7:07 AM

The strong Polar disturbance that is more developed than guidance suggested a few days ago is an important clue and reminder for the forecast later this week.  For now, that disturbance represents another push of a Polar/Arctic air mass after Tuesday afternoon.  The key to the forecast over the next several days is the progression, strength, and overall track of these Polar disturbances.  The HPC this morning with a statement that basically the operational GFS and the ECMWF have a poor handle on the Polar jet stream over the Pacific and that influences the credibility of model guidance for the short, medium, and even long range of the operational guidance.

Based on the lack of credible guidance through this week, it is time to think outside the box a bit and look at the overall pattern and not model trends.  What do we know up to this point with this pattern?

1. We know that the Polar jet stream is relaxing and the Sub Tropical jet stream is starting to gain some strength.  The strong negative NAO is relenting but not breaking.  Thus there is still a strong cyclonic influence at 500 MB over the Northeast and Mid Atlantic.

2.  We know that there are plenty of disturbances in the Polar jet stream over the north Pacific that will be able to introduce fresh Polar/Arctic air masses into the Great Lakes, Northeast, and Mid Atlantic.

3. We know that a strong Sub Tropical disturbance will develop an area of low pressure in the Gulf of Mexico.  This low pressure system will have plenty of moisture to tap into.

4. We know based on this pattern the storm will be able to move only so far north as the Polar and Sub Tropical jet streams remain separate and progressive.

What we don’t know.

1. We don’t know the timing of the Polar disturbance therefore we don’t know what type of air mass will be in place over the Mid Atlantic and thus no way of knowing the precipitation type nor duration of any precipitation type.

Okay, so there is a lot we know going into this week, but a key factor that trumps everything we know for the storm for next weekend.  The forecast for much of this week will be pretty straight forward.  High pressure will be in control today with dry yet cold conditions once again.  Another day in the 20′s and lower 30′s can be expected for this afternoon.  Tonight and tomorrow, a strong cold front will approach with moderating conditions ahead of the cold front, which will support temperatures to bring into the mid to upper 30′s along the coast for the first time in some time.  I should point out that these temperatures are still generally slightly below normal in many locations.  The cold front will pass on Tuesday night with perhaps a passing snow shower, but generally dry conditions can be expected.  Colder conditions will briefly return on Wednesday with temperatures once again struggling to break into the lower 30′s.  Moderation will being once again for Thursday, Friday, and Saturday afternoon with temperatures finally pushing into the lower 40′s along the coast.  These temperatures are near normal for this time of year and will be a welcomed experience for many.  Again, conditions are expected to remain dry through the week.

Then this pattern gets very interesting.  A cold front is expected to move through the northern Mid Atlantic on Saturday night, introducing a cold Polar/Arctic air mass into the region.  As temperatures fall and high pressure becomes established over the Great Lakes, the Sub Tropical disturbance will drive an area of low pressure towards the southern Mid Atlantic.  The speed at which the Polar air mass builds into the Mid Atlantic will be key for this time period and will determine the rain/snow line as the coastal low from the Sub Tropical disturbance moves north and deepens.  There is potential for a heavy precipitation event on Sunday afternoon through Monday morning, however the details of what region gets what type of precipitation event is clearly unknown at this time.  There is potential for a heavy snow event, however this storm will require that all features interact just right to produce that scenario.  One thing is certain is that this set up will likely not be handled by model guidance very well for the next few model runs and I expect changes in this forecast.