Friday, May 29, 2015

Weekend Forecast and General Weather Thoughts

The upper level disturbance that brought a round of severe weather to New England yesterday has moved offshore and it has taken the humidity with it.  It left a mark in Methuen as a microburst (a real confirmed one) with 70 mph wind gusts  uprooted 20-30 trees.
Tree, Utility damage in Methuen, MA (image credit Boston Globe)
Emery Street, Methuen, MA (image credit Morgan Murphy/CBS Boston)
Overall there were many wind reports in New England and even a few hail reports.
5/28/2015 SPC preliminary storm reports
Temperatures this morning are in the 70's, on the way to low 80's inland and mid 70's near the coast.
2 m temps 10 am (image weatherbell)
Here is the surface chart as of 8 am.  Notice the cold front to the south of the region and also the front in the upper Midwest.  High pressure is in control over the interior northeast.  This is temporary
WPC Surface analysis 8 am
 At 500 mb
12z NAM 500 mb vorticity 8 am (image NCEP)

 By later this evening the high will slide offshore and the front from the Midwest will slowly move east.  Dew points will rise into the 60's again tomorrow, but not before a nice evening in which temperatures will not drop out of the 60's in Southern New England.  Up north temperatures will fall into the 50's.
WPC surface forecast 8 PM tonight
As the high moves offshore Southwesterly flow will resume so tomorrow will easily reach the mid 80s.  The atmosphere will be unstable tomorrow but with the front well to the west and temperatures warm aloft (mid levels) it will be difficult to get thunderstorm formation.  A few pop up storms are possible especially in the Northwestern half of New England (if we slice from Caribou to Stamford).  Therefore if you are in the Lakes region keep an eye to the sky especially late afternoon.
SPC Day 2 (Saturday) Thunderstorm outlook

Saturday night is fine as any convection should die down as we lose the heating of the day.  Sunday looks to be unsettled region wide.  While not anticipating a total washout the threat of rain will linger all day and into Sunday night.  Temperatures are around 70 (will get warmer with any breaks of sun) and dew points in upper 50's/low 60's.

GENERAL WEATHER THOUGHTS
As you may have noticed much of Southern New England is experiencing a moderate drought.  Some have asked how is this possible after all the snow this winter?! The answer is that we didn't receive as much precipitation as you might think.  Since it was so cold the snowfall ratio's were on the order of 20-25-1.  That means for every 1 inch of precipitation we got 20-25 inches of snow.  Normally we see a 10-1 ratio.
US Drought monitor, released 5/28/2015 (NOAA)
Yesterday's storms really didn't help much
24 hour observed rainfall (AHPS precipitation analysis)
While a soaking rain is possible on Monday the long term outlook is not positive.  The Climate Prediction Center is forecasting these conditions to continue through August.  Hurricane season begins on Monday so we may have to hope for a tropical system to replenish our water supply.

CPC seasonal drought outlook (NOAA)
Speaking of hurricanes the seasonal forecasts are out and by all reputable accounts we are in for a "down" season.
NOAA, Colorado State, and Weather Channel predictions (image Weather Channel twitter)
 While this appears to be good news the truth is it does not mean much unless you are someone like me who gets excited to track a tropical storm near the Canary Islands.  Given that our already quite low to impacted by a tropical system a down season does not do much to decrease ours odds.  In fact in 1991 which was a down year Hurricane Bob blasted SE New England and the perfect storm battered the coast late in the season.    The reason for the down forecasts? Perhaps you have heard of El Nino.
OSPO Sea Surface Temperature Anomaly 5.28.15
This is a sea surface anomaly chart.  Please notice the red/orange along the equator in the Pacific Ocean near Central and South America.  This is abnormal as usually the warmest water relative to average in the pacific is in the Western Pacific.  Basically trade winds blow east to west across the Pacific.  There are two ocean currents, one on each side of the equator that also flow east to west.  As these currents move west they are heated by the sun and tend to pool water in the West Pacific.   For comparison here is 2013, a "neutral" year
OSPO Sea Surface Temperature Anomaly 5.30.2013
Along the equator there is a weaker current that moves west to east.  At times this current becomes stronger as the trade winds weaken.  The warm water sloshes back east and thus we have an El Nino.  Due to this constant wind the Western Pacific sea surface sits a few meters higher than the east.  This evens out during warm events.  But why does this cause a disruption to the Atlantic Hurricane season?  All the warm water in the eastern Pacific allows for favorable thunderstorm growth in that region.  With all the rising air there it creates a ripple effect of stronger than normal winds in the eastern Atlantic and higher pressures than normal in the Caribbean Sea.  Those factors suppress thunderstorm development.

