Weather Briefing: Friday, January 19th, 2018

HIGHLIGHTS: A warm-up for the weekend and a wet start to next week

 Climate Prediction Center measurement of the PNA Index with 10 day Forecast. The black line in the middle separates positive values from negative values.

Climate Prediction Center measurement of the PNA Index with 10 day Forecast. The black line in the middle separates positive values from negative values.

After this past week's winter weather and snow, even the most fervent snow-lovers would probably agree that we need a little time to thaw out from the wintry start that we've had to 2018. Thankfully, it finally appears that a significant pattern change is occurring, one that will give us predominantly warmer than normal temperatures for at least the next 7-10 days. For a majority of the winter so far, ridging has occurred over the Western United States and Eastern Pacific Ocean, while troughs have been predominantly located over the central and eastern parts of the United States. One way that this has been observed is through an index called the Pacific North American Oscillation (PNA) Index. When the PNA Index is positive, we typically see colder than normal conditions here in North Carolina. On the other hand, when the PNA Index is negative, we typically see warmer than normal conditions here in North Carolina. Since December 1st, the PNA Index has been positive for approximately 90% of the time. Luckily, the PNA Index (according to model data) is about to shift to a prolonged negative period for the first time since the middle of November.

 ECMWF (European) Model Forecasted 500-mb Heights (lines) and Anomaly (shading) for Sunday, 21 January 2018 0000 UTC (Saturday, 7 p.m. EST). This map highlights the pattern shift where warmth will be concentrated in the east and colder temperatures will be concentrated in the west.

ECMWF (European) Model Forecasted 500-mb Heights (lines) and Anomaly (shading) for Sunday, 21 January 2018 0000 UTC (Saturday, 7 p.m. EST). This map highlights the pattern shift where warmth will be concentrated in the east and colder temperatures will be concentrated in the west.

 ECMWF Model Forecasted Precipitation for 0000 UTC Tuesday, 23 January with Map Features Analyzed by hand. This map illustrates the setup for Monday night into Tuesday morning.

ECMWF Model Forecasted Precipitation for 0000 UTC Tuesday, 23 January with Map Features Analyzed by hand. This map illustrates the setup for Monday night into Tuesday morning.

This shift is also reflected in the model-forecasted upper-level flow patterns for the weekend and into next week. As we head through the weekend, a ridge will begin to build over the Eastern United States, as temperatures will climb into the 50s and 60s for high temperatures on Saturday and Sunday. An upper-level trough and the surface disturbance associated with it will swing through the area on Monday and Tuesday, creating somewhat of a break in the warming trend. However, this trend looks to continue as we head into the latter half of next week and into the weekend, as models are suggesting that another, possibly more intense ridge may develop for the 26th-28th. The aforementioned surface disturbance predicted to move through our area Monday evening into the early hours of Tuesday morning will bring precipitation that will fall exclusively as rain, the amounts of which are disagreed upon by the models. The European Model wants to paint a wetter picture with most areas seeing 1/2" or more, while the GFS Model tends to keep precipitation amounts closer to 1/4". Regardless, it does look like some part of Monday or Tuesday will be wet. After the rain passes through, it looks like the remainder of next week should be quite calm weather-wise, with predominantly sunny skies and relatively mild temperatures.

 ECMWF Model Forecasted Precipitation amounts through 0000 UTC Wednesday, 24 January 2018. 

ECMWF Model Forecasted Precipitation amounts through 0000 UTC Wednesday, 24 January 2018. 

 GFS Model Forecasted Precipitation amounts through 0000 UTC Wednesday, 24 January 2018. 

GFS Model Forecasted Precipitation amounts through 0000 UTC Wednesday, 24 January 2018. 

 ECMWF Model Forecasted 500-mb Heights (lines) and Anomaly (shading) for 1200 UTC Saturday, 27 January 2018. This map illustrates how another ridge looks likely to build over the Eastern United States late next week.

ECMWF Model Forecasted 500-mb Heights (lines) and Anomaly (shading) for 1200 UTC Saturday, 27 January 2018. This map illustrates how another ridge looks likely to build over the Eastern United States late next week.

Have a great Friday!

Chase Scott Graham