Thundery and mild tonight – December reality returns on Monday

Our mild weather is coming to an end in the next 24 hours as rain moves in followed by cold.  A lot of uncertainty in the longer range outlook for late this week right through Christmas Eve.  Monitor later forecasts as this is a big travel week.

Outlook

Into tonight….Continued mild with increasing clouds.  Band of showers arrives KC late evening and STL/SEMO/SW IL overnight.  Could be some rumbles of thunder. Temps hold nearly steady or only fall slightly…rain becomes more showery for KC after midnight into the early hours Monday.

Monday…Rain chances wind down to drizzle by mid morning in KC.. and by afternoon for STL/SEMO/SW IL.  There may be some spot showers in KC during the afternoon as cold air rotates over the area. Becoming breezy and colder after a mild start.  Temps in the 50s early will fall. Mid 40s or lower likely by sundown.

Tues-Thurs…Back to “December reality” with highs in the mid 30s to around 40 and lows in the 20s. A weak upper level system could bring some light snow or flurries north or light rain/flurries south..but not expecting any major issues at this time…due to dry low level air.

Friday..Sunday…Temperatures remain near average for later December with 30s-near 40 for highs and 20s for lows. Questions arise with next Pacific storm and track of upper low.  U.S. model prints out some snow.. The Canadian dissipates the low with emphasis on a later system. The operational European model swings the storm far to our south.. and brings big snows to Memphis/ Nashville/ Cincinnati corridor with another big snowmaking Nor ‘easter for DC/NYC/Boston.  Essentially to early to call a definitive track, but something to keep an eye on since they’ll be a LOT of holiday travel regionally and nationally.

Christmas Week…Seasonable temperatures expected to continue (30s/40s and lows in the 20s). We’ll have to watch a system forecast to make landfall in CA NEXT Saturday.  Where that system tracks very much up for grabs.. timing could bring it somewhere nearby around Christmas. This system is at the outer edge of our numerical prediction models.

Rainfall on the way…

This afternoon we have a very wrapped up Pacific storm over the High Plains.  The visible satellite/radar image shows a band of showers and thunderstorms from central OK through S to NW KS.  Note it is a pretty narrow band.  Snow is falling behind a cold front over NE CO and that will spread into western NE this evening.  The clouds have thinned locally, allowing temps to rise well into the 60s.

2014-12-14-1425-SATSFCRAD

The water vapor channel shows the classic “comma” shape of the storm with the moist air (purple and blue) wrapping into the storm to the north and east and the dry air (orange/gold) wrapping in from the south and west.

2014-12-14-1426-SATSFCRAD

The high resolution guidance shows rainfall amounts look to be variable and moderate at best.  The heaviest amounts are expected west, with decreasing amounts to the east.  The high resolution rapid refresh (HRRR) model only goes out to 5AM Monday (right) so it does not capture rain for SEMO/SWIL/STL completely. On average 1/4″ should be a total for most areas, with localized areas up to 1/2″ and isolated spots west under the heaviest showers 1″.  With the warmer temperatures, there could be some thunderstorms in the mix as well.  Severe weather is not expected.

2014-12-14-1426-18ZNAM433 2014-12-14-1426-19ZHRRR15

Rainfall to date: SEMO/SW IL running below while the I-70 corridor has done much better

Let’s take a look at where we stand in terms of 2014 rainfall to date.  St. Louis is running a surplus of nearly 3″ to this point in the year, while KC is running a surplus of just under an inch.  STL/KC have both exceeded their average annual rain, so there is no way either location can come in anything less than above average for 2014, even if no more rain/snow were to fall through New Year’s Eve.  For KC, this represents the first time since 2010 that the city will record an above average year.  SEMO/SW IL have had a much different year — thanks in part to several heavy rains in October bypassing the area.  Farmington is running a 7 1/2 inch deficit. Yearly rainfall in Farmington around 43″ with just over 35″ so far.  It would be unlikely for 7″+ of rain to fall there by the 31st.  Farmington is well above the driest year (1953) when just over 24″ of rain fell.  Click on any of the graphs to make them more readable.

2014-12-13-0808-LSXACCRFL 2014-12-13-0808-FAMACCRFL 2014-12-13-0808-EAXACCRFL

Mid to late week:

Behind Monday’s rain we’ll be watching another storm system expected to track from the SW through the central and eastern U.S.  Temperatures will be colder, and some snow may be an issue.  There is currently not a lot of agreement either within the individual models or between the differing models on what will take place.  When dealing with snow, a good indicator of where it will fall is the track of the low just over half a mile up.  Snow tends to fall along and north of the track of the low aloft.

