First Chance of Snow for the DC Area

By Christopher M., chief forecaster.

(Washington D.C.) Our first chance of some wintry weather and even accumulating snow is increasingly likely as new data comes in. 

The second storm system of the week is making its way up the east coast, which will cause major travel disruptions for morning commuters, especially in the north and western suburbs of Washington D.C. For now, a couple of rain showers will linger, but they will move out by early tomorrow morning.

Penn State Meteorology: Northeastern U.S. doppler radar.

The next system moving in holds a lot of moisture, and by a lot, I mean a LOT.

It is expected to produce a wintry mix and snow for parts of the area. The computer models are now in good agreement of where this system will track, how much snow will fall, and its timing. The timing is pretty well situated where I think the system will arrive early Thursday morning, where temperatures will be cold enough for snowflakes, even in Washington D.C., and especially in north and western communities, such as Leesburg, Manassas, Frederick, MD, Winchester, and Front Royal.

Tropical Tidbits: GFS 6-hour averaged surface reflectivity.

According to the GFS and European models, the system will move in early Thursday morning. Rain will stick to the south, but it will transition into freezing rain, sleet, and snow as it tracks northward into Northern Virginia as it comes into contact with the cold air mass.

Temperatures are expected to be slightly below freezing Thursday morning, and due to the increase in cloud cover over the next 48 hours, radiational cooling during the evening hours will be slim to none, whereas the incoming solar radiation that warms the air during the day will only raise the temperature by two to five degrees. Most areas will not get above 35 degrees Thursday, some will stay near or slightly below freezing, while D.C. and Baltimore will be slightly warmer, both around 39 degrees.

Thursday morning’s forecasted lows.

The snow is expected to start around 5:00 to 6:00 AM Thursday and it will last to about noon for those east of the Blue Ridge Mountains, before transitioning to mixed precipitation and rain. For those WEST of the Blue Ridge, the snow should last until about 4:30 PM, but it will likely stay as sleet or freezing rain, as temperatures will struggle to top 33 degrees.

For now though, a Winter Storm Watch has been issued for the Shenandoah Valley and parts of West Virginia, and it will likely get extended eastward tomorrow, with advisories east of Loudoun County.

So, what about the snow totals? This is really tricky for two reasons,

  1. The standard ratio between rain and snow is typically 1 inch of rain equals 10 inches of snow, but this is different for months like November, March, and April, where it is significantly less.
  2. The surface temperatures on the ground are warm, which will reduce any accumulation you would get than if it were December, January, or February.

The three most used forecast models; the GFS, ECMWF, and NAM, are all predicting significant snowfall totals…

EUROGFSNAM
Washington D.C.4 inches2 inches13 inches
Manassas, VA5 inches6 inches14 inches
Leesburg, VA7 inches5 inches13 inches
Winchester, VA11 inches10 inches13 inches
Front Royal, VA11 inches11 inches14 inches
Harrisonburg, VA7 inches8 inches16 inches
Charlottesville, VA3 inches8 inches17 inches
Culpeper, VA5 inches9 inches14 inches
Fredericksburg, VA3 inches6 inches12 inches
Baltimore, MD5 inches4 inches13 inches
Petersburg, WV13 inches8 inches15 inches

Out of these three best snow forecast models, the NAM is totally worthless crap when it comes to its forecast. There is just no way that there is going to be 17 inches of snow in mid-November in Charlottesville, nor is it likely for most of the other areas (only exception was the Veterans Day Snowstorm of 1987).

The GFS and European models are also overestimating the possible snow totals, but they are much more realistic and would even be possible if we were to get colder air in place than what we are getting.

Due to warm surface temperatures in the soil and on paved surfaces, plus the low rain to snow ratio for November, the snow totals are likely to be half of what all models averaged show. Models simply do NOT pick up surface temperatures and the low rain to snow ratio when they make their model runs.

So, with that said, here is FirstWatch Weather‘s snow forecast for the DC area, Thursday into Friday.

Snowfall Forecast: Thursday Morning thru Friday Morning.

The bottom line is that some accumulation is possible. I even think D.C. might see a dusting to half an inch before the rain melts it all, but as for the northern and western suburbs, we are looking at 0.5 to 2 or more inches, some of which may stay through Friday afternoon.

As WeatherBELL meteorologist Joe Bastardi always says,

“Enjoy the weather, its the only weather you got.”

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Heads Up! Michael Set To Slam Florida Panhandle

October 9, 2018: 10:37 P.M. E.T.
By: Christopher M. (FirstWatch Weather Chief Forecaster)

This is the latest infrared satellite imagery from NASA’s Satellite, which I got off of Tropical Tidbits. These infrared satellite images measure the temperature of the cloud tops in the storm. The colder the cloud top, here it is the darker brownish colors, the higher the clouds are in the atmosphere, which means that there is a lot of convection occurring in the eyewall, allowing the storm to gain strength.

