The Northeast Weather Blog...

Upper level troughing by week's end...

By: Blizzard92, 8:18 PM GMT on July 28, 2010

A gentle eroding wind blows against the long-standing sign, "COMING SOON: Luxury Homes." Weeds grow upon the posts as it sits gently along a farm field. But in recent weeks, the sounds of a crisp cool morning have been eroded by bulldozers, dynamite, etc. The ancient sign that posed a hollow threat for nearly ten years has finally made its accusation. Unfortunately this meant the realization for those of us, that our beautiful mountain landscape would be drastically harnessed permanently. The wheat fields that once grazed a myriad of wildlife are destroyed. The wheat fields that once served as shelter for packs of deer is no more. The wheat fields that once provided a window into the beauty of the ridge and valley region has been eliminated. Torrents of dust, dirt, and mud exist and the blowing amber fields of grass along the base of Blue MOuntain is only a distant memory. Along the mighty creeks serving as a resource for the ridge to serve as a flood reservoir, no contain floods of brown mud serging along the babbling brook's rocks. In a time where economic concerns prevail throughout the housing markets, and scores of local contractors ending their construction for new neighborhoods early, why is necessary to destroy once protected land. For years this sign has only been a source of laughter. "Ha, that coming soon sign has been there for years." Yet as soon as the chuckle ended before our eyes, one day the field was destroyed. Due to a score of concerns for our neighborhood, many attended local township meetings to deter the contractor from their construction, but it was no such luck. Now we wait as homes slowly construct themselves along the base of a mountain and up onto the mountainside. Once a large Native American Reservation and Patton's Fort, eventually matured into local farmland, now finally to be built up as just another fancy neighborhood. While beautiful real estate, it is such ashame that thousands of stories just like this are occuring all across the United States and world. I am far from a those enthrowed with anthropogenic global warming, but concern for local environments is important in its own sense. Oiled black asphault is not my idea for a picture perfect setting. And tis all why I hope to eventually mitigrate towards a quiet mountainside community with a successful career as I come of age.

Onto the weather... Recently a unique collection of severe thunderstorms exhibited themselves across the Keystone state and the rest of the northern Middle Atlantic. While everyday scores of thunderstorms migrate across the globe with electrons striking their lightning fury overy the harsh landscape, these thunderstorms proved unusual in their makeup. The majority of thunderstorms across the northern Middle Atlantic organize themselves into squall lines and/or large clusters. Unlike the Midwest and their associated supercells, our thunderstorms rarely have echo tops as high as the bottom of the stratosphere. Most of the time run of the mill thunderstorms are common in our region due to several inhibiting factors. But this week, several days offered unique supercellular characteristics creating the catalyst for several tornadoes in the northern Middle Atlantic. Across the heartland flat praires in close proximity to the gulf stream offers the perfect opportunity for thunderstorms to grow with few preventive factors. Closer to home the Appalachian Mountains and cool easterly Atlantic flow causes several detering factors in severe weather.

Local model guidance exhibited several characteristics that offered evidence for the potential for supercellular formation. The GFS and ECMWF both highlighted a slow moving warm front across the region with a strong upper level low in Canada dragging on a cold front through the Ohio Valley. The warm front served as the lifting mechanism and a bubble of upper level ridging over the Tennessee Valley helped to feed heat and humidity into the region. Moisture from deteorating Bonnie also helped to aid boundary layer dewpoints in the mid to upper 70s with PWATs aloft +2SD at nearly 2.0in. Concentrated areas of higher helicity along the warm front created a natural upper level rotation, along with shear values crossing the impressive 50knots threshold. But a problem did exist, 700mb heights were near the critical CAP threshold at 8-9C. Typical strong CAPs exist around 9-10C, but this unique instability setup did allow for thunderstorms to form. Thunderstorms develop on the basis of contrasting thunderstorms, warm air at the surface and cold air aloft. The contrast helps create healthy cellular updrafts and downdrafts. But when the air column is warm with little atmospheric cooling as one increases elevation, then this puts a CAP on convection development. This helped to prevent thunderstorm formation in southern areas in southern Pennsylvania and all of Maryland/Delaware. Closer to the warm front with steeper lapse rates, thunderstorms were able to form. SBCAPE values rose to near 3000j/kg with MUCAPE up to an astonishing 4000j/kg. Remember CAPE is convective available potential energy. Therefore the higher the number, the higher the instability. Anything above 1800j/kg is usually a good sign for strong thunderstorm development in Pennsylvania posing that there is a lift for formation.

