7:00 AM | **Accumulating snow winds down slowly later today; 3rd biggest snowstorm ever this late in the season at DCA and 2nd biggest March snowstorm ever at Dulles**

6-Day Forecast

Today

Cloudy and cold with periods of snow continuing into the afternoon hours, an additional 1-3 inches of snow can accumulate in some sections, highs in the low 30’s

Tonight

Mainly cloudy, very cold, lows near 25 degrees

Tuesday

Mainly cloudy, cold, low-to-mid 40's

Tuesday Night

Partly cloudy, cold, near 30

Wednesday

Mostly cloudy, chilly, chance for a few rain showers, upper 40’s

Thursday

Partly sunny, milder, mid 50’s

Friday

Partly sunny, mild, upper 50’s

Saturday

Partly sunny, mild, showers possible, near 60

Discussion

Reagan National Airport (DCA) has received 7.2 inches of snow (as of 7am) which has made this the 3rd biggest snowstorm ever for this late in the season and 10th biggest March snowstorm ever. Dulles Airport has received 10" of snow so far making this their 2nd biggest March snowstorm ever. Elsewhere, 8" of snow has been reported near BWI Airport, 8" or so in Bethesda, MD and these high amounts extend all the way to the New Jersey coastline where Cape May, NJ has already piled up 7" of snow with more still to come.

Snow will wind down quite slowly around here today with some lingering into the afternoon hours. Low pressure centered off the North Carolina coastline will move out to sea today and cold high pressure will build into the region from the north for tonight and tomorrow. A frontal system could cause some rain showers on Wednesday and then the latter part of the week will get noticeably milder (spring begins on Thursday). This late week warmup will not be part of anything sustained, however, as there is certainly plenty more in the way of cold for at least the next few weeks.

Video

httpv://youtu.be/LCSN205kTtI

2:00 PM | **Accumulating snow arrives early tonight in much of the Mid-Atlantic region**

Discussion

What a difference a day makes! Arctic air seeped into the Mid-Atlantic region right on schedule in the overnight hours anchored by strong high pressure currently situated over south-central Canada. As a result, today’s high temperatures will be considerably lower than yesterday’s spring-like readings which reached the 60’s in many areas. Meanwhile, a massive area of moisture [latest radar above courtesy mesonet.org; NOAA GOES water vapor image below] is now heading northeast towards the Mid-Atlantic region. This very impressive area of moisture is well supported by strong upper-level dynamics and there are even numerous severe thunderstorms today across the Deep South with tornado warnings in some isolated locations. As this moist air runs into the cold, dry, dense low-level Arctic air now in place across the Mid-Atlantic region, its progress to the northeast will slowly grind to a halt and eventually it will be forced to move eastward with a sharp precipitation gradient on the northern edge.

The end result of this will be that the highest snowfall accumulations from early tonight into early Monday will tend to be in southern sections of the Mid-Atlantic region such as around the DC metro region, the Delmarva Peninsula, and the southern half of New Jersey. However, moderate amounts of snow accumulation are expected to reach as far north as the city of Philadelphia and its northern and western suburbs. [Note: the Philly National Weather Service does not currently have any of the counties in southeastern Pennsylvania in a "winter weather advisory", but I believe that will (and should) change later in the day]. The least amount of snowfall from this storm along the Mid-Atlantic I-95 corridor should be in the New York City metro region. The precipitation will arrive in the DC metro region early tonight in the form of plain rain, but, it should change over to all snow rather quickly. Virtually all of the precipitation that falls north of the PA/MD border during this storm should be in the form of snow and it should begin during the late evening hours.

Here is the latest thinking on tonight's snow accumulations in the Mid-Atlantic region:

New York City metro region: on the northern edge; anywhere from a coating to an inch or so

Philly metro region: 1-4 inches on average with the higher amounts generally in southern parts of the area [Note - Philly Airport needs only 2.6” of snow to match the 2nd snowiest winter ever of 1995-1996 (65.5”); definitely within reach from this storm]

DC, Delmarva Peninsula and southern New Jersey:: 4-8 inches with isolated higher amounts for this the “southern-most” section of the Mid-Atlantic region

Stay tuned for possible further updates as a small shift can still make a big difference.