 WHAT DOES IT ALL MEAN?
It means that we are looking at a warm dry summer!  That's what the odds say.  Every El Nino behaves differently.  A particular interest of mine in college was how El Nino and La Nina's behave.  In 2009
the Pacific was also bringing on an El Nino event.  The summer of 09 was horrible in New England; rain and cool.   The oceans and atmosphere are different this time around so if you work in an industry that is dependent on water be aware that this will likely get worse before it gets better.

Have a good weekend and thanks for reading

-Zack

Thursday, May 28, 2015

UPDATE 12 PM- Severe Thunderstorms Possible Today

 As anticipated, the Storm Prediction Center in Norman, OK (SPC) has issued a Severe Thunderstorm Watch for most of New England (and parts of NY, NJ)
SPC Severe Thunderstorm Watch 233, valid uptil 7 PM EST
 The Southern New England radar is quiet for now
NWS Boston radar 1130 am
But to the northwest storm coverage is increasing.  Nothing is severe...yet
NWS Burlington radar 1202 pm
With temperatures expected to max in the mid to upper 80s and clear skies
GOES-EAST visible satellite 1115 am (NOAA)
I feel scattered thunderstorms will develop.  Boston-Worcester-Hartford north and west has the greatest chance to see a severe storm, though the Blackstone Valley and Eastern CT are not out of the woods.  Keep an eye on weather.gov/box or NWSBoston on twitter for severe thunderstorm warnings.  Facebook is not reliable during severe weather.

-Zack

PREVIOUS DISCUSSION BELOW


Welcome back to the blog.  A severe thunderstorm watch was issued for the northwestern half of New England yesterday.  The primary hazard was wind and this verified
5/27/15 preliminary storm reports
Offshore high pressure has introduced a southwesterly wind in Southern New England.  With this comes warm and humid temperatures.  Dew points are already in the mid 60's
11z HRRR 2 m dew points valid 8 am (image weatherbell)
All our atmosphere needs is a trigger with heat and humidity already in place.  As we look at the surface chart we see our trigger moving through the Great Lakes
WPC 5 am surface analysis
This is not the main front but rather a trough in the upper air pattern.
06z NAM 500 mb vorticity valid 11 am (image NCEP)
This mean that we will stay in the warm in muggy pattern until the main cold front can sweep through the area Sunday or Monday.  Today highs will climb into the mid 80's
11z HRRR 2 m temps 2 PM (image weatherbell)
The storm prediction center (SPC) has most of New England at risk for severe thunderstorms.Yellow indicates scattered severe storms possible, green indicates isolated severe storms possible.
SPC day 1 severe weather outlook
The greatest threat other than heavy downpours and dangerous cloud to ground lightning will be the possibility of wind damage
SPC day 1 severe wind outlook
Small hail will be possible in the strongest cells.  Storms will fire around 12-1 PM out west and to the north.  They will move east throughout the afternoon most likely screwing up the evening commute.
11z HRRR simulated radar coverage 1 PM (image weatherbell)
By 4 PM solid coverage from Maine to SW CT is likely
11z HRRR simulated radar coverage 4 PM (image weatherbell)
I will update this post when any severe weather watches are posted.

-Zack

Rain Ending As Snow For The Blackstone Valley Tuesday

Tomorrow is Tuesday and surprise, surprise...precipitation is in the forecast.  WBZ went back and found that there has been measurable preci...