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mid-atlantic discussion

Mid-Atlantic Discussion – November 30 – December 1

The SPC has been slowly creeping the Slight severe area northwards, as is no surprise. At this point, I think that the Slight will end up along the SE PA and through the northern parts of NJ going into Wednesday morning. SNE may also have a “See Text” threat past 14Z.

Anyway…

As we get closer to the zero hour, it’s become easier to decipher the model trends as far as where the warm front will be able to lift to and who is under the gun Tuesday night into Wednesday morning. The main area of concern will be NC/VA/SoMD where the dynamics and the warm sector can interact the most efficiently to produce severe weather in the form of a linear SSW-NNE line of storms along the cold front. The severe threat will extend up through the northern parts of the region, but as the SPC stated mid-level stability is more of a factor in areas north and west of the D.C. area, which means less reports and slightly weaker winds along with a lesser chance for tornadoes.

The GFS appears to have a better grasp on the timing, but the NAM’s instability parameters are much more favored due to the mesoscale nature of the event. However, as we saw with the severe event from two weeks ago, neither model had a true grasp on how unstable the LL air actually was. This could be attributable to the strong advection of low-level instability by the LL jet, which was likely mishandled and under-represented by the models.

All-in-all, I wouldn’t be surprised if this ended up being similar to our 11/16 event, with the severe reports shifted about 150-200 miles south. D.C. impact from the line of storms will likely be around 4-6 AM Wednesday morning.

 

Very cold start this morning

We are getting quite a blast of arctic temperatures in late November. Temperatures this morning are into the low 20s in and around the DC region and below freezing temperatures as far south as central and North Carolina. Interesting, it is warmer along the Canadian border in Minnesota than it is in the DC area. Some slightly warmer temperatures are on tap today and tomorrow, but not much above normal (50°F). Mark will elaborate more on the meteorological side of things today or tomorrow.

Other things on tap are early initiation of the Great Plains Storm Chase Expedition 2011 which both myself and Mark will be going on this year. This will be Mark’s inaugural central plains chase and my seventh overall (going back to 1997 and since 2006). Most of the planning pages will appear on my subsite (ChaserQuest.com) which is part of my main site at WeatherWarrior.Net. The first page so far is a base Cost Worksheet using some past years data and current information to help properly budget for this trip.

The good thing about chasing this year is that MAD US Weather will be a source for following us with daily logs, forecasts, nowcasts and more being posted here in the blog. You’ll also be able to easily link to the live video stream when we are actively chasing, and track us even live even on down days.

Mid-Atlantic Discussion – November 16

Looks like we’re in store for another high shear/low CAPE event later today and into tonight as a developing low pressure system swings its cold front through the region. Given the vast amount of pre-frontal precipitation and cloud cover, along with the timing of the storms, I will not be chasing today. My expectations will be to see a weak line of thunderstorms form along the cold front this evening, which will push into eastern VA, NC and southern MD/Delmarva in the early AM. A mesoscale discussion for this area will probably be put up in the evening, with a 30-50% chance of a TOR watch in the next 24 hours.

I won’t expect to see more than a half-dozen severe weather reports in the region today, with no more than 1-2 tornadoes. It’s another day of SPC hyping it up for the region.

Mid-Atlantic Discussion – October 14

Going to bed soon, so the discussion will be brief. Upper-levels look excellent for storm potential if we can get the cells to fire. High shear/low CAPE day as early afternoon convection tries to fire up over SE VA and DELMARVA. Just got off the phone with Jason… looks like if we go we’ll be heading to the southern half of DELMARVA for the fun.

The SPC is rather bullish for the event, but the text does include the necessary “let’s not get to hasty” wordage:

…MID ATLANTIC COAST STATES INTO SOUTHERN NEW ENGLAND… CONVECTIVE POTENTIAL DURING THIS PERIOD WILL BE LARGELY DEPENDENT ON THE LOCATION OF THE INITIATION OF STRONGER SURFACE WAVE DEVELOPMENT…AND THE TRACK OF THE DEEPENING SURFACE CYCLONE. SPREAD AMONG THE MODELS/MODEL ENSEMBLES HAS BEEN CONSIDERABLE… BUT THE 13/12Z NAM IS NOW SIMILAR TO THE 13/00Z ECMWF… SUGGESTING RAPID PRESSURE FALLS MAY COMMENCE ACROSS PARTS OF EASTERN VIRGINIA…NORTHEASTWARD THROUGH NORTHERN MID ATLANTIC COASTAL AREAS THURSDAY AFTERNOON AND EVENING. IF THIS OCCURS… POTENTIAL WILL EXIST FOR NORTHWARD MOISTURE RETURN AND BOUNDARY LAYER DESTABILIZATION THROUGH THE WARM SECTOR OF THE DEVELOPING SURFACE LOW…COINCIDENT WITH STRENGTHENING LOW-LEVEL AND DEEP LAYER VERTICAL SHEAR. INSTABILITY MAY BE WEAK…BUT NAM FORECAST SOUNDINGS AND HODOGRAPHS ARE SUPPORTIVE OF THE RISK FOR SUPERCELLS CAPABLE OF PRODUCING TORNADOES…PARTICULARLY ACROSS PARTS OF SOUTHEASTERN/EASTERN VIRGINIA THROUGH THE DELMARVA PENINSULA AREA…BEFORE THE LOW MIGRATES OFFSHORE AND BEGINS TO OCCLUDE THURSDAY NIGHT.

Mid-Atlantic Discussion – October 11-12

Nice thing about today are the LL and ML lapse rates over the region, which could keep strong storms sustained for a long period of time once they develop. Shear is decent, but mostly unidirectional flow will favor some bowing segments. Cells should be relatively isolated today due to the limited moisture available. Taking a look at the SPC, I agree with it for the most part, but they could bring down the wind threat to areas S of the MA/PA border. TOR threat probably isn’t there… might get one TOR warning in PA today. I’m sure SPC is just playing it safe today give the potential for the strong winds and bowing segments to evolve a bit.

Mid-Atlantic Discussion – September 27-28

Monday

Strong, twisting winds aloft ahead of a cold front will be the big player as the cold front approaches the Mid-Atlantic Monday and pushes through on Tuesday (from the SE no less!). Weak to moderate thermal instability on the order of 250-750 J/kg CAPE will provide the additional fuel to initiate storms. The strongest threat for severe storms is in CeVA/WeVA as helicity values max out in this area, which creates the greatest twisting motion needed for tornadic development. The upper-level jet is not in the most favorable position for storm initiation, but it could aid in sustaining long-lived cells.

Once these storms get going on Monday, they have the potential to continue well into the evening and overnight hours so long as the CAPE holds out ahead of the storms. Because of the initiation zone and potential life span with these storms, the threat for severe weather could extend NE/NNE following the storm motion into NoVA and MD. The northern extent of best CAPE values does not extend much further N than D.C., so the mesoscale evolution in this region will have to be closely monitored throughout the day for local severe weather potential.

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Chase potential: 85%

Chase target(s):
SoVA/CeVA
NoVA/MD

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Tuesday

The severe threat pushes north and east as we head into Tuesday. The chance for severe thunderstorms will diminish quickly in the region as the cold front pushes through the area, taking the good helicity values with it. Remnants from Monday and/or quick initiation Tuesday morning could spring up severe cells along the Coast. The HPC has the surface front progged to be just east of BWI in a N-S orientation at 12Z, so the front may be moving too quickly for severe storms to initiate locally on Tuesday. Other than that, the synoptic setup is the virtually the same. The upper-level support will be marginally better in NJ Tuesday compared to SoVA/CeVA on Monday, but lower-level speed and directional shear will not be quite as robust.

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Chase potential: 15%

Chase target(s):
DELMARVA/NJ

Mid-Atlantic Discussion – September 22

WARNING: Technical discussion.

While there is a cold front approaching the area from the NW, the overall synoptic setup leaves much to be desired. The main player for severe weather today will be weak mesoscale forcing along with the cold front, which is visible this morning as lines of showers drape NE-SW over central OH, western PA and additionally over the southern Appalachians. Synoptically, a large area of high pressure moving off the coast leaves behind plenty of dry air in the region.

Upper-level forcing remains weak in our area as the jet stream remains well to our north. The jet could provide enough upper-level divergence for a small tornado risk in NoPA/EaPA and in NoNJ and SoNY, but speed shear will be weak further south. There is marginal directional shear in the lower levels throughout the region, but flow remains unidirectional in the mid and upper levels.

Steep low-level lapse rates will aid in creating strong outflows from mature storms, some of which could get to the severe level. CAPE and LI values are good, but dry air near the surface could hinder TCUs from forming. Storms that do form will largely be pulse-type, with isolated bowing cells possible.

All-in-all, I would expect today to perform much like the severe weather events we experienced early in the summer, which led to an under-performance based on the SPC outlooks. The severe threat in areas south of I-80 in central PA will be marginal at best.


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Chase potential: 25%

Chase target(s):
EaPA/NJ