Todd Gross' Boston Weather and Southern New England Forecasts

USING T1 to Forecast Highs - Sunday Warmth

Most meteorologists use "MOS" projected high temperatures for forecasting highs and lows. This is fine, but I prefer to use data that is one step more raw, the T1 layer (boundary layer) temperature on the NAM FOUS. Any colleagues that have worked with me on this have been equally impressed and one is even tracking the performance of doing forecasting this way, but the key really is the wind direction. Well tomorrow I have an interesting problem. Will the wind (210 degrees) be blowing SSW or WSW. If WSW we might REALLY warm up despite being behind on the cold producing side of the storm as it moves away...

As it is, conventional thinking would be that behind the storm, cold air will come pouring into New England, but downslope winds force the T1 to +9 for 48f, which with a due west wind would mean a high well over 50, and with SW wind off the water, it may be tempered down to 50 or so, but that is STILL very warm right after a storm blows through and drops the 1000-500mb thicknesses (conventional way to determine temps) down to the low 530s. Nevertheless, I may be forced to forecast highs at or above 50 in places Sunday as much as it goes against the grain, based on the T1 and the downslope winds. Below is the FOUS showing where it happens, at 30 Hours, SW wind (210 deg) 15kits,  hours, T1 : +9. S

OUTPUT FROM NAM 12Z FEB 04 06        
TTPTTR1R2R3 VVVLI PSDDFF HHT1T3T5    
BOS//682154 00113 133210 50060603    
06000723559 -1614 140810 50070603    
12000978970 -1104 090819 53040704    
18049998970 06401 990914 57041206   
24004984267 -2705 962109 53070903   
30000764125 01612 942115 44090499   
36000773404 01507 942123 32050094    
42000686623 -0112 942323 28029691    
48000635821 00816 982424 26009489    

Vertical Velocity through the roof!

WARNING: This discussion is "more" technical than usual.

Talk about a high V.V. (vertical velocity). Rising air currents in winter storms are so frequently associated with thundersnows, but what about during a rainstorm. Sure, why not? It may be winter but check out the "FOUS" from the NAM computer model below. I have highlighted the whopping +38.1 vertical veloicty which happens to occur just at 1pm when winds are 1428 (SE , 28 kts) in the lower layers of the atmosphere. If that doesn't spell a troublesome rain squall, or thunderstorm in the midst of this low pressure/storm going by, I don't know what does. However, if you look at my "secret agent"(little known source) map, upper left CLICK ON IT. And look REAL closely, you will see the "counterpart" of Vertical Velocity, known as Omega. It too represents rising air currents but is the opposite, the more negative it is, the worse. You can see that a slug of -35 omega (+35 VV) moves into southern NH after having whipped across central Mass., inferring that Boston may get off easy compared to Worcester and points west, we'll see, as normally I would worry about winds on the S. facing shorelines... but here a thunderstorm may bring down the wind gusts locally more on hilltops in central Mass. Here is that FOUS from 7pm last night...

OUTPUT FROM NAM 00Z FEB 03 06        OUTPUT FROM NGM 00Z FEB 03 06
TTPTTR1R2R3 VVVLI PSDDFF HHT1T3T5    TTPTTR1R2R3 VVVLI PSDDFF HHT1T3T5
BOS//724554 -2616 181812 45050199    BOS//724857 00616 181711 45040099
06000897059 02915 191413 46040200    06000867470 02314 171617 46040300
12011989665 04405 131021 49040402    12000979793 02405 131325 48050501
18077989848 38101 011428 56091105    18051969956 09502 051632 54100904
24011871918 -4007 042421 52100706    24009893338 -1902 042429 52130802
30000752839 00413 092517 50070405    30000803571 -1312 112723 50070403
36000754964 05413 122504 49050504    36000874288 00813 152914 47040603
42000768869 02207 080908 52070701    42000776778 02413 141006 48060502
48040989369 03601 990817 56041106    48000949999 03603 071025 53050703

Above, left, I have highlighted the .77" of rain in 6 hrs, the 38.1 vertical velocity,
and the strong SE winds at 28 knots. I am using the "NAM" fous, left, not the NGM,
right, which is the "No Good Model" inside meteorological circles :)

NOTE: THE ONLY GOOD SOURCE FOR READING WEATHER CHARTS THAT I KNOW

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Winter to Turn Colder? NAO

The "North Atlantic Oscillation" or NAO has for years been known to be a major controlling factor in our weather here in the Northeast. Usually, if it 'goes negative', it means that there is a High Pressure ridge developing up over Greenland, which forces colder than normal weather our way. For the first time, in awhile, the NAO is predicted to just barely go negative next week. While that doesn't mean it will remain that way, it is the first sign of a colder winter to come. But will it snow as well? Initially the jet stream looks dry next week after the weekend rainstorm coming up. By the way, you can access this link and so many more in Todds World of Links in the sidebar. So far I have 88 links posted!

