Saturday, April 1, 2017

Certain as the Sun...

No comments:
"Certain as the Sun, rising in the East..."

Sunrise at the Neuschwanstein Castle in Bavaria, Germany

8:00 AM 4/1/17 Storms come. Forecasts go. Seasons change, then we look back on the Winter that was, and wonder amid a tale as old as time, "will next year be different?

While we cannot promise unbelievable skies on a magic carpet ride, it can be said the seasons ahead are revealing early clues about what dreams may come. 

Summary of this report:
  • Lessons learned from the March 2017 failed Big Kahuna, and what it tells us about storm forecasting in La Nina Winters.
  • Growing potential of El Nino returning by this summer, with implications for winter storm forecasting in Winter 2017-18. 

"Something there, that wasn't there before." 

Part 1 - Lessons Learned from March 2017 Big Kahuna

When evaluating present day patterns coming off last month's semi-failed Big Kahuna, we think Mrs. Potts best captures the theme with that one line.



A) What we saw in the data:
  • 1) Wavering lines. Multi-day trend in the models showing the rain/snow line from this storm would waver back and forth

  • 2) Big snow, then no. General agreement in the models of significant snow for most areas, until about 24 hours before, when the rain/snow line wavering scenario returned.  
  • 3) Late stage changes in the short range. Late Monday night into early Tuesday, a few hours before the infamous sleet beast exploded across the region, the NOAA High Resolution Rapid Refresh model (the HRRR). This model has a consistent record of accuracy, and in past storms, failure to consider the short range data had major impact on forecast accuracy. Around 10:30 PM, this model began showing a more defined westward movement of sleet than had been previously depicted. 
  • As shown above, the HRRR projected sleet initially staying south of the PA line, and lasting 3-6 hours. By 3 AM Tuesday, the situation had changed drastically, with sleet forecast to continue through 10 AM and extend well north of I-70 into southern & southeast PA. In some places, sleet began 2 hours earlier than forecast and before radar returns had even identified a change in precipitation type. By the time many readers awoke, expectations for 6-12" had been dashed by the window pinging of unwelcome sleet.
B) What we should have seen: Climate indicators and past storms as prologue. Having studied the intricacies of winters influenced by El Nino & La Nina, and knowing the patterns that usually play out when a strong signal exists from either phenomenon, we should have seen the evidence refuting a large snowfall accumulation in the southern Mid-Atlantic (south of the PA line) from this data.
  • 1) Are big Mid-Atlantic snowstorms likely during moderate La Nina years? Answer: Not really, backed by analysis of 50+ years of Nino/Nina data correlated with winter storm outcomes in the Mid-Atlantic in those years. An excellent overview of the data is published at this link to a study by the Sterling VA NWS Office.
  • 2) Have major snow forecast busts occurred in La Nina winters? Yes. 
March 6, 2013 was the most significant bust in Foot's Forecast team history, as calls for 6-8" of snow across the region by us, the NWS and most other media outlets resulted in virtually nothing. 
March 5, 2001, though predating FF, was perhaps the single greatest storm forecast bust in the modern digital era. Official and private forecasters alike called for up to 24-36" from Washington to Boston. The result: Schools and governments closed a day early to prepare, then the storm shifted east and the metro areas, including Baltimore and Philly received 1-3" of slushy wet snow.  
What we will do different next time? 
  • We will simply ask the question: Did a similar storm occur in a previous winter under conditions that resemble present day? If not, why not and what happened.
Part 2 - Next Winter: Early signs & signals

  • Analysis in progress, article coming soon. Until then, enjoy the sunrise and the welcome arrival of April heralding our true change into the Spring season.
Sunrise over Stonehenge







Tuesday, March 14, 2017

Is That It?

1 comment:
Is there more, or is this it?
  • INTERMITTENT SNOW SQUALLS into the overnight hours, with light accumulation up to 1/2" possible overnight from central PA to northern MD counties.
  • SQUALLS likely to return mid-morning Wed into afternoon hours, could produce a coating on untreated roads and sidewalks.
  • SIGNIFICANT LATE SEASON COLD AIR (YES, MORE) is set to arrive early next week into next weekend, keeping much of the month's  temperatures below normal. 
  • THREE SYSTEMS TO WATCH next 2 weeks are this Saturday, next Tuesday and the 25th-26th for potential winter weather mischief. See below for 8-14 Day Long Range ideas.

6-10 Day Temperature Outloook: 
NOAA Climate Prediction Center

                                                        

What comes after the Kahuna?

57 comments:
What comes after the Kahuna?
  • INTERMITTENT SNOW SQUALLS into the overnight hours, with light accumulation up to 1/2" possible overnight from central PA to northern MD counties.
  • SQUALLS likely to return mid-morning Wed into afternoon hours, could produce a coating on untreated roads and sidewalks.
  • NEW PULSES OF SIGNIFICANT LATE SEASON COLD AIR are set to arrive early next week into next weekend, keeping much of the month's  temperatures below normal. 
  • THREE SYSTEMS TO WATCH next 2 weeks are this Saturday, next Tuesday and the 25th-26th.