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Satellite Imagery Courtesy of Tropical Tidbits and NASA GOES

However, the hurricane doesn’t look as strong as it did earlier, as you can see in the loop, because it is appears to be undergoing an eyewall replacement cycle. 

The eyewall of a tropical cyclone is a big ring of tall vertical thunderstorms surrounding the eye that produce intense rainfall and also have the strongest winds in the storm. When the structure of the eye and eyewall change, wind speed may change. The eye of the storm may shrink or grow and the eyewall may duplicate, forming two eyewalls; the inner and the outer. Very strong cyclones sometimes have some of the rainbands organize into one ring of thunderstorms called an outer eyewall, which may take moisture from the eyewall, which causes the storm to weaken. However, in other cases, the outer eyewall may simply replace the inner eyewall, which causes the storm to regain its intensity or become stronger than previously. The second scenario is what seems likely at this point.

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Right now, the winds are at 110 knots, which makes the storm a Category 3 storm, however, some models suggest it is pushing toward Category 4. And as you can see, this is a fast moving system. This system will not stall, this is completely different than what we saw with Florence a few weeks ago.

The current water temperatures are 82 degrees Fahrenheit, which is the exact water temperature that sustains tropical cyclones. With that in place, and the eyewall replacement cycle going on, I see NO chance of this storm slowing down as it approaches shore. The only weakening I see from this storm is when it slams the Florida coast, as the moisture supply to the storm gets cut off. But warm water isn’t the only thing that powers a tropical cyclone. As water evaporates, it rises and cools with altitude. This cooling causes the water vapor to condense into water droplets we see as clouds. Heat is released in the process of condensation and the heat released increases the temperature in that area of the atmosphere making the air lighter which allows it to rise even further. As this occurs, the denser and cooler air sinks and undercuts the warm air, which is felt as very strong wind at the surface. This is why the storm loses power and intensity as it moves over land; there is a lack of moisture and heat being supplied to the storm, causing it to dissipate quickly, as we mentioned earlier.

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Map courtesy of weathermodels.com

Now, setting aside meteorology for modelology, we are going to look at what the models have to say. Before we go into that, I would like to say that I for one do not like using models ALONE to predict where a hurricane will make landfall, but models are a vital factor in weather forecasting. And when we look at the models, all are in very good agreement. The GFS actually performs pretty well with the European model. There is very high certainty that this storm will slam the Florida panhandle. It is a good thing that both Alabama and Florida have declared a State of Emergency as this system plows into the coast by midnight tomorrow. Heads up Tallahassee and Pensacola!

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Now, with the models combined, our FirstWatch Weather forecast is showing this storm will slam the Florida panhandle as a Category 3 or 4, but quickly become a tropical storm. From there, it should move up through the Southeast as a depression before moving out to the Atlantic as a low pressure system.

As I said, before this is a fast moving system, which means this will be gone as soon as it came.

Now, one thing the models did not pick up is the high pressure northeast ridge we got, which is going to make the system repel from the Northeast Atlantic.

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And for those of you not within direct threat, it doesn’t guarantee you are safe from some sort of impact. Many will see high storm surges and others will see lots of flooding due to the amount of rain associated with this storm. Locally, areas could see an upward of 12 inches of rain. The last thing I would like to add, is that October hurricanes are a good implication of a cold winter for the eastern U.S. So, we will see how this plays out folks. Anyhow, for the time being, please check on loved ones, family, and friends. Please be safe everyone.

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Global Temperature Update – August 2018 | 0.1745°C

The ClimateGuy

According to Dr. Roy Spencer‘s and Dr. John Christy’s measurements, the global lower tropospheric temperature anomaly for August 2018 was 0.19°C above the 1981-2010 long-term average. This is down 0.13°C from July 2018, which was 0.32°C.

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UAH Global Temperature Anomaly for August 2018 | 0.19°C via drroyspencer.com

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Meanwhile, the global land and sea surface temperatures for August were lower than the global lower troposphere, at 0.159°C above average, down 0.066°C from July, which was 0.225°C.

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NECP Global Temperature Anomaly for August 2018 | 0.159°C via WeatherBELL

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Because the UAH dataset only includes the global lower troposphere, and NECP only includes the land and ocean surface, both are NOT totally 100% accurate global temperature measurements in my opinion. In order to find the actual anomaly, we need to average both datasets together. When we do this, we get 0.1745°C for August 2018, which is the coolest month since July of…

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Extremes

This year we have went from one extreme to the next in temperatures. In Northwestern PA, after an unbearable string of days that ranged from 15 to 20 degrees above average temps, we are now experiencing 15 to 20 below average.

Wide temperature variations are making gardening very difficult. First, it was too hot to go and weed IF you were fortunate enough to have gotten seeds and plants in. Now, it has become cold enough that we have lit a fire in the woodstove. We are crossing our fingers that these wide swinging temperatures will not encourage fungus, mold and insect pests.

I am sure this will be a summer full of strange surprises as we venture further into the GSM!

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