Each day of the stalled warm front allowed discrete supercells to form with concentrated areas of severe damage. While the thunderstorms were not widespread, their actual makeup was very impressive. They featured echo tops nearly to 50,000ft, almost into the stratosphere. Also they contained VIL values near 50-60. VIL is a measure of hail formation; simply put the higher the number above 30, is usually a good sign for hail. Fortunately the freezing level aloft was nearly well aloft, so hail was not a major threat. With strong vertical and horizontal shear, tornadoes became a threat. Several reported tornadoes occured along the New York/Pennsylvania border bringing the number of reported tornadoes in Pennsylvania to 12 for the year. Average number per year is nine.

The final day of the severe weather featured the approach of the cold front drapped across western Pennsylvania Sunday July 25 during the morning. A decaying MCV (mesoscale convective vortex) provided the lift for a bowing line segment over central Pennsylvania and on eastward. But across the Lower Susquehanna Valley, a unique combination of impressive kinematics and thermondynamics allowed for a few discrete supercells to form out ahead of the line. These cells produced several tornado warnings, but no actually tornado reports.

This poses my main point. Across southeastern central Pennsylvania from the Lower Susquehanna Valley into the western Delaware Valley is a unique geographic location that offers each severe weather season several unique thunderstorms. While I am not saying this region focuses the most severe weather per year, but it does pose the threat for the most intense thunderstorms (supercells). The geographic region has several factors that offers the nickname the 'tornado valley of the east.'

The Appalachian Mountains pose a looming existence just to the west of the region. Blue Mountain is the first ridge as one travels from east to west. From there westward, exists many ridgetops topping elevations around 2000ft until the Alleghany Plateau. This creates the orographic lift for thunderstorm formation until they traverse east of the Blue Ridge on to flat land with elevations below 500ft. To the east of the region is the Atlantic Ocean which offers an easterly moisture anomaly into the factor. And to the south is the Chesapeake Bay offering another unusual moisture factor which helps to nose up dewpoints on summer days. The combination of the flat land downwind of a large mountain chain in correlation with several moisture anomalies from large boundaries of water, creates a natural spin to the atmosphere. Countless times once thunderstorms move downwind of the mountain, they strengthen rapidly peaking across Lancaster County and immediate surrounding areas. Each year thunderstorms in this region develop the strongest and produce several anomalies over the region. While statistically western Pennsylvania (Westmoreland County to be specific) sees the most severe weather reports per season, the Lower Susquehanna Valley and eastward offer unusually strong thunderstorms which develop supercellular characteristics. The Oklahoma Climatology Survey even advocates that while the national average is one tornado per 10,000 square miles, there is small isolated concentration of 3 per 10,000 square miles in the Lower Susquehanna Valley. To keep in relativity this number reaches nine for a max per 10,000 square miles across the Oklahoma tornado alley heartland.

