Archive for July, 2007

Where Are The Hurricanes?
July 31, 2007

The 2007 hurricane season has certainly been unspectacular so far. Early in the season it was obvious that high altitude winds were interfering with the development of tropical waves in the Caribbean and Gulf of Mexico. Water temperatures were marginal as well. Those winds may have been the last gasp of a weakening El Nino. It is interesting to note that there has been significant rainfall in the Gulf Coast region, especially Texas. Could this have been the result of “unfulfilled hurricanes”? It would make an interesting research project.

By August, hurricane development usually begins to shift eastward. The satellite image below shows that at the end of July the Gulf and Caribbean have warmed considerably. The western Atlantic is still relatively cool. There is speculation that excessive dust blowing off the Sahara Desert may be partially responsible for this. At any rate, some hurricane forecasters are beginning to backpedal a bit on earlier outlooks for an exceptionally busy season. Keep in mind, though, that the peak of the hurricane season is still ahead. There is more than enough time for a significant number of storms to develop. The danger is far from over.


(Image Courtesy StormCenter Communications, Inc.)

This image shows sea surface temperatures in the Atlantic Ocean and the Gulf of Mexico on July 26, 2007. Water that is warm enough to fuel hurricanes is yellow, orange, and red, while water that is too cool to sustain a hurricane is blue. The relatively shallow Gulf of Mexico and the Caribbean are warm and hurricane-ready. Hurricane Alley, the warm swath of water between Africa and the northern tip of South America where hurricanes frequently form, was just beginning to heat up. The image was made from data collected by the Advanced Microwave Scanning Radiometer (AMSR-E) flying on NASA’s Aqua satellite.

Keep track of the hurricane season everyday on WBAL-TV 11 and on wbaltv.com or on our 24 hour, seven day a week digital weather channel, Insta-WeatherPlus.

John Collins

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Much Needed Rain …. For Some
July 30, 2007

The past couple of days have been warm and very humid in the Baltimore area and several rounds of thunderstorms have developed in this tropical air. This is good news for an area that is suffering from a recent lack of significant rainfall. While some of the rain has been heavy, it hasn’t been evenly distributed around the region.

The graphic below is an image from the Sterling, Virginia, National Weather Service radar. It shows the estimated rainfall amounts measured by the radar for the weekend storms up until Sunday evening.

The green and yellow shadings show the areas that received the heaviest rainfall. A scale is provided at the bottom of the image. Notice that the 1″ to 3″ rains fell in a narrow arc from Frederick County north-northeastward into Pennsylvania and then turn southward into Harford and Cecil counties on down to parts of the Eastern Shore. A good portion of the Baltimore & Washington metropolitan area was left out of the significant rainfall.

On Sunday alone, BWI-Marshall Airport and the Maryland Science Center received less than a tenth of an inch of rain (up until 6:00pm) while the instruments at our studio on TV-Hill just a few miles away measured just over a half inch of rain. Hardly equal treatment.

Precipitation chances continue through Monday so maybe a few additional areas will get some of that much needed moisture.

John Collins

The Cool Down Begins
July 26, 2007

The normal high for Baltimore today is 87, which is no big deal, in and of itself. But yesterday the normal high was 88, and the one degree drop today is the first time this year the normal high has gone down. The normal high or low is calculated using 30 year averages. Currently we are using the 30 year averages from 1971 to 2000 as our normal temperatures. From now through mid winter the normal temperatures will continue to cool, until we hit bottom with a normal high of 41 and a normal low of 23 from January 11th through January 26th. For summer weather lovers today’s subtle drop in the normal high temperature is a warning to enjoy the next couple months because changes are underway. For cool weather fans, today’s news provides hope that the hottest part of the year is coming to an end and cooler days are not too far away.

Normal High Temperatures:
Jul. 26th: 87
Aug. 26th: 84
Sep. 26th: 75
Oct. 26th: 63
Nov. 26th: 53
Dec. 26th: 43
Jan. 26th: 41

Tom Tasselmyer

More On The Area Drought Situation
July 22, 2007

Below is information from the National Weather Service in Sterling, Virginia on the drought situation in the region.

