Contest # 1 - The Forecasts

Forecasters: 19
New: 8
Veterans: 11

Welcome to all the new folks and welcome back to the old timers. Good luck to all.


The consensus heavy snow (12"+) axis runs from BGM - BTV - CAR - CON - BGM.

All individual forecasts have been posted to the NEWxSFC web site. Follow the link to 'Latest Forecasts.' The forecasts are ranked from minimum to maximum storm total snowfall (STP) for all stations.

Minimum STP: 94" - jefcled
Maximum STP: 536" - joesco
Average STP: 186"
10th percentile: 115"
90th percentile: 256"

Two entries were rejected b/c the more than 95% of the stations had zero as the forecast snowfall. One entry was rejected b/c it was received outside the grace period.

Verification snowfall amounts will be posted Friday evening. They are considered preliminary and subject to change / challenge for 24 hours.

Arctic Nation

Brisk cross-polar flow.



Click image to animate.

Watch arctic HIGHs migrate E from Siberia across CN/s NW Territory and into Lower 48.

The ECMWF/s Stealth Miller B

Does today/s 12z ECMWF D+5 forecast a deepening Great Lakes upper LOW capturing and intensifying the M-A surface LOW toward the 'benchmark' @ 40°N / 70°W...

...or does it excite a 'back-door' Miller B and drag it onshore?

The upper LOW is shown coming in the back-door from ern CN instead of its more common direct approach from the NW. The upper LOW would be expected to develop a surface reflection on the E side of the short-wave trof. Given the deep...unstable vertical temperature and moisture profile...cyclogenesis would be rapid and intense.

Note the orthogonal (90°) crossing angle of the MSLP isobars (equivalent to the geostrophic wind @ the boundary layer/s top) and 5H Z to the E of the LOW indicating veering vertical shear and strong UVM from WAA. These dynamics will build the downstream short-wave ridge enhanced by the release of latent heat and slow the easterly progression of the upper air features.

The low resolution of the model post-processing may prevent the depiction of this feature.

Should the 'back-door' scenario come to pass...the snows over the M-A would pale in comparison.

Standby for Contest #1! - Again

What could be this winter/s one and only contest storm appears likely to affect a good portion of the M-A and SNE early next week. MR progs continue to depict a strong frontal wave forming over the GOM states. The storm forecast track takes it ENE across the M-A on its way toward the western Atlantic Ocean where it undergoes cyclogenesis as it passes the benchmark @ 40°N / 70°W.

An easterly extension of the parent HIGH pressure...centered over western CN...into SNE and northern portions of the M-A will play a key role in determining the position of the RN / SN line.

Latest trend analysis shows the edge of 32°F SFC isotherm creeping slowly N + W with time. Should the trend continue...best snows would fall INVOF the DCA - BWI area. The main caveat in play...even within 24 hrs of the event...is NWP models long-held difficulty in resolving the southern extent of low-level arctic air. The models often fail to forecast the freeze line far enough south wrt to the verifying analysis.

If the upper LOW INVOF the Great Lakes is able to capture the surface LOW and pull it toward the coast...big snows would be in store for SNE...too.

LES is More

Big time lake effect snow event along the windward shore of Lake Ontario this past week with historic snowfalls recorded at some stations.

The observed conditions @ Watertown, NY on February 4 are of particular interest.

METAR KART 041756Z AUTO 28014G18KT M1/4SM +SN FZFG VV001 M12/M14
METAR KART 041856Z AUTO 27012G31KT M1/4SM +SN FZFG VV001 M11/M13
SPECI KART 041942Z AUTO 25015G33KT M1/4SM +SN FZFG M11/M13
METAR KART 041956Z AUTO 27019G31KT M1/4SM +SN FZFG M11/M13
SPECI KART 042014Z AUTO 26017G29KT M1/4SM +SN FZFG VV001 M11/M13
SPECI KART 042051Z AUTO 26016G24KT M1/4SM +SN FZFG M11/M13
METAR KART 042056Z AUTO 27012G22KT M1/4SM +SN FZFG M11/M13

From 1756z until 2056z...there was considerable falling or blowing snow. Visibility was frequently reduced to less than 1/4 SM. The wind frequently gusted to above 35 MPH (30 KTS). These observations depict near-blizzard conditions from lake-effect snow. Had these conditions lasted a little while longer...they would have meet the three hour threshold for a blizzard.

The theta diagram shown below shows deep layer instability from the surface up to ~750 mb.