2:45 PM | *Accumulating snow threat continues for much of the Mid-Atlantic region with the highest amounts expected in southern sections*

Discussion

There are quite a few similarities between this upcoming event and the storm system that affected the Mid-Atlantic region earlier this month. That storm which occurred on March 3rd resulted in 4 to 8 inches of snow on average in the region between DC and the southern New Jersey Shore, 3.4 inches in South Philly at the airport, but very little in the Philly suburbs and virtually no snow in the New York City metro region. In both cases, a strong Arctic high pressure system pushed in from the north with very cold, dry, dense low-level Arctic air. Additionally, in both cases the main area for accumulating snow was gradually suppressed to the south by the computer forecast models as the event time approached. Finally, there was a pretty sharp cutoff to the snowfall accumulations on the northern edge on March 3rd and that scenario appears to be setting up for this time as well.

The ultimate result of all of this is that the highest snowfall amounts coming during the late Sunday/Monday time period appear to be headed for the same region between DC and the southern New Jersey Shore. While the Philly metro region is still in the ball park for some accumulations, the New York City metro region will likely be on the extreme northern fringes. Any precipitation that falls north of the PA/MD border should be virtually all snow and, while there can be an initial period of rain or sleet in the area between DC and New Jersey, the vast majority of the precipitation should be in the form of snow in that region as well. Here is the latest thinking on snow accumulations for the period of late Sunday into early Monday:

NYC: on the northern edge, anywhere from a coating to an inch or so PHL: 1-4 inches is possible with the higher amounts in southern parts of the area (e.g., southern Chester County) DC to the southern Jersey Shore: 4-8 inches is on the table for this “southern-most” section of the Mid-Atlantic with the highest amounts to the south and west of the District

Stay tuned for any possible further updates, a small shift can still make a big difference.

2:45 PM | **The threat remains for accumulating snow in the Mid-Atlantic region later Sunday into Monday - but stay tuned**

Discussion

Overview While chances do remain for accumulating snow in much of the Mid-Atlantic from late Sunday into Monday, there is nothing certain at this time and a small shift can mean a big difference. After a relatively mild day on Saturday, colder air will push into the Mid-Atlantic region from the northwest on Saturday night and Sunday. This injection of fresh Arctic air will be anchored by strong high pressure that will be edging into southeastern Canada later Sunday into Monday – a good location for holding cold air in the Mid-Atlantic region and a crucial player in this upcoming threat for accumulating snow. At the same time, an area of low pressure - supported by a couple pieces of energy in the upper atmosphere - will organize in the Southeast US and it will head northeastward towards the Mid-Atlantic region with plenty of moisture to “overrun” the dense, cold Arctic air mass. One important question that still remains at this time is “exactly how far to the north and east in the Mid-Atlantic region can the moist air advance as it encounters this fresh cold, dense and dry Arctic air mass”. Right now, it appears that there is a greater chance for significant snow to the south and west in the Mid-Atlantic region (e.g., from DC to the South Jersey Shore) and less to the north and east (e.g., NYC metro region); Philly is certainly still in the ball park.

Details Precipitation is likely to break out in the DC metro region during the mid-to-late afternoon hours on Sunday and then perhaps in Philly a few hours later. The precipitation may start as rain in the DC metro region before changing over to snow, but would likely begin as snow in the Philly metro region. Snow may then continue into early Monday in the DC metro region - and perhaps as far north and east as Philly - and while there can be a mixture at times with sleet and/or freezing rain, snow accumulations are likely by Monday morning. At this time, the New York City metro region appears to be on the northern fringes of the precipitation field for this upcoming event and it is definitely too early to make any kind of a confident call for accumulating snow up there.

General notes Snow accumulations this late in the winter season are sometimes largely dependent on “altitude” and “time of day” in that snow has a much better shot at sticking on the ground during nighttime hours and at higher elevation locations which will tend to accumulate much quicker than lower spots in marginally cold situations this time of year. One other note, Philly Airport needs only 2.6” of snow to match the 2nd snowiest winter ever of 1995-1996 (65.5”) and it is 15.8” behind the snowiest winter ever of 2009-2010 (78.7”)…just saying.

