Winter Returns

Weather is most interesting and changeable. For Nov we averaged (at Harrisburg since its the closest point with accurate data) 40 degrees for the month and then Dec we are at 38.  Nov was 4 degrees below average, and Dec will be about 3 above average.  So similar temps made for a cold Nov and a warm Dec!  
Statistics are fun to play with. Now on to the daily weather. 


Expect a good week weather-wise. Much colder. More like winter. But lots of sunshine over-all. It will be at least partly sunny every day at least through Friday.  Temps will be near 40 Mon, mid 30s Tue and upper 20s to 30 Wed and Thu and then low 30s Fri. Most nights will be bottom out in the 15-20 degree range for Tue - Fri night.  


What about the storm over the weekend? 


DO NOT TRUST ANY FORECAST RIGHT UNTIL THU.   
Cut off upper lows coming out of the SW are tricky esp. since there is  split flow in how air is traveling across the us. Air can start from the Pacific, into AK and then go S or SW  upper low in CA, AZ then east to NC. The other  option is for air to from the Pacific north to AK, then SE through Canada and off the VA coast. Voila: Split flow. How that low interacts with energy in the other stream is key. Timing in everything. The options for Late Sat - Mon Morning: 

1. The two streams could join forces (phased storm bringing rain to us). 
2. The northern flow could dominate and the gulf coast, SE US gets soaked. But nothing here but dry and cold. 
3. The two streams could fight to a draw. Meaning decent storm with lots of moisture just to our south. This could bring a big snow or mix snow/ice to us.

 The problem is that models are notoriously bad at moving these SW upper lows out of the SW eastward across the US.  So what to do if you have to forecast?   Look at what is happening now. 



I do see the cold pushing south. It is strong and keeping moisture away from us Mon-Tue of this week so no light snow at all. This could be a key indicator since the amount of cold air we are dealing with is impressive across Canada and much of US now.  This leads me to believe that options #2 and #3 are the most likely. I really doubt option #1 will happen. I will have more on this storm New Year's Eve. 


Until then ... Enjoy the sunshine!