We’re in for a very quiet week this week, if current outlooks verify, as the long advertised “December break” from the cold really approaches its peak next weekend. We’ll have a bit of a setback early-mid week, but that will be short lived and give way to pronounced warming by late week and NEXT weekend.
At a glance:
Monday.. a little milder with 40s and near 50
Tuesday-Thursday…seasonably chilly with highs 38-42 and lows in the 20s
Friday.. transition to a warmer pattern..back in the 50s
Next weekend.. MILD.. highs approaching or in the 60s
We’ve been stuck in low clouds, fog and low level moisture since late last week which has kept conditions cool, but just to the west out in the Plains where skies have been clearer, it’s actually been quite mild. Temperatures Saturday and today (Sunday) were in the mid 50s to low 60s from western NE/KS into the Panhandles and eastern CO. We’ll have a weak upper level system passing through during the night/early Monday which may squeeze out a spot light shower, but nothing major and no freezing/frozen precipitation issues are expected. Patchy fog might put in an appearance for yet again overnight into the early morning hours Monday.
Since Thanksgiving weekend, we’ve seen a pattern dominate where the Pacific is in firm control of our weather. There has been a “flamethrower” strong and fast jet stream from the Asian coast to almost the North American coast. Wind speeds at around 40K feet have approached 200 mph. This is in stark contrast to the pattern we had in November when a weaker, wavier north-south jet locked in warmth and dryness out west and cold and dryness here. This pattern has brought the heavy rain to CA/AZ/NV and wet storms to the eastern seaboard. This graphic shows the pattern Monday night.
Air flows along the lines in a counter-clockwise direction around the graphic, with the yellows/orange/red/brown totals showing wind speeds aloft of 120 KTS-plus and the cooler blues and greys “lighter” winds of less than 85 kts. Arctic cold is “locked” away from the U.S. by this strong jet stream and is in large part confined to the Arctic circle and especially Siberia. Take a look at the 6AM (central time) temperatures over Asia (anything in the cold grey-green to hot pink is below zero):
Most of Russia east of the Ural mountains is below zero..in some cases -20 to -40. There is no question where the Arctic air is dominating. Now take a look at North America, for the same time, 6 AM this morning (Sunday):
Notice the below zero area is smaller, hugging Hudson’s Bay and then retreating northward into the Canadian Arctic and north Alaska. The deep purple zero degree line is actually far to the north over northern British Columbia, Alberta and Yukon. That’s our source region for Arctic air..and there’s little to be found thanks to that strong and mild Pacific jet. So no worries about Arctic chill this next week or so.
This pattern is very active.. although not for us. Both coasts will get slammed with heavy rains and snows.
The west coast will get another dose of heavy rains. This image is a snapshot of the moisture available throughout the depth of the atmosphere available to produce rain (or snow). Grey, and browns are very dry air while greens/yellows/reds are very moist air. There is a connection of moisture from the depths of the tropics across Hawaii to California. This is called the “Pineapple Express” and is a signature of a heavy rain event along the California coast. That moisture runs into the coastal range and rains out. After crossing the Rockies, pretty well all that’s left are high clouds.
Here’s a look at the 6 day total rainfall forecast, which shows the Pineapple Express producing another 4’+ for northern CA and 1-3″ for the coast from LAX to SFO. You can also see how effective a rain barrier the Sierra Nevada and costal range are with little to no rain forecast by the time you reach Las Vegas or the Colorado River Valley.
Out east.. rains and snows will be the issue with a big snow event possible for the inland northeast including the ski resort areas of NY/VT/NH. Much of upstate NY, ME, northwest MA, and parts of PA will get heavy snow. The good news is that warm Atlantic air flowing into the storm will keep the snows away from the big cities such as Boston, NYC, Baltimore and DC. There may be flight delays, but probably not as bad as if snow were to impact all the big northeast terminals.
For us, these distant weather systems will have indirect influence on our weather. The big east coast storm will be blocked from moving out to sea by stronger high pressure to its north and east. This will cause the big low to spin in place much of the week. That will keep northerly flow nearby to our area and open the door to weak systems dropping through the Great Lakes. Take a look at the upper air pattern late week. You can see how the upper air low is “blocked” from moving out.
That will allow us to experience a cool down Tuesday (to seasonable temperatures) and help keep that cool air around through Thursday. The western system will spill high clouds over the Rockies and that acts to filter the weak December sun and also maintain the cooler air. The net result will be temperatures in the upper 30s to low 40s for highs Tuesday-Thursday and lows in the 20s.
By NEXT weekend, the news is much better. The northeast low is finally gone and the high clouds from the “Pineapple Express” have shifted away. Much of the center of the U.S. is forecast to enjoy temperatures 10 to 30 degrees above average. This would equate to highs from near 60 to in the 60s across the district.
Looking further into the distance, there remain NO SIGNS of any major snowstorm for any part of the district for the next 7+ days or right through Dec 14- nor any major Arctic outbreaks, and right now we have high confidence in the expected weather through then.
The picture gets a little more unclear at mid month. The fast flamethrower” Pacific jet is forecast by most models to break down in this time period. The weather pattern will begin to undergo a transition as the flow aloft slows down and gets more “wavy”. This more amplified flow means more opportunities for storm systems in the central U.S. and more opportunities for cold to return to western Canada and the U.S. Where these storm systems at the surface are projected to form and move and where the upper level troughs supporting them are expected to track will frequently change in the coming week, so there is low confidence in any specific forecast for the week 2 period right now. That’s the reason you may see big changes (from day to day or channel to channel) at the end of the 7-day forecasts you see on TV or online for the middle of NEXT week and beyond as we move through the middle of this week. The expected flip to a largely colder pattern would follow this transition period. Considering that the week 2 period will include the weekend before Christmas we’ll follow forecast trends closely and attempt to identify stable trends (if possible) by the end of the week.
Taking a look back at last week’s rain:
Thursday and Friday’s rains totaled anywhere from .30″ to over 2″ over the district. The highest totals were over SW & south central Illinois from near the Randolph/Monroe county line east-northeast through Mount Vernon and on over into Indiana. The chart below combines radar estimates with ground station reports.
In the district, KC Downtown had the least rain with less than .40″ while Belleville IL the heaviest at 2.29″ of rainfall. All areas got a nice steady rain which will really help prevent the expansion of drought. Here are two close up-maps of the National Weather Service rainfall observation maps. (click to make more readable):
A wider view shows the track of the rain area out of Arizona & New Mexico through a narrow region of the Central Plains and then expanding eastward and southward over the Mid South, Midwest, Ohio Valley, Appalachia and the Mid Atlantic.
Taking a look back to see how well the computer model guidance performed, the 6AM high resolution run of the North American Mesoscale (NAM) model did the best with regards to placement and rainfall amounts, not 100% perfect but not bad either:
It should be noted that prior to Wednesday evening, most, if not all long range models were calling for little if any significant rain last week. That shows how changeable cool season weather can be and that forecasts should be monitored even if through the long range outlooks may be showing a “mild and dry” pattern.