Negative Tilt Trough on the Way

No doubt about it, we are playing with dynamite on Sunday evening. The upper air chart depicted on the left (click on it) is illustrating a "negative tilt trough" , one that usually powers a storm and intensifies it as it races up the Eastern Seaboard in classic fashion. This often leads to what is called "bombogenesis", a term which some folks scoff at, but is an actual meteorological slang word adopted by most eastern seaboard Meteorologists for a strengthening coastal storm, similar to a quickly deepening hurricane. Some have even adopted the new term Wintercane", but this is just a re-hash of an older term I believe, "Neutercane" (sp?) which was popular after the blizzard of 1978. For information on how to read weather charts, computer models, etc, on the Internet, I recommend Peter Chaston's book Weather Maps, 3rd Edition, which you can order by clicking here or by emailing me at  toddwx@yahoo.com.

Cape Cod Last to Change

The Cape is closest to the storm center but will probably not get the most snow for a couple of reasons.

1. The snow from this system is really from an upper level trough coming down from the Gt. Lakes, not the offshore storm.

2. The temperature just falls below freezing aloft for the first time around 9 or 10pm in Hyannis as show by the sounding left. This is a vertical profile of the atmosphere, and both the temperature and dewpoint fall to the left of the line (at least above the immediate surface) or in other words, below 32f, 0c starting by 10pm. Before that, it is too warm aloft. So the Cape may just get a dusting at the tail end.

SMALL SNAG TUES. EVENING

It ain't over 'till it's over, said Yogi to the dreaded Yankees, but he of course was always right. The storm is still "out to sea" as projected exclusively here at toddgross.com, however, a feature at upper levels (which is crucial to look at) that the GFS model had all along , is suddenly being adopted by the NAM model and leads me to believe there will be just barely enough support to keep precipitation going Tue. evening while it is cold enough to snow. It is an upper level short wave, or vorticity maximum, circled, coming down from the Gt. Lakes, kicking out the first one, which is controlling the coastal storm and bringing it out to sea. The one from the Gt. Lakes (as illustrated at 7pm tomorrow night, click on chart) has enough energy and is supported by a very slight "warm advection field" and it may keep light snow going until midnight causing slippery roads, and maybe up to an inch of snow.

THE WARM LAYER TUE. AM

There is a reason I am not too concerned at least for early Tuesday from the upcoming close call. The reason is simply this: It is too warm aloft, even in the interior. Take a look at the vertical profile of the atmosphere, called a "sounding" (click left). It is for Fitchburgh, well inland, Tue. AM. I drew the 32f line as a solid black line. As one goes up into the atmosphere, the temperature RISES for a change, and does not drop, up through around 5,000 ft, then it declines. this will melt snow on its way down from up top, at least early in the day , until that layer can get wiped out. And yes, if the storm moved close enough to us, not only would we be in trouble with a NE wind and coastal flooding, but the intensity of the precipitation would draw cold air down quicker, wiping out the warm layer. In other words, if the storm strengthens and moves a bit closer to us, we have a better chance at getting snow at all, than if it was farther away and weaker, contrary to the normal "thinking" of good students of meteorology!

SPECIAL UPDATE: Storm back on?

SPECIAL UPDATE: Computer models have flip-flopped again and are now bringing together that coastal storm for Tuesday with mostly snow. It is still a close call, but there is enough potential for this to be a hard-hitting quick Noreaster that we will watch it like a hawk for you. Best chance of snow would be inland, but the heaviest precipitation will be SE, so somewhere in our area there could be a belt, where there is all or mostly snow, and lots of it.

WEST COAST RIDGE may signal change

The west coast ridge is key to the unlocking of cold polar air, and on the latest ECMWF (European) computer model for next weekend, there is finally a pattern change. This could mean not only cold air being unleashed more frequently, after one of the warmest January's on record, but it could mean the tapping in of Gulf moisture to produce coastal storms. So far this season, despite mild weather, parts of Central Mass. has been pounded with well above normal snowfall, over 40" already, although not much of it has remained in placed the whole winter due to the mild air.

Weaker System Tuesday?

The Tuesday storm is having difficulties coming together correctly to move this far north, be organized, and a true "Noreaster" according to overnight computer models. Still checking on the latest ECMWF which comes out late.. but two major models, the NAM and GFS both keep this thing from forming into something big. Here's why. Take a look at the chart on the left, (click on it) that is the 500mb "upper air" chart for Tue. morning. Rather than each little "short wave trough" or vorticity maximum (area of counterclockwise twist) lining up and combining with each other, they are offset and "fractured" coming together too late when the storm is already gone. You can see that fracturing here. The result is limited warm advection in the end, and some light spotty precipitation. Of course, this could be just a "hiccup" or one-time change from what we saw earlier, so stay tuned!