7:00 AM | Nice air mass to start the new week, but hot and humid weather returns for Tuesday through Thursday; much cooler air moves in for Friday and Saturday

6-Day Forecast

Today

Mostly cloudy, refreshingly cool, highs in the mid-to-upper 70’s

Tonight

Mostly cloudy, not as cool as last night, lows by morning in the upper 60’s

Tuesday

Becoming mostly sunny, very warm and humid, near 90

Tuesday Night

Partly cloudy, mild, near 70

Wednesday

Partly sunny, very warm, humid, chance for showers and thunderstorms late or at night, near 90

Thursday

Partly sunny, very warm and humid, showers and thunderstorms likely and some of the storms can be strong, near 90

Friday

Mostly sunny, breezy, less humid, cooler, mid 70's

Saturday

Mostly sunny, cool, low 70's

Discussion

A cool front passed through the region on Sunday and the new work week will start with comfortable temperatures and humidity levels as yet another Canadian-born high pressure system heads our way. The high will quickly shift off the coast on Tuesday and this will open the door for hot and humid conditions to move back into the Mid-Atlantic region for the period of Tuesday, Wednesday and Thursday. A strong cool front will then pass through the region on Thursday bringing with it the chance for strong thunderstorms, and then another cool air mass will follow for Friday and Saturday. In fact, this next cool air mass will likely be the coolest yet this season with highs on Saturday struggling to escape the lower 70's.

Elsewhere, Tropical Storm Humberto has formed in the eastern Atlantic. It has a chance to become a hurricane within the next 48 hours or so. If this happens, it would be the first hurricane of the season which is very late for that to occur. In fact, if Humberto does not reach hurricane status by Thursday then this would be the latest start to a tropical season without a hurricane in the satellite era (since mid 1960's).

Video

httpv://youtu.be/mcmSJjqlfis

10:45 AM | Rocket launch tonight at NASA Wallops Island Facility should be visible in the Mid-Atlantic region; 11:27 PM launch sends NASA back to the moon

This image shows the Minotaur V rocket that will carry NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) on a pad at NASA’s Wallops Flight Facility at Wallops Island, Va. Credit: NASA EDGE

Discussion

There will be a rocket launch tonight at NASA’s Wallops Island Virginia facility and it should be visible throughout the Mid-Atlantic region and much of the east coast. The launch time is set for 11:27 PM and the mission is to explore the very thin lunar atmosphere and moon dust. The spacecraft poised to liftoff atop the brand-new 5-stage Minotaur V rocket is nicknamed LADEE – short for Lunar Atmosphere and Dust Environment Explorer – and it will be the first spacecraft to be launched into outer space from Wallops Island as it will fly to the moon by way of Virginia’s Eastern Shore. The unmanned Minotaur V rocket consists of converted intercontinental ballistic missile motors. A peace treaty between the United States and Russia specifies the acceptable launch sites for those missile parts; Wallops is on that short list.

The mission will investigate the fragile atmosphere of the moon and study how moon dust behaves above the lunar surface. Apollo astronauts first spotted a strange lunar glow on the moon's horizon during NASA's lunar landing missions in the 1960s and 1970s, but scientists still do not understand what causes the strange phenomenon. The moon's atmosphere is much thinner than Earth's - perhaps about 1/100,000th the density of that on Earth. Because the lunar atmosphere is so thin, temperatures reach 273 degrees Fahrenheit (134 degrees Celsius) on the sunny side of the moon, but the temperature can get as cold as minus 243 degrees Fahrenheit (minus 153 degrees Celsius) on the far side of the moon. The moon's atmosphere, referred to as "exosphere", is so thin that its individual molecules don't interact with each other. The Earth has an exosphere too, though it is located hundreds of miles up, higher than the orbit of the International Space Station. On the moon, this exosphere is extremely close to the surface, making it a good target to study in order to learn how such atmospheres behave over time. Similar exospheres have been spotted on Mercury, the icy moons of planets in the outer solar systems, and even on some asteroids.

