Scott's Apr 2007

Mid-Atlantic Radar

Scott's April, 2007 Blog
(blog descends chronologically)

Rain and Storms...Slight Risk of Severe Stuff
Thursday, April 26

Not much to change from ideas presented here last Sunday and Tuesday so this will be a brief tune-up update. Back door Cold Front is currently draped across southern Virginia and will hang out there today. High Pressure has slid well off the East Coast; its clockwise flow pumping warm, moist air over the Southeast and Mid-Atlantic...opening the door for the storm that produced killer tornadoes in Texas to now move northeast. This system will produce strong to severe weather...possibly tornadoes...from Mobile up through the Ohio Valley today. With that back door Cold Front hanging across the Mid-Atlantic, much of Virginia and points north will on the cool side of the boundary; therefore it is unlikely severe weather develops north of Roanoke-Lynchburg-Norfolk. But, as the storm to the west pushes energy east, rain and some thunderstorms overspread the region.

Heavier rain should get into the Mid-Atlantic by Friday's morning drive. Thunderstorms are more likely on Friday, especially east of Washington-Charlottesville-Danville. Some storms could become severe especially in areas where limited sunshine heats up the atmosphere. As always, check our Severe WeatherCenter for real-time information.

Cooler and Cloudy...Storms On The Way
Tuesday, April 24

Gone, but not forgotten is the mantra for Sunday and Monday's delightful weather in the region. Today's storm over the Southern Plains should fire up tornadoes and strong storms for Tornado Alley; check the large Moderate Risk area for today. Check our storm report page for yesterday's 26 unofficial tornado reports...that total should be exceeded today!

Meanwhile, the frontal boundary discussed in Sunday's blog will hang over the Mid-Atlantic to produce cloudy and unsettled weather. Shouldn't be much precipitation today however some moderate rain could squeeze out of isolated storms. Thunder rumbles are possible but nothing strong to severe anticipated.

Unsettled weather continues with a better chance for rain and storms Wednesday evening into Thursday. A couple models hint there could be severe weather on Thursday for the area...this shows up in Thursday's storm outlook putting interior Mid-Atlantic under a Slight Risk on Thursday.

Temperatures will stay in the 60's and 70's across the region until High Pressure begins to take over by the weekend when skies clear and high's get back into the 70's and some lower 80's.

It's High Time for Spring. And...
Blowing the Dust off the HurricaneCenter
Sunday, April 22

High Pressure dominates the Mid-Atlantic region making us the beneficiaries of delightful warm and dry air. The Ridge will ebb Southeast and clockwise flow will pump even warmer air into the area on Monday. Should see widespread 80's across the area today...mid 80's on Monday!

Backdoor Cold Front up over the Northeast will have minimal impact for the Mid-Atlantic, however, the potent Midwest storm will drag another front toward the Mid-Atlantic on Tuesday and this may squeeze out a few showers then.

Another severe outbreak should develop on Tuesday across lower Tornado Alley before reaching the Ohio Valley and Mid-Atlantic States on Thursday. Though nowhere near as strong, scattered thunderstorms will erupt across the area on Thursday night with the potential for heavy rain north of the Mason-Dixon Line. We'll tune up this discussion on Tuesday with another update here on the blog.

Hurricane Model Maps: It won't be long before our attention turns to the tropics and the upcoming hurricane season. Our world famous hurricane model maps return and next month we'll begin subscriptions for the 2007 season. We do offer a "pre-season" discount to those who subscribe before June 1; the official start of hurricane season. If you'd like to get on the mailing list for advance info on subscribing to our model maps, click here. As always, our HurricaneCenter is public and free of charge. Mid-Atlantic WX.com remains, to my knowledge, about the only commercial weather site on the Internet without advertising jumping out all over your monitor.

Let's Go Hokies! This has been a damn tough week, especially in our area so affected by Monday's events at Virginia Tech. In a very real sense this has been and remains a local story to those of us here. Tech is part of the fabric of this area and everyone knows someone affected by the shootings...everyone.

My oldest daughter attends a different University here in Virginia and I've called her every day, just to hear her voice. It shouldn't take senseless evil to prompt us to call our kids and tell them how precious they are to us.