Quiet weather appears to exist the coming few days outside a quick cold frontal passage on Thursday. A quick-moving cold front will move downwind of the Great Lakes Wednesday night and Thursday through early afternoon. A bit of elevated CAPE near 1000j/kg will allow thunderstorms to develop along the front and move southeast Wednesday night. Simulated radar from the 4km HIRES NMM WRF indicates a broken line of steady showers and thunderstorms forming over western Pennsylvania tracking eastward. Average QPF pools from a GFS/NAM correlation indicate an average .2-.8in basinwide with lower amounts across the south and east. Convective feedback problems over northern Pennsylvania show 1in QPF, but that will likely be isolated. By Thursday morning, showers and thunderstorms will be moving across central Pennsylvania. Unfavorable timing will likely inhibit most severe weather for Pennsylvania despite adequate shear 0-6km near 30-35knots. But isolated severe weather is possible over Maryland and Delaware as the cold front moves over the region by early to mid afternoon. Highs are dependent on the front's timing, but it is possible for southern areas to reach 90F ahead of the front in the southwest flow. Northwestern areas will remain in the lower 80s. Not all areas will receive rain and it is likely parts of Pennsylvania remain dry as the front passes through during the diurnal min. By Friday upper level troughing over the region will maintain slightly below normal temperatures and sunshine over the region.

Friday will likely feature the best weather in nearly weeks along with Saturday and possibly Sunday. Humidity will remain low with partly cloudy skies. Highs will be in the mid to upper 70s over the higher elevations with lower 80s in the major metropolitan regions. Lows will even drop into the low 50s near Bradford with adequate radiational cooling conditions.

By late Sunday into early next week, a stationary boundary will lift slowly northward from North Carolina to the Ohio Valley which will bring a return to the heat and humidity by early next week with diurnal threats of showers and thunderstorms. At this time widespread severe weather does not look likely through the next seven days. Looking ahead into August, a positive NAO and roaring La Nina will likely favor increasing heat again for the month with above average temperature montly departures. Another hot month looks to be in store with normal precipitation.

Thursday- A chance of showers and thunderstorms will be ongoing in the morning spreading eastward throughout the day. An isolated severe storm is possible with wind damage being the primary threat. Highs will be in the low 80s in the northwest to near 90 towards Washington DC. Mostly cloudy skies will dominate

Friday-Sunday- High pressure and a northwest flow will maintain 70s to 80s for highs and lows in the 50s regionwide with low humidity and clear skies.

Regional updating radar...


"Here north of Harrisburg 2010 statistics"
(Severe Weather Stats...)
Severe Thunderstorm Watches- 10
Severe Thunderstorm Warnings- 9
Tornado Watches- 1
Tornado Warnings- 1
Total Thunderstorms- 15

(Precipitation Stats...)
Flood Watches- 3
Flood Warnings- 1
Monthly Precipitation- 0.83inches
Yearly Precipitation- 23.13inches

(Temperature Stats...)
Heat Advisories- 5
Excessive Heat Watches- 1
Excessive Heat Warnings- 1
90degree days- 28
Highest Temperature 101F (x2)

Weekly Forecast

Updated: 12:42 AM GMT on August 05, 2010

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Continued ring of fire pattern across Northeast...

By: Blizzard92, 7:56 PM GMT on July 20, 2010

There are many whom are quick to comment on the state of modern education. Unfortunately many of those are politicians with little experience in modern education outside of personal anecdotes. As a current student, I experience the differences in education on a nearly daily bases. While people are quick to assume teenagers have little to say other than complaints about school, constructive critiscm often occurs in many of my honors classes. For instance in my Calculus class this past year, we often recognized the changing math program for younger students learning the simple multiplication and division tables. There are new methods to solving for instance 24*36= instead of the old fashioned method. One method even makes fancy boxes in a latice method, which takes much longer, but is simpler. The problem is in higher mathematics, you need to be able to solve problems like this in a quick manner while understanding the process. Also even in division, long division is non-existant. Another method is used, again simpler, but defeats the purposing of understanding how division works. When these students reaching PreCalculus and Calculus, they will suffer many setbacks in solving problems and doing simple things like finding the derivative or antiderivative in Calculus. But I am not here to dwell on the math program... I think another issue is statistics. It is no longer considered important to remember dates. Example A: Few modern students would be able to tell you the year of the moon landing, 1969. Dates and extraneous facts are considered unimportant. This poses problems not only in understanding the foundation of world cultures, but also using science. Every day, I use a many statistics to create forecasts and new theories on the evolution of climate. Records and statistics are critical to the success of understanding and applying meteorology, but also just general science. Science is simply a subject to explain how the world revolves therefore having applications in all subjects. 2010 is an important year for records as the following will note, and unfortunately the application of statistics, records, and dates is a declining cause in modern education.

