7:00 AM | Strong cold front reaches the coast tonight; heavy rainfall and strong storms can be expected; nor’easter forms along the front and affects the early weekend weather
Mostly cloudy, still warm and humid, but not quite as warm as yesterday, occasional showers and possible afternoon thunderstorms, any shower can be heavy and some of the PM thunderstorms can be strong-to-severe with heavy rainfall, strong wind gusts and hail, highs in the upper 70’s
Mostly cloudy, mild early, turning cooler late, occasional rain and a couple of thunderstorms possible, some of the rain can be heavy at times and any storm can be strong-to-severe with heavy rain, strong gusty winds and hail, lows in the upper 50’s by morning
Mostly cloudy, windy, much cooler, lingering showers likely, low 60’s
Mostly cloudy, windy, chilly, showers likely, mid 40’s
Lots of clouds, windy, cool, lingering showers likely, low 60’s
Becoming partly sunny, breezy, cool, mid-to-upper 60’s
Mostly sunny, cool, near 70
Partly sunny, milder, low-to-mid 70's
Big changes are on the way for the Mid-Atlantic region over the next couple of days as the pattern transitions from summer-like to rather winter-like by early this weekend with a full-fledged nor'easter developing off the Northeast US coastline. The transition from summer's warmth and humdity to yet another chilly air mass has actually already begun as the peak in the heat occurred yesterday with highs in the upper 80's in many parts of the region. Temperatures will actually drop more than 40 degrees over the next couple of days from yesterday's highs in the upper 80's to weekend lows in the middle 40's. As a powerhouse cold frontal system approaches the east coast today, there will be occasional showers and thunderstorms. Any shower can contain heavy rainfall and any thunderstorm that forms this afternoon and evening can reach strong-to-severe levels with heavy rain, strong gusty winds and hail. In fact, there will likely be scattered strong-to-severe thunderstorms up and down the east coast later today from the Carolinas to New England as this strong cold front heads to the coast.
Once the cold front reaches the east coast later tonight, a strong upper level low will dig into the Mid-Atlantic region, and this will to cause the frontal system to grind to a halt as a nor’easter-type of coastal storm develops at the same time much chillier air pours into the region. As a result, Friday will turn out to be breezy and much cooler than today in the Mid-Atlantic region with lots of clouds and residual showers and, as the coastal storm only slowly pulls away to the northeast, Saturday will likely also turn out to be quite cloudy, windy and cool with the continued threat for showers. The colder air mass will actually allow for the possibility for snowflakes to fall in some of the interior, higher elevation (>2000 feet) locations of the Mid-Atlantic and Northeast US early this weekend (e.g., Adirondacks, Green and White mountains). By Sunday, strong Canadian high pressure should finally take control of the weather and there will be some clearing and then Monday looks like the best day of the three this weekend with plenty of sunshine expected. Temperatures will stay below normal, however, on Sunday and Monday (normal high is now 75 degrees).
1:10 PM | Big changes coming to the Mid-Atlantic over the next few days as summer-like pattern becomes kind of winter-like; heavy rainfall, and possible strong storms, to occur during the transition between tonight and the weekend
To say it doesn't look like beach weather for this upcoming holiday weekend is looking more and more like quite an understatement for the Mid-Atlantic region and the Northeast US. Big changes are coming to the Mid-Atlantic region and Northeast US over the next few days as the weather changes from today’s summer-like pattern to one that is actually kind of winter-like - and strong-to-severe thunderstorms with heavy rainfall are likely during the transition between later tonight and the early weekend. Summer-like weather continues today in the Mid-Atlantic region with high humidity and temperatures well up in the 80’s in Philly and DC, and well up in the 70’s across the NYC metro region. This sultry air mass can help to spark some shower and thunderstorm activity later tonight and any storm that forms can be on the strong side. An even better chance for heavy rainfall and strong thunderstorms will occur later tomorrow and tomorrow night as a powerhouse cold front heads to the east coast. In fact, strong-to-severe thunderstorms are likely later tomorrow from New England to the Carolinas associated with this strong frontal system.
Once the cold front reaches the east coast later tomorrow night, a strong upper level low will dig into the Mid-Atlantic region, and this will to cause the frontal system to grind to a halt as a nor’easter-type of coastal storm develops at the same time much chillier air pours into the region. As a result, Friday will turn out to be breezy and much cooler than Thursday in the Mid-Atlantic region with lots of clouds and residual showers and, as the coastal storm only slowly pulls away to the northeast, Saturday may also turn out to be quite cloudy, windy and cool with the continued threat for showers; especially, from eastern Pennsylvania and New Jersey to points north and east to New England. In fact, it's starting to look like a lost weekend for places up the northeastern coast such as in Boston, MA where rain and wind could hang on through Sunday. The colder air mass will actually allow for the possibility for snowflakes to fall in some of the higher elevation (>2000 feet), interior locations of the Mid-Atlantic and Northeast US early this weekend (e.g., Adirondacks, Green and White mountains). By Sunday and Monday, strong Canadian high pressure should finally take control of the weather, but temperatures will remain well below normal for this time of year.
