Quick Moving Snowstorm Tomorrow Night


Winter continues to stick around as we head into early March. A coastal low will develop tomorrow evening, bringing plowable snow to the I-95 corridor. While this season has been besieged by multiple complex storm systems, tomorrow’s storm is a fairly standard nor’easter from a meteorological perspective.

Currently, our storm is moving across the Rockies into the Plains. By tomorrow morning, a large swath of snow will develop over the midwest. As the storm moves east, it will intensify and move off the coast. In the southeast, there is a high risk of severe storms. Areas north will be impacted by snow (rain in coastal regions):

namconus_ref_frzn_us_25.png

Without significant blocking to the north, this storm is a fast mover. Precipitation will commence in the Delaware Valley by 5 PM tomorrow and end by 3 AM Monday morning. The GIF below illustrates the storm’s quickness:

NAM-WRF 3-km Metro Regions Northeast US Simulated Radar.gif

In areas south of I-95, precipitation will mainly fall as a cold, nasty rain. Philadelphia will likely be a battleground between rain and snow. Areas north and west of the city should stay as all snow for a majority of the storm:

index 03

Impacts

Monday’s rush hour will be impacted in the northern and western suburbs. When most people wake up on Monday morning, 4-6 inches of snow will be on the ground. Frigid air will follow the storm, which will slow down any melting until late next week.

index.png

Next Week

One last arctic blast will plunge temperatures 20 degrees below normal next week. Unseasonably cold weather will continue into next weekend and into mid-March. Based on long-range model runs, we should return to normalcy by the end of the month.

 

Advertisements

A Wild Wintry Ride Tomorrow


Hello all! We’ve been in an interesting pattern this winter. Most storms have taken an inland path, generally staying away from the coast. This type of pattern brings warm-ups during storms followed by brutal cold periods between them. Tomorrow’s storm will be more of the same.

An area of low pressure will track north from the lower plains tonight into tomorrow morning. As it intensifies over the Ohio Valley, an area heavy snow will push into our area by tomorrow morning. The snow will be heavy at times, accumulating quickly by the evening rush. By sunset, warmer air from the south will enter the upper atmosphere. This will cause a SW to NE changeover from snow to sleet to freezing rain. Eventually, a complete changeover to rain across the area will occur.

nam3km_mslp_pcpn_frzn_neus_44

nam3km_mslp_pcpn_frzn_neus_51.png

We will warm up considerably on Thursday, with highs reaching close to 50. This should be enough to melt away any remaining snow on paved surfaces.

Impacts

Travel on Wednesday afternoon and evening will be trecherous, especially before the changeover to rain. Please take it slow and, if possible, consider working from home in the afternoon. Thursday morning could still be slick in spots, but rising temperatures should improve road conditions as the day goes on.

Future Outlook

I am currently tracking a possible coastal storm next Wednesday. Depending on how the models react to the current pattern, we could be looking at our first large nor’easter of the season. Stay tuned.

Analysis of the Winter Storm this Weekend: Watch for Ice


Hello all! With a weak El Niño in place, most forecasters expected a colder and snowier winter in the northeast. Thus far, these predictions have been largely incorrect. This winter has been warmer and largely snowless for many areas. Recent signals, however, have hinted a pattern change toward a colder pattern into Febrary. This shift begins with a large storm system impacting the northeast tomorrow into Sunday.

The forecast is difficult, with a classic battle between warm and cold air assembling over the I-95 corrider. As a result, the margin determining a full fledged snowstorm, icestorm and rainstorm is extremely small. This tight setup is shown below from the short range model:

nam3km_mslp_pcpn_frzn_neus_40

This model directs the storm off of the NJ coast during the day on Sunday. In northern areas like upstate NY and New England, ample cold air aloft will keep the primary precipitation type as snow. In areas further south, the oceanic influence will bring warmer air into the upper atmosphere, changing snow over to either sleet or freezing rain. Currently, this winter battle ground is forecast to occur over Central PA, the Poconos, Northern CT, and the Boston metro area. In the Delaware Valley, the amount of warm air will invade not only aloft but also at the surface, changing our precip type from snow to rain by Sunday morning. The GIF below shows the quick changeover:

nam3km_mslp_pcpn_frzn_neus_fh26-45.gif

While I am predicting a primary rain event for Philadelphia, any southernly shift in track will have a significant impact. If the low ends up 50 miles south than forecasted (which has happened in the past, especially with a complex upper atmospheric setup like this), then the battle ground will migrate over a good chunk of the Delaware Valley. A major ice storm would be catastrophic for the area, especially when nobody sees it coming. Therefore, I recommend observing temperature reports tomorrow into Sunday. If temperatures remain below freezing Sunday morning, then freezing rain will fall and cover any exposed surface with dangerous ice. I will provide an update tomorrow if conditions begin to look grim.

Risk of Flash Freeze Sunday into Monday

After we dry out Sunday afternoon, an area of polar air will stream down from Canada. This will cause temperatures to plunge 30-40 degrees from Sunday afternoon to early Monday morning.

download.png

With the ground remaining mostly wet or damp, this change in temperature will cause a flash freeze on many untreated surfaces. Large areas of black ice on both roads and sidewalks are likely. Fortunately, the volume of cars on the road will be diminished on Monday for the holiday. Regardless, if you plan on driving or walking around, take extreme caution on side roads and untreated sidewalks.

Total Impacts

1-3 inches of snow Saturday evening followed by a rapid change to sleet, freezing rain, then rain by late Saturday. Precipitation will be heavy at times Sunday morning before ending in the afternoon. Rapid drop in temperature Sunday night will cause a flash freeze on any untreated wet surfaces.

 

 

 

A Rare November Nor’easter Analysis


Winter is starting early on the eastern seaboard with the first real chance of snow and sleet since March. While most teleconnections do not indicate a major snow event, the current weather pattern promotes storm development along the active jet stream.

As it stands, we are drying out from a fairly substantial nor’easter last night. Tomorrow will be a sunny, chilly day, as an area of high pressure dominates to our northwest. Simultanously, a disturbance will begin to form out of the Gulf of Mexico and strengthen as it slowly moves northeast:

9-km ECMWF USA Cities United States Precip Type & MSLP 36

As the disturbance moves offshore, it will continue to intensify. The storm will gather a massive amount of moisture from the warmer than average Atlantic as it moves along the coast and partially phases with an upper level disturbance over the Ohio Valley:

9-km ECMWF USA Cities undefined undefined 60.pngThe area of high pressure will be pushed eastward, setting up a cold flow from the north. This arctic air will fuel the west side of the storm, bringing a widespread area of wintry precipitation to the Northeast from Thursday into Friday.

While we’re only 40 hours from the event, there is still uncertainty regarding  precipitation type along the I-95 corridor. Surface temperatures will be cold enough to support frozen precipitation, but the upper atmosphere will be heavily influenced by the warmer Atlantic ocean. For our area, this means an intital period of snow, followed by sleet (as the upper atmosphere warms). For areas south and east of I95, the sleet will eventually turn primarily to rain. From I-95 northward, the precipitation type will continue to be a mixed bag.

Below shows the descrepency between a warmer upper atmosphere (540 mb rain/snow line over central NY) and colder surface temperatures. This setup is the perfect recipe for a sleet storm:

The simulated radar from the short range NAM model shows the mass of sleet overtaking the region on Thursday evening (marked by the orange):

NAM-WRF 3-km Northeast US Precipitation Type.gif

By Thursday night, the sleet will be mixing with rain in most areas and temporarily end overnight. The backend of the storm will bring a second round of rain/snow to the area early Friday morning. Depending on the amount of cold air aloft, parts of the area could receive an additional coating-1 inch of snow by sunrise. The map below shows the projected backend hit:

namconus_ref_frzn_neus_46.png

Timing:

11 AM – 1 PM: Snow starts from south to north. Minor accumulation on grassy surfaces.

1 PM – 6 PM: Snow changes over to sleet. Temperatures remain around freezing.

6 PM – 12 AM Friday: Sleet changes to rain along I-95. Precipitation slows down south to north

12 AM Friday – 8 AM: Potential for backend precipitation, heavy snow possible in parts of the area.

Snow Totals:

November snowstorms are not known for their accumulations and for good reason. The ground this time of year is relatively warm, which impedes snow totals. However, I believe the front end snow has the potential to deliver a quick 1-3 inches in the Philly suburbs on grassy surfaces. Most of it will melt by Friday, as the high temperature reaches the upper 40s. Conditions will be pretty nasty on Thursday, but roads will stay wet. As in any major storm, drive slow and take care when the visibility is low.

With a weak El Niño arriving, history indicates it will be an exciting winter for the eastern seaboard (see my past posts from the winter of 2013-2014 for a preview 🙂 ). I will be providing full coverage of incoming winter storms and patterns as we officially head into winter. Prepare for some snowy times ahead!

Quick Overview on Hurricane Michael


Hello all! Hurricane Michael is bearing down on the Florida panhandle with sustained winds of 120 mph (as of 8 PM Eastern). He is expected to slightly strengthen before making landfall on the Florida panhandle. Hurricane force winds will impact much of the panhandle, bringing destructive winds and storm surge along the coast:

213230

Michael continues to move northward at a steady clip. His eye structure remains well formed and there is ample convection around the center of circulation, shown in the satillite loop below:

goes16_wv-mid_14L

Most global and hurricane models are in agreement with Michael’s track. After making landfall, the storm will get picked up by the active jet stream and move northeast. Major flooding is likely to occur in the Carolinas into Virginia. The Delaware Valley could see 1-2 inches of rain from Michael, with much of the rain falling Thursday into Friday.

Total Precip mid atlantic.png

The amount of precipitation will depend on how quickly Michael gets picked up by the jet. If the interaction is later, Michael will track further north, bringing flooding rains to our area. If the interaction occurs earlier, then we will avoid the worst of the rains. A southern track looks more likely, sparing our area from additional rain and flooding.

Regardless of Michael’s impacts on the Philadelphia area, he will be an extremely destructive storm along the Florida panhandle. Stay safe!

Hurricane Florence: An Overview


Hello all! I am back to discuss Hurricane Florence and its possible impacts on the Eastern Seaboard.

Initially a tropical wave off of the Cape Verde coast of Africa, Florence formed as Tropical Depression #6 on August 31st. After entering favorable conditions in the Atlantic, she rapidly strengthened into a major category 4 storm (reaching sustained winds of 130 mph) and continued to move northwest.  As she moved north, Florence was slowly ripped apart by vertical wind shear, weakening into a tropical storm. Over the past 24 hours, Florence has begun to reorganize and has regained hurricane strength. She will continue to intensify over the next 48 hours, fueled by a combination of warm ocean waters and low vertical wind shear.

Below is a current satellite loop of Florence. Convection remains strong on her northeast side as she moves NW:

goes16_ir_06L.gif

Ocean water temperatures stay above average in the Northwestern Atlantic. This will allow the storm to strengthen into at least category 3 strength:

cdas-sflux_ssta_atl_1
Sea Surface Temperature Anomalies – North Atlantic
06L_intensity_latest
Hurricane Model Strength Projections

While most forecasters and models agree over Florence’s strength over the coming days, there is disagreement on where she will end up. A significant factor in determining the track of Florence is a broad ridge of high pressure to the north of the storm (shown as orange/red in the maps below). If the ridge remains strong, it will steer Florence further south and prevent her from re-curving out to sea. The European model projects this below:

9-km ECMWF Global Pressure East Coast USA 500 hPa Height Anom.gif

This scenario would be catastrophic for the Carolinas and mid-Atlantic as the storm makes landfall Thursday night. From a meteorological standpoint, the European model checks out. As Florence digs into the ridge, it will begin to curve northward and eventually northeastward as the ridge shifts to the west. Other hurricane-focused models are showing this solution as well:

06L_tracks_latest.png

What some of the models are perplexed with, however, is when exactly this shift occurs. The GFS is having difficulty pegging where Florence will go once the ridge shifts. It stalls the storm off the NC coast until other atmospheric features interact (including a tropical system) and push it out to sea:

GFS Pressure Lev East Coast USA 500 hPa Height Anom.gif

The UK model is having the same issues collapsing the ridge but keeping Florence largely stationary:

UKMET 17 km East Coast USA 500 hPa Height.gif

While I am leaning toward the European solution over the GFS and UK, there are a couple factors that need to be ironed out. First and foremost, the models will have to reach consensus on Florence’s interaction with the ridge. Without agreement, it will be challenging to predict her track. Second, we need to determine what the impacts will be on the coast and prepare accordingly. The European solution brings hurricane force winds into NC/SC and significant rains into the Southeast:

9-km ECMWF USA Cities Southeast US 10-m Wind 114.png

While the Delaware Valley doesn’t appear to be in the direct path of the storm, please keep a watchful eye on this system. Regardless of Florence’s potential track, the NJ/DE/MD coastline should begin to prepare for rough surf and high winds late in the week.

I will continue to post updates as we gain greater clarity on the situation. Thanks and stay dry!

 

Another One – March Nor’easter #4


What a month this has been. We continue to experience a very active weather pattern that favors storm development off the Atlantic coast. Our fourth March nor’easter is a complicated setup that will arrive in two parts, beginning tomorrow and ending early Thursday morning. This post will separately review both stages of the storm and their impacts on our region.

March Nor’easter #4 Round One

The first piece of the storm will arrive midday tomorrow with mixed precipitation in the form of snow, sleet, and rain. There will be minor accumulations on grassy surfaces, but the roads should remain mainly wet.

nam_ptype_slp_east_9.png

By Tuesday night, some models have indicated a prolonged period of freezing rain, which could make road conditions slippery by Wednesday morning. Regardless of precipitation type, impacts from round one will be manageable. Even with a period of freezing rain, roads will be mainly wet.

nam_ptype_slp_east_12 (1).png

Round One Timing

10 AM-12 PM: Precipitation starting as a snow/sleet mix from south to north

12 PM – 7 PM: Mixed precipitation continues, heavy at times. Minor accumulations expected on grassy surfaces

7 PM – 3 AM: Mixed sleet/rain/snow possibly changing over to freezing rain. Precipitation will slow down by 2-4 AM before transitioning to light snow.

March Nor’easter #4 Round Two

As the first system moves east, it will phase with a secondary low off the coast and begin to strengthen. The storm will begin to display the hallmark features of a nor’easter as it begins to move northeast. A resulting area of widespread snow will overtake the I-95 corridor from DC to Boston.

nam_ptype_slp_east_17.png

While a prolonged period of snowfall is expected, accumulations will be diminished because of the storm’s timing during the daytime hours. Since it’s late March, the angle of the sun is relatively high (equivalent to early October), which means any snow that falls will have issues sticking on paved surfaces. Even with these opposing factors, roads will still be very slick by Wednesday afternoon, and I would recommend against unnecessary travel after 12 PM.

Round Two Timing

7 AM – 11 AM: Light sleet/freezing rain changing to snow during the morning hours

11 AM – 5 PM: Moderate to heavy snow, plowable accumulations expected. Roads will be slush covered and slick. Widespread power outages from fallen trees and power lines.

5 PM -12 AM Thursday: Snow moving out south to north. Watch for re-freeze overnight.

Round Two Totals and Impacts

Forecasting March snow totals are particularly challenging because of the previously mentioned high sun angle and warmer surface temperatures. Based on model guidance and knowledge of the surface conditions, a general 6-10 inches of wet, heavy snow is likely throughout the Delaware Valley. Widespread power outages are possible from trees and power lines weighed down by the dense snow. Travel will be arduous Wednesday afternoon; please take precautions if you need to drive.

hires_snow_nj_61.png

This will be a very entertaining event with all types of precipitation and significant accumulating snowfall. I will provide any updates at the top of this post. Enjoy and stay safe!