Scott's Feb 2008

Mid-Atlantic Radar

Scott's February, 2008 Blog
(blog descends chronologically)

Ready For The Rollercoaster?
Sunday, February 24

A little wet snow and rain at our weather office tonight...that is moving east over the region as an Upper Level Low (ULL) swings through the area overnight. Not much of an event as snow/ice pellets/rain will be scattered over the Mid-Atlantic into Monday morning.

High Pressure comes in for a 1-night stand; providing a mini-warm-up Monday and Tuesday featuring temps at or above normal, thanks in part to a Warm Front zipping through in front of our next weather maker. Low Pressure now over Colorado reaches Ohio by Tuesday afternoon before aiming at Portland, Maine on Wednesday. This storm's Cold Front will cross the Mid-Atlantic on Tuesday and most of the East and South will notice Wednesday temps 15 degrees colder than Tuesday's!.

The storm's track is not conducive for snow along the coast south of Portland, so we'll go with rain for the I-95 Corridor. Northern PA, Upstate NY and most of interior New England are braced for another bout of winter weather with widespread accumulations exceeding four inches.

Western slopes of the Appalachians will again see several inches of accumulating snow late Tuesday into Wednesday morning. East of the Appalachians, there should be little to no snow as the system will pass to the northwest. I can't rule out a wayward flurry late Tuesday night from the foothills to the Blue Ridge, but no accumulation is expected.

All this is subject to change with the actual track making a slight shift to the south. Right now it doesn't appear that will happen, but I'm certainly watching for the possibility of this sneaky development.

I've been watching the European model (ECMWF) which has been steady as a rock on the forecast for the balance of the week. The "EC" is the preferred medium-range model...especially in winter. Very cold air moves in on Thursday with temperatures colder than Wednesday. I'd expect Thursday to average ten degrees below normal, even with sunny skies. Temps moderate Friday and Saturday as another storm approaches but misses the Mid-Atlantic and tracks into the Northeast and could pull in some light rain or a little snow for locations south of the Mason-Dixon Line. This doesn't appear to be an impressive event but it is 6 days away so we'll watch and see.

I Dub Thee: "The Moses Storm of 2008".
Friday, February 22

Tropical storms and hurricanes have names while winter storms do not...at least "officially". We weather people have our own names for winter events. One need say only "President's Day" to know this is the February blizzard in 2003. Then, there's the "Pamela Anderson" storm of 2001; aptly named as it was the biggest bust observed in years! Well, by the powers invested in me, by me, I now name today's underachiever as The Moses Storm of 2008.

Not since Moses parted the seas has such a split been observed on Earth! While there were pockets of freezing rain, much of North Carolina and most of Virginia south of I-66 awoke this morning to nothing...no snow, sleet or freezing rain. Roads were generally wet but clear. Every model, apparently every NWS office, private weather company (you know who I mean!) and numerous meteorologists totally missed this one. And, we'll put yours truly in that category, too!

What happened?

To oversimplify, 2 things: 2 Lows and thunderstorms.

High Pressure over the region indeed set up a wedge across the area just as forecast. Last night's Sea Level Pressures across Virginia and the Delmarva were around 30.20" and dew points away from the coast hovered in the low to mid teens, resulting in a cold, dry air mass at and just above the surface. I noticed numerous wet bulb readings in the area remained several degrees below the dry bulb (actual) temperature...another clue precipitation will struggle to reach the ground.

Next, the precipitation came in two separate pieces; one moving into the Ohio Valley and the other toward the Southeast coast. Precipitation indeed moved up into the Mid-Atlantic however cold, dry air absorbed much of it prior to reaching the surface. Here's the Thursday evening National Radar composite at 6PM EST:

The two distinct areas of precipitation are easily observed...with Virginia right in-between! Normally, the precipitation falling over the Southeastern US would move northeast...toward the Mid-Atlantic States. Cold air at the surface with advancing warmer air and moisture aloft is the reason many regional forecasts featured snow/sleet changing to freezing rain. But...take a closer look at the Texas/Louisiana border and the Florida Panhandle in the image above. What do you see? Thunderstorms!

So did the Storm Prediction Center; they issued several severe thunderstorm and tornado watches. Here's a Tornado Watch prompted by the TX/LA cells seen above increase and cross Louisiana:

Now, what do thunderstorms in the Deep south have to do with freezing rain in the Mid-Atlantic? The answer is everything!

