Where Are the May Showers?

Southwesterly flow ahead of a cold front in the Ohio Valley is sending balmy temperatures all the way up the Atlantic Coast into northern New England this afternoon. Locally, temperatures reached typical early June levels with readings of 80° or above by 3pm at all Washington DC metro area locations except for river-breezed Quantico.

As Josh explained earlier, needed precipitation will be quite scarce over the next several days; this morning's GFS model has the DC area on the northern edge of minimal precipitation at best for at least the next 48 hours. The afternoon NAM model is only a little less stingy; it comes up with less than 0.10" through Saturday.

Temperature chart at 3pm today from Unisys

Tonight and Tomorrow

Under mainly cloudy skies later tonight, low temperatures will have a hard time breaking below 60 in the District and mid 50s in the 'burbs. Friday will feature considerable cloudiness for much of the day but only a 30% chance of showers. Highs should be able to reach the mid 70s, closer to 80 if there is more afternoon sun.

April Showers Drying Up

Mid April's rain took a bite out of the 2006 precipitation deficit, but we're likely to be once again over 30% below average in the next few days. April showers are supposed to bring May flowers, but in the most recent 30-year climatological reference period, April is the driest month in Washington, with an average of only 2.77" vs. 3.82" for May. (February is lower in absolute terms, but of course it has 2 fewer days, on average.) The daily average increases over 50% from a low of 0.08" on April 15 to 0.13" by May 12. So far this year, we're going directly against that trend.

CapitalWeather.com chart from NWS data, photo © Kevin Ambrose

D.C.'s Dryness Continues

Some scattered showers in the region this morning fell apart before reaching the Washington metro area, although Hagerstown did manage to squeeze out a trace of rain, and Charlottesville had 0.01". The persistent clouds kept temperatures from rebounding quickly above the summer-like overnight lows in the low 60s, but more sunshine later pushed most readings into the mid 70s by mid afternoon.

Tonight and Tomorrow

Broken clouds this evening will give way to clearing skies by morning, with lows in the mid 50s in the city and upper 40s in the colder 'burbs. Tomorrow will be sunny and dry with highs around 79.

"Another Nail in the Coffin"

Today's WaPo has an article, "Study Reconciles Data in Measuring Climate Change", which describes a government report resolving the previously reported discrepancies between surface temperature measurements and those reported by satellites. This is described as "really a major step forward" and "the nail in the coffin of [the skeptics'] argument" against global warming. Courtesy of MIT's Knight Science Journalism Tracker, here are some more links to the study report:

• New York Times: Federal Study Finds Accord on Warming
  
• Associated Press: Global Warming Differences Resolved
  
• NOAA Press Release: Report Reconciles Atmospheric Temperature Trends

The entire report is available for download in PDF format. The usual suspects don't seem to have found a way to attack the report yet, but they will undoubtedly come up with something.

Squeeze Play Sends Fine Weather Into Extra Innings

An atmospheric squeeze play is extending the fine spring weather from April into May in the Washington DC metro area. A ridge of high pressure extending along the entire east coast of North America is being squeezed from two directions by "cut off" low pressure areas over the upper Midwest and near Bermuda. While the ridge holds in place, the sunny, dry weather will continue over the Mid Atlantic area as Jason describes below, but the unusual northwestward motion of the eastern low will bring the threat of some clouds and rain to New England.

Surface pressure (solid lines) and 500 mb height (colors) at 8am today from Unisys

At mid afternoon today, 68° was the lowest reported reading around the region; most places were 70° or higher. The bright sun was accompanied by delightfully dry dewpoints of 45° or less. The nearest showers were over the lower Ohio Valley and eastern New England.

Tonight and Tomorrow

Mostly clear skies should continue through tomorrow afternoon, with only a few clouds late in the day. Lows tonight under light winds should again be in the mid to upper 40s city to near 40 in the colder 'burbs. Highs tomorrow will be near 72.

Capitol Climate

The American Meteorological Society has posted more details on the next Capitol Hill Environmental Science Seminar this week:

• Topic: Changes in Cold Places: A Look at the Greenland Ice Sheet, Arctic Sea Ice and the Antarctic Ice Sheet
  
• Date: Wednesday, May 3, 2006
  
• Time: 12:00 Noon - 2:00 pm
  
• Location: Russell Senate Office Building, Room 428

The public is invited; no pre-registration required.

The questions to be addressed are:

Are parts or all of the Greenland and Antarctic Ice Sheets undergoing a net melting? What is the nature of the observational evidence of melting? How far back in time do these observations extend? Are the melting and rates of melting consistent with model simulations and projections of melting? What are the factors deemed responsible for the melting? Is Arctic Sea Ice thinning? If so, by how much and over what period of time? What is the nature of the observational evidence for this thinning? Are the thinning and rates of thinning consistent with model simulations and projections of thinning? What factors are deemed responsible for the thinning of Arctic Sea Ice? Are there implications with respect to sea level rise? Is there any evidence of a fundamental change in the rate at which the Greenland ice sheet is changing and the manifestation of those changes? If so, why? How well do model simulations capture the dynamics of ice sheets and sea ice relative to observations? How well are these ice sheet models poised to project future changes in ice sheets, sea ice and sea level?

Photo, via AMS, is also the cover picture for the April 2006 Weather Magazine of the Royal Meteorological Society (Special Issue: Climate Change in high latitudes 2). It shows surface melt water entering a moulin in the Greenland Ice Sheet.

