Why The Abrupt Cooler Pattern in the Northeast?

After the warmest April on record in places like Cleveland, Ohio and across much of the Ohio Valley and much of the eastern US, the pattern has not only reverted back to spring, it took several steps back resembling elements of winter. Throughout April, this high pressure ridge stayed east which allowed the ridge across the eastern US to build allowing above normal temperatures. Many were fooled into thinking that summer was here and we were in the clear to plant gardens. Not so fast!

Look at April temperatures versus the 30 year average:

Now look at the first week or so of May per the American model (GFS).

Why the sudden flip?  In this case, we have to look over Greenland for the answer.

Remember that across the mid-latitudes, troughs and ridges (valleys and peaks in the upper levels of the atmosphere) travel like a fluid through the atmosphere. When one location is lucky enough to be blanketed by a ridge, fair weather typically is the result. Once the succession of trough and ridges is changed by an interruption in the wave pattern, the weather will change at the surface. These changes (too much to go into here. See Southern Oscillation Index) often originate over the Pacific Ocean and propagate east. Currently, these changes are reflected over the northern Atlantic and Greenland.

Notice the red (high pressure) at the top inching west blocking/stalling the blue (low pressure systems) over the NE

We can quantify the strength of this ridge using the NAO of the North Atlantic Oscillation.  The more negative the index goes, the stronger the Greenland ridge. The NAO has been forecasted to drop close to -300. Historically this has only happened once in the month of May since record keeping began.  That was back in 1993.

NAO drops to -300 soon

But be warned, historically, this pattern over Greenland in May doesn't always produce a cold and rainy May. Look at the high temperatures in Cleveland during these years of record low May NAO:

Look at the resultant upper level pattern across the US in each of these years. All but 1948 and 2008 show dominant warmth.

May 1948 - DOMINANT COLD OVER GREAT LAKES/NEW ENGLAND

MAY 1951 - WIDESPREAD WARMTH ACROSS US. COLDER SOUTHWEST

MAY 1962 -  WIDESPREAD WARMTH ACROSS US

MAY 1980 - WIDESPREAD WARMTH ACROSS US

MAY 1993 - MORE US WARMTH. COLDER DEEP SOUTH

MAY 2008 - MUCH OF US BELOW NORMAL

The NAO this low (or any other index) isn't always a great predictor of temperature and the overall pattern. 

Unfortunately, unlike any of the previous instances of strongly negative NAO in May, this cold is locked in for at least another week.  So get ready for rain, scattered frost and perhaps some light snow!

5 Distinct Snow Makers This Week

Coldest air of the season Friday and Saturday

Snowfall forecast by Thursday early afternoon

Winter Pattern Unrelenting: More Arctic Cold

Our winter weather outlook back in late October featured a below normal temperature (much colder winter) with above average snowfall.  Given the weak central based El Nino, cool pool in the northern Pacific, warmer west coast and warmer east coast, a stronger southern jet stream phasing in with the polar jet to the north driving big snowfalls from nor'easter type storms in New England shouldn't be surprising.

The areas of the ocean that went into our winter outlook are circled in red. All pointed to colder than normal temperatures in the east.

This is different from last winter when the warm west coast cool of ocean was located in the north central Pacific near the Gulf of Alaska. The central based El Nino (Modoki) hadn't developed yet.

I want to emphasize that these warm and cool pools aren't and weren't the only drivers of our last two winters. But they are significant. Here was our initial best match as we formulated out winter weather outlook (December through February temperatures) back before Halloween.

The overall pattern remains very cold. More cold this weekend--Polar Vortex type cold!

Well below zero across much of the northeast Friday and especially Sunday morning. Even Florida will see lows in the 20s Sunday morning (February 16th) from Jacksonville to Pensacola. The orange crop might take a hit!

Below zero wind chills will reach northern Georgia and the Carolinas with -20 to -30 chills across the Great Lakes.

Here we are in mid February when the cold usually starts to retreat as the first pushes of spring emerge across the deep south. Will the cold air break sooner or later?

The often overlooked Canadian model shows the trough east/cold east continuing through the end of the month. The other models show this too.  However, the trough is retrograding back west a bit. This would shift the cold into the Great Plains by the end of February.

Cold Pattern thru end of February

In droughts, extremely hot conditions will feed off of the extremely dry air above the dry ground. This creates more evaporation which feeds the heat. This chain reaction is very hard to break. In perpetually cold patterns like this, the drivers are very strong and very difficult to break. The cold air can feed the upper air pattern reinforcing the trough in the east and cold/ridge and warmth in the west. In essence, the overall pattern remains stuck.

Good news is that heading into March even during the coldest Marches in Cleveland, 60+ degree warmth shows up by the middle of the month.

That said, the southern branch of the jet becomes very active in March. This could lead to a few more panhandle type storms in March which always have potential for reach Ohio.  Stay tuned.

Which Decade Had The Most Snow?

So which decade in northern Ohio had the most snow?  Try the 2000s not the 1970s as many believe.

