Clouds will stay around…

 

Grey weather will continue through the weekend with milder conditions to start Christmas week.

Outlook

Friday…Fog potential early for KC..otherwise a grey and seasonable day.  Highs in the 30s. Could be a few passing flurries in the south Friday night.

Weekend…Lots of clouds, with perhaps a break or two of sun.  Highs near/in 40s and lows in the 30s.

Christmas Week…Watching and evolving storm system..looks mild with rain to start, colder later.

Christmas Day…Right now it looks dry and cool, but we’ll have to watch trends in the coming days.

Light snow event targets western areas including KC

Our minor storm system played out pretty well as expected for the region, best totals in the west and minor to insignificant totals east.  Here’s the radar/satellite map at 2:40 this morning showing the snow in KC and a burst of snow over SEMO/SW IL. The snow over E KS/W MO would rotate east through that area through the rush hour, while significant precipitation ended for SEMO/SWIL until some wrap around snow showers returned mid to late morning.

2014-12-18-0240-SATSFCRAD

Here is the National Weather Service’s Total snowfall accumulation map. Anywhere in grey had a trace to 2″ while light blue 2-4″. Aqua areas were 4″+.

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Here is a storm total graphic produced by NWS Kansas City MO:

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We’ll compare this to the last high resolution runs of the North American Mesoscale Model (NAM4) taken at 6PM last night (click to make them more readable):

2014-12-18-1134-00ZHRNEAXVER 2014-12-18-1134-00ZHRNLSXVER

Not bad for SEMO/SW IL/STL, where we weren’t by any stretch expecting a significant event, but definitely a little underdone for KC where as much as 5″ fell downtown. The models typically have a tough time when the snow is “convective” or showery in nature as opposed to a larger defined area.

One factor which had to be overcome was a dry layer aloft that we discussed on yesterday’s post.  From yesterday’s post:

“That layer shows up well on the morning weather balloon sounding.  The green line traces the dew point (an indicator of the moisture in the air) and that sharp jag to the left indicates much drier air. With snow events we always have to deal with dry air at the onset of the event, which means some of the snow that falls will evaporate into the dry air before reaching the ground.  This will happen until enough snow evaporates to moisten the layer and allow the snow to reach the ground. In short-duration events like this, that means we “waste” some of the snowfall time moistening up the air which cuts down the snowfall totals.  How fast that dry layer goes away and how much it has changed (shrunk/expanded) since this sensor reading was taken at 6AM will go a long way toward determining snow accumulation.”

Take a look at the weather balloon information from 6AM Wednesday, showing the dry layer and an area of temperatures above freezing aloft:

2014-12-17-1434-SGF12ZUAPLOT

By 6PM Wednesday night, we can see that the dry layer has narrowed and moistened (it does not jag as far to the left).  The layer of warmer air aloft has also shrunk (the slice of the red line to the right of the diagonal blue dashed line.

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Finally, by 6AM this morning we can see the dry layer is gone and the atmosphere is below freezing to the surface where it was 32.  The red and green lines together tell us the atmosphere was saturated (100%) humidity which shows clouds and precipitation.

2014-12-18-0943-SGF12ZUAPLOT

This event produced the first 1″ snow in Kansas City of the 2014-2015 season, which is just 5 days later than the long-term average and was 291 days after the last 1″ snow of the 2013-2014 season.  The average length of time between the last and first 1″ of snows for the season in KC is 277 days.

Minor system this weekend..stays south

Attention now turns to the weekend system. Last weekend into Monday this system was really being wound up in the models as a potentially significant system for the Ohio Valley/Mid South and East Coast. Since then, the message has been clear that this would be a minor system and that message continues today. That’s certainly good news for travel plans this weekend before Christmas. Most (if not all) of the limited effects of this system will go far enough south to bypass the district. We may see a few flurries or snow showers brush SEMO/SW IL, but the latest thoughts keep minor accumulating snows to the south.  This system has essentially become a ‘non-event’.

2014-12-18-1442-EDDPAH48HSNW

48 hour snowfall forecast for SEMO/SW IL

Christmas Day:

Let’s take a look at the available model guidance for 6AM Christmas Morning.  If we accept them at face value, (which is a big risk 7 days out) we can see a storm system of some sort over either SE Canada or the Northeast and a low pressure area of some sort in the Central Rockies or Great Basin.  Relative high pressure is nearby the district.

2014-12-18-1336-12ZECMSLP168 2014-12-18-1336-12ZGEMSLP168 2014-12-18-1336-12ZGFSSLP168 2014-12-18-1336-12ZGFXSLP168

At face value the models would give us this type of weather Christmas Morning:

EC: Dry, temperatures 25-30.

GEM: Dry, temperatures in the 20s

GFS: Dry, temperatures in the low to mid 30s.

GFX: Dry, windy and cold with temperatures in the teens or 20s.

The consensus from this morning’s data would be relatively uneventful weather for Christmas Day with the biggest issues the potential for windy weather (from one model).  We’ll have to watch this however, as we’re on the backside of a strong weather system to our northeast.  If the guidance is too fast on this system, we could see it slow down (often times guidance is initially too fast with incoming systems) which might wind up bringing the system in closer to Christmas, instead of it already being gone by then.  We’ll also see if the projected (now) distant storm remains strong in future model guidance or winds up being nothing much at all. We’re in a changing overall pattern and that has an adverse effect on computer guidance.

Finally, the NWS Climate Prediction Center (CPC) released the January temperature and precipitation outlook today.  An important thing to remember is that this is an outlook and not a forecast.  The CPC just predicts the probability an area will be above/below and not how much above or below. The darker shadings indicate a higher probability of being above/below not how far above/below, no shading indicates there is no strong signal either way.

2014-12-18-1426-CPCJANTEMPRB2014-12-18-1426-CPCJANPCPPRB

The outlook indicates enhanced probabilities of a cooler-than-average January over the district, with the highest probabilities in the west.  There is no strong signal for precipitation, although western areas are closer to a higher probability than eastern areas.

This fits in with the overall pattern forecast to become established after Christmas.  The Greenland Block makes a reappearance along with a ridge over NW Canada.  This will allow an active southern storm track to tap Arctic air which is always an interesting combination.

2014-12-18-1442-12ZECMH500240

 

 

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