Archive for November, 2008

Snow To Impact Westbound Travelers
November 25, 2008

keysers-ridge-445pm-25nov081 tt_travel2 Heavy snow showers are back in western Maryland…just in time for holiday travelers!  With temperatures below freezing from western Allegany Co. into Garrett Co., the snow will make roads slick tonight and Wednesday.  Gusty winds will create some blowing and drifting of snow, reducing visibilties.  While the snowbelt areas of Maryland, West Virginia, Pennsylvania and New York will experience tough travel conditions on one of the biggest travel days of the year, elsewhere around the nation, generally good travel weather is expected.  Some rain and snow is possible in northern New England and a storm rolling in from the Pacific may bring heavy rain showers to southern California and the desert southwest.  But the big airport hubs in Chicago, Denver, Dallas and Atlanta are expected to have mostly clear skies on Wednesday.  Be safe and have a happy Thanksgiving!

Tom Tasselmyer

January-like in November
November 25, 2008

tt_cold_november

Weather conditions from November 17th through the 23rd were not very typical of a pre-Thanksgiving week in the Baltimore area. In fact, the cold temperatures were more like January! Average highs for the week were 13.6 degrees below the 30 year normals, while the average lows were 6.5 degrees below normal. With heavy snow in the mountains and the first flakes of the season dusting the Baltimore area, this final stretch of autumn has felt quite wintry.

Tom Tasselmyer

The Chill Continues
November 24, 2008

Temperatures have certainly taken a turn in November. The first half of the month was relatively mild with most daily high temperatures at or above the seasonal average. Readings took an abrupt turn mid month. The high temperature on November 15 was 73 degrees and the high on the next day was 22 degrees colder. Readings have continued to tumble and it appears the pattern is firmly in place.

Sunday morning temperatures took a very cold turn in the northeast U.S. with a scattering of single digit low readings.

jc_suncoldesttemps

A preliminary survey of lows across the United States turned up the fact the the Elkins, West Virginia low of 5 degrees was the coldest reading in the lower 48 states.

On Monday, southerly winds ahead of an approaching storm will bring temperatures “close to normal” for a day or so but on average it will remain unseasonably cold.

This string of cold readings will include Thanksgiving. Typically, November 27 would register high temperatures in the low 50s and lows around freezing. The record high for the date is 74, set in 1896 and it looks like temperatures will be running 20-25 degrees colder than that this time around. If it is any consolation, the record low maximum temperature for November 27 is 30 degrees, set in 1903. Thankfully it looks like it will be warmer than that with forecast highs close to 50 degrees.

John Collins

Winter Weather Advisory Changes
November 21, 2008

Winter weather is on our doorstep. Temperatures have turned sharply colder and a few flurries and snow showers have fallen around Baltimore. Significant snows have fallen in the mountains.

I wanted to pass along a word about some changes the National Weather Service is making regarding their Winter Weather Advisories.

The threshold for issuance of various advisories on winter weather hazards has been lowered for specific time periods in the Baltimore and Washington metropolitan areas. Highway travel in the metro areas has become much more congested in recent years and it has become evident that even the slightest snow or ice accumulations can cause major traffic headaches. The folowing information was released by the National Weather Service explaining the new guidelines.

PUBLIC INFORMATION STATEMENT 

NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC

1119 AM EST THU NOV 13 2008


…THE NATIONAL WEATHER SERVICE BALTIMORE/WASHINGTON WEATHER FORECAST OFFICE WILL MODIFY LOCAL WINTER WEATHER ADVISORY THRESHOLDS EFFECTIVE 10:00 AM EST NOVEMBER 17 2008…


A WINTER WEATHER ADVISORY IS ISSUED FOR HAZARDOUS WINTER WEATHER THAT CAUSES SIGNIFICANT INCONVENIENCES…AND IF CAUTION IS NOT EXERCISED…COULD LEAD TO LIFE-THREATENING SITUATIONS. IN PAST COLD WEATHER SEASONS…WINTER WEATHER ADVISORIES WERE ISSUED WHEN FORECASTERS HAD A 80 PERCENT OR GREATER CONFIDENCE OF AT LEAST 2 TO LESS THAN 5 INCHES OF SNOW AND/OR SLEET WITHIN A 12 HOUR PERIOD.

