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Posted at 11:15 AM ET, 06/15/2010

Forecast: Less heat and humidity

By Matt Rogers

Storm chances increase tomorrow; weekend heat

* Thunderstorms: Fickle & capricious for sure *
* Outside now? Radar temps & more: Weather Wall *

Today's Daily Digit
A somewhat subjective rating of the day's weather, on a scale of 0 to 10.
7Today is a definite improvement with lower humidity & nice start. Thicker p.m. clouds and shower chance knock the digit down a notch.
Get tomorrow's 'Digit' on Twitter tonight


Today: Partly to mostly cloudy. A few p.m. showers. 81-85. | Tonight: Mostly cloudy. Chance of a few more showers. 61-66. | Tomorrow: Decent chance of p.m. storms with variable clouds. 82-86. | A Look Ahead | Get Express Forecast by E-mail


The debate is over. The science is settled. We need RAIN. Despite our record snowy winter (wow, that seems so long ago), National Airport is running more than 5" below normal for the calendar year. The worst of the current situation is definitely from the District eastward. We at least have a chance of some showers today and especially tomorrow. We'll also need to watch the hot weekend for more storm chances.

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

Today (Tuesday): Partly sunny skies this morning should turn to thickening clouds this afternoon and we'll run a 30% risk of afternoon showers or a thunderstorm. We should take a slight break from the heavier humidity of the last few days as temperatures peak out in the low-to-mid 80s. Light winds from the east and northeast are expected. Confidence: Medium-High

Tonight: Mostly cloudy tonight with a 30% chance of a shower or storm, mainly after midnight. Lows should range through the 60s with winds again light from the east and southeast. Confidence: Medium

Keep reading for the forecast through the weekend...

Tomorrow (Wednesday) will find more humidity back into the area as winds start coming from the south again. Clouds should prevent us from getting too hot though and temperatures should top out in the low-to-mid 80s again. The best chance for storms (up to 60%) is in the afternoon into evening and some could be locally heavier, but unfortunately rainfall totals will not be consistent around the area...anywhere from .01" to .25" probably. Confidence: Medium

Tomorrow Night:A continued 40% chance of showers and storms especially through about midnight. Cloudy skies with lows in upper 60s to low 70s. Confidence: Medium


Thursday is currently favored to see mostly sunny skies, lower humidity again, and highs in the low-to-mid 80s. This is looking to be our best day of the week. Thursday night should find partly cloudy skies with lows ranging through the 60s. Confidence: Medium-High

Friday should see mostly sunny skies again, but temperatures are forecast to increase to the upper 80s or maybe touch 90 around the area. Humidity should still stay on the lower side compared to earlier this week. Confidence: Medium-High

We are developing a very bad habit of hot weekends. Just like the last one, we are currently expecting low-to-mid 90s along with partly sunny skies and the threat of afternoon into evening thunderstorms, especially on Sunday. The chance of storms is around 20% on Saturday and up to 40% on Sunday. Humidity will be back to bother us, so the lows on Saturday and Sunday morning will probably only drop into the upper 60s (suburbs) to low-to-mid muggy 70s in the city. Confidence: Low-Medium

By Matt Rogers  | June 15, 2010; 11:15 AM ET
Categories:  Forecasts  
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Next: String of floods raise climate change questions


Hey, guys! Could you post a brief explanation of why thunderstorm activity is so hard to predict? In the past week I've put off evening grilling plans a number of times because everyone (not just the CWG) was forecasting thunderstorms, often including the ominous "some may be severe." Then we get either no rain at all, or maybe 8 drops. Since forecasting temps, humidity, wind, etc. has become impressively accurate, why do thunderstorm events remain so hard to nail? P.S. Love your blogs! They're the best in town.

Posted by: BruceSorrell | June 15, 2010 7:21 AM | Report abuse

Same here...Several rain chances, no hits...until last night...I go out just after 8 PM and get drenched before I can even make it to the front, sidewalk...and that, "much-needed rain" crowd, was WITH an umbrella!!! That was very mean of you, hitting me with that downpour, when I'm trying to get to a bus stop. Had to stay least there was "no dance lesson" at Chevy Chase Ballroom...meaning the place might have been "dead" with a reduced crowd...just better not try these shenanigans tonight [Clarendon], tomorrow [Buddhist mtg.] or Friday for my big dance of the week.