The SkewT-logP diagram shows the vertical temperature profile is nearly dry adiabatic from the surface to ~750 mb...moist adiabatic from the LCL near 900 mb...and deep moisture in the column up to ~700 mb. With such an unstable sounding and cold temperatures aloft...it/s surprising there were no reports of +TSSN. Also note the low tropopause height near 350 mb (~25K')


More interesting and extreme LES obs from Buffalo, NY
SPECI KBUF 032210Z 24029G38KT 0SM R23/0600V2200FT +SN FZFG BLSN VV001 M08/M09
[...]
SPECI KBUF 032359Z 24032G40KT 0SM R23/1800VP6000FT +SN FZFG BLSN SCT004 BKN015 OVC040 M09/M12

Zero visibility although runway visual range reported a low value of 600' (~0.1 SM). Wind gusts to 46 MPH.

Snow Storms...They/re Only A Week Away

5H Z and MSLP


85H T and MSLP

MR models are at it again with teaser progs for this winter/s first significant EC snow storm and as usual...it/s just a week away.

This 'now-you-see-it...now-you don/t' scenario has played itself out several times this season. Sooner or later...odds are the atmosphere will get around to pulling the trigger instead of our thumb.

Today/s D+7 prog from the ECMWF depicts a classic cold air damming signature over the NE with strong arctic HIGH pressure centered over the Upper Great Lakes...supported downstream by an area of mid-level confluence...multiple sea-level isobars nosing SW along the Appalachian Mtns as far south as the GA / SC border...and an inverted trof along the SE seaboard indicative of a coastal front.



One big problem with the setup @ this point is the progressive nature of the flow regime as multiple short-waves are shown embedded in the westerlies. This suggests the storm might not be inclined to hang a left and hug the coast as it continues NE.

Snow Moon

Native American folklore holds February/s full moon...which occurs tonight...was known as the Full Snow Moon...supposedly b/c the heaviest snowfalls occurred during the second month of the year.

Maybe the tribes of northern and eastern America called it that...maybe they didn/t. All too often...Anglo-saxons have come up with pleasing stories about native peoples with little or no basis in fact.

Nevertheless...it would make for better folklore...regardless the origin...if it were based on observations that February is the climatologically favored time of year for good snows in the NE.

Too bad it/s not so. For most stations in the NE CONUS...January has the highest period of record normal (PORN) snowfall. In some cases...the difference between one month and the other is small...and maybe a statistical test on the difference between the two means would fail to reject the null hypothesis...but the data suggest the Snow Moon probably belongs to January.

Forecast Credibility

Wx web logs...forums...and message boards were all aflame yesterday with full-throated forecasts for a 'significant' snowfall in advance of the winter storm coming out of the GOM this evening.

Amateurs and pros alike hoisted 48-60 hour forecasts for wide swaths of 4-8" (meets and exceeds NWS warning criteria for heavy snow)...pockets of 6-12"...and 8+".

In light of more recent information...these collectively absurd forecasts have little chance of verifying.

Back in the day...forecasters knew better than to post snowfall forecasts with such long lead times. And they knew better not to segue the MR with the SR. Details portrayed in the the MR are pure fantasy. Timing...intensity...centers of circulation depicted in the MR are purely guidance of impending events. Same is often true about the SR progs...but they are much closer to the truth.

The lead time for a snowfall forecast with the best chance of verifying should be issued no more than 24 hours before the event. The current state of NWP is such that timing...intensity...and centers of circulation is too crude to attempt a forecast at such an extended time range.

A forecaster/s credibility needs to be preserved if they are to be taken seriously. Issuing a snowfall forecast more than two days before the first flakes fly is frought with danger and should be always be avoided.

FWIW - Verification of NCEP Week2 5H Z Anoms

Remember this?


It/s NCEP/s Ensemble Mean forecast for 500 mb height anomalies VT 1/26/2007...issued January 12. So...how good were the action center predictions?

500 mb height anomalies

Negative height anomalies...
...over NE CONUS verified farther N and E over the CN Maritimes
...over SW CONUS had minor displacement error N and W
...along and W of the IDL verified along IDL but farther E over the Aluetians
...over Greenland missed the NAO ridge.

Positive height anomalies...
...NW CN verified spot on
...ATL along ~40°N missed broad trof from CN Maritimes to NW Africa.

Good skill with PNA-type ridge-W...but completely missed the NAO dipole.

500 mb heights

Coastal Teaser #4

Click to animate. Loop speed = 1 frame / 3 sec

Wave forms on tail end of strong baroclinic zone courtesy arctic frontal boundary across the GOM. Dynamics from hot STJ provides the UVM.

Forecast problem is whether the storm will chug harmlessly out to sea or be held closer to the coast from the fx of a shortening wavelength.

Trying to forecast the timing and intensity of the numerous short-waves rotating around the PV is like playing roulette...even at shorter time ranges.

Sooner or later...something good has to come from the combination of the ern 2/3 of the CONUS flooded and continualy refreshed with arctic air and a hi-amp...short wavelength pattern.