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mid-atlantic discussion

Mid-Atlantic Discussion – July 4th holiday weekend

Expect temperatures to be near normal to above normal this holiday weekend, with highs in the upper 80s to mid 90s Saturday through Monday (for the lower elevations). Scattered clouds should bring some relief from the sun, with isolated showers and thunderstorms possible each day.

Organized storms and severe weather seems unlikely during this period, but individual storms could be strong to severe, with hail and gusty winds. Most storms should form in the mid afternoon to early evening hours, with little morning and overnight activity expected.

…just your normal summer weather! Shouldn’t be too different from the weather we have been seeing over the last couple of weeks.

Mid-Atlantic Discussion – Jun 23-24, 2011

It’s been awhile, but I felt motivated to write about Thu/Fri… it’s been so long since the last organized severe threat (i.e. not this pulse-storm and failed MCS crap we’ve been getting) that I felt a true discussion was in order.

Though the main low is expected to be stacked/decaying as it pushes into the eastern U.S., the system should remain organized enough for the region to experience severe storms this Thursday and Friday. Along with the upper-low, the system also features a moderate jet streak ejecting out of the base of the trough, which will help give the storms upper-level support and increase storm longevity. A cold front moving through the region could help initiate/sustain storms as well.

The atmosphere will be somewhat unstable as well, though cloud cover and precipitation remain concerns as mid-level lapse rates could suffer. Regardless, so long as there is some sunshine, temperatures should climb into the lower 90s during the afternoon, creating favorable low-level lapse rates. Coupled with decent/good wind shear, the atmosphere seems favorable for at least some severe weather as we head into the end of the work week.

Mid-Atlantic Discussion – Apr 20, 2011

SPC has been playing up what I consider to be a more marginal event in the Mid-Atlantic today. The main threat is for individual cells or small lines of damaging winds from storms that are expected to develop along the cold front as it passes through this afternoon/evening. Storms should be isolated, but those that do form have good mid-level lapse rates to gain momentum off of. Somewhat dry low-levels and downsloping WSW-erly surface winds will inhibit these storms to a degree, with high-level clouds and high LCLs also working against storm development.

Any storms that do form should die off quickly once the instability fades around sunset. There won’t be any chasing today, but there’s still a chance that some storms could develop locally to video and photograph. It certainly doesn’t look like a widespread event, and I don’t expect much beyond some spotty reports to come out of today’s storms.

 

Mid-Atlantic Discussion – Apr 11-12, 2011

A wall of precip. to our west will be slowly pushing eastward today as a secondary low develops over the TN valley. Timing the line will be rather difficult as the secondary low slows the progression of the front, and the threat for severe storms could extend into early afternoon tomorrow in the far eastern parts of the region.

The main concern with this system will be damaging winds along and just ahead of the cold front. The northern end of the line, which has a more E-W tilt than the bottom part of the line, will drape itself across the northern parts of the region. The northern part of the line down to the change in the orientation of the line could be an enhanced tornado risk, though the risk is still on the low side. This area is expected to be in WV, SoPA, NoVA, and NoMD as we head into the late afternoon through the overnight hours. The main tornado threat should stay north and west of most of the region, but we’ll see what happens.

Tentative chase area is SW PA or S-Cent. PA.

Mid-Atlantic Discussion – Apr 4-5, 2011

This may be my only update for the week as I have quite a busy schedule which includes moving.

The severe threat looks to be pretty marginal overall for the region Monday afternoon into Tuesday morning, with the key issue being timing as the cold front works with limited/no instability. West Virginia has the greatest risk for severe as a few pre-frontal storms and a QLCS (quasi-linear convective system) move into the westernmost parts of the region the late afternoon and evening hours. The line of storms will weaken and push east during the overnight hours, moving off of the coast by late morning or early afternoon. These storms are currently modeled to hit the DC/BWI region around morning rush hour, depending on the overall speed of the line. During the overnight hours, these storms are expected to be rather weak and/or elevated, but a loose line should be able to make its way through the coastal areas.