A significant percentage of visitors to this site are not located in the Mid-Atlantic area but you should know the outpouring of outrage, concern, sympathy and prayer has been received and sincerely is appreciated. I have a good friend near New Orleans who suffered greatly from Katrina. In the storm's aftermath I asked if she was aware of how deeply we all felt their loss and how very much we want to help. Her reply: "Yes, it keeps us going to know we're not alone". Same thing today from deep in the heart of Hokie Nation.

Update #2 on Historic April Nor'easter. Flooding Now!
Strong Winds Arrive Sunday Night.
Sunday, April 15

The "IRS Storm" now ramping up should live up to or exceed the hype!

Low Pressure currently (10:30AM) over west-central North Carolina getting ready to move off shore and crank up into a powerful Nor'easter...possibly the most intense April Nor'easter recorded!

Current 24 hr Sea Level Pressure trend at our wx station in Lexington, Virginia:

This graph will begin to rise as the Nor'easter cranks up off the coast and heads toward NJ and the NE coast. Rising pressure behind the storm will produce a very tight pressure gradient and strong winds will quickly begin howling tonight over the Mid-Atlantic. As noted in Fridays blog, unlike tropical cyclones, winds will not be fiercest directly under the Low...this may reduce the most severe coastal effects brought on by off shore winds. Still, it looks good for 25-40MPH winds along the coast from VAB up the Jersey Shore today. This evening the Nor'easter will be moving up to the Northeast and winds will shift to the NW and weaken. Inland...different story! Winds will pickup to 20-25MPH late this afternoon...increasing to 25-35MPH by 8PM tonight. Gusts over 40MPH will be common with stronger gusts approaching 60MPH into Monday morning. Saturated ground and strong winds combine to produce downed trees and limbs...expect power failures tonight and tomorrow in some locations of the region and the Northeast.

SEVERE/TORNADOES: The storm will continue the severe threat for much of FL and eastern GA/SC/NC and perhaps SE VA into this afternoon. Note current Tornado Watch boxes now in effect. As the Front pushes east winds will shift to the NW, except for South FL where thunderstorms rumble into early evening. Several Tornado Warnings have been issued this more for Southeaster US States (nothing confirmed as of this time)...click here for more.

FLOODING: numerous Flood Watches and several Warnings now in effect. Flash Flood Guidance looks minimal for most areas south of the Potomac, however an additional inch or two of rain will trigger flooding...especially over Eastern VA, Delmarva, SE PA and NJ. Flood Warnings currently for Covington, VA to Lewisburg, WV, portions of NOVA, Washington DC and MD...click here for real-time map.

SNOW: Rain mixes and changes to snow for interior northern PA, Southern Tier/Upstate NYS...all snow for Northern New England Mountains. Terrible driving tonight in the I-81 Corridor north of Harrisburg, PA. Slight variation of intensity between the GFS and the NAM but agreement on heaviest snow from Scranton, PA-Binghamton, NY up into western ME... very possible most of this area takes a thumpin' with well over one foot of snow!

Wrap around snow and snow showers will kick up along the western slopes of the Alleghanies and Virginia Highlands tonight...3 to 5 inches not out of the question along WV western slopes. Highest elevation and maybe the Blue Ridge will see some wet snow after 9PM tonight. The RUC (Rapid Update Cycle) model is also mixing in some snow down into the NW mountains of North Carolina tonight. The Air Force MM5 keeps all frozen precip locked up in WV and along the highest elevations of the NC mountains overnight and early Monday morning; this is reflected in tonight's Winter Storm Warning south of Boone, NC.

EXTENDED: Looks like the East will stay below normal for several more days with Ridging over the Central US to keep a trof over the eastern US. I don't see the current blocking features giving up their grip for another week. Temps bump up slightly by midweek, but remain below normal into next weekend. As Elton John said: "Don't Shoot Me, I'm Only The Piano Player".

