||The warmth of mid-November to mid-December 2006 over the Mid-Atlantic region are examined. Emphasis is focused on the conditions associated with the two record warm events of 1 and 17-18 December 2006. The large scale pattern, the relationship to the NAO, and ENSO are examined. Northern hemispheric snow deficits are presented to show the context of the warmth. It is unclear weather this is an ENSO/NAO impact or whether it might even be related to global warming. But the NAO signal appears to be the most coherent.
||Late season severe event of 2006. The largest December severe weather event with 133 reports of severe weather. One of the largest late season severe weather events in the eastern United States eclipsed by the 10-11 November 2002 and 20 November 1989 events in number of reports.
This event featured several December firsts to include the first tornado, first deadly tornado, and the first F2 tornado.
The strongest squall line developed in the dry slot late in the day producing most of the severe weather over eastern portions of the State.
||A late season severe weather event affected the northeastern United States on Friday, 1 December 2006. There were over 133 reports of severe weather between 1200 UTC 1 December 2006 and 1200 UTC 2 December 2006 (Fig. 1). Most of these events were observed between 1500 1 December and 0100 UTC 2 December 2006. There were an additional 46 severe weather reports on the 30th of November, most of these were observed after 0300 UTC on 1 December.
In addition to the large number of severe weather reports, there were 3 tornadoes observed in Pennsylvania. The F1 tornado in Greensburg, Pennsylvania was the first recorded tornado in the State. The F1 tornado in Halifax was the first fatal tornado in the State, and the F2 tornado in Fairview Heights was the first F2 tornado in December.
Prior to 2006, the largest December had 46 reports of severe weather on 16 December 2000. The event of 1 December had the largest number of severe weather reports compared to any previous December event and had more tornadoes than the December events listed. However, the relatively small severe weather events of 11 and 21 December 1967 each had 3 tornadoes.
This event shared many of the feature found in many late season events including:
• A deep surface cyclone with below normal surface pressure tracking north and west of the affected region.
• An anomalous southerly jet with strong 850 hPa winds on the order of +2SDs above normal or greater.
• A surge of above normal PW in the warm sector ahead of the strong frontal system.
||A strong frontal system brought heavy rains and severe weather to the eastern United States on the 15th and 16th of November 2006. Ahead of the frontal system, a large swath of severe weather was reported (Fig. 1) with over 127 and 40 severe reports on the 15th and 16th respectively. The tornado outbreak in the southeastern United States included a deadly F3 tornado in North Carolina.
The rainfall over the northeast valid for the 24-hour period ending at 1200 UTC 17 November is shown in Figure 2. Though hard to see over 6 inches of rainfall was observed in some eastern Pennsylvania locations. Along the frontal zone, intense convection produced 1.5 to 5 inches of rain, mainly over eastern portions of Pennsylvania. Though not shown, heavy rains were observed in the Gulf States on the 15th. Over 8 inches of rain was observed in southern Louisiana and a wide swath of 2-6 inches of rain extended from Louisiana, Alabama, Georgia and into southwesternmost North Carolina.
The anomalous 850 hPa winds were responsible for the widespread reports of wind damage in Pennsylvania and New York. The intense and anomalous low-level jet, at +5SDs above normal at 1200 UTC 850 hPa was in close proximity to the deadly tornado in North Carolina shortly before 1200 UTC on 16 November 2006. The value in anomalous 850 hPa V-wind anomalies in forecasting and refining high threats of severe weather continues to be validated by repeated cases over the past 7 years of observations.
||Summary of the heavy rainfall events of October 2006. Emphasis is on the patterns of heavy rains over Pennsylvania. The events studied impacted most of the northeastern United States. Four events are examined. Hardest hit areas of the country included southeastern Texas and Louisiana where the monthly rainfall exceeded 20 inches in some areas due to an intense event on the 16th & 17th ; the 19th; and the 26th and 27th of October.
The events along the Gulf Coast may have indicated the open Gulf and the flow of moisture into the northeastern United States which led to heavy rains in the northeastern United States to include Pennsylvania on the 12th, 18th, 20th and 28th of October 2006. The heavy rain events of both 18 October and 28 October were proceeded by heavy rains in the Gulf States.
||High wind event over eastern United States. Mostly advisory level winds in central PA. Massive 968 hPa cyclone in Quebec. Shared the characteristics of many past events, deep cyclone and anomalous winds in ensembles and models.
