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Posted at 11:00 AM ET, 07/23/2009

Forecast: Finally, A Decent Chance of Rain Today

By Camden Walker

But still only 50/50; Warm and humid this weekend

* Nats-Cardinals Forecast | Cool Summer Here, But Not Everywhere *

EXPRESS FORECAST

Today: Partly to mostly cloudy. Humid. 50% chance of showers/storms. Low-to-mid 80s. | Tonight: Muggy. Chance of evening showers/storms. Upper 60s to low 70s. | Tomorrow: Partly sunny. Isolated p.m. showers/storms? Mid-to-upper 80s. | A Look Ahead

FORECAST IN DETAIL

Today brings our best shot at showers and storms in quite some time, with another decent chance expected for Sunday. Meanwhile, mugginess, while varying a bit from day to day, seems like it's in no hurry to leave town after taking so long to arrive. And temperatures? Not bad today. But weekend highs near 90 will be warmer than we've grown accustomed to this summer. Dress lightly, and wear that sunscreen.


Radar: Latest regional radar loop shows movement of precipitation over past two hours. Powered by HAMweather. Refresh page to update. Click here or on image to enlarge. Or see radar bigger on our Weather Wall.

Today (Thursday): The first half of the day starts off with the chance of a shower or two. During the late afternoon and evening, an approaching cold front may then trigger scattered showers and thunderstorms (50% chance), some with the potential for brief downpours and gusty winds. Partly to mostly cloudy skies should limit highs to the low-to-mid 80s. But it will be even more humid than yesterday. Confidence: Medium

Thundercast:
Probability: 50%
Coverage: Scattered

Tonight: We'll see mostly cloudy skies tonight with a continuing 50% chance of some showers or storms in the evening. Then, just an isolated shower overnight. Winds, outside of any storms, will be light out of the east. Look for muggy overnight lows only dropping to the upper 60s to low 70s in most spots. Confidence: Medium

Keep reading for the forecast through early next week...

Tomorrow (Friday): We'll see a blend of clouds and sun on Friday with moderate, but not horrible, humidity levels, as light winds out of the northwest or west dry out the air just a bit. Overall, not a bad day, with highs in the mid-to-upper 80s. But still the afternoon or evening may bring a few isolated showers or storms. Confidence: Medium

Tomorrow Night: After the chance of an isolated evening shower or storm, expect partly cloudy skies with lows in the 60s. Confidence: Medium

A LOOK AHEAD

Yeesh, it will be on the hot side on Saturday, with mostly sunny skies and highs near 90 or into the low 90s. And let's not forget about some moderate summertime humidity. We haven't had many hot weekend days like this in summer 2009. Confidence: Medium-High

Instability enters the area on Sunday in the form of the next cold front. That means shower and storm chances are back in the forecast. As of now, I foresee a 40% chance. Highs could get to near 90 again as humidity remains. Confidence: Low-Medium

Monday looks more like upper 80s for highs. We may have to keep some showers and storms in the forecast. It all depends on how far to the south Sunday's front settles. Confidence: Low

By Camden Walker  | July 23, 2009; 11:00 AM ET
Categories:  Forecasts  
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Comments

"Finally, a decent change of rain"??

Yeah, finally on the one day I have plans (Haines Point golf anyone?), it looks like the rain will come in. If it's raining on my 4:20 teetime, I'm personally holding you, Camden, responsible...

Posted by: JJones-CapitalWeatherGang | July 23, 2009 7:59 AM | Report abuse

Awwww. Golf is not a real sport so a little rain and lighting shouldn't hurt your score.

Posted by: sheepherder | July 23, 2009 8:37 AM | Report abuse

Ha! sorry about some of these anti-golf showers. But look north around Baltimore. Eesh there is some heavy stuff up there!

Posted by: Camden-CapitalWeatherGang | July 23, 2009 10:15 AM | Report abuse

I don't believe in rain anymore. I will take some convincing that storms can approach and hit or form inside the beltway.

So there.

Posted by: bikerjohn | July 23, 2009 11:47 AM | Report abuse

I've posted before that with "60% chance show/thunderstorm" (like today) it should roughly rain 60% of the time, over a long period of time. After all that's what the number means right? Unfortunately it's been my observation that "60%" is more like "20-30%".

Therefore I wonder weather services in general just pump up that number to alert the public. Would rather err on the side of caution, right???

I also make the prediciton that we will see no substantial rain until Sept Hurricane season!

Posted by: LoudounGeek | July 23, 2009 11:55 AM | Report abuse

Plenty of humidity, and large cumulus congestus clouds, but no rain, so far.

Posted by: Bombo47jea | July 23, 2009 12:01 PM | Report abuse

Nice little thundershower ongoing in Dupont Circle.. a few close cloud-to-ground strikes.

Posted by: Ian-CapitalWeatherGang | July 23, 2009 1:41 PM | Report abuse

Bring that thundercast up to 4! I just heard a huge clap of thunder, and it's not really even raining here.

Posted by: KBurchfiel | July 23, 2009 1:53 PM | Report abuse

Anyone report hail downtown? some radar indications there could be some.

Posted by: Camden-CapitalWeatherGang | July 23, 2009 1:54 PM | Report abuse

Just had about a minute of thick rain drops falling straight down for about 1 minute. No wind. There was a similar episode this am that also lasted 1-2 minutes. That's all folks!
-NE DC Capitol hill area

Posted by: jojo2008 | July 23, 2009 1:56 PM | Report abuse

Radar estimating over 1" already near Georgetown area and on VA side of river. Storm not moving much.. National airport still dry.

