In today’s weather discussion we began by recapping the historic cold outbreak over much of the Eastern half of the United States during February. Baltimore Washington International Airport (BWI) for February had a monthly average of 25.3 degrees F and a departure from average of -10.5 degrees F. This makes last month the second coldest February and fifth coldest month ever at BWI, with records going back to 1873. Other notable records broken were Boston had the second coldest month and snowiest month on record and New York City had the third coldest February. Much of this record cold can be traced back to a large ridge over the Western third of the United States, which forced a trough to form over the Eastern US. The ridge over the West coast of the US, has persisted for most of February and was classified as a ridiculously resilient ridge (RRR). This pattern of a large ridge over the West and trough in East is similar to last winter, but the trough this winter was more over the New England than the Great Lake regions.
www4.ncsu.edu/~nwsfo/storage/training/jets/anafront.html
Then we discussed the possibility of wintry precipitation associated with an anafront moving through the Mid-Atlantic region Wednesday Night into Thursday. An anafront is a cold front with precipitation that falls after the front passes through a region, compared to a regular cold front where there is no precipitation after it moves through. The cold front that is moving through our region on Wednesday night is a prime candidate to form into an anafront because of the slow movement of the front. The slow speed of the cold front allows warm air to be advected over the cold airmass behind the cold front. This will cause there to be vertical lift and precipitation after the front moves through.
We looked at the 12z GFS, NAM, and European models to see how the evolution of Thursday’s transition from rain to snow could occur. The NAM was the warmest of the of the three models and took the longest for Central Maryland to turn over to snow, around 8AM Thursday morning. The GFS was quicker with changing over to snow and has the highest snowfall for the region. The European model was in the middle between the NAM and the GFS in terms of when the rain will transition over to snow. While there is still some uncertainty when the rain will switch over to snow, most of the models agree that a possible high impact snow storm could affect the region Thursday.
12Z GFS output from wxbell.com
Finally, we looked at the global model predictions for various teleconnections, the AO, NAO, and EPO, over the next 10 to 15 day period. All of the models agreed that the AO will rise to very positive territory over the next 7 to 10 days and the NAO will also rise during this period, which is unfavorable for East Coast snow. The ridge over the West for most of February was associated with a negative EPO and the models suggest that the EPO could rise to neutral or possibly positive territory. This would indicate that the ridge could collapse and allow more seasonal temperatures to return to the Eastern US. Does that mean Thursday’s snow storm is Winters’ last hurrah?