Sunday, March 18, 2018

GOT THIS FEELIN'

3 comments:
"I got this feelin' inside my bones..."


A PERSISTENTLY COLD PATTERN INTO NEXT WEEK WILL CREATE MULTIPLE WINTRY PRECIPITATION EVENTS THROUGHOUT THE MID-ATLANTIC. 

IT MAY BEGIN FEELING LIKE A SEQUEL TO BILL MURRAY'S GROUNDHOG DAY, WHEN YOU CONSIDER THIS FORECAST:


THE QUICK SUMMARY
  • MON-TUE: RAIN & SNOW MONDAY EVENING CHANGES TO ALL SNOW OVERNIGHT, WITH 2-4" REGION-WIDE BY TUE AM IMPACTING THE COMMUTE.
  • WED-THU: SECOND COASTAL LOW TO FORM, ADDITIONAL SNOW POSSIBLE & OVERNIGHT REFREEZING MAY IMPACT AM COMMUTES INTO THU. 
  • FRI-SAT: JANUARY-LIKE TEMPERATURES PERSIST INTO THE WEEKEND, WITH A  NEW CLIPPER & COASTAL THREAT FOR SATURDAY 3/24.

7:45 AM 3/18/18 - Just when you thought winter's luck had run out, that feeling starts creeping up on you and it makes us think maybe there is one more chance: 
  • NWS Sterling VA "Model guidance is agreeing more and more each run that we are anticipating a winter storm to some degree of magnitude."
  • NOAA Weather Prediction Center: "CURRENT DAY 2 WPC PROBABILITIES SHOW THE GREATEST CHANCE FOR SNOWFALL ACCUMULATIONS TO EXCEED 4-INCHES CENTERED ALONG THE PENNSYLVANIA / MARYLAND BORDER."

WHAT ARE THE PROJECTIONS & TIMING?

European and GFS models both show a series of coastal low pressures developing in different arrangements but each working in tandem with a High in southern Canada to introduce 32 F and below temps Tue AM and Wed AM.
  • MON NIGHT: Overnight onset & changeover indicates snow will be able to accumulate in areas north & west of the major cities, especially north of I-695, north of I-70 and west of I-270. 
  • TUE MORNING: Areas in Baltimore metro that are west of I-95 but east of I-83 may take the longest to changeover, perhaps not until just before daybreak.
  • WED MORNING: A lull in precip Tuesday night will allow colder air to filter south behind coastal # 1, reinforcing a sub-freezing surface and strengthening the potential for coastal # 2 to develop accumulating snow once again.

HOW MUCH & WHERE ?
  • Preliminary projections from the Sterling VA NWS provide two glimpses of possible snowfall. 
  • The "1 in 10 chance" map is secretly conveying to you the notion that various different runs of the European and GFS are showing significantly higher snowfall, upwards of 8-12" for the DC-Baltimore-Philly corridor. 
  • However it is too far out in time to truly nail down that potential with any certainty.




PROBABILITIES & BUST POTENTIAL?

There's always bust potential in every storm. Given this is March and surfaces are warmer, daylight is longer and cold is harder to come by, coastal Lows- or any kind of Low, has a lot to overcome for there to be actual accumulating snow on the ground. So we break down the probabilities like this - for 7 AM Tuesday morning:
  • 50% chance of at least 1" in all areas north of Route 100 in Howard County.
  • 40% chance of 2-4" all areas north & west of I-95 & north of 495.
  • 10% chance of 4" or more (all the way up to the 8-12"+ shown in some models)
Yes, we know it's March, but this time with a cold high in Canada, overnight timing and northeast winds, we feel there's enough good soul in our feet to overcome that sunshine in the pocket and deliver on the dream for one good snow.


If that's true, by Tuesday morning some of you will have nothing left to do 
but just dance, dance, dance. The rest of us who have to move in it, 
well you already know...so just imagine (another messy commute).


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