Are the snow-maker weather systems influenced by the fall line?
"This cold-to-warm transition zone is further increased by the presence
of the Appalachian Mountains, which are found to the west of the I-95
corridor. This elevation increase starts at the fall line, the
geological boundary between the low-level coastal plains and the
foothills of the Piedmont.
"The fall line is the historical edge of this
range mountains and is the point at which the elevation of the land
starts increasing. In the short distance between Washington National
Airport and Washington Dulles Airport, both near Washington DC, the
elevation increases over 300 feet (90 meters)"
"The new results from the Arctic show ... larger supercooled water droplets, classified as drizzle, play a much more important role in producing secondary ice particles than commonly thought.
" "When an ice particle hits one of those drizzle drops, it triggers freezing, which first forms a solid ice shell around the drop," explained Fan Yang, a co-author on the paper. "Then, as the freezing moves inward, the pressure starts to build because water expands as it freezes. That pressure causes the drizzle drop to shatter, generating more ice particles."
"... drizzle freezing fragmentation can enhance ice particle concentrations in clouds by 10 to 100 times -- and even 1,000 on occasion!"
"The purpose of this article is to summarize our current understanding about this unusual wintertime event.
"This article describes where and when thundersnow happens, the ingredients needed to make thundersnow, and new efforts at understanding and forecasting the occurrence of thundersnow."
Six forecast stations in the northeast portion of the forecast area set new daily snowfall records on the first day of Snow Storm #1. Two daily records had stood for over 100 years.
Mid-Atlantic winter wx enthusiasts couldn't ask for better synoptics than the current long wave flow regime.
- High amplitude ridge to the West.
- Full latitude trof in the East.
- Sub-tropical jet in a split flow
- Split stratospheric polar vortex with the stronger daughter vortice over eastern North America to boot.
So WTF?
If times be so good ... then bro ... where's my fookin' snow?
Us snow crows nesting here in the eastern half of the mid-Atlantic will most often get our winter wx fix when ...
1) LOW pressure spawns over the Gulf of Mexico & proceeds to crawl slowly up the east coast and
2) A strong Arctic HIGH (1040-ish mb; 30.70" Hg) parks herself over Maine and
3) The wavelength between the Ridge-West / Trof-East pattern contracts i.e., becomes shorter. As the wavelength shortens ... storms spin-up (intensify) the same way ice skaters spin-up when when they draw their arms inward (see Conservation of Angular Momentum)
Wicked winter wx 'round here has always been a tricky combination of having a deep layer of Arctic / Polar air in place ... ready to interact with moisture surging from the south.
The current long wave flow regime is certainly delivering in spades with the cold air component; however ... it's coming on too strong ... in effect suppressing moisture from coming north.
FWIW ... the world-wide federation of numerical weather prediction (NWP) models have been tilting toward an adjustment to the long wave pattern in mid-range; a shuffling of the deck so to speak (more like re-setting the tumblers in a one-armed bandit).
Climatologically for snow crows ... FEB is our time 'round here ... especially the period either side of mid-month. Whether the coming pattern change produces the weather we be waiting for is anyone's guess.
Even though long-range NWP offers us nothing more than possible outcomes ... outcomes more often fantasy than fact ... it's one of those j'ne sais WTF reasons why we all be Weather Weenies.
Minor snow event over extreme northern portions of the forecast area today forced by a lifting 5H LOW centered @12z over SE Canada and 2ndry SFC LOW occluding INVOF the Gulf of ME.
Forecast stations observing their MAX monthly snowfall during Winter '17 / '18 in ...
DEC - 0
JAN - 7 (CAR ... PVD ... ACY ... SBY ... RIC ... ORF ... RDU)
FEB - 0
MAR - 18 (all the rest)
Leaving aside for the moment the fact FEB has 28 days and all other snow-season months have 31 ... 72% of our forecast stations observed their highest monthly snowfall total in MAR -- yes MAR -- this season.
Climo finds most of the contest/s forecast stations (14) observe their MAX monthly snowfall in JAN. MAX monthly snowfall happens in FEB at 10 of the remaining 11 stations with only BDL having its greatest monthly climo snowfall in DEC.
No station/s monthly snowfall climo reached its maxim in MAR which makes the winter '17 / '18 all the more remarkable.
OCT-17's snow advance index is negative.
Snow Crow suicide watch now in effect.
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AER reports a statistically significant correlation between their 'winter severity index' and how quickly Eurasian snow cover advances during OCT.
They define the 'winter severity index' by the state of the North Atlantic Oscillation / Arctic Oscillation (N/AO) and interpret it as an indicator of 'high latitude' blocking potential during D-J-F.
More blocking.
More winter.
More better.
Here's the model ...
"When snow cover advances rapidly (slowly) across Eurasia in October, this is an indication that the upcoming winter will be more severe (milder) for the Eastern US [sic], Europe and East Asia.
