On the 7:30 a.m. CDT update to the Day One Severe Weather Outlook, the SPC slightly expanded the Slight Risk area, moving it north of Birmingham. Here is a sneak peek at the latest severe weather info for this afternoon’s forecast package.
TIS THE SEASON: Alabama is a climatologically favored place for severe weather the first week of April. On this map from the SPC, you can see where significant tornadoes are most likely across the nation during the first week of April.
There is a bulls eye over North Alabama the first week of April where the probabilities are highest for having a significant tornado (EF2 or greater). This peak period actually blooms over North Alabama around March the 11th and expands until April 22nd, when it begins to shrink and consolidate with a similar maximum over Oklahoma and northern Texas. The Sooner State becomes the sweepstakes winter in the significant tornado department. The maximum sets up over Oklahoma and North Texas by April 15th. It peaks at about a probability of over 0.35% and expands, but gradually lessens and shifts north toward Iowa and Nebraska by the middle of June.
FORTUNATELY even though this is prime season for significant tornadoes in our area, the probability that one will occur within 25 miles of any place in the maximum area is only 0.25%. Not 25%, but 0.25 percent, so well less than 1%.
UNFORTUNATELY: Today is one of those days when there may well be a few significant tornadoes across the state. The best chance of a significant tornado is over southwestern parts of the area, south and west of a line from Cuba to Pine Hill to Atmore, except for southern Mobile and Baldwin Counties. But there is a decent chance (5%) that there will be a tornado within 25 miles of you if you live north of the significant risk area, but south of the official Slight risk issued by the SPC. The northern boundary of the 5% tornado probability and slight risk area extends from near Hamilton to Carbon Hill to Hoover to Tuskegee. We will have to watch out for damaging winds as well, especially late tonight as the threat transitions from discrete supercells to a squall line.
SECRET WEAPON: You say it doesn’t feel like severe weather out there today. But the secret weapon of severe weather outbreaks will be brandished by our system tonight: the low level jet. As a strong upper level trough progresses eastward, surface low pressure near the Texas coast will move northeast and intensify this afternoon and evening. By 10 p.m., it will be near Vicksburg. As the low strengthens, an area of strong winds at about 5,000 feet will develop over Louisiana. This low level jet as it is known, will do two things. It will transport lots of warm, moist air northeastward rapidly and the fast moving air will cause significant wind shear in the lower layers of the atmosphere. Neither of these pieces of news are ever good in a severe weather situation.
PARAMETER PARTY: Let’s peg the geek meter for some severe weather parameters off the morning run of the 4 km NAM. As noted in the previous paragraph, low level wind shear will not be a problem. The low level jet will produce 0-1 km helicities on the order of at least 250 m2/s2, and they will most likely be higher. Bulk shear values, which is a measure of the difference in wind speed with altitude will be high as well, meaning storms won’t have any trouble staying organized. The question will be whether there is sufficient instability. The models might actually be downplaying the eventually CAPE values over Alabama tonight. Currently, the NAM depicts around 500-750 j/kg. That Is sufficient for severe weather in Alabama, especially in light of the shear available. And they could go higher.
DYNAMIC SYSTEM: I am always concerned when I see rapid transformations of the atmosphere like this one. As noted earlier, the morning and early afternoon did not have a typical severe weather feel. The low level jet will take care of that, pushing temperatures from mostly 50s in the rain-cooled air this afternoon to the middle 60s after midnight. And dewpoints will climb from around 50F this afternoon to the lower 60s tonight. That sort of dynamic change is troublesome. So this will be a system we have to watch carefully. The NWS Birmingham noted this morning that similar systems in the past almost always have produced at least one tornado, but that they were usually weak. At the same time, they noted that the prospects of underestimated instability might make for a more serious situation.
While we can’t rule out a tornado anywhere across Central Alabama overnight and early Monday morning, the best chance will be south and west of a line from Haleyville to Springville/Pell City on to Tuskegee, Ozark and Seaside. This area, which is also the slight risk area for the day, was expanded slightly on the 8:00 a.m. update from the SPC. There is an enhanced area of slightly higher tornado probabilities (10% chance with in 25 miles) over southwestern parts of Alabama, south and west of a line from Livingston to Camden, Pine Apple and then east of Evergreen. It does NOW include coastal Mobile and Baldwin Counties.