Stay tuned to “thesiweather.com” this weekend for updates noting that there is still quite some time to go before this potential storm reaches our area and a small swing to the south or north can make a big difference.

7:00 AM | **Accumulating snow threat later Sunday into Monday**

6-Day Forecast

Today

Clouds this morning will give way to full sunshine, becoming noticeably milder this afternoon, highs in the upper 50’s

Tonight

Mostly cloudy, chilly, chance for a shower or two late, lows in the upper 30’s

Saturday

Partly sunny, mild, low 60's

Saturday Night

Partly cloudy, turning colder, lower 30’s for lows by morning

Sunday

Sunshine followed by thickening clouds, colder, rain likely to develop late in the day or at night then it changes to snow with accumulations possible, low-to-mid 40’s

Monday

Cloudy, cold, snow likely, possibly mixed with sleet and/or rain at times, more snow accumulations possible, mid 30’s

Tuesday

Partly sunny, cold, low 40’s

Wednesday

Partly sunny, cool, chance for a few showers, low 50’s

Discussion

A significant rebound in temperatures will take place today throughout the Mid-Atlantic region and the milder conditions will continue at the beginning of the weekend. A cold front, however, will pass through the region later tomorrow and colder air returns for Saturday night and Sunday. This injection of fresh Arctic air will be anchored by strong high pressure that will be edging into southeastern Canada later Sunday and Monday – a perfect location to sustain cold air in the Mid-Atlantic region and a crucial player in this upcoming threat for snow.

At the same time, low pressure will organize in the Southeast US and it will begin to head northeastward towards the Mid-Atlantic region with plenty of moisture and supported by a strong upper level trough. There are still plenty of details to work out in terms of how much moisture can penetrate this far north and east right into the heart of the Arctic high pressure system, and how much mixing of the precipitation will take place around here, but there is enough evidence to suggest that accumulating snow, possibly on the significant side, could occur in the I-95 corridor from DC-to-Philly-to-NYC late Sunday and Monday.

Video

httpv://youtu.be/6zH6Fw3xcM4

1:30 PM | **Accumulating snow threat for later Sunday into Monday**

Discussion

First, let me start by saying that I am just the messenger. Despite the fact that the middle of March is fast approaching on the calendar and climatology is increasingly against the idea of snow this time of year, there is a real threat for accumulating snow later Sunday into Monday in the Mid-Atlantic region. After today’s bitter cold wind chills in the Mid-Atlantic region, there will be a noticeable rebound of temperatures on Friday and those milder conditions will continue on Saturday as well. However, a cold frontal system will slip through the region later Saturday and colder air will push in from our northwest during Saturday night and Sunday. This injection of fresh Arctic air will be anchored by strong high pressure that will be edging into southeastern Canada later Sunday and Monday – a perfect location to sustain cold air in the Mid-Atlantic region and a crucial player in this upcoming threat for snow. At the same time, low pressure will organize in the Southeast US and it will begin to head northeastward towards the Mid-Atlantic region with plenty of moisture and supported by a strong upper level trough. There are still plenty of details to work out in terms of how much moisture can penetrate this far north and east right into the heart of the Arctic high pressure system, but there is already enough evidence to suggest that accumulating snow could develop in DC, Philly, and perhaps even New York City, later in the day on Sunday. Stay tuned – winter lives on.

7:00 AM | **Continued very windy and cold today, but temperatures modify significantly on Friday**

6-Day Forecast

Today

Becoming partly-to-mostly sunny, continued very wind and unseasonably cold, winds could gust to 40 mph or so out of the northwest, highs held down to the mid and upper 30's which is well below normal for mid-March

Tonight

Mostly clear and very cold with diminishing winds, lows by morning near 20 degrees

Friday

Mostly sunny, considerably milder, mid 50’s

Friday Night

Mostly cloudy, chilly, upper 30’s

Saturday

Partly sunny, even milder, near 60

Sunday

Increasing clouds, colder, upper 40’s; chance for snow and/or rain at night

Monday

Cloudy, cold, chance for snow and/or rain, upper 30’s

Tuesday

Partly sunny, cold, near 40

Discussion

Winds will continue on the strong side for much of today gusting up to 40 mph or so out of the northwest. Despite plenty of sunshine, temperatures will have a hard time escaping the 30's for highs which is way below normal for this time of year. After a very cold (but calmer) night, temperatures will rebound noticeably on Friday and then remain at mild levels on Saturday before more cold air returns to the region on Sunday. By Sunday night and Monday, moisture in the Southeast US will begin heading towards the Mid-Atlantic region and - depending on how far northeast it can come - the result could be some snow around here early next week.

