Snow Storm #6: Preliminary Verification

(updated below - Update II - Update III)

Preliminary storm-total snowfalls from CDUS41...PNS...and CF6 bulletins for Sunday.

Four new daily records.
PWM - 11.5" (11.2"; 1979)
CON - 10.3" (7.7"; 1994)
ORH - 8.2" (6.5"; 1948)
BGM - 3.8" (2.5"; 1978)

One daily record tied.
PVD - 7.5" (7.5"; 1948)

CAR SN:H2O was the only suspect report...given the low densities reported by most other stations. Storm-total snowfall amount looks reasonable in comparison to vicinity reports carried in the PNS; therefore...no adjustments indicated.

Please report errors in Remarks.
Final results and storm summary Tuesday evening.

UPDATE
Regarding PNS snowfall totals referenced in Remarks; The Local Climate Bulletin (CDUS41) is the primary source for snowfall verification data. The snowfall reports in the PNS do not always reflect the official data in the CDUS41.

The BOS PNS issued today @ 1:15 PM EST carries a 3.2" snowfall report for PVD valid @6:50 AM EST SUN...18 JAN. METARs show snow continued for another six hours 41 minutes. The 1751z METAR 6-group reported 0.52" liquid. The 4-group...which rounds to the nearest inch...increased from 3" to 7" between 12z and 18z.

The same holds true for BOS (PNS report time was 7:00 AM EST...18 JAN)...ORH (6:50 AM...EST 18 JAN) and BDL (6:50 AM EST...18 JAN).

Thanks to the poster 'Anonymous' for taking the time to eagle-eye the verifications.

UPDATE II
In Remarks...poster 'Anonymous' links to a WFO CAR summary report where BGR/s FSS reported a two-day snowfall of 11.2" @ 8:00 AM EST MON...JAN 19 and questions whether preliminary verification value of 4.4" is accurate.

The two-day storm-total liquid precipitation...as reported in METAR 6- and 7-groups... totaled 0.43"...of which 0.32" fell before the end of the verification period (11:59 PM EST SUN...18 JAN).

The density of 11.2" frozen precipitation from 0.43" of liquid precipitation is 26:1. If the same SN:H2O is applied to the 0.32" liquid observed during the verification period...an adjusted BGR snowfall total of 8.3" seems reasonable.

UPDATE III
Daily record tied @ MDT - 1.5" (1.5"; 1958)

Going Coastal

SPC weighed in on Storm 6 this afternoon...

"MAXIMUM SURFACE PRESSURE FALLS HAVE BECOME CENTERED ALONG WARM FRONT ACROSS COASTAL ME...DOWNSTREAM OF INTENSIFYING CYCLONE OVER MA BAY AT 16Z. AN INTENSE BAROCLINIC ZONE / CHARACTERIZED BY A SURFACE TEMPERATURE GRADIENT OF 45 F OVER 200 NM ACROSS ERN ME/ HAS RESULTED IN SUBSTANTIAL LOW-LEVEL WAA /INFERRED BY LARGE CYCLONIC HODOGRAPHS IN GRAY AND CARIBOU VAD PROFILERS/ AND SNOWFALL RATES REACHING 1 IN/HR /PER 16Z METARS IN BRUNSWICK ME AND PROVIDENCE RI/.

WAA WILL STRENGTHEN AS THE LLJ INTENSIFIES THIS AFTERNOON WITH APPROACH OF SHORT WAVE TROUGH /CURRENTLY ROUNDING BASE OF LARGER-SCALE TROUGH OVER TN VALLEY/.

MORNING MODEL GUIDANCE QPF CORRESPONDINGLY INCREASE WITH BOTH GFS/NAM INDICATING PEAK AMOUNTS AROUND 0.50 IN FROM 21-00Z. ALTHOUGH SURFACE TEMPERATURES MAY WARM ABOVE FREEZING ACROSS IMMEDIATE COASTAL AREAS S OF THE US-1 CORRIDOR EAST OF ROCKLAND...HIGH SNOW TO LIQUID RATIOS FARTHER INLAND SHOULD RESULT IN SNOWFALL RATES OF 1 TO 2 IN/HR BECOMING PREVALENT."

..GRAMS/DARROW.. 01/18/2009

Graphic and discussion courtesy SPC.

Stellar Dendrites

High SN:H2O were observed in this morning early snowfall reports.

ORH - 23:1
CON - 24:1
BDL - 25:1

Ratios are well above normal.



Image courtesy Cooperative Institute for Precipitation Systems



12z Skew-T from GYX shows cloud-top ~-18°C...the cold edge of favored stellar dendrite growth region. Note the strong warm-air advection near 700 mb acting on the elevated moist layer where mixing ratios reach their maximum value.

Skew-T courtesy SPC.



Snowflake morphology courtesy SnowCrystals.com

Snow Storm #6: The Forecasts

13 forecasters...including 2 rookies...for the season/s sixth storm. Forecasts in the table above are ranked by expected storm-total snowfall.

Station forecasts here.



Typical Winter '08 / '09 snowfall distribution favoring northern forecast stations.



+PNA delivering the cold.



Evolution of coastal front is a key element in the forecast.

Snow Storm #6: Call for Forecasts

Poor consensus today between NAM and GooFuS concerning Sunday's snow storm over the forecast area.

GooFuS solutions depict more mid-level energy digging deeper into the eastern trof...which excites cyclogenesis along the southeast coast and a second snow storm on Monday.

NAM is more progressive as it shunts the bulk of its impulse into New England.

Given the present uncertainty...the verification period for this event will be be restricted to 12:01 AM EST to 11:59 PM EST on Sunday. This leaves the door open for a 'Call for Forecasts' on Saturday for Snow Storm #7.

