initiate storms today, and you can see on this radar image that it is already storming our way. My guess is that scattered thunderstorms will arrive in the northern part of the state between 11 AM and 12 PM. However there is a lot of room for error in that guess, so don’t hold me too hard to it. Main risk is large hail and damaging winds, so be looking out for that.

THE NWS STORM PREDICTION CENTER HAS ISSUED A SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

NORTHEASTERN             ARKANSAS

SOUTHERN KENTUCKY

MISSOURI BOOTHEEL

FAR NORTHWESTERN MISSISSIPPI

WESTERN AND MIDDLE TENNESSEE

EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 215 PM UNTIL 800 PM CDT.

HAIL TO 1.5 INCHES IN DIAMETER…THUNDERSTORM WIND GUSTS TO 70 MPH…AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

DISCUSSION…THUNDERSTORMS HAVE DEVELOPED ALONG A ZONE OF WEAK CONVERGENCE IN NERN AR/WRN TN AND ARE EXPECTED TO DEVELOP NEWD INTO SRN KY. STRONG INSTABILITY COMBINED WITH STRONGER WINDS ALOFT WILL LIKELY RESULT IN STORMS WITH SEVERE HAIL…LOCALIZED DOWNBURSTS AND HEAVY RAINFALL.

The probabilities for the watch are:

Tornadoes: Very Low (<5%)

EF-2+ Tornadoes: Very Low (<2%)

Severe Wind: Low [10 or more wind events (20%)]

65 kt+ Wind: Low (20%)

Severe Hail: Moderate [10 or more hail events (30%)]

2″+ Hail: Low (20%)

Probability of 6 or more combined severe hail/wind events (60%)

The tornado risk for today is nearly non existent due to lack of helicity (wind shear), and therefore the SPC doesn’t even show a tornado risk over Tennessee. I don’t know what the SPC is looking at, but they are saying that there is enough deep layer shear to sustain these multicell lines, and warrant the risk of hail and damaging winds. I sure hope they are right, because I am itching for a good storm! There are great CAPE values for the day, and I have also noticed that there is very weak capping over Middle Tennessee today. This may be beneficial in preventing the weaker storms from developing. Then again, maybe not… I am still learning a lot about forecasting, so who knows. Enough of my blabbering, here is what the SPC has to say.

…DELMARVA WWD ACROSS THE SRN LOWER OH AND TN VALLEYS…

SEVERAL FEATURES SHOULD AID IN SCATTERED TO NUMEROUS THUNDERSTORMS DEVELOPING ACROSS THE REGION THROUGH THE AFTERNOON HOURS. FIRST FEATURE IS REMNANT MCV…CURRENTLY APPROACHING WRN PA. CURRENT MOTION/EXTRAPOLATION PLACES THIS FEATURE INTO S CENTRAL PA/MD PANHANDLE BY MID AFTERNOON. WEAK CONVECTION HAS ALREADY DEVELOPED AHEAD OF THIS SYSTEM OVER WV…AND SHOULD INTENSIFY AS MOVES INTO VA/MD PANHANDLE/SRN PA THIS AFTERNOON… REFERENCE MESOSCALE DISCUSSION 784.

FURTHER WEST…ANOTHER WEAK SURFACE LOW WAS LOCATED IN FAR NWRN OH…WITH A SURFACE TROUGH EXTENDING WSWWD INTO CENTRAL MO. THIS TROUGH WILL MOVE SLOWLY SWD AND CONVERGENCE WILL BE ENHANCED AHEAD OF IT AS AN UPPER THERMAL TROUGH SHIFTS EWD ACROSS THE TN/OH VALLEYS. DEEP LAYER SHEAR AT 20-30 KT WILL BE SUFFICIENT FOR SUSTAINED MULTICELL STORMS…AND IN CONJUNCTION WITH MODERATE INSTABILITY…SEVERE HAIL AND DAMAGING WINDS WILL BE POSSIBLE DURING THE AFTERNOON/EARLY EVENING HOURS.

Right now there is a mesoscale discussion in effect for western Tn, where a Severe Thunderstorm Watch appears possible. There may be one issued for northern Mid Tn later, but for now I will post the discussion.

AREAS AFFECTED…

NERN AR…BOOT HEEL OF MO…WRN TN…KY CONCERNING…

SEVERE POTENTIAL…WATCH POSSIBLE

VALID 031758Z – 031900Z

A PRE-FRONTAL ZONE OF LOW LEVEL CONFLUENCE CURRENTLY EXTENDS FROM NERN AR…NEWD ALONG THE OH RIVER INTO NRN KY. THIS AXIS WILL LIKELY BECOME THE FOCUS FOR STRONG THUNDERSTORM DEVELOPMENT OVER THE NEXT FEW HOURS AS BOUNDARY LAYER CONTINUES TO WARM/DESTABILIZE. GIVEN THE MARGINAL DEEP LAYER SHEAR IT APPEARS MULTI-CELL UPDRAFTS WILL BE COMMON WITHIN MODERATELY UNSTABLE AIRMASS. LOCALLY STRONG DOWNBURSTS AND HAIL COULD ACCOMPANY THE MORE ORGANIZED STORMS.

