Vencore Weather
1Mar/15Sun

8:45 AM | ***Accumulating snow and the threat for a significant buildup of ice***

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[US radar image with plenty of moisture headed to the Mid-Atlantic region; NEXRAD image courtesy University of Wisconsin]

Discussion

Overview
Dense, cold Arctic air sits on top of the Mid-Atlantic region this morning and copious amounts of moisture (radar map) is streaming in from the west – a bad combination that spells big trouble for the I-95 corridor region from DC-to-Philly-to-NYC. Accumulating snow is likely in all areas along I-95 at the onset of today's precipitation event, but that ultimately will not be the biggest problem. Milder air moving northward in the upper part of the atmosphere will generate a changeover from the snow to sleet and then to freezing rain in most areas and there can be a significant buildup of ice on untreated surfaces (e.g., trees, grass, untreated roadways) with slick travel conditions. While the upper atmosphere turns milder, the dense, cold and below-freezing Arctic air at ground level will be reluctant to retreat; thereby, setting the stage for some serious ice buildup later today and early tonight in portions of the area.

Details
Snow is likely to break out by mid-morning in the DC metro region perhaps even mixed with some sleet in southern sections, in the late morning to mid-day hours across Philly, and then during the early afternoon in the NYC metro region. Then, after a period of accumulating snow, there will then be a transition later today from south-to-north of the snow to sleet and then to freezing rain although snow will hang on for much of this event in higher elevation locations north of I-80 (e.g., NE PA). Before the changeover to ice, snow should accumulate from a coating to an inch or two in and around the DC metro region, 1-3 inches in the Philly metro region, and 2-4 inches in the NYC metro region. The higher amounts in those snowfall accumulation estimates will occur to the north in a given metro region and the lesser amounts to the south. A significant ice-buildup (quarter to half an inch) is possible later today into early tonight in the entire I-95 region from DC-to-Philly-to-NYC. Precipitation winds down by or shortly after midnight in most of the I-95 corridor.

“Banding” could enhance snow (or ice) totals in parts of the area
One final word of caution on today’s event…there will be an impressive thermal gradient in the Mid-Atlantic region and strong upward motion in the atmosphere as a powerful upper-level jet streak (purple area on 300 millibar map) plows through the region from west-to-east. As a result, in this type of dynamic atmosphere, “banding” is likely to develop in the precipitation field later today causing varying rates of precipitation and there could be an enhancement of the snow (or ice) in a given area in a short period of time. We’ll monitor the precipitation pattern as the day progresses and make adjustments to accumulation totals if necessary.

300mb_sf
[Sunday AM 300 millibar winds showing powerful jet streak (purple) which is headed right into the Mid-Atlantic region; courtesy NOAA]

Another interesting and complicated threat at mid-week
Another complicated precipitation event is likely to occur in the I-95 corridor from Tuesday into Thursday. Precipitation ahead of another strong Arctic frontal system is likely to arrive late Tuesday and it could start as a wintry mix in the I-95 corridor. However, as milder air pumps in from the south, the precipitation is likely to change to plain rain for Tuesday night and early Wednesday and some of the rain can be heavy. Temperatures could climb into the 50’s in portions of the I-95 corridor during the day Wednesday before colder air returns. The Arctic frontal system may then stall as it reaches the east coast on Wednesday night and there is a chance low pressure develops along the frontal boundary and rides up along it into the I-95 corridor region. If this takes place, it could very well turn cold enough for some snow around here in the late Wednesday night/Thursday time frame. Stay tuned on that one.

Filed under: NYC, PHL, WMA Comments Off
28Feb/15Sat

12:00 PM | **Looks like a real mess on Sunday with a buildup of snow and/or ice depending on location; another complex and interesting precipitation event comes in the Tuesday-Thursday time frame**

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[Mid-day US surface weather map with very strong Arctic high pressure centered right over the Mid-Atlantic; courtesy NOAA]

Discussion

Overview
The weekend begins with very strong Arctic high pressure sitting right on top of the Mid-Atlantic region (surface map above) assuring us plenty of sunshine today along with light winds. Atmospheric pressure readings at mid-day are as high as 30.85 inches (1045 millibars) in parts of the Mid-Atlantic region associated with this very dense and cold Arctic air mass. The combination of this entrenched dense, cold dome of Arctic air and moisture streaming in from the west on Sunday spells big trouble for the DC, Philly and NYC metro regions with accumulating snow or a significant buildup of ice or both real threats as we close out the weekend.

Details
As the high pressure shifts off the east coast on Sunday, a warm advection pattern will set up with light snow likely to break out in the pre-dawn hours across western and central portions of the Mid-Atlantic region. During the mid-morning to late-morning hours, snow is likely to break out in the I-95 corridor and it will likely change to a wintry mix in the DC metro region after a few hours, but not before there is a coating to an inch or two of new snow accumulations. The snow will continue for a longer time period across SE PA with 2-4 inches likely before any changeover and areas to the north of I-80 are probably the luckiest of all as the snow up there could hang on for most or all of this upcoming precipitation event; thereby reducing chances up there for any serious ice buildup. The New York City metro region should receive several hours of snowfall before any changeover takes place with 3-5 inches of accumulation possible in that area. The period of icing following the initial “thumping” of snow can produce a significant buildup of ice later Sunday into Sunday night; especially, in the region from the N and W suburbs of DC to the N and W suburbs of Philly. All precipitation winds down in the pre-dawn hours early Monday and the rest of the day remains cold and becomes quite breezy.

