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Posted at 10:45 AM ET, 05/27/2010

Forecast: Steamy day sets stage for thundery night

By David Streit

Some storms could be strong to severe

* Severe T'storm Watch and Flash Flood Watch for metro area *
* When a drought is not a drought | Revolving doors in TV weather *
* Outside now? Radar,& more: Weather Wall | StrasCast | BeachCast *

Today's Daily Digit
A somewhat subjective rating of the day's weather, on a scale of 0 to 10.
5Unless I'm in Finland, I can do without this sauna. At least storms should come after rush hour.
Get tomorrow's 'Digit' on Twitter tonight


Today: Hot & humid, isolated p.m. thunderstorm. 88-92. | Tonight: Chance of thunderstorms. 66-69. | Tomorrow: Cloudy, showery. 73-77. | A Look Ahead | Get Express Forecast by E-mail


By David Streit, CWG Meteorologist

The only comforting thought about the sweltering today is that it'll be gone tomorrow! The problem is that dislodging this heat requires a cold front and that may mean some strong thunderstorms later today. The cooling comes at a price as we'll be socked in with clouds and showers tomorrow. Part of Saturday and all of Sunday are worth the wait, both promising to be mild with sunshine returning. Memorial Day marks the start of summer in style with above normal temperatures and the return of humidity under a bright sun.

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 (Thursday): Sunny skies and rising humidity levels lead to discomfort by mid-morning with little breeze to help cool. The clouds start popping up early afternoon but any thunderstorms (20% chance) would be isolated and mainly in the northwestern suburbs. Highs peak in the upper 80s to lower 90s. Confidence: High

Probability: 40-50%
Coverage: Scattered
Most likely timing: 5-10 p.m.

Tonight: A cold front interrupts our muggy evening, possibly triggering thunderstorms. The cold front is a "back door" variety sweeping down from New England instead of the typical west to east slider. Storms that develop have the potential to be severe with damaging wind gusts, large hail and heavy rain. After a possible initial line of intense evening storms (40-50% chance -- not everyone will get hit), scattered thundershowers may continue off and on overnight (50-60% chance). Lows fall to the 70s in the showers and bottom in the upper 60s overnight. Confidence: Medium-High

Keep reading for the outlook through the Memorial Day weekend...

Tomorrow (Friday): Dampness is the rule with dense clouds supporting drizzle and occasional showers (80% probability). Light winds from the east keep the moisture flowing in from the Atlantic. Temperatures will be lucky to gain a degree an hour to peak in the low-to-mid 70s. Confidence: Medium-High

Tomorrow Night: The damp lingers through the evening with a 60% chance of a shower mixed in with the drizzle. Evening readings hold in the upper 60s to lower 70s. Support for the showers dies out after midnight but clouds persist. Lows fall to the upper 50s to lower 60s. Confidence: Medium-High


Saturday depends strongly on the winds from the east dying out early to allow the clouds to break. This is a tall order and the best bet is that the breaks won't begin to show up until late afternoon. Temperatures spend their time in the 60s in the morning but should reach low-to-mid 70s in the afternoon. There is a 20% chance of a lingering early morning shower, especially south of the city. Confidence: Medium

Sunday weather wins the award for best in class. The morning readings quickly jump from 60s to 70s but stop in the lower 80s by mid-afternoon. A distinct lack of clouds through the day should be a treat. The final icing on a great day is low humidity and light winds. Confidence: Medium

Memorial Day gets back to the business of summer with both climbing temperatures and humidity. Sunny skies ensure a quick jump in the morning from 60s at daybreak to 70s by mid-morning and upper 80s by late afternoon. A pop up thundershower by late afternoon can't be ruled out but the probability is only 20%. So if you get wet at least I can say you were warned! Confidence: Medium


The weather at the beaches is conspiring to keep you at work on Friday! From Cape May south to the Outer Banks, including the Maryland & Delaware shore, shower chances range around 70% with highs in the upper 60s from Cape May to Ocean City and lower 70s for points south.

Saturday is the transition day with clouds slowly parting along the Jersey shore around midday as sunshine works slowly southward through the Md./Del. beaches and down to the Outer Banks by evening as high pressure builds in from the north. Nobody's warm as onshore breezes come off waters that are still only in the 60s, keeping highs in the upper 60s. Good news is ocean temps are warmer than average this year so hitting the surf won't be too painful if you're so brave. Waves will be potent reaching heights of 3 to 5 feet in most areas through the weekend, so be careful.

Sunday is a marked improvement up and down the coast with highs in the low-to-mid 70s under mostly sunny skies.

Memorial Day will make you wish for another week of vacation with highs in the upper 70s to lower 80s. An intense sun will require plenty of the high SPF lotion for any tanning. Have a great holiday weekend!

By David Streit  | May 27, 2010; 10:45 AM ET
Categories:  Forecasts  
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Why has the NWS issued a Flash Flood Watch?

