Archive for March, 2013

NOAA issues spring 2013 outlook
March 24, 2013

By Meteorologist Mike Skurko

This past week NOAA released their Spring Flood Risk Assessment, as well as their 90-day Temperature and Precipitation Outlook for the spring season.

New England has not been identified as being at-risk for significant, widespread flooding this spring.  Heavy rains and/or a drastic snowmelt from a sudden warmup can both cause flooding and flash flooding at any time during the spring season.  However, the map below shows that New England is not expected to be a target for predictable, major flooding compared to other areas of the country.  For example, a deep snow pack in North Dakota means certain areas “have a 50 percent chance of rising approximately two feet, which would flood 20,000 acres of farmland and roadways.” according to the NOAA report.  Such dire conditions are not likely for New England.

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Good news for temperatures this spring, as NOAA predicts above-normal warmth from April to June.  The dark orange regions on the map below (which includes western Massachusetts) represent a 50% or greater probability of above-average temperatures over the next three months.  The Climate Prediction Center has cited a neutral El Nino/La Nina pattern, sea surface temperature anomalies warming up and getting black closer to average from the winter, and drought across 51% of the country to attribute to their 90-day temperature outlook.

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Above-normal precipitation through the northern Great Plains and Great Lakes region should help ease drought conditions across the northern Midwest.  However, generally drier conditions predicted for much of the South will lead to persistent drought from Texas to California and much of the West.

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NOAA’s full report can be found here.

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Major snow for eastern Hampden County
March 8, 2013

By Meteorologist Mike Skurko

Snowfall predictions for the immediate downtown Springfield/Holyoke/Northampton corridor were pretty accurate, with about 2 slushy inches reported in these locations through early Friday morning.  A half-foot of snow for the eastern slopes of the Berkshires/hilltown was also pretty accurate, with Chester and Huntington reporting about 7 inches of snow.

However, residents of eastern Hampden County … Ludlow, Wilbraham, Palmer, etc … were unpleasantly surprised with nearly a foot of snow early Friday morning, more than double what was anticipated for those eastern locations.  This very finicky storm produced a wide variety of snow bands, with the heaviest occurring through eastern Massachusetts.

Below is our Pinpoint Doppler radar’s “Snow Vision” which is the radar estimated snowfall amounts for this storm.  Two things are clear … eastern Massachusetts saw the widespread heavy snow, some of which sneaked into eastern Hampden County, while the Interstate 91 corridor just had a minor little snow event to deal with.  The cutoff was very drastic.

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As moisture continued to move in from the coast, the cooler air inland helped create these heavy snow bands across eastern Massachusetts.  Topography is a very likely reason for the significant accumulations sneaking into eastern Hampden County, but dropping off rather quickly for the downtown Springfield/Northampton areas.

Most of us are more familiar with the setup for the hilltowns … those higher elevations and cooler temperatures will likely generate more snow for a given snowstorm.  As the air lifts up over the Berkshires, that lift helps enhance the storm clouds over these locations and squeeze out more snow (meteorology 101: rising air = low pressure = cloud development … sinking air = high pressure = calmer weather)

For Worcester County, that phenomenon also occurs.  Below is a topography map showing the elevation changes across western Massachusetts.  For a storm moving on shore from the east, the moisture moves past the coastal plain and is lifted up into the higher elevation of Worcester County.  This will enhance (or at least help keep together) those snow bands and continue carrying them to the west.  After depositing it’s snow in our eastern towns, it dies out.

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This radar image is from 7 AM, but this situation was occurring a lot throughout this storm, even more dramatically than usual … the dark blue (heavy snow) appeared on the radar across eastern Massachusetts into Worcester, sneaked into eastern Hampden County, and then sharply dropped off immediately to the west.  It then picked up in intensity a little bit again as it started its climb back up the eastern slopes of the Berkshires.

The slow-moving/stalled-out nature of this storm system allowed this pattern to continue throughout the night and this morning, which then continued to exaggerate the wide discrepancy in snowfall for Hampden County over such a short distance.

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Delicate nor’easter setup provides tricky snow forecast
March 7, 2013

By Meteorologist Mike Skurko

This has been a very tricky snowfall forecast for New England, one that continues to bounce around the expected snowfall totals.  In the last few days, we’ve seen everything projected from a total miss to over a foot for parts of Massachusetts.  The reason for this is because two systems will delicately work together as one … but no one, not even the computer models, are 100% sure exactly how these systems will help strengthen one another.

First, the basic setup: A low pressure system spinning offshore will throw bands of snow at us, with wind gusts coming in from the northeast … a classic, but not overly strong, nor’easter.

