Coastal Cyclone of 23-24 January 2014
By
Samantha Ballard
and
Richard H. Grumm
National Weather Service State College, PA
1. Overview
An East Coast Winter Storm (ECWS: DeGaetano et al. 2002) brought heavy snow for
Pennsylvania along with its neighboring states. The storm evolved from a southern system off
the Gulf Coast which then moved up and off the East Coast and eventually combined with a
northern Canadian low strengthening the off shore system (Figure 1). The evolution of the low
is shown in figure (Figure 2). A large percentage of the historic snowstorms along the East
Coast typically involved a surface cyclone, which comes up the East Coast. This particular storm
contained an 850 hPa low level jet with -2 to -3𝜎 u-wind anomalies and 2 to 3𝜎 v-wind
anomalies (Figure 3 & Figure 4).
Forecasts of this storm will be shown from an NCEP ensemble perspective. The extent of the
southern surface low into Pennsylvania provided a gradient in snowfall totals and forecasts
across the state. The NCEP guidance originally placed the highest precipitation south of
Pennsylvania into Maryland and Northern Virginia. However, the highest snowfall totals were in
eastern Pennsylvania and New York City area into New England, the areas to the south mainly
saw rain. The storm snowfall totals ranged between 1 inch and a maximum of 7-8 inches for
the heaviest hit regions (Figure 5). Some of areas in New England with higher snowfall totals
were later affected by the 23-24 January 2015 Major East Coast Winter Storm.
This paper will document the pattern and anomalies associated with the ECWS of 23-24 January
2015. Section 3 will focus on the pattern and standardized anomalies to put the event into
context. As with all high impact weather events, the forecasts and the communications of
these forecasts are important. The 4th section will examine the forecasts produced by the NCEP
ensemble forecast systems and what these data implied.
2. METHOD AND DATA
The large scale pattern was reconstructed using the Climate Forecasts System (CFS) as the first
guess at the verifying pattern. The standardized anomalies were computed in Hart and Grumm
(2001). All data were displayed using GrADS (Doty and Kinter 1995). For storm-scale details the
00-hour analysis from the hourly NCEP HRRR were used (see Figure 2).
The precipitation was estimated using the Stage-IV precipitation data in 6-hour increments to
produce estimates of precipitation during the even in 6, 12, 24 and 36 hour periods. Snowfall
was retrieved from National Snow Analysis website.
Snowfall data was obtained from both NWS public information statements and the National
Snow site. The National Snow site was used to retrieve and plot data. The data were plotted
over the Stage-IV QPE data using GrADS.
The NCEP SREF were retrieved and examined in real-time and archived locally. These data
helped identify the different predictability horizons of the forecast systems. The NCEP CFS data
may not reflect public forecasts or perceptions of the forecasts. Many forecasters use a diverse
set of forecast tools and often lean on the European Center model and post processed forecast
data.
3. Pattern overview
The 500 hPa pattern shows the progression of an elongated trough in a typical northeastern
snow storm pattern with a high ridge in the West. The trough builds in strength starting in
Texas at 1200 UTC 23 January 2015 and moves out of the southern stream extending over the
East Coast at 1800 UTC 24 January 2015 (Figure 6).
The evolution of the surface pattern is shown developing in the Gulf and gaining strength just
off the shore of New Jersey, Maryland and Virginia (Figure 1). The higher resolution HRRR
shows the southern surface low merge with the Canadian low to the North and strengthen off
shore putting eastern Pennsylvania and New Jersey in the sweet spot for precipitation (Figure
2d).
The HRRR 850 hPa winds shows -2 to -3 𝜎 u-winds strengthening the system from the south
right over Virginia starting at 0000 UTC 24 January 2015 and moving to the east off the coast at
1500 UTC 24 January 2015 (Figure 7). Generally the HRRR u-winds have a similar pattern
compared to the CFS u-winds (Figure 3), however the CFS runs showed slightly higher 𝜎 uwinds.
The interaction of the northern and southern stream lows caused for a variation in precipitation
amounts for Pennsylvania with distinct ranges of precipitation, higher totals increasing for the
Southeast and decreasing towards the north and west. The higher QPE (Figure 8) values from
0000 UTC January 24th 2015 to 1200 UTC 24 January 2015 were observed in southeastern PA,
New Jersey, Maryland and Northern Virginia, which are areas closer to the amplified low off the
East Coast. The maximum QPE in these areas was 25 mm range. The range for Pennsylvania was
between 12-16 mm for the Philadelphia Area and uncertainty in the central regions from 2- 12
mm. The interaction of the two streams likely contributed to the uncertainty in the longer
ranges forecasts of this system.
4. Ensemble Forecast
i) NCEP SREF
The SREF shows the interaction between the southern and northern surface systems between
0900 UTC and 2100 UTC 23 January 2015. However the SREF puts the southern low closer to
shore with and more to the south (Figure 9). Since the SREF had the southern surface low off
the coast of Maryland and Delaware the SREF produced a high probability of 12.5 mm for
Maryland, Delaware, New Jersey and extended into southeastern/eastern Pennsylvania
regions. These regions are in the northern and western portions of the surface low, indicating
high probability for precipitation. The probabilities were much lower for the central
Pennsylvania regions (Figure 10). A few members even extended the precipitation shield into
New York City. The high probabilities for 25 mm in the SREF were along the coastal regions of
Delaware and Maryland situated just west of the southern surface low in the Atlantic (Figure
11). The SREF mean QPF and each 25 members contour (Figure 12) showed that the SREF
produced 25 mm or more for Eastern Maryland, Delaware and Southern New Jersey with a
sharp cut off along the Pennsylvania boarder. The SREF 12.5 mm contour included Southeastern
Pennsylvania, New Jersey, Maryland, Delaware and Northern Virginia (Figure 13). Overall, the
SREF had a sharp western edge to the QPF shield and also under-estimated the western extent
of the storm.