The two most recent comparitive high wind events in central Pennsylvania include Post cold frontal high wind event of 01 December 2004 and 11 November 2004 (2004-11-04). The strongest and most damaging event in recent years was observed on 13 November 2003 (Grumm 2003-11-13). This NCHW event was observed from Illinois to New York and did significant damage in Chicago.
||Strong cold front with lots of uncertainty with timing. SREF confidence shown and probability of severe weather. Radar images show two severe storms in southeastern Pennsylvania. One storm, in Cumberland County, produced a short-lived tornado.
||This case emphasis is on the QPFs from the MREF, GFS, and SREF during the extratropical transition of Tropical Storm Ernesto as it interacted with a strong frontal system in the Mid-Atlantic region. The GFS tended to over forecast the rainfall in the frontal zone and missed the rainfall with the tropical air. The SREF was at a distinct disadvantage due to the lack of the tropical system. Each EPS and the GFS core of the MREF had some high and low points in the forecasts of the rainfall.
||Overview of the impact of tropical storm Ernesto as it interacted with the frontal boundary over the Mid-Atlantic region on 2-3 September 2006. Focus is on the conditions and how the event unfolded over Pennsylvania.
||Severe weather event of 3 August 2006 associated with the "heat wave ending " cold front. In Pennsylvania, most of the severe weather was over the northern and southwestern areas. Convection may have been limited from extending farther south and east due to the unseasonably warm air to the south and east were 700 hPa temperatures were 10 to 12C. SREF forecasts showed the warm air and high CAPE. The highest CAPE and EHI were forecast over Ohio where severe weather reports were more numerous.
||An evaluation of forecasts from the NCEP MREF/GFS and CMC Ensemble Prediction System (EPS) of the August 2006 heat wave. The focus is on the heat wave over the eastern United States and key predictors such as 925 hPa and 850 hPa temperatures; precipitable water, and 500 hPa heights. The NCEP MREF and GFS were too warm at 925 hPa and the CMC was a bit too cool. The wide use of the GFS/MREF likely contributed to MOS guidance being too warm and slight over prediction of the high temperatures along the East Coast during portions of the event.
||Massive heat wave with a strong subtropical ridge began with heat wave in California. The ridge moved eastward spreading heat and temperatures over 100F across the intermountain west and the plains at the end of July. The first 100F reading in the eastern United States were observed on 1 August.
A review of the event and a focus on the MREF forecasts in the eastern United States is provided. This heat wave showed the classic signals and had strong thermal anomalies east of the Rocky Mountains.
||A cold front sagged south-southeastward through the northeastern United States on 18 July 2006 triggering convection over portions of the region. This cold front brought relief from the heat episode that had impacted the region for approximately 3 days.
Severe weather was anticipated over much of the region and Pennsylvania was out looked for the potential in advance of the event. However, forecasts of instability (CAPE) and shear suggested a high instability low shear day. As will be shown, CAPE forecasts indicated very high values of CAPE, in excess of 2400JKG-1 supporting large updrafts.
This paper will examine the updraft-dominated severe weather event of 18 July 2006. Focus is on diagnostic forecast products from the NCEP short-range ensemble (SREF) forecast system is presented in identifying and anticipating the evolution of this event.
||A strong upper-level ridge over the western United States, with a closed 5490 m contour and height values near +2.5 standard deviations above normal (Fig. 1), brought unseasonably high temperatures to the Midwest and eastern United States from 16 through 18 July 2006. High temperatures more than two standard deviations above normal for 1-2 consecutive days is one potential measure of a heat wave. These values are difficult to achieve, thus a regional approach would require 1 or 2 locations to achieve such temperatures during the heat wave.
During the heat event of 16-18 July 2006, most locations in Pennsylvania experienced 1 to 2 standard deviations above normal below normal for 2-3 days. The 98F reading at Philadelphia was exactly +2 standard deviations above normal. Varying definitions of a heat make it difficult to quantify this event, which was clearly a heat episode sharing many characteristics of the July 2005 and May 2006 eastern United States heat episodes.
The NCEP MREF forecast this event well in advance, a clear NCEP-MREF success story.
||Prolonged heavy rain event 24-28 June 2006. Major flooding at some points along Susquehanna, Delaware, and Mohawk rivers. Some areas saw in excess of 12 inches of rain during this mulit-day event. This document focus is on the NCEP SREF performance during the heavy rain peroid. It did well with the pattern but not as well with the details of the precipitation.
||Widespread severe weather event Ohio Valley to Pennsylvania. Over 40 reports of severe weather in Pennsylvania. SREF forecasts indicate extreme instability over a large region from Illinois to Pennsylvania. Joint probabilities of EHI and CAPE showed strong signal in Ohio and Pennsylvania.
||MCS formed over Michigan. Moved over PA providing rain but no significant weather. SREF pointed to development but missed the more southward track the system followed.
||Pulse storms, mainly hail producers over eastern and southeastern areas of Pennsylvania. Good example of pulse storms and SREF to outline areas of modest storms using conditional probabilities.
||This paper will examine the conditions associated with Memorial Day heat episode of 29-30 May 2006. Climatic anomalies will be used to show the character of the event and model and ensemble forecasts will be presented to show their value in forecasting these events. In early season heat waves, such as the Memorial Day 2006 event, record high temperatures and moisture are often insufficient to create HI value much above 100F. However, these early season events can cause heat stress problems to acclimated individuals.
||Heavy rains in southern New England. Flooding was observed along the Merrimac River. This was a long duration event. The pattern which produced the rain was well forecast by the NCEP short-range ensemble predictions system. Uncertainty with the timing and amounts of precitation caused the ensemble data to appear to have missed the event. However, monitoring forecasts of accumulated precipitatino revealed a relatively well forecast event from a QPF perspective and heavy rainfall pattern perspective.
||Significant Spring cyclone over Michigan was well forecast by the NCEP MREF and the new 15-member MREF. New bias corrected data and probabalitistic anomaly data were used to show forecasts of this storm.