The LADEE spacecraft is about the size of a small car and weighs about 844 pounds (383 kilograms). Once it reaches the moon, which should take a couple of months, the probe is expected to spend about 100 days studying the lunar environment before running out of fuel and crashing into the moon's surface.

Weather conditions look to be very favorable for this evening with clear skies expected up and down the east coast. Look low in the horizon shortly after launch in the following directions: southeast if in the DC metro region, south if in the Philly and NYC metro regions. The initial flight path of LADEE will be to the east over the Atlantic Ocean, where it will drop its first three (ICBM) stages. A live broadcast of the launch will air on NASA TV at http://www.nasa.gov/ntv

This map shows the maximum elevation in degrees above the local horizon the Minotaur rocket will reach across the east coast on Sept.6, 2013. Ten degrees is equal to about the width of your fist at arm’s length. Credit: Orbital Sciences

7:00 AM | A true taste of autumn as we close out the work week

6-Day Forecast

Today

Sunny, refreshingly cool, highs in the mid 70’s

Tonight

Mostly clear, still quite cool, lows by morning near 50 degrees

Saturday

Mostly sunny, pleasant, near 80

Saturday Night

Mostly clear, cool, near 60

Sunday

Partly sunny, comfortable, low-to-mid 80’s

Monday

Mostly sunny, pleasant, upper 70’s

Tuesday

Mostly sunny, a bit more humid, low 80’s

Wednesday

Mostly sunny, warm, more humid, maybe a shower or thunderstorm, mid 80’s

Discussion

The coolest air so far this season will stick around through tonight and then modify some this weekend, but it will continue to be quite comfortable with low humidity levels. High temperatures today will hold in the refreshingly cool middle 70’s, but a rebound to 80 degrees is likely on Saturday afternoon. Another cool front will pass through the region on Sunday and this will pave the way for another pleasant air mass for early next week, but warmth and humidity will return to the Mid-Atlantic region by the middle of next week.

Video

httpv://youtu.be/NnAayuTKwDE

7:00 AM | Coolest air yet this season moves in for tonight, tomorrow and tomorrow night

6-Day Forecast

Today

Mostly sunny, comfortable, breeze picks up this afternoon, highs in the low 80’s

Tonight

Mostly clear, very cool, lows by morning in the low 50’s

Friday

Mostly sunny, refreshingly cool, mid 70’s

Friday Night

Mostly clear, still quite cool, low-to-mid 50’s

Saturday

Mostly sunny, nice, near 80

Sunday

Partly sunny, comfortable, maybe a shower, low-to-mid 80’s

Monday

Mostly sunny, pleasant, upper 70's

Tuesday

Mostly sunny, a bit more humid, low 80's

Discussion

Another cool front will pass through the region today and this will usher in the coolest air of the season so far. Temperatures by early tomorrow morning should bottom out in the low 50’s in some of the normally colder northern and western suburbs. Highs on Friday will hold in the middle 70’s, but should rebound on Saturday afternoon to near the 80 degree mark. Another front will approach the region on Sunday and a shower cannot be ruled out. That next frontal passage will bring in more pleasant weather for early next week, but warmth and humidity is likely to return by the middle of the week.

Video

httpv://youtu.be/qXSpICT-Q3o

12:55 PM | Coolest morning so far coming on Friday

Discussion

One cool front passed through the Mid-Atlantic region yesterday morning and a secondary front will move through later tomorrow. It is this second front that will usher in the coolest air so far this season for the Mid-Atlantic region with 40’s likely as low temperatures early Friday morning in some of the northern and western suburbs of the big cities along I-95 between DC and NYC.

The atmospheric setup tomorrow night will be quite favorable for temperatures to drop rapidly as high pressure settles in right on top of the region (see 12Z NAM forecast map for Friday morning). The move overhead of this Canadian-born high pressure system will allow for clear skies and the tapering off of afternoon northwest breezes in the Mid-Atlantic region. Some interior sections of the Mid-Atlantic could drop into the 30’s by early Friday morning (e.g. Poconos) and frost is not out of the question in portions of upstate Pennsylvania, New York and interior New England. Meanwhile, the city of Philadelphia is likely to bottom out in the low-to-mid 50’s which would be the coolest morning there since late May (current normal morning low around 65 degrees at PHL). High temperatures on Friday afternoon will hold in the refreshingly cool low-to-mid 70’s in most Mid-Atlantic locations, but will rebound to near 80 degrees on Saturday as the high shifts to an offshore position.

