Cold Again Tonight, January Thaw Next Week?

After a cold start to 2013 temperatures look to rebound later this weekend and next week.  That said the cold Wednesday, Thursday, and Friday morning will be bitter.  Overnight low temperatures fell into the single digits for much of Central and Northern New England.  Some places in Maine fell as much as 10-15 degrees below zero
Northeast Temps, 1/2/13 7 am EST (1)
The EURO overdid the cold just a bit and the GFS and NAM were too warm.  Temperatures this afternoon should moderate to the mid 20's under mostly sunny skies.  There will be light winds so temperatures will feel like the upper teens/lower 20's.  By tonight the mainly clear skies will allow for rapid heat loss to space.  The NAM and GFS are warmer than the EURO and the EPS, so I'll balance them.  Tonight temperatures should drop close to zero for much of Central and Western MA.  Some locations in Metrowest and Merrimack Valley will also approach zero.  Here is the EPS for the 1 AM to 7 AM period tomorrow morning
EURO ensemble 1/2/13 00z run (2)
The GFS citygram for Worcester shows
1/2/13 06z GFS citygram Worcester (3)
This likes temperatures to fall to about 4 degrees overnight but then one can see the warm up.  So how does one get cold temperatures like this?  As always we will start at the surface and work up in the atmosphere.  Remember that we measure height in the atmosphere with units of pressure.  For example the surface is usually 1010-1015 mb but we will use 1000 mb.  850 mb is approximately 5000 feet up, 700 mb is 10,000 ft, 500 mb is about 18,000 feet and 300 mb is 30,000 feet (jet stream).

Surface analysis 7 am EST 1/2/13 (4)
High pressure in Ontario is helping to push cold Arctic air into the Northeast.  A weak Arctic front is going to push through the region today which will re-enforce the cold tonight.  Here is the 850 for 7 PM tonight
temperatures at 850 are forecast to be below -10 C (5)
At 500 mb
ridge is pumping in the west, trough digging in the east (6)
And at 300 mb
jet streak with winds in excess of 150 MPH (7)
I use 300mb in winter and 200 mb in summer due to the atmosphere being more dense in the winter time in the Northern Hemisphere but either one would work for a forecaster.  Analyzing these trends I expect the coldest temperatures to be Indianapolis to Cincinnati Harrisburg then diagonal to NYC.  This is because the jet seperates the warm air from the cold air.  When it has a 150 mph streak (purple) the gradient is strong.
The data supports temperatures near zero.

The jet will play a role in our pattern going forward.  Since the winds are strong to the right of the Midwest trough and strong to the left of a trough over the Atlantic the Midwest trough will weaken and lift north while the trough over the Atlantic will strengthen and move south.  During this process a ridge is likely to develop over the east US in time.

By Friday Night here is the EURO 500 mb
1/2/13 00z EURO valid Friday 7 PM EST (8)
At 850 mb
1/2/13 EURO 850 valid Friday 7 PM EST (9)
This is a fast pattern with lots of smaller scale features moving across the United States.  A couple of days in the 30's look good early next week.  However predictably is low
Relative Measure of Predictability (10) Day 5
Temperatures in the 6-10 range look like this, according to the CPC
CPC 6-10 (11)
Certainly the 6-15 day range will be above normal with temperatures.  There is still quite a snowpack so its possible the warmth is overdone a bit.

Rather than re-write the blog I should mention that the latest American GFS is coming in and has let up on the warmth this weekend.  So while temperature will not be approaching zero it will still feel like January

Pictures 1, 2, 3, 8, 9 courtesy of Dr. Ryan Maue and Weatherbell a premium weather site
Pictures 4,5,6,7,10,11 all available through US government agencies free for all


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