Issued Tuesday May 19 2020 12:00pm

I can hear you out there now. Where is the %^&^$^%( warm weather!

Patience young Jedi….warm weather is on the way though it is delayed a little bit.

A few forecast posts ago I spoke about the pattern change that we were looking at in the long term. I gave a rather extensive explanation about long and short waves and how they influence the weather pattern in the short and long term. Well, all of that still applies. Additionally, just like the check in the mail, the warm weather is on the way.

First, let’s look into why we are still so cool. You need not go too far to figure it out either. Let’s look at this morning’s weather map:

The surface map from 8am shown above paints the chilly picture over the northeastern United States. A large high pressure area over Quebec, which will press toward the SE over the next 48 hours is pumping some rather cool maritime polar (mP) air into the northeast. Add this to a persistent long fetch E-NE wind which is blowing over sea surface temperatures which are in the middle to upper 40’s and you’ve got the recipe for temperatures to be well below seasonal norms. This pattern is a smaller scale low level phenomena as opposed to the larger scale trends we were talking about last week.

What do those larger scale features tell us about our weather? Have they changed? Let’s take a look:

Looking at the two charts above we see that the longwave pattern looks largely like we thought it would. So, on average, given the 500 mb pattern presented we would expect above average temperatures in the east and cooler than average temperatures in the western part of the country. The devil, as they say, is in the details.

The details can be found on the right most chart which represents the 500 mb forecast with short and long waves included. The heavy pinkish line that I’ve drawn on the chart shows where the main 500 mb flow is. As you can see, it looks a lot like the 500 mb long wave pattern shown on the left. What does that mean? It means that the 500 mb long wave pattern that we were talking about last week has evolved exactly as we thought. So why isn’t it warm?? Details…..details. The chart on the right helps to explain why the pattern is the way it is. First, we have what we call a “cut off” low floating over the Tennessee Valley/Ohio Valley region of the country. We call it a “cut off” low quite literally because it is cut off from the main upper level low. This cut off represents a pool of cool air at mid and upper levels of the atmosphere. This kind of low pressure area allows cool and rainy/showery weather to persist over an area over extended periods. Cut off lows tend to form at this time of year as the upper atmosphere is still rather cool from the winter months. As a result, its easier for these cold pools to develop and split away from the main upper level flow. Cut off lows also take a while to exit an area mainly because they are seperated from the primary upper air flow. Essentially, there is nothing to move them along. This cut off, basically gumming up the upper air flow, and the cold canadian high pressure area, which will persist over us for a bit, will combine to keep us in the cool, kind of moist but not that cloudy flow through Wednesday.

So, how does the combination of all these factors influence surface weather?

Looking at today’s high temperature map you can see that is pretty cool over much of the Eastern and Central United States. These cool conditions are a response to the upper level cut off low over the Tennessee Valley and the cool maritime polar air flow coming down from the high pressure to the north of New England. The only warm place in the eastern part of the country is the far SE and Florida panhandle where temperatures are in the mid 80’s to lower 90’s which is about average for this time of the year.

Notice, however, that there is a stretch of rather warm air from Texas right up the spine of the Central and Northern Plains states. This is an expression of the influence of the long wave ridging that is present despite the cool pool that exists over the east. You can also see the cooler weather over the Western United States which is also reflective of the long wave pattern. So, it stands to reason that if we got rid of the transient cut off low pressure area that temperatures would start to respond and warm up. Well, that’s exactly what happens.

By Friday the upper level pattern begins to change as the cut off low gradually fills and becomes an open wave which will allow it to reintegrate all that upper level energy back into the general west to east flow.

On Friday (shown above) we’ve got warming temperatures throughout the east and northeast (except where it will be raining throughout the Mid-Atlantic states). Temperatures in the 80’s and 90’s will expand into the south and Florida will see above normal temperatures especially in the central sections of the state.

So, bottom line, keep the faith. Warmer weather is baked into the current pattern and we will see it. We just need to get the winds to stop blowing over the giant fridge to our east. 🙂

Issued: Sunday May 17 2020 12:15 pm

When people ask me why I’ve lost so much hair, I give them one simple answer….”weather forecasting”. Yes, today is one of those hair pulling days forecasting New England weather. We are oh so lucky to have that dripping in moisture….gigantic refrigerator (at this time of year) called the Atlantic Ocean immediately to our east. The good ole Atlantic managed to take some of its low level moisture and spit it back at us during this morning in the form of a low to middle cloud deck that fouled up the supposedly mostly sunny day I forecast for today. Oh the joys of forecasting the weather in New England in the spring.

Fear not, however, some of Sunday (a misnomer…..”Sun”day) will be salvaged as the satellite loop does show that the low level moisture is eroding and some partial clearing will be possible by a little later this afternoon. This should allow temperatures to get up into the low 60’s today along the coast and into the middle to upper 60’s inland. We’ll take it.

At 11pm last night the National Hurricane Center named Tropical Depression #1 “Arthur”. The current position fix of Tropical Storm Arthur is:

SUMMARY OF 1100 AM EDT…1500 UTC…INFORMATION

LOCATION…30.5N 77.4W
ABOUT 345 MI…550 KM SSW OF CAPE HATTERAS NORTH CAROLINA
MAXIMUM SUSTAINED WINDS…45 MPH…75 KM/H
PRESENT MOVEMENT…NNE OR 15 DEGREES AT 9 MPH…15 KM/H
MINIMUM CENTRAL PRESSURE…1002 MB…29.59 INCHES

On satellite Arthur’s presentation is a bit ragged with very little deep convection near the center. There is, however, a well defined low level circulation. Arthur’s convection should pep up a little later today with the heating of the sun, favorable SST’s and relatively low wind shear. Satellite imagery shows decent outflow in the northern, western, and southern quadrants of the storm. There may be a little bit of SW shear staunching the outflow to the east of the storm center. On the whole, I don’t expect Arthur to strengthen much if at all over the next 24 hours.

Arthur’s track will take him to just off Cape Hatteras, NC by tomorrow morning and then he will take a sharp right turn passing harmlessly out into the Atlantic by Tuesday morning.

At 5:00pm the National Hurricane Center designated the disturbance off the Florida east coast as Tropical Depression #1 (TD #1), the first official tropical system of the not even officially started Atlantic hurricane season.

Here is the position fix of TD#1:

SUMMARY OF 500 PM EDT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...28.4N 78.6W
ABOUT 125 MI...200 KM E OF MELBOURNE FLORIDA
ABOUT 505 MI...810 KM SSW OF CAPE HATTERAS NORTH CAROLINA
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...NNE OR 20 DEGREES AT 13 MPH...20 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES

Looking at the satellite presentation of TD #1 it seems like there is a very well defined low level circulation which is flanked by deep convection mainly to the east of the circulation center. The depression will remain off shore through the next 24 hours. Beyond that time will tell if the track of the depression veers away from the coast out to sea. It certainly seems like TD#1 may get close enough to the US east coast to make the waters choppy, especially off of the Carolinas and the Mid-Atlantic states.

It seems like the pattern should track TD#1 out to sea after 48 hours as it gets caught up in the westerlies.

Issued Friday May 15 2020 9:15 pm

The line of showers and thunderstorms we’ve been monitoring tonight has made its way through most of Massachusetts and is now pressing toward the SE into the Providence, Brockton, Taunton, and Plymouth area. The storms did weaken significantly in Eastern MA once they got inside of 495. This is likely due to the more stable atmosphere closer to the coastline. These storms still had rather gusty winds and heavy downpours. There are still a few stronger cells further west in the Oxford/Milford/Woosocket, RI area as well as in central CT. These storms are pressing toward the east at 50 mph or better.

As the storms approach the southern portions of CT, RI and the Cape Cod canal the tendency should be for these storms to continue to weaken due to a more stable air mass in those areas. Still, you will see gusty winds, heavy downpours, and thunder and lightning.

Issued Friday May 15 2020 7:55pm

A line of strong showers and thunderstorms are pushing through central and western MA and SW and central NH as of 7:45pm this evening. This line of thunderstorms may contain cells which may generate damaging winds, hail, frequent lightning and the potential for small isolated tornadoes. The National Weather Service also has most of Massachusetts under a Tornado Watch until 10pm this evening. This line of thunderstorms should arrive in the Worcester area around 8:30 pm, into the western and northern suburbs of Boston by around 9:00pm, into the Boston area itself by 9:15pm and to the Cape Cod Canal by 10:00pm.

Particular attention should be paid to the skies if you are outdoors as this line of thunderstorms approaches your area. Lightning detection is showing quite a bit of strike activity associated with these storms as they approach and radar indicates some bowing of the radar returns. This indicates the potential for strong damaging winds. No reports of Tornadoes have been received and we don’t see any indication of hook echos at this time.