A positively-tilted upper-level trough will become neutral as an UL vort. lifts N+E through the region. At the same time, an UL jet will intensify just W of the cold front, putting the Mid-Atlantic in the right-exit region of the jet. The dynamics that we need for severe weather are there because of these UL features along with the surface front, but without any thermal instability that potential could be lost for most of the region as the storms skirt by. Directional shear isn’t terribly impressive for most of the region, with largely unidirectional winds out of the SW. The biggest threat will be from wind as a LL jet with a speed max of 70-80 kts around 900mb orients itself over the region. It would take minimal surface-based convection to bring severe-level gusts of 50+ kts to the surface, but getting surface-based convection will prove to be difficult once the late evening hits. Dry air out ahead of the front will also hurt instability as the column tries to saturate just ahead of the front. The risk for hail and tornadoes is minimal threat for most of the region, with an isolated risk for those in the western parts of WV.

18z NAM and GFS showing somewhat better potential for strong/severe winds tomorrow night into Tuesday morning compared to previous runs with weak instability in the mid-levels… will continue to monitor possible nocturnal instability as just a small amount is needed for the severe winds to occur.

Jason and I are thinking about heading to SW PA to intercept storms just ahead and along the cold front during the late afternoon and early evening as instability fades. Directional shear should be decent enough there for isolated tornadoes if the storms can tap into enough instability.

Mid-Atlantic Discussion – Mar 23, 2011 and this weekend

TOMORROW:

A rather unusual severe weather setup as a low pressure system rides along a frontal boundary that is NW-SE oriented from central OH into central MD. Warm-sector instability on the order of 500-1000+ J/kg SBCAPE will develop over WV and western VA during the afternoon, which will help initiate a few areas of showers and storms. A convergence area over the Appalachians will help trigger storms early, with better instability upstream ahead of the southward-moving cold front that will move through OH and WV during the late afternoon and early evening. Things will look a little messy on radar at first, but eventually some strong/severe cells will form in the westernmost parts of the region. The main threat from these storms will be hail and wind damage, with an isolated threat for a few tornadoes. Speed shear is good with this system, but winds will be largely unidirectional, which will hinder tornadic development. Upper-levels are somewhat favorable as left-exit region divergence and some support from the 500mb vort. provide good synoptic lift.

As these storms push east into the Apps. and coastal plain, they will likely lose some intensity as the surface instability wanes. However, elevated instability should be sufficient to maintain thunderstorms with hail (maybe severe) and gusty winds (likely not severe) as the storms reach the DC/BWI region in the early evening. Depending on the amount of the elevated CAPE, storms could maintain themselves rather well and provide the area with a good lightning show.

Chase-wise, I’m considering taking I-68 to Morgantown, WV and then waiting to see where storms initiate. Should storms end up more favorable to the south, it will be a quick drive on I-79 towards Charleston, WV to get into better position.

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THIS WEEKEND:

It appears as though the cold air is a lock for Friday and Saturday. A storm system passing by to our south on Saturday is expected to bring some cold rain and possibly snow into the region (…so much for that Southeast ridge). Should the colder temperatures and precipitation verify, a swath of 1-3″ or more of snow is possible in the northern half of the region. Timing the precipitation with the colder temperatures will be key in getting widespread snowfall to occur, so this system will be revisited later this week and could include a snowfall forecast map.

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I will forgo this week’s What to Watch Fore(cast) as 1) I am already behind and 2) there’s plenty to track regionally this week.

Mid-Atlantic Discussion – December 16, 2010

A brief update…

Snow will start to fall in the region tomorrow morning, with WV and southern VA getting hit the hardest as snow totals top out in the 5-8 inch range. Closer to home, 1-2″ of snow is expected in the D.C. and northern VA areas. Richmond could be looking at 2-4 inches. The snow should start falling around noon in the D.C. area.

For D.C., the event should be rather short-lived, lasting only through the late evening tomorrow, with some light snow showers possible in the early morning hours.

An update on this weekend’s potential storm will hit the web on Friday.