Getting Better All the Time

This afternoon's weather map shows a cool, dry high pressure area centered over southern Canada and dominating the entire Atlantic coast. Despite the northerly breeze veering somewhat easterly at times, the entire Washington metro region was enjoying sunny mid 60s temperatures by mid afternoon. Even the Bay and Eastern Shore locations were mainly over 60, although Ocean City was a brisk 57 with a northeasterly wind gusting to 26 mph. Today's models are unanimous in saying that Camden's earlier weekend assessment may have been a bit pessimistic; the sunny and dry conditions are predicted to continue right on through Sunday.

Surface weather map and satellite picture at 2pm today from HPC/NCEP/NWS

Tonight and Tomorrow

For tonight, clear skies and light winds should allow temperatures to drop to the mid 40s city, as low as the mid 30s in the colder 'burbs. Tomorrow earns the CapitalWeather.com Seal of Approval, although the high near 67 under sunny skies will be only marginally "room temperature".

Tropical Topics

As the clock ticks down to the beginning of another tropical season, the American Meteorological Society's 27th Conference on Hurricanes and Tropical Meteorology is winding up today in Monterey, CA. There have been a number of interesting presentations, especially on the controversial issue of the relationship between global warming and hurricane activity.

Colorado State University's Dr. William Gray, whose claim to fame appears to be mainly based on statistical forecasting, goes out on a limb with his strong denial of any connection. His presentation is certainly "in your face"; the introduction is a quote from an ideologically partisan oil-state senator and the closing is a statement from the public relations person of the American Association of Petroleum Geologists about a science fiction book. Gray's scientific assertions regarding the oceanic thermohaline circulation (THC) are thoroughly demolished at RealClimate.org, where a spirited discussion has generated over 60 comments in the last couple of days.

MIT Prof. Kerry Emanuel, author of the recent book Divine Wind, is a joint author with two researchers from the University of Miami of a paper, Could hurricanes form from random convection in a warmer world?. This study uses physical modeling to assess whether increases in sea-surface temperatures could induce spontaneous generation of hurricanes without the usual prerequisites.

Abstracts for all the conference presentations, as well as many extended versions with graphics, are available on the conference web page.

FEMA Found FUBAR; Weather Not

Yesterday's cloud-enhanced chill in the Washington DC metro area has been replaced by much more seasonable readings. Wednesday's official high of 59° was the lowest since the 57° on the 9th, but nearly all locations were at or above 70 by mid afternoon today ahead of a cold front bringing a reinforcing shot of cooler air for tomorrow.

CapitalWeather.com chart from NWS data, photo ©
Kevin Ambrose

Tonight and Tomorrow

Tonight will be variably cloudy with lows from the upper 40s to near 50 in the city and lower 40s in the cooler 'burbs. Tomorrow will be mostly sunny with highs around 66, but northeasterly winds could bring in more clouds and cooler temperatures east of the immediate metro area.

Preparedness Disaster

The AP reports via the online WaPo that the Senate Committee on Homeland Security and Governmental Affairs has recommended that FEMA be abolished and replaced by a National Preparedness and Response Authority. The committee report concludes that

1) long-term warnings went unheeded and government officials neglected their duties to prepare for a forewarned catastrophe; 2) government officials took insufficient actions or made poor decisions in the days immediately before and after landfall; 3) systems on which officials relied on to support their response efforts failed, and 4) government officials at all levels failed to provide effective leadership.

Notice the emphasis on the fact that the catastrophe was "forewarned". The meteorological community, and especially the staff members of the National Hurricane Center, can take pride in the recognized excellence of the forecasts leading up to the storm's landfall. The report singles out the "strongly worded advisories from the National Hurricane Center (NHC) and personal warnings from NHC Director Max Mayfield".

Meanwhile, Reuters reports that the White House is opposed to the committee's recommendation that FEMA be scrapped. Hurricane season officially begins in 34 days.

Dry Afternoon; Liquid Likely Later?

The rain associated with a strong cold front and a weak low pressure area approaching from the Ohio Valley had made it only as far as the Pittsburgh area by mid afternoon today. Current indications are that showers will continue to develop along the front, but any rain in the Washington metro area is likely to hold off until the low pressure area swings eastward through central Virginia late this evening. If you're headed outdoors this evening, bring rain gear, but there is a good chance that the Nats game will be dry until at least the late innings. The NatCast has been adjusted to reflect the later arrival of precipitation. For the outlook the rest of the week, see Matt's post below.

Drought Busters

The weekend's rain went a long way toward relieving the drought in the Washington DC area. The map of the Maryland/DC/Virginia area, from the National Weather Service's experimental Precipitation Analysis, shows the rainfall for the 24 hours ending at 8am Sunday. There was a wide variation across the area, from the merely generous to the nearly stupendous. Notice the southwest-to-northeast banding structure, with the heaviest amounts both northwest and southeast of the District. As Jason explained earlier, showers and thunderstorms are likely late tomorrow, especially south of the Beltway, but the rest of the week looks quite fine.

Tonight and Tomorrow

Lows tonight under mostly clear skies will be from the low 50s in the city to the upper 40s in the colder 'burbs. Clouds will increase tomorrow afternoon with highs around 71. There is a 60% chance of showers and possibly thunderstorms late tomorrow afternoon through the evening, with higher amounts likely in the southern portion of the region.

Deficit Reduction

The above-average precipitation so far in April has reduced the accumulated yearly deficit from around 40% at the beginning of this month to 24% as of today. The chart shows the official observations at National; weekend rainfall at Dulles was over twice as high. At Dulles, nearly a month's normal rainfall fell in one day, but the total is still well short of the April monthly record of 7.35" set in 1973.

CapitalWeather.com chart from NWS data, photo © Kevin Ambrose

Capitol Climate

The American Meteorological Society's Environmental Science Seminar Series on Capitol Hill continues next week on May 3 with the topic, "Changes in Cold Places - A Look at the Greenland Ice Sheet, Arctic Sea Ice and the Antarctic Ice Sheet".