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2017-03-14

The 14 March 2017 East Coast Winter storm Slushmageddon: A rapidly developing surface cyclone (Fig. 1) moved up the East Coast of the United States on 14 March 2017. This strong cyclone produced a large swath of heavy precipitation from the southeastern United States into New England (Fig. 2). The first guess snowfall plot from gridded snowfall reports is shown in Figure 3. These data show a wide swath of 16 inches or more of snow over central and northeastern Pennsylvania and over 32 inches of snow in northeastern Pennsylvania and the Catskill region of New York. Snowfall of 31 inches was observed in Binghamton, NY and over 40 inches was reported in West Winfield , New York State (Table 1). This event also occurred on the heels of an exceptionally warm February which did not produce significant snow over the Mid-Atlantic region. Despite the February warmth, the event produced record to near snow in many locations. However, snowfall amounts were generally lower along the coastal plain and along the heavily populated corridor from Washington-Baltimore to Philadelphia, New York City, and Boston. Unlike the Megalopolitan storm of 11-12 February 1983 (Sanders and Bosart 1985) and the Superstorm of March 1993 (Kocin et al. 1995), this storm spared the major cities from a crippling snow event. It will be shown that this storm was forecast with relatively long lead-times. However, the details related to the exact storm track, intensity, and precipitation type were not as skillfully forecast. There was considerable uncertainty in these varied forecasts. Thus, the precipitation type became a critical forecast aspect of this storm. Initial forecasts implied relatively high confidence in a significant snow event for much of the Megalopolitan corridor though the confidence in an all snow event diminished as the forecast length decreased. The convergence toward a mixed precipitation and rain event along the coastal plain evolved with 18 to 42 hours of lead-time. High resolution ensemble forecast systems such as the NCAR 3km ensemble (Schwartz et al. 2015) performed relatively well during the event as did the 3km HRRR. It will be shown that at forecasts lengths of 6 to 36 hours these mesoscale ensembles produced guidance of critical value relating to snow fall and precipitation type. This paper will document the winter storm of 13-14 March 2017. The pattern, the areas of snow and higher QPF are presented along with forecasts and issues related to forecast uncertainty.

2017-03-10

Mid-Atlantic and southern New England Snow 10 March 2017:A well forecast short wave and frontal system ahead of a surge of arctic air produced 2-10 inches of snow across central Pennsylvania eastward across southern New England. The heaviest snow fall was in the mountains of west-central Pennsylvania where 3 to 10 inches of snow was observed. Higher snow amounts were confined to the higher elevations of central Pennsylvania. As shown both the NCEP GEFS and 3km HRRR did relatively well forecasting the snow, the timing of the snow and general snow amounts. The HRRR QPF was well aligned with the observed QPE. However, the HRRR produced too much QPF in the Poconos of northeastern Pennsylvania.

2017-02-25

The 25 February 2017 severe weather and tornado event:A late winter severe weather event affected the Mid-Atlantic and the northeastern United States on 25 February 2017 (Fig. 1). There were around 231 reports of severe weather and 6 tornadoes. There were two tornadoes reported in both Pennsylvania and Massachusetts. The Massachusetts tornadoes were the first known February tornadoes recorded. Serendipitously there was a similar severe weather and tornado event 366 days earlier on 24 February 2016 (Grumm 2016) which produced the first tornadoes in Pennsylvania since 16 February 1990 which was the proceeded by the tornadoes of 11 February 1887 (MWR 1887). February tornadoes in the northeastern United States used to be a less common occurrence. This paper will document the pattern associated with the severe weather event of 25 February 2017. It should be noted that this event was associated with a strong cold front which ended the epic eastern United States warm episode of 20-25 February 2017 (Grumm and Ross 2017). It will be shown that the storms occurred ahead of this strong cold front in a region of high shear and low CAPE . The issues with high shear and low CAPE (HSLC: Sherburn et al. 2016) severe weather events in the eastern United States is well documented. Frey ET. al. (2016) stratified tornado events across the United States by region and season.

