Winter '09 / '10 - Snow Storm #1 - The Forecasts

26 forecasters...including 10 rookies...issued 550 stations forecasts for this season/s inaugural snow storm.  Forecasts are ranked by storm total precipitation (STP) in ascending order.  Blue (red) values are in the 25th (75th) percentile.

Forecasts here.

Consensus heavy snowfall axis from IAD - DCA - BWI - PHL - EWR - JFK - ISP -ACY - IAD.

Amplifying flow regime evidenced by rising PNA and cold air source indicated by strongly negative values for NAO and AO.  Oscillations come on the heels of a minor stratospheric warming event that slowed and split the PV.  Arctic region surface pressure rose as the one piece of the PV moved from eHEMI to wHEMI...where opposing flow between the two circulations created weak ridging near the pole.

986 surface LOW over HSE SAT 19-DEC-09 at 12z crawls to a position abeam the southern end of Delmarva peninsula 12 hours later laying down a wide swath of heavy snow from VA to MD on its way to SNE.

Verification period ends 11:59 PM EST...SUN 20-DEC-09.  Preliminary storm-total snowfall totals will be posted the evening of MON 21-DEC-09.

Winter '09 / '10 - Early Snow...Cold Snap Hits NW Europe

"The iconic Eiffel Tower was closed to visitors, and train and bus services were delayed in many areas, as daytime temperatures dropped below zero for the first time in the year and black ice coated northern roads.

"Snow also fell in Britain, Germany, Belgium and the Netherlands and weather experts forecast worse to come, with disruption especially in Scotland and northern England.

"The northern Netherlands experienced the worst falls in four years, with snow up to 25 centimetres deep in places..."

More...

Winter '09 / '10 - Snow Storm #1 - Call for Forecasts

Today's PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION from HPC:

"THE 12-18Z NAM NOW SHOW SNOW OF HISTORIC PROPORTIONS IN THE CORRIDOR FROM SOUTHWEST VA TO WASHINGTON DC AND BALTIMORE."

Snow may begin falling late FRI evening over southern forecast stations.  Any snow that accumulates before the verification period begins will not be included in the amount of storm-total snowfall for those stations.

Deadline: 10:30 PM EST FRI...18-DEC-09

Forecast element:  storm-total snowfall

Verification begins: 12:01 AM EST SAT...19-DEC-09
Verification ends: 11:59 PM EST SUN...20-DEC-09

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

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:  NYC 1917

Winter '09 / '10 - Coastal Teaser #2

The European starting showing signs of life in the eastern Gulf of Mexico and offshore from Georgia the last few runs.  Today...GooFuS came on board after several days of sending the storm out to sea.

Prospects for a Miller 'A' storm coming up the coast now looms in the medium range. 

Extension of the parent arctic air mass... centered south of Hudson Bay...will be over land as far south as CHS on Saturday... providing an excellent baroclinic zone along the SE coast for cyclogenesis as short-wave dives into base of trof on NW flow aloft.

Progressive westerlies currently progged suggest storm will skirt the M-A coast and not affect SNE.  More energy entering into the trof from the NW than forecast may cause a more northerly trajectory of the surface LOW.

Winter '09 / '10 - WSI - December Update

WSI Energycast Outlook Calls for Colder-Than-Normal Period in US, Especially in Northern States

Dr. Todd Crawford - WSI seasonal forecaster:

"The general pattern of cold-north and warm-south observed during the winter so far will generally continue into early spring. The warmest temperatures, relative to normal, will be in the south-central and southeastern states while the coldest temperatures will continue to be observed in the north-central states.  The cold Pacific Ocean suggests that the upcoming aggregate three-month period will be relatively cold nationwide, relative to normal, especially in March and April.  An incipient stratospheric warming event, which appears to be historic in magnitude, may continue to favor more Arctic air masses in mid-latitudes and increases confidence in the widespread cold forecast of the US these upcoming few months."

In February:

Northeast - Colder than normal

In March:
Northeast - Colder than normal

More...

Is -NAO Over-valued as an Antecedent Condition for Significant NE Snowfall?

Introducing another round of posts in a series of posts... challenging the conventional wisdom about the relationship between a negative North Atlantic Oscillation (NAO) and north-eastern US snowfall.