“Banding” possibility could enhance snow (or ice) totals in parts of the area
One final word of caution on tomorrow’s event…there will be impressive upward motion at mid-levels of the atmosphere centered around northeastern Maryland and southeastern Pennsylvania late in the day. The 12Z NAM forecast map (below) for early tomorrow evening shows this area of mid-level upward motion (850 millbar absolute vorticity) centered near the eastern part of the Mason-Dixon Line. Often times with this kind of concentrated upward motion, there can be “banding” that sets up in the precipitation field and this could lead to enhanced snowfall (or ice) amounts in a short period of time over parts of the area…something to watch for later tomorrow.

nam_namer_036_850_vort_ht
[12Z NAM forecast map of 850 millibar absolute vorticity early Sunday night; courtesy NOAA]

Another interesting and complicated threat at mid-week
Another complicated weather pattern is setting up for the I-95 corridor for the time period from later Tuesday into Thursday. Precipitation ahead of yet another strong Arctic cold frontal system is likely to arrive Tuesday afternoon and it could start as a wintry mix in the I-95 corridor. However, as milder air pumps in from the south ahead of the front, the precipitation is very likely to change to plain rain for Tuesday night into early Wednesday and some of the rainfall can be on the heavy side. Temperatures could actually climb into the 50’s in portions of the I-95 corridor during the day Wednesday before colder air returns to the region. The Arctic cold frontal system may then stall out as it reaches the east coast on Wednesday night and there is a chance that low pressure develops along the frontal boundary zone and rides up along it right into the I-95 corridor - and into the incoming colder air. If indeed this takes place, it could very well turn cold enough for accumulating snow around here sometime in the Wednesday night/Thursday time frame. Stay tuned.

Filed under: NYC, PHL, WMA Comments Off
27Feb/15Fri

1:15 PM | **Another weekend and another accumulating snow and ice threat for the Mid-Atlantic**

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[Total snowfall forecast by the 12Z GFS for the upcoming event; map courtesy "tropicaltidbits.com", NOAA]

Discussion

Weekends have featured very active weather in recent weeks in the I-95 corridor and it looks like this weekend will be no exception. In fact, it appears that there could be a quick “thumping” of accumulating snow later Sunday; especially, in the region between Philly and New York City, and this accumulating snow will be followed by a period of icing. Sound familiar, in many ways this pattern resembles last weekend's situation in which bitter cold weather on Saturday was followed by accumulating snow and then a period of ice on Sunday. In fact, in another similar twist, much of last weekend’s frozen precipitation event took place with an unusual southerly wind direction as high pressure moved off the east coast – usually a recipe for rain around here - and a similar pattern is likely late this weekend. There does appear to be one difference from this upcoming event compared to last weekend and that is the idea that it appears the “thumping” of accumulating snow may take place farther north than last weekend - this time from Philly-to-NYC instead of from DC-to-Philly.

Currently, it looks like precipitation should arrive in the I-95 corridor in the form of snow during the afternoon hours on Sunday with accumulations likely at the onset. The snow will likely change rather quickly to a wintry mix in the DC metro region, but it could hold on as snow for a longer time in the region between Philly and NYC where a few inches can accumulate before a changeover finally takes place and there is a buildup of ice. Much like last weekend, a layer of crusty ice is likely to form on any snow that does accumulate in the I-95 corridor and precipitation should end by early Monday. Temperatures will start off the weekend at very cold levels in the single digits in some suburban locations, but should turn (temporarily) warmer next week before yet another impressive blast of Arctic air arrives on Thursday.

Filed under: NYC, PHL, WMA Comments Off
27Feb/15Fri

7:00 AM | Quite cold as we end the work week and possible record cold as we begin the weekend…wintry mix likely later Sunday into Monday

6-Day DC Forecast

Today

Scattered early morning snow showers; otherwise, partly sunny skies, quite cold, highs not far from 30 degrees

Tonight

Mainly clear and very cold, lows not far from 10 degrees

Saturday

Mainly sunny, still quite cold, upper 20’s

Saturday Night

Partly cloudy, very cold, lows in the middle teens

Sunday

Becoming mostly cloudy, cold, chance for a wintry mix of precipitation late in the day and at night, mid 30’s

Monday

Becoming partly sunny, not as cold, low-to-mid 40’s

Tuesday

Mostly cloudy, colder, chance for a wintry mix that becomes plain rain, upper 30’s

Wednesday

Mostly cloudy, much milder, rain likely, upper 50’s

Discussion

Cold weather will close out the work week and the weekend will remain well-below normal for this time of year. In fact, record cold is possible early Saturday as temperatures overnight will plunge towards the 10 degree mark in most areas which can break some local records. February ends on Saturday and it will end up being one of the coldest February's ever in the area - Dulles Airport has had an amazing 9 mornings this month with single digit low temperature readings. As March begins on Sunday, a cold front will approach the Mid-Atlantic region. This front will likely generate a wintry mix in the region from later Sunday into early Monday. The 50's are likely for highs by the middle of next week, but it'll be accompanied by rainfall, perhaps heavy at times, and then another batch of Arctic air should return on Thursday.

Video

Filed under: WMA Comments Off