Scott's Jan 2008

Mid-Atlantic Radar

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

Everything From Ice to Thunderstorms!
Thursday, January 31

Very brief discussion as I'm on the road until this evening.

High Pressure is migrating as planned and will be over New England tomorrow. Southern storm coming up and will bring copious moisture into the Mid-Atlantic later tonight. East of VA Route 29/South of VA I-66 this looks to be a rain event...maybe some sleet pellets thrown in to remind us it is winter.

Cold wedge sets up from extreme NW NC mountains up through the New River, Roanoke and Shenandoah Valleys, along the Blue Ridge and into eastern WV. I'm not as sold as is the NWS on a prolonged ice event, but you'll certainly want to heed their advice on current Ice Storm Warnings and Winter Storm Watches. These areas will see more wintery weather and a high probability of "black ice" overnight and Friday morning before temps quickly surpass 32°. I-81 Corridor up into Western MD and central PA look like early target zone for icing before a change to rain.

Significant snow-ice-rain event as one traverses PA from west to east on Friday.

There is a possibility of strong to severe thunderstorms tomorrow for the Delmarva, eastern VA, eastern NC and the OBX! Strong storms, damaging straight line winds may also be accompanied by bow echoes and a very slight risk of an isolated tornado. More about this tonight so please check back this evening.

Have a great day!

UPDATE, 10:30PM: Surface map below is from 10:00PM tonight and nicely depicts current situation:

The dark blue lines are isobars (lines connecting points of equal pressure) and clearly show High Pressure we've discussed is located over New England. You can also easy see how those lines are forming a wedge from New Jersey down into Virginia and central-eastern North Carolina. While not "classic", this is a good visualization of Cold Air Damming (CAD). This is a chilly and dry air mass so it'll take time to moisten up but inland locations will be right at or very close to freezing when precip finally reaches the surface overnight.

You can also see precipitation moving up from the Southwest...that's associated with Low Pressure now moving up towards the Great Lakes. While all of it is not reaching the ground, when it does it will begin as freezing rain in areas outlined here previously: west of Route 29 and along/north of I-66 in Virginia. To the south and east of these locations, a touch of freezing rain and perhaps sleet, but mostly rain...heavy at times.

You can see how confidence builds for this forecast by looking at the current temperatures below (note: the above map is not current, but the temps below are):

The approaching storm is coming from the south and will pass to the west of the Mid-Atlantic States: Low Pressure spins counter clock-wise so this set up will push warmer air up from the south. The warmer air will come in above the cold air wedge (shown in the top map above) and therefore will fall as rain until reaching the colder air at the surface. That's why this will not be a snow storm for the Mid-Atlantic...but may be a significant ice storm along and west of the Blue Ridge where the coldest air will hang tough until well into Friday morning.

Tricky part remains how long will the cold air hold: the longer t takes to warm up at the surface, the more freezing rain will fall. Best bet for prolonged ice is the I-81 Corridor from Southern PA down to near Virginia Tech (Blacksburg). As this is written (10:45PM) temps in this portion of the I-81 Corridor are at or above freezing with low humidity and many single digit dew points. The wet bulb at our wx station in Lexington, VA currently is 28° and it is challenging to forecast how low the actual surface temps will drop overnight before heavy rain pulls down warmer air and temps begin climbing. This prompts the Ice Storm Warnings and Winter Storm watches along and near the Blue Ridge Mountains. I'm still thinking many risk area temps across the Mid-Atlantic States will get above freezing by mid/late morning and precipitation then evolves to all rain. But travel will be perilous overnight and early Friday in those areas getting freezing rain!

Piedmont and eastern NC and VA will be, as mentioned, mostly or all rain. Temperatures by Friday afternoon should be well above 32° across the region. Liquid precipitation totals may approach and even exceed one inch for much of the area.

The one caveat I always mention with this type of storm is watching Radar along the north-central Gulf Coast. Many, many times, a line of strong convective storms develop here and essentially "steal" moisture from the Mid-Atlantic area. This could again occur Friday and if it does, precipitation totals will be below what are currently forecast. So, keep an eye on your local conditions and check Radar along the Gulf Coast.

There remains a risk of severe weather in the Mid-Atlantic...specifically east of the I-95 Corridor from the Delmarva to Myrtle Beach, SC. Persons in this area should monitor our Severe WeatherCenter for real-time information on Friday afternoon.

Wednesday Night Thoughts on Thursday-Friday Storm System.
Wednesday, January 30

I thought the wintry mixed precipitation event advertised here last Sunday was right on track...until tonight! The 0Z models are getting jumpy about the storm and what type of precipitation will arrive Thursday night.

High Pressure is building in behind today's very windy Cold Front; this High will migrate up over New England and the Gulf of Maine, setting up an on-shore East wind for the region. *Nothing* good ever blows in on easterly winds and colder air has been forecast to set up a Cold Air Damming (CAD) event. Meanwhile, Low Pressure currently over west Texas tracks toward NOLA before heading up into the Great Lakes. Moisture from this system overspreads the region on Thursday night and with cold air coming in around the High, we should have a sleet event over western NC...with a touch of freezing rain mixing in with plain rain for the Piedmont. Virginia locations east of the Route 29 corridor would have a very cold rain with temps just above freezing. West of Rt. 29, precipitation has been forecast to be in the form of freezing rain and thus the Winter Storm Watches and Warnings.

Tonight's runs of the Nam and the GFS models now push the Low a bit further northwest up into the Lakes. This delays the onset of precipitation...possible until Friday morning at which time temps would be climbing above the 32° mark for all but western and elevated locations. If this pans out we'll see mostly rain in Virginia except along and west of the Blue Ridge where there should be some sleet and a little freezing rain.

Lower Lakes probably takes a thumpin' from this storm...especially from Central IL through Western NYS. PA and the Southern Tier of NY may end up with a significant sleet storm.

We'll need to take another look at this in the morning but for now there are signs just enough warm air comes up to produce more rain over a larger area of the Mid-Atlantic. As always, check your local forecast here at Mid-Atlantic WX.com and visit our Winter StormCenter for real-time information.

Next update here at the blog by Noon on Thursday. Have a good night.

Another Change At The Top of NHC...And...
Some Warmer Weather Awaits, Then Wintry Mix and Rain.
Sunday, January 27

Brief discussion as I am flying to Atlanta today to attend a short conference. Fortunately, the weather here in the Mid-Atlantic region will be rather tranquil while I'm away.

More news out of the National Hurricane Center as Bill Read has been appointed the new director. Read comes from the NWS Office in Houston, TX and more recently has served as NHC's acting deputy director since last August. NHC's press release is here.

Weather-wise...Low Pressure organizes off the Mid-Atlantic coast and heads Northeast as High Pressure deep in the heart of Dixie moves East. This High will bring warmer air from the south up over the Mid-Atlantic region into the middle part of the week...before the next Cold Front approaches late Tuesday with a high probability of rain late Tuesday into Wednesday. High Pressure builds back into the area behind this front with another Cold Air Damming (CAD) event setting up on Thursday. Another storm heads up towards the East and wintry precip is possible inland and for the higher terrain...freezing rain north of the VA I-64 corridor. As this second storm is coming up from the south, warmer air will over run the CAD and should scour out cooler air, making for a significant rain event into Friday. We'll need to tune up the timing and precipitation types with another update to the blog on Wednesday evening...so please check back then.

Little warmer early this week...enjoy! :)
.

Winter Weather Again Approaching on Tuesday...and...
The Cold Will Hold Till The Weekend.
Monday, January 21

The savage Ridge of High Pressure is now sliding off shore and with it just one more night of brutal cold.