The following maps are posted with LOW confidence in any one solution vs. another; we’ll get a better idea of where things are going early this week.

The higher resolution GFS tracks the low from Colorado through the Panhandles, Oklahoma, then through southern MO and W KY.   That produces some light-moderate snow for the district.

2014-12-14-1120-12ZGFXSNW

The old standard GFS model tracks this low along the I-44 corridor with the most significant snows along that area.

2014-12-14-1120-12ZGFSSNW

The Canadian model really has no defined low aloft, and the only snows it sees are from a weaker mid week system.

2014-12-14-1332-12ZECM132

The European model, on the other hand, opts for a track from the Gulf Coast through the Southeast. This brings the TN and southern Ohio Valley big snows and bypasses the district.

2014-12-14-1120-12ZECMSNW

Just as an FYI and for a ‘behind the scenes” look at some of the data examined when making a long-range forecast. There was a FB post this morning showing how one model’s ensemble projection for potential snow through Christmas Eve.  What you see here are ensemble snow forecasts for the Midwest. In addition to the deterministic –or official run– of each computer model, there are 51 different “versions” (called members) of that run and one control version of this model. They are all run using the same data at start time but are each run with slightly different equations. Doing this yields an average of all the versions in addition to the official version.

Take a look at how the different members all play out snowfall accumulations through Christmas eve.  You’ll notice some have heavy snow south of us, others north. Still others have no snow and a few give us a bull’s eye.  The fact that they are all so different, means it’s unwise to treat this run of the model with anything but low confidence.

2014-12-14-1450-12ZEPSSN1  2014-12-14-1450-12ZEPSSN2

If you average all 51 solutions together, you get an “ensemble mean”, showing areas more likely to see snow and areas most likely to see more significant snow from this ONE model run:

2014-12-14-1450-12ZEPSSNM

This one model run seems to focus on southern reaches of the district. Again, what you’d want to see is some sort of continuity from one run to the next of this model and between it and other models.

 

There is also a “control run”, which is just one member run on kind of a “default”. Don’t read into this chart as an absolute, it’s just used as an example.

2014-12-14-1450-12ZEPSSNC

When all the members are vastly different, we have lower confidence that the event will occur, when they are more or less similar, the confidence is higher.. What we need to see in the days to come would be ALL of the data continuing to argue in favor of this solution to have higher confidence in the possibility it will occur. Right now, with the holidays 10 days away, just something to keep an eye on. Again..there is LOW confidence in any one solution or in one model over another at this point.

Christmas Week: Something to keep an eye on but details far from clear

Below are three forecasts for the weather chart at 6 AM Christmas Eve morning. All three show some degree of a weather system in or near the central U.S., from along the Gulf Coast (European) to in the Great Lakes (Canadian) or the Tennessee Valley (U.S). Taken at face value the European version would have us under increasing clouds Christmas Eve morning with temperatures in the 30s..while the Canadian model would argue for windy and cold with scattered flurries and finally the U.S. model would being accumulating snows.

2014-12-14-1332-12ZECM240 2014-12-14-1332-12ZGEM240 2014-12-14-1332-12ZGFX240

It should be noted these are all at the furthest point these respective models are run to (240 hours from 6 AM this morning – or 10 days). This possible system evolves from an upper level low expected to reach southern California NEXT Saturday. That system is currently just a vortex or spin in the atmosphere on the southeast coast of Siberia near Vladivostok, Russia.  This area will go through a lot of changes between now and reaching southern CA (if it even does) so in addition to the question of whether or not the system will even exist, there is the potential for it to slow down or track somewhere else completely.  Since it is Christmas, we’ll keep monitoring the outlook in the coming week and this is currently JUST SOMETHING TO BE AWARE OF as you make holiday plans.  Unlike the outlook for Thanksgiving from 10 days out we can’t say with much certainty that there will be dry and calm weather, at least not yet.

Return of the Chill

Long-term charts are now picking up on the change in the pattern Christmas week, as the flow which has contained the cold in Siberia and across the Pole begins to change.

Current charts of 5,000 ft temperatures show the coldest air from Greenland through north of Alaska and into eastern Siberia. Mild westerly flow has kept temperatures warmer than average across western Canada.

2014-12-14-1542-12ZEC850M

By Christmas eve, we can see cross-polar flow beginning to develop with the cold air rebuilding south into Canada as northerly flow begins to replace the mild Pacific flow.

2014-12-14-1542-12ZEC850F

Although temperatures will return to December averages this week, the true cold air won’t arrive until Christmas or New Year’s week as it appears right now.

We’ll update the rain totals, and the lead-up to Christmas forecast Monday.

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