First and foremost the types of precipitation each area will get strictly relies on the temperatures outside when they fall, and a simple 1-2°F makes a huge difference when the temperatures get within the freezing mark. With that said, the models have been varying the temperatures 1-2°F lower, then higher over the past 48 hours of model runs, which means that tomorrow model's runs will be much more accurate with temperatures as they'll be based off of tonight's actual low.
Monday night's current outlooks:
For NYC and Long Island: The last model update puts temperatures another 1-2° warmer for Monday meaning it's a slightly better outlook, less wintry precip falling and rain taking over a few hours earlier (like Saturday morning's model runs, vs. Saturday Night's slightly lower temps). While it's a better trend it's only 1-2° so it's a cautious improvement.
Chance of scattered mixed rain/sleet around 7PM, slightly more around 10PM, all rain by midnight, no accumulations with temps above freezing and mixing with rain.
Westchester has a worse outlook, the 1-2° lower temperatures mean that the lows of 34° are now 32° making accumulations now a possibility. For now there seems to be .50-1.5" accumulations of snow/sleet before rain mixes in, which is later at 4AM now vs the prior 2-3AM.
Putnam/Duchess worse as well, with 1-2° temperatures are now down to 29-30°F, so with an absence of rain mixing in during the night (the rain will only arrive Tuesday morning) the sub-freezing temperatures will cause all snow/sleet to accumulate, though a silver lining is that it doesn't look like there will be freezing falling now so ice on the ground may not be a factor.
A tentative estimate of accumulations puts the area at 4-6" sleet, .50-1" snow before the change to rain around 10AM the following morning. Again this can decrease radically if temperatures increase by just 2°F, or change more to snow if decreasing by just 1°F.
Orange/Sullivan has remained the same more dangerous outlook as before, slightly more sleet vs. snow but still a similar result, with freezing rain still a key issue towards the morning. The low temperatures are still in the 29-30° range, however with
1-2" Snow with 2-3" of sleet will fall, around 4AM the snow and sleet switches to freezing rain and sleet, with .05-.10" ice possibly accumulating until 9-10AM causing major issues for the morning commute. When the freezing rain stops normal heavier rain will take over, with sleet ending around noon, though it will take the early afternoon to get rid of the ice and the end of the day to possibly get rid of all wintry precip.
SW Connecticut (Fairfield & New Haven) has remained the same as before, except the chance of freezing rain has been removed. With lows just below freezing around 31°, 2-3" of snow/sleet will fall until midnight, sleet remaining until 6AM with rain mixing in around 4AM. The morning should see the frozen precip remaining on the ground as the rain starts to wash it away, most of it should be gone by the mid-late afternoon with the help of 45° temps.
Again, tomorrow model's runs will be more accurate with temperatures as they'll be based off of tonight's actual low, as those temperatures are key to determining the types of precip each location will get.