2010 has been a remarkable year weatherwise on a global perspective. Recovering from one of the strongest El Ninos since 1998, average temperatures worldwide have been starkly mild, even hot! There will be many quick to point to anthropogenic global warming, but a quick rebuttal will surmise in response. As supposed to be in all instances, climate is measured over a long period of time while the term weather designates the short term. The official American Meteorological Society defines climate as...

The slowly varying aspects of the atmosphere–hydrosphere–land surface system. It is typically characterized in terms of suitable averages of the climate system over periods of a month or more, taking into consideration the variability in time of these averaged quantities. Climatic classifications include the spatial variation of these time-averaged variables. Beginning with the view of local climate as little more than the annual course of long-term averages of surface temperature and precipitation, the concept of climate has broadened and evolved in recent decades in response to the increased understanding of the underlying processes that determine climate and its variability.

2010 has proven its share of records including eight extreme global high temperatures with a recent one occuring for the new hottest temperature ever recorded in Russia (111F). Also impressive upper level 850mb thermals have proven record values with several days this year ranking as some of the hottest average temperatures on a global perspective ever recorded. From record heatwaves in July in Africa to record high temperatures across Canada during January-March, this year has proven to be very mild. The following are global sea and surface temperatures during the last three months...

April...


May...


June...


As noted, primary concentrations exceed normal values across the globe both and on land and sea. But it is important to note as with 1998, that El Nino plays an important role is this above normal warmth. Typically El Nino years provide warmer than normal temperatures on a widespread level to many locations. Now many in the Northeast are quick to point to the record snowy year for many major metropolitan regions. This is the same time where the El Nino reached its max anomalies in the equitorial Pacific which rate in the strong category...
Nino 4 ~(+1.5C)
Nino 3.4 ~(+2.0C)
Nino 3 ~(+1.6F)
Nino 1+2 ~(+1.2C)
While yes this wintry proved to serve extraordinary snow values for many locales, actual surface temperatures were not cold. A well thought idea in forecasting winters is cold=dry and mild=snowy and/or rainy.

If it had not been for a record negative NAO and Ao, this past winter would have been a rainy disaster for the entire Northeast. I am certain the upstream blocking in combination with the split jet from El Nino allowed for the record snowstorms. It takes all parts to make a puzzle, therefore with upstream blocking and no split jet, it would have been dry and cold. But if we no upstream blocking with a split jet, then it would have been rainy and very mild, which is typical of that of El Ninos. As the El Nino peaked in February or so, downstream global effects are usually felt several weeks later. Therefore while positive anomalies are peaking, effects globally will not occur for a bit of time. This explains the very mild March globally. Since March the northern Middle Atlantic has featured above normal temperatures and near record values at that. Again this all pinpoints to the reasoning for very mild temperatures worldwide, which are also evident during the strong El Nino of 1998. But rapid changes in the southern oscillation are allowing for a growing La Nina. Yes SST anomalies have already dipped into the La Nina region, but it will not be designated as a La Nina until those values hold for three months. Using a few extropolation methods, a moderate La Nina is very well possible by meteorological Fall...

The CFS is already predicting a strong La Nina by winter. Rapid swings from strong El Ninos to strong La Ninas occur less than 20% of the time, so this would be a rare instance. But climate forecast models typically overestimate SST values, so likely a modified prediction would be a better forecast. Essentially in laymen's terms, this means the above normal global surface temperatures will be declining during the next few months. In fact cooler temperatures than normal are likely to develop over the Pacific northwest as the PDO drops back to well into negative values again. Also Europe can expect a rapid decline in temperatures in the coming months. Also with this recent Nina development, the 2010 hurricane season will likely be a bit more benign than originally expected. Unfortunately it only takes one hurricane to make a season (1992-Andrew).

Closer to home in the northern Middle Atlantic, above normal conditions will be persisting through at least the next two to three weeks. Early indications from the ECMWF were showing a cool down by the end of July. But recent prognostics indicate a growing abnormal >588mb ridge stretched from the east to west coasts of the US during the end of the July time period...

The defining difference in the coming warmth, will be that the bubble of heat will be displaced to the south of the Middle Atlantic. This positions the Maryland/Pennsylvania/Delaware region in the ring of fire. Essentially this means series of warm fronts and decaying cold fronts will move through the region with a series of MCS and/or convective events. While precipitation will be spotty, diurnal chances of thunderstorms will be on the increase. 7/20/10 12utc GFS even prints 2.8in of QPF for KMDT during the next sixteen days. Drought conditions will be waning regionwide fortunately.

Now in the shorter term... A cold front will slowly slide south over Pennsylvania during Tuesday night and Wednesday. But little cooler air is expected with H85 heights remaining near 20C. This front will meander over the northern Middle Atlantic through the entire week creating almost a daily threat of showers and thunderstorms. But several days will have high probabilities than others. Wednesday will feature mild temperatures with dewpoints creeping into the low to mid 70s as far north as interstate 80. Increasing precipitate waters near 2.2in will allow for a steady stream of thunderstorms during the day Wednesday as a weakening MCV moves into western Pennsylvania during the early morning hours. This complex will allow for several outflow boundaries to form across the central Alleghanies creating a catalyst for afternoon convection. With a close proximity to the right front entrance of the low level jet, shear values near 40-50 knots 0-6km aloft will create the threat of damaging winds. Several hundred helicity values will also create the potential for a bit of rotating winds aloft. Therefore the threat of supercells is highly possible during the day. GFS instability thermodynamics indicate CAPE values of 2000-2500j/kg to form in an instability axis from central Maryland up through the eastern half of Pennsylvania. Morning debris clouds may limit instability for areas farther west. The cold front will slowly sink south, so therefore severe convection will likely be in the morning and early to mid afternoon with a high threat towards evening over Maryland and Delaware. Thunderstorms will form in small broken line segments and/or supercells. Damaging winds is the primary threat. A few higher echo tops may tap into the freezing level creating large hail, but the potential remains slightly low.

By Thursday the cold front will sink southward giving way to partly cloudy skies for Pennsylvania with the more humid conditions over southern Maryland and southern Delaware with the threat of diurnal convection in those southern areas. But the front will begin to lift northward by Thursday night and Friday as a growing heat ridge of thermals greater than a 588mb thickness develop over the central Plains. The chance of thunderstorms will begin to increase after 10pm over northern areas as a few nocturnal thunderstorms develop along the now warm front. With a close proximity quasi-stationary front, thunderstorms will be possible Friday through Saturday. Towards Sunday a rapid moving cold front through the Great Lakes will promote more convection Sunday afternoon with another threat of severe weather with steep lapse rates and high shear values. Details though will be sorted out closer to the date.

In quick summary...

Wednesday- Widespread highs in the upper 80s with high humidity and partly to mostly cloudy skies. Thunderstorms will be possible with some severe weather likely with damaging winds as the primary threat.

Thursday- Partly cloudy skies with a chance of isolated thunderstorms over southern areas in Maryland and Delaware with clear skies over Pennsylvania. Highs will be in the lower 90s.

Friday- Partly to mostly cloudy skies with increasing humidity and higher dewpoints. Heat indices will approach 105-110F for major metropolitan regions with surface temperatures in the low to mid 90s for lower elevations. A chance of thunderstorms will also exist along the stalled front over the northern Middle Atlantic.

Saturday- Partly cloudy skies with a chance of thunderstorms all day as highs approach 90F for many areas.

Sunday- An approaching cold front will bring afternoon thunderstorms and a threat of severe weather. Highs will be in the upper 80s to lower 90s.