This is a very strong Ridge as evidenced by a peak reading of 30.76 inches this morning at our weather station in Lexington, VA. Current barometric trend (click graphic for our weather station):

Current US Surface Map shows High Pressure right over the Mid-Atlantic while Low Pressure is noted over the Central Plains...this is our next weather-maker coming on Tuesday. This system will be over the Lower Lakes on Tuesday with the attendant Cold Front reaching the Gulf Coast, Southeast and Mid-Atlantic States by afternoon. The atmosphere should be relatively stable but thunderstorms could fire up Tuesday from LA to SC.
Different story from NW SC into PA...generally along the mountains and the I-81 Corridor...as cold air will hold and wintery precipitation is expected. Light snow and freezing rain will overspread this area in the morning before a change to rain and drizzle by afternoon (except along and west of the Alleghenies where snow will continue during the day). Snow totals will be modest: less than 1.5 inches and freezing rain won't accumulate but will produce some glazing and "black ice"; therefore extreme care is needed for the morning commute. Temps for most of the area will exceed 32° by late morning...before dropping again tomorrow night when snow may again fall over the mountains and highlands.

This setup is very conducive for Lake Effect Snow (LES) and several inches should pile-up in typical locations into early Wednesday morning.

Next precipitation comes in early Thursday with an Alberta Clipper bringing in a little moisture that may produce light snow early Thursday. A final infusion of cold air follows the Clipper with temps much below normal back in the forecast. Another system approaches next weekend, probably arriving on Sunday...but this should be a rain event.

Temperatures will remain very cold into Friday at which time we'll see a rebound to near and normal temps into the weekend and early next week. I noticed today's 12Z of the GFS sets up a High Pressure Ridge off the SE US coast next week which if true, would warm up the region beginning the 28th. We'll see!

Off Topic: How I Spent My Weekend: As mentioned in the last blog, I went camping with the Boy Scouts this weekend in the mountains of Virginia. Mighty cold! Saturday's high was 35°, the overnight low was 10° and it was 17° on Sunday morning. The purpose of the weekend camporee was to teach boys winter skills and how to have fun outdoors in the cold. One such challenge is to start a small fire using 2 matches and one wet piece of wood. I took a picture of this activity (click thumbnail below to enlarge):

In the foreground you see a tub filled with cedar logs floating in warm water. Teams of Scouts were told to take one cedar log and two matches. In the background a couple teams working on this challenge are visible: their objective being to make a small fire that burns a suspended string 18 inches above the ground. Accelerants were prohibited but the Scouts were permitted to use anything else they could carry (dryer lint is a favorite). Those who came prepared had pocket knives and a camp hatchet while others carried twigs in a zip-lock bag. They were given 15 minutes to accomplish the challenge. Of the 24 patrols attending, 17 met the challenge. Over 120 local boys attended the event and all learned leadership, winter survival and team building skills. These are the guys who are the leaders of tomorrow and that's why I am so optimistic about the future. But...it could have been a few degrees warmer!

Next scheduled update here at the blog on Sunday (prior to a trip to Atlanta)...sooner if conditions warrant.

Saturday Storm Solely in the South...While ALL Aboard the Arctic Express!
Friday, January 18

Time to prepare for The Next Big Thing...the second storm to affect part of the Mid-Atlantic States in three days.

Low Pressure over the western Gulf of Mexico moves east today and gets organized south of the Florida Panhandle tomorrow...before tracking off the SE US coast tomorrow night along a frontal boundary now draped over the GOM and Florida. Model map below shows anticipated track forecast from the GFS and NAM models (click graphic for more maps and models)

Radar now shows some mixed precip SW of Dallas/Ft. Worth as the system moves east...producing rain along the north-central Gulf States later today. Cold air now in place will allow for some snow/mixed precip along the northern edge of precipitation; likely to be northern counties of MS, AL and GA (more snow for northern suburbs of Atlanta!). As the Low tracks off shore, a stripe of snow should develop from extreme NW GA along a line to SE VA. Right now, the heaviest band of snow looks to be roughly from Asheville/Spartanburg, NC to Raleigh/Durham, NC and over to Emporia, VA. If this pans out, this area may see totals exceeding 4 inches by Saturday. This is going to be a pesky storm (no...I'm not a Red Sox fan!) in that the distance between accumulating snow and nothing will be very narrow...so this is merely a preliminary guess on snow totals. I am skeptical we'll see more than a dusting to one inch north of VA I-64. As always, check your local forecast and visit our Winter StormCenter for real-time information.