Posted by: Ian-CapitalWeatherGang | July 23, 2009 1:57 PM | Report abuse

SW DC's dark and blustery with rain starting and lots of close lightning.

Posted by: map408 | July 23, 2009 1:58 PM | Report abuse

@Kburchfiel

I think the Thundercast rating is just about right. Clicking on the "Thundercast" link gives you the category definitions. 2 lightning bolts = "Typical thunderstorm potential. Heavy rain, lightning and/or gusty winds likely. Isolated storms may produce frequent lightning, damaging winds (50 mph or higher) and/or small hail."

Posted by: CapitalWeatherGang | July 23, 2009 2:03 PM | Report abuse

I think the percentages of rain chances are dependent on the season. 30% in Spring means 60%, but in the Summer it means 30%, especially if you live near Fredericksburg or Southern Maryland. We definitely have very different weather patterns here than our neighbors in Pennsylvania and southern Va.

Posted by: rocotten | July 23, 2009 2:04 PM | Report abuse

Wow! There is a big rain cloud that is just dumping cats/dogs on us for the past 10 minutes or so. Hope it makes it to my house in S. Arlington!
NE DC Capitol hill area

Posted by: jojo2008 | July 23, 2009 2:16 PM | Report abuse

Good call, Camden, in lowering the NWS % of precip from 70% to 50%. There's an interesting interplay of forces between subsidence of air from the quasi-tropical activity off the coast on one hand and the front to the west on the other. It will be interesting to see exactly which areas get wet and how much.

Posted by: CapitalClimate | July 23, 2009 2:17 PM | Report abuse

"I've posted before that with "60% chance show/thunderstorm" (like today) it should roughly rain 60% of the time, over a long period of time. After all that's what the number means right?"
Is this correct? I always assumed a 60% chance of rain means there's a 60% it will, and a 40% chance it won't (with no indication of duration). Was I absent on the wrong day in high school?

Posted by: LCFC | July 23, 2009 2:19 PM | Report abuse

LCFC: you were. "over a long period of time" does not mean "rain over a long period of time". It means the pattern will manifest itself over many repetitions (which requires a long period of time.)

go back to high school and take up simple statistics again.

Posted by: LoudounGeek | July 23, 2009 2:22 PM | Report abuse

@CapitalClimate
Interestingly, NWS (at least on our 6-day at a glance) seems to have come down to 50% this afternoon.

Posted by: CapitalWeatherGang | July 23, 2009 2:27 PM | Report abuse

Meanwhile on the border of PG Co and MoCo in Beltsville the sun is peeking out and it's as dry as a bone. I hope some of the rain makes it this way, it's crispy, crunchy out there.

Posted by: ana_b | July 23, 2009 2:34 PM | Report abuse

Another cell fired just north of DCA but the airport still appears dry. Had this all been 2-3 miles south driest July would have been an idea of the past.

Posted by: Ian-CapitalWeatherGang | July 23, 2009 2:52 PM | Report abuse

"...If it's raining on my 4:20 teetime..."

you know the that Scottish saying(?): "if it's nae wind, and it's nae rain, it's nae golf."

such a wuss.

Posted by: Ichristian | July 23, 2009 2:57 PM | Report abuse

LoudounGeek: I really didn't (and still don't) understand how "long period of time" is used in this context. But it doesn't seem worth a return trip to HS to figure it out!

Posted by: LCFC | July 23, 2009 3:02 PM | Report abuse

Anyone know about the rainfall in the Huntington area of Alexandria? I left a cardboard box out on the back deck and won't be home for another hour to retrieve it. I blame that oversight on the fact that I didn't really believe it would ever rain again ;-)

Trying to figure out if it will be just damp or soaked within an inch of its life/no chance of moving it without it falling apart.

Posted by: kallieh | July 23, 2009 3:05 PM | Report abuse

Eyeball analysis seems to confirm the 50%, at least so far, with National at a trace and Dulles at 0.77". BWI has 0.14".
MoCo is much happier than FFX.

Posted by: CapitalClimate | July 23, 2009 3:51 PM | Report abuse

Yeap, we got screwed again in Vienna. Must have less than .05" this month.

Posted by: rocotten | July 23, 2009 4:37 PM | Report abuse

"I really didn't (and still don't) understand how "long period of time" is used in this context."

I'm not sure either but think LoudounGeek might be saying that if you look back at 100 days with a forecasted 50% chance of rain, it should've rained on about 50 of them...? LG can correct if that's not what he/she meant.

Where my confusion comes in is with weather.com's hourly forecasts. They may forecast 20% chance of rain for 40 hours straight but that doesn't seem to really mean that it will rain for 8 of those hours. It seems to really mean that it probably won't rain at all but there may be a shower.

Posted by: spgass1 | July 23, 2009 4:41 PM | Report abuse

spgass1 - thanx for clearing up for me. I've been too buried in meetings to explain myself well. My experience has been out of these 100 "60% chance rain" days I've been seen rain in only 20-30 days of them. That's my theory, and I'm sticking to it.

Now, 20% shower? Forget about it!

Posted by: LoudounGeek | July 23, 2009 9:16 PM | Report abuse

The comments to this entry are closed.

 
 
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