Wednesday, May 25, 2016

First Look- Memorial Day Weekend

The unofficial start of summer is Memorial Day weekend and for once Mother Nature agrees.  Although temperatures will back off from the mid to upper 80's on for Sunday/Monday it will still be warm.  There will be isolated afternoon showers/thunderstorms on Friday but I am hopeful that most of the action on Saturday is to our west.  On Sunday a front from our east will touch off isolated showers before moving back east on Monday.

General Overview
High pressure is now in control as yesterday's low pressure system departs.
WPC Surfae Analysis 8 AM
Our wind direction hasn't completely flipped to the west yet so temperatures are in the low 70's in some places.  But even I was write this and look at the local weather station network I notice a lot of stations are rising rapidly.  Local high resolution guidance is forecasting upper 80's for most this afternoon.  Look how awesome it captures the sea breeze effect.
14z HRRR 2 m max temps 4 PM (image Weatherbell)
So why does the sea breeze have such a profound effect on the coast?  The answer lies in the ocean temperatures.  They are still chilly from the Mid Atlantic on north.
NOAA/NCEP Sea Surface Temperatures (image Weatherbell)
*I will reference this map again in a bit but please notice the streaks of yellow off the Carolina coast*.  As for sea breezes the land heats up, warm air rises but cools with height.  It then sinks over the ocean and spreads out.  The ocean returns the favor by forcing the air back onto land.  This graphic will explain much better
NOAA COMET program Sea Breeze diagram
For those heading to the coast this weekend you are now warned that it will be much cooler at the coast than inland.

Low temperatures Thursday morning will be around 60 region wide.  A cold front will push south on Thursday.  This front will be fairly weak but it may set off a shower or thunderstorm later in the day.  Temperatures will be similar to today with highs in the mid to upper 80's.  Dew points will be higher tomorrow so it will feel more humid.  Here is the forecast surface chart tomorrow evening.
WPC Surface Forecast Thursday 8 PM
A greater chance of scattered showers/storms will be overnight Thursday into Friday.  This cold front will stall and lift north a warm front.  The precipitation wanes by daybreak and we will be left with a warm and sunny day.  Here is the Friday AM surface forecast.  I do want to watch and see if the shower activity holds on a bit longer Friday morning.
WPC Surface Forecast Friday 8 AM
Temperatures Friday will be in the mid 80's north and west of the Boston-Providence-Hartford line as some ocean air works into the coastal plain.  The usual warm spots- Connecticut River Valley, Merrimack Valley will be the warmest.  It will also be humid with dew points in the 60's.  Hopefully the southwest wind will be strong enough to keep everyone comfortable.
NWS NDFD max temp forecast Friday (Image Weatherbell)
Saturday is simply hot and humid.  I believe the day will be mostly dry in Southeastern New England but I can't rule out a shower/thunderstorm in Western MA.  This is Worcester, Boston and Providence's best day to hit 90.
NWS NDFD max temperature forecast Saturday (Image Weatherbell)
The forecast for Sunday is bit more tricky.  First of all before people get worried I am not forecasting a crappy day in fact it could be the pick of the weekend in some spots.  But a front may back in off the Atlantic and cool everyone off and bring some rain.  Here is the projected surface chart
WPC Surface Forecast Sunday 8 AM
The boundary will linger in the area Sunday and Monday.  If you are to the west or south of the boundary temperatures will be in the 80's.  If you are to the east or north of this temperatures could drop into the 60's.  Anytime there is that steep a temperature gradient there is a chance for showers/thunderstorms.  Monday the front weakens so odds favor a mild and sunny day.  I'm thinking temperatures around 80, cooler at the coast.

Now notice the area of low pressure sitting off the Georgia coast Sunday AM.  If you can recall the sea surface temperature graphic above you will remember this is sitting over warm water.  Hurricane season does not start until next Wednesday but it is possible a Tropical or Subtropical Storm forms off the Carolina coast.  This will have no bearing on the weekend forecast here in Southern New England but it may play a role in our weather next week.  There isn't much to move this system so it will sit and spin offshore.  It may enhance moisture in New England the middle/end of next week.  The National Hurricane Center gives the low a 50% chance of developing into a tropical/subtropical storm in the next 5 days.
NHC 5 day formation outlook
If this storm receives a name it will Bonnie.  Are you on the list this season?  Here are the names (Alex formed in January-very rare but counts to the 2016 season)
2016 Atlantic Hurricane Names
I will be posting a video later today going over my weekend forecast.  Enjoy the warm weather

-Zack Green

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