Northward progress of this storm isn't an option due in part to the approaching Mother of All Cold Fronts on Saturday. Brutal Arctic High Pressure (1035mb) now over Alberta will dive into the Nation's Heartland and will push a frontal boundary into the Eastern US on Saturday. Behind the front, air of arctic origin will produce the coldest temperatures of the season through Tuesday. This pipe-bursting Ridge will migrate over the Mid-Atlantic States before sliding off shore midweek...setting up a weak return flow with temps closer to normal.

I don't see a prolonged warm-up coming, but rather, an active sequence of storms with cold air holding over the next 10 days.

Current PNA analysis:

Current AO Ensemble forecast:

I'm oversimplifying things, but as a rule, a +PNA and a -AO signal cold and stormy in the Eastern US. The opposite is often observed: recall the weather in early January...warmer than normal and dry in the East. Note at that time the PNA was negative and the AO was negative but rising. A +PNA coupled with a -AO will accompany High Pressure in the West and a trof in the East. Again, I'm painting with a very broad brush and there are several other factors but these indicators teleconnect with future weather trends. If you'd like to see these charts or learn more about them please visit our Winter StormCenter and scroll to the "Forecast Graphs & Charts" drop-down box.

Next update will be on Sunday as I am going to a winter camporee with the Boy Scouts this weekend. Forecast low temperature at the camp on Saturday night is 8 degrees! I'll return to the blog on Sunday after thawing out my hands!

Stay warm and have a good weekend!

Let it (Mostly) Snow, Let it Snow, Let it Snow!
Thursday, January 17

Low Pressure now tracking from Florida Big Bend will be over OBX/VA-NC border tonight. High Pressure over the Northeast slides east as the Low heads up the coast tonight and tomorrow. Last night's tune-up on the forecast looks good with generally a snow event from west-central NC, VA, MD and Metro Washington DC. Richmond again right on the line with a mixed bag of mostly liquid precip along the I-95 Corridor with coastal location above freezing with rain. Current temps from our exclusive Mesonet Map:

This map also shows the CAD event we've discussed...cold air at the surface is prevalent along and east of the mountains into the Piedmont. Thinking is VA locations west of Route 29 probably are all snow or snow to a brief period of freezing rain/drizzle. Snow totals should be in the 3 to 6 inch range...more possible over higher ridges. East of Route 29, temps ebb up to and a little over the freezing mark this afternoon with a change to some freezing rain/drizzle. Along and east of the I-95 Corridor (including the Delmarva), temps are above freezing with rain being the main p-type.

Forecast looks good to the Northeast with snow roughly from Scranton, PA into "The County" in Maine. Heaviest accumulations from the Berkshires to Bangor.

9:30AM this morning: 2 inches outside the Mid-Atlantic WX.com office in Lexington, VA:

I'll have another update this evening so please stop by here at the blog.

UPDATE 11:35PM: Precipitation has pulled away from the Mid-Atlantic as the Low moves toward New England. 4.75 inches recorded at our wx station in Lexington, VA. Snowfall amounts generally in line with earlier forecasts: winner looks to be Swoope, VA in Augusta County where 8 inches has been reported. Interestingly, I am camping this weekend at a Boy Scout Camp in Swoope...figures!

Attention quickly turns to the next system to impact the region late Saturday. I'll have a quick update tomorrow morning by 10AM.

"GO" for Snow Before Brutal Cold Comes Calling From Canada!
Wednesday, January 16

Low Pressure over the GOM is currently (10:30PM) south of the AL/MS line and will track up into the Coastal Carolinas on Thursday. Chilly air mass in place...it snowed in Atlanta today...and precipitation shield now moving from Gulf/Southeast US into the region. Very dry air at the surface will take time to moisten up and so precip may hold off north of I-85 until early Thursday morning. For a snap shop of conditions, check our exclusive wet bulb located in Lexington, VA...click here to visit our weather station.