HOW THE SYSTEM WILL UNFOLD: Moderate to heavy rain with embedded thunderstorms moved over South and South Central Alabama this morning. More light to moderate rain was moving northeast by mid-morning and will affect the rest of Central Alabama into the afternoon, increasing with time. Most of the thunder should be limited to South Alabama, although some lightning was showing up southwest of Demopolis at 9:30 a.m. There will be some more thunder through the afternoon.
As the surface low moves into Central Mississippi this evening, a warm front will be pushed north over Central Alabama. This will be accompanied by increasing rain and storms. While those shouldn’t be severe, they will be loud. Locations south of the front will be in the warm sector with rising temperatures and dewpoints and increasing instability leading to strong to severe thunderstorms. Discrete storms ahead of the front will be especially troublesome given the magnitude of the wind shear. Rain and thunderstorms will continue for much of the night across much of the area. The main activity should push east of I-65 by lunchtime, continuing to affect East Central and Southeast Alabama with a severe weather threat. There will be some lingering showers into the afternoon over western sections into the afternoon and eastern sections into the evening.
FLASH FLOOD THREAT: A Flash Flood WAach went into effect at 10 a.m. CDT for all of Central Alabama. It will be in effect until Monday afternoon. Widespread 1 to 2 inch rainfall amounts with some locally higher amounts between 3-4 inches could cause flooding.
TEMPERATURES: Readings have been slow to climb over Central sections due to the clouds and increasing showers. Areas that get rain earlier may hae their highs limited to the upper 50s today, while you will find 60s the further north you go. Lows tonight will actually come early in the evening in many spots as the warmer air moves in. Official lows will probably be in the upper 50s, but by morning, readings will be in the middle 60s. Highs tomorrow will likely rise to near 70F, before tumbling back into the lower and middle 40s Monday night.
There is a threat of severe weather this afternoon over South Alabama, spreading northward into West Central Alabama south of US-82 this evening and over areas south of US-78 and west of I-65 during the overnight. The SPC has the southwestern quarter of Alabama in a “slight” risk for severe weather, their standard severe weather forecast.
Thunderstorms will intensify through the day along the Gulf Coast across southern Louisiana, southern Mississippi and southwestern Alabama. Damaging winds and tornadoes will become a problem this afternoon over this region, including New Orleans, Lafayette, Hattiesburg, Meridian, Mobile and Jackson, Alabama. The SPC has a 10% tornado probability (chance of one within 25 miles of a point) in this area, including a hatched area, which indicates a likelihood of significant (EF2 or greater tornadoes.) Here are the tornado probabilities. The slight risk outlook corresponds to the 5% tornado threat area.
The threat of damaging winds and tornadoes will lift northward with the warmth, moisture and instability Sunday evening, overspreading West and Central Alabama. Accordingly, the SPC has their standard basic severe weather risk in place for this afternoon and tonight south and west of a line from Hamilton to Jasper to Hoover to Rockford to Tuskegee to Ozark and back to Destin.
CAPE values will rapidly increase to 500-750 j/kg as far north as US-82 by 1-2 a.m. and this moderate instability will spread up to areas south of US-78 and east of I-65 before sunrise. So it appears there will be the requisite instability. And wind shear will be in good supply as well, with 0-1 km helicity values reaching 200 m2/s2 by evening. This combination could produce tornadoes and damaging winds in the risk area. The greatest threat will be south of a line from Livingston to Camden to Atmore and back around to Mobile.
WATCH THE WARM FRONT: Wind shear will be enhanced along the northward moving warm front during the late afternoon and evening hours. We will have to watch storms along this boundary for the threat of tornadoes as well.
SEVERE WEATHER THREAT SHIFTS EASTWARD: Monday morning, the threat of severe weather will shift eastward over southeastern and East Central Alabama ahead of the cold front that will move eastward. The bulk of the rainfall should be east of I-65 by late morning with just a few lingering showers into the afternoon.
DON’T FORGET: There is a flash flood watch that will go into effect at 10 a.m. this morning for all of Central Alabama.
The NWS in Birmingham has issued a flash flood watch that will go into effect at 10 a.m. Sunday morning for much of Central Alabama.
The watch includes:
Autauga, Barbour, Bibb, Blount, Bullock, Calhoun, Chambers, Cherokee, Chilton, Clay, Cleburne, Coosa, Dallas, Elmore, Etowah, Fayette, Greene, Hale, Jefferson, Lamar, Lee, Lowndes, Macon, Marengo, Marion, Montgomery, Perry, Pickens, Pike, Randolph, Russell, Shelby, St. Clair, Sumter, Talladega, Tallapoosa, Tuscaloosa, Walker and Winston Counties. It will go until 1 p.m. CDT Monday.
Widespread 2-3 inch rainfall amounts are expected between late tonight and early Wednesday, with some isolated heavier amounts. The bulk of the rainfall will occur between noon Sunday and noon Monday.
A line of severe thunderstorms continues to push eastward across western Mississippi, southeastern Arkansas and northern Louisiana tonight. They are prompting numerous severe thunderstorm warnings and at least three tornado warnings. No reports of actual tornadoes on the ground in the Delta counties of Mississippi yet tonight. The warnings are based on radar indications.
Tornado watches cover the Mississippi Valley from Central Illinois southward to Central Mississippi and Northeast Louisiana. They also curve back across southern Arkansas and northern Louisiana.
The activity over western Mississippi will arrive in western Alabama around 5 a.m.
The tornado threat has increased a bit to our west early this morning as wind shear has been increasing. But we still expect these storms to weaken after they get into Alabama toward sunrise. They won’t reach the I-59 corridor until later in the morning, between 8:30 a.m. and 10 a.m.
The SPC continues their standard slight risk severe weather outlook through the overnight hours for the northwestern corner of the state. Then a slight risk outlook is posted for the rest of the day for the rest of Central Alabama, with the exception of the I-85 corridor.
No changes in thinking this morning on the severe weather threat.
A mesoscale convective system is pushing eastward across southern Arkansas early this morning, trailing southwestward into northern Louisiana and northeastern Texas.
The activity is still nearly four hours west of the Alabama border.
The new SPC Day One Severe Weather Outlook is out. It includes the standard slight risk for all of Central Alabama except for the I-85 corridor, and excludes Franklin, Colbert and Lauderdale Counties in Northwest Alabama.
This is the outlook that goes into effect at 7 a.m. CDT:
It reflects the expected weakening of the storm complex to our west tonight and foretells of more development by afternoon ahead of the cold front. The afternoon storms will present the threat of damaging winds and hail, but the tornado threat will be negligible.
Here is the text of the new Day One:
…CUMBERLAND PLATEAU TO MS/AL..
EXTENSIVE CONVECTIVE OVERTURNING IS PREVALENT FROM THE LOWER OH
VALLEY TO TEXARKANA THIS MORNING. MOST OF THIS ACTIVITY SHOULD BE
ONGOING AT 12Z WITHIN A SWATH OF 50S/60S SURFACE DEW POINTS AND
SUFFICIENT DEEP-LAYER SHEAR FOR ORGANIZED LINE SEGMENTS. BUT
CONVECTION SHOULD LARGELY OUTPACE THE PLUME OF MODERATE TO STRONG
INSTABILITY W OF THE LOWER MS VALLEY. IN ADDITION…LOW-LEVEL WINDS
AND FORCING FOR ASCENT WILL SUBSIDE WITH SRN EXTENT AS THE PRIMARY
CYCLONE SHIFTS NEWD. THUS…MCS/S SHOULD BE IN A WEAKENING STATE
DURING THE LATE MORNING…BUT WITH A RISK FOR ISOLATED DAMAGING
WINDS. IN THE WAKE OF MORNING ACTIVITY WHERE POCKETS OF STRONGER
HEATING OCCUR…ISOLATED STORMS SHOULD DEVELOP ALONG THE COLD FRONT.
A MODEST COMBINATION OF SHEAR/INSTABILITY/LIFT MAY POSE A SEPARATE
/LARGELY MARGINAL/ SEVERE RISK.
Everything is quiet across Central and North Alabama this evening. Skies are partly to mostly cloudy with temperatures still in the lower 70s with a few upper 60s over eastern Alabama. Dewpoints are mostly in the 50s still, with some lower 60s over southwestern sections. Tuscaloosa’s dewopint was up to 60F in Tuscaloosa. A steady southerly wind is blowing at about 10 mph.
The surface low tonight is passing northeast of Kansas City. It is not impressively strong (about 1002 mb) and is pretty far away. That’s good for us.
Everything is still well west of the Mississippi River. The closest storm to western Alabama right now is 220 miles west northwest of Pickens County, over southeastern Arkansas. That storm is not severe at this time.
The main line is still back over eastern Texas into southwestern Araknsas. The NWS Shreveport has just issued a severe thunderstorm warning for several counties in southwestern Arkansas and northern Louisiana north of Shreveport. Here is the radar with warnings displayed.
A new tornado watch is coming shortly for southern Arkansas, northern Mississippi and southwestern Tennessee. It will include Memphis, Greenville and Oxford.
No tornado warnings are in effect nationally now.
There could be strong to severe storms overnight as the storms get into western and northwestern Alabama. The line should be weakening as it pushes into the I-59 corridor, but we will monitor them all through the night.
Here is a loop of the 4 km NAM showing the storms getting into northwestern Alabama between 4:30-5:30 a.m. with the main activity reaching western Alabama around 6:30 a.m. and then the I-59 corridor around 10 a.m.
The model shows additional development ahead of the slow moving cold front during the afternoon. The airmass will still be relatively unstable during the afternoon and some of the storms could be strong to severe. Hail and damaging winds will be possible.
The new SPC Day One Severe Weather Outlook will be out within the hour and we will post it here as soon as it is received.
A nice looking Sunday is in progress across Central Alabama. A few low stratocu clouds hung around Northeast Alabama through the overnight and into the early morning hours, but they quickly dissipated after sunrise leaving bright blue skies for everyone. Temperatures hovered around 40F this morning. It was 37F in Tuscaloosa, 40F in Birmingham and 43F in Anniston. A few high, fibrous clouds were trying to work their way across South Central Alabama, and others are working across Mississippi, but they were of no consequence.
Temperatures will top out in the middle 60s generally, with a few upper 60s in southern sections and several places closer to 62F over northeastern sections.
FROSTY MORN: With clear and absolutely calm conditions overnight tonight, lows will drop into the middle and upper 30s on average. This will result in frost that could damage sensitive plants. Be sure to protect budding flowers or plants that are vulnerable.
DRY RUN: The next chance of rain will not come before late Thursday, so enjoy this upcoming fine weather. Monday will feature middle 70s with near total sunshine and a light easterly wind shifting around to the southwest. A few clouds may show up around sunset as a front tries to approach the area on Tuesday. But a strengthening subtropical high off the coast of the Carolinas will repel the approaching boundary and its attendant cooler airmass., sending it packing back to the north.
It will remain to the northwest Wednesday, keeping thunderstorm chances over parts of Texas, Oklahoma, Arkansas and Missouri for the most part. It may edge close enough to bring shower and thunderstorm chances to western Tennessee, northern Mississippi and northwestern Alabama by Thursday. We will flirt with 80F Tuesday and Wednesday, as well as perhaps Thursday. Rain and storms Friday morning will likely lower highs a bit Friday afternoon.
Something you don’t see everyday…
A severe thunderstorm warning in Hawaii.
The NWS Honolulu issued only four severe thunderstorm warnings last year and no tornado warnings.
BULLETIN – EAS ACTIVATION REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE HONOLULU HI
1055 AM HST SAT MAR 29 2014
THE NATIONAL WEATHER SERVICE IN HONOLULU HAS ISSUED A
* SEVERE THUNDERSTORM WARNING FOR…
THE ISLAND OF MOLOKAI IN MAUI COUNTY
* UNTIL 1130 AM HST
* AT 1047 AM HST…RADAR SHOWED A SEVERE THUNDERSTORM CAPABLE OF
PRODUCING QUARTER SIZE HAIL…AND DAMAGING WINDS IN EXCESS OF 60
MPH. THIS STORM WAS LOCATED 2 MILES NORTHWEST OF KAUNAKAKAI…OR 41
MILES NORTHWEST OF KAHULUI. THIS STORM WAS MOVING EAST AT 10
* LOCATIONS POTENTIALLY IMPACTED INCLUDE…
KAWELA AND KAUNAKAKAI.