Quite cloudy this morning; still threatening rain. I thought today was supposed to be a dry day. For a predicted "dry" summer, we sure have been getting the rain threats, even if they don't always pan out.

Posted by: Bombo47jea | June 15, 2010 7:52 AM | Report abuse

So the forecast for today is partly sunny, a nice start, and lower humidity? The forecast doesn't seem to match the reality. In Fairfax it's been clouded over since sunrise, the humidity is currently 79%, and the dew point is an uncomfortable 65. Doesn't seem like a "nice start" to me. And if it's only going to go downhill from here (as you predict) then I'd call this a blown morning forecast.

Posted by: rwalker66 | June 15, 2010 8:21 AM | Report abuse

I just walked the dog and temperatures are definitely cooler than yesterday morning and overall more pleasant. The clouds are heavier this morning and we may still get some breaks at times this morning into midday before more afternoon clouds build in. I did see partly sunny skies here in northwest. But after our hot weekend, I still contend that this morning is a nicer start than yesterday with regard to comfort levels.

To answer the other question, thunderstorms are difficult to forecast because they are smaller-scale events. These smaller features are more challenging for the super-computers to handle, because they can frequently develop and move based on very localized ("mesoscale") factors. This is especially true when you don't have a strong forcing mechanism like a pronounced cold front to drive the convection. Meteorologists will sometimes call these storms "garden-variety" storms because they are scattered and you don't quite know what will come up.

Posted by: MattRogers | June 15, 2010 8:33 AM | Report abuse

@Bruce, that's why you can't cancel any outdoor plans unless the storms are imminent. I used to skip the bike commute based on predicted afternoon storms, and after riding the Metro home on countless sunny afternoons, I now just take a chance. Most of the time it works out fine, though a handful of times, I've gotten drenched.

Posted by: mmurphy70 | June 15, 2010 8:51 AM | Report abuse

hey guys, any chance you could move those wednesday storms to today or thursday? i have afternoon/evening plans for wednesday that i'd rather not have affected by rain/thunder. thanks in advance.

Posted by: walter-in-fallschurch | June 15, 2010 9:41 AM | Report abuse

Walter, my windows are open (about an inch) at the park and ride. Answer: no.

Posted by: eric654 | June 15, 2010 9:47 AM | Report abuse

dang...i don't like that answer, so i'm skeptical... ;-)

Posted by: walter-in-fallschurch | June 15, 2010 10:33 AM | Report abuse

I love receiving requests for moving weather activity, haha. So I will give you the classic meteorologist response: "We will see what we can do" :-)

Posted by: Camden-CapitalWeatherGang | June 15, 2010 10:51 AM | Report abuse

Be careful what you wish for - could end up like some of those places with the flash floods. I would like a few days of good not-too-heavy soaking rain to help bring us closer to normal. I wouldn't want it all at once!

Posted by: msienkiewicz | June 15, 2010 11:13 AM | Report abuse

well, i didn't request not to have any rain, just that it be moved away from wednesday.

Posted by: walter-in-fallschurch | June 15, 2010 11:17 AM | Report abuse

Hi Matt, how about just increasing the model resolution? Or is convection always going to be less predictable?

Posted by: eric654 | June 15, 2010 11:18 AM | Report abuse

It's all well to say not to cancel outdoor plans unless thunderstorms are "imminent," but that doesn't seem like a good idea when the plan is hiking. I'm annoyed because I've cancelled weekend hikes a couple of times now only to see no storms whatsoever. At the same time I don't want to run the risk of getting hit by one when I'm in the middle of a trail with no cover. Ok to just take my chances and go early in the morning when storms seem less likely?

Posted by: javachip | June 15, 2010 11:19 AM | Report abuse

re: thunderstorm predictability

Will repeat an analogy I've used before: heat up a pan of water and try to predict where a single bubble will be and how big it will be... that's like trying to predict thunderstorm activity... there's a certain degree of randomness which make it impossible to forecast with pinpoint accuracy.

Posted by: CapitalWeatherGang | June 15, 2010 11:23 AM | Report abuse

So, regarding the "D" word... is it on?