THE AREA CONTINUES DRY…WITH LITTLE OR NO RELIEF IN SIGHT. AS OF
JULY 17…THE DROUGHT IS RATED “SEVERE” IN TERMS OF A HYDROLOGICAL DROUGHT ACROSS LOWER SOUTHERN MARYLAND AND NORTHERN VIRGINIA. SURROUNDING THE SEVERE DROUGHT AREA IS A LARGE AREA OF MODERATE DROUGHT WITH ABNORMALLY DRY CONDITIONS OVER THE EASTERN WEST VIRGINIA PANHANDLE. AGRICULTURE INTERESTS ACROSS THE REGION ARE ALSO EXPERIENCING MODERATE TO SEVERE DROUGHT CONDITIONS.

THIS DROUGHT IS ON A PAR WITH THE DROUGHT OF SUMMER 2002. IN THAT YEAR…FOR THE PERIOD COVERING MAY 1ST THROUGH AUG 31ST…DCA ONLY MEASURED 9.82″ OF RAIN…AND BWI MEASURED 11.00″ NORMAL RAINFALL FOR THIS 4-MONTH PERIOD FOR DCA IS 14.05″…AND FOR BWI…14.91″. THAT DROUGHT WAS BROKEN BY MID SEPTEMBER 2002 AS THE UPPER LEVEL PATTERN SHIFTED ALLOWING MORE FREQUENT RAINFALL DURING THE FALL.

SO FAR THIS YEAR…FOR THE 81-DAY PERIOD MAY 1ST THROUGH JULY 20TH…DCA HAD MEASURED ONLY 4.46″. THIS RANKS AS 4TH DRIEST FOR THIS TIME PERIOD ON RECORD. AT BWI…6.01″ HAD BEEN MEASURED FOR THE SAME PERIOD RANKING AS 14TH DRIEST ON RECORD. OF COURSE…THIS IS A RATHER ARBITRARY RANKING PERIOD…AND THE NATURE OF WARM SEASON PRECIPITATION IN THE FORM OF SCATTERED SHOWERS AND THUNDERSTORMS CAN HAVE A LARGE IMPACT ON RAINFALL MEASUREMENTS…MAKING THESE RANKINGS NOT THAT SIGNIFICANT. STILL…IT IS VERY DRY ACROSS THE ENTIRE MID ATLANTIC REGION. A LOOK AT THE TROPICS SUGGESTS MINIMAL CHANCES OF ANY TROPICAL CYCLONE DEVELOPMENT IN THE NEXT WEEK.

NWS/LWX 21 July 07 … 10:49am

The National Weather Service statement made mention of the weak chance for Tropical Cyclone development in the near term. Tropical systems, or the lack thereof, will often make or break a drought.

A surface low pressure center near the coast on Monday and an upper low pressure area over or close to the region the rest of the week will provide a chance for rain but it will likely be light and scattered in nature and ultimately, probably not have a very significant impact on the dry conditions.

John Collins

Drought Conditions Expand
July 21, 2007

Unusually dry conditions are becoming very apparent across the region. Weather systems have brought rain to the area from time to time but the coverage has been spotty and hot temperatures have helped to dry out the soil. Temperatures have soared into the 90s a dozen times since June 1.

As of Friday evening(July 20), BWI Marshall has received 2.87″ of rain in July, .38″ above average. Since June 1 the airport has measured 5.79″, .85″ below average. This may not seem too extreme until put into perspective. Rains in the area have not been evenly distributed. The Inner Harbor has received only 1.74″ in July and 4.19″ since June 1 while TV Hill has measured only 1.49″ for July and 3.46″ since June 1. These numbers highlight the scattered nature and varied amounts of rainfall the region has received so far this summer.

Below is an Associated Press story on the drought situation in Maryland followed by a map prepared by the TV-11 Art Department outlining the degrees of drought in the state.