7:00 AM | Cool frontal passage early yesterday to be followed by another later tomorrow

6-Day Forecast

Today

Sunny, comfortable, highs in the low 80’s

Tonight

Mostly clear, cool, lows by morning near 60 degrees

Thursday

Mostly sunny, pleasant, low 80’s

Thursday Night

Mostly clear, quite cool, low 50’s

Friday

Mostly sunny, refreshingly cool, mid 70’s

Saturday

Mostly sunny, nice, near 80

Sunday

Partly sunny, pleasantly warm, maybe a shower, low-to-mid 80’s

Monday

Mostly sunny, comfortable, near 80

Discussion

A strong cool front passed through the region early yesterday ushering in comfortable air for the Mid-Atlantic region that will last right through the week. In fact, a secondary cool front will move through the region later tomorrow and this frontal passage will usher in the coolest air mass yet for the season with low 50's possible as low temperatures by early Friday morning in some of the northern and western suburbs. Highs on Friday will hold in the mid 70's, but should rebound rather quickly on Saturday to highs near 80 degrees.

Video

httpv://youtu.be/GVzOXyFycJU

7:00 AM | More comfortable air moves in for the rest of the week

6-Day Forecast

Today

Becoming mostly sunny after morning clouds, turning less humid, highs in the low-to-mid 80’s

Tonight

Mostly clear, cool, lows by morning in the upper 50’s

Wednesday

Mostly sunny, pleasant, low 80's

Wednesday Night

Mostly clear, cool, upper 50’s

Thursday

Mostly sunny, pleasant, low 80’s

Friday

Mostly sunny, refreshingly cool, mid-to-upper 70's

Saturday

Mostly sunny, pleasant, low 80’s

Sunday

Mostly sunny, still pretty comfortable, mid 80’s

Discussion

Today will be a transition day with a cool frontal passage between the warm, humid and unsettled conditions that we experienced during the long holiday weekend and much more comfortable weather for the remainder of the week. Some clouds this morning will be replaced by increasing amounts of sunshine and less humid air will become established by later today and tonight. Nice weather will continue for the rest of the week with comfortable temperatures and humidity levels and plenty of sunshine each day. The coolest day of the week may turn out to be on Friday following the passage of a secondary cool front with highs possibly holding in the mid-to-upper 70's to close out the work week. August turned out to be cooler-than-normal by 1 degree in the DC metro region, but September should be slightly above normal despite the cool start to the new month this week.

12:00 PM | The Carrington Event of 1859 - a solar superstorm

Discussion

It was this time of year 154 years ago when the solar superstorm, now known as the Carrington Event, took place during solar cycle 10. The event has been named for the British astronomer, Richard Carrington, as he observed from his own private observatory the largest solar flare during this event which caused a major coronal mass ejection (CME) to travel directly toward Earth. The 33-year-old astronomer - widely acknowledged at the time to be England’s best - also recorded in detailed fashion the appearance of the sunspot regions that he saw at the time.

From August 28, 1859 to September 2, 1859 numerous sunspots and solar flares were observed on the sun and auroras were being observed in different parts of the world. Just before noon on September 1st, Richard Carrington was using his telescope to project an 11-inch wide image of the sun on a screen and he carefully drew the sunspots that he saw. Suddenly, two brilliant beads of blinding white light appeared over the sunspots and he realized that he was witnessing something unprecedented. He left for about one minute to find another witness and found upon their return that much had already subsided.

Just before dawn the next day, skies all over Earth erupted in red, green and purple auroras - even in tropical locations like Cuba, the Bahamas and Hawaii. The massive solar flare caused a major CME that reached the Earth some 17.6 hours later. Normally such a journey takes 3 or 4 days, but an earlier CME actually cleared the way of the ambient solar plasma for the second blast to move so quickly. The auroras were so bright over the Rocky Mountains that their glow awoke gold miners who began preparing breakfast because they thought it was morning. People in the northeastern US could read a newspaper by the aurora’s light. Telegraph systems all over Europe and North America went haywire and, in some cases, telegraph operators were literally shocked as sparks were flying and telegraph paper was often set on fire. Some systems continued to work despite being disconnected from their power supplies as aurora-induced electric currents still allowed messages to be transmitted.