Convection near and along the north-central Gulf coast will frequently "rob" the Mid-Atlantic of precipitation and that's what happened last night and this morning. As powerful storms fired up from Louisiana to Florida, one could observe this moisture transport in water vapor loops. Rain destined for the Mid-Atlantic diverted instead to powerful storms closer to the Gulf.

This very development is something I've preached for years: with every southern stream storm, don't watch Radar from the Mid-Atlantic or Northeast, watch it from the Gulf Coast. While keeping an eye on water vapor loops and National Radar I noticed the amazing "parting" of the storm's precipitation and was most surprised. Then storms fired up and the SPC dispatched watches and warnings along the Gulf and, well, as Col. Potter always said on M*A*S*H: "that tears it!" I knew this event would bust for north-central NC and much of VA and the Delmarva.

I was never gaga over this system's potential to become a major storm south of the Mason-Dixon Line. Snip from last Sunday's discussion (below ) from the blog: "Low Pressure shoots out of Four Corners and Texas as the Southern Stream gets cranked up...hence...the potential for southern stream moisture over running cold air at the surface. This combination brings a *low confidence* potential for inland snow and freezing rain for Thursday night and Friday."

Elsewhere, forecasts were good...with accumulations of 3 inches plus for Philly and nearly 10 inches for interior Southern New England. But, in Virginia south of NOVA and the I-66 Corridor, this will be "The Moses Storm of 2008"!

I'll be back Sunday for a look at the last week of February. Out like a Lion...or a Lamb? Stay tuned!

Wintry Weather to Feature Ice for Portions of the Mid-Atlantic.
Wednesday, February 20

Tonight's surface map shows Low Pressure over Texas along a Cold Front stretching to Norfolk/Virginia Beach, VA. High Pressure over the Upper Plains will build into the region on Thursday with much colder temperatures. The Texas Low will approach the Mid-Atlantic later Thursday. Light-modest snow totals coming from Northern OK into OH...perhaps 3 to 5 inches..

Freezing rain and plain rain fall just south of this area, prompting travel delays and road hazards on Thursday. South of the freezing rain/rain mix will be all rain.

Mid-Atlantic States again the bulls-eye for a wintery mixed event! High Pressure will move east and set up a cold air wedge (CAD) east of the mountains. This cold air will be trapped at the surface with warmer air and rain aloft. This over running should trigger freezing rain and very cold rain from north central NC, Southside VA, the New River and southern Shenandoah Valleys...as well as the Piedmont/Central VA area west of I-95. Timing is a bit problematic, with the NAM and the GFS at odds by several hours but would think precip begins reaching the ground late Thursday afternoon in NC and Southside VA...moving north overnight Thursday into Friday morning. Northern VA (NOVA) and points north should be mostly snow although the I(-66 Corridor from Winchester over to Arlington may quickly transition to freezing rain. Metro Washington-Bal-Philly will mostly be freezing rain. Much of PA should be all snow with totals generally in the 2 to 4 inch range. Southern Tier of NYS and interior southern New England could see higher accumulations.

Late Thursday and much of Friday will be the worst travel times in Mid-Atlantic. Check our Winter StormCenter for real-time information.

Brief discussion tonight as the Lunar Eclipse is underway and the clouds have broken away at my location. I'm heading out!

Cold and "Interesting" Week Ahead.
Monday, February 18

Not much in the way of new ideas from what was discussed here yesterday. Low Pressure dives under the Great Lakes and approaches the Mid-Atlantic this week. This should be a typical Alberta Clipper type system with light snow Tuesday and Wednesday morning for the Lower Lakes States (not a LES storm). Upslope snowfall may reach 4-5 inches for the western slopes of the Alleghanies of WV with very dry flurries possible from the mountains to the Blue Ridge and also north of the I-66 Corridor. A dusting is about all that's expected although 1-2 inches may sneak in over MD, DE and lower PA. The atmosphere will be very dry and negligible accumulation expected east of the mountains.

Windy with below normal temps for the balance of the work week as Southern Stream storm heads west of the Appalachians with a secondary Low forming off the Mid-Atlantic coast late Thursday. Cold air is expected to be wedged over the region and NC and VA again become the battle zone for winter precipitation. Snow will be the main precipitation type from the Central Plains into the Northeast with a smaller stripe of freezing rain/sleet across the TN Valley.