 

STARTING THIS COLD WEATHER SEASON 2008-2009…THE NATIONAL WEATHER SERVICE BALTIMORE / WASHINGTON WEATHER FORECAST OFFICE WILL EXPAND THE WINTER WEATHER ADVISORY CRITERIA LISTED ABOVE FOR SPECIFIC HIGH-TRAVEL AREAS DURING RUSH HOUR PERIODS BASED ON ADVERSE PUBLIC-IMPACT. IN ADDITION TO THE CRITERIA LISTED IN THE PREVIOUS PARAGRAPH…A WINTER WEATHER ADVISORY WILL NOW BE ISSUED WHEN FORECASTER CONFIDENCE IS 60 PERCENT OR HIGHER FOR AT LEAST 1 INCH TO LESS THAN 2 INCHES OF SNOW AND/OR SLEET THAT IS FORECAST TO ACCUMULATE DURING WEEKDAY MORNING OR EVENING RUSH HOURS. WEEKDAY RUSH HOURS ARE DEFINED AS MONDAY THROUGH FRIDAY /EXCLUDING FEDERAL HOLIDAYS/ FROM 4:00 AM TO 9:00 AM AND 2:00 PM TO 7:00 PM.

The National Weather Service map below defines the areas affected by these new guidelines.

wsy_threshold

 

It really comes down to the likelihood that there will be more winter weather advisories this season, not necessarily because of more storm activity but because of the impact even minor storms have on our crowded highways.

John Collins

Key to our cold: the NAO
November 21, 2008

nao-13-day-fcst-20nov08

One of the most reliable predictors for cold weather in the mid Atlantic states is an index meteorologists call the North Atlantic Oscillation (NAO).  The NAO is a back-and-forth fluctuation in the atmosphere between low pressure over Greenland and the subtropical high north of Bermuda.  When there is a large difference between the two pressure centers, with a strong Greenland low and a strong subtropical high, the index is positive and the mid Atlantic tends to be warm.  This is because the Greenland low pulls the cold out of Canada before it has a chance to drive south into the mid Atlantic states.  But, when pressures rise over Greenland and the subtropical high weakens, there is less pressure difference between the two key areas and the NAO index is negative.  In the negative phase the mid Atlantic region is susceptible to cold air masses moving south.  This is in response to the cold in Canada being blocked and shunted south by the higher pressures over Greenland.

The NAO’s impact on the mid Atlantic is felt most dramatically in the cold weather seasons.  The chart posted above shows the index over the last several months with distinct positive phases around mid October and early November corresponding nicely to unseasonably warm temperatures, while the strongly negative NAO index of the past few days lines up well with our current cold weather.

The chart is also a forecast for the next 13 days and shows the NAO staying negative into early December.  This could mean our early taste of winter will be sticking around for a while.

Tom Tasselmyer

For the first time in 262 days…
November 19, 2008

tt_md_lows_19nov081
The low this morning at BWI Thurgood Marshall Airport dropped to 24°, the coldest of autumn so far and the first temperature below 25° since last March 2nd, 262 days ago. Some other sub 25°locations in the state this morning, not shown on the map posted above:
Garrett College, McHenry, Garrett Co.: 15°
Green Ridge State Forest, Allegany Co.: 18°
Antietam National Battlefield, Washington Co.: 19°
Catoctin Mtn. Park, Frederick Co.: 19°
Dayton, Howard Co.: 22°
Reisterstown, Baltimore Co.: 22°
Bel Air, Harford Co.: 23°
Bowie, Prince George’s Co.: 24°

Tom Tasselmyer

Skier’s Delight…29″ at Snowshoe!
November 19, 2008

snowshoe-mtn-18nov08
The outbreak of cold air enveloping the mid Atlantic and northeastern United States this week is turning into something skiers can be truly grateful for as we head for the Thanksgiving holiday. Reports out of far western Maryland and West Virginia indicate 6-12″ of snow has fallen at elevations above 2,000′ and 12-24″ of snow has been reported up above 3,000′. At Snowshoe Mountain in Pocahontas County, West Virginia, where the summit of the mountain reaches 4,848 feet, an incredible 29″ of snow has been measured as of late this afternoon. That brings their seasonal total to 38.5″! with the fresh powder on the slopes the ski resorts are planning on opening early.  Check the individual resort web sites for updated snow reports and opening day headlines, but as of this afternoon Snowshoe Mountain is scheduled to open this Friday, November 21st.  Wisp Resort is planning on opening Friday, November 28th.