Make the best forecast and you/ll win one month of FREE access to StormVista GOLD. Details here.

Deadline: 10:30 PM EST Saturday...17 January 2009

Forecast element: storm-total snowfall
Verification period begins: 12:01 AM EST Sunday...18 January 2009
Verification period ends: 11:59 PM EST Sunday...18 January 2009

Enter your forecast here.
Follow the link from 'Enter Storm Forecast.'

More prizes will be awarded at the end of winter for the best over-all forecaster. Details here.

As always...there/s no cost...or fee...or annoying requests for personal information to enter.

If you are making your first forecast this year or you entered the 'season-total' forecast contest...you/ll need to create an account (user name / password / valid e-mail...if you want a copy of your forecast sent to your Inbox) before entering a forecast.

Image: March 1888 Blizzard - NYC

Interim Standings

After five snow storms... donsutherland1 holds the lead... shanabe holds onto second...and Donald Rosenfeld lunges from sixth into third.

Under the ‘two-thirds’ rule…forecasters who have entered at least four forecasts are included in this interim summary.

Forecasters who will be eligible for Interim Standings ranking...if they enter a forecast for Snow Storm #6:

• anthony
  
• dmcuriman
  
• emoran
  
• Mitchel Volk
  
• Newa
  
• Raven
  
• skiGirl
  

Full interim forecaster error statistics table and charts here.

Forecaster storm summary data here.

SUMSQ errors for each contest snow storm are normalized with a 'Z-score'...then averaged to compute the standings. Forecasters who have entered at least 2/3 of all snow storm contests are included in the standings.

If a forecaster has participated in more than two-thirds of all snow storm contests...then Z-scores from two-thirds of their best forecasts are used to calculate Interim and Final standings. Same idea as dropping the lowest quiz score before the final grade is computed.

Previous Interim summaries here and here.

Snow Storm #5: Results

Senior forecaster emoran made the best synoptic-scale forecast for NEWxSFC/s fifth snow storm. His 23 station forecast verified with 68.8 SUMSQ error points (Z-Score = -1.352)...which was a 66% improvement over the average error of 205".

He hit the trifecta with lowest Total Absolute Error (29.9") and Average Absolute Error (1.3"). His 63% R-SQ score...a measure of how well a forecast captures the variability of the observed snowfall... ranked second.

This is emoran/s second...first place finish this season.

Emoran had the lowest station errors @ HYA PVD BDR ALB MDT DCA.

Congratulations emoran!

Emoran wins one FREE month of StormVista GOLD for his forecasting acumen.

2nd Place: anthony (75.1"; -1.290)
3rd Place: donsutherland1 (96"; -1.082)

Donald Rosenfeld...TrekkerCC...and skiGirl came within 5% of the 58.1" storm-total snowfall. skiGirl missed by a mere 0.65"!

Full forecast verification and results summary here.

Snow Storm #5: Preliminary Verification

Preliminary storm-total snowfalls from CDUS41...PNS...and CF6 bulletins for Saturday and Sunday.

One new daily record.
BGM - 5.5" (5.3"; 1957)

ORH/s 3.1" value is suspect and should be rejected based on vicinity SN:H2O and spotter report, and empirically-derived SN:H2O estimates.

Vicinity SN:H2O calculations were ~14:1...which suggests ORH storm-total snowfall was 4.6".

A Worcester ham radio spotter reported 4.8".

KORH/s SN:H2O...based on 0.33" liquid precipitation...is 9.4". Surface temperatures during the storm ranged between 16° and 19°...which supports a SN:H20...based on empirical evidence...of 20:1 or 6.5".

KORH is notorious for underreporting snowfall b/c their SN:H2O is always 10:1.

Recommend KORH/s STP be adjusted to 4.6" for this event.

Please report errors in Remarks.
Final results and storm summary Tuesday evening.

Interim Standings

After four snow storms...donsutherland1 moves into the lead...trailed by shanabe...who moved up from 5th and dmcguriman holding in third.

Under the ‘two-thirds’ rule…forecasters who have entered at least three forecasts are included in this interim summary.

Full interim forecaster statistics table and charts here.

Forecaster storm summary data here.

SUMSQ errors for each contest snow storm are normalized with a 'Z-score'...then averaged to compute the standings. Forecasters who have entered at least 2/3 of all snow storm contests are included in the standings.

If a forecaster has participated in more than two-thirds of all snow storm contests...then Z-scores from two-thirds of their best forecasts are used to calculate Interim and Final standings. Same idea as dropping the lowest quiz score before the final grade is computed.

Previous Interim summary here.

Snow Storm #4: Results

Senior forecaster 'shanabe' made the best synoptic-scale forecast for NEWxSFC/s fourth snow storm. His forecast verified with 36.7 'SUMSQ error' points (Z-Score = -1.201) which was a 60% improvement over the average of all forecasters 'SUMSQ errors' of 91.

He completed the trifecta with a tie for the lowest 'Total Absolute Error' (13.4") and 'Average Absolute Error' (1.03"). His 'storm-total precipitation (STP) forecast for 31" had an error of 1.6".

Shanabe had the lowest station errors @ PWM CON BDR ALB EWR DCA and made a perfect forecast @ BDL.

Congratulations shanabe!
Shanabe wins one FREE month of StormVista GOLD for his efforts.

2nd Place: donsutherland1 (40.9"; -1.107)
3rd Place: nynjpaweather (43.0"; -1.061)

Shanabe and donsutherland1 tied for 'Total Absolute Error' (13.4"); however...Shanabe had a lower 'Average Absolute Error' b/c he made 13 station forecasts and donsutherland1 made 11.

Full forecast verification and results summary here.