There's no shortage of options on the table but one I do not believe will verify is significant snowfall south of the Mason-Dixon Line. We'll have a wedge of cold air bottled up and a great deal of moisture transported in on the southern jet but I believe the primary Low tracks well west of the Alleghanies...pushing warmer air from the southeast into NC and Virginia. We'll see how this sets up but this would initially lead one to suggest freezing rain as a viable option. Next player is how strong does the coastal Low get...and how far off-shore does it track. Too soon to say with precision.

Keep an eye on your local forecast and the Winter StormCenter here at Mid-Atlantic WX.com this week.
I'll try to get an update here on Wednesday night.

Ice Storm "Big Fizzle"...Some Severe Possible Monday...Winter is Back Next Week?!?!?!
Sunday, February 17

No blogs last week due to traveling, but now back in the saddle. Last Sunday's frontal passage and associated widespread wind storm led me to my first ever "tree and roof chasing day"! I lost power for the better part of nine hours (no blogs) and devoted the day to calling in the diameter of downed trees to the NWS, along with "chasing" reports of roofs blown off buildings and overturned outbuildings. I've been a SkyWARN Spotter for many years but that was the first time I went looking for trees rather than dodging them! While on-the-road, my youngest daughter sent me a text indicating a large pine tree came down in the backyard and bent the flagpole:

Yesterday was the first opportunity to remove the tree and clean up the yard! Last Sunday's event produced a wind gust of 62MPH with sustained winds of 55-58MPH at our wx station in Lexington, VA; this was the third highest non-thunderstorm wind speed observed since the wx station went into operation in 1996.

TODAY: Excessive warm air advection eliminated any threat of freezing rain. Widespread morning temps at or above 40° along with dry air at the surface delayed onset of any precipitation, and that fell as plain rain.

MONDAY: Curious set up for tomorrow: a Warm Front will bulge up into the Mid-Atlantic immediately in front of a rather sharp Cold Front. The low level jet stream will howl and if there is sufficient instability with these two fronts there could be strong to severe storms Monday morning and early afternoon. As noted by the SPC, threat will be east of I-95 and south of the Chesapeake Bay. Lines of heavy rain and strong winds would likely be the most notable features.

Monday afternoon, the Cold Front pushes through and any severe threat will diminish...as will the temperatures! Winds will increase out of the W-NW and temps will tumble by Monday night.

WINTER RETURNS NEXT WEEK? Prepare for a very active weather pattern! First up, an Alberta Clipper should advance late Wednesday or Thursday morning. all appearances now are this will be moisture starved by the time it reaches the Appalachians...but western upslope snow is not ruled out. West of the mountains back to the Lower Lakes, accumulating snow is a good bet...perhaps several inches in favored Clipper/LES locations.

Temps Wednesday evening into Friday will be well below normal as High Pressure builds in behind the Clipper, then sets up over the Northeast next weekend. Winds will shift to the East and we then must consider the development of cold air damming (CAD) wedge. Meanwhile, Low Pressure shoots out of Four Corners and Texas as the Southern Stream gets cranked up...hence...the potential for southern stream moisture over running cold air at the surface. This combination brings a *low confidence* potential for inland snow and freezing rain for Thursday night and Friday.

One potential monkey wrench in all this is how strong with the Southeast Ridge be...and where will it set up by next weekend? If high pressure strengthens over the SW Atlantic the door is open for warmer air to ride in with the advancing Southern Stream storm. Translation: probably rain with the potential for interior freezing rain. Right now, I do not see a way for cold air to lock in so I'm skeptical of a late week snow event south of the Mason-Dixon Line.

Progressive pattern continues next weekend but temperatures should be at or a bit above normal by Sunday (2/24).

I'll briefly update the blog tomorrow (Monday) evening after the Cold Front passes...I'm curious as to how the models will will "see" how much cold air is coming in and how the Southeast Ridge is being handled. Please check back then...and stay tuned...an interesting week is upcoming!

Storms and Damaging Wind Approaching the Mid-Atlantic Today.
More Tornadoes Possible.
Wednesday, February 6

I can't recall a more devastating February tornado outbreak than what occurred yesterday and last night. Death toll now at 45 and certain to rise with today's morning light. This is always the aspect of extreme weather that makes those who are so passionate about it pause and reflect. Sometimes, knowing how many DID survive because of faster warnings and quality storm chasers just isn't enough.

Impressive hail from a tornadic storm last night near Nashville, TN:

I believe there is a possibility portions of the Mid-Atlantic will upgrade to a Moderate Risk today.