So, updates will come later as things progress. I would say it is safe to assume that if you are within the slight risk area, you will see some t-storms today. I just took a look at the SPC Hourly Mesoscale Analysis, and i see more favor in those models. As you can see, thunderstorms are already developing in western Tn. I will be sure to update if we get a severe thunderstorm watch.

The SPC has expanded its slight risk for today into northern and western Middle Tennessee. A squall line is pushing in from Kentucky, with the main threat being large hail and deadly lightning. I am forecasting this from my phone, so I have no idea what the timing is on the squall but I can tell you a weak tornado or two cannot be ruled out. The SPC has us under the 2% tornado risk, so we will see how that goes. Now I will post the SPC graphics.

So, I will see if I can add more info to this post, but that is all for now. This could be a fun one =).

“Sources of uncertainty in this seasonal outlook

1: Predicting El Niño and La Niña (also called ENSO) impacts is an ongoing scientific challenge facing climate scientists today. Such forecasts made during the spring generally have limited skill.

2: Many combinations of named storms and hurricanes can occur for the same general set of climate conditions. For example, one cannot know with certainty whether a given climate signal will be associated with several short-lived storms or fewer longer-lived storms with greater intensity.

3: Model predictions of sea-surface temperatures, vertical wind shear, moisture, and stability have limited skill this far in advance of the peak months (August-October) of the hurricane season.

4: Weather patterns that are unpredictable on seasonal time scales can sometimes develop and last for weeks or months, possibly affecting seasonal hurricane activity.”

The outlook says that there is an 85% chance that this hurricane season will be above normal, 10% chance of a normal season, and a 5% chance of a below normal hurricane season. The outlook also says that if this forecast ends up being true, and hurricanes tend to be on the upper end of the forecast, this 2010 hurricane season could be one of the most active on record. The Climate Prediction Center says the following in their outlook:
“We estimate a 70% probability for each of the following ranges of activity this season:

14-23 Named Storms,
8-14 Hurricanes
3-7 Major Hurricanes
An ACE range of 155%-270% of the median.”

ACE is the Accumulated Cyclone Energy index, and it forecasts the intensity and longevity of hurricanes for a particular season. A quote about ACE, “According to NOAA’s hurricane season classifications, an ACE value above 117% of the 1950-2000 median reflects an above-normal season. An ACE value above 175% of the median reflects an exceptionally active (or hyperactive) season.” In other words, there may be a lot of hurricanes this year. However, this does not predict hurricane landfall, only formation. The Climate Prediction Center does say, however, that historical records show that active seasons have an increase in hurricane landfall.

Yet another quote, “Because of the ongoing oil crisis in the Gulf of Mexico, we are including some historical statistics of tropical cyclone activity for this region (excluding the Bay of Campeche) based on past above normal seasons. These statistics do not represent an explicit forecast for tropical cyclones in the Gulf of Mexico during 2010, as it is impossible to reliably predict such activity so far in advance. Historically, all above normal seasons have produced at least one named storm in the Gulf of Mexico, and 95% of those seasons have at least two named storms in the Gulf. Most of this activity (80%) occurs during August-October. However, 50% of above normal seasons have had at least one named storm in the region during June-July.”

So, this hurricane season may be one bumpy ride! As tropical storms develop over the next few months, I will make forecasts here on the website and try to constantly update as much as I can. Having family live right on the gulf, some of which were badly affected by hurricane Ike, it is definitely something personal. My hope this year is to be able to intercept a hurricane, but I would much rather no hurricanes at all. So, as we come into hurricane season, get your plan together.

…LWR MS/TN VLYS ENE TO THE MID-ATLANTIC…

BANDS OF MAINLY ELEVATED TSTMS WILL CONTINUE ALONG AND N AFOREMENTIONED FRONT AND ASSOCIATED OUTFLOW BOUNDARIES FROM THE SRN OZARKS ENE TO THE MID ATLANTIC STATES THROUGH THIS MORNING AS MOIST /WITH PW AOA 1.50 INCHES/ LOW-LVL FLOW CONTINUES. COMBINED WITH MODERATE TO STRONG HEATING…SUFFICIENT CAPE /2000-3000 J PER KG/ SHOULD DEVELOP FOR NUMEROUS NEW STORMS ALONG THE SRN FRINGES OF MORNING ACTIVITY. GLANCING INFLUENCE OF GRT LKS TROUGH MAY SUPPORT ORGANIZED ACTIVITY FROM KY NEWD TO THE MID ATLANTIC CST.

40-45 KT WSW MID-LVL FLOW ON NRN FRINGE OF UPR RIDGE SHOULD SUPPORT ORGANIZED STORMS/STORM CLUSTERS AND PERHAPS MARGINAL SUPERCELLS…ESPECIALLY FROM KY/TN TO THE CNTRL APPALACHIANS…AND OVER CNTRL/SRN PA TO THE MID ATLANTIC CST. EMBEDDED BOWS MAY YIELD BOTH DMGG WIND GUSTS AND SVR HAIL. THE SVR THREAT SHOULD DIMINISH THIS EVE.

