Feb 2, 2014: Three Storms Coming Up

Forecast Highlights:

snowmap1aThe most significant warm up in half a month is currently underway, with temperatures expected to reach the upper 40s with some lower 50s in the area today. A colder and snowier pattern is on the way again, however, starting with a moderate snow event on Monday with heavy snow south of the area, followed by a significant snow and ice event on Wednesday and another snow/rain storm next weekend.

Due to the length of today’s discussion, shortcut links are available for a brief summary for the storms on Monday, Wednesday and Saturday. Additionally, the 8-day outlook page has been updated, translating the forecast discussion into an easy-to-read localized forecast.




Today: Warmth Briefly Returns For Super Bowl

radsfcus_exp_newThe latest surface analysis and radar mosaic from the Weather Prediction Center (WPC) has been posted to the left, as of 12z this morning (7am). Looking at northern New England, a weak wave of low pressure is centered just west of northern Maine, having produced a wintry mix from the Great Lakes into northern New England last night. The associated cold front extends southwest through western PA into Tennessee, with light to moderate precipitation falling behind the front, ultimately stalling out near Texas where an area of heavier precipitation is located just ahead of a mid level shortwave trough over New Mexico. As the low pressure continues to track northeast, the frontal boundary will slowly move through the region today, supporting mostly cloudy skies, westerly winds and highs in the 45-52 degree range for the NYC area, with a few isolated showers possible this afternoon as most of the showers remain well to the west of the area but with some possibly surviving east of Pennsylvania. The Super Bowl will occur in East Rutherford, NJ tonight, starting at 6:25pm; the outlook is for mostly cloudy skies, a light NW wind, and temperatures in the 42-37 degree range.


Tonight – Monday: Moderate Snow Expected

As the cold front departs, however, winter will make a quick return into the region, with an active week ahead likely to mark one of the snowiest time frames of this winter. The mid level shortwave trough currently over New Mexico will quickly eject out of the southwest US and rapidly track into the region with a progressive upper level southwesterly flow given ridging in the southeast US. The shortwave is expected to move overhead on Monday afternoon before flattening out as it moves out of the region, supporting the heavy precipitation over Texas moving to the northeast as well and producing widespread snow/rain in the region. As previous updates noted, the model guidance has been inconsistent with this system, depicting most precipitation staying well south of the area with a weaker and drier system until at least the 12z runs on Friday, 1/31; typical model biases throughout this pattern include underestimating ridging in the southeast US as well as the amplitude and strength of shortwaves entering the western/northern US, and the model guidance on Friday night into Saturday gradually corrected towards a slower frontal passage on Sunday and a stronger and more amplified shortwave trough, while reflecting in the surface output as a further north and more moist system. As a result, moderate snow is expected to affect the central-northern Mid Atlantic region on Monday, but with the mesoscale aspects of the system remaining slightly uncertain.

12z NAM hour 27, at 15z Monday (10am), depicting the heavy snow band placement over southern PA into central NJ, with NYC in the northern end (image credit: PSU e-Wall).

f27Impact Analysis: While the wave of low pressure will remain weak, heavy precipitation is nonetheless expected to affect the region with favorable dynamics especially between the 700-500mb layer, with higher upward vertical velocity values and frontogenesis within this layer between approximately Washington DC/Delaware into east central PA and central NJ. This supports a band of heavy snow setting up between northern Maryland/southern Pennsylvania into central New Jersey, with heavy precipitation extending south of Washington DC as well but with a warm temperature column leading to precipitation type remaining as rain. North of the banding, a tight precipitation gradient is expected to set up with a sharp cutoff between moderate snowfall and little to no snowfall. The main uncertainty remaining is exactly where this banding sets up, how much snow it produces, and how much rain is initially expected. As the frontal boundary will slowly push south of the area with a light NNW wind, temperatures will gradually cool down overnight, and are expected to reach the low-mid 30s when precipitation begins around 1-4am. Some mixing with rain is expected with the onset of precipitation for most of the area, but with a changeover to snow anticipated by at least 6am, except for Long Island which may take slightly longer to change over to plain snow, while temperatures remain in the low 30s for the majority of the event. Further south, the temperatures will be more marginal, especially between Washington DC/Baltimore into southern New Jersey, where surface temperatures are expected to be slightly above freezing with the onset of heavier precipitation. With the initially mild temperatures, I went slightly lower than the model guidance with the southern end of the snowfall zone, although rain to snow changeover events often include lower confidence due to the potential of significantly lower or higher totals than predicted.

With the heaviest banding expected to set up near south central/SE PA into central NJ, the uncertainty in these locations is how much snow accumulates. Given significant moisture associated with this system and the aforementioned dynamics, heavy precipitation is expected, but with precipitation totals varying between at least 0.50 to 1.10 inch, with the short range high-res models favoring the higher end of this range. At this time, a narrow swath of 6-10 inches of snow is expected in these locations; while my snow map below is slightly more conservative with snow totals east of southern PA, localized totals up to 10-12 inches are possible through southern PA into central NJ depending on the snow rates. Further north into the NYC area, the northern extent of the banding is likely to reach NYC and Long Island, where at least 4-6 inches of snow are expected. North of NYC, however, a sharp gradient in snowfall is expected; this sets up for slightly lower confidence than average as a small shift would lead to more significant changes in snow totals, although at this time continuing with the aforementioned banding setup, snow totals of at least 2-4 inches are expected north of I-80 in NJ and into coastal CT, with 1-3 inches in SE NY. Another area of uncertainty to keep in mind is that with most recent storms, despite a persistent northwest trend in the 84-hour range as observed in this case, there were often minor revisions towards a slightly further south and/or drier system within the 24 hour range, which need to be monitored in this case, but along with a recent continued trend for an even further north banding setup which if verifies, would place NYC, I-80 and Long Island under at least 5-8 inch totals.


snowmap1aOutlook for NYC Area: As the frontal boundary shifts southeast of the area tonight, temperatures will fall into the low-mid 30s by the early morning. Light rain/snow will develop towards 1-4am, with a steadier light to moderate snow falling by 7am. South of at least I-80 into NYC and Long Island, moderate to occasionally heavy snow is expected to fall, while light to moderate snow is expected north of the aforementioned axis. Snow is mostly expected to end by 3-4pm, ending from west to east.

Snow totals of at least 4 to 6 inches are expected along and south of I-80 into NYC and Long Island, with 2-4 inches in northern NJ/southern CT and 1-3 inches further north. Given the timing of the snow, hazardous traveling conditions are expected to develop during the morning commute, especially after 7-8am, continuing through the mid afternoon hours and ending prior to the evening commute. Some slight uncertainties remain with the exact positioning of the snow bands along with accumulations, however; some of the latest high resolution models have included NYC within the 5-10 inch snow axis, and while at this time I am anticipating the heaviest snow to remain south of the area, this potential will continue to be monitored. Occasional storm updates will be posted on Monday morning into the early afternoon.




Tuesday – Wednesday: Heavy Snow, Ice, Some Rain Expected

Little break from the stormy weather is anticipated as with the active southwesterly flow pattern, the next system will follow shortly behind Monday’s snow event. As the shortwave trough moves through the region on Monday, an even more robust shortwave trough, currently off the coast of Oregon, will be situated over the southwestern US, and with the continued progressive upper level flow will move through the central US on Tuesday as it becomes neutrally tilted. With confluence present near northern New England, however, the shortwave is unlikely to be able to further amplify, and instead is likely to flatten out as it moves through the region, which is expected to aid in a transfer from the primary surface low pressure in the eastern Ohio Valley to a coastal low pressure near the coast. While there is high confidence on the overall synoptic setup, the smaller details remain somewhat uncertain, making for a complex forecast regarding the storm track and precipitation types.