Here’s the tricky part: An upper-level disturbance, known as a shortwave, will come diving down from the Great Lakes tonight.  These shortwaves are very tough to forecast an exact track/strength for, as it is not a surface system.  This shortwave is expected to help tug the coastal system back towards the coast … helping to draw in more moisture back towards us from the Atlantic.  What remains uncertain is the exact implications of this, exactly how much this would help strengthen the storm.

Take a look at the maps below.  The first group is the ensemble (“average”) model for that upper-level shortwave at 1 a.m. tonight, right during the middle of our expected snow.  The top image was for the computer model run late last night, the bottom image was from the model run this morning just 6 hours later.  Generally speaking, they line up closely with one another.

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Now, here is the expected precipitation and pressure map for 1 a.m. late tonight as well.  The top image is the first model run, the bottom image is the second.  They are also very similar … with a surface pressure of 1016 mb passing right through western Massachusetts, light and heavy precipitation distributed in the same places, a red 540-line (roughly the rain/snow line) right through the Cape, and a 996-mb low pressure center just off the image frame.

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Together, these two computer models that were run just six hours apart would suggest relatively the same snowfall totals, right?  Well take a look at the next set of maps.  These are the probability maps of 4+ inches of snow from 7 p.m. tonight to 7 a.m. Friday.

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The first model run has put a 65% chance or better for at least 4 inches of snow across the Berkshires, Worcester hills, and the Interstate-95 corridor southwest of Boston.  The second model run has spread that 65% chance all over western Massachusetts.

What is certain now is that nothing is certain.  Most snowfall forecasts have been like the first run above, with 4 or more inches confined to just the hilltowns.  However, it’s model runs like the second that are continuing to provide doubt as to how delicately this storm will act … which is why the snowfall forecast continues to bounce around.  We will have a much better idea once the snow starts accumulating by judging how much is on the ground and at what point in the evening.

Saturday night technical discussion
March 2, 2013

By Meteorologist Mike Skurko

A bit of good news as we continue to monitor the potential coastal storm for Wednesday/Thursday … today’s computer models have now backed the storm down to the south.  The consensus of this morning’s model data seems to favor a more southern track and just a glancing blow instead of a moderate snowstorm.  Here are the same three computer models, same time frame of yesterday’s blog post.  You can scroll below to yesterday’s entry to compare Friday’s maps versus today’s.

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Comparing these maps to yesterday’s model runs, you’ll notice the different location of the center of the low pressure system.  Yesterday’s model runs had the low over the Delmarva Peninsula.  Today’s model runs have pushed it south into North Carolina.  High pressure over eastern Canada is also becoming better defined and sliding a little southward as well, which would help block the storm away from us.

Overall, the chance of a major snowstorm now is much less than yesterday’s forecast.  We’ll still keep snow in the forecast just to stay alert over the next few days.  We’ve seen this low oscillate back and forth over the last few days.  Thursday’s model runs match closer to today’s.  Who knows if tomorrow’s new model runs will move the low back towards us again similar to Friday’s discussion.

February 2013 recap; next snowstorm brewing
March 1, 2013

By Meteorologist Mike Skurko

February 2013 will forever be remembered for the “Blizzard of 2013” that produced around 2 feet of snow across western Massachusetts.  It goes without saying that this has put us well above average for snowfall so far this winter … in fact we have now exceeded our normal snowfall for the whole winter:

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As for temperatures, our average high was 36.5 degrees, which is 2 degrees cooler than normal.  Our average low temperature was 21.9 degrees, which was a degree above normal.  With those numbers being pretty close to normal, I think it’s fair to say this February was seasonal.

Throughout the entire meteorological winter (December, January, and February), high temperatures finished 1.2 degrees above normal, and low temperatures finished 2.6 degrees above normal.  Again our temperatures didn’t do anything too out of the ordinary this past winter.

On to our next order of business … the potential for our next coastal storm system that may provide moderate to major snowfall across southern New England Wednesday and Thursday.  The images below are three different computer model’s projection for 7 pm Wednesday night (GFS, CMC, and ECMWF models respectively).  Images courtesy Penn State Meteorology

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This is still 5 days away, and drastic changes to these scenarios can occur.  For example, some of yesterday’s model runs had this same low pressure system staying about 300 miles south and it’s precipitation missing us entirely.  For the time being, the threat of a winter storm will be featured in our forecast to keep people aware of something brewing for mid-week.  Stay posted!

Update:

Ok … here is a great example of how computer models are going to bounce this system back and forth in the days to come.  The image below is the same model as the top image above (GFS model), but it’s newest update completed just 6 hours after the images above (many models, such as this one, update 4 times a day).  It has this storm missing us to the south again:

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