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Posted at 5:00 AM ET, 07/25/2010

Forecast: Cold front late today signals break in heat

By Brian Jackson

Temps drop and drier air arrives tomorrow

(updated at 12:30 p.m.)

* Severe Thunderstorm Watch N & NW of District (map) until 7 p.m. *
* Heat advisory through 8 p.m. | Recap of yesterday's heat | Photos *
* Outside now? Radar & more: Weather Wall | Tropical Tracking *
* Consec days 90+: 12; Total 90+: 42 (Apr: 2; May: 3; Jun: 18; Jul: 19) *

Today's Daily Digit
A somewhat subjective rating of the
day's weather, on a scale of 0 to 10.


Heat lasts for one more day, but relief less than 24 hours away.
Get the 'Digit' on Twitter


Today: Hot & sticky, chance of p.m. storms. 95-99. | Tonight: Partial clearing. 72-77. | Tomorrow: Not as hot, drier. 88-92. | A Look Ahead | Get Express Forecast by E-mail


While we may be able to avoid the century mark today, we'll still have to deal with one more day of rather stifling conditions. This heat combined with an approaching cold front provides the ingredients for possible afternoon thunderstorms. Once they're through though, some more comfortable heat settles in for the first part of the week . Another front approaches by late Wednesday and will bring another threat of thunderstorms. So was anyone this desperate for shade yesterday?

Temperatures: Latest D.C. area temperature map powered by iMapWeather (base map by Google). Click and hold on map to pan. Double-click to zoom. Refresh page to update. See larger map on our Weather Wall.

Today (Sunday): We've seen the peak of this current hot-streak come and go, but we've got one more steamy day to pull through. Sunny morning skies will once again push the mercury into the 90s but building afternoon clouds should keep us to highs in the mid-to-upper 90s rather than triple digits (if they hold off until after 3 p.m., 100 may be in reach again, however). Some relief might also come in liquid form as there is a fair chance (40%) that a fairly significant cold front approaching will initiate some boomers into the afternoon/evening. A few of these storms could pack a punch with damaging winds and torrential downpours. Winds will be out of the west at around 10 mph, but higher around the storms. Confidence: Medium-High

Probability: 40%
Coverage: Scattered
Most likely timing: 3-8 p.m.

Tonight: Showers and storms should be exiting the area by the overnight hours and by morning we'll see some welcome improvement to our conditions. Skies will gradually clear overnight, and a wind from the northwest will begin to dry us out. Lows will be in the low-to-mid 70s. Much better than the 80s, no? Confidence: High

Like today's weather? Vote your call for today's Daily Digit (see Daily Digit box above). And keep reading for the forecast into next week...

Tomorrow (Monday): Future me says "Ahhhhhh". Even though above average temperatures remain, a significant drop in both temperature and humidity will feel quite nice as we head back into the week. Skies will turn mostly sunny. Although there's a good chance that we'll see our 90s streak extended, barely, at least we'll be able to enjoy it! The winds will produce a "cooling" breeze from the north-northwest at 5-10 mph. The lingering front to our south, means those from mid-Virginia south may see significantly cloudier and damper conditions. Confidence: Medium-High

Tomorrow Night: A tranquil night is in the cards with mostly clear skies dominating. Rather refreshing as well, as we could see our lows dip into the 60s for the first time since July 4th. Though inside the beltway, the lower 70s will more than likely be our lower limit. Confidence: Medium-High


Tuesday presents another nice, albeit warm, summer day. Southerly flow returns, meaning our humidity will begin to creep up but we'll remain in relative comfort through the day. Skies will be mostly sunny, with some additional clouds late, and daytime highs in the lower 90s. Overnight, we'll have partly-to-mostly cloudy skies, with lows in the low-to-mid 70s. Confidence: Medium-High

Wednesday another front spells shower and thunderstorm chances for our region that may stick around for a day or two. Expect afternoon thunderstorms to pop up amongst partly sunny skies, and our daytime highs to reach the upper 80s to lower 90s. Confidence: Low-Medium

By Brian Jackson  | July 25, 2010; 5:00 AM ET
Categories:  Forecasts  
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Statistical question: longest period D.C. official temp has remained above 80 degrees. Does not appear to have dropped below 80 last night and it's been at 80 or higher since some point in Friday 7/23 a.m. rush hour. (Friday's low of 77 was shortly after 5 a.m.) Thanks.

Posted by: JerryFloyd1 | July 25, 2010 7:32 AM | Report abuse

CWG, question for you all. Why is it that most alleged cold fronts that come throkugh here, do so during suppertime? Why not for breakfast or lunch? I understand that airmass tstorms occur during the heat of the day, afternoons and evenings, but what about fronts?

Posted by: VikingRider | July 25, 2010 9:40 AM | Report abuse

Do you suppose IAD could break a record again today? It would only have to hit 97 to tie 1987's mark according to your almanac.

The airport read 90 degrees at 10 AM, while my thermometer here in Sterling is currently showing 91.5.

Posted by: Sterlingva | July 25, 2010 10:11 AM | Report abuse


While the timing of today's front is late afternoon/evening, it's not the case that frontal passages occur preferentially at suppertime. It may just seem that way because airmass thunderstorms tend to occur then and/or because even when a front is in the vicinity but not passing until later (or sometimes having passed by earlier) - storms may fire up out ahead of (or behind) it to coincide with peak heating.