Both the 18Z and the 0Z NAM showed more precip and a return to colder air after a very slight overnight warm-up...this would produce more snow and less freezing rain over western and central NC as well as much of VA west of I-95. That Cold Air Damming (CAD) scenario outlined in yesterday's discussion also looks good, so this may be mostly snow along and west of the I-95 Corridor. In fact, tonight's soundings are *colder* than what the 18Z models depicted, bolstering confidence there will be more snow and less ice. So, accumulation totals will be tricky in areas warmer air moves in just above the CAD. We also need to see if the anticipated "dry slot" comes through and curtails precipitation totals. Lots of variables here!

Unless you are east of I-95 this should be a mostly snow event. Is this the storm that finally puts snow in Richmond? I think so! Widespread 3-5 inch totals likely from west-central NC through the Piedmont and interior Mid-Atlantic, central MD and then into New England. Please visit our Winter StormCenter for updated watches and warnings.

Well advertised brutal cold makes it into the East on Saturday...just in time for another storm to zip through. Check your local forecast for snow potential on Saturday and Sunday.

For a quick update and status report on this event please check here at the blog on Thursday morning after 10AM.

Mixed Mess for Mid-Atlantic Before The Icebox Opens!
Tuesday, January 15

As is often the case for the Mid-Atlantic, here's the typical storm genesis:
Forecast 1: snow, except the coast.
Forecast 2: snow changing to freezing rain.
Forecast 3: quick burst of snow then freezing rain, followed by rain.
Forecast 4: freezing rain, then rain.
Forecast 5: rain.

I'm exaggerating, but only a little! While the Thursday-Friday event has never been advertised here at the blog as a Mid-Atlantic snowstorm, we are seeing "warm creep" into the models...very common 2 days before a storm.

Current setup calls for High Pressure to build in from the west over the Mid-Atlantic States while Low Pressure gets going over the Gulf and heads up the coast off the OBX on Thursday evening. High Pressure will keep temps cold enough for precip to begin as snow from the mountains of GA/TN/SC/NC up into Virginia west of
I-95. Timing looks like early Thursday morning from the interior SE, morning commute Charlotte to Roanoke-Lynchburg...then overspreading areas to the north by early Thursday afternoon. Mountains and western highlands could be in the 2-3 inch range before warm air noses in just above the surface causing a change to sleet or freezing rain. Differing precipitation types based on elevation and how shallow the warmer layer will be as it moves into the region.

Near and east of the I-95 Corridor this should be rain with a slight risk of freezing rain pockets north of Petersburg-Richmond.

Another tricky feature is as the High slides off there could be a cold layer right at the surface...similar to a classic Cold Air Damming (CAD) event. This is when colder air is blown inland on east winds and stacks up (dammed) along the eastern slopes of the mountains. This very shallow surface layer is colder than the air just above it and can change the precipitation type with very slight changes of elevation. So, we need to see how this will develop. Most interior Mid-Atlantic areas will see snow changing to freezing rain while Piedmont and areas east of I-95 will generally be rain.

The Low tracks just enough to the west to keep warmer air along the coast so this should be a rain event up and east of I-95, perhaps as far north as Portsmouth, NH. Inland New England should be all snow with several inches possible.

Behind the departing storm, the Polar (Northern) Jet dives deeply into the eastern US with a fresh supply of very cold air. Saturday night temps should be the coldest of the season with very cold highs on Sunday and Monday as the Arctic High will be directly overhead.

Active sequence will continue with Gulf moisture poised to head into the region Saturday night and another system taking aim on the Southeast and Mid-Atlantic region on Tuesday. By then, the High should be moving off shore and that will allow some moderation in temperatures by mid-next week.

Several snow bands made it over the Alleghanies this morning; here's how it looked at 8:45AM today at Virginia Tech in Blacksburg, VA:

Incidentally, the new Virginia Tech April 16 Memorial is in the foreground. If you care to read more about this tribute, please click here to visit the Virginia Tech site.

I am on the road tomorrow but will try for a brief tune-up update late Wednesday evening. Please check back then!

Wimpy Weekend...Midweek Maybe.
Sunday, January 13

Quick update to be followed by more discussion this evening. Nil on white stuff today for Mid-Atlantic however as the trof swings through there will be showers/light rain and possibly some mixed snow over the western mountains. Coastal Low still on track to organize tonight before pulling away and threatening the Northeast on Monday.