The storm brought a late season snow to Wisconsin and much needed rains to the Mid-Atlantic region. A Widespread 1-2 inch rainfall in Pennsylvania with some areas seeing over 3 inches. This system stalled bringing heavy rains to New England.
||A heavy rain event impacted the East Coast of the United States on 22-23 April 2006. The rainfall put a substantial dent in the rainfall deficits over much of the East Coast. There were some isolated reports of over 6 inches of rainfall on Long Island.
Overall, the large scale pattern favoring heavy rains was well forecast by both NCEP EPS’s. The focus here was on the SREF forecasts. These forecasts showed the surge of above normal precipitable water and anomalous low-level (850 hPa) jet. The PWAT and thermal fields implied a quasi-north south boundary with the heaviest rains falling along and on the warm side of the boundary.
||A strong cold front brought severe weather to the Mississippi and the Ohio Valley’s on 7 April 2006. There were 768 severe weather reports and reported 64 tornadoes. This was the second massive event with killer tornadoes in April, though it was not as big as 2 April 2006 event. This case shows the need for standardized climatologies to gage the breadth of a severe weather event. To make that point, this event is compared to the May 2003 events. This case also shows some NCEP short-range ensemble (SREF) products to help identify potentially large severe weather events. Thanks for assistance on this from the Storm Prediction Center (SPC).
||Two day event of severe weather with over 800 reports and deadly tornadoes in the middle of the country on 2 April. High CAPE and high shear dominated. As the strong front moved eastward, severe weather was observed in the east, but much less, on the 3 April. Above normal CAPE in Pennsylvania, but too low to support big updrafts and strong shear produced a line of storms which mainly produced small hail. Severe weather was hard to come by in central Pennsylvania.
||Frontally enhanced bands brought 1-3 inches of snow to portions of central Pennsylvania. The snow arrived with intensity from Altoona to Lockhaven before sunrise. This created extremely icy roads for the morning commute. In and around State College 1-3 inches of snow was common with most snow falling between about 5-730 AM. The warmth of earlier days and falling temperatures created dangerous road conditions. A high impact event for a low snow total.
||Warm episode in Pennsylvania with above normal temperatures on the 10th and 13th. The cold front that ended the warmth produced an extensive severe weather event in the Midwest on the 12th of March. An examination of MREF and SREF forecasts using climatic anomalies is presented related to both the near record warmth and the severe weather outbreak.
||Mini ice storm in central Pennsylvania on 2 March 2006. Snow was observed in New York State. This event is examined using SREF plumes to forecast the precipitation type and SREF confidence forecasts. The low confidence in the 850 hPa temperatures were coincident with the area of ice in Pennsylvania.
||An arctic front brought high winds and severe weather from Arkansas to New York. In the cold air, heavy snow and blizzard like conditions were observed. The massive anticyclone that brought the abnormally cold air into the United States was well forecast by the NCEP MREF 7 to 9 days in advance.
||Record snowfall of 27 inches in Central Park, New York. Tight storm with mesoscale heavy snow area from Washington, DC to Boston. Early forecasts of this storm demonstrate marked uncertainty with serious forecast changes on 8 February, first identifying the storm and then SREF-ETA member errors on 9 February.
Models also showed the signals of a significant event with a deep cyclone and highly anomalous low-level jet. The storm lived up to its record setting potential with MSLP, PWAT, 850 U and V wind anomalies.
||Line of showers which produce convective wind damage in York County from near Hannover to just north of York. The line of showers and thunderstorms downed trees and took the roof off of a hotel near I83 and route 30. Thirty rooms and 30-40 cars were damaged by the roof materials. I tractor trailer on the I83 ramp was over turned by the winds. This damage occured around 850 PM Saturday evening...4 February 2006.
||Comparision of the relatively cold December 2005 and warm January 2006. The NCEP re-analysis data suggested that the flip-flop occurred around 22-23 December and it is shown that most large scale fields were near normal for the month after averaging below normal through 22 December. January was above normal for heights, thickness, and temperatures over most of the United Statess. A comparison to the flip-flop cold to warm of December 1989 and January 1990 is presented.
||Cold frontal passage during afternoon and evening hours. This sytem brought light rain, which rapidly changed to snow. Many locations had thunder snow and gusty winds. Minor limb damage was reported with the winds. Farther east, hail accompanied the passing frontal boundary. A rare large hail event in January in eastern Pennsylvania, New Jersey, and Long Island.
||Winter storm of 23 January 2006. This event produced some snow in southern New York and northeastern Pennsylvania. Central Pennsylvania saw mainly freezing rain and sleet. Rain dominated in the southeast, where up to 1 inch of rain was observed. Another well forecast event by the NCEP SREF based on model precipitation type forecasts. Human forecasts emphasized more snow than was observed.
||Ice storm event on evening of 17 January in central Pennsylvania. Then mostly rain with flooding in north-central areas. Temperatures rose into the 60s in the southeast ahead of the cold front. Also, example using SREF plumes and local WRF model.