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Winter 2011-2012 forecast verification

This was an ugly forecast… pretty much the exact opposite of what actually happened. There was virtually no blocking this year (I was relying on blocking for the cold pattern), and a fairly persistent and strong trough over Alaska prevented any sort of real, long-lasting cold from entering the U.S.

DJF temperature forecast: F

December 2011: F

January 2012: F

February 2012: D-

DJF precipitation forecast: D

Radar watching – Bay- and ocean-enhanced snow

Some parts of the Mid-Atlantic have received and are still getting anything from light flurries up to a half inch of snow from bay-enhanced and ocean-enhanced snow this morning:

Steep lapse rates right near the surface and a veering wind profile are allowing the low-level clouds to suck up moisture from the Atlantic Ocean and from the Chesapeake Bay, which gets deposited in the Mid-Atlantic as snow. The area of snowfall is expected to switch over to sleet and then rain or freezing rain eventually as the mid-level temperatures warm. It is not a big concern as the precipitation remains light and widely scattered in nature, but it is something to take note of in areas that see more persistent precipitation.

Coldest morning of the season in the Northeast

A lot of locales in the Northeast are experiencing their first sub-zero lows of the winter, with temperatures as cold as -24F in Watertown, NY! (Yes, it’s -24, not -23. The software rounds the Celsius conversions oddly in some cases)

A 1030mb high centered over southeastern Ontario is allowing for light to calm winds under mostly clear skies.

UPDATE: Grabbed the hour with the coldest temperatures and updated the map.

Quick thoughts on tonight’s/tomorrow’s snow

This rain-changing-over-to-snow event has been the main snow event to watch over the past few days, and now it looks like it will come to fruition… at least for those from DC and points north as the tail-end of precipitation rolls through the region between 2-5am.

The latest HRRR is putting down some light accumulation east of the mountains for those north of DC:

I would be a little weary for the total amount of accumulation east of the mountains, but it certainly is possible if the “thump” of snow is strong enough.

Some isolated flurries are also possible during the day tomorrow east of the mountains if enough moisture is available.

Snowfall Verification for Dec 7-8

Quite a trying forecast, but overall it wasn’t a complete loss. Verified the mountain areas and highest totals fairly well, but the more heavily populated areas left much to be desired. Looking back, I could have been less generous with the 2-4 inch range in northern MD and southeastern PA, but other than that and bringing the 1 inch cut-off further north in MD I don’t see much that I could have done to change my overall thinking for this event.

The changeover from rain to snow was fairly messy east of the mountains, and most did not even transition to 100% snow. On top of that, the snowfall ended more abruptly and sooner than I had expected, which prevented the stronger cooling to make it to the surface in tandem with the back edge of the heavier precipitation. That slightly warmer boundary layer is what turned 1-4 inches into little to no accumulation.

Going to be a little generous and give myself a C- overall, though it wouldn’t take much convincing to push that to a D+ considering the bust in south-central/southeastern PA and MD and the western edge of the snowfall.

Winter Storm Threat: Dec 7-8 (final call)

Had to make some big changes in the northern areas… the boundary layer temperatures did not cool off as much as I thought it would on the models in addition to a quicker end to the snowfall.

I think that a couple of areas will be able to top out just above 8 inches in the mountains, so I left a small area over some of the WV/MD pandhandles.

Snowfall totals should not get hurt too much after the transition to snow finally occurs as a small period of sleet during the transition could/should provide a decent base layer for the snow to accumulate on. Keep eyes and ears peeled for the possible thundersleet/thundersnow during the transition from rain, especially from the northern VA/DC region up through central PA.

Winter Storm Threat: Dec 7-8 (first call)

Think 10/29 redux, only the temps and QPF line up a bit better for the changeover on the back-end:

The upper-level vort. max is potent enough to create an area of strong dynamics along the back edge of the system, which will pull cooler air down to the surface and make it cool enough within the boundary layer for some accumulation as the coastal low forms and tracks northeastward. Some banding will allow for locally higher totals along the axis that has the greatest snowfall through the WV/VA mountains, south-central and eastern PA and northern NJ.

I took the 12z Euro Op. solution and shifted the low center northwestward to account for for some model biases, which actually lines up fairly well with the 18z NAM after that adjustment. I believe the 12z and now 18z GFS solutions are too suppressed with this system given how strong the vort. max is.

The snowfall totals could go up as the storm’s track and QPF amounts get honed in on the models.

Snowfall is expected to start in the mountains of southern WV/VA/NC Wednesday evening, working into the DC region Thursday morning and departing the PA/NJ region Thursday afternoon.