Regional updating radar...


"Here north of Harrisburg 2010 statistics"
(Severe Weather Stats...)
Severe Thunderstorm Watches- 9
Severe Thunderstorm Warnings- 9
Tornado Watches- 1
Tornado Warnings- 1
Total Thunderstorms- 14

(Precipitation Stats...)
Flood Watches- 3
Flood Warnings- 1
Monthly Precipitation- 5.19inches
Yearly Precipitation- 22.29inches

(Temperature Stats...)
Heat Advisories- 3
Excessive Heat Watches- 1
Excessive Heat Warnings- 1
90degree days- 25
Highest Temperature 101F (x2)

Weather Pattern Observations

Updated: 12:27 AM GMT on July 26, 2010

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Unsettled weather on the horizon...

By: Blizzard92, 9:33 PM GMT on July 14, 2010

After a period of dry weather and near term isolated drought conditions, a recent change in the jet stream pattern has aided in a relocation of the heat ridge allowing for cold fronts to penetrate across the northern Middle Atlantic and washing out to the south in Virginia. 500mb analysis indicates a relocation of the Bermudian high slightly farther south and east in the Atlantic. But above normal temperatures will continue across the region courtesy of global abnormal thermal heights. Cold air is very absent across much of the globe, especially in the north Arctic where sea ice conditions are down at a record negative pace.

The upcoming pattern will continue favor above normal temperatures, but slightly enhanced precipitation in the rainfall department courtesy of an anomalous flow out of the Gulf of Mexico. Recent heavy rain during the past three days is courtesy of enhanced PWATs originating from the south with a near +2SD. SREF guidance quickly pinpointed to the higher 700mb moisture anomalies several days in advance of the heavy rain. Local groundwater conditions continued to heed below normal values especially in localized areas across northcentral Maryland and parts of the middle Susquehanna Valley in Pennsylvania where drought conditions on the Palmer Index entered D1. With soil moisture anomalies well below normal, the threat of flash flooding actually increases as the water washes quick away into urban areas and is not allowed to soak into the ground. FFG at the time was a general 4in/12hr across much of the state, but global model guidance indicated a heavy rain threat several days in advance. GFS meteograms for KMDT indicated nearly 1.5in of rain with local 4km WRF output near 6in for parts of southeastern Pennsylvania, likely courtesy of convective error. Monday, 14 July 2010, produced an interesting weather day across much of central Pennsylvania where near stationary convection developed on an axis of instability on a surface front ahead of the general cold front. PWATs near 2in with CAPE values near 2000j/kg produced a complex of thunderstorms on the leeward side of the Alleghanies with a general storm track and momentum to the east-northeast at 75degrees.

30knot wind shear 0-6km aloft allowed high echo tops from thunderstorms to bring down some higher wind gusts. Widespread wind damage was reported along a narrow corridor along the lower and middle Susquehanna River. General damage reports were courtesy of wet downbursts and straightline winds. Heavy rainfall rates were also reported ranging from 4-7in/hr for short periods of time courtesy of tapping into near tropical air aloft in the lower troposphere. Rainfall totals from the training thunderstorms were reported ranging from 1-4in. These complexes of thunderstorms later tracked into eastern Pennsylvania, but in a slow general weakening state by evening.

As the potent upper level trough lifts out of the region, the general shortwave will move offshore. Taking a near tropical depression outlook on local satellite imagery, the deformation axis of precipitation will move offshore by Wednesday evening with additional QPF generally .1in for eastern Pennsylvania. High pressure will return with an anti-cyclonic flow, but the airmass has non-polar origins therefore continuing the above normal temperature pattern. As the 1020mb high pressure moves offshore by Thursday evening, the clear skies featured on Thursday will be invaded by higher cirrus by 6z Friday. 2m temperatures look to be a general 90-95F for most locations in Pennsylvania, Maryland, and Delaware below 1000ft. Across the higher elevations such as the Laurels, Poconos, and Northwest highs will be a less salty 80-85F.

