Sunday, December 09, 2007

Alberta Clipper - 05 DEC 2007


Source:
NASA Earth Observatory

An energetic clipper system put 3 - 7" of high-fluff snow on the ground in the DCA - BWI - ACY area last Wednesday. Forecasts generally underestimated the storm-total snowfall.

Temperatures in the crystal factory were -12°C...the low end of favorable conditions for growing stellar dendrites. Other contributing factors were 1) strong veering vertical wind profile...2) 'moist' boundary layer...3) column stretching as the impulse migrated east of the mountains...4) track of the 5H vort max...and 5) SN:H20 of 30:1...all of which were well-modeled by NWP well in advance of the event.

Saturday, December 08, 2007

More Like '55


The images shown below depict time-section plots @ 5H between 20N° and 90°N using NCEP daily data (operational and re-analysis) of CLIMO...current...and CPC/s seven La Nina years for the period 15 November through 07 December.

Any similarities / analogs between current conditions and conditions from past La Nina years?

1955...perhaps?


CLIMO..........Current..........1970..........1988


1950..........1955..........1973..........1975


The winter of '55 / '56 featured a strong La Nina that began in early '54 and continued for almost two years until the very end of '56. PDO was negative...as were most winters back then. PDO these days has bi-polar tendencies. QBO flipped E in January -- it/s E now having peaked in OCT. AO ranks 36 out of 57 years. NAO ranks 52 out of 57 years.

'55 doesn/t show up on any analog for this winter...but there it is. Best qualitative match with mid-level geo-potential heights during the past three weeks.


Make your own...
Time Plots / Hovmoller diagrams

Image credit:
NOAA/ESRL Physical Sciences Division, Boulder Colorado

Thursday, December 06, 2007

Contest # 1 - Results


Chief Forecaster donsutherland1 issued the best forecast for Storm #1. He placed 1st in "SUMSQ Error'...'Total Absolute Error'...'Average Abosulte Error' and 'R²' categories of forecast skill.

Full results @ the Contest web site.
Follow the link to Forecast #1 to see full forecast verification
Follow the link to Results #1 to see forecast and contest summary information.


Click to Enlarge

Wednesday, December 05, 2007

Contest # 1 - Surface Analysis


Click to Animate

Contest # 1 - Verification


Preliminary storm-total snowfall based on final CDUS41 bulletins from Sunday...Monday...and Tuesday.

New daily records
12/4
BGR: 12.3" (8.8"; 1989)
JFK: 0.9" (0.1"; 2003)

12/5
BGM: 2.4" (1.4"; 1972)

Please report any errors in 'Remarks' along with a link to the correct data.

Final results and contest summary will be posted Thursday evening.

Monday, December 03, 2007

Bully Wind

Rapid deepening of the surface LOW in the Gulf of ME today ginned-up a good bully wind along the east coast from VA to ME.

Buoy 44018 is 20 SE of Nantucket


The 24-hr pressure fall was ~1.2" Hg (~40 mb)...far exceeding NCEP/s 'Heavy Snow' prognostic expectation of a 20-30 mb deepening.

Strong WNW flow whipped around the backside of the LOW..too...screaming past Buoy OSGN6 from across Lake Ontario near Oswego...NY.


Make your own...
Northeast USA Recent Marine Data

Trends in NHEMI Snow Cover


Tony Wood of the Philadelphia Inquirer writes in his Weather or Not column today about trends in NHEMI snow cover. Areal coverage has been decreasing and the spring melt has come earlier. An earlier post on NEWxSFC suggested similar trends.

Tony reports some interesting observations made by Rutgers University/s geography professor David Robinson and AER atmospheric scientist Judah Cohen on the subject and what it all might mean.

"First, and curiously, the snow cover in other seasons (summer, fall and winter) hasn't shown big changes, Robinson says.

"Second, after falling off in the late 1980s, reaching a record low in 1990, the snow cover rebounded - until three years ago. So the decreases in complete calendar years 2004, 2005 and 2006 could constitute an anomaly.

