Heavy rains and Thunder Possible Overnight Wednesday into Thursday

For several days now computer forecast guidance has been extremely consistent with the potential for a rather strong and intense storm system, however, the consensus with regards to the track of the storm was up in the air.  Over the past few days a consensus has been drawn that the system will indeed pass well to our west.  With a track so far to the west we will not see snow (perhaps early AM Wednesday we would see some frozen precipitation with the first part of the storm), however, we will be dealing with the potential for some extremely heavy rainfall and even the potential for some thunderstorms. 

The graphic below is from today's (2/21) run of the GFS computer forecast model looking at the 500mb heights/winds.  What we see here is a very deep trough pushing towards the east coast of the United States associated with very intense winds at the 500mb level forecasted to be as strong as 110-120+ knots (indicated by the purple colors).  Notice at this time how the core of these winds are just to the southwest of southern New England.  This will place the region in a very favorable position for very strong and rather intense lifting which will enhance the potential for heavy rains as well as the potential for thunderstorms.   

The GFS forecast model is indicating some anomalously high precipitable water values pushing into southern New England overnight Wednesday with values as high as 1.3'', an indication that some areas could receive at least 1'' of rainfall!

Another interesting aspect of this system is the forecasted instability right now.  The GFS right now is advertising a decent surge of elevated instability (instability which occurs above the boundary layer) moving into the region overnight.  This perhaps occurs due to steepening lapse rates in the mid-levels of the atmosphere coincident with decreasing temperatures aloft while temperatures in the lower levels and the surface increase (along with moisture content):

Forecasted lapse rates overnight Wednesday into Thursday:

Forecasted MUcape overnight Wednesday into Thursday:

All in all for snow lovers this system is bad news, however, for any weather enthusiasts this will be a fun system to watch given the dynamics involved.  We will see some pretty heavy rains push through the region along with the potential for thunderstorms and strong winds.  More to come as the week progresses!

Monday, February 8th, 2016 CT snow map/discussion

Our active weather pattern continues as more snow is targeted for the state of CT as we begin a brand new work week.  However, unlike Friday where some spots saw some pretty impressive snowfall amounts (as much as 6-12''!!) this system likely won't match those totals, however, there will be some impacts to travel.  While we are about 12-15 hours away from the onset of snowfall there is still a little bit of uncertainty with exactly how far west the storm tracks and where the strongest lift traverses over.  This will ultimately determine how much snow we receive and where the highest totals occur.  With this said, I believe the storm will end up tracking a bit too far east for CT to really get into the heaviest snows, especially for any prolonged period of time.  I do believe many areas (especially the further east you are in the state) will see at least a brief period of moderate to heavy snow.

With the following graphics below we can sort of see where some of the uncertainty comes from.  The following images are a bufkit profile for over Windsor Locks, CT from both the American GFS (top graphic) and NAM (bottom graphic) computer forecast models.  The area highlighted in purple is the best snowgrowth zone.  This is indicated by the purple and yellow contours.  The area highlighted in orane is vertical velocities with the red contours indicated upward motion (great for generating precipitation!).  The more contours you have, the stronger the lift!  You want these contours to run right through the best snowgrowth zone.  If you look at the difference between the GFS and NAM you see the GFS has a -10 contour while the NAM only has a -5 contour run through this zone.  This is indicating that the GFS is forecasting stronger lift than the NAM which would result in a period of heavier snowfall and perhaps higher totals.  Other sounding locations across CT yield similar looks.  This right here is the reason for the bit of uncertainty.

Looking past this uncertainty, this is not a very long duration storm system, however, we will see on and off snow-showers through Wednesday thanks to the upper-level trough which will be associated with this coastal storm.  Given how this is not long-duration, this is another reason why totals should not be all that significant.

Early morning rush hour traffic should not be terrible as the snow may not really break out until the mid-morning hours, although light snows could break out as early as 7-8 AM.  As the morning progresses, snow rates will vary between light to moderate and perhaps even briefly heavy at times reducing visibility.  Snow should taper off by the late afternoon hours so any impacts to the evening commute should be confined to wet roadways beginning to ice over.

Below is what I am expecting:

Monday, February 8th, 2016 Storm Potential

The past few winters have featured February's which not only saw a good deal of cold here across the region but also featured numerous snow events.  February 2016 looks to continue the trend for active February's as the pattern we are entering will be quite favorable for numerous snow chances.  While we just finished with a snow event another one looms on the horizon and just a few days away.

Over the past 24-hours or so, a few of the medium/long-range computer forecast models have featured a decent shift to the north and west with what appears to be a rather significant storm system.  While there is still a great deal of uncertainty with regards to how close to the coast the system will track, the latest trends have been rather interesting.  

Below is a graphic from today's 18z run of the American GFS computer forecast model valid for Sunday evening looking at the 500mb level.  There are two areas highlighted which will be of major interest over the coming few days.  The first area of interest is the northern stream trough which is expected to dig into the United States at the end of the weekend/beginning of the upcoming work week.  How this feature develops and behaves will be extremely critical.  The second highlighted area of interest is the very strong piece of shortwave energy in the southern stream.  This will be responsible for the development of a very strong and rather intense storm which at this time is off the coast.  If this trough digs in faster and sharper (sharper meaning digging further south) it may act to pickup the storm and allow the storm to not only work further north and west but come very close to the coast, perhaps enough to give us precipitation:

The uncertainty right now exists not only because of what was just mentioned above but also due to computer forecast ensembles.  Today's 12z GFS ensembles show some individual members bringing the storm close enough to the coast to give us impacts while other members remain further east.  However, the rather interesting thing to note is how the models have come north and west over the past 24-hours or so.  In fact, even the European model had a shift to the north and west this afternoon.  Below are some of the GFS ensemble members:

As newer data becomes available and the situation should begin to become much more clear.  If overnight computer forecast models continue coming further north and west I think we definitely start having to prepare for a storm on Monday.  However, if tonight's models start going back towards the south and east the potential for impacts will likely decrease.  This will be a pretty potent system so if it does track west enough someone could end up with a quite a bit of snow.  Stay tuned!

Snow surprise! Accumulating Snow expected Friday, February 5th, 2016

Over the past couple of days computer forecast models have been insisting that an area of low pressure which develops along a cold front stalled to our south and east will track far enough to the west to bring precipitation, including snowfall into portions of southern New England.  Well over the past 12 hours or so, computer forecast models have really come further west and now we are looking at the potential for accumulating snows as far back as western CT.

The following graphic is looking at the 500mb level and 500mb vorticity.  What we are looking at is a very potent piece of shortwave energy traversing through the 500mb level.  This very strong piece of energy will be responsible for the continued development and strengthening of a surface low pressure along with low pressure centers developing at the 925mb and 850mb levels:

One of the computer forecast models, the GFS model has been quite aggressive with precipitation and lift across our area.  However, several other computer forecast models have also been either similar to the GFS or trending towards the GFS.  Below is an image from the latest 18z run of the GFS showing vertical velocity at 700mb.  The brighter colors indicate very strong and rather intense lifting.  We should see a period of very strong lift push through CT and help enhance snowfall intensity:

As far as impacts go, expect a very traitorous Friday morning commute given the timing of the snowfall with snowfall breaking out either overnight Thursday or very early AM Friday and continuing through the early to mid afternoon.  Expect poor driving conditions along with numerous delays.  Below is my snowfall forecast: