In depth Model Discussion

[johnholmes]

like most so called rules in meteorology they are NOT rules but guidelines.

The snow is falling partly due to the intensity of the ppn, evaporation and cooling are lowering the zero isotherm to at or near the surface for elevations quite low down.

[Glacier Point]

Excellent progression from both ECM and GFS12z (inspite of huge potential for model error as the jet phases twice over North America) to suggest that a -ve NAO pattern is not far off now.

First up.... I've been waiting to use this one, and to paraphrase Monty Python, that westerly QBO is dead (well almost):

30 hPa zonal wind anomalies have declined to 0 values over the last few days to suggest that the switch to an easterly QBO. This matters, not least if we look at the reanalysis for weak westerly QBO and correlation for Feb March QBO:

Weak westerly QBO

Feb/March linear correlation to easterly QBO

Remember the second image is for a linear correlation not anomaly values so a -ve (easterly) QBO is the opposite or inverse to what the correlation shows. This verifies quite nicely with the last few days' pattern across the NH - note the match on the Atlantic pattern with low a low pressure solution to our west and height rises extending from Greenland to Norway:

Next up...the AO continues to show a -ve tendency with +ve height and temperature anomalies prevelent with the prospect of a sustained Stratospheric warming starting to feed downwards:

http://www.cpc.noaa.gov/products/precip/CW...index_mrf.shtml

http://www.cpc.noaa.gov/products/precip/CW...hgt.ao.cdas.gif

Then we have the North Atlantic showing a tripole suggestive of -ve NAO conditions (cold anomalies to the north - warm central north Atlantic - cold to the south:

http://weather.unisys.com/surface/sst_anom.html

Then the GFS and ECM are starting to pick out the development of a classic Feb weak El Nino / -ve NAO / -AO pattern, not least through tonight's t168-240 resulting in a possible re-run of the last 48 hours:

http://www.meteo.psu.edu/~gadomski/ECMWF_12z/hgtcomp.html

http://www.ecmwf.int/products/forecasts/d/...0912!!/

http://www.ecmwf.int/products/forecasts/d/...0912!!/

http://www.wetterzentrale.de/pics/Rtavn2281.html

Give it another day or so, and I will start to get very hawkish about this one...

GP

Edited February 9, 2007 by Glacier Point

[Evo]

Then we have the North Atlantic showing a tripole suggestive of -ve NAO conditions (cold anomalies to the north - warm central north Atlantic - cold to the south:

http://weather.unisys.com/surface/sst_anom.html

Then the GFS and ECM are starting to pick out the development of a classic Feb weak El Nino / -ve NAO / -AO pattern, not least through tonight's t168-240 resulting in a possible re-run of the last 48 hours:

http://www.meteo.psu.edu/~gadomski/ECMWF_12z/hgtcomp.html

http://www.ecmwf.int/products/forecasts/d/...0912!!/

http://www.ecmwf.int/products/forecasts/d/...0912!!/

http://www.wetterzentrale.de/pics/Rtavn2281.html

Give it another day or so, and I will start to get very hawkish about this one...

GP

Great post as ever GP!

I've been watching that tripole develop in the Atlantic too and I've also been keeping an eye on the PSU Height Comparisons. It seems to me that the signal now is for a -ve NAO-like pattern but twisted towards the Eastern US coast, with blocking over Greenland and a dominant West Atlantic trough - is that right?

Looking at the mean height comparisons, the GFS seems to be hinting at an omega block of sorts. Also intersting are the low mean heights progged over much of Russia, in fact GFS has no mean ridge from 0 to 180E

[Stephen W]

Excellent progression from both ECM and GFS12z

GP

Brilliant post GP - i hope your analysis comes to fruition and I shall be following the progress of this with much interest. Glad to see your enthusiasm back over the last week! If you could conjure up a slightly colder source for those of us in the E/NE that would be great - we've had little in the way of snow during the past two cold snaps!

Edited February 10, 2007 by Nick F
No need for whole quote - cuts down on scrolling

[BrickFielder]

For the first half of next week the forecast temperatures in the stratosphere would give a signal for a strong Mid atlantic low.

Later next week the straospheric vortex moves towards scandinavia and we should expect a signal for high pressure towards scandinavia.

This should bring cold air over the UK from the east.

With the prospects for snow during the later half of next week looking promising/

There are a few spoilers in the mix most noticeably the signal for a low pressure system towards alaska, which in turn means a north east canadian high with Atlantic low pressure systems to the east of the high. Time will tell but history shows the upstream signal may well win out.

[Stratos Ferric]

It'll be interesting to see how this pans out, because cold in some shape or form looks likely, if not certain. In the frothing and wailing around the too extreme prospects modelled last night the bigger picture is being missed.

The attached plot compares last night's 18z with today's 06z, and highlights my own take on the ciritical development to watch for in the context of the HP as-was modelled. Even this modified run offers a cooler SE'ly, and HP builds off N Scandanavia in the sluggish air as the main core of the jet stays well S.