Dec 8, 2014

Nor'easter Update

Latest data continues a trend of slightly colder and also much more moisture, that is, more precipitation. I am still looking at the potential for the area from Albany and points south through east to see snow at the start then a mix or change to sleet, pockets of freezing rain or a cold rain.

Areas to the west by north of Albany will see mostly snow and the higher elevations will easily see a foot of snow, if not more, thanks to the combination of elevation and colder temperatures along with upslope winds enhancing already strong lift.

Here is a comparison of this morning's 7 AM models from various national and international meteorological centers. Maps are from www.meteocentre.com


 The maps to the left are initial panels for the 4 main forecast models valid for 7 AM this morning (8 Dec). Clockwise from upper left to lower left your are looking at the CMC Global of GEM model, to the right is the US GFS model; bottom right is the UKMET office model and lower left is the European of EC model. The contour bands are the upper air contours for the 500 hPa level and thr black lines are the surface isobar.



The maps to the right are the forecast charts for the surface and upper-air valid for Wednesday morning 7 AM, 9 December 2014. All of the models are in very good agreement as to placing an intensifying low near or just off of the Mid-Atlantic coast. They all also show a strong "blocking" area of high pressure over Newfoundland. As you will see on the following forecast maps, this high remains nearly stationary. Thus the coastal storm cannot move quickly and this is why this storm will be a long duration event for the region.

The maps to the left are the forecast surface and aloft (500 hPa) for Wednesday morning 7AM December 10th. The UK and EC (bottom row of  maps) have the low very close to Islip Long Island. The GFS upper right has the low near the South Shore of Long Island (south of Islip) while the GEM (upper left) has the low over New York City.  Comparing the forecast maps from Tues morning to Wednesday morning you can see that the low both intensifies and moves very slowly while the high retrogrades west to over Quebec Province.

The maps to the right are the forecast maps for Thursday morning December 10th. The top two maps are from the GEM and GFS and both indicate the low lifting north toward Canada or Northern New England and weakening. The EC and UK indicate the low weakening but still lingering over south-central New England. For the past three days the EC and UK have been very consistent in their model output. For the forecast that follows, I have heavily leaned on these two models. 

The following map is the cyclone track map for the UK. 
UK Cyclone Track comparison last 2 runs

The EC is very similar, too. During the late fall and winter with a low forecast to track very close to the East Tip of Long Island more often than not Eastern NY State winds up with heavy precipitation; if t is cold enough this precip falls in the form of snow. With the high retrograding in time cold air will persist to the north and west of Albany and this will allow for predominantly snow to fall. With a low near Eastern Long Island warmer air especially aloft should result in snow mixing with or changing to rain and sleet to the south and southeast of Albany with a snow sleet rain mix up through the Berkshires, Capital District and the Eastern Mohawk Valley and Southern Saratoga County

For now here is what watches and warnings have been posted by the NWS:


The winter storm watch has been upgraded to a warning in places (lavender color regions). NWS is keeping the watch up for the Mid and Upper Hudson River Valleys and points east and has now added a Winter Weather Advisory for areas to the south through southeast of Albany. The flood watch remains in effect for the Lower Hudson Valley and NW Connecticut.

Storm Details
STORM HAZARDS:

Heavy precipitation

Heavy snow: across the Catskills and Hilltowns and Southern Adirondacks where accumulations will exceed 12 inches.

Heavy Rain: Lower Hudson Valley and NW Connecticut after a period of accumulating snow. Potential small stream and urban flooding

Wind:

Periods of gusty East winds with gusts to 40-50 mph possible across the higher terrain of the Catskills, Taconics, Berkshire and Green Mountains during Tuesday could cause blowing snow and perhaps some sporadic power outages.

START TIME: Daybreak Tuesday over the Lower and Mid-Hudson Valley, Capital District between 9AM and Noon with areas north of the CD between Noon and 3 PM

The snow and mixed precip will taper off some late tomorrow night then redevelop during the day Wednesday into Wednesday night. Expect lingering mostly snow to fall (lighter) during Thursday. Here is my snowfall map.

Its is forecast snow accumulation by Wednesday evening. There will likely be another couple to few inches overnight Wednesday into Thursday. There will also be some pockets of freezing rain especially when the snow begins to transition or change to rain. Right now some areas of ice accretion are possible but for the moment heavy icing doesn't appear to be a major concern.





Cyclogenesis of the expected  Nor'easter 
While not unprecedented it is not too often that a low to develops well of the East Coast and then moves northwest toward the coastline before turning to the north or northeast and head toward New England.

East Coast cyclones (low pressure systems) of a non-tropical nature are classified into three main groups. Miller A and Miller B systems as documented by J.E. Miller. Its a simple classification scheme: Miller (type) A lows develop over or on the Southeast US Coast or Gulf of Mexico often on stalled or slow moving cold fronts.

Miller (type) B lows can develop over the region from the Mid-Atlantic Coast to the New England coast. These are called "secondary lows". They form in association with an area of low pressure moving across the Lower Great Lakes or Ohio Valley. The low to the west is usually filling and the secondary low redevelops to the east usually on the primary low's warm front or at the "triple point" of the primary low - that is the point where occluded, cold and warm fronts meet.