Also, this risk will continue throughout the weekend, with severe thunderstorms expected tomorrow (saturday) and possibly even sunday night. When all is said and done, a possible 2-3 inches, if not locally higher, will have been dropped on the state. This may cause a few flood problems with the already bloated rivers, so keep an eye out. Click on this image to the right to show an animation of how the next few days will pan out. Also, I thought I would post what the Hazardous Weather Outlook says about the next few days.

.DAYS TWO THROUGH SEVEN…SATURDAY THROUGH THURSDAY

THE COLD FRONT THAT PASSES THROUGH TODAY…WILL BECOME STATIONARY NEAR THE ALABAMA BORDER ON SATURDAY…THEN BEGIN MOVING NORTH AS A WARM FRONT BY SUNDAY. ISOLATED SEVERE THUNDERSTORMS WILL REMAIN POSSIBLE ON SATURDAY…WITH DAMAGING WIND GUSTS…LARGE HAIL…AND HEAVY DOWNPOURS.

IN ADDITION TO THE SEVERE WEATHER POSSIBLE ON SATURDAY…MIDDLE TENNESSEE IS EXPECTED TO RECEIVE BETWEEN TWO AND THREE INCHES OF RAINFALL THIS WEEKEND AND INTO MONDAY…WITH LOCALLY HIGHER AMOUNTS POSSIBLE. FLOOD PROBLEMS MAY DEVELOP AS THE WEEKEND PROGRESSES… ESPECIALLY IN AREAS WHERE HEAVY THUNDERSTORM RAINS REPEATEDLY OCCUR.

Currently there are storm firing up around Middle Tennessee, on with a severe thunderstorm warning on it for large hail and winds in excess of 60 MPH. Thunderstorms are expected to progress as the day goes on, and then convection will weaken by evening hours. Here is todays HWO.

.DAY ONE…TODAY AND TONIGHT

A COLD FRONT WILL PUSH ACROSS THE MID STATE TODAY AND PRODUCE THE LIKELIHOOD FOR THUNDERSTORMS…A FEW OF WHICH COULD BECOME SEVERE… WITH DAMAGING WIND GUSTS…LARGE HAIL…AND HEAVY DOWNPOURS.

Pretty self explanatory, isn’t it? I took a brief look at the RUC forecast models, and was quite shocked at how much instability there is. Right now we have roughly 3000 j/kg CAPE values across a large portion of the state! It made me wonder why we were under such a minimal risk… well, I took a look at the helicity forecast and saw why. We have VERY little wind shear, only enough to support hail risk. Tornadoes seem unlikely at this point, due to the severe lack of wind shear. So don’t expect anything too crazy. You may see some decent sized hail, but other than that the severity is small.

A BROKEN BAND OF SHOWERS AND THUNDERSTORMS WILL MOVE ACROSS THE AREA TONIGHT WITH PASSAGE OF A COLD FRONT. BRIEF DOWNPOURS ARE EXPECTED…WITH QPF AMOUNTS UNDER ONE QUARTER INCH. SOME OF THE STORMS COULD BE BRIEFLY SEVERE WITH STRONG WINDS BETWEEN 6 PM AND MIDNIGHT.

Some of the models have changed since then, but it is the same general idea. Before I get any further, some of you are probably wondering if this will affect any of the flooding. The answer is no. As said in the above statement, rainfall will be under 1/4 of an inch, and also very localized if more. This should not be a continuance of the flooding, so do not worry there. This cold front will pass fairly quickly and won’t linger like last weekend, which caused the flooding.

Now, it has been a VERY long time since I have done this, so I am rather excited. I will be pulling out the good ‘ol Skew-T chart! For those who don’t know, a Skew-T chart is a product that shows different characteristics of the atmosphere for that hour. Weather balloons are sent up, and they collect data that is compiled onto the chart.  Now, a strong reminder is that a Skew-T chart is only valid FOR THE HOUR IT WAS CREATED. However, we can use it to look at the characteristics of the atmosphere that may apply to the whole day.

Moving on, the Skew-T chart has picked up a nice little bit of instability, and a really strong cap. Instability is expected to increase throughout the day as daytime heating weakens ad eventually breaks the cap. That will happen around the same time the cold front pushes through, allowing thunderstorm development. Also, the nice little indent in the dewpoint part of the graph shows an ok potential for hail, one of the main threats.

(click on images to enlarge them) Now, here is the part that gets a little tricky… earlier models were showing not so great levels of wind shear, but as the day has progressed the models have increased the amount of helicity. Same goes for EHI . The EHI models were low, but now are pretty high. What does this mean? I have no idea… I am not too terribly experienced, but it is possible we will have a slightly larger tornado risk issued later. That is just speculation, I am still learning a lot but we will see how things pan out. Plus, with Lift Index at -6 I have no doubt there will be some form of severe weather, I just doubt how severe it will be. It will be interesting to see how it all pans out, so check back for updates!