12z 7/14/10 GFS indicates an approaching cold front by Friday as a 1004mb low pressure moves through Ontario. A bubble of higher H85 thermals near 20C will center over the northern Middle Atlantic for Friday with very warm temperatures topping well over 90F for most locations outside the higher elevations. Southern urban locations such as Washington DC will feature highs in the upper 90s with widespread haze and poor air quality. 2m dewpoints are estimated to be regionwide in the 70s for a very oppressive day. Heat indices will approach 100-110F during the 11am-4pm heat of the day.

NAM/GFS QPF fields indicate the highest probability of rain occuring in northwestern portions of Pennsylvania. Increasing SBCAPE Friday afternoon near 2000j/kg with winds aloft near 40knots will allow for stronger convection to accompany the front in broken lines. EHI values approach 1-2 will also allow for the threat for a few rotating low levels in the strong thunderstorms. The highest threat for severe weather on Friday exists for northwestern Pennsylvania, but as convection seeps southwards Friday night, isolated wind damage may still occur as far south as northern Maryland. Not all areas will receive rain with southern areas progged at below .1in QPF. The latest 7/14/10 18z NAM remains especially dry for areas south of I-80.

Of interesting note, the GFS has recent gone under a major upgrade and this will take effect in the coming week. First expected to debut in June, recent delays in enhancing resolution has caused a slight later date.

TECHNICAL IMPLEMENTATION NOTICE 10-15
NATIONAL WEATHER SERVICE HEADQUARTERS WASHINGTON DC
853 AM EDT FRI APR 2 2010

EFFECTIVE JUNE 22 2010...BEGINNING WITH THE 1200 COORDINATED
UNIVERSAL TIME /UTC/ RUN...THE NATIONAL CENTERS FOR
ENVIRONMENTAL PREDICTION /NCEP/ WILL UPGRADE THE GLOBAL
FORECAST SYSTEM /GFS/. THE RESOLUTION OF THE GLOBAL FORECAST
MODEL WILL BE INCREASED FROM T382 /35 KM/ TO T574 /27 KM/.
THE HIGH RESOLUTION PORTION OF THE FORECAST WILL BE EXTENDED
FROM 180 HRS TO 192 HRS. WITH THIS EXTENSION 3 HOURLY OUTPUT
WILL BE MADE AVAILABLE OUT TO 192 HOURS... Link.

A seconday cold front is progged by latest GFS to move across the northern Middle Atlantic and wash out over northern Maryland. This will allow for another day of convection, some of which could be severe. Strong areas of lift in the right front entrance of the low level jet will allow for higher winds aloft to be reached by strong thunderstorm echo tops. Highs will once again reach 90F for many areas outside the higher elevations, but will be 4-6F cooler than Friday. Humidity levels remain high with PWATs near 2.0in. Models diverge on solutions for the beginning of next week, with the ECMWF bringing the cold front boundary northward as a warm front as early as Sunday with accompanying showers, but the GFS delays this northward progression. In any case unsettled conditions will continue through the middle of next week with a boundary located over the northern Middle Atlantic. This will allow for daily diurnal convection and accompanying threats of flash flooding. Meanwhile the fast zonal jet streamal flow will promote a rapid progression of a strong shortwave early next week across the northern tier. For now this ring of fire looks to be north of the northern Middle Atlantic, but details remain uncertain. At this time, it appears the threat of a widespread wind damage outbreak from a derecho is possible across the northern tier United States. SPC already highlighting the threat in their long term outlook...

ZCZC SPCSWOD48 ALL
ACUS48 KWNS 140850
SPC AC 140850

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0350 AM CDT WED JUL 14 2010

VALID 171200Z - 221200Z

...SEVERE WEATHER EPISODE FROM THE NRN PLAINS ACROSS THE GREAT LAKES
AND INTO THE NERN STATES POSSIBLE DAYS 4-6...