Significant Storm To Impact Eastern US!
Friday, April 13

I'm tempted to make a Friday the 13th reference as a powerful storm is developing and looms on the horizon. Let's get the players on the field with this water vapor image (click graphic for animated loop):

The menacing cyclone on Friday morning is organizing over the SW US and will tack east, bringing everything from tornadoes to flooding rains, winds and heavy snow. Colliding cold and warm air masses will trigger strong storms and possible tornadoes today across eastern TX/OK and into AK. Later today and tonight the severe threat should reach LA/MS and early Saturday may extend into the west central Tennessee Valley. Persons in the affected areas need to closely monitor changing weather and always be alert for tornadoes after dark.

While there is generally good agreement among most computer models on the track, things will shift and be adjusted over the next 36 hours. Here's this morning's look at the GFS and the NAM (click graphic for more model maps). Note, I do not believe the GFS (green) will verify as it is probably too far west/inland from where the storm will actually track:

I am concerned the sever/tornadic threat spreads across the Southeast as well as north-central Florida on Saturday night as it is expected the atmosphere will really become unstable in this area.

Looking ahead to the Mid-Atlantic and Northeast...all locations near and east of the track will be rain, so this looks to be a stormy and windy event for NC/VA/Delmarva and right along the coast up to southern New England. While models are still adjusting the track, it seems most unlikely there will be snow south of the Mason-Dixon line with the exception of locations west of the Blue Ridge Mountains (more later).

I want to share snips from HPC's morning discussion. First, for the Southeastern US:

"...PROLONGED OFFSHORE FLOW LIABLE TO BRING WELL BELOW NORMAL TIDES CHES BAY/DEL BAY WITH A THREAT OF SOME SOUNDSIDE TIDAL FLOODING NC OUTER BANKS. THIS EVENT HAS SIMILARITY TO EARLY APRIL 1975 BLOWOUT EVENT. THIS AFFECTING SHIPPING IN DEL/CHES BAY HARBORS. A HIGH CONFIDENCE FORECAST. POTENTIALLY HISTORIC EVENT."

The referenced blowout event produced remarkable low water levels in the bay (I've heard stories of unseen shipwrecks being observed). This can happen when prolonged strong winds push water out of the bay...you can see how by looking at the storm track...Low Pressure spins counter clock-wise, so the bay is under a lengthy north wind flow and water begins to be pushed out to sea (blowout).

Next from HPC, a snip for inland Mid-Atlantic and Northeast:

"...COLD ENOUGH FOR SNOW ACROSS INTERIOR PORTIONS OF NEW ENG/NY/NWRN NJ/PA AND POSSIBLY SWD DOWN THE CENTRAL APPLCHNS. HEAVY SNOW THREAT. HIGH CONFIDENCE FORECAST AND A POTENTIAL HISTORIC EVENT."

An item I often mention for the Mid-Atlantic is how our moisture can be robbed by strong thunderstorms along the north-central Gulf Coast is actually mentioned in this morning's AFD from the NWS Blacksburg, VA office:

"...AS LOW PRESSURE STRENGTHENS SATURDAY AND TRACKS EAST-NORTHEAST FROM GA/AL INTO THE CAROLINAS....CONVECTION DEVELOPING OVER THE GULF COAST STATES MAY STEAL MOISTR FOR THE MID-ATLANTIC REGION AND CUT DOWN ON RAINFALL AMOUNTS FOR THE CWA"

To oversimplify, the stronger and more widespread convection develops over the South, the less available moisture streams up into the Mid-Atlantic. This is observed by watching the Water Vapor Loop (click map above). Sometimes one literally sees deep moisture simply stop advancing to the Northeast toward the Mid-Atlantic...that's when the area is robbed.

While conditions deteriorate across the Gulf and Southeast States on Saturday, weather should be calmer for the Mid-Atlantic with clouds moving in from south to north by late afternoon. Rain is expected to overspread the region early Sunday morning. Rain will be moderate to heavy with thunderstorms not advancing past VA I-64.

But make no mistake...this will be a HISTORIC storm! By Sunday, the Low Pressure center will be bombing out near Delaware and most models put the pressure at around 984 millibars. Folks, that is the minimum central pressure of a Category One hurricane! But, unlike tropical cyclones where winds are strongest nearest the center, this type of storm has an expansive wind field far away from the center...especially if the Low stays just off shore. I'm watching the 12Z NAM now coming in and it puts the center at 984mb (29.06") literally just off the NJ coast south of Manhattan.