How about daily 6 inch snowfalls per decade?

Don't Be Fooled. Lots of Winter Left!

Winter arrived very early this year across much of the US. Per NOAA, the average contiguous U.S. temperature was 39.3°F, which is 2.4°F below the 20th century average. This ranked as the 16th coldest November in the 1895-2014 record, and was the coldest November since 2000.

US snowcover for the month was the most since 1966, a 48% increase from last (2013) November's snowcover.

November temperatures in northern Ohio were the 8th coldest on record at 37.1 degrees with a stretch of 9 days below 40. November snowfall was the most since 1996. We are ahead of last year  when we count days with at least ONE INCH of snow cover at 12 (only 9 as of Dec 9th last year).

Many people falsely believed that the arctic cold would continue into December. Look at the top 16 coldest Novembers (16th is this year) in the chart below. Then look at the Decembers that followed. The temperature ranks are no where as cold relative to normal. The Decembers that followed had an average temperature rank of....48th!  Only 2 cracked the top ten coldest.

Here is a comparison of November vs December through the 9th.  December temperatures are not as cold relative to normal. The coldest air has lifted back into central Canada.

So what does this mean looking into our winter future?

All of the factors that went into our winter weather outlook are still present and valid. Nothing has changed.

1) Central Based El Nino has developed or is developing depending on which index you use. This central based Pacific El Nino favors colder than normal temperatures across the eastern US. Note the warm pool along the equator and the smaller cool pools flanking it. The cool pools are indications of a Modoki along with warm pool extending along the west coast of North America.

Are their similar years to what we see above?  Yes.  Below is a blend of those similar years. The scale is a bit different but the warm and cool pools are in similar locations and intensities. They're not exact matches but they are close.

2) Warmer than average water off of the west coast along with the cool pool north of Hawaii strongly favor ridging in the western US, troughiness in the eastern US. The Pacific North American Index (or PNA Index) measures this tendency. In most Decembers where the PNA is more than +1, the temperatures across the eastern US are usually below normal.

 The forecast continues to favor a POSITIVE PNA into mid December.

3) The wild cards are always how the Arctic and North Atlantic will behave.  The Arctic Oscillation and North Atlantic Oscillations are indices that measure changes in the pressure patterns over each location. The AO is more of a player earlier in the winter, the NAO during the second half. If the indices are negative, the pressure patterns favor a more variable jet stream with a tendency for more cold air outbreaks.

4) The QBO (another wild card), read about it here, are stratospheric winds over the tropics which alternate direction easterly to westerly every 2 years. These easterly winds have been shown to disturb the Polar Vortex over the arctic making it more unstable. The propensity for cold outbreaks is higher across North America but not guaranteed. We monitor warming in the stratosphere over the arctic. Sudden warming can be a sign of a weakening of the jet stream and colder outbreaks. A good description of these warming events is on this site. Check out this site for more on Sudden Stratospheric Warming events and their potential effects on our winter weather.

Each one of these variables should not be overstated. One factor doesn't make-it or break-it. Our outlook is a blend of the combined influences that each one of these variables bring to the table. All told, our Winter Weather Outlook from early November still stands

HERE IS THE LINK

ABOVE NORMAL SNOWFALL AND BELOW NORMAL TEMPERATURES FOR NORTHERN OHIO FROM DECEMBER THROUGH FEBRUARY.

Huge Changes - CURRENT RADAR LOOPS and OHIO TEMPERATURES

CURRENT RADAR LOOPS AND CURRENT OHIO TEMPERATURE, TEMPERATURE FORECAST THROUGH SATURDAY MORNING



Current OHIO temperatures


Current Ohio Valley radar loop


Temperature forecast for this afternoon...70s...dropping into the 50s...40s by early morning.

Huge Temperature Changes...Severe Weather Possible

It's not all that unusual to see large temperature changes driven by strong cold fronts this time of year. Even though it is technically still summer, the sun isn't as strong as it was in early August. The early pushes of cooler air are becoming stronger and larger in extent.  The polar jet stream is starting to become a more dominating force driving mid latitude systems the US and Canada much faster and with more punch. The front forecast to push through the Great Lakes late Wednesday/early Thursday is a prime example.

HUGE temperature contrast along the front.

Incidentally, last year almost to the day, we had a similar cold front and huge temperature contrast. We went from 96 and 95 to 62 in under 48 hours!

Atmosphere is very buoyant.

 Precipitable water values are well over 2 inches!

 

Jet stream winds are very strong. Right-rear quadrant of the jet streak (diverging air aloft) over the mid-west will enhance the severe storms as they pass over Indiana and western Ohio.

Storm Prediction Center continues to show a slight risk for severe storms into northwestern Ohio for late Wednesday and early Thursday.

At this writing, line of storms should pass through northern Ohio between midnight Thursday and Thursday at 6am.

Temperatures will fall into the upper 50s and lower 60s Saturday.

The cool push of air is very strong and will envelop the northern 2/3rds of the US.