MEDIUM RANGE GUIDANCE IS COMING INTO BETTER AGREEMENT MOVING A SHORT
WAVE TROUGH RAPIDLY EWD ACROSS THE NRN TIER OF A STATES FROM ND
ACROSS THE GREAT LAKES AND TOWARD NEW ENGLAND DURING DAY 4 /JUL 17/
THROUGH DAY 6 /JUL 19/. LATEST SEVERAL RUNS OF THE GFS AND ECMWF
SHOW QUITE SIMILAR TIMING AND AMPLITUDE OF THE SYSTEM...AND ARE
CONSISTENT WITH THE 12Z ECMWF ENSEMBLE MEAN SOLUTIONS. STRONG LOW
AND MID LEVEL JETS ARE FORECAST TO TRANSLATE EWD IN ASSOCIATION WITH
THE FAST MOVING FRONTAL SYSTEM...WITH GUIDANCE INDICATING AMPLE LOW
LEVEL MOISTURE/INSTABILITY AND STRONG VERTICAL SHEAR ACCOMPANYING
THE SYSTEM. SEVERE STORMS ARE EXPECTED TO DEVELOP DURING DAY 4 /JUL
17/ OVER THE ERN DAKOTAS AND SPREAD EWD ACROSS THE UPPER MS
VALLEY...WITH THE SYSTEM CONTINUING EWD ACROSS THE GREAT LAKES AREA
ON DAY 5 /JUL 18/. BY DAY 6 /JUL 19/ THE CONVECTIVE SYSTEM IS
EXPECTED TO CONTINUE EWD ACROSS PARTS OF THE NERN STATES. OVERALL
JET PATTERN SUGGESTS POTENTIAL FOR A MORE WIDESPREAD DAMAGING WIND
EVENT DURING THIS PERIOD ALTHOUGH IT IS TOO EARLY TO PROVIDE DETAILS
OF THE CONVECTIVE EVOLUTION.

For the time being the excessive dry and hot weather will remain absent from the northern Middle Atlantic allowing for a more active weather pattern to resume. Heavy rain and near term flash flooding will be primary threats in the coming seven days. Recent Mt. Holly rainfall analysis indicates excessive rainfall over much of the eastern half of the northern Middle Atlantic.

Heavy rains have also impacted the Philadelphia metropolitan region...
As of 5 PM... Philadelphia International Airport reported nearly 3 inches of rain today... 2.88 inches to be exact... most of that occurring in a 2 hour period this afternoon.
A quick recap for the forecast for the coming few days across most areas in the northern Middle Atlantic...

Thursday- General sunshine with high pressure dominating, but temperatures remain mild in the lower 90s.
Friday- A shortwave and accompanying cold front approach from the northwest with an increase in humidity and heat. Thunderstorms are also possible over the region with the highest threat during the late afternoon over northwestern Pennsylvania. A few storms may be severe. Highs in the mid 90s.
Saturday- A seconday cold front approaches with more showers and thunderstorms with mostly cloudy skies and highs in the upper 80s to low 90s.
Sunday- Chance of spotty showers/thunderstorms with mostly cloudy skies and highs in the 80s.

Regional updating radar...


"Here north of Harrisburg 2010 statistics"
(Severe Weather Stats...)
Severe Thunderstorm Watches- 6
Severe Thunderstorm Warnings- 7
Tornado Watches- 1
Tornado Warnings- 0
Total Thunderstorms- 13

(Precipitation Stats...)
Flood Watches- 3
Flood Warnings- 1
Monthly Precipitation- 4.09inches
Yearly Precipitation- 21.19inches

(Temperature Stats...)
Heat Advisories- 2
Excessive Heat Warnings- 0
90degree days- 22
Highest Temperature- 101F (x2)

Weekly Forecast

Updated: 11:10 PM GMT on July 19, 2010

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About Blizzard92

Ph.D. Student - Earth System Science (UC Irvine), B.Sc. - Atmospheric Sciences (Cornell University)

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