The last type of low - which is how tomorrow's Nor'easter has developed  is called a "blocked low". This not too common of how a Nor'easter forms. This type of development has been documented by James Andrews in an article from Mariners Weather Log. Te low development sequence occurs when a strong high pressure area is over Canada, the Maritimes or Northern New England. The low develops well off the coast over warm Atlantic Ocean waters.

Due to the high "blocking" the low from continuing on an out-to-sea track, the low turns west or northwest around the high towards the East Coast.

Intensification of the low is possible as it moves across the Gulfstream waters as well as additional energy that exists because of the strong temperature contrast during the cool season between the chilly land and the warmer ocean.  Last, when a strong upper-air trough approaches from the west this further aids in the intensification process.  From Andrews' article in the Mariners Weather Log Look for the following to happen at the surface:

While in the upper atmosphere the planetary pattern or if you will jetstream is undergoing a "pattern change" that leads to the development of "cut-off" pressure systems surface and aloft (both high and low pressure). "Cut-off" systems tend to be slow movers.

Here are surface and upper air analysis for 7 AM 8 December 2014. The surface map shows a weak low well offshore to the east of the Carolina's Coast.

The 500 hPa map shows the approaching upper-air disturbance (dashed line over Central US) that will aid in the offshore storm's intensification.

7 AM 8 Dec 2014 EST Surface map
7 AM 8 Dec 2014 EST 500 hPa analysis

Below are the forecast surface and 500 hPa charts for Tuesday morning 7 AM 9 December 2014. The low is a bit stronger and has now neared the Mid-Atlantic Coast. As the upper-air disturbance approaches from the west the winds aloft ahead of it are now out of the SSW and the surface low is turning toward the N or NNE.
Fcst surface map 7AM EST Tues 9 Dec 2014
Fcst 500 hPa chart 7AM EST Tues 9 Dec 2014

  By Wednesday morning 10 Dec a strong Nor'easter is near the NJ coast
Fcst Surface Map 7 AM EST Wed 10 Dec 2014
 While at 500 hPa the upper-air feature is strengthening and becoming "cut-off"

Fcst 500 hPa chart 7 AM EST Wed 10 Dec 2014
As the low aloft over takes the surface low and "captures" it, the whole system slows down. Resulting in what will be a long-duration storm.

References:

J.E. Miller, "Cyclogenesis in the Atlantic Coastal Region of the United States", Journal of Meteorology, Vol 3, No. 2, June 1946

J.F. Andrews, "Cyclogenesis Along the East Coast of the United States", Mariners Weather Log, Vol.7, No. 2, pp. 43-46

Major Winter Storm Heading Our Way

A complex , significant, slow moving and muti-hazard winter storm will affect the region from Tuesday through (at least) Thursday night. Even though the start time of the storm is now less than 18 hours from starting, weather data regarding the actual evolution and track of the storm is still uncertain.

The uncertainty in the storm's track will be VERY CRUCIAL in determining precipitation type. If the low tracks right along the coast towards New York City and western Long Islnad then precipitation, while initially starting as snow could mix with or change to sleet and rain in the Hudson Valley and points east late Tuesday and Wednesday; a slightly more east or offshore track to the storm will allow for colder air to remain in place and a mostly all snow will then fall.

One thing is certain about this storm it will have a lot of moisture associated with it thus precipitation amounts will be heavy. Where this precip falls as ALL snow, snowfall totals will be very high likely exceeding a foot with perhaps some areas near 2 feet possible. Right now the central and northern Catskills and the southern Adirondacks as well as the higher terrain to the west of Lake George appear to be mostly snow.

Elsewhere, snowfall amounts will range from a few inches across the lower Hudson Valley and northwest Connecticut to as much as 6-12 inches from about Hudson north (including the Capital District) to Glens Falls. Expect similar amounts to the east across Southern Vermont and the Berkshires. Its over these latter two locations where a better chance for snow changing to or mixing with rain or sleet could occur as temperatures here will be warmer.

The Hudson Valley region may be subjected to the snow mixing with or changing to sleet, freezing rain or rain. In addition "downslope" easterly winds may cause a “precipitation” shadow to develop here. If this were to happen then the air would dry and warm lessening the amount of preciptation. However if the shadow is NOT strong and warmer air doesn't allow for the snow to mix or change to rain or sleet then snowfall amounts here will be much higher.



The above map shows most of Western New England, Eastern and Central New York State under a Winter Storm Watch (WSW). In addition the Lower Hudson Valley and Connecticut while NOT under a WSW ARE under a FLOOD WATCH

STORM HAZARDS:

Heavy precipitation

Heavy snow: across the Catskills and Hilltowns and Southern Adirondacks where accumulations will exceed 12 inches.

Heavy Rain: Lower Hudson Valley and NW Connecticut after a period of accumulating snow. Potential small stream and urban flooding

Wind:

Periods of gusty East winds with gusts to 40-50 mph possible across the higher terrain of the Catskills, Taconics, Berkshire and Green Mountains during Tuesday could cause blