4/13/04 FCST: Carolinas and Mid-Atlantic

George Tincher

I just happened to click on SPC's Day 3 outlook and was floored by some of the wording:

"ETA SUGGESTS THE ERN CAROLINAS WILL REMAIN EAST OF PRIMARY SURFACE
LOW/COLD FRONT FOR MUCH OF THE DAY...WITH SURFACE DEW POINTS WELL
INTO THE 60S. SHOULD THIS OCCUR AS ETA FORECASTS...A SIGNIFICANT
SEVERE WEATHER EVENT /INCLUDING DAMAGING TORNADOES/ COULD UNFOLD
TUESDAY AS EXTREME SHEAR OVERRIDES A MARGINAL TO MODERATELY UNSTABLE
WARM SECTOR".

I must say I hadn't even considered the East Coast and was already looking ahead to next weekend. Evidently, the above forecast is dependent in large part on what happens the day before and morning of, as on-going precip may lessen the threat significantly. But seeing a Day 3 with 25% severe probs and wording that strong definately grabs my attention.

-George
 
Originally posted by George Tincher
I just happened to click on SPC's Day 3 outlook and was floored by some of the wording:

\"ETA SUGGESTS THE ERN CAROLINAS WILL REMAIN EAST OF PRIMARY SURFACE
LOW/COLD FRONT FOR MUCH OF THE DAY...WITH SURFACE DEW POINTS WELL
INTO THE 60S. SHOULD THIS OCCUR AS ETA FORECASTS...A SIGNIFICANT
SEVERE WEATHER EVENT /INCLUDING DAMAGING TORNADOES/ COULD UNFOLD
TUESDAY AS EXTREME SHEAR OVERRIDES A MARGINAL TO MODERATELY UNSTABLE
WARM SECTOR\".

I must say I hadn't even considered the East Coast and was already looking ahead to next weekend. Evidently, the above forecast is dependent in large part on what happens the day before and morning of, as on-going precip may lessen the threat significantly. But seeing a Day 3 with 25% severe probs and wording that strong definately grabs my attention.

-George
Click to expand...

Thats the one of the strongest wordings I have seen in a Day 3 Outlook, the mention of "DAMAGING TORNADOES" is what really gets me. Will be interesting to see what happens.

I have also been watching late next week into next weekend, for the Plains/Midwest/and Ohio Valley regions...Looks like there is some potential for severe weather there. And to finish off the spectrum of weather events, I have been closely watching this system sneaking up from the Gulf for Monday/Tuesday, and just how much cold air will be in place across Michigan...Climatologically, Michigan gets some of its worst snowstorms in April...

Robert
 
After reviewing the 00Z Apr 12 ETA, I am interested but less impressed for Tuesday April 13. Pros for the eastern Mid-Atlantic: The ETA shows the low over WVa, shifting to western NC which gives backed winds through SE Va, E NC, and E SC. The jet at 250 mb is blasting across the area from the SSW at approx 100 knots. There are also high winds at the the 500 mb level at 60 (?streak approaching at 80) Unfortunately, the upper level winds are unidirectional from the SW until the surface where they are backed because of the low. The CAPE is forecast to be only about 500. I am also less impressed with the SRH of 150 (a narrow area of 200 at 1800Z) and LI's of 0. I agree that a long recovery of the airmass is needed. If an area of clearing and heating can persist, maybe there will be rotating storms. I am still getting my equipment ready though I think the best area will be too far to my south (Richmond, Va) to chase after I finish work at 5PM.
 
Wow - this is looking to be a big day if clouds can clear out early enough. Also could be a lot of minor/moderate flooding problems in the mountains.

I'm staying up for a while and watching this one, possibly heading east in the morning.
 
Nice Setup!

What a great setup for severe weather. Here is my page for tomorrows outlook, has my forecasts, discussions, and math , plus a couple maps, showing the tornado intensity feature.

My Target is Central Western in the State of Virginia if I was chasing!

http://www.powow.com/orbiteradds/severe.html

Kevin Martin
 
[Broken External Image]:http://www.waveformpc.com/southeast_outlook.GIF

Risk Region "1" - Slight chance of severe thunderstorms with damaging winds the primary threat.

Risk Region "2" - Moderate chance of severe thunderstorms with isolated tornadoes and damaging winds the primary threat.


Overall, looks like a decent setup for severe weather across the region tomorrow. Latest SFC analysis indicates a developing low pressure across eastern AL. A warm front extends ENE from this low, through central SC/NC/ and very extreme SE VA. Temps and dewpoints south of this boundary were in the mid 70's/low 60's respectively. Expect this warm front to lift northward, allowing warm and moist air to surge all the way into southern VA by 18Z TUE. Looking at the latest mid level RH fields from the 00Z ETA and 00Z RUC, the liklihood if any breaks in the clouds appear minimal. Even without strong diurnal heating, instability should rise with CAPEs of 1500J/KG available across much of the outlooked region/but more spefically in the risk "2" region, with temps in the mid 70's/dewpoints in the low 60's.

Helicity is over 400M2/S2 at 18Z across southern VA, but this is mainly along and north of the warm front, and well away from any instability. As the warm front lifts northward/instability builds into the northern NC and southern VA region, helicity values quickly drop off to 200M2/S2, but this should still be sufficient for a couple of tornadoes. Speed shear is excellent, as a 90KNT 500MB jet slides into the region, but this will also cause storms to be fast movers. Also of importance is a dry air intrusion which will be pushing in from the southwest at 700/500MB levels, which may enhance thunderstorm downdraft/microburst potential. Expect storms to fire around 18Z-21Z as the cold front sweeps into the region from the WSW...Continuing ENE through 00Z-03Z WED into the risk "2" region.

Given the above, expect the main threats to be a couple of tornadoes, a few hail reports, and damaging winds, but if SFC winds can back more southeasterly, tornado threat may increase accrodingly. Expect mostly linear/bow echo type storms, but isolated supercells may be possible. The greatest threat for tornadoes appears to be in the risk "2" region, where the best instability and low level helicities will be maximized around 00Z, albeit not the best combination.


Robert
 
It is 4:00AM EDT Tuesday, and I just arrived in Raleigh, NC after a 5 hour drive from Charleston WV. On the way, I plugged in the WxWorx at Winston Salem - and of course, from there to Raleigh watched intense storms move across my home state of WV just 2 hours behind me! Oh well, I hope this setup here in NC delivers as it looks. Will be watching the satellite before noon for clearing and picking a target then, most likely just north of RDU.

Going now to catch a few hours of sleep........
 
I am doing a quick analysis before work this A.M. With yesterday evenings upper air, there are winds blasting across central and eastern Va/NC from the SW at 110 at the 250 mb, 35 from the SW at the 500 mb level (and a jet streak at 55 currently over northern GA), and SW winds of 35-40 at the 850 level in NC and SE Va. On the surface at 1043 Z, temps/dewpoints are both in the mid 40's across VA, most of NC except the extreme eastern section of NC. Winds are from the NE, SE along the coast. The warm front is located from NE NC extending to the SW across NC into SC. The low is over northern Georgia. On the 9Z RUC, expected CAPE is only about 500 to 1000 over E Virginia, E North Carolina. Helicity Values will be about 200 across the area. I am not sure how far the warm front will move northward by this evening. I am also concerned about the extensive grunge that will retard heating. I am still expecting strong storms, brief tornadoes near the warm front with areas of backed winds at the surface. My initial target is Emporia near the VA/NC border. Gotta be at work in 10 minutes, can't analyze again until noon. If I am lucky, I cange t out a bit early to chase today.

Bill Hark
 
A nice storm just passed through Tucker County around 6:30 this morning. Nothing severe or anything but lots of nice cloud to ground lightning. Forecasts are calling for storms possible throughout the day/evening, and radar is looking promising, so maybe the fun isn't over yet! :D
 
I'm really worried about the big precip shield moving N into the forecast area. It is moving fast, but it looks doubtful it will move on out before peak heating can get started. Furthermore, it looks like the warm front is embedded in all that mess. If we do get clearing, it will be well after the warm front, and its associated low-level shear, has moved north. The precip is already encroaching on my target area- I didn't expect to be forced into a critical decision this early. I'm trying to decide whether to leave now and stay ahead of it, or wait here for the grunge to clear out and play my chances with better instability if it ever materializes. It's a tough call.
 
[Broken External Image]:http://www.waveformpc.com/southeat_outlook2.GIF

Risk "1" - Slight chance of severe thunderstorms with damaging wind the primary threat.

Risk "2" - Moderate chance of severe thunderstorms with damaging wind and an isolated tornado or two the primary threats.

Threat not looking as good as it was a few days ago, but still a somewhat good setup. Analysis indicates the cold front is across northeast GA as of 13Z...With a warm front lifting northward from northeast GA into extreme northeast NC. Temps along and south of the warm front were in the low to mid 70's, with dewpoints close to 70F in a few locations. Regional radar also shows plenty of precipitation occuring in SC, which has held temps down in the mid 60's there...And this precipitation should slide into NC/VA early this afternoon. Behind this main area of precipitation, a few breaks in the clouds have occured across GA, but it appears as though the break is filling in with low level clouds/towering cu.

Latest RUC shows CAPE building to 1500J/KG across the Risk 2 region by 21Z, just before the front comes through, with temps in the mid 70's and dewpoints in the upper 60's. Given the degree of low level clouds and precipitation, I am a bit concernecd that CAPE may not reach this high, unless some SFC heating does occur and is able to keep temps in the mid to upper 70's. Current meso-analysis from SPC suggests SFC BASED CAPE is already around 1500J/KG across ESE NC, just ahead of the main area of precipitation, so it may be possible. Using the RUC, helicity approaches 300M2/S2 across the Risk 2 region by 21Z, with a helicity maxima of 450M2/S2 located off-shore. Given the relatively low instability, anticipate the tornado threat to be diminished to only a few isolated tornadoes at best. Main threat still appears to be damaging winds given the dry slot which will be punching into the region at 700-500MB, and the very strong jet max at 500MB of close to 90KNTS.

Expect the current precipitation are to break up and continue NE into NC/VA...With more development expected along the cold front around 21Z. Expect the main action to come through the Risk 2 region around 21Z, with mainly linear/bow echo type storms, but an isolated supercell cannot be ruled out.


Robert
 
Dan...I can agree that this is a complex situation. Instability ahead of the main precip shield is AOA 1500J/KG...While instability drops off quickly as one heads into the precip shield. It looks like the cold front is riding right along or just behind this precip shield, leaving little chance for SFC instability to develop south of it. Several things could happen with this precip area -

1) Break up and allow for some SFC heating (temps only need to hit mid 70's)

2) Instability builds ahead of it (what is already occuring), with embeded isolated severe storm or two

3) Speeds up ahead of the cold front, allowing a gap between the precip and the cold front, with potential SFC heating in between.

4) The precip hangs around and pervents much in the way of instability (AKA total bust).

RUC keeps the precip hanging around, but still has some SFC instability of 1250J/KG-1500J/KG...All in all, its not looking very good, but if you must chase, the best region would be NE of Raleigh in NE NC and SE VA.

Robert
 
I got burned by this one. Not only did I see nothing in NC, I missed not one, but TWO rounds of intense storms back home in West Virginia while I was gone. WV saw a nice overnight MCS on Monday night-Tuesday morning, then things cleared out under the core of the low and fired again Tuesday afternoon. There were reports of hail covering the ground in the southeastern mountains! I watched everything as it happened on radar, 400 miles away. Ouch.
 
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