One of the joys of living on the East Coast – especially this time of year – are back-door cold fronts. They’re prevalent most of the year, but in the spring, when summer-like heat from the south often borders on winter’s lingering grip to our north, they often gather a head of steam (or mist if you will) and come roaring down I-95, resulting in crazy temperature contrasts both in time and by region. Today, a very strong backdoor cold front will begin pushing into the region late this afternoon, arriving in northeastern MD first, accompanied by a stiff east wind and rapidly falling temperatures. We’ll go from the 70s (perhaps low 80s, especially in the southern portions of the region) to 50s – even 40s – after the front comes thru. Tonight will be a total reversal of last night’s summer-like sweat-feast; cold, windy, damp… with rain by morning as the main cold front approaches from the west. Ironically, the air behind the main cold front will actually be warmer than the air behind our back-door cold front (Dam!!)
Our north-Atlantic blocking high is still at it, causing storms to stall over eastern North America and funneling cold air down into the Northeast and Mid-Atlantic. The chart below shows the temperatures and winds at 850 mb (~5,000 ft up), and while much of the west and south has a warm signal, we remained under winter’s lingering firm grip. The forecast chart is valid for Tuesday morning; hard freezes are likely Tuesday and Wednesday. Ugh….
Below is a graph of the Baltimore/BWI season total snow dating back to the late 1800s. Note the recent extremes, with a “boom or bust” tendency.
Today’s GFS-derived (MOS) temperature departure forecast for Friday illustrates the battle going on between the PNA (Pacific-North American pattern) and the NAO (North Atlantic Oscillation). The PNA is in a negative phase, which means we have a southward dip in the jet stream over the west and a ridge of high pressure trying to form downstream over the Southeast.. Meanwhile, the NAO is likewise negative, with a blocking high over the northern Atlantic attempting to force a southward dip in the jet stream over the eastern U.S., in opposition to the PNA’s Southeastern high. The net result is illustrated nicely in the image below, which is the forecast departures from normal for Friday, February 22, 2013.
Here’s a fun little graphic courtesy of the Penn State E-wall The chart below is the total liquid-equivalent precipitation for the upcoming weekend from all of the different short-range ensemble forecast models that were run at 15z (10 am, EST). Each panel represents a different model run, and the color scale – given on the lower right-hand side – is hundredths of inches. We use these to establish 1) what the envelope of uncertainty is; 2) how much agreement there is amongst the models; and 3) which direction the guidance is leaning. Well, this latest set of model data has everything from a blizzard… to nothing. That should help straighten this out!
The National Weather Service’s Hydrometeorological Prediction Service (HPC) overview forecast for Wednesday, Feb 13th is interesting indeed. Could it be?! This will likely change, but for now, there is hope.
A very nice winter-storm analog page put together by the Cooperative Institute for Precipitation Systems · Saint Louis University provides some food for thought for this upcoming storm. While the models are more or less insisting this storm bypasses us, the analogs, based on the 12z (7 am EST) run of the NAM from Thursday, are certainly interesting.
The mean snowfall for the Top 15 analogs, shown below, certainly is tilted toward a snowy event.
I’ve also included a snapshot of all the top analogs below; the date is at the top. The scale can be found on the preceding “mean snowfall” map.
Below is a forecast comparison from Friday’s model runs for next Wednesday morning for the Canadian (Top) and GFS (Bottom). The Canadian has a developing East Coast storm, while the GFS has nothing. Hmmmmm….
A look at the latest Short-Range Ensemble Fcst (SREF) suggests a pretty good shot at an inch of snow tonight. Something to watch for!