11:00 AM ET 3/14 - PRECIP BELOW PA/MD LINE ENDING BY 2 PM, HEAVY SNOW IN PA CONTINUING THROUGH AFTERNOON. Let us know your precip and road conditions, and here is what we see for the 24 hours ahead:
  • OVERNIGHT.. what happened? A significant push of warm air from the Atlantic worked into the region in the early morning hours, changing snow to sleet and then freezing rain for many areas south of I-70. This cut way into earlier expected snow totals. Computer models and forecasters alike did not identify the potential intensity of this warm air push until after it was showing up on the ground - and hadn't even been showing on the radar. Hence, the "Look Out The Window" model.
  • CURRENTLY, as the Low begins pulling north, cold air is moving into the region on the west side, and will reduce the duration of sleet/freezing rain. However, next 2-3 hours may see intense precipitation rates as 1/2" of liquid or more is working north and west from the Low center.
  • MORNING & AFTERNOON: By 9 AM, we expect all precip to change back over to snow in most areas north of Route 50, with areas south of that over to snow between 9-10 AM. Another 1-2" through 12 PM on top of icy roads and sidewalks will make for treacherous and dangerous travel.
  • OVERNIGHT INTO WEDNESDAY: Temperatures plunge into the teens or low 20s, refreezing over hard any standing water or snow, creating widespread road ice issues for the PM commute and Wed AM as well.
NWS HOURLY FROM TIMONIUM, MD to represent how rest of the day will progress.



Monday, March 13, 2017

Something Wicked This Way Comes

61 comments:
Big Kahuna To Blizzard The Northeast


  • BLIZZARD WARNINGS EXPANDED (RED) TO INCLUDE PHILADELPHIA METRO, EASTERN PA & NORTHERN NEW JERSEY FOR 18-24" 
  • WINTER STORM WARNINGS (PINK) IN EFFECT THIS EVENING THROUGH TUESDAY AFTERNOON. Check your local NWS office for latest official details on current statements. Click Advisory map -->
  • HIGH IMPACT EVENT with multi-hazards. Please refer below to Storm Information Graphic and NOAA Winter Weather Safety graphics.
  • POST-STORM: Sub 20F temps & widespread refreezing of snow melt each morning. 


Current Regional Radar 



National Radar



"Something Wicked This Way Comes..."
-Macbeth, Act 4, Scene 1

UPDATE FROM 3:00 PM SUN 3/12

Friday, March 10, 2017

Seriously?

27 comments:
Big Kahuna 2 years in a row? 

11:00 AM ET SAT 3/11 UPDATE
  • No major changes to current storm forecast ideas noted below. Some computer models have shifted tracks a distance east or west, as is expected and customary in the days prior to a major event. 
  • Confidence remains high for accumulating snow across the region, however finer details of how much falls in which locations is not yet fully established due to changes in liquid amounts.
  • Cold air to remain in place prior to and after the event, enhancing impact to roads in all areas regardless of starting or ending precipitation type. 


If computer models stay on target with current ideas, many of us may 
have some heavy lifting to do soon. If not, this picture can stay in your memories.
  • SIGNIFICANT WINTER STORM MAY AFFECT PORTIONS OF MID-ATLANTIC REGION EAST OF I-81 TO WASHINGTON-BALTIMORE-PHILADELPHIA METRO REGIONS MONDAY NIGHT INTO WEDNESDAY MORNING.
  • LIQUID EQUIVALENTS OF 1.0-2.0 INCHES MAY PRODUCE INTENSE SNOWFALL RATES EARLY TUESDAY MORNING.
  • SNOW AMOUNTS OF 5" OR MORE MAY BE COMMON THROUGHOUT THE REGION, WITH HIGHER AMOUNTS IF THE STORM SHIFTS WEST.
  • TEMPERATURES IN TEENS OVERNIGHT INTO WEDNESDAY AND THURSDAY, IMPACTING SCHOOLS AND COMMUTERS DUE TO EXTENSIVE REFREEZING OF SNOW MELT RUNOFF.

SURFACE MAP: 8 AM TUESDAY MORNING: 
Looks like a Big Kahuna to us.


LATEST STORM SCENARIOS

SCENARIO A - 60%: Big Kahuna significant accumulating snow event across the Mid-Atlantic region with up to 5" common by Tuesday morning.

SCENARIO B - 20%: Some But Not A Lot due to a westward shift in track that moves axis of heaviest snow into morthern & western MD and southern to central PA, leaving 95 corridor with 5" or less.

SCENARIO C - 20%: Big KaNONa with a last minute pull to the East, bringing heaviest snow to coastal Eastern shore and leaving 95 corridor and interior areas with flurries. 


