John Homenuk

PM Update: Winter weather set to impact the area

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A strong cold front, which crossed the region earlier today, is ushering in a much colder airmass — and a record breaking arctic airmass to the Central and Western United States. A developing disturbance along the front will touch off more precipitation in our area later this evening into Saturday. The dramatic cold front has not yet delivered arctic air to the East Coast, but the arctic gates have opened over much of the Midwest, Northwest and North-Central United States.

Some fascinating numbers evidencing the strength of the cold front include:

1) A minimum temperature reading of 28 degrees in NW Mississippi, and a maximum temperature reading of 84 degrees in SE Mississippi.

2) Temperatures in the upper single digits and lower teens as far south as Oklahoma, Texas, and Arkansas, where several inches of snow has fallen.

3) A minimum temperature reading of -23 degrees in Montana, and a maximum temperature reading of 87 degrees in Florida. A 110-degree temperature gradient across the country!

RAP analysis on Friday evening, showing a dramatic cold front over the Eastern US and an arctic airmass over the Central and Western US.

RAP analysis on Friday evening, showing a dramatic cold front over the Eastern US and an arctic airmass over the Central and Western US.

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John Homenuk

Forecast: Dense fog, warmth before big cold front

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Friday Morning Update: Dense fog advisories have been canceled by the National Weather Service (despite the title of our article remaining the same) this morning. Periods of fog are still possible, but won’t be as thick or widespread. Showers are expected to become numerous over the next few hours and rain may become steady to briefly heavy at times. Temperatures will begin to drop throughout the area later this morning in response to an approaching and passing cold front.

The cold front, which will cross on region on Friday, will also bring periods of showers and unsettled weather throughout the day. More importantly, it will mark the end of any semblance of a warm airmass with its passage as temperatures will plummet behind it on Saturday through the second half of the weekend. In fact, rain and showers may end as frozen precipitation on Saturday morning, especially across parts of the interior. Any accumulations are expected to be minimal, but stay tuned for updates as it likely will be a short term/nowcasting type situation.

Surface analysis from late Thursday night into Friday morning showed an approaching cold front, with warm conditions still in place throughout the area.

Surface analysis from late Thursday night into Friday morning showed an approaching cold front, with warm conditions still in place throughout the area.

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Doug Simonian

Clearing the fog in today’s forecast

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Many of us woke up to dense fog this morning, and are still experiencing dense fog as we speak. Normally, fog forms in the early-morning hours and then dissipates after sunrise when the atmosphere warms up and the fog can lift. However, this dense fog has lingered all morning and will continue to linger throughout the entire day, though somewhat diminish in intensity during the afternoon, but may become a bit more dense again during the evening hours. The cause of the fog is a warm front that is approaching the area, helping to advect lots of moisture into the region.

Current surface analysis shows a warm front moving into the area, which is bringing southeast winds off of the Atlantic Ocean, explaining the moisture and the dense fog today. Image credit goes to weatherroanoke.com

Current surface analysis shows a warm front moving into the area, which is bringing southeast winds off of the Atlantic Ocean, explaining the moisture and the dense fog today. Image credit goes to weatherroanoke.com.

To the west of the warm front is a low pressure system and a cold front, and this front will eventually bring us rain for tonight and Friday night. In between the cold front and warm front are southwest winds, which is a warm wind; so south and west of the warm front, there is more warmth, which helps to lift any fog away. Closer to the low pressure itself and the cold front is rain in western PA, which will stay to our west throughout the day. However in our area, we are further ahead of the low pressure, which brings us southeasterly winds at the surface. This brings in warm air for winter standards, but still relatively chilly Atlantic Ocean air, as well as abundant moisture to form the fog. The warm front is the boundary between the warmer southwest winds, and the cooler, but still mild and moist/Atlantic contaminated southeast winds.

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Doug Simonian

Colder weekend could lead to a wintry mess on Sunday night

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As temperatures have moderated along the east coast, an abnormally strong cold airmass has entered the Western half of the United States. This cold airmass is thanks to a strong -EPO ridge over Alaska, which helps to dislodge Arctic cold into the United States. However, because of the +NAO, +AO, and -PNA, this cold is forced into the West, and will initially have a lot of resistance as it tries to head eastward. This pattern is illustrated very well by today’s 12z European model, valid for Thursday night, shown below.

Today's 12z European model valid for Thursday night shows what we call a "gradient" pattern with very cold air to the north and warm air to the south and east. This battle zone between the two airmasses will create the chances for precipitation. Image credit goes to the WSI Model Lab.

Today’s 12z European model valid for Thursday night shows what we call a “gradient” pattern with very cold air to the north and warm air to the south and east. This battle zone between the two airmasses will create the chances for precipitation. Image credit goes to the WSI Model Lab.

The strong -EPO ridge is evident as there are high 500mb heights into Alaska, which is forcing an Arctic airmass into the Northern Plains. This airmass has the chance to break records, and will try to spill eastward with time; however, it has a lot of resistance thanks to the strong ridge in the Southeast. This very warm air in the Southeast and Arctic air in the Northern Plains will create an impressive temperature gradient in the northern Mississippi Valley and Ohio Valley region, and this gradient is where some storms will form. As these storms form, the ridge in the Southeast will force them to track to our west, leading to warm air and rain for Thursday night and Friday. However, the passage of each low pressure will try to gradually shift this gradient eastward due to counterclockwise flow behind them — it is a step-down process. The image below illustrates how strong this gradient really is, and it’s pretty mind-boggling.

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