Now we know that solar flares happen frequently, especially during solar sunspot maximums, but in those days there were no X-ray satellites or radio telescopes and no one knew flares existed until that September morning. “It is rare that one can actually see the brightening of the solar surface which takes a lot of energy to heat up the surface of the sun” says a modern day NASA astronomer. “In the 160-year record of geomagnetic storms, the Carrington event is the biggest.” In fact, going back farther in time by examining Arctic ice (energetic particles leave nitrates in ice cores), it is estimated that this event may have been the biggest in 500 years and nearly twice as big as the runner-up.

In today’s world, electronic technologies have become embedded into everyday life and are, of course, quite vulnerable to solar activity. Power lines, long-distance telephone cables, radar, cell phones, GPS, satellites – all could be significantly affected by an event like this one. The good news is that observations of the sun are a constant in today’s world with a fleet of spacecraft in position to monitor the sun and gather data on solar flares. The bad news is that the Carrington Event occurred during a weak solar cycle (10) which actually resembles rather closely our current solar cycle (24) so we always have to stay on guard for a potential powerful solar storm - even during times of weak solar cycles.

Above: A modern solar flare recorded Dec. 5, 2006, by the X-ray Imager onboard NOAA's GOES-13 satellite. This flare was so intense it actually damaged the instrument that took the picture. Researchers believe Carrington's flare was much more energetic than this one.

7:00 AM | Showers and thunderstorms threaten the region for the upcoming holiday weekend

6-Day Forecast

Today

Mostly sunny, warm, slight chance for a shower or thunderstorm, highs in the mid 80’s

Tonight

Partly cloudy, mild, lows by morning in the upper 60’s

Saturday

Partly sunny, warm, humid, chance for afternoon showers and thunderstorms, mid-to-upper 80’s

Saturday Night

Mostly cloudy, mild, chance for showers and thunderstorms, upper 60’s

Sunday

Partly sunny, warm, chance for showers and thunderstorms, mid 80’s

Monday

Partly sunny, warm, chance for showers and thunderstorms, mid-to-upper 80’s

Tuesday

Partly sunny, more comfortable, more showers possible, near 80

Wednesday

Mainly sunny, pleasant, near 80

Discussion

A series of frontal systems will keep the weather unsettled around here this weekend with the daily threat for showers and thunderstorms and some of the rain can be heavy at times. The strongest of the fronts headed this way will be a cool front arriving early next week and it looks like we won’t have genuine clearing until the passage of that front by late Tuesday/Wednesday of next week.

7:00 AM | Shower and thunderstorm threat for the upcoming long holiday weekend

6-Day Forecast

Today

Clouds this morning then partial afternoon sunshine, warm, just a slight chance for a shower or thunderstorm, highs in the mid 80’s

Tonight

Partly cloudy, mild, lows by morning in the upper 60’s

Friday

Mostly sunny, warm, just a slight chance for a shower or thunderstorm, mid 80’s

Friday Night

Partly cloudy, mild, upper 60’s

Saturday

Partly sunny, warm, chance for showers and thunderstorms, mid 80’s

Sunday

Partly sunny, warm, chance for showers and thunderstorms, mid 80’s

Monday

Partly sunny, warm, chance for showers and thunderstorms, mid-to-upper 80’s

Tuesday

Mainly sunny, pleasant, near 80

Discussion

Weak high pressure will build into the Mid-Atlantic region today and control our weather for the next couple of days; however, a shower or thunderstorm cannot be completely ruled out on either day. The weekend looks quite unsettled with numerous fronts to deal with in the Mid-Atlantic region and a daily threat for showers and thunderstorms. The strongest front appears to be a cool front headed to the region early next week and we may not get genuine clearing until the passage of that front beginning around Tuesday of next week.