Foot's Forecast | Weather Intelligence

SORRY MARYLAND:

WHY SATURDAY'S SNOW STAYS IN PA

UPDATE: SAT JAN 10 - 6:45 AM. I see that the snow shield extends across most of Pennsylvania this morning, leaving just about all of Maryland high and dry for now. My forecast below remains as it was: even if the bulk of precip arrives tonight, accumulations will be limited to a light coating from northern MD to the WV panhandle. From central MD south to DC, today's rain may end as a wintery mix this evening. A note to weekend readers: I will be reorganizing the current post and sidebar links to display relevant storm tracking and impact information more efficiently. I so wish I could move comments to top of the post, any HTML experts out there willing to lend a hand?

SUMMARY: FRI JAN 9 - 1:45 PM. I suspect that Saturday's snow may end up farther north than is currently projected by Accuweather and the NWS. Northern Maryland may get just enough to cover the grass and look nice, but this is not a Winter Storm Warning type event for us. Central Maryland will get a smattering of the precip-du-jour these days, any guesses? How about something different, like "wintery mix" which is a tidy little way of saying "NO SNOW FOR YOU."

My canary in the coalmine is the North Atlantic Oscillation. It is just one of many climate teleconnections that meteorologists and many others use to monitor changes in the global distribution and change in air masses. When the NAO Index is trending negative, pressure differences between the Icelandic (Subpolar) and Azores (Subtropical) High permit the Subpolar Low to be in closer proximity to North America. This leads to colder, stormy conditions in the Eastern US. A positive trend can result in several outcomes, including the "backing off" of dominant cold air, and if the drift to neutral occurs "gently" enough, an approaching surface low pressure system will shift ever so slightly north as it moves east.

My favorite example was the President's Day Storm of 2003 (known as PD II), because we had a negative NAO trending neutral with a huge swath of moisture running into a giant dome of cold high pressure. Because the NAO trended so slowly, it actually blocked the southern system from escaping harmlessly into the Atlantic, and the incoming moisture arrived faster than the cold air could leave. The pressure gradient between the two intensified the cold and snowfall. Perfect setup, and the rest is history. While Saturday will be no PDII, folks along the PA border and northern MD should not get too excited about bigtime snow from this. Blame it on the NAO.

COLDEST DAYS IN 10 YEARS?

(Note 1: Scroll down to see why Saturday's snow stays in PA)

(Note 2: Scroll waaay down to find the comments link, sorry)

SUMMARY: FRI JAN 9 - 6:45 AM. This is a Happy Friday to celebrate for several reasons:

1) It is generally the date throughout the Mid-Atlantic where SUNRISE finally joins it's late day sibling in the long journey back to summer. If you've been feeling, like basically UGH all this week, perhaps it is because sunrise has been frozen at 7:26 since the 1st. After today, light is added to the clock at both start and end of day, to the tune of 2 minutes a day or more. Just think, MSA's and HSA's will be here be in a flash, how exciting! ;-)

2) Today's seasonal temperatures in the upper 30's will be the last day of it's kind for some time. We are staring into the abyss of an Arctic outbreak that by Wednesday will keep temperatures at least 10 degrees below normal (read, mid-to-upper 20's) for 10 or more days, sprinkled with super-frigid days nearly 20 below normal (upper teens, lows around zero.) A map of the source region for this cold will be posted shortly, but for now, shiver at the prospect some of this air is producing daytime highs around -50 F (if you call that a "high") and there's even colder stuff INSIDE THAT.

3) This cold blast WILL be accompanied by several promising opportunities for accumulating snow between the 10th and 25th. In fact, climatological data uncovered by other weather watchers has yielded some very giddy-like results: In 7 of the past 8 similar cold periods since 1960, major snow events occured in the Baltimore-Washington area either in the middle of the outbreak, or towards the end. Those analog years include: 1961 (anyone remember the Kennedy Inauguration?), 1977, 1983, 1985, 1994, 2000, 2003. All these years (1978 was the outlier), featured memorable snow or ice storms on the east coast that followed historic cold. To all the powderhounds out there, help is on the way!

4) The Winter Storm Watches/Warnings spread across ALL OF PENNSYLVANIA today, and resulting light snow Saturday are the opening act in what will blanket a large part of the country with "white in the winter night." Once a snowpack develops, it tends to enhance arriving High pressure systems (their core air pressure remains steady or declines slower ), and in turn helps to distribute cold, dry air over a larger area.

HPC: Nature's Icebox Hangs Wide Open
from the Hydrometeorological Prediction Center's 1/7 Extended Forecast

THU JAN 8 - 9:45 AM. I discovered this map and related analysis posted by a meterologist on the Eastern US Weather Discussion site. Both the European and GFS computer models are pointing towards what might be the biggest Arctic outbreak in 10 years. Need some evidence of what's coming? This is a snippet from the 1/8 forecast discussion in Dallas/Fort Worth:

"ALL EXTENDED MODELS SHOW STRONG AMPLIFICATION WITH RIDGING INTO THE GULF OF ALASKA AND TREMENDOUS NORTH-SOUTH POLAR JET EAST OF THE ROCKIES. THE AMPLITUDE WILL EXCEED 40 DEGREES OF LATITUDE...USHERING BITTER ARCTIC AIR INTO THE CONUS. MCGRATH AK HAS AN AVERAGE HIGH TEMP OF -33.6F SO FAR THIS MONTH. NORTHWAY AK WAS ANCHORED AT -60F MUCH OF THE DAY TODAY. SOME SITES IN EASTERN INTERIOR ALASKA AND ADJACENT YUKON TERRITORY REMAINED BELOW -50F THE PAST FEW DAYS."

The first salvos of this big chill should arrive in the Mid-Atlantic by next Wednesday 1/14. Interspersed with clippers to lay down snowcover, and followed by reinforcing cold Highs, this potentially historic outbreak may continue until January 25. The core of cold looks to be in the 1/20-23 time frame, with overall temperatures across the Mid-Atlantic approximately 15 to 20 degrees below normal. (provided there is no snowpack to enhance radiational cooling) For a place like downtown Baltimore, this could mean several days of highs not breaking 20, and overnight lows easily in the single digits. Those of you in the exurbs of northern Maryland, southern Pennsylvania, the WV panhandle and similar areas could see lows well below zero for several days, and that's not counting wind chill. The source region of this Arctic air has been bottled up in Alaska for some time, and climate watchers have known it was going to make a push south once atmospheric dynamics properly aligned.

In fact, the "Pineapple Express" (as shown by the water vapor loop), causing an historic heavy rain and flood event in the Pacific Northwest will help set the upper level stage for next week. A change in the jet stream flow will permit Arctic air to ride out of the Canadian rockies southeast and unload bitter cold into the eastern half of the country by this time next week. Before the weekend, I will post some thoughts on basic preparation for homeowners...unless you'd rather celebrate "broken pipe season" instead watching the Inauguration!

FOR TEACHERS: Curriculum alignment basis for incorporating this information in a lesson, from the Maryland VSC, Goal 2 - Concepts of Earth/Space Science (links in left sidebar)

INDICATOR 2.3.1 The student will describe how energy and matter transfer affect Earth systems.

Assessment limits:

*Atmospheric circulation (heat transfer systems – pressure gradients, general global circulation, Coriolis effect)

INDICATOR 2.3.2 The student will explain how global conditions are affected when natural and human-induced change alter the transfer of energy and matter.

Assessment limits:

*Ocean-atmosphere-land interactions (changes, continental movement, El Niño, La Niña)
*Cloud cover (amount, type, albedo)
*Climate type and distribution (temperature and precipitation)