UNDATED (AP) – The latest information compiled by the National
Drought Mitigation Center shows three quarters of Maryland is
experiencing a moderate to severe drought.
The drought map released yesterday shows drought conditions in
all or parts of 20 counties and the city of Baltimore. Three of
those counties — Charles, Saint Mary’s and the southern part of
Calvert — are the areas listed as having a severe drought.
The moderate drought area includes the lower two-thirds of the
Eastern Shore and most of central Maryland. The extreme western and
northeastern corners of the state are listed only as “abnormally
dry.”
Moderate and severe drought are the least serious of the four
drought categories measured in the weekly survey by researchers at
the University of Nebraska-Lincoln.
A spokesman for Governor Martin O’Malley says state officials
are considering asking the federal Department of Agriculture to
declare a drought emergency for parts of Maryland. The designation
would free up federal aid for farmers who have lost crops.

On the Net:
http://www.drought.unl.edu/dm/monitor.html

(Copyright 2007 by The Associated Press. All Rights Reserved.)

The area will be getting some relief from the extreme heat and humidity for the next few days but significant rainfall appears to be unlikely in the near future.

John Collins

Thursday Bow Echo Storms
July 20, 2007

Thursday, thunderstorms developed in the humid air ahead of a cold front. The greatest area of instability was just south of the Baltimore-Washington area and some powerful thunderstorms developed what is called a “bow echo”. Below is the statement from the National Weather Service concerning the storms and radar and satellite imagery of the situation.

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1003 PM EDT THU JUL 19 2007

…PUBLIC INFORMATION STATEMENT…

…BOW ECHO ACROSS NORTH CENTRAL VIRGINIA AND LOWER SOUTHERN
MARYLAND…

EARLIER THIS AFTERNOON…A STORM PRODUCED WIND DAMAGE ACROSS PORTIONS OF NORTH CENTRAL VIRGINIA FROM FAUQUIER…STAFFORD AND KING GEORGE COUNTIES EASTWARD ACROSS SOUTHERN MARYLAND.

THIS WAS A WELL ORGANIZED TYPE OF CONVECTIVE STORM CALLED A BOW ECHO. SURFACE WINDS ASSOCIATED WITH THIS STORM WERE MEASURED BETWEEN 60 AND 65 MPH…WITH GUSTS UPWARDS OF 80 MPH.

THE STORM RAPIDLY ORGANIZED INTO A BOW ECHO AS IT CROSSED THE POTOMAC RIVER FROM VIRGINIA INTO MARYLAND. A LARGE AREA OF HIGH WINDS WITH GUSTS MEASURED AT NEARLY 65 MPH SPREAD OUT FROM THE STORM SYSTEM ALONG THE GUST FRONT. AT TIMES DOPPLER RADAR
INDICATED WINDS COULD HAVE BEEN AS HIGH AS 80 MPH AS THE STORM MOVED ACROSS SOUTHERN CHARLES COUNTY AND INTO ST. MARYS COUNTY IN LOWER SOUTHERN MARYLAND.

THIS TYPE OF STORM SYSTEM IS NOT UNCOMMON IN THESE PARTS. THEY CAN OCCUR UNDER CERTAIN COMBINATIONS OF ATMOSPHERIC INSTABILITY AND VERTICAL WIND SHEAR. ALTHOUGH MUCH OF THE AREA HAD CONSIDERABLE CLOUDINESS EARLIER DURING THE DAY…THE AIRMASS ACROSS WEST-CENTRAL AND NORTH-CENTRAL VIRGINIA AND LOWER SOUTHERN MARYLAND EXPERIENCED A GOOD DEAL MORE SUN THAN THE REST OF THE REGION. ALSO HIGHER MOISTURE IN THE LOWER ATMOSPHERE IN THIS SAME AREA HELPED FUEL THE STORM. WINDS JUST ABOVE THE SURFACE WERE AROUND 25 MPH FROM THE SOUTHWEST WHILE ALOFT UP AT 10-15 KFT…THEY WERE MUCH STRONGER…RANGING FROM 50 TO 60 MPH FROM THE WEST AND NORTHWEST. THIS
CREATED A FAVORABLE VERTICAL WIND PROFILE TO HELP MAINTAIN THE STORM FOR SEVERAL HOURS.

Notice on the satellite picture above that the line of storms is moving out over the Atlantic Ocean and there is a band of low clouds running out ahead of the main area of convection. This is an indication of the strong outflow from the mature storms that had earlier moved over southern Maryland.