2017-02-24

The historic warm episode of February 2017: A record breaking warm episode affected much of the eastern United States from 18 to 25 February 2017. The peak warmth in the eastern United States and Mid-Atlantic region was focused on 23-25 February 2017. On the 24th and 25th of many sites in the east set record high temperatures for the month of February and some sites achieved the all-time high for meteorological winter. Despite the record and the prolonged period of warmth, the pattern over much of the eastern United States was not that extreme. The 500 hPa height and 850 hPa temperature anomalies were ranges 1 to 2 and 2 to 3 above normal. Thus relative to the record warm episode of March 2012 the pattern was not overly remarkable. However, the 2m temperatures and 2m temperature anomalies were more impressive in the CFSR and the GFSBC forecasts. However, both were too cold relative to the observed conditions. The estimation of the GFS and CFSR 2m temperatures suggests they can capture the sense of an extreme event but miss the true impact and magnitude of the event. The often asked question is was this warm episode due to climate change. The short answer is we do not have the data to definitively state that it was. In State College, February 2017 will likely end up being the 5th warmest February on record. It will hold the record for the 6-day highest mean maximum temperature, and it set the all-time February high temperature record and the highest all-time observed winter maximum temperature. These kinds of records were broken at many other stations. However, some of the record warm periods have occurred before with 1930 and 1954 showing up at many sites. Thus there is a strong meteorological component to this event. That said, over time climate change predicts we should have more warm episodes and fewer extreme cold episodes which is supported by the data in Table 1. This implies there could be a climate change component to this event.

2017-02-15

Examples of Two February Squall lines Mesoscale features are often difficult to Predict On February 13 and 15 2017 two squall lines cross portions of the Mid-Atlantic region. The first squall line was observed during the evening hours of Sunday 12 February . Radar signatures implied 30 to 40dBZ echoes of 8-10,000 feet, low topped squalls which produced 73 reports of severe weather (Fig. 1). There were reports of lightning though lightning plots implied most of the lightning in Pennsylvania was located at turbine locations. The second squall line occurred in a slightly colder air mass and in central Pennsylvania the squalls contained snow. There were no known reports of severe weather. During the snow squalls visibilities dropped to 1/4SM in snow and blowing snow. Despite temperatures above freezing the rapid snow rates coated the ground . Similar to the 13 February event, there were isolated reports of thunder in the initial squall line though reports came from locations close to windfarms, the data showed most strikes along the line near or over wind turbines (Fig. 2) and larger windfarms. However, western portions of State College had several reports of thunder at least 12 miles from the nearest wind turbine. February snow squalls are not uncommon with strong cold fronts and arctic fronts. However, squall lines containing thunder are more unique and squalls producing severe weather are climatologically relatively rare in Pennsylvania and most of the Mid-Atlantic region. These two events offer a contrast in predictability. It will be shown that the squall line of 13 February was relatively well predicted and the squall line of 15 February was poorly predicted. Another interesting issue is the impact of the wind farms on lightning strikes.

2017-02-09

Northeastern United States Snowstorm of 9 February 2017: A strong shortwave produced a stripe of precipitation from the western Plains to East Coast on 8-9 February 2017 (Fig. 1). Most of the precipitation along and north of the track of the surface cyclone (Fig 2) fell as snow (Fig. 3). The highest snowfall totals were observed from northern New Jersey across Long Island and into New England. Though not shown, radar and lightning data showed an intense band of snow and a prolonged period of thunder-snow in the band from southern Maine into Massachusetts. Areas in this band received over 16 inches of snowfall.

2017-01-13

Minor Winter Flooding Event in northwestern Pennsylvania 12-13 January 2017 The combination of unseasonably warm air and an intrusion of humid air likely helped produce snow melt in northwestern Pennsylvania and southwestern New York. This likely reduced significant water from the snow pack. This combined with a widespread rainfall event of 1-2 inches (Fig 1) led to localized flooding over the region. Additionally, much of the region affected by the higher rainfall amounts received most of the rainfall in a 6-hour window. Many locations received 1 to 1.5 inches of QPE in a relatively short 6-hour window. The pattern in which the rainfall developed was relatively well forecast (not shown). The NCEP GEFS was able to predict the potential for 1 inch or more QPF but was limited in its ability to produce much more than 1.5 inches of QPF. Due to the frozen ground, snowmelt, and the 2 inches of rainfall, this relatively low end QPF/QPE event did produce minor flooding. The threshold for flooding is typically a bit higher, in the 3 inches and greater range in the warm season. However, in this case the antecedent and current conditions favored a better hydrologic response with relatively low rainfall amounts.

