2/4/15: February Changes

High pressure is building into North Dakota behind the disturbance that brought some snow to especially the southern part of North Dakota yesterday.

NGP.fronts.20150204.15
Morning Surface Analysis

With high pressure, fresh snow in some locations the lows this morning were correspondingly much colder.  Several pockets of -10s and -20s associated with the fresh snow.  Locations a bit warmer either didn’t clear much overnight or more often, have minimum or no snow cover.

Minimums
Minimums for 2/4/15

There will be several more fast moving low pressure areas moving through the area this weekend, but today and tomorrow look to be dominated by high pressure keeping the area dry and cold.

But Friday through early next week, 3 disturbances will be moving through the area riding the fast West / Northwest Jetstream that has dominated the weather much of this winter.

nam_jet_300_conus2_20
Progged Friday 2/6/15 Jetstream

 

The first disturbance should arrive during the day on Friday and impact northern North Dakota more so than the southern part of the state.  Early indication are a strong disturbance will do the same on Saturday.  Both of those disturbances will bring with them warmer temperatures.

nam_precip_mslp_conus2_19
Friday Noon Projected Surface features and prescipitation

This pattern I do believe will continue through at least the first one-half of February.  The projected 500 mb (18000 feet) flow is presented from the Canadian long term model below.

progged 500 mb (18000 feet) wind flow and anomalies for February 18
progged 500 mb (18000 feet) wind flow and anomalies for February 18

 

It is toward the end of the month that the flow may transition from the West / Northwest flow to a southwest (more wet) flow as the PNA pattern becomes more negative.

pna_cfsv2_32ens_2015020406

 

An examination of what a negative PNA entails is presented in the graphic below:

 

negative PNA

The analysis from the graph above is from the GFS (American Long-term Model), but the European model suggests the same with slightly lower PNA numbers (more negative).  Therefore a slightly colder and wetter pattern may develop (southwest flow).  This pattern also shows up in some of my analog years (similar weather years in the past) that I have been using for this winter.

As recently as the winter of 2012-2013 we recorded a major shift toward the second half of the winter.  Although in no way do I think as a radical shift as that year is coming, even a shift to more average snowfall would seem to be a “shock” as this winter as been so dry to this point.  But late February through mid March has been a period I have been expecting some change to the over all pattern and there are at least some hints to this at the moment.  But emphasis is on no change for the near future and possible change toward the end of the month.

Daryl Ritchison