'49 / '50 Analog on Life Support

Accu-Wx went into a defensive crouch today with a missive by WxMatrix/s Jesse Ferrel where he advanced the arguments 'winter hasn/t started yet' and 'it/s not over...until it/s over'.

Both arguments are silly on their face.

If winter has yet to begin...then why does AW/s Winter Outlook include details about early and mid-DEC. Ferrel then argues their outlook covers NOV through MAR. So which is it?

The 'A forecast hasn/t busted until the event has come and gone' maxim is true altho that/s a mighty thin reed given the current state of winter to date and trends in LR NWP.

Accu-Wx/s Winter '07 / '08 outlook is heavily weighed by the '49 / '50 analog where cold temperatures @ the start of DEC flipped to abnormal warmth mid-month and stayed above normal through FEB.

The time series shows 5H geo-potential heights (left two images) and SLP (right two images) from the pole to 10°N during the first nine days of DEC for 1949 and 2007. Hard to see anything other than weak correlations.

The northern polar stereographic view for the same nine days @ 5H depicts one similar feature...the weak trofs off the west CONUS coast...and several that are at markedly @ odds with each other. Note the analog year trof INVOF the Azores and a ridge in the observed. There/s an analog year trof in the GOM and ridging in the observed. There/s a ridge INVOF the Hawaiian Is. in the analog year and an observed trof.

In the mass fields...both years have HIGH SLP over Siberia...altho it/s much stronger in the analog. Evidence of a GOM LOW in the analog is missing in the observed where a broad area of LOW pressure is centered along the International Date Line.

Not looking too good ATTM for our friends at Accu-Wx. They/ve made a lot of noise and thumped their chests since October hawking the near-certain expectation for a sudden...and dramatic about face in temperatures that would occur mid-DEC. At this point...the '49 / '50 analog might need to be placed on life support.

Calling Doctor Howard...Doctor Fine...Doctor Howard.

Had intended to post the analog / observed comparisons last week...but a good contest snow storm came along...and seeing how that/s the reason why we/re here...it was delayed. Will post an update with a look at the period that/s passed since then.

Return of Hi-Latitude Easterlies

Note the ECMWF/s D+8 forecast for the return of deep tropospheric...hi-latitude easterlies over the pole suggesting a return of a negative AO index toward the end of DEC.

The time-height section also shows the 70mb mean zonal wind from the east over the Equator...indicating the negative QBO.

Negative QBO favors a negative AO...which is associated with a less stable...and slower polar vortex. These conditions present good opportunities for arctic outbreaks....storminess...and the potential for hi-latitude blocking.

Contest # 2 - Results

Rookie Forecaster pjc368 issued the best forecast for NEWxSFC/s Snow Storm #2.


pjc368 placed 1st in 'SUMSQ Error'...'Total Absolute Error'...and 'R²' categories of forecast skill. Bold forecasts for CAR and BTV put him over the top.

Close call for 2nd place where donsutherland1 edged out TQ by 0.1 SUMSQ Error points!

Full results and summary @ the Contest web site.

Follow the link under Forecasts to 'Contest #2' to see the complete...station-by-station forecast verification.

Follow the link under Results to 'Contest #2' to see forecast and contest summary information.

Teslacles/s Deviant to Fudd/s Law

On the afternoon of December 16...a rapidly deepening secondary LOW had moved to a position over Lower NY Bay... having advanced NE hugging the shorelines of VA...MD...and NJ during the morning.

The center of circulation passed directly over NDBC/s moored buoy 44017 around sunset...evidenced by the becalmed wind observation just before the minimum pressure was recorded.

The green pressure trace below reveals a 24-HR pressure fall of 1.45" Hg (~49 mb) which...after Sanders... more than constitutes a 'meteorological bomb.'

Sanders 'bomb' definition related to explosive cyclogenesis where the 24-hour pressure fall was greater than or equal to 1 mb per hour @ 60°N.

The reason the surface wind had approached zero as it migrated past the buoy was b/c converging air...brought to the LOW/s center by the pressure gradient force...had no where else to go but up.

Here we have a real-time example of meteorology/s 'Continuity Equation'...which is all about 'Conservation of Mass'...also known in some quarters as 'Teslacale/s Deviant' corollary ("What goes in...must come out") to Fudd's Law (“If you push something hard enough, it will fall over”).