Coastal flooding north of the Chesapeake (and noted by HPC for Southsound at OBX) may develop on Sunday and beach erosion is also a worry. If heavy rains persist the ante rises for flooding; notably for NOVA/DE and Eastern MD).

Current model guidance on precipitation (click graphics for current info):

Sunday:

Monday:

Winds will quickly increase as the storm moves to the northeast and gusts will exceed 40MPH from NOVA into NE PA. This is going to be a major Nor'easter, replete with gale and storm force winds up to New England.

Backlash snow is expected then to get going by Sunday evening along and west of the Blue Ridge. Sustained NW winds will enable significant accumulations for favored western upslope locations of the Appalachians. I'm not overly concerned on accumulations for the Shenandoah/Roanoke or New River Valleys, however the Highlands could see wet snow accumulate at elevations over 2,000 feet.

Significant snow should also pile up from interior PA (Poconos) up through interior New England...check our Winter StormCenter for current info.

Wow! What an exciting storm to watch develop and forecast...especially in mid-April! Keep current by visiting our Severe StormCenter and Winter StormCenter as well as checking local watches and warnings for your hometown. How do I know this will be a big storm? I am going camping this afternoon and when I camp, you bet it will be damp. I hope to have an update online here Sunday morning so please check back then.

25 to 30 Degrees Below...
Wednesday, April 11

NORMAL!!! That's the average departure from normal temperatures today across the region. Brief "semi-warm-up" tomorrow before next in the seemingly never ending train or storms approaches the region. High Pressure remains blocked over Northeast, continually reinforcing cold air coming off the Atlantic from the east. Always remember: NOTHING good ever blows in on east wind. So, here we are, stuck in a CAD (Cold Air Damming) event three full weeks into Spring. Meanwhile a Cold Front will cross the Mid-Atlantic tonight, yet another Closed Low will for near the Lakes and bring rain as it tracks east. Could be thunder rumbles late tonight and rainfall totals will approach and exceed one inch in many locations. Heavy rain may stack up along the Blue Ridge to squeeze out totals around two inches by Thursday morning...slight risk of lowland and urban flooding...but after reviewing flash flood guidance, only a minor issue, if at all. I'm doubtful any thunderstorms that roll through will approach strong to severe but believe downpours are possible.

Quiet and dry Thursday afternoon to Friday night when next batch of precip approaches from the south. Not a big deal but the cloudy, drizzly and raw weather will be back.

Late Saturday/Sunday morning a Coastal Low develops near the Virginia Capes and all I can say is: Oye! Not certain I'm on board with the latest GFS depiction of a vary strong Nor'easter type storm quickly spinning up, but this doesn't look good. Forget the balmy Sunday and Monday high temperatures seen elsewhere...ain't gonna happen! I think it likely the Sunday storm hugs the coast or perhaps comes just inland around New Jersey bringing with it a variety of nasty weather on very strong winds. Hmmm...maybe this will be nicknamed "The IRS Storm"! Certainly a rainmaker for east-central NC and VA with the strong potential for backlash snow buffeted by strong winds over the mountains. DC-BAL-Philly might even get some mixed precip. I think there's ample opportunity for wet snow from the Poconos up into the Green and White Mountains! We'll need to get a better grip on this storm's track to see what the future holds for the I-95 corridor north of Richmond, VA.

Next update here at the blog will be Friday morning. I'm away Friday afternoon through Sunday morning...camping! You'd think the weather guy could pick better weekends.

Mid-Atlantic Snow...BAH!
Friday, April 6

Humbug I say to the approaching Clipper that is likely to paint much of eastern West Virginia, Virginia and possibly the Delmarva Peninsula with a white coast just in time for Easter. Friends, this simply is galling!