Models (GFS in particular) still on board with potential winter event Thursday-Friday and tonight's discussion will see how we look with the 0Z model runs. For now, the possibility of winter weather remains on the table for later this week.

Time to catch some football. Please stop by this evening for an update here at the blog.

UPDATE 11:00PM: No changes with tonight's 0Z models in coming together on late Wednesday-Thursday winter event. Low Pressure will form near the TX Gulf coast and move toward Big Bend and then the Georgia coast before heading up the coast. Snow could mix with sleet for northern AL, MS and into NW GA late Wednesday. This set up is favorable for snow over interior SE as well as interior NC and VA before the Low warms temps nearer the coast on Thursday afternoon. Should this pan out, accumulating snow inland with a changeover to mixed precip is possible Thursday. Still early to pin it down but we can expect winter weather from the northern Gulf Coast states into the TN Valley, WV and Mid-Atlantic. I'll update the blog on Tuesday and invite you to stay close to our Winter StormCenter.

The Cold Will Take Hold...And...
VERY Active Pattern Will Bring the Storm Train East, For 2 Weeks...At Least!
Saturday, January 12

A multiplicity of storms loom on the horizon as we undergo a significant pattern change that will put an end to the temperature roller coaster in the Eastern US. Polar Vortex is migrating, Northern (Polar) Jet Stream will buckle south and cold High Pressure builds in: yep, the pattern is changing.

Low Pressure will develop over Texas and migrate across the Gulf of Mexico this weekend. Looks like a somewhat negatively tilted trof (good if you like storms) forms as the Low gets pulled together near the Carolinas coast; this is depicted by the GFS and the NAM on the model map below (click image for more graphics):

I don't believe this storm is much of a winter weather maker for the Lower Mid-Atlantic with coastal rains being the main feature. Can't rule out a wet snow/rain mix along and west of the Blue Ridge Sunday morning, or a slight chance for a wet snow mix over the Piedmont, but temps will exceed 32° during the day on Sunday, so I'm not enthusiastic about accumulation.

The storm departs the Mid-Atlantic coast on Sunday night and as is often the case, strong winds will blow behind the storm along with some upslope "back lash" snow for the mountains. A quick glance at the model map above screams one word: "Nor'easter"! Track and timing look good for a widespread snow event from the Poconos through northern New England into Monday night. Thinking right now is 4+ inches of snow east of the I-81 corridor, north of the Potomac River. Philly will likely see slushy wet snow and I think NYC has a genuine opportunity for 3-5 inches of white stuff! Worcester, MA into interior Maine could see the Mother lode of 12+ inches when all is said and done. Check our Winter StormCenter for real-time info and keep an eye on your local forecast right here at Mid-Atlantic WX.com.

I'll update the blog on Sunday morning, so please check back for the latest on this storm.

Cold High Pressure keeps temps at or below normal into Wednesday at which time the Ridge will slide off the coast and bump up temperatures for the Mid-Atlantic and Ohio Valley areas. This is when a new Low will form over the Gulf and head up the East Coast. This system will bring rain to the north-central Gulf Coast and Southeastern US States and may pose a winter threat for the Tennessee Valley and interior Mid-Atlantic on Thursday. As always, strength and track are to be determined but a snow/freezing rain to rain scenario is possible from the NC Piedmont into Virginia and the DC-Baltimore Metro on Thursday. This system will be monitored with updates next week here at the blog.

A third storm is hinted in long range model for next weekend for much of the East Coast, showing we are in an active pattern and one that I believe will hold through the balance of January.

Cool Cold Front: On Friday, a weak Warm Front was moving up across the Mid-Atlantic while a Cold Front tracked east as Low Pressure spun over the Great Lakes. You can see these features on the morning surface map for Friday, January 11:

Frontal boundaries frequently show up on satellite and that was the case on Friday morning:

What appears to be a line from Buffalo, NY south into central NC is the advancing Cold Front pushing up clouds along the boundary. To the east of the line, low clouds and fog are apparent in the warm sector.

This classified as a Cold Front that was "very cool"!

Please check back here at the blog during the week as I'll have updates on the upcoming active sequence of storms.

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