12z GFS at hour 72, for 12z Weds (7am), depicting the low pressure over Virginia, with heavy snow north of the area and ice/rain over the area. The GFS is close to an average between the colder ECM and warmer 12z CMC outputs (Image credit: PSU e-Wall).

f72Model Analysis: As previously noted, the models have been very consistent with the storm signal for this time frame, but with occasional inconsistencies regarding the exact output. 2-3 days ago, the model guidance depicted a stronger shortwave with weaker confluence over northern New England allowing for more amplification of the shortwave trough and thus a stronger and further north low pressure, driving enough mid level warmth to support mixing with ice/rain as far north as central NY state and the I-90 corridor in New England. Over the last two days, however, the shortwave has been modeled to end up weaker than originally anticipated, which along with increased confluence over northern New England supported a weaker and further east primary low, which transitions to a coastal low pressure near the Delmarva Peninsula. Given the positioning of the mid level low, enough warmth would advect northward to support mixing reaching at least southeast NY and coastal New England, but with the early transfer leading to significantly higher snow totals than indicated a few days ago; for example, the latest GFS run supports a snow to sleet to snow event, with widespread snow totals over 6 inches, along with the ECMWF, while the CMC is slightly warmer but with the mixing line not far to the north of NYC.

This trend has contradicted the majority of recent storms, which have generally trended stronger, more amplified and further inland within the short-medium range, as was the case with Monday’s event. Onset of precipitation is at least 66 hours away; while typically, this would be enough to gain confidence in the modeled outputs, this winter has seen frequent model shifts, sometimes significant, within the short range, and such potential remains for this event. Typical recent model biases include underestimating the strength and amplitude of shortwaves entering the western US, and in cases similar to this one, underestimating the strength of the mid level low, which has often supported a short range northwest trend in the surface low pressure. While the latest models are in generally decent agreement at this time, additional slight revisions are likely, and the potential remains for a slightly further north/stronger system than currently modeled. As such, I revised my thinking towards a somewhat colder solution than previously anticipated but not to the full extent of the significantly colder ECM/GFS, while waiting to determine whether the current trend will continue through the short range or is simply a transient trend before a short range north correction.


Impact Analysis: With the above factors considered, the next aspect of the forecast to analyze is the anticipated dynamics, heavy precipitation placement, and precipitation types. As the shortwave trough gains a neutral tilt over the central US, moisture from the Gulf of Mexico will be pulled into the system, supporting widespread heavy precipitation from the Ohio Valley into the Mid Atlantic and Northeast regions. Particularly strong lifting is expected in the mid levels with high upward vertical velocity and strong frontogenesis between southern Pennsylvania/NJ into the area and the mid-Hudson Valley, extending eastward into southern New England, where the heaviest precipitation is expected to set up particularly between at least 3am-10am. With the column initially cold enough to support snow, moderate to heavy snow is likely to spread into most of the area between at least 3-7am, with NYC and Long Island the most likely to switch to rain by the morning hours. Snow rates are likely to be heavy enough to support a quick moderate snow accumulation with snow rates near or over 1″/hour possible. Mid level warming with a southerly wind is progged to continue through at least noon, while the surface cold takes longer to erode, especially inland of NYC, supporting a changeover to sleet and freezing rain for the morning hours for these locations and possibly including NYC, while the lower Hudson Valley and interior CT north of the coast are likely to remain with plain snow. Forecasting freezing rain accumulations is often difficult due to the uncertainty between sleet and freezing rain, as well as runoff from heavy freezing rain which often leads to less significant icing than a prolonged freezing drizzle would, although at least light freezing rain accumulations up to 1/4 inch are supported at this time. As the surface and mid level lows transfer to the coast, colder air will begin to filter in, with a changeover back to snow possible in the mid-late afternoon before precipitation tapers off.