7:00 AM | Another summerlike day with heat and humidity; strong storms possible today and Thursday; much cooler this weekend
Clouds this morning, partial sunshine this afternoon, very warm and humid, chance for showers and thunderstorms this afternoon and any storm that develops can be strong, highs in the mid 80’s
Mostly cloudy, mild, chance for showers and thunderstorms and any storm that forms can be strong, low-to-mid 60’s
Mostly cloudy, warm and humid, showers and thunderstorms likely and some of the storms can be strong-to-severe, near 80
Mostly cloudy, mild early, turning cooler late, chance for showers and thunderstorms, mid-to-upper 50’s by morning
Mostly cloudy, breezy, cooler, chance for residual showers, upper 60's
Slow clearing, windy, cool, still cannot rule out a couple of showers, low-to-mid 60's
Mostly sunny, breezy, cool, mid-to-upper 60's
Partly sunny, still on the cool side, near 70
A taste of summer will continue today in the Mid-Atlantic region as temperatures will climb well up into the 80’s in most locations and humidity levels will stay on the high side. Dew points climbed into the middle 60’s on Monday in the Mid-Atlantic region and then they reached the even more stifling upper 60’s on Tuesday to go along with summerlike temperatures. Showers and thunderstorms can break out at just about any time this afternoon and evening although much of the time will be rain-free. Any storm that forms this afternoon or evening can be on the strong side with some briefly heavy rainfall and perhaps hail and high wind gusts. By tomorrow, a strong cold front will be moving through the Ohio Valley on its way to the east coast and this will enhance the chances for shower and thunderstorm activity in the Philly metro region and there is a decent chance that strong-to-severe storms will develop later tomorrow and tomorrow night in the entire region between the Carolinas and New England.
Once the cold front reaches the east coast by early Friday, it will tend to slow down a bit as a coastal storm develops and this will allow for mostly cloudy skies to continue on Friday along with cooler conditions and the threat for residual showers and this may even linger into Saturday as well. By later in the weekend, strong Canadian high pressure will build into the Mid-Atlantic region and, similar to many previous springtime scenarios, much colder-than-normal air will spread to the eastern states with this high pressure system. As a result, it does not look at all like a “beach-type” weekend for coastal locations in the Mid-Atlantic and Northeast, and frost is actually not out of the question for some interior, higher elevation locations. Cool and dry weather is likely to continue into the latter part of the Memorial Day weekend.
One final note: the tornado that struck Oklahoma on Monday has now been upgraded to an "EF-5" classification level which is the most intense type on the "Enhanced Fugita" scale and it is suggestive of 200+ mph winds.
Tornadoes require clashes of air masses to form generally to include cold, dry air in the upper atmosphere and very warm and humid air in the lower atmosphere. For much of the spring, the missing ingredient for this scenario in the US was the influx of very warm and humid air from the Gulf of Mexico thanks in large part to the persistent cold pattern in the central and eastern US that acted to inhibit Gulf of Mexico air from advancing northward. The cold air masses, however, began to retreat a couple of weeks ago and subsequently, dew points, which are a true measure of moisture content in the air, have consistently climbed in the central and eastern US and this increased dramatically the prospects for severe weather.
Indeed, the combination of very warm and humid low-level air with a vigorous cold upper-level low pressure trough on Monday helped to spawn the powerful tornado that struck portions of Oklahoma with a major impact on Moore, a heavily populated (50,000 residents) suburb of Oklahoma City some twenty miles to its south. The preliminary estimate is that the one-to-two mile wide tornado that struck the town of Moore reached EF-4 status on the “Enhanced Fugita” scale (5 being the most intense) with winds of nearly 200 mph, but these estimates will be re-evaluated over the next several days/weeks as tornado experts on the ground closely assess the damage and I think it may very well end up being classified as an EF-5. The tornado lasted for about 40 minutes causing destruction over a 20 mile swath.
The overall weather pattern that helped to produce the severe weather yesterday (i.e., warm, humid low level air, strong cold upper-level low with a powerful jet streak, strong surface cold front) will continue for the next couple of days with the severe weather threat zone slowly shifting eastward. There is a threat today for severe weather from the southern Plains to the Upper Midwest, and then likely in the Ohio Valley on Wednesday, and then perhaps in the Mid-Atlantic and Northeast US late Thursday as a strong cold front approaches the east coast. Strong-to-severe thunderstorms are possible later Thursday in the region from the Carolinas to New England as all the atmospheric dynamics shifts towards the east coast. This afternoon’s video includes some time-lapse video of yesterday’s tornado and a detailed discussion as to why the previously quiet tornado season has ended.