Posted by: Jason-CapitalWeatherGang | July 25, 2010 10:11 AM | Report abuse

Any thoughts on how severe the thunderstorms associated with the cold front might be? Is there a concern about tornadic activity? Supercells?

Posted by: JedinBethesda | July 25, 2010 11:15 AM | Report abuse

While I liked Steampocalypse, and especially Hotpocalypse, I think with the earthquake thrown in you really have to call this a Shake 'n Bake Summer. :-)

Posted by: DopplerPat | July 25, 2010 11:16 AM | Report abuse

Jed, I wouldn't put too much worries toward tornado's, the main threat looks to be straight line winds with a squall line that's forming back in western PA. Even if some isolated storms get going ahead of the line, there isn't a whole lot of shear that would start them spinning.

Posted by: Brian-CapitalWeatherGang | July 25, 2010 11:22 AM | Report abuse

It's a great day to clean my basement storage room. Nice and cool down there . . .

Posted by: Gunga2009 | July 25, 2010 11:36 AM | Report abuse

Thanks, Brian! That's good to know.

Posted by: JedinBethesda | July 25, 2010 11:37 AM | Report abuse

Thanks CWG. You confirmed that airmass tstorms generall occurr afternoon/evening, and fronts can come thru anytime, unless they don't.
Scariest tstorms I've ever seen were in Wyoming on a early summer vacation to Yellowstone and Grand Teton. Even when the storms don't come over you, the mountains tend concentrate and echo thunder so it seems far louder and closer than it actually is. And the sky is so BIG out there, lightening really does look like a a bolt from Thor.

Posted by: VikingRider | July 25, 2010 11:55 AM | Report abuse

It's hotter 'n whoopee in woolens.

Posted by: Hoyas4Ever | July 25, 2010 12:16 PM | Report abuse

Looking at the Mosaic radar, that line of thunderstorms in western PA is moving very fast, decreasing the chances of officially hitting 100 today. Oh well, when you're hot, you're hot and when you're not, you're not.

Posted by: JerryFloyd1 | July 25, 2010 12:28 PM | Report abuse

HA! Figures, no sooner do I downplay the tornado threat, the NWS issues a tornado warning for Garret County. I doubt there's anything on the ground but still...

Posted by: Brian-CapitalWeatherGang | July 25, 2010 12:41 PM | Report abuse

We're going to get whalloped today with these thunderstorms...

Posted by: fleeciewool | July 25, 2010 12:52 PM | Report abuse

The cell in W MD didnt look very impressive rotation wise. The only real risk for tornadoes IMO is with a supercell out in front of the line and the conditions are better to the north for that. SPC mentioning a new watch for this area is likely.

Posted by: Ian-CapitalWeatherGang | July 25, 2010 1:30 PM | Report abuse

The FIREDRAGONs will be driving up to Frederick MD sometime between 4:00 & 6:00PM; returning by 11:00.
When I asked the Magic 8 Ball whether we would have to drive in bad t-storm conditions it gave no clear opinion. That thing has always been useless.
I think that at some point we'll be driving in a rainstorm. Could be the camera.

Posted by: FIREDRAGON47 | July 25, 2010 1:53 PM | Report abuse

The big threat with these straight-line winds/squall lines/derechos: POWER OUTAGES, which can make these frontal transitions a steamy mess since A/C goes off, no TV means no entertainment or information, food spoils if fridges stay off too long, and you can't even READ if the lights don't come back on after dark!

If there's a dance on schedule and the power goes off, forget it! DJ's can't "spin" their records, and most live bands depend on electronic acoustics nowadays. Perhaps we've gotten too darned dependent on electric power these days...anyway, a prolonged storm-induced power outage is the worst possible hazard nowadays. You can't even go to the grocery store, as all their cash registers are computerized and even if the sales clerks can revert to manual operation, the darned cash registers won't operate manually! Back when I was a boy, the sales clerks could go back to manual...a process which slowed things down, but at least kept the economy running. Nowadays we could all get shut down for good if someone targeted the power distribution system. Apparently all it might take is the electromagnetic pulse from one nuclear detonation at high altitude. Even an extremely intense solar discharge might do the trick...we're starting a new sunspot cycle.

Generators might help a bit...but you'd better be sure you don't turn it on in a confined space indoors...carbon monoxide can be a threat.

Posted by: Bombo47jea | July 25, 2010 2:01 PM | Report abuse

BWI is on the verge of tying the all time record of 100+ days, 99 this hour.

Posted by: Ian-CapitalWeatherGang | July 25, 2010 2:12 PM | Report abuse

From Leesburg: my indoor/outdoor thermometer, which I had always thought was accurate - it read 102 yesterday - is currently at 104.7 and rising. I thought today was supposed to be less hot than yesterday?? Crazy heat.

Posted by: TerpInTime | July 25, 2010 2:23 PM | Report abuse

TerpInTime, I've found that a lot of cold front days overperform heat wise. I think we get some help with compressional heating right ahead of a front.

Posted by: Ian-CapitalWeatherGang | July 25, 2010 2:28 PM | Report abuse

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