Increasing threat of eastern cyclogenesis February 5-7...
Another significant storm threat is headed towards areas east of the Mississippi River in the Friday to Sunday time frame. Recent guidance suggests an anomalous trough with accompanying shortwave causing the allowance of an increased chance of cyclogenesis along the eastern seaboard. But unlike the previous event, the polar vortex and 50/50 low remain slightly dislocated from a favorable position therefore allowing for effects to be reached farther inland. While this threat remains nearly 5-7 days in advance, this blog attempts to outlook the scenarios highlighting the highest threats at this point. Variability is likely throughout the week courtesy of a much more volatile H5 jet, which will allow for a much more difficult and complex forecast.
Lets dive right into the thick of things highlighting the favorable synoptic setup. MREF guidance using GFS ensembles, indicate spaghetti plots to have relatively high confidence in a disturbance located along the eastern seaboard with an anomalous trough.
The GEFS mean plot produces the polar vortex northeast towards Nova Scotia favoring a more southwest to northeast orientated jet streak, unlike the previous west to east suppressed flow. KU analogs suggest this to be a relatively favorable plot for at least 4-5 indirect matches. A relatively stagnant negative NAO will allow for continued blocking towards the Hudson Bay through Greenland, but a high amplitude ridge in the western Atlantic will be the catalyst for allowing confluence in New England to remain slightly disjointed.
0utc ECMWF 1/31 showed a few concerning factors that remain highly subjective in terms of snowfall potential.
First of critical note is the anomalous trough negative tilted orientation towards the Mississippi Valley. This is slightly farther west than favorable analogs therefore favoring phasing to occur a bit earlier than one might expect for a typical Miller A storm system. Origins are definitely out of the Gulf of Mexico, but with the 50/50 low dislocated (as highlighted above) to the northeast, the primary low may transverse towards the Tennessee Valley. The ECMWF remains the western outlier, but highlights a few critical concerns that the southeast biased GFS may be lacking. Also of importance, note the increasing amplitude in the western Atlantic ridge. If this increases in any more gains in northern amplitude, it may try to cut of all confluence in northern New England and southern Canada courtesy of the high pressure slightly disjointed towards western Newfoundland. But the ECMWF does support weak blocking upstream and a large negative EPO western ridge therefore supportive of an increasing threat of cyclogenesis and a widespread precipitation event across the eastern United States from Florida to Maine. More recently the 1/31 12utc ECMWF radically shifted farther south and east with the primary courtesy of 50/50 relocating more favorably towards 50N/50W. While this pattern remains highly subjective, guidance in this medium range is definitely diverging on a few solutions. The solution as listed above with several unfavorable factors fits the 'near miss' KU category favoring west Virginia up through western and central Pennsylvania up towards Albany, New York. In that scenario rain would be likely into areas east of the mountains at some point. Also of critical note is the closed 500mb low the ECMWF is highlighting in the 0z run up towards Kentucky, which is a good rule of thumb for precipitation type issues east of the Blue Ridge.
Despite the warmer, inland storm, the UKMET and GGEM remain steadfast on another very interesting scenario.
The 12utc GGEM 1/31 cycle indicates a more favorable scenario fitting the threshold for widespread significant snowfall over the eastern seaboard. The trough turns negatively tilted towards the southeast favoring rapid cyclogenesis as the low approaches Hatteras. There also remains more confluence to the north around northern New England to Nova Scotia, but make a critical note that the high pressure remains in a slightly unfavorable location. Lastly note the impressive 100knot jet streak along the east coast bringing +2SD moisture up the coastline from the Gulf of Mexico and Atlantic Ocean.
Looking at teleconnections, they remain supportive of east coast cyclogenesis with a negative NAO and positive PNA. Also favorable is the phase 7-8 MJO, which has finally remerged after a benign pattern most of January.