The analysis will use data from a paper by Paul Kocin and Dr. Louie Uccellini published in the Bulletin of the American Meteorological Society (BAMS - 2004).

The Northeast Snowfall Importance Scale (NESIS) categorizes and ranks snowstorms affecting the NE CONUS by snowfall and population distribution.

More about NESIS here and here.

Data for the analysis comes from Table 6 in the BAMS article.  Storm-day NAO values...as well as NAO values for the three days preceding the event will be examined to determine their correlation to notable snowfalls.  Contributions from the Arctic Oscillation (AO) and the Pacific-North  American (PNA) index will also be assessed.

Previous analysis on the subject have shown a weak...yet statistically significant relationship... between increased snowfall @ stations in the NE and mid-Atlantic regions during winters (D-J-F) where the average NAO is negative but no statistically significant relationship between -NAO and individual snowfalls of any amount.

Forecasters and wx enthusiasts often pine for the westerlies to align is such a way for the NAO to b/come negative in the mistaken belief this pre-condition is an essential requirement for decent snows over NE CONUS.

NAO values leading up to and those observed during the so-called 'Storm of the (20th) Century) stands this idea on its head.

VCP32 - No Surprise to Me

 

Winter '09 / '10 - Strike 2

Second contest-worthy storm in less than a week to be poorly forecast with enough lead-time to make a call for forecasts.

Early NWP forecasts indicating three-to-four hour snow burst followed by change-over to rain were way underdone.  HPC/s winter weather products also failed to indicate a decent event was coming for New England until it was too late.

ALB:  7.3" between 0836z and 1551z  (~7.5 hrs)  New daily record.

BGM:  6.4" between 0553z and 1216z  (~6 hours)  New daily record.

BDL:  6" between 0906z and 1251z  (4 hours)

ORH:  7.5" between 0933z and 1503z  (4.5 hours)

CON:  8.3" between 1117z and 1848z  (7.5 hours)

PWM:  4.3" between 1248z and 1839z  (6 hours)

BGR:  4" between 1534z to post time  (7 hours and counting; 8 - 12" forecast)

CARL  6 - 10" forecast

At least three other forecast stations measured nuisance snowfall amounts.

Image:  Winter in VT 1933

Winter '09 / '10 - C-C-C-O-L-D December - Part Deux

Amplification of the long-wave patten over NOAM appearing more likely with every model run.

The long-advertised deepening of the Arctic Oscillation (AO) index to near record-levels...aided by on-going weak stratospheric warming event weakening the polar vortex... appears set to get under way the next day or two along with an off-the-chart...near record-setting rise in the Pacific-North American (PNA) index.  Essential ingredients poised to fall in place for a stormy end of the month.

The return-period for an AO index less than or equal to -5.0 is 3.9 years for a total of 32 days since 1950 with no days observed that low since OCT-02.  The record value of -7.433 was set 15-JAN-77.

The return-period for a PNA index greater than or equal to 2.5 is 5.6 years for a total of 24 days since 1950 and no days observed during winter.  The record value of 3.397 was set 24-SEP-08.

Week 2 forecasts show broad positive (negative) 500 Z anomalies over the North Pole (across the western Atlantic) a perfect inverse match to the AO's loading pattern.  Note the negative anomalies south of Alaska marking the position of the Aleutian LOW and an east coast CONUS storm track custom-made for Miller 'A' cyclogenesis.

Week2 positive sea-level pressure anomalies located at high latitude along the Prime Meridian and south-central Canada allowing arctic air to drain into low-latitudes creating a strong baroclinic zone along the Gulf of Mexico and SE CONUS coasts.

Daily teleconnection index values here.

Earth System Research Lab - Physical Sciences Division/s Week 2 Tercile Probability Forecasts here.

EDIT:  corrected dates of record AO and PNA index values

Winter '09 / '10 - Opening Day

Winter/s inaugural snow storm was poorly forecast by NWP up until just before the event began.

NCEP/s HPC had a 10% probability of +4" over SE VA near the time a decision would be made whether the storm was contest-worthy.  Storm-total snowfall amounts were marginal...even if the an accurate numerical forecast had been more timely.