Mar 8, 2014: Warmth Returns Mon-Tues

Forecast Highlights:

Temperatures surged into the upper 40s to mid 50s across the area today, nearly 10 degrees above average in Central Park, the first time widespread above average temperatures were observed since February 23. A brief cool down is expected tomorrow followed by even warmer temperatures for Monday and Tuesday, likely reaching the mid-upper 50s near NYC, before returning back to below average on Wednesday and Thursday as a storm system affects the region with rain and possibly snow.

Tonight – Tuesday: Brief Cool Down, Then Warm Again

Posted above from left to right are the latest available surface analysis and radar composite from WPC, and the initialized GFS 500 millibar heights and vorticity from NCEP MAG; both are valid at 18z (1pm). The coastal low which affected the Mid Atlantic region with coastal rain and high elevation snow/ice has since moved offshore; the system was primarily driven by the southern stream, with virtually no interaction with the northern stream. With this lack of connection, the northern cold front lagged behind the coastal low, only moving through the region this afternoon. This delayed timing allowed for a warmer air mass aloft to advect into the region, with a downsloping westerly flow allowing for much warmer temperatures this afternoon, generally peaking in the low-mid 50s with temperatures as warm as 59 degrees in Newark, NJ and 57 degrees in Central Park. This marks the first time temperatures were above average in Central Park since February 23, ending a 12 day consecutive streak of below average temperatures, tied with December 7-18 as the longest period of below average temperatures this winter.

As the cold front continues to progress offshore, another cold air mass will enter the region tonight into Sunday. This will set up for continued partly to mostly cloudy skies on Sunday but with highs in the 35-42 degree range, coldest in interior NW areas and warmest near NYC, with a NW wind at 8-15 mph. More significant warming is expected in the early week, however, as a strong jet streak currently entering the NW US and southwestern Canada continues to rapidly progress eastward, cutting off a trough in the southwestern US and setting up for a relatively zonal flow over the northern US. Meanwhile, as a relatively weak area of low pressure over southern Canada rapidly tracks eastward north of the region, a warm air mass will be advected into the region again. After a period of scattered rain/snow showers on Monday morning, partly to mostly cloudy skies are expected with highs rising into the mid 40s to low 50s. Warmer temperatures are expected on Tuesday as a cold front slowly approaches the region, with partly cloudy skies and highs expected to reach the low to mid 50s, with the possibility for upper 50s near NYC and NE NJ.

Wednesday – Beyond: Rain/Snow Likely Weds, Cooling Down Again

Another complex upper level setup is expected to take shape on Wednesday as a relatively strong shortwave trough enters the NW US on Monday morning, continuing ESE into the central US and allowing for the cutoff upper level low, having drifted into northern Mexico by this time, to accelerate ENE through the southeast US; at this time, this southern shortwave is likely to remain separate from the system. The key interaction to watch for is with the central US shortwave and a northern stream trough digging SSE from Canada and bringing in another cold air mass, with the extent of phasing determining the track and strength of the surface low pressure, as well as how much, if any snow falls in the area.

The latest model guidance, not surprisingly for a day 4-5 outlook, continues to display some run-to-run discontinuities, with the GFS generally depicting a mixed precipitation event for the area, starting as rain and changing to a mix or snow, while the ECM is warmer with most of the snow north of the area, and the latest 12z CMC run keeps the snow well north of the area. Focusing on the 500mb height layer, the model guidance does not appear to have a strong handle on the three main features, the southern US shortwave, central US shortwave, and the northern stream originating in Canada; all of these features are still in regions of poor upper level data sampling. The exact positioning of the polar vortex is also somewhat uncertain, although in this case the polar vortex is likely to be centered near eastern Canada, far northeast enough relative to the March 2-3 storm to prevent significant suppression. There is no well defined trend at this time, although the latest runs have trended towards more amplification of the northern stream originating in Canada, which is typically underestimated by the models in the medium to long range.

Uncertainty remains too high to predict snow totals at this time, with additional changes expected over the next 1-2 days as the model guidance gradually gains a better handle on the key features. The southward extent of snow depends on the strength of the system, with a weaker and more suppressed system increasing snow chances for the area, provided that it is not too weak such that boundary layer temperatures end up marginal, and a stronger and further north system keeping most of, if not all of the snow staying north, with a cold rain affecting the NYC area. Since February 15, recent trends have often favored more suppression than modeled in the long range, although the GFS ensemble members are split between a suppressed and amplified scenario. Probability of precipitation is high in this time frame, with at least a 70% of precipitation, but with exact precipitation totals still uncertain. Given the above, preliminary thinking at this time is for rain to develop on Wednesday afternoon, potentially changing to snow overnight with accumulations possible before ending on Thursday morning, although at this time probability of a major snowstorm does not appear high in the area. More information will be posted over the next few days.

Following the Wednesday storm, colder temperatures will return for Thursday with highs likely in the upper 20s-low 30s, with overnight lows possibly falling into the 10s away from NYC and the immediate coast. Gradual warming is likely towards next weekend back into the 40s, but with another cool down possible by early next week. The next possibility of widespread precipitation appears to be towards early-mid next week.