Computer Model Discussion for Thursday

UPDATE 7am - Friday: I should have believed my own technical discussion below, follow along as the radar threw me off my original track by reading oldest to newest posts, bottom to top. Note how my forecast was on target Wednesday, but I lost confidence in my convinction on Thursday.

The important factor of course, that I was getting at, is how the warm advection field, got stopped dead in its tracks. That is on the chart at the bottom right, and is airbrushed orange. ALSO NOTE HOW WELL "THE SECRET AGENT" MODEL DID (my nickname for it) 24 hours ahead of time, unreal. Click on it so you can see the nothing for Boston and big storm for SE Mass. It isn't always that good!

UPDATE 1pm Thursday: You believe this? The radar certainly is running against the NAM and the NAM based 'secret agent model' left. The RUC in fact is agressive with snow all the way up to Rt. 2, so I am upping accumulation predictions at this time along the Pike, but the NH border STILL gets shut out. Heavy amts SE Mass.

UPDATE: 7am THU: My "secret agent" model shows we have a forecast problem. Click on it. What if the belt of precipitation were to migrate just 30 miles north, a mere 30 miles. That would throw off the forecast by leaps and bounds. Right now it NO precipitation from Boston north, and yet moderate snow within a stone's throw of Rt. 128, just minutes away.

UPDATED 6pm Wed: Correct people who posted, thank you! The left shows a good belt of positive vorticit y advection moving in , but where is the warm advection. Even if you pictured a SW wind blowing "across" the shown temperature gradient aloft on the right hand panel, you can see that ribbon of temperature by 00z (7pm) is already out to sea, leaving us little time for an accumulating  snow this far north. Ideally for good snow you need to have the PVA pass OVER the warm advection area. Neither works well by itself. Oddly, last weekend south we had the warm advection, but not the PVA and places ended up with just an inch, this time it is the other way around. 

UPDATED 11:30am WED: Map below still stands, latest NAM and GFS are simliar to the Canadian GEM map below. The left is the vorticity map, the right is the surface wi th thickness lines, isotherms, if you will.. have we figured out why it isnt going to snow a lot yet? Please post your comments my friends! .. or if you want the answer handed to you, just click on option 3, technical forecasts and search down  the list, over and over again we miss out the best storms when a key ingredient is missing. What is it? *sorry to get playful, but hey, bear with me on this, it is going to be helpful* HINT : Missing element is on the right hand map.

UPDATED 7am WED: Here is a map. Ok, students of meteorology. What element is missing tomorrow 7pm, and wh at element is quite present?

Comments

[Todd Gross]

CORRECT! thank you everyone. On the left, the area of positive vorticity advection IS FAIRLY FAR NORTH (although a bit farther south this past 18z run) but the baroclinic ribbon of warm advection, even at 700mb ,(not shown) is just too far south, it comes in and out like a bullet, never giving the storm a chc to grab hold up in Boston, even the cape it is "close"

THANK YOU!

[Jay Usher]

Hey Todd. My guess would also be that The Warm Air Advection is too far out to cause the heavier snow..Also the storm center is passing outside of the "Benchmark" to far to our south..Jay

[Deb]

Just looked at the map again... does it have something to do with the 540 line? Taking another stab :)

[Deb]

I thought it was warm advection too, but isn't it dividing Plymouth from the Cape, and wouldn't that be where the frozen/rain line would be? Everything north of Plymouth would be frozen (sleet/mix, then snow in N.MA/S.NH?), with the Cape in the rain zone? I'm not too sure about this.

[andrew]

gotta be "warm air advection"

[Todd Gross]

Come on folks, somebody take a crack at this...