Thursday, March 28, 2013

New Look For Storm Prediction Center Web Site

The NWS Storm Prediction Center (SPC) launched it's new home page today, sporting a sharp new look and quick, easy access to SPC products. SPC is responsible for forecasts and watches for severe thunderstorms and tornadoes over the contiguous United States. The SPC also monitors heavy rain, heavy snow, and fire weather events across the U.S. and issues specific products for those hazards.

The Overview map with the tabs across the top remains the centerpiece of the page but is off on the left side. On the right side a window contains thumbnails and links to all SPC graphical outlook products. Tabs on this window can be used to view the convective outlooks, current watches, mesoscale discussions, and fire weather outlooks. On the bottom half of the page are windows to severe weather climatology, public awareness and education material, case studies, and publications. Gone is the long menu list on the left hand side of the page that still is a feature of most NWS web pages.

The pages behind the home page still utilize the old web page design so you will still have to deal with the old menu structure until these are changed.  However, the home page provides users with a clean "at a glance" overview and access to severe weather information.

Monday, March 25, 2013

One Good Thing About Spring Snow

It's March 25th and the weather headlines look like they should be dated December 25th. Ground zero for Day 3 of this storm was an area from east-central Missouri through central Illinois. There was an initial burst of snow early Sunday morning that left up to 3 inches of snow in some locations, followed by several hours of no precipitation. In many areas the snow that fell overnight melted off as temperatures rose to the mid-30s. By late morning and early afternoon Sunday heavy snow was quickly spreading eastward across Illinois.

The Mesoscale Convective Discussion graphic at
11:52 a.m. CDT March 24 from the Storm Prediction Center
The atmospheric conditions were set up for a sustained heavy snow event. Low pressure was moving slowly eastward though southern Missouri, and warm, moist air aloft was streaming northward. This  combined with instability and strong upward motion in the atmosphere to produce the heavy snow. Thundersnow was reported at a number of locations from St. Louis into central Illinois. Snowfall rates of 2 to 2.5 inches per hour occurred over a sustained period, and the result was widespread snowfall of 8 to 12 inches, with a number locations west and northwest of Springfield, IL reporting 15 to 18 inches of snow. The CoCoRaHS Observer at IL-SG-17 (Springfield 4.4 W) reported 16.5 inches of snow. This was a heavy wet snow, with snow-to-water ratios on the order of 9 to 1 (9 inches of snow to one inch of water).

48 hour snowfall accumulation map through 7:00 a.m. March 25 for central Illnois

Snow from this system also piled up from Indiana through southern Ohio and northern Kentucky to West Virginia. The storm still has a little punch left tonight, with Winter Storm Warnings in effect for the central Appalachians.

72 hour snowfall accumulation through 7:00 a.m. March 25
There is one good thing about a late spring snow, especially if you are tired of it. The higher March sun and temperatures above freezing quickly melt the snow on pavement reduce the snowpack. By late afternoon today where I live roads were mostly dry and you could tell that there already was a significant reduction in the depth of snow on the ground from the 10 inches I measured this morning.The hazard the next couple of nights will be refreezing of melting snow on roads as temperatures drop into the 20s overnight.

Sunday, March 24, 2013

Major Storm Continues Slow March East

A spring storm that already has dumped more than 12 inches of snow on eastern Colorado and another 4 to 8 inches in eastern Kansas and western Missouri will continue to affect the central and eastern portions of the country through Monday.

48-hour snow accumulation ending the morning of March 24.           

Surface weather map at 10:00 a.m. CDT March 24
As of mid-morning the center of the sprawling low pressure system was located over the lower Ohio and Tennessee Valleys.  Snow was falling from Missouri east through Illinois and north into Iowa. The system is being fed by an ample supply of moisture from the Gulf of Mexico, and that combined with the strong upper level system is producing heavy snow from eastern Missouri through central Illinois. CoCoRaHS observers have reported snowfall rates of 2 inches per hour.  There is a possibility for thundersnow in the southern portion of the heavy snow band.

Snow accumulations will be heavy with this storm. There is a high probability of 4 inches or more from central Missouri to western Virginia, and a good chance of 8 inches or more within this band.from eastern Missouri into southern Indiana, as well as in the mountains in western Virginia.  As of  1:45 pm CDT today 6 to 8 inches has already accumulated in west-central and central Illinois with heavy snow still falling.

24-hour probability of 4 inches or more of snow (left) and 8 inches or more of snow (right)

Winter storm warnings are in effect from Missouri eastward into Pennsylvania and eastern West Virgina.
Watches, warnings, and advisories as of 2:00 p.m. CDT March 24

Cooler, drier air plunging south in the wake of this system has raised the fire danger in southern Texas and red flag warnings are in effect today, Freeze warnings are in effect for northeastern Texas and northwestern Louisiana tonight.