"Third, Robinson, who contributed to the blue-ribbon Intergovernmental Panel on Climate Change (IPCC) reports, says that one could make the interesting argument that the world is warmer because of less snow.

"It's a chicken-egg question," he says.

Judah Cohen adds...
"The physical mechanism isn't fully understood, Cohen says, but fall snow coverage evidently affects air pressure patterns that influence other changes: An above-normal snowpack in Siberia in October correlates with below-normal temperatures in the United States in winter.

"October is the key, Cohen believes, because when the sun is strongest (summer), the snow is scarce; when the snow cover peaks (winter), the sun is absent. October has both."

More...
Rutgers University Snow Lab
sCAST from AER...Inc

Sunday, December 02, 2007

Contest # 1 - Teleconnections


Sharp decline in AO and NAO the right before the storm day. Small rise in otherwise flat / negative PNA.

Near-simultaneous drop in AO / NAO and rise in PNA reflect L/W amplification associated with the storm.

Contest # 1 - The Forecasts

(updated below)


Click to Enlarge

Sixteen Fifteen forecasters...one rookie...and one late entry pending approval

Storm Total Precipitation (STP) forecasts range from a low of 55.7" (smadsen8486) to a high of 108" (Mitchel Volk).

Average STP is 78.9"

Clearly a northern New England event...where the consensus heavy snow axis (+6") extends from BTV - CAR - BGR - PWM - CON - BTV.

All individual forecasts have been posted to the NEWxSFC web site. Follow the link to 'Contest # 1 - The Forecasts'. The forecasts are ranked from minimum to maximum STP for all stations.

UPDATE: The 16th entry was disqualified b/c the forecaster took into account model data not available to other forecasters who entered on deadline.

The forecasts posted on the web site will be updated during verification.

Saturday, December 01, 2007

Contest # 1 - Call for Forecasts


Hot on the heels of the ‘season-total’ contest deadline…the first storm of the new ‘individual storm’ season is progged to affect a good portion of the forecast area Sunday through early Tuesday. We/re off to a good start compared to last year when the first contest storm didn/t happen until February.14.

Deadline: 10:30 PM EST Saturday, 01 December 2007
Forecast verification begins: 12:01 AM EST Sunday, 02 December 2007

Forecasts must be entered via the Contest/s web site
Follow the link to 'Enter Storm Forecast.'

Forecasters need to register once before entering…even if they were registered last year.

Registration is simple… requiring only a user name and password. If you provide a valid e-mail address…a copy of your forecast will be sent to you. Please ensure your browser is enabled to accept first-party cookies.

All forecasts will be posted to the NE_Wx Google Group by the Contest Administrator before 11 PM EST Saturday, 01 December 2007 and to the Contest web site by Sunday evening.

More information about the contest/s rules…forecast verification…and scoring can be found at the main web site.

Updates and announcement are posted on the Contest/s web log

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Contest subject to cancellation before the deadline, if forecast conditions warrant.

Each contest must have a minimum of seven forecasters for the results to be included in the end-of-season scoring.

Please enter 0.05 for trace amounts instead of a 'T.' if no snow is expected at a station, please do not enter a zero, just leave it blank, instead.

The NE.Wx Snowfall Forecast Contest (NEWxSFC) is a multi-month event that continues into late March or early April. In general, contests are held whenever a decent, synoptic-scale storm rears its head and threatens at least a half-dozen forecast stations with more than nuisance snowfall amounts. Forecasters are called to post their 'storm total' snowfall predictions, on deadline, for 27 NWS / FAA observing stations scattered about New England and the Mid-Atlantic regions. The Contest Administrator determines the deadlines for entries; verifies all forecasts, and publishes the final results to the Contest/s web site.

Please be sure to read the rules before entering the contest b/c your entry constitutes agreement to abide by them.

You can find the Contest Rules and additional information about Error Scoring, current monthly snowfall climatology from NCDC, daily CPC teleconnection indices, daily NESDIS N-Hemi snow cover, and NWS Daily Climate Bulletins (CDUS41) by pointing your browser @ www.newx-forecasts.com

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