Clouds continue..rain early next week

We continue to be stuck in the grey overcast and those clouds aren’t going anywhere for long for almost the entire forecast period.  The good news is our warming trend is still expected this weekend, but we would be downright mild if we were able to lose the overcast.

Outlook:

Friday…more grey on tap but temperatures begin to moderate.. 40s to near 50.

This weekend…Lots of clouds but temperatures much milder.. mid to upper 50s. Rain holds off until Sunday overnight or Monday.

Next week…Wet weather opens the week, how much rain still open for debate.  Seasonably chilly to follow.. clouds may still be tough to get rid of.

Everyone is tired of the grey skies, and you don’t have to go far to see sunshine, but that direction is up.  The overcast is only anywhere from 3,300 feet in Topeka to around 6,000 feet deep in SEMO/SW IL.  Above that layer of clouds skies are clear. Take a look at the weather balloon sounding from the upper air station of Topeka KS. The red and green lines track temperature and dew point as the balloon rises and provide us with temperature and humidity readings (among other things) aloft.  On the chart, left is cooler/drier and right is warmer/wetter. Note how the lines are together in the lowest part of the graph.  That represents saturated air and cloud cover. Note also how the lines quickly separate leftward (green-indicating much drier air) and rightward (red-indicating warmer air) just over 1 KM (3,300 feet). The increase in temperature as you go up is called an inversion (warmer air over colder air) which is opposite of the typical setup (cooler as you go up). Inversions can be very stubborn to get rid of.  On the right side of the chart you can see the wind barbs, and you can see how light the winds are all the way up through the atmosphere. That means there is little there to mix the drier warmer air aloft into the cooler, moist air below.  Mixing is a good way to break down an inversion and clear out low clouds in this type of situation. Unfortunately, this does not appear to be likely the rest of the week.

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The mid day satellite image shows the low clouds very well across the Plains and Midwest:

2014-12-11-1146-SATSFCRAD

Where’s the cold air?

This morning’s charts show a surprising lack of Arctic air over North America.  Temperatures below zero are limited to the north slope of Alaska, Nunavut, the NW Territories and northern Yukon.  A small area is over northern Quebec as well.  20s, 30s and 40s are common for most of Canada southward into the U.S.

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Eastern Asia remains the one area which is suffering the true brutal Arctic chill in the Northern Hemisphere.  Readings are -30 to -50 over central and eastern Siberia.  Western Siberia, and Europe are seasonably cool but no more so than North America.

2014-12-11-0909-06ZGFSASA

What we’ve seen recently and continue to see for now is a very stable overall weather pattern.  A deep cold vortex is over eastern Siberia and is being blocked in place by an upper high southwest of the north pole.  That combination funnels the coldest air around the upper high and upper low over Eurasia.  Some cold peels off and heads through far northern Canada.  South of the big upper low, a stable and strong upper high is found over the subtropics. The Jet stream is funneled between the upper low and upper high across the Pacific at high speeds.  The jet slows down and becomes a little more wavy as it approaches the west, coast, but the overall pattern features a semi-permanent low in the Gulf of Alaska.  That low helps to feed mild Pacific air (off of the warmer than average ocean) into western Canada and the western U.S.   Each “ripple” or wave in the jet stream represents another Pacific storm system. Currently, in addition to the one on the west coast, there is another near the Dateline and a third just north of Japan.

2014-12-11-1128-NORPAC500

This pattern has brought the “Pineapple Express” to the west coast.  This is a phenomenon where tropical moisture is drawn up from the Tropics near Hawaii and arrives on the west coast bringing heavy rains and frequent storms. This graphic showing the amount of moisture through the depth of the atmosphere available to produce rain.  The channel of moisture to California from Hawaii is easy to see. Also easy to see are the storms shown in the graphic above; each one has a connection to the deep tropical moisture.

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The latest Pacific storm is now just offshore. A part of that system will bring our next chance for rainfall.

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Rain system for early next week

Part of that Pacific storm is slated to bring the next chance for measurable rain to the region, but not until early next week.  The mid to upper level center is forecast to track very close to the region and that always is problematic for rainfall totals. Rain is likely, but how much remains in question. With cool season weather systems there are often two areas of significant precipitation; one to the north and west of the mid to upper level center called a “deformation zone” and the other to the east and south of the center associated with warm air wrapping and lifting into the center of circulation.  There can often be an area of relatively light rains between these two areas – or even a complete break. Sometimes a big thunderstorm complex can intercept the moisture flow in the warm air wrapping into the system and leave areas downstream moisture starved.  That’s the issue we’re dealing with now.  2 of the 3 models available for the time period in question develop big thunderstorm complexes in the ArkLaTex region which cut down measureable rain for a part of the district.  Placement of this (or even the existence of) the thunderstorm complex will change in the coming days, so rainfall amounts of 1/4 to 1/2″ look reasonable at this point as a starting point, but confidence in this is medium at best, while confidence in some rain occurring vs none is high.

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Rumors of snow:

2014-12-11-1317-12ZECMTSN

One of the major computer models brings through a follow-up system late next week and the NEXT weekend (Fri 19th-Sun 21st) along a southern track and manages to print out some accumulating snowfall. (White Christmas) This is the first time this has shown up in this model and no other model shows this solution so there is “zero” confidence in this right now, but it does look interesting nonetheless. It also highlights the beginnings of a possible pattern change. Chances are it is a phantom storm and will be gone by tomorrow.

Weather Event Impact Matrix:

Last year we had the winter storm potential index, which rated the chance for a significant winter storm within the next 7 days which would produce 4″ of snow or greater or 1/4″ of ice or greater within the next 7 days. The issue was that risks could be different for varying parts of the district and the index didn’t communicate the confidence (likelihood) and impact an event would have.  This year we’ll simplify things a bit.

The grid below is a Weather Event Impact Matrix. Bottom to top on the left side is the confidence (ranging from very low to high) while below the grid from left to right is the impact the possible event may have (also from very low to high). Each potential incoming event would be rated using those criteria.  For example a high confidence in a low impact event (such as light snow) would be something to just be aware of – not need to get prepared for well in advance. On the other hand, a medium confidence in a high impact event (such as a major snowstorm) would be something that getting prepared for would definitely be warranted. When there is a high confidence in a high impact event, its time to take action.

THREAT MATRIX

Weather events this will be used for include heavy snow, freezing rain, heavy rain, high winds, wind chill or extreme cold. There is also a more generic “winter storm” when heavy snow and heave ice are expected. When multiple threats exist, only the highest impact weather will be shown. When different areas of the district are to be impacted in different ways, again, only the highest impact weather will be shown. Which areas are threatened will always be discussed in the blog or post.

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