12:00 PM THU 3/9 UPDATE BELOW


Think of it as an early April fools.
  • CONFIDENCE GROWING FOR A SIGNIFICANT LATE WINTER STORM TO AFFECT THE MID-ATLANTIC & NORTHEAST REGIONS MONDAY NIGHT INTO WEDNESDAY.
  • NEAR-BLIZZARD CONDITIONS POSSIBLE ALONG COASTAL & BAY AREAS.
  • OVER 1.0" OF LIQUID SUGGESTS HEAVY WET SNOW A PROBABLE OUTCOME, ACCUMULATIONS OF 5" OR MORE LIKELY FOR AREAS WEST OF I-95.
  • AM TEMPS 15-20 F WED-FRI TO BRING EXTENSIVE REFREEZING & ROAD ICE.
  • IF NOT HAPPY ABOUT THIS, NEITHER IS THE SNOWCAT. 
5:00 AM ET Fri 3/10  - Now that the word is getting around you will have snow next week, no doubt there will be lots of questions for details. For Winter's last hurrah, we invite you to join the Insiders for direct access to our forecasts via app, notifications and text alerts. 
FANTASTIC SNOW IS COMING BACK, AND WE KNOW WHERE TO FIND IT. Visit the Insiders portal for details, and be a true Powderhound for the grand finale you've been waiting for all season!

How much? Let's just say...more than you've seen in March for a long, long time. Many areas in the Mid-Atlantic are likely to see 5 inches or more, if the most probably scenario plays out as expected. Below is a short version in 3 steps to how your snow dreams may come true next week in the Northeast U.S., especially if you are a teacher, student or Powderhound-at-large.

Remember last time the European model locked onto to a major storm solution 5 days out?
You guessed it, January 2016. Here's the map for 8 AM Tuesday 3/14 (Known as Pi Day)

  • STEP 1: FRIDAY.  A fast-moving clipper on Friday unlocks the gates to Canada, and much colder air. What you get: The chance to watch wet snow fall in the daytime from your office, home or classroom window, and not stick much.
  • STEP 2: SATURDAY-SUNDAY. Truly Arctic air rushes in behind that southern system we discussed in the previous "You may fire when ready" article. What you get: Highs in the 30s, lows in the teens. That's serious cold for March. 
  • STEP 3: MONDAY-TUESDAY. Now the fun part. Since the southern system this weekend would have been pushed SOUTH, you thought that means the Mid-Atlantic escapes, right? In reality, leftovers from that system interact with Gulf and Atlantic moisture, which starts riding back north. By Monday, a fast moving upper level disturbance is expected to "activate" that moisture and develop it into a surface Low near the Carolinas. What you get: A potentially significant coastal winter storm with some similarities to the December 19, 2009 storm. A multi-day event that would "interfere" with next week with accumulating snow starting Monday night.

Tuesday, March 7, 2017

You may fire when ready

2 comments:
"You may fire when ready."
- Grand Moff Tarkin, Star Wars

  • ARRIVAL OF MUCH COLDER AIR LATE THIS WEEK TO PRODUCE FAVORABLE CONDITIONS FOR AN INTERIOR & COASTAL SYSTEM WITH ACCUMULATING SNOW BY THE WEEKEND FOR THE MID-ATLANTIC.
  • POSITIONING OF A HIGH IN SOUTHEAST CANADA AND A LOW IN THE TENNESSEE VALLEY POINTS TO A CLASSIC "COLD AIR DAMMING" SCENARIO BY SUNDAY MORNING.
  • DESPITE MILD CONDITIONS WED-THU, COLD AIR THU-SAT, OVERNIGHT ONSET AND AMPLE MOISTURE INCREASE PROBABILITY OF SNOW OVER RAIN.  

4:30 AM 3/7 - Although Princess Leia's famous opening line of "...only you could be so bold" in Star Wars Episode IV was directed at Darth Vader, the brashness of the situation is similar. Known for unorthodox, brash and persecuting methods -- Vader and Governor Tarkin are the analogy we select to describe this upcoming potential winter weather assault.

Friday, February 24, 2017

She drives me crazy

3 comments:
"She Drives Me Crazy." - Part 2
-Fine Young Cannibals, 1989
  • La Nina: The main source of your weather frustration due to inconsistency of patterns this season. Why? Lack of a strong signal from multiple factors (Weak polar air, limited moisture transport from oceans, reduced snow cover) produces the type of erratic outcomes we have seen in 2016-17.
  • Are we done? Probably not. Potential is rising for a resurgent period of significantly colder air in the eastern U.S. from March 3 through 15. Several clippers in this period would have favorable conditions to produce snowfall, including ample moisture and overnight freezing temperatures enabling accumulation.
  • Hope for the future: NOAA Climate models are pointing to rising  chance of a weak El Nino by this coming Fall, with some similarities to the 2002-03 episode that produced a snowy winter in the East. Until then, the temperature trends are one reason why the current La Nina pattern drives us crazy -- see below for the flip flop that's coming in the next 2 weeks.
TEMPERATURE TRENDS THROUGH FRI 3/3
(Red is above normal, Blue is below normal)


TEMPERATURE TRENDS THROUGH FRI 3/10