The longer range forecasts (not shown) indicated that there was considerably uncertainty with
the areas to be affected by snow and heavy snow. This was likely related to the interaction of
the waves in the northern and southern streams pointed to in section IIII.
5. Conclusions
A southern stream surface low combined and strengthened with a Canadian surface low
between 1200 and 1800 UTC 24 January 2015 in a favorable position on the downstream of an
elongated trough. The off shore surface low coupled with the upper air positive vorticity
pattern associated with a deep trough extending from Canada provided the foundation for the
ECWS 23-24 January 2015. The higher QPE and snow amounts were observed in in eastern
Pennsylvania, northern New Jersey, the New York City metropolitan area northeastward into
Connecticut and Massachusetts. The snowfall totals in these areas averaged 5-7 inches.
Moderate snowfall totals extended westward into central Pennsylvania, National Weather
Service State College measured 5 inches of snow accumulation for State College, Pennsylvania.
This is an example of the SREF underestimating the western edge of snow accumulation,
previously mentioned in the Ensemble Forecast section.
These areas of greatest snow accumulation aligned in the region North and West of the surface
low, which is favorable for precipitation. The regions of higher snow accumulations were also
aligned with the stronger 850 hPa winds and u-wind anomalies Overall, the SREF indicated that
the storm would hit more to the south than observed. The SREF produced much of its
precipitation to the south in Maryland, Delaware, southern New Jersey, which were regions all
in line with the 25 mm contour. These areas received rain and mixed precipitation. However
the 12.5 mm contour included the areas of southeastern Pennsylvania, northern New Jersey,
and the New York metropolitan area, most of which saw heavier snowfall.
Overall, the NCEP guidance succeeded captured the winter storm along the coast. Thus the
model correctly focused the higher QPF and snow amounts closer to the coast and coastal
plain. However, longer range forecasts under estimated the QPF and thus the potential for
snow fall in central Pennsylvania. The higher snow amounts along the western edges of this
winter storm implied some predictability issues. It is always difficult to forecast accurate in
edges and strong gradients. This ECWS had some forecast issues long the western edge of the
storm system.
6. References
Doty, B.E. and J.L. Kinter III, 1995: Geophysical Data Analysis and Visualization using GrADS.
Visualization Techniques in Space and Atmospheric Sciences, eds. E.P. Szuszczewicz and
J.H. Bredekamp, NASA, Washington, D.C., 209-219.
DeGaetano, A. T., M. E. Hirsch, and S. J. Colucci. 2002. Statistical prediction of seasonal East Coast winter
storm frequency. Journal of Climate 15:1101–17.
Kahneman, D, 2011: Thinking Fast Thinking Slow. Farrar,Straus, and Giroux, NY,NY. 511pp.
Kalnay, Eugenia, Stephen J. Lord, Ronald D. McPherson, 1998: Maturity of Operational
Numerical Weather Prediction: Medium Range. Bull. Amer. Meteor. Soc., 79, 2753–
2769.
Roebber, P.J., M.R. Butt, S.J. Reinke and T.J. Grafenauer, 2007: Real-time forecasting of snowfall
using a neural network. Wea. Forecasting, 22, 676-684.
Figure 1. Climate forecast system (CFS) reanalysis showing the track of the surface low in 6 hour
increments from a) 1200 UTC 23 January 2015 through f) 1800 UTC 24 January 2015. Return to
text
Figure 2. HRRR 00-hour forecast in 3 hour increments from a) 0000 UTC 24 January through f) 1500 UTC 24 January
2015. Return to text
Figure 3. CFS 850 hPa winds and 850 hPa u-wind anomalies. Return to text.
Figure 4. CFS 850 hPa winds and 850 hPa v-wind anomalies. Return to text.
Figure 5. Plot of accumulated estimated precipitation (mm) and snowfall (inches). Black text is less
than 4 inches, light blue greater than 4 to 6, darker blue 8 to inches. Return to text.
Figure 6. CFS 500 hPa heights and standardized anomalies in 6 hour increments from a) 1200 UTC 23
January to f) 1800 UTC January 24 2015 Return to text
Figure 7. HRRR 850 hPa winds and 850 hPa u-anomaly winds. Return to text
Figure 8. Estimated stage-IV QPE (mm) form 0000 UTC 24 through 1200 UTC 24 January 2015 Return to
text
Figure 9. SREF ensemble showing the track of the surface low every 3 hours from a) 0000 UTC 23
January to f) 2100 UTC 24 January 2014 Return to text
Figure 10. SREF probabilities of 12.5 mm or more QPF for a 12 hour period ending at 1200 UTC 24
January 2015 Return to text.
Figure 11. SREF probabilities of 25 mm or more QPF for the 12 hour period ending at 1200 UTC 24
January 2015. Return to text
Figure 12. SREF 12 hour ensemble mean QPF and each member 25 mm contour for the period
ending at 1200 UTC 24 January 2015. Return to text
Figure 13. SREF 12 hour ensemble mean QPF and each member 12.5 mm contour for the period
ending at 1200 UTC 24 January 2015. Return to text