3/07 All Zones Late AM Update: Mild with Rain Today, Snow Threat South This Weekend?

A warm front moving is producing periods of mostly light rain over the region this morning. Rain will taper off early this afternoon, as warm front lifts northward. But skies likely remain mostly cloudy with perhaps for few breaks of sunshine later this afternoon. Temperatures with a southwest flow will still rise well into the 50s this afternoon. Some areas further south over Central and Southern New Jersey, may see enough clearing for temperatures to reach or exceed 60 degrees.

More showers or periods of rain are likely as cold front moves through later tonight into early tomorrow morning. Better dynamics with this front are still over the Great Lakes region. So rainfall should mostly light or moderate side. Behind this front, will later Wednesday behind this cold front. But downsloping west to northwest winds will still cause temperatures to rise above normal in the 50s, until cold-air advection increase later in the afternoon.

As previous discussions, a new pattern evolution will be taking place later this week. This frontal system impacting the region today will be intensifying rapidly into very strong and deep closed low into moving north into Hudson Bay and enhancing blocking over Greenland/Davis Strait. Latest model guidance has been trending stronger with the blocking in more north to south oriented fashion. This forces a lobe of the polar vortex over Hudson Bay and Southeast Canada, to swing further south over the Northeast by this weekend. At the same, a faster, more active pacific jet remains. If this were to continue as a trend, chances the storm will further south, with perhaps northern fringes passing over southern zones.

 

GFS model trends with 500mb heights f

GFS model trends with 500mb heights over North America

 

However, there have been some trends over the past couple days with the Bering Sea ridge to perhaps connected to more high-amplitude ridging over Northern Rockies and Western Canada, as trough/upper-level low over British Columbia also shifts back southwest over Northeast Pacific. If this trend continues, this cause flow to buckle more resulting more phasing Pacific and Polar shortwave energy, before reaching the East Coast.

Before that happens pacific shortwave energy will be moving over the Mid-Atlantic region Thursday night into Friday. Latest GFS models indicate more meridional flow with this system. More height rise ahead of this system along the east coast and over Northern Rockies. This height pattern gives more room for amplification, if this is correctly shown by this morning NAM and GFS models.

A colder, drier airmass over Northeast during this time frame, is also likely to enhance a gradient north of this low support there frontogenesis and isentropic lift for overrunning snow or wintry mix of precipitation over parts of the region. Also a strong dual jet and PVA (positive vorticity advection) at 500mb level moving through will also enhance more lift. However, there is still some model disagreement on the track and intensity of this system and some question with boundary level temperatures supporting significant snow accumulation. So confidence remains currently low with any impacts from this system.

GFS showing mid-frontogenesis with wave low pressure passing over Delmarva region Thursday night

6z/07 GFS showing some mid-frontogenesis with wave low pressure passing south of the region Thursday night

We are also still watching a third shortwave coming out the Pacific for a potential for another storm system next week. Behind this shortwave models show a stronger ridge developing over the Northern Rockies. However, the blocking over Greenland/Davis Strait appears be in much weaker state. So the pattern may trend too progressive for this system to dig more and phase with polar shortwave energy, before reaching the east coast. But synoptic features on the deterministic guidance can still change drastically, from this range.

Stay tuned for more zone forecast and other updates on these winter threats for this week.