About this website

Welcome to Jason Godwin's weather website. I am a recent master's graduate from the University of Miami Rosenstiel School of Marine and Atmospheric Science. On this website, I post blogs on tropical meteorology and other interesting weather phenomena, as well as some information on some of my research (which lies in tropical cyclone predictability).


United States Weather Discussion

Monday, January 26, 2015

For the latest information on the winter storm impacting the northeast, see the blog post below.

A major winter storm will impact the northeast and New England today and Tuesday (for more information see the blog post below. Elsewhere, a weak shortwave trough moving through the Upper Midwest will bring a light dusting of snow (generally less than 4 inches) to parts of the Michigan Upper Peninsula, Wisconsin, and northern Illinois. A few isolated areas could receive up to six inches of snow.


Latest Blog Entry

Historic Winter Storm Poised to Impact the Northeast U.S.

Update 2 (2:05 PM EST Monday 1/26)

The 12Z GFS forecast snowfall accumulation has gone back up a little compared to last night, and now shows about a foot of snow falling in New York City, with about two feet falling in Boston. These values however could be on the lower side since the heaviest snow will fall where strong convective bands set up, something difficult to forecast at this time. In their morning forecast discussion, the NWS office in New York City stated, "the mid level low centers and intense mid level frontogenesis will promote heavy snow bands...but it is impossible to predict their location this far out." This mid level frontogenesis (the strengthening of a temperature gradient with time) will be key to watch. Currently, light to moderate snow showers are affecting northern New Jersey, New York City, Long Island, and coastal parts of Connecticut, Rhode Island, and the southern coast of Massachusetts. Expect conditions to continue to deteriorate throughout the day as the surface low off the coast of North Carolina intensifies and approaches the northeastern United States.

The was one slight concern in the forecast this morning at the 12Z sounding out of Long Island showed a dry pocket in the lower levels of the atmosphere, but given that the dewpoint temperature at the surface at LaGuardia Airport has increased by about seven degrees since that sounding was taken, the low levels appear to be moistening up.


700 mb temperature (blue dashed lines), heights (black solid lines), and frontogenesis (purple lines).

Update 1 (12:31 AM EST Monday 1/26)

The latest GFS forecast has backed off a little on the snowfall forecast for New York City, though it has increased for Boston and eastern Massachusetts. This event is starting to look like it will be more of a Boston event than a NYC event. Here are the 1800Z/1 PM EST and 0000Z/7 PM EST forecasts. The main reason for this shift in the forecast appears to be that the 00Z run of the GFS takes the surface low on a more eastward track.


GFS forecast sea-level pressure (black contours), 1000-500 mb thickness (red/blue contours), and 6-hour precipitation accumulation (shading) valid 1 AM Tuesday. Forecast initialized at (left) 1800Z Sunday and (right) 0000Z Monday. The surface low off the coast of New York has shifted south and east in the latest forecast, resulting in less snow for New York City, but potentially more snow for Boston and eastern Massachusetts.

At this point however, it is important to stress that where the heaviest snow will fall will be largely dependent on where the heaviest snow bands set up, something that is very difficult to forecast until the event is occuring in realtime and we have radar imagery of the snow bands.

Original Post

The consensus of model and official forecasts is beginning to suggest that the winter storm forecast to impact parts of the northeast and New England over the next 48 hours could be potentially historic. The National Weather Service has issued Blizzard Warnings for coastal New Jersey, the New York City Metropolitan Area, Long Island, Connecticut, Rhode Island, eastern Massachusetts, coastal New Hampshire, and coastal Maine (Fig. 1). The cities of New York, Hartford, Providence, and Boston are included in the warning area.


Fig 1.: blizzard warnings issued by the National Weather Service.

In winter weather forecasting, there are a few ingredients we look for:

  1. Ascent/Lift: We need a source for large-scale vertical ascent, or lift. This mostly commonly comes in the form of an approaching upper-level trough and/or strong warm air advection at the surface.
  2. Moisture: In order for there to be precipitation, there must be deep moisture in place. Moisture depth is key, because very dry air at the surface can cause precipitation to evaporate before reaching the ground.
  3. Cold Air: Obviously, for there to be snow, it must be cold enough (i.e. below freezing, 32 F/0 C) to support frozen precipitation.
The main source of lift with impending winter storm is a potent upper-level trough currently over the central United States (Fig. 2). As this trough moves east towards the east coast of the U.S. on Monday morning, the strong positive/cyclonic vorticity advection associated with the trough will result in upward motion. This upward motion will result in the development of a surface low (Fig. 3).


Fig. 2: RAP analyzed 500 mb heights (contours) and absolute vorticity (shading). A strong trough is noted over the central United States, with a large area of highly positive absolute vorticity over Oklahoma, Texas, Arkansas, Louisiana, and Mississippi.

Fig. 3: GFS forecast surface pressure (contours), temperature (shading), and winds valid 1:00 PM EST Monday.

The strong surface low will produce strong winds out of the south that will act to pull moisture north towards New England on Monday and Tuesday. At the same time, cold will move south. Temperatures are already in the upper 30s across southern New England, and should fall below freezing (and stay) by midnight tonight. As the rich moisture wraps around the north side of the low where temperatures will be well below freezing, conditions will be favorable for snowfall. Fig. 4 shows a below freezing, and saturated profile over New York City Monday evening. The forecast sounding for Boston (not shown here) looks very similar.


Fig. 4: GFS forecast sounding for New York - LaGuardia Airport valid 7 PM Tuesday. The entire profile is below freezing and is saturated from the surface up to 250 mb (about 33,000 feet above the ground).

Given the very strong vertical ascent, cold air in place, and very deep moisture, it is no surprise that the consensus amongst major computer models is for a significant amount of snow to fall across southern and coastal New England (Fig. 5). Both the GFS and NAM models agree on well over a foot of snow falling across much of southern and coastal New England as well as the New York City Metro Area. It is difficult to know how much snow will fall where given that the finer details depend on where heavy bands will set up during the actual event, but widespread totals of over one foot appear likely.


Fig. 5: GFS forecast snowfall accumulation ending 1 PM Tuesday. The heaviest snow is forecast to fall in a corridor extending from central Connecticut through Massachusetts, southern New Hampshire, and into southern and coastal Maine where over 20 inches of snow is being forecast.

The official forecast from the National Weather Service shows higher totals with over two feet of snow being expected in the corridor from New York City and Hartford, and over one foot of snow falling across eastern Pennsylvania, much of New Jersey, southern New York, Connecticut, Rhode Island, Massachusetts, southern Vermont, southern New Hampshire, and much of Maine (Fig. 6). Accumulations of over three feet will be possible in isolated spots across southern New York and Connecticut.


Fig. 6: official snowfall accumulation forecast from the National Weather Service.

People across the affected regions, particularly those in northern New Jersey, southern New York, New York City, Long Island, Connecticut, Rhode Island, Massachusetts, southern New Hampshire, and coastal Maine should prepare for very heavy snowfall and to be stranded at home at least through Wednesday morning. Very strong winds will lead to blinding blowing snow which will make travel extremely treacherous. The strong winds will also lead to some power outages. Snow is expected to begin falling in New York City by late morning and reach Boston by late afternoon. Conditions will not begin to improve until late Tuesday at the earliest. Stay tuned for further updates and the latest forecasts.


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