Study period seems surprisingly short seeing how contiguous monthly Eurasian snow cover data begins in 1970. How well does the SAI correlate with the N/AO index prior to 1988?
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Snow Advance Index (SAI) backgrounder from AER here.
Earlier Eurasia snow cover posts here.
Cohen projecting above normal Eurasia snow cover for OCT ahead of an expected weak La Nina winter (D-J-F).
Nine previous weak La Nina winters ... including the famed 1995 - 1996 season ... have been observed during the Eurasia snow cover period of record (1967 - 2016). Only two NEWxSFC forecast stations -- BGM and ALB -- have a statistically significant correlation between season-total snowfall and above normal Eurasia snow cover.
The season/s third contest-worthy snow storm out-performed not only the suite of numerical models but the professional meteorologists responsible for issuing the official forecasts.
As of Wednesday afternoon (04-JAN) ... the progs and public forecasts for the Friday/Saturday award-winning event (06-JAN thru 07-JAN) all indicated a low probability (40%) for a meager 4" snowfall across a narrow slice of SE VA and NE NC.
When all was said and done ... heavy snowfall was observed from SE VA (up to 12") ... the Delmarva (up to 13") ... LI (up to 7") ... and Cape Cod (where near-blizzard conditions were reported and up to 16"). Eleven contest stations measured at least 4".
Four new daily records:
PVD 10.7"
ISP 9.7"
RIC 7"
SBY 9"
SLRs where at least 4" of snow was observed ranged between ~12:1 and ~25:1
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Some have suggested a 'Call for Forecasts' be issued whenever a potential snow storm looms.
That way ... a contest-worthy storm would seldom be missed.
Sounds like a good idea and it would be if there wasn't four hours of work involved when issuing the call.
Hundreds of email 'invitations' have to been sent (50 at a time ... 30' apart so as not to be flagged as spam or blocked by my ISP).
The contest/s web site has to be updated. The contest/s web log has to be updated. The contest/s Facebook page has to be updated.
--- Then it becomes a judgment call during the evening of the deadline ... deciding whether the storm will be contest-worthy (six to eight stations with more than nuisance storm-total snowfall i.e., >= 4").
Collecting surface ... upper air ... and remote sensing data used in the final analysis and storm summary reporting takes time while the event is unfolding. All for naught if the storm fizzles.
Believe you me ... no one is more disappointed than me when a good snow storm slips through the cracks. Bottom line: a contest-worthy storm has to be reasonably well-predicted by the numerical weather prediction models and WPC 36-to-48 hours before the first flakes fall for a 'Call for Forecasts' to be issued.
Concord ... NH (KCON) set a new daily snowfall record on 29-DEC-2016.
New record: 8.3" (12.2:1 SLR)
Old record: 7.1" (1956)
Light snow began falling over the station shortly before noon on the 29th ... turning heavy and increasing to an inch to an inch and one-half per hour between 5 and 8 PM EST.
On-set of convection heralded the change from liquid to frozen precipitation.
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KBED 300112Z 32011G19KT 1SM R11/6000VP6000FT -TSSN BR VV004 01/M01 A2941
RMK AO2 LTG DSNT SE AND S TSB06 P0001 T00061011
KBOS 300119Z 31015G25KT 3SM -TSSNGS SCT006 OVC015 01/01 A2938
RMK AO2 PK WND 32028/0056 RAE07SNB01GSB13 TSB10 LTGICCC W TS W MOV E P0007 T00110006
99/00 - spawned on USENET/s ne.wx newsgroup to discover which poster(s) made skillful forecasts for synoptic-scale snowfalls in the NE and Mid-Atlantic. No formal entry process. Forecasts gleaned from newsgroup posts. Contest storms: 5
00/01 - Permanent station list created. (RDU - CAR). Rules and scoring formalized. First Contest 12/30. Contest storms: 10
01/02 - 'Season-total' forecasting contest launched. Twenty-five forecasters predicted each station/s 'total snowfall' for the winter. First Contest storm 12/9. Contest storms: 9
02/03 - First Contest storm 11/27. Contest storms: 10
03/04 - Web site launched. Developed online entry forms. Streamlined forecast reporting and verification processes. Added two forecast stations (BGR, BGM). First Contest storm 12/14. Contest storms: 10
04/05 - First Contest storm 12/20. Contest storms: 9
05 /06 - First Contest storm 12/5. Contest storms: 4
06/07 - Regular season starts late with first Contest storm 2/14. Contest storms: 5 (last one in April)
07/08 - Record number of forecasters (36) enter 'Season-total' Contest. Regular season starts 12/3.
08/09 - 10th anniversary!
18/19 - 20th anniversary!
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NEWxSFC appreciates greatly the on-going support from Senior Forecaster Donald Rosenfeld who began sponsoring the Contest/s web site in 2003 and enabled the development of our online entry forms.
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