Posted by: ennepe68 | June 15, 2010 11:37 AM | Report abuse

re D word,
There are plenty of definitions of drought so it is a bit of an open ended question. I will say that a simple rule of thumb I have used working in the agricultural community is that the area should be at 60% or less of normal rainfall for at least 3 months. National Airport is currently at 65% of normal for the past 3 close but not quite. We could be there in two weeks, if the heavens don't open up!

Posted by: davidstreit1 | June 15, 2010 11:50 AM | Report abuse

Drought???...Come on, now...if this were a REAL drought, we would be sitting under a ridge...none of these incessant afternoon/evening rain threats, no dance-wrecking "soakers" like what I had to go through at 8:15 yesterday evening...but that was Monday night, and now the "much-needed rain" crowd is threatening me with a REPEAT for tonight's Clarendon Ballroom event--not to mention the sudden severe weather threat for tomorrow night's Buddhist meeting.

Let's just hope we don't have a power outage tomorrow--I have to do a "reading" for that meeting!

Posted by: Bombo47jea | June 15, 2010 12:20 PM | Report abuse

Addendum: Last week this time, the prediction for tomorrow was "fair and dry", not "severe weather threat".

In addition, there's more rain forecast for Sunday afternoon--yet another W&OD Trail hike down the drain! Last time I was on the Trail was some time in mid-May.

Posted by: Bombo47jea | June 15, 2010 12:26 PM | Report abuse

walter-in-fallschurch, I didn't intend to refer to your post - for me one day or another doesn't matter that much. It was more in response to the original article... it helps to be specific about what you want (as you were).

Posted by: msienkiewicz | June 15, 2010 12:53 PM | Report abuse

while thunderstorms may be difficult to predict, individuals have access to radar like never before. On my mobile device I can get radar snapshots easily. On over-air digital TV, channels 4, 7 and 9 all have weather on their secondary channels. Channel 9-2 runs the radar only all the time, not to mention the internet from a computer. So before going out, Ive found it rather easy to get a good idea of the chance of getting caught in a storm in the next few hours and work around it. Hosting guests for a cookout or planning an all-day hike may be more difficult, but I think you have lots of tools available to make good safe decisions in advance while enjoying summer activities.

Posted by: apeirond | June 15, 2010 1:42 PM | Report abuse

H Gang! Love this blog! Wanted to see if you could make a Wolf Trap rain prediction? I'm scheduled for lawn seats at Wolf Trap tonight, do you think we will be sitting in the rain? 30% chance doesn't seem to bad but husband doesn't want to take chances! TIA!

Posted by: alcw1 | June 15, 2010 2:25 PM | Report abuse


While can't rule out a shower this evening, by and large I think the showers we've seen around during the early-to-mid afternoon are going to quiet down with not much happening during the evening, and the next best chance of showers waiting until a brief window overnight toward early morning, and then again later in the day tomorrow. So, bottom line is I'd hope for the best and plan to head out to Wolf Trap, but maybe bring a small pocket umbrella just in case.

Posted by: Dan-CapitalWeatherGang | June 15, 2010 2:34 PM | Report abuse

Wolf Trap....on the lawn.....muggy summer evening.
Don't forget to bring a towel.
In fact, bring two.

Posted by: FIREDRAGON47 | June 15, 2010 2:42 PM | Report abuse

Thanks Dan! :-)

Posted by: alcw1 | June 15, 2010 3:26 PM | Report abuse

FINALLY, someone at CWG who stands up to admit we NEED THE RAIN! Thank you, Matt, your post is very much appreciated!

Does anyone know how water levels are holding up in the reservoirs that supply metro DC (located in western Maryland)?

Posted by: TominMichiganParkDC | June 15, 2010 4:24 PM | Report abuse

Several of us have mentioned that is has been dry, but we're not yet in drought. I posted the same image last week in the comment section. We've definitely had some issues seeing widespread solid precip since maybe Feb 10. Bombo is sort of right in that it might not feel like drought given relatively frequent precip chances, but in most cases those events have hit pretty small areas. We are probably still close enough to normal that one solid event would remove worries for a while, but the trends right now seem to want to introduce at least low level drought in parts of the area fairly soon.

Posted by: Ian-CapitalWeatherGang | June 15, 2010 4:58 PM | Report abuse

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