Upper Level Low (ULL) over Northeast is still hanging on and the persistent trof over the Mid-Atlantic continues to drain cold air over the region. A strong (*very* strong for April) Clipper storm will track southeast from the Upper Plains and cross the Ohio Valley and Mid-Atlantic before ejecting off shore at Virginia and heading up the coast. Sufficient cold air is in place for a mix of snow or rain/snow across portions of the Virginias, NW North Carolina, MD, DL and lower PA. It looks to me like the 12Z models may be trending a bit more to the north so the white stuff could expand into SE PA, interior NJ and the northwestern suburbs of NYC (btw, snow flurries last night at Yankee Stadium!).

NWS Blacksburg, VA is bullish on accumulating snow for the border mountains of the Appalachians south and west of Hot Springs, VA. Elsewhere, and inch or two is possible along the Blue Ridge and north of the I-64 corridor. Egads! Snow finally falls in Richmond and Norfolk? Perhaps! South of VA I-64, it looks like there will be ample flurries but little to no accumulation. Give the forecast track and location of the Jet Stream, one should look to the south and east of Washington-Baltimore for heavier accumulations. Soundings indicate virtually all snow for this area but rain may mix in right along the coast. Otherwise, there should be locations receiving two to perhaps four inches of snow...particularly from Fredericksburg across the Chesapeake and Delmarva Peninsula.

This afternoon, Lake Effect snow and flurries over Pennsylvania will diminish before the dastardly white stuff invades the Mid-Atlantic. Precipitation crosses the Appalachians early this evening (7-9PM?) and clears of of the region by early Saturday afternoon. I'll tune this up tonight with an evening update here on the blog. Snow slides up the coast and begins falling over northeastern New England by late Saturday afternoon.

Back this evening with more gory details!

UPDATE: Typical Clipper style snow bands crossing the mountains should put down totals for the mountains and highlands overnight as detailed in today's earlier post. A few flurries or light snow along the Blue Ridge with negligible accumulation...if any. Areas south and east of Washington will see accumulations of up to three inches as Low Pressure fires up off the Virginia coast early tomorrow morning. This may bring back lash snow and flurries to the mountains later Saturday afternoon. Let's see if Richmond and even Norfolk get snow (I think RIC is around one-half inch for the season). Temps will struggle to reach 20 degrees *below* normal on Saturday...not much better on Easter Sunday.

The Cold Front Cometh!
Wednesday, April 4

All on schedule for big cool down for the Mid-Atlantic and Northeast as a strong Cold Front is swooping from the Ohio Valley and will clear the Mid-Atlantic later today. Severe threat has diminished although some storms will fire up later this afternoon east of the I-95 Corridor from the Delmarva to Hilton Head Island, SC.

No t-storms for the northeast but much colder air and snow will be in the forecast north of the NYS Thruway and Mass Pike...in fact, significant snow could accumulate today and tonight over northern New England with snow showers/sleet reaching as far south as Boston.

Into the weekend...a large Upper Level Low (ULL) closes off over the northeastern US and is blocked by High Pressure so this feature will sit and spin into next week. Curious to note a couple models are printing out snow showers for the upper Mid-Atlantic Friday night and Saturday! Not a pleasant Easter Weekend forecast by any stretch of the imagination. While I knew this Cold Front was coming I did have fleeting thoughts of mowing grass on Friday...wonder if I'll be brushing snow off the doorstep?!?! The cold air will continue pouring down over the Eastern US through early next week, thanks to the ULL and blocking High Pressure that will keep a steady stream of arctic air over the region. Overnight lows will plummet to near or below freezing all the way to Atlanta so I hope everyone didn't try to fool Mother Nature by planting annuals last week when it was in the 70's and 80's!

Next update here on the blog will be Friday morning.

RANT: Our wx station has been unable to connect to our server since 2AM this morning...the issue is with our ISP. Maybe it'll be online when you read this. Silly me, I thought Adelphia was unreliable but since Comcast took over the bankrupt, non-defunct company, our service has been even worse. I call and complain with such a high frequency that they know me on a first name basis. We are exploring alternative methods of Internet connectivity as this is "no way to run a railroad" or a time-sensitive wx station. Fortunately, this chronic issue is unrelated to our server; Mid-Atlantic WX.com has been up and online an impressive 99.68% of the time over the past six months! Must be because Comcast has nothing to do with it! :(

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