Another complicated snow forecast

Monday afternoon (March 2)

The very heavy rains expected tomorrow and especially tomorrow night have been long advertized and they should happen.  Earlier rain estimates suggested 2″-3″ for the Louisville area.  Most recent forecasts are pushing totals even higher, more like 3″ to 4″.  Either way, we should be prepared for a lot of lowland flooding tomorrow night/early Wednesday.  It looks like we’ll see quite and mess with the excessive rainfall.  Overall, the NAM is a little slower with the timing of this system (heavy rain potential continues until at least midday Wednesday.  The NAM continues to focus the heaviest rain right along the Ohio River and about 75 miles north and south of the river.  Meanwhile, the GFS is faster with any heavy rains over by midnight tomorrow night.  The GFS also places the axis of heaviest rain south of Louisville – over central KY with Louisville on the northern edge of the 2″ + zone.

For several days those heavy rain forecasts have come with a tantalizing suggestion that the rain will turn to snow before ending.  As we’ve drawn closer, snow is looking like a very good possibility.  As I mentioned last week, the key to this part of the forecast was whether the southwestern U.S. upper trough would phase, and merge, with the stronger northern system.  As expected, rather than merging, the southwest system “cut-off” from the main system.  As a result, there will be no strong surface low at the end of this winter storm.  Just frequent ripples of energy, but no strong center of the storm system to dominate the action. But the SW system will provide ample (more than ample) moisture to the northern system’s energy.  Thus our threat for flooding rains.

But with no strong energy surge to come along and clean things out, it greatly enhances our chances for snow.  In fact, it is settling into a rather classic pattern that usually puts down  a 1″-3″ snow cover as cold air changes the rain to snow for the last few hours of precipitation.  As wet as the storm looks to be and as cold as the air is behind the cold front, it could easily jump up a notch to 2″ to 4″ of snow.  Big question, however, is where is the snow going to accumulate with all the water all over the place?

So, trying to smooth out the variations between the models, here’s my latest forecast:

Tonight:  Increasing cloudiness and cold.  Temperatures rising into the upper 30’s by morning.

Tuesday:  Warmer, with light rain developing during the morning.  Rain will become heavy at times during the late afternoon.  High…53.

Tuesday night:  Rain, heavy at times.  Widespread minor flooding likely.  Temperatures rising to the upper 50’s, but then falling after midnight into the low 30’s by morning.  Rain changes to snow overnight with a possible accumulation of 2″ to 4″ by midday Wednesday.

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