The above analysis assumes that the model guidance will trend towards a slightly stronger and further north system than currently modeled over the next few days. Considering recent model performance this winter, however, additional changes are anticipated in the short range and can lead to a somewhat different scenario than currently anticipated, and as with every storm a bust potential exists. The following section reviews the additional possibilities and their likelihood based on current indications. One scenario includes a weaker and less amplified shortwave along with more confluence, supporting a weaker and further south low pressure, which would keep the area with a primarily snow event, mixing with sleet/freezing rain in the southern half of the area but failing to change over to rain, which would support at least 6+ inches of snow for most of the area. The other scenario includes the model guidance correcting again towards a further north low pressure which would result in a shorter duration of snow followed by more significant interior icing and rain elsewhere, while the heaviest snow sets up between central NY state and central-northern New England. The latter scenario is slightly less likely than the former, although both are valid potentials that will continue to be monitored.


Outlook for NYC Area: Based on the latest outlook, snow showers are expected to develop towards 1-2am for most of the area, with moderate to heavy snow spreading in by at least 3-4am, continuing through 7am while Long Island and NYC gradually mix with and change over to rain. Through the rest of the morning hours, sleet and freezing rain are likely inland of NYC, while NYC and Long Island observe a cold moderate to heavy rain. Precipitation type may change back to snow for a short period of time in the early-mid afternoon before ending between at least 3-5pm.

Assuming the storm scenario noted above, snow totals of at least 1-4 inches would be likely in NYC and Long Island, and at least 3-6 inches of snow inland of NYC with over 6 inches towards interior CT and the lower Hudson Valley. Sleet and freezing rain are likely further inland as well, with light ice accumulations likely. As previously noted, however, uncertainty remains regarding the specific details which are subject to some changes; the latest model guidance is colder and snowier than the current forecast, and should signals of consistency continue regarding the current modeled output, future outlooks may increase snow and ice totals for the area. Stay tuned for more information with later updates.




Thursday – Next Weekend: Colder Late Week, Another Weekend Storm

Regardless of the uncertainty with the midweek storm, there is higher confidence on cold temperatures making a return for the late week as a cold air mass shifts southeast into the northeast US but struggles to significantly advance southeast with the continued ridging over the southeast US and progressive southwesterly flow in the mid to upper levels. This will support the return of colder temperatures into the region, but with the southward extent of the cold uncertain, which the models often tend to exaggerate in the medium range. With a strong high pressure positioned over the region, mostly sunny skies are expected for Thursday and Friday with high temperatures in the upper 20s-low 30s likely with lows in the 10s.

The next shortwave trough is expected to set up over the western US on Friday before shifting east towards next weekend, reaching the eastern half of the US between Saturday and Monday, aiding in the development of another surface low pressure and resulting in a high likelihood of precipitation affecting the region. As this storm is at least a week away, specific details are uncertain at this time and cannot be determined with high confidence. However, some hints regarding the potential outcome of the storm can be determined based on the overall synoptic setup. With the initial high pressure over the region, and the cold air mass placed overhead, the potential for snow exists in the area, with the strength of the low pressure and precipitation totals, along with the exact track and precipitation type, depending on the handling of the trough. As of now, a high probability of precipitation can be placed for this time frame across the region and a moderate probability for the area, associated with a widespread storm system affecting the region with snow and rain, although the remaining details cannot be determined with high confidence at this time. More information will be posted on this time frame over the next few days.

5 thoughts on “Feb 2, 2014: Three Storms Coming Up

    • NYC Area Weather Post authorReply

      One of the issues to consider is how much time it will take for the snow to accumulate given initially marginal temperatures. Considering that moderate snow is likely to develop by 7am, the possibility is there for a snow day.

    • NYC Area Weather Post authorReply

      Widespread snow and ice accumulations are likely through Wednesday morning, so a moderate to high likelihood of delays and/or snow days exists on Wednesday, especially in northern NJ, SE NY and southern CT, depending on the timing of changeover to ice and whether precipitation changes over to rain or not. In the warmer case scenario where a changeover to rain occurs, which would likely occur around 7-9am and likely affect northern NJ and coastal CT, those locations would have higher odds of a delay, but with a colder scenario favoring more snow and prolonged ice, increasing odds of a snow day.

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