The MJO phases of 7,8, & 1 remain favorable for high amplitude in western United States ridging and anomalous east coast troughing. The benign MJO is part to blame for the zonal Pacific airmass January most of the United States record, so now we are in a pattern closer in relation to that of December 2009. The active subtropical jet remains the culprit for the shortwave over the southeast later this week that will ride along the eastern periphery of the trough; wherever that may be. All of this coupled with a significant statosphere warming event and near record negative AO, will keep confidence high in a major winter weather event towards the weekend.
Finally the 1/31 12utc GFS operational shows another scenario with some relation to the double barrel low feature on the 0z ECMWF.
The primary low tracks up through the Tennessee Valley with redevelopment near Hatteras before the PV kicks this system eastward before it can gain latitude. A critical note of 4-7 medium range guidance is for PV positions to be progged too far to the south and west. So taken in account the southeast bias of this current prognostic, this system would likely be allowed for more widespread impacts north of 40N. Phasing of the northern and southern stream will be critical with a more phased approach allowing for this low pressure to track closer towards the coast with a strong primary back through the Tennessee Valley and into Kentucky.
With all of this in mind, my mean solution at this point highlights some very critical features. First off the blocking and confluence seems very disjointed to classic nor'easter tracks with widespread snowfall. In fact the H5 pattern resembles that more of an Appalachian snowstorm than a suppressed event. Also some guidance is suggesting a weak S/W across the Great Lakes region, which in most past instances typically is not favorable for an east coast track with widespread snowfall. But that being said spaghetti plots are very indicative of a heavy precipitation event across the east coast in the Friday through Sunday time frame with potential high impacts especially as one gains latitude. Also of one concern is the trend of guidance suggesting a stronger initial catalyst shortwave out of the Rockies, which would therefore allowing phasing to occur sooner with an Ohio Valley track. Therefore with a steep trough and lack of significant blocking I put suppression with this system at less than 30%. For those steadily watching model runs, expect radical changes in each cycle throughout the week as the pattern is highly volatile. This will cause many forecasting headaches. As for recent model verification the GGEM leads the pack in the medium and short range for the synoptic cyclogenesis events this winter along the east coast, but still the ECMWF leads the way in medium range 500mb verification. The GFS remains poor, typically with a southeast cold bias. Looking in conclusion I am concerned for precipitation type issues from the Blue Ridge up through Pennsylvania on eastward, but especially from I-95 on eastward. And I still would not be surprised for this system to track along the coastal plain with heavy snow thrown back into the Appalachians. 12utc model cycle trends were encouraging as for the 50/50 low placement straying away from an Ohio Valley storm system. Keep in mind with many days of the week ahead, any solution remains on the table, but I hope I highlighted several of the more favorable scenarios to make tracking this storm threat a bit more simpler. As far as analogs I have highlighted March of 1959, February of 1964, and January of 1978 with slight synoptic similarities. But generally I would not focus too much on analogs considering the fragile pattern in which a good deal can go wrong for those southeast of Hagerstown-Harrisburg-Allentown. Have a wonderful day!!!
"Here northeast of Harrisburg 2009-2010 winter statistics"
Current Snow Cover- 3.75in
Monthly Total- 3.75in
Seasonal Total- 21.85in
October Total- 0.0in
November Total- Trace
December Total- 16.0in
January Total- 2.1in
February Total- 3.75in
Winter Weather Advisories- 5
Winter Storm Warnings- 1
Ice Storm Warnings- 0
Blizzard Warnings- 0
Freezing Rain Advisories- 2
Winter Storm Watches- 1
Lowest High Temperature- 18.8F
Lowest Low Temperature- 11.7F
Wind Chill Advisories- 0
Wind Chill Warnings- 0
(Winter Storms Stats)
Dec 5 - 1.5in - First accumulating snow of season
Dec 8-9 - 2.5in - Snow changed to plain rain
Dec 13 - .1in - Freezing rain
Dec 19 - 9.0in - Heavy snow, higher amounts to south
Dec 31 - 3.0in - 2.5hr warm air advection event
Dec 31 #2 - .2in - Freezing rain/sleet later in day
Jan 8 - 1.5in - Light snow associated with clipper
Feb 2 - 3.75in - Weak coastal storm