Wednesday, March 20, 2013

Three Weeks Into Spring

Illumination of the Earth by the Sun
at the March equinox, as seen from the Sun.
The vernal equinox was at 6:02 AM CDT this morning, marking the start of astronomical spring. The minutes of sunlight will be increasing each day until the summer solstice on June 21st. As we all know, spring is the transition between the coldest period of the year (winter) and the warmest (summer). For those of us in the weather and climate field, spring actually started on March 1st and will continue through May 31st. Why do we use the calendar seasons instead of the the astronomical seasons?  Generally it is much easier to compute averages and other statistics for a fixed number of days. The occurrences of the solstices and equinoxes can vary by a day or so each year making the seasons different lengths. And, it turns out that the meteorological seasons are closer to reality in general.. A study done in 1983 by a researcher at the University of Illinois (now with the National Center for Atmospheric Research) found that, for the mid-latitudes of North America, the seasons (in terms of temperature) more closely follow the calendar than the astronomical events.  In fact, the astronomical seasons are only appropriate over the oceanic areas of the Southern Hemisphere. The response of the atmosphere to solar radiation lags by about 27 1/2 days at mid-latitudes. This means that during summer, for example, the peak heating would tend to occur during mid-July, 27 1/2 days after the summer solstice.  Defining summer as June 1 to August 31 makes sense since mid-July is the midpoint of the meteorological summer (June, July, August). However, the calendar alignment isn't perfect for a number of reasons. For example, if we were to base the seasons in the Northern Hemisphere strictly on mean temperature, spring would be the period from March 9 to June 8. 

March 1st or March 20th - this year some will argue, with good reason, that spring still isn't here!

If you have an interest in the astronomical you will find the U.S. Naval Observatory (USNO) web site a wealth of information. The USNO serves as the official standard of time for the entire United States. You can determine sunrise or sunset for any location in the country or find out when the phases of the moon will occur at any point in the future, or get the dates and times of the equinoxes and solstices. The Sky This Week describes what planets can be viewed and what other astronomical phenomena can be observed.

Trenberth, Kevin E., 1983: What Are the Seasons? Bulletin of the American Meteorological Society, Vol. 64, No. 11, pp. 1276-1282.

Tuesday, March 19, 2013

Ol' Man Winter Just Won't Let Go

Here we are, almost three weeks into meteorological spring and much of the country is dealing with below normal temperatures and winter precipitation. Winter Storm Warnings are in effect from eastern New York through much of New England, and warnings and advisories are also in effect in the lee of the Great Lakes.
Warnings, watches, and advisories as of 1:00 p.m. EDT March 19.

The reason for this is a double-barreled low pressure system. The main center was located near the eastern end of Lake Superior while a secondary low was located just south of Long Island, NY.

Surface weather map as of 11:00 a.m. EDT March 19

CoCoRaHS new snowfall map for March 19
Snowfall amounts from 6 inches to more than a foot are possible in the warned areas of New England. As of this morning 6 to 10 inches of new snow had accumulated from southern Vermont and New Hampshire into eastern Massachusetts. The snow will continue to progress northward today and some of the highest storm totals are likely over Maine. With temperatures hovering near freezing this is one of those pain-in-the-back storms with heavy, wet snow. 

Snow also blanketed northern Minnesota, much of Wisconsin, and the Michigan Upper Peninsula yesterday and last night. Snow continues today on the downwind side of the lakes.

24 hour snowfall ending the morning of March 19 in the upper Midwest

It's likely that winter will hang on for most of March. The latest 6 to 10 day outlook from the Climate Prediction Center which takes us through March 28 depicts a very high probability of colder than normal weather for the eastern one-half to two-thirds U.S.  This is quite a contrast with the record warm March of 2012, and it is the type of thing that makes meteorology such a fascinating field.

CoCoRaHS observers will need to keep those snowboards out just a little longer.

Thursday, March 14, 2013

SnowNews is Good News

Snow Water Equivalent map for the central Rockies
Despite what your own feelings about snow may be, there is no question that winter snow in the western United States does more than provide scenic landscapes or downhill runs for skiers. The snow that piles up in the mountains of the western U.S. during the winter provides 50 to 80 percent of the annual water supply used for drinking, irrigation for agriculture, and water needed to maintain flows in rivers and streams for power generation.

The snow that falls each autumn through early spring eventually melts as the weather warms, and the runoff from the snow melt is captured in lakes and reservoirs or flows through streams and tributaries into major rivers such as the Colorado and Columbia. In order to be able to successfully manage this resource water managers need to have information on how much snow has accumulated, where it has accumulated, and most importantly the water content of the snow. Since the 1930s the Natural Resource Conservation Service (NRCS) of the U.S. Department of Agriculture has coordinated the Federal, state, and private efforts to measure and evaluate the snowpack in the western U.S.

If you think measuring the water content of 15 inches of snow with a CoCoRaHS gauge is difficult, measuring mountain snow tens of feet deep and its water content is a whole other ballgame. It takes specialized equipment, skills, and training to conduct these snow surveys. The monitoring of the mountain snow made strides in the late 1970s when the first SNOTEL (for snow telemetry) stations were put into operation. There are currently more than 730 SNOTEL sites in 11 states, including Alaska, that collect and transmit data in near real-time to a central computer in Portland, Oregon. Most are located in areas that are difficult to access.