Posted by: wzitlau | May 27, 2010 7:57 AM | Report abuse

That is a great question! It looks like they are considering two different threats. The first one is those afternoon pop up thundershowers west of the city particularly in the I-81 corridor. They will be very slow moving so they could rain on one spot for an extended period of time resulting in isolated flooding. The other concern is the band of severe storms that should come through late this evening. They could contain brief heavy downpours that would also result in isolated flooding, mainly to the east of the city. Bottom line: any flooding will be isolated in nature.

Posted by: davidstreit1 | May 27, 2010 8:19 AM | Report abuse

Looking at, looks like it will clear earlier out in Shenandoah -- rain more likely tomorrow and nice Saturday & Sunday. Is that your read?

Posted by: kimcycles100 | May 27, 2010 8:38 AM | Report abuse

You are right! The Shenandoah would have a better opportunity to break out earlier on Saturday than in the city since it is farther from the Atlantic and the inflow of moisture that will be going on for the first half of the day in the region.

Posted by: davidstreit1 | May 27, 2010 8:59 AM | Report abuse

Today gets a "10" on the ThinkSpring scale. Heat, humidity, and afternoon thunderboomers.

Had a fantastic run on the Mall this morning. Got a good sweat going and got good work in.

Posted by: ThinkSpring | May 27, 2010 10:34 AM | Report abuse

I think the appropriate term for today would be: juicy

Posted by: Brian-CapitalWeatherGang | May 27, 2010 10:38 AM | Report abuse

Looking at accuweather, it looks like we might have a narrow window of sun during Jazz in the Garden, but is showing rain all day.

Which is it?

Posted by: GoodOmens | May 27, 2010 10:54 AM | Report abuse

Yay beachcast!

Swellinfo reports the water temp is 62. Not sure I believe that. Still taking the full suit down with me. Looks like it's gonna be a chilly day on the beach Saturday.

Posted by: wiredog | May 27, 2010 11:00 AM | Report abuse

I wish I had better news, but it is highly unlikely that there will be sun for Jazz in the Garden tomorrow. In fact an umbrella will be necessary as showers are very likely during the event.

Posted by: davidstreit1 | May 27, 2010 11:32 AM | Report abuse guys still calling for severe storms in this area, even if the line comes through this evening after dark, with surface cooling and added stability? That will take some dynamics. This afternoon, NWS has CAPE values possibly up to 3000, but you expect that to continue after dark?

Posted by: MMCarhelp | May 27, 2010 12:00 PM | Report abuse

MMCarhelp, this is a discussion (somewhat technical) from the Storm Prediction Center regarding our severe storm threat.

Posted by: MattRogers | May 27, 2010 12:04 PM | Report abuse

Already 90 at DCA!

Posted by: Ian-CapitalWeatherGang | May 27, 2010 12:05 PM | Report abuse

Mechanical lifting by the cold frontal passage could counteract cessation of the normal diurnal heating cycle after dark, hence the continued severe threat overnight.

What remains to be seen is how nasty the continued and MUCH-UNNEEDED prolongation of rainy crud due to easterly flow will be through the period beginning tomorrow. In previous years, predicted nice, sunny Memorial Day weekends have "melted" into raw, cloudy basket cases due to these nasty backdoor cold fronts. They might be welcome to relieve a mid-July heat wave but can easily wear out their welcome by turning Memorial Day weekend into a soggy, nasty mess. Since I have a potential dance every night this weekend, a prolonged wet raw and cloudy spell would be HIGHLY UNWELCOME! One of the major factors involves these late-May Rex blocks, and I suspect the much-needed rain crowd is off on another one of their anti-Bombo "crusades".

Posted by: Bombo47jea | May 27, 2010 12:20 PM | Report abuse

MMCarhelp, Instability will remain in the atmosphere long after the sun goes down. Take last night as an example, our 00z, evening, sounding had ~2500 Joules of CAPE (a measure of instability). Even after cooling all night, our 12z, morning, sounding still had a CAPE value of near 1000, though this was elevated away from the surface. Even if our surface layer cools 5-10 degrees before the forecast MCS, or other thunderstorms arrive, the ongoing convection should have plenty of uplift with it to tap into this leftover available instability.

Posted by: Brian-CapitalWeatherGang | May 27, 2010 12:31 PM | Report abuse

bombo, I actually prefer clouds without rain....a nice, DRY, overcast stratus or stratocumulus deck. This time of year, IMO, that's the best of both worlds. The high sun angle and Bermuda-High southerly flow this time of year can be a real pain in the ***, although this time, the heat, unusually, is retrograding south from Canada, not being pumped around a Bermuda High.

Posted by: MMCarhelp | May 27, 2010 12:35 PM | Report abuse

Sure glad I have indoor seats for tonight's Michael Franti concert at Wolf Trap.

Posted by: chunche | May 27, 2010 12:47 PM | Report abuse

Good call, chunche - I love sitting on the grass (cheaper, can have picnic, etc) but in the hotter months I do worry about rain & storms!

Posted by: Camden-CapitalWeatherGang | May 27, 2010 2:18 PM | Report abuse

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