Current outlook:

Severe parameters are reasonable for strong storms to fire up just ahead of the Cold Front rapidly approaching the region. Soundings show instability with marginal CAPEs and low LIs along with some shear...if there's sufficient sun to heat this extremely warm and moist air (amazing for early February), the cap will break and strong storms quickly get going. For this reason, caution is urged and everyone in the "Slight Risk" areas highlighted above should stay close to NOAA weather radio and reliable media for quick information. Of course, our Severe StormCenter is the place to be for real-time warnings and information.

Parameters do not support the intensity and longevity of yesterday's outbreak...however very strong storms can develop especially where sunshine heats up the lower levels and raise dew points already in the 50's and lower 60's. These storms will be capable of producing very strong straight line winds and downbursts of wind and heavy rain. Hail doesn't appear to be a significant threat today but we can't rule it out, particularly in strong to severe storms. Tornadoes are possible and you'll want to remain alert for the potential of tornado watches migrating into the Virginias and Carolinas today.

Target zone as outlined by SPC this morning is Western MD, extreme eastern WV and Virginia down the I-81 corridor and west of I-95...but...includes the Metro Washington DC-Baltimore areas, I-66 and the Beltway..as well as Richmond. This set up often produces tornadoes along the I-66 corridor from Winchester to DC...something to watch for today.

Timeline looks like early afternoon for WV with severe weather potential peaking around 5-6PM along the Blue Ridge Mountains. Storms should be firing east of the Blue Ridge this evening, weakening as they pass I-95 as the Cold Front pushes off shore.

Please check your local forecast and monitor real-time conditions and any weather watches and warnings at our Severe StormCenter.

12:00 NOON UPDATE: Severe threat has diminished in the Mid-Atlantic. Extensive cloud cover from debris clouds in the outflow of last night's storms is keeping much of the region out of the sun. Temps and dew points also are dropping. as showers and rain cross the mountains.

This changes previous thinking on the timeline and risk level of severe weather. Looks like this outflow will provide a moderate-high level of cloud cover over the region into this evening and as such, the cap probably remains on and there will be little to no low level convection. The Surface Low is projected to move up into the Ohio Valley before tracking into western PA tonight. The strong Cold Front will drag to the south of the Low and this may be the focus of activity. Most of the system's energy appears to be along the frontal boundary and with the Low...therefore strong to severe storms may still fire up tonight as the boundary approaches the Appalachians. I am concerned there could be severe weather between 5PM and 11PM...time frame for the Cold Front to cross the Mid-Atlantic states.

Obviously, night time severe weather is a special concern and skies could become more clear as the front approaches. Without daytime heating the lower levels will be more stable but there's a tremendous amount of mid-level energy coming that will be capable of producing strong storms. This dry slot shows up nicely on the animated Water Vapor Loop...click here. Add in veering winds aloft and there remains some threat for tornadoes as the Front approaches the area. It is important to note SPC has significantly reduced the tornado threat for the Mid-Atlantic...but we are not out of the woods!

Very hectic schedule as you may imagine but I'll try for a quick update here at the blog late this afternoon.

Super Tuesday Tornado Outbreak!
Tuesday, February 5

Severe storms are producing numerous confirmed large tornadoes ahead of an approaching Cold Front. Storm Prediction Center nailed a rare HIGH Risk area today for AR-W TN/KY and N MS. Long lived tornadoes have been on the ground in Arkansas and severe damage has been reported near Memphis, TN. Reports streaming on WMC-TV indicate a shopping mall just outside Memphis has been hit...along with a manufacturing plant and warehouse. Video I've seen indicate this could have been a major EF-3 tornado, but that's an unofficial opinion. Damage is reported along I-40 and at Union University at Jackson, TN. There is also damage at Memphis International Airport. The local NWS was also evacuated of non-essential personnel.

Live weather stream below from Ustream.tv:

Sadly, I've seen a report on a storm chase blog of at least 2 fatalities at Atkins, AK.

Tremendous swath of Tornado Warnings are seen below on this radar image taken at 6:57PM EST:

Overnight Danger Zone tonight will probably be eastern AK, western-central KY and southern Indiana. This area may see tornadoes...possibly long lived twisters on the ground.. Our Severe WeatherCenter has live real-time coverage.

The threat shifts into the Eastern US on Wednesday...but will weaken overnight and on Wednesday. Thunderstorms may develop along a squall line Wednesday with a slight risk for isolated tornadoes but straight line winds posing a bigger threat. Check your local forecast and our Severe WeatherCenter overnight and on Wednesday.

Stay safe.

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