Tom Tasselmyer

Cold Coming With Some Snow
November 18, 2008

wisp-5-in-snow-17nov081 keysers-ridge-4pm-17nov081 frostburg-webcam-4pm-17nov081

Cold, winter-like air is sweeping east across the mountains into central Maryland tonight.  With the Great Lakes still unfrozen the cold air can pick up lots of moisture on its track southeast.  The cold, moist air flowing up the west side of the Appalachian mountains results in heavy snow showers for Allegany and Garrett Counties in western Maryland.  As of late afternoon Frostburg, MD reported 2″ of new snow and the Wisp ski resort near Deep Creek Lake in Garrett County reported 5″.  Pictures posted here show the the snow on a wooden deck near Wisp, wet pavement but a snow covered shoulder on I-68 at Keyser’s Ridge and a snowy farm field near Frostburg.  These areas are under a Winter Storm Warning with the potential for 6-12″ of snow by the Wednesday afternoon.  At times, a strong surge of cold air like this will be accompanied by a weather disturbance in the upper atmosphere which can bring the snow showers east of the mountains.  Watch for rain showers to mix with or change to snow showers in and around Baltimore tonight and Tuesday.  Low pressure is expected to develop just east of the coast as the cold air moves over the warm ocean Tuesday.  If the low is close enough to the coast, some heavier snow showers may develop east of Baltimore.  With this possibility in mind, the National Weather Service in Mt. Holly, NJ, outside of Philadelphia, has issued a Winter Weather Advisory for Maryland’s central eastern shore as well as central and southern Delaware.

Tom Tasselmyer

Leaning Closer To Winter
November 17, 2008

This weekend there was an abrupt change in the weather. High temperatures were in the 70s on Saturday but a strong cold front reintroduced a sense of reality to the weather by Sunday.

At this point in the autumn season average high temperatures are in the mid 50s and lows are in the mid 30s. The temperature trend over the next week or so will be running below the seasonal average.

A look at the record books gives a good indication of the variety of the weather at this time of year and it also is very telling as to where we are headed and how rapidly winter is approaching.

In the coming week record highs are in the mid 70s and record lows are around 20. By the end of the month, record low temperatures drop into the mid teens.

Snowfall records are also indicative of the changes coming. This week the record snowfall totals are in the one to two inch range. Next week the records are in the range of three to eight inches. Quite a jump.

Speaking of snow, the lake effect snow machine has set up in the strong northwesterly flow. Those same winds are piling moisture up against the mountains to our west and snow showers will be providing light accumulations.

Computer models are developing a disturbance to the west that is expected to move across the region Monday. Not all of the models agree on the results but this disturbance will support a considerable degree of cloudiness by afternoon and increase the risk of sprinkles or flurries at a minimum by the end of the day.

nam_pcp_036mNOAA Forecast Chart

The forecast chart above shows one computer model of forecast conditions in the predawn hours of Tuesday. Green shading indicates enhanced precipitation chances over the Chesapeake Bay. Temperatures at this time would support snowfall, most likely in the form of flurries or snow showers with no accumulation because the ground is so warm.

The jury is still out on exactly how this disturbance will behave so continue to check our forecast for updates.

Deeper into the week, computer models hint at an additional disturbance generating flurries on Thursday. One model is also developing a more significant storm on Saturday that could be a rain or snow maker. That forecast is a long way off and is subject to considerable fine tuning over the next few days. As the say, stay tuned.

John Collins

Thunder Ahead Of Cold Blast
November 15, 2008

tt_h5_15nov08_2pmtt_svrfcst_15nov08

A deep trough of low pressure up around 18,000 feet is forecast to sweep east into the mid Atlantic states this weekend. The strong jet stream east of the trough (160 mph winds measured at 30,000 feet by the balloon launched near Detroit this evening) will combine with warm, moist air being drawn northward along the eastern seaboard to produce strong to severe thunderstorms along the advancing cold front. Late Friday evening tornado watches were posted for southwest Georgia, the Florida panhandle and much of South Carolina. Theses storms may develop farther north during the warmest part of the afternoon on Saturday. The cold front is forecast to move through Baltimore later Saturday evening, ending the severe storm threat. South winds will turn to the west and then northwest Saturday night into Sunday, ushering in a week of colder than normal temperatures with the possibility of snow on the west side of the Appalachian divide and maybe even a few flurries east of the mountains.

Tom Tasselmyer