None of this purports to answer the age-old musical question..."How can you be in two places @ once...when you/re not a-n-y-where @ all?"

Contest # 2 - Verification

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

SN-to-H2O ratios are average values where combined storm-total snowfall is divided by storm-total melt water...which can mask the effect of changes in the vertical temperature profile SN:H2O was 12:1 on Saturday @ BTV and 18:1 on Sunday. BGM/s ratio is not reported b/c it was contaminated by Saturday/s freezing precipitation; however...Monday/s 1.2" FES SN:H2O was 40:1.

New daily records
12/16
BOS - 7.6" (5"; 1896)
ORH - 8.4" (6"; 1896)

12/17
CAR - 9.2" (7.3"; 1978)

Final results and storm summary on Wednesday.
Please report errors in 'Remarks.'

Contest # 2 - Surface Analysis

Click to animate.

Contest # 2 - Teleconnections

Contest Storm #2 got no help from the PNA index as it was negative during the period. Positive PNA is frequently cited as an important ingredient for decent snowfalls in the NE CONUS. A positive PNA index doesn/t hurt b/c it oft times favors cyclogenesis off the SE CONUS coast...but it/s not an absolutely necessary ingredient.

LOW heights dominating the NHEMI polar region resulted in an above normal AO index as the s/w trof lifted NE into the forecast area. The index declined slightly while the event unfolded on Sunday.

The negative NAO index...currently @ nadir...was a likely consequence of the decaying Rex block over Europe with the westerly extension its trof axis INVOF the Azores rather than significant ridging over Greenland. The vortex over NE CN / Davis Straits was also a contributing factor.

The teleconnection indices associated with Contest Storm #2 offer more evidence that +PNA and -AO / -NAO are not prerequisites...as all too commonly presumed...for decent snows across the NE.

Contest # 2 - The Forecasts

Maximum...average...median...and minimum station forecasts
Eighteen forecasters...three rookies.

Storm Total Precipitation (STP) forecasts range from a low of 46" (Superstorm) to a high of 145.8" (smadsen8486).

Average STP: 87.9"
Median STP: 80.6"

Forecasters expect this snow storm...like the first contest storm...to be a northern New England event...where the consensus heavy snow (6"+) axis extends from BGM - ALB - BTV - CAR - BGR - PWM - ORH - BGM.

All forecasts have been posted to the NEWxSFC web site. Follow the link from Storm Contest Forecasts 'Contest # 2'. Forecasts are ranked from minimum to maximum STP.

Distribution of normalized STP forecasts by forecaster
Click images to enlarge.

Missed Opportunity

The deadline for Contest #2 is Saturday evening but in hindsight...it should have been Thursday evening given the respectable amount of snow that fell across SNE today.

Always hate to miss a good opportunity to hold a forecasting contest...especially given the dearth of decent events the past few years.

The NAM/s 00z Wednesday run continued it/s previous scenario for a marginal contest event (less than six (6) stations; nuisance snowfall) across the forecast area. The 12z GFS had shown good continuity from earlier runs but b/c we/re inside 48HRS...model consensus is an important factor when deciding whether an event is contest-worthy. NCEP and ALR/s servers were jammed Tuesday evening when the 00z Wednesday runs were posted and the GFS was not accessable.

Next go'round...when there/s uncertainty about how the event might unfold...a 'call for forecasts' will be issued and if it later becomes apparent the storm is heading for the crapper...the contest will be canceled.

Contest # 2 - Call for Forecasts

Potent nor’easter poised to rake northern portions of the forecast area with a big contest snowfall late this weekend.

Deadline is earlier than usual b/c of the storm/s expected duration and the snowfall/s start time over upstream stations.

Deadline: 7:00 PM EST Saturday, 15 December 2007
Forecast verification begins: 7:00 PM EST Saturday, 15 December 2007

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

All forecasts will be posted by the Contest Administrator to the NE_Wx Google Group before 11 PM EST Saturday, 15 December 2007 and to the Contest web site by Sunday afternoon.

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

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

Registration is simple… requiring only a username 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.

Each contest must have a minimum of seven (7) forecasters for the results to be included in the end-of-season standings.

Please enter 0.05 for trace amounts instead of a 'T.'

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.

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)