Heads UP! Extensive upper air storm goes to extremes.

UPdate 8pm ET:
From the National Weather Service forecast discussion, a possibility of ice after sunset on Tuesday….
SNOW/ICE FCST…CURRENT THINKING IS THAT EVAPORATIVE COOLING WILL LEAD
TO THE DEVELOPMENT OF SNOW/SLEET ACROSS THE LOWER HUDSON VALLEY
AFT SUNSET TUE. THE QUESTION IS HOW MUCH COLD AIR DAMMING WILL
OCCUR TUE NIGHT AS THE SFC HIGH MVS OFF THE COAST AND INCREASING
E-NE WINDS WARM BOUNDARY LAYERS. COULD SEE UP TO 2 INCHES OF
SNOW/SLEET THEN FREEZING RAIN BEFORE THE CHANGEOVER TO RAIN AFT
MIDNIGHT. STAY TUNED.

In other words, as the rain starts to fall after sunset (sun sets about 5:30 local time), falling rain evaporating in drier air near the ground may cool the air enough so the rain drops will freeze into snow for sleet for a while in northern Westchester, Orange and Putnam Counties. But by morning, warm air moving in will change the falling ice to rain for the rest of the day into Wednesday. “STAY TUNED” i.e., check your local weather forecast for updates tomorrow and don’t linger too late at work Tuesday evening if you commute to north of NYC-northern NJ-coastal CT area.

WIND FCST…ALTHOUGH A STRONG LOW LVL JET OF 50-60 KT DEVELOPS AROUND
925 MB AHEAD OF THE APPROACHING LOW TUE NIGHT UNDER THE TIGHTEST
PRES GRADIENT…LOW LVL INSTABILITY WILL BE LIMITED AND PREVENT
SOME MIXING. CURRENT THINKING IS THAT A WIND ADVISORY WILL BE NEEDED
NYC EAST.

The air should be stable enough to keep the strongest winds up above us, but the winds that do get down to the ground will be strong enough for wind advisories for gusts over 40 mph in NYC and areas to the east of NYC.

– end of update – read the following for more background information.

A strong upper air storm will allow warm air to move northward ahead of it and bring with it lots of moisture to the northeast coast of the US. The upper air storm will drift slowly eastward as the jet stream traffic stalls over us.
Then the other side of the storm will allow colder air southward, perhaps bringing winter temperatures back to the northeast and north-central US.

To get snow (and freezing rain) on Tuesday or Wednesday, you’ll have to go inland of I-84 in NY and I-287 in NJ and north of I-84 and I-691 in Connecticut.
And to get significant snowfall, you’ll need to be at higher elevations or Albany and northward.

NWS map of percent chance of four inches or more of snow Tuesday and Wednesday.

NWS map of percent chance of four inches or more of snow Tuesday and Wednesday.

The heaviest rain is mostly likely Tuesday night into Wednesday morning.
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Then colder air will mosey on down into our neighborhood. A traffic jam in the jet stream will keep that river of colder air flowing into our area, perhaps through next week. High temperatures will start out on Thursday in the 30’s for the NYC metro area, then we may see highs only in the 20’s for a day or more around March 5th. The coldest air is forecast to stay up in northern Canada.

gfsx_1000_10d
Colors are temperature near the surface in degrees C ( 0 = freezing). Arrows show winds moving cold air (dark blue and purple) from northern Canada. Map for Tuesday, Mar. 6, 7pm ET.

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