Video

httpv://youtu.be/IPJzEpvP8Dc

3:00 PM | **Potentially damaging wind gusts and scattered power outages**

Discussion

Overview A rapidly intensifying and already powerful low pressure system currently sits over southwestern Pennsylvania with its latest central pressure reading at 29.14 inches. This storm will travel across the state over the next several hours and swing an intense cold front across the region this evening which will result in a dramatic plunge of temperatures later tonight. Damaging wind gusts of 50 mph or so are a real threat in this pattern and these excessive winds can occur during the passage of the frontal system and also in the cold air behind the front later tonight into tomorrow morning with scattered power outages possible. So far, NOAA has not posted any tornado watches for the Mid-Atlantic region, but that is still a possibility as the afternoon progresses. Farther north, an all-out blizzard is now occurring in places like Cleveland, OH, Buffalo and Rochester in New York State with heavy snow, strong winds, and even some thunder and these blizzard conditions will extend shortly to interior sections of New England where more than a foot of snow can accumulate by morning.

The frontal passage (5-9PM) Temperatures have spiked this afternoon to spring-like levels ahead of the approaching cold frontal system and a line of showers and embedded strong-to-severe thunderstorms along the front will move through the metro region between the hours of 5 and 9PM. This is a “fast-moving” and “narrow” line of showers and thunderstorms, but any one of these storms can produce brief heavy rainfall and damaging wind gusts of up to 50 mph or so. The cold frontal passage will definitely not end the threat for extreme wind gusts in the region.

“Post-frontal” weather for the rest of the night and Thursday Once the front moves through the area, winds will shift to a northwesterly direction and they will gust up to 50 mph or so during the rest of the night and right through Thursday morning. Temperatures will plunge from early evening levels near 60 degrees to late night values close to 20 degrees and there will be single digit wind chill values across the region by morning. Scattered snow showers are likely later tonight and, while little or no snow accumulations are expected, some icy spots can form as a result of the rapid drop in temperatures to below freezing levels. Temperatures tomorrow will be way below normal for this time of year throughout the region - despite the return of sunshine - likely holding below 30 degrees for highs. A quick rebound in temperatures will occur on Friday in the Mid-Atlantic region following a very cold (but calmer) Thursday night. Looking ahead, after a mild Saturday, colder air returns to the region early next week and there is even the threat for some accumulating snow later Sunday into Monday.

7:00 AM | **Near 70 degrees for highs today and then in the low 20's for lows early tomorrow; this dramatic transition will be accompanied by rain, strong-to-severe thunderstorms and possible damaging wind gusts as a powerful cold front sweeps through the metro region**

6-Day Forecast

Today

Occasional showers today with possible late afternoon thunderstorms, some of the storms that form can be strong-to-severe with damaging wind gusts and brief heavy rainfall, spring-like warmth today with highs not far from 70 degrees

Tonight

Rain showers and a possible strong-to-severe thunderstorm early then becoming sharply colder with whipping winds and possible snow showers late tonight, winds can gust up to 50 mph or so out of the northwest late tonight, the rapid drop in temperatures to below freezing levels can generate some icy spots, lows by morning in the low-to-mid 20's with even lower wind chills

Thursday

Becoming partly-to-mostly sunny, very windy and cold for this time of year, wind gusts could reach 40 mph, temperatures will struggle to pass the freezing mark

Thursday Night

Mostly clear, brisk and very cold, low 20’s

Friday

Mostly sunny, not nearly as cold, near 50

Saturday

Mostly cloudy, milder, near 60

Sunday

Partly sunny, colder, upper 40’s

Monday

Cloudy, cold, chance for snow or rain, near 40

Discussion

Some wild weather is in store for the region between late today and early tomorrow morning that will include spring-like warmth, rain, possible strong-to-severe thunderstorms, damaging wind gusts, plunging overnight temperatures and possible snow showers. Showers will break out today as low pressure intensifies rapidly on its way to Pennsylvania and this storm will push an intense cold front towards the DC metro region. Temperatures will spike ahead of the front and a line of strong-to-severe thunderstorms is likely to form by late in the afternoon as the frontal system approaches the I-95 corridor. Any storm that develops later today can contain damaging wind gusts and brief heavy rainfall. In fact, unstable atmospheric conditions later today could warrant tornado watches to be implemented by NOAA for parts of the Mid-Atlantic region; especially, south of the PA/MD border.

Once the front clears the region later this evening, temperatures will plunge and rain showers could changeover to snow showers. While little or no snow accumulation is expected, some icy spots can form on roadways as temperatures nose-dive to below freezing levels in the overnight hours. Winds will howl late tonight and tomorrow from a northwesterly direction with gusts possible of up to 50 mph through the night and up to 40 mph for much of the day on Thursday. Temperatures tomorrow will be held to near freezing for highs - rather amazingly low levels for this time of year - despite the return of sunshine. Looking ahead, after a mild start to the weekend, colder air will move into the Mid-Atlantic region on Sunday. At the same time, moisture will be building in the Southeast U.S. and snow is indeed a threat around here in the Sunday night/Monday time frame.

Video

httpv://youtu.be/sXR5KTEABBs

12:45 PM | **Wild weather in the Mid-Atlantic region from later tomorrow into Thursday to include spring-like warmth, rain, strong thunderstorms, possible damaging winds, plunging temperatures and snow showers**

Discussion

Overall Summary Wild weather is in store for the Mid-Atlantic region from later Wednesday into Thursday that could include all of the following: spring-like warmth, rain, strong thunderstorms, howling and perhaps damaging wind gusts, plummeting temperatures, snow showers and even icy spots on the roadways. A potent and intensifying storm, fueled by a vigorous upper level jet streak, will cross right over the state of Pennsylvania later tomorrow and it will swing an energetic cold front into the I-95 corridor that will produce wild weather and dramatic temperature changes in the region.

The "warm sector" weather details Powerful low pressure deepens rapidly later tomorrow reaching 984 millibars (29.06 inches) or so by the time it reaches the eastern part of Pennsylvania (12Z NAM surface forecast map for early tomorrow evening - below) and rain will break out throughout the region. Temperatures should spike tomorrow ahead of the front to 60+ degrees in the I-95 corridor and as the front approaches, a line of strong thunderstorms is likely to form (high-resolution 12Z NAM simulated radar map for early Wednesday evening - above, courtesy Penn State eWall]. This line of thunderstorms should reach the DC and Philly metro regions during the late afternoon or early evening hours and there can be some damaging wind gusts and isolated tornadoes cannot be ruled out.

The "post-frontal system" weather details Once the front clears the region later tomorrow night, temperatures will nose-dive some 40 degrees or so from the spring-like afternoon highs to near twenty degrees by early Thursday morning. Winds will howl behind the front up to 50 mph or so producing a second opportunity for damage in the Mid-Atlantic region. Rain showers are quite likely to changeover to snow showers later tomorrow night in locations north and east of the PA/MD border as temperatures plunge to below freezing. While snow accumulations should be on the minor side in the I-95 corridor, there can be some icy spots that form given the expected rapid drop in temperatures to well below freezing levels by early Thursday morning. Winds stay strong on Thursday in the Mid-Atlantic region gusting up to 50 mph or so out of the northwest and high temperatures will be confined to rather amazingly cold levels for this time of year reaching only the upper 20’s or lower 30’s despite the return of partial sunshine.

Looking ahead to next week After a mild start to the weekend, colder air will move into the Mid-Atlantic region on Sunday. At the same time, moisture will be building in the Southeast U.S. and snow is indeed a threat in parts of the Mid-Atlantic region in the Sunday night/Monday time frame. In addition, there may be more cold air masses to deal with later next week along with other systems that could produce snow in the region.