HIGH and Dry

Well, not really dry, but the major snow event that looked like a lock from mid-week on last week will now struggle to accumulate 4" or so +/- in KMDT.  It certainly now appears that the heaviest snowfall will occur somewhere (as it has occurred all season) nearer the Mason-Dixon Line.  I had a discussion last week with a few interested parties that the concern of mixing will be an issue.  Only at the onset, if much at all as the numerical guidance often under plays the strength of the cold, dense, dry air.  Well, this is some SERIOUS cold air for this time of year as evidenced by the strength of the high pressure currently residing over the Dakotas and ridging back up into Manitoba, Saskatchewan, and Alberta.  The leading edge of the cold, dense, dry air is now entering NW PA as I pound this old Dell keyboard...

Look at the current temps...that is some serious cold back up in MN and southern Canada.  That air is what will create the overrunning boundary for the precip from the area of weak low pressure on a deep SSW flow.  Just where that boundary sets up IS the million $$ question!

Although I personally believe it to be a bit further north than shown, this High-Resolution NAM graphic nicely shows the deep plume of moisture advecting straight from the warm Gulf of Mexico and heading towards the Mid-Atlantic states.  As indicated, the higher pressures to the north keep PA in the drier air and thus will tend to limit the precip during Sunday night and Monday.  But, as you can see, even a small jog to the north would greatly alter the forecast significantly.

The Euro and the Canadian have held their progs the best over the last several runs.  Frankly, the American suite of modeling has been absolutely pathetic with their consistency.  I admire computer modelers and their skill in writing programs that are able to simulate what the atmosphere or how any other fluid and dynamic event might result based on a specific set of algorithmic outputs.  A talented pool of people to be sure!  But, there has to be some serious studies as to how the modeling can be so inconsistent as a major wx event is within the "near-term" range.  With all of that said, here is the Euro's overnight run for snowfall potential...

Again, a southern tier major hit!  Does this warning map from the NWS look familiar?  Persistence is a forecast skill that could have been used quite effectively this winter.  It simply is the idea that it's cold where it wants to be cold; it snows where it wants to snow, it's "droughty" where it wants to be "droughty"...you get the idea!

Now a little meteorology lesson.  Look at the 700 mb (2 miles up) winds for early Monday.  The best divergent flow is over MD and northern VA.  This will allow for better uplift and greater precip rates (red circle) as opposed to where the flow is more convergent (yellow circle) creating air to have a net downward movement and ultimately suppressing precip.  Just exactly where this type of upper air dynamics set up WILL have a major effect as well as to the exact location of the true arctic boundary.  Also, the greater the wind speed, the stronger the upward motion.  The best 700 mb jet is clearly to the south of PA!  This is a very tricky call...

Note how the 700 mb jet best depicts the forecast of most precipitation from HPC...

But cold will rule this first week of March; of that I am quite certain.  Look at that monster high keeping the Arctic locked in over the northeast this week!  It's been quite a cold winter!  With any appreciable snowfall, Wednesday morning will be absolutely frigid!  I'm expecting that 2 record low temps will go by the wayside this week at KMDT.  

Ok...enough said other than I am truly humbled by the fact that many of you truly do read these posts and put some faith into my interpretations of all of this wonderful stuff we call the world of weather.  And I do apologize that I was not able to address the changing forecasts yesterday (Saturday) as our family was celebrating a milestone birth of my wonder sister; the Smith Family "matriarch of sorts" with the passing of my mother now over a decade ago.  And what a wonderful way to spend the bulk of my Saturday!  I am truly blessed to have such a great group of human beings to call my family.  This is an astounding testament to my 2 wonderful parents who raised 5 of us in a manner consistent with love and discipline.  The values and ethics Mom and Dad instilled in us 5 is clearly being passed down through the extended families.  Admittedly, it was refreshing to see! I hope I am not offending any of you reading this, but I am truly proud of our extended family.  I jokingly commented to several of my relatives yesterday that the next time we all gather, we will have to have a program listing of all the cousins, 2nd cousins, grand-kids, etc running amok since we just frankly don't gather often enough.  It was a great celebration of family!

With that said, and many of my family members being Pirate fans, I'll sign off with this classic hit from the Sister Sledge from 1979. (Touch of Irony...Sister Sledge is from Philadelphia, PA!)  Enjoy the "disco" and baseball flashback!

Smitty

AA:  A moderate snowfall is in store for KMDT Sunday night into Monday.  Looking at 4" or so officially at KMDT.  I will have closer to 6-7" since I am not trying to suppress snowfall totals as I have no Global Warming agenda.  Northern MD looks to potentially get a foot or so!  But a VERY COLD week ahead. One week buddy!