Category Archives: Winter Weather

Winter Weather

MONDAY WINTER WEATHER OUTLOOK

A winter-time precipitation scenario is setting up for our area on Monday.

A front moving through this weekend will return as a warm front, but with over-running precipitation and cold air damming.

What was originally forecast to be a quick change from light snow to rain has evolved into a “cold air damming” scenario where cold air trapped at the surface likely will result in a prolonged period of sleet or freezing rain. (The models are showing mostly freezing rain.)  The GFS also shows some dynamic cooling- as the precip increases, the surface temperatures drop.

Some amount of wintry mix may be falling into the late afternoon and longer north and west of the city.

The QPF is expected to be light and the predicted snow accumulation is about 0.5 inches, but the prolonged freezing rain possibility may present a travel issue.

GFS Categorical Precipitation type for 2 PM on Monday. Click for larger image

The ‘event’ is more than 50 hours in the future time frame.  The higher resolution models, with the exception of the NAM NEST, only predict 36-48 hours in the future.

These things are tricky to forecast.  In our area, the models tend to under-predict the duration of the mix precip.

Stay tuned.

 

Winter Weather

WEDNESDAY WEATHER UPDATE

[su_note note_color=”#defcdc”]Update Tues 9:45PM: The latest NAM data suggests that a wave develops along the front, increasing the precipitation and delaying the end of the snow.

Current QPF  values have increased to 0.35 inches water equivalent during a time when the precipitation type will be snow. Using my own method and accounting for melting and warmer ground temps, it seems that about 2 inches of snow are possible.  Snow flurries and showers may linger until 10-11AM.

10 :15 PM Update: The NAM built-in snow algorithms show less than 1 inch of snow. The latest WRF models are closer to the NAM, so my 2 inch total isn’t supported by the built in algorithms. We’ll see what happens.

10:45 PM Update:  Latest GFS doesn’t show the enhanced precipitation nor does it delay the snow ending. It maintains a snow total of about 1/2 inch.  [/su_note]

I’ve had a chance to review the afternoon model runs.  Both the GFS and the NAM still predict just a coating (0.30 and 0.50) of snow falling after midnight and ending about 7-9 AM, based on their built-in snow algorithms.

As mentioned in my previous post, using my old, time-tested (but not always accurate) NAM FOUS data technique, I’m coming up with 1.5 to 2 inches of snow.

I’ve never been a big fan of the built-in snow depth algorithms.

Interestingly, this afternoon’s Canadian High Resolution Model (HRDPS) has been consistently predicting ~1.6 inches of snow.

The latest RAP (Rapid Refresh) just available shows 1 inch of snow and ends with light flurries about 9 AM.

So it will be interesting to see how things turn out.    I’ll be looking at the NAM data which comes out about 9:15 and the NAM FOUS data which becomes available about 9:35 PM tonight.   Check back later for an update.