John Collins

Too Dry For Some
July 13, 2007

Despite some rainfall in the past week, not everyone has been treated equally. A couple of examples make the point. On July 10, BWI-Marshall Airoprt received 1.84″ rainfall while the Inner Harbor measured only .40″ and TV Hill received only .26″. On Thursday, July 11, a very small storm cell past over Ellicott City and produced .29″ of rain in a brief period, the airport received only .10″, the Inner Harbor.01″ and TV Hill 0.00″.

Officially, BWI-Marshall stands at 2.84″ rainfall for July, 1.39″ above average for the month but 2.52″ short for the year. The only reason July shows above average rainfall is the heavy rain that hit the area around the airport Tuesday while other areas received substantially less rain.

The spotty nature of the recent rain is fairly typical in the summer and it really takes the occasional remnant of a tropical weather system to keep the rainfall averages up and keep agricultural interests out of trouble. As of today(July 13)the stress of drought conditions is being felt most intensly in Maryland south of Annapolis and Washington where “moderate drought” conditions exist. The rest of the state continues to experience “abnormally dry” conditions.

The weather pattern over the next week is expected to produce some periods of rain, probably scattered in nature. A break in the marginal drought conditions is not likely but some relief should help out some of the lawns and gardens is the area.

John Collins

First Snow In 89 Years
July 12, 2007

A welcome cold front is moving through Maryland tonight, promising to bring some relief from our classic mid-Atlantic summer weather, but in Buenos Aires, Argentina earlier this week, a much stronger cold blast has produced the first snow in 89 years! The BBC report: Buenos Aires sees rare snowfall , said many people cheered at the sight of the city’s first snowfall since 1918, but there were hardships and even some deaths associated with the record cold blast as well. Just think, in a mere 5 months winter will return to the northern hemisphere!

Tom Tasselmyer

The 9 Hottest Days In Baltimore
July 11, 2007

July 10th has come and gone and the all-time record for the highest temperature ever in Baltimore lives another year. Set back on July 10th 1936, the record high of 107 was set the same day that Frederick and Cumberland hit 109 to set the all-time record high for the state of Maryland. Interesting that the record goes back to the early part of the 20th century because all the talk about global warming these days might lead you to believe the hottest days around here occurred more recently. In fact, the hottest temperatures ever officially recorded here are 107, 105 (four times) and 104 (four times). That makes nine times that the temperature has hit 104 or higher in Baltimore and of those nine days, 7 were in, or prior to 1936. Here’s a list of the nine hottest days:

107 on…
July 10, 1936

105 on…
August 20, 1983
June 29, 1934
August 7, 1918
August 6, 1918

104 on…
July 16, 1988
August 5, 1930
July 21, 1930
July 3, 1898

Our current heatwave has not set any records, but the cooler, less humid air that is scheduled to get here on Thursday will certainly be welcome nonetheless!

Tom Tasselmyer

Turning Up The Heat
July 9, 2007

We are now into the second significant heat wave of this summer season. The last was a three day affair back in June. This one is expected to be a bit longer and have a little more punch to it.

The high temperatures Saturday and Sunday were 90 and 94 respectively but it was reasonably comfortable because the dewpoint temperatures held in the 50s during the day. The really steamy conditions kick in when dewpoint readings reach into the 60s to around 70 and it looks like that starts on Monday. The combination of high temperatures and high humidity make it hard for the body’s cooling system to work efficiently.

Will it get hot enough to tie or break any heat records? Probably not. Sunday BWI-Marshall was 6 degrees short of the 1993 record of 100. Monday’s record is 103, set in 1936. There is a small chance that the official airport high could reach 100 but upper 90s is more likely. Tuesday’s record high of 107 set in 1936 is also the all-time record high for Baltimore. A temperature that hot is rare in this area and this heat wave is not likely to be that extreme. Tuesday’s high temperatures will likely be affected by some cloudiness and possibly some isolated thunderstorm activity and temperatures in the mid-upper 90s are expected. Wednesday’s record is 100 set in 1988 and we are expecting highs in the mid 90s.

Even if records are not threatened it will be very hot and high humidity levels will make it feel worse. Just take it easy and try to keep cool. Temperatures by the end of the week are expected to return to more seasonal readings in the mid 80s.

John Collins