2017-01-12

Eastern United States Warm Episode of 11-12 January 2017: A large ridge of the southern United States (Fig.1) with +1 to +2500 hPa height anomalies brought period of warm weather to much of the eastern United States from 11 to 13 January 2017. During this period of time about 809 maximum temperature records were set or tied and 540 maximum low temperature records were set or tied (Table 1). The warmest day over much of the Mid-Atlantic region was 12 January 2017 when temperatures peaked in the 60s over much of Pennsylvania and Maryland. The warmest day over the Mid-Atlantic region was the 12th of January ahead of the cold front. There was a surge of high precipitable air ahead of the front (Fig. 3c) and the 850 hPa temperatures were well above 0C and were +1 to +2 above normal over much of the eastern United States with the highest standardized anomalies over the northeastern United States.

2017-01-08

The California Extreme Precipitation Event of 8-10 January 2017: A strong Pacific jet and a surge of high precipitable water (PW: Fig. 1) brought extremely heavy precipitation to portions of California on 8-9 January 2017 (Fig. 2). Rainfall amounts in excess of 200 mm were observed and there were reports of extreme snowfall to include. NBC news reported “epic snowfall” in the Sierras. The Los Angeles Times reported flooding, record snow, extremely high winds at higher elevations, extreme snowfall, and blizzard conditions in the Sierras on 8-9 January 2017. Squaw Valley reported winds of 99 MPH with gusts as high as 159 MPH . The strong Pacific system was associated with a near classic pattern for significant precipitation events in California which included a surge of high PW (Fig. 1) also known as an atmospheric river (AR: Neiman et al . 2008), a deep trough off the West Coast, a strong Ridge over the north Pacific and a ridge to the east (Fig. 3). This results in a strong 250 hPa jet (Fig. 4) moving into then over the affected region (Junker et al. 2008). It will be shown that the general pattern was well forecast and thus the NCEP GEFS was able to forecast the general regions of heavy rain in California. This probably was an easy forecast as the mountains act as fixed forcing for the impinging moisture and energy from the Pacific. This paper will provide an overview of the event and examine NCEP GEFS forecasts of the QPF. This was a multi-day event and the focus was on the heavy precipitation from 0000 UTC 8 to 0000 UTC 10 January. There was a significant event prior to this and another surge of precipitation after this time.

2017-01-07

East Coast Winter Storm of 7-8 January 2017:A winter storm produced snow and areas of heavy snow from North Carolina to southeastern New England on 7-8 January 2017 (Fig. 1). The snow overnight Friday into Saturday fell mainly from North Carolina to Virginia (Fig. 1: upper). Much of eastern North Carolina had ice pellets and freezing rain which limited the snow totals. Coastal Virginia and the Delmarva had heavy snow during the morning and early afternoon of 7 January. Later in the day the snow shifted to Long Island (Table 1) and southern New England (Table 2). Some of the higher snowfall amounts, in the 12 to 19 inch range were observed in southeastern Massachusetts and Rhode Island. The broad area of 12 to 16 inches of snow in southern Massachusetts was where the higher snow amounts were observed (Fig. 1: lower). The snow was the result of a relatively deep 500 hPa low (Fig. 2a), a surge of cold arctic air into the eastern United States (Fig. 2b), a surge of deep moisture along the East Coast (Fig. 2c), an elongated low off the east coast. The snow fell in the region of strong northwesterly flow between the cyclone and the strong anticyclone to the west (Fig. 2d). Note that during the peak of the event in the southeast the 850 hPa temperatures were in the -8 to -12C range as far south as northern Georgia (Fig. 2b). This paper will examine the East Coast Winter Storm (ECWS) of 7-8 January 2017. The focus is on the pattern and forecasts of the event. The storm occurred over a weekend which may have limited the overall impact of the storm. Additionally, with the exception of Boston, MA the major cities of the Mid-Atlantic and Northeast did not receive significant snowfall with this event.

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