A SNOTEL site in Truckee, California

The NRCS National Water and Climate Center and the Snow Survey and Water Supply Forecasting Program publish a quarterly newsletter called SnowNews. It's not just about snow, but there is plenty of snow-related content. It is a comprehensive newsletter that addresses water and climate related topics that impact all resource managers and stakeholders (e.g. commercial, government, tribal, non-government organizations).  It has the latest news on web-related resources, what’s happening within NRCS water supply monitoring networks (SNOTEL covering the western states and SCAN, the Soil Climate Analysis Network, covering the nation). The just-released Spring 2013 issue features an article on the implications of the current drought in much of the U.S. and the seasonal water supply forecast for the western United States.

You can learn more about the importance of snow in the west and how this critical resource is monitored in Snow Surveys and Water Supply Forecasting.

Tuesday, March 12, 2013

What a Difference a Year Makes

Last March at this time we were approaching the end of the first half of the warmest March on record in the contiguous U.S.  This year, things are quite different through the first 10 days of March.

At this time last March the warmest part of the month, especially in the central U.S., lie just ahead. The highest number of temperature records occurred between March 14 and March 24, 2012. Maximum temperature and high minimum temperature records were not just broken - they were shattered by 10 and 20 degrees or more. By the end of March 2012 were more than 15,000 daily records for warmth broken across the country. So far in March 2013 there have only been 374 warm temperature records set.

Thursday, March 7, 2013

A "Weather Active" March Weekend

CoCoRaHS observers across much of the country will be busy measuring precipitation of one kind or another this weekend.

Western Atlantic surface map, 7:00 EST March 7
Those in southern New England are still dealing with the storm the moved off into the Atlantic late yesterday. This storm has intensified and stalled out over the Atlantic east of Virginia.  A sharp ridge of high pressure to the east of this storm, and another intense low to the east of the high are blocking the eastward progression of this system. Strong easterly winds are pumping a steady supply of moisture into southern New England, much of which is falling as snow. Snow amounts from 6 to 12 inches are forecast across southern New England. This is a wet snow, and the weight of the snow combined with the high winds means that power outages will be likely. In addition, the winds are pushing the water toward coastal areas, and coastal flood warnings are in effect from Rhode Island to Maine through tomorrow morning.

In the west an upper level system will come ashore in southern California early Friday heading toward the southern Rockies. Rain and snow will accompany this system as it makes its way across the Southwest, and winter weather advisories, watches, and warnings are in effect for a number of western states. This southern system will merge with another disturbance in the Northern Plains, and by Saturday morning will be bringing snow to a large portion of the central and southern Rockies and the Northern Plains. Ahead of this system, strong southerly winds will feed moisture to fuel showers and thunderstorms eastward through the Midwest.

Quantitative Precipitation Forecast (QPF) from 7:00 p.m. EST March 7 to 7:00 p.m. March 10.

Wednesday, March 6, 2013

A March Lion

Surface weather map at 7:00 p.m. EST March 6
The storm currently moving out to sea off the Virginia coast affected a large portion of the country this week. Tonight storm warnings are in effect offshore and gale warnings are in effect for Chesapeake Bay, Delaware Bay, and Long Island Sound. Coastal flood warnings are in effect for southern Virginia, Delaware, and the southern two-thirds of New Jersey as strong easterly winds gusting to 60 mph push water inland.

On Tuesday heavy snow fell in the Midwest, and overnight the snow shifted to the Appalachians. Snowfall reached 18 to 24 inches in the mountains of Virginia today with amounts tapering off toward the coast. The Washington DC metro area dodged a bullet, with only an inch or two of snow.

We're not done with this storm yet. The precipitation with this system will be spreading into southern New England tonight and Thursday, with some snow and rain hanging around through Friday. Heavy snow is possible at times Thursday from the Adirondacks to the southern New England coast.

Forecast map for Friday, March 8

Monday, March 4, 2013

Don't Put Away Those Snowboards Yet

24 hour snow fall
A storm that moved from the Pacific into British Columbia on Saturday will be affecting the eastern half of the U.S. the next two days. It has already brought widespread snow to the Canadian Rockies, Montana, and the Dakotas with amounts from 12 to 18 inches.  This evening the low pressure center was just south of Fargo, North Dakota, and by Tuesday evening the low is expected to be in the Ohio Valley. At rush hour on Wednesday the morning the storm should be located near Norfolk, Virginia.  Winter storm warnings and winter weather advisories are in effect from the Dakotas to the mid-Atlantic coast.

Watches, warnings, and advisories in effect at 10:00 p.m. CST

Heavy snow will be the main feature of this storm, but freezing rain and sleet will be causing problems along the southern periphery of the storm track,

Probability of 4 or more inches of snow for the period from 6:00 p.m. CST March 4 to 6:00 p.m. March 5 (left), and from 6:00 p.m. CST March 5 to 6:00 p.m. CST March 6 (right).