Friday, March 16, 2018

Remember the time

7 comments:
"Do you remember the time?"
- Micheal Jackson in the 1991 hit single Remember The Time

5:30 AM ET Fri 3/16 - With the supposed "last storm of the season" earlier this week failing to turn us into believers for one more snow, maybe you're ready to write this winter off, having dealt with enough disappointment thus far. 

That's part of the grand curse of a La Nina March: Cold at the wrong time, rain changing to snow, wind that won't leave. It's like being a senior official in the Executive branch: You don't know what's going to happen next, better check Twitter to see about the weather... or maybe your job. 

In the Mid-Atlantic, we remember the time when:
  • Snowfall occurred during the regular winter season (say, between December 1 and March 15) 
  • March was sometimes cold and windy. but usually got warmer as the month went on.
  • Snow days somehow managed to take place before winter had officially ended.         
But now, when looking at the Day 5-6-7 projections, we don't know whether to laugh or cry.
  • We don't remember a time this season when two of the biggest and most oft-cited weather computer models (the European and the U.S. Global Forecast System) were in general agreement for a potentially-long duration coastal precipitation event. Below is the GFS operational map for 8 AM next Wed 3/21. European shows a Low in almost exactly the same spot off Norfolk VA at nearly the same pressure.  

  • Some remember the last time something like this occurred so late in the season: All the way back in March 1958. We can laugh about the possibility, but you might end up crying if you had to to clear 4 feet of heavy wet snow after winter had already ended! 

(Below: March 1958 storm in southern PA)


- Winter Stormcast Team of Foot's Forecast

Thursday, March 8, 2018

Believer

14 comments:
"You made me a believer..."
 "Believer" by Imagine Dragons in the 2017 album Evolve

Tired of the way things have been this season? Any chance of "real snow" to warm the hearts 
of Powderhounds? Let's just say the pain of this winter may have been worth the wait.

THE CLAIM:

WHAT IS THE PRECEDENT?
  • The pattern we last saw from February to March of 2017 is reoccurring this season. Recall when last year, temperatures over President's weekend ramped up to 75 F under sunny skies?
  • A few weeks later, just as many had written winter off, the mid-Atlantic was clocked by a 2-day snow and ice storm on March 13-14 with January-like temperatures to seal the deal. 
  • Many schools in the Baltimore-DC region were closed 2 days in a row.

WHERE IS THE EVIDENCE?
  • Explanation: Winter 2017-18 has been influenced by the same major climate factor as last season: La Nina. The irregular cooling of the eastern equatorial Pacific in a strange way produces all kinds of stranger things in winter for the U.S. eastern seaboard: Wildly fluctuating conditions, a variety of precipitation types all in the same storm, snow in unusual places and at unusual times of the year.
  • Examples: Christmas snow in Charleston SC? How about the 70 degrees then snow 2 days later in Baltimore, only to climb back to near 80 two days after?! Oh yeah, then we had a historic windstorm, then another snow event. Tired of this pain train? It shows no sign of stopping. 
  • Evaluation: The largely overnight timing of precipitation events this season has exacted a toll on school schedules, not that any students or teachers are complaining. Though some parents are way past done with the back and forth of school being open, then closed, then open again. For now, at least most of us have 4 normal, calm weather days ahead from today to Sun 3/11.
PRELIMINARY EXPECTATIONS
  • Sunday evening 3/11: With weekend temperatures across the region to hold near January-like levels, overnight lows will have dropped back to the 20s several days in a row. A moisture laden system moving from the southern Plains is expected to gain energy from a northern Plains system. By early evening, snow should be moving northward from some type of coastal system developing along the Carolinas. 
  • Monday morning 3/12: The map above is one scenario for 8 AM Monday, with snow possible along the I-95 corridor for the morning commute. However, an old rule about winter storm forecasting will be back on the table -- "If you want snow, DON'T be in the bullseye 5 days out." Why? This allows a couple days for the computer models to resolve toward a more consistent solution -- and depict any westward drift that can occur with a coastal system. Conversely, the chances of the model showing a perfect all-out snowstorm scenario 5 days in the row is very low. Instead, we adhere to what's called the "most probable" outcome.
  • Winter weather graphics from the NOAA Winter Weather desk spell it out: The areas noted in light green currently have at least a 25% probability of 0.25" or more of liquid precipitation falling in some frozen form Sunday night into Monday. That may not seem like much, but with each passing day the probability of that scenario builds if the pattern remains consistent.

REASONING
  • By Sunday evening, we believe several key factors will be in place: A southern system able to interact with energy from the northern jet stream, evening to overnight timing of precipitation, ample moisture, a nearby High pressure system, a projected rain/snow line to setup well east of the major east coast metro areas, and all this coming on the heels of 4 days with sub-32 F overnight lows to chill the ground throughout the mid-Atlantic & mid-South.
  • A 5 day projection may not be enough to make you a believer, considering it is March and time is running out. However one question is clear: Since FF has barely posted anything this whole season, why bother now? Winter is probably over, right? Let's just say it is a case where "good things come to those who wait," because we wouldn't post a long report like this without...believing there was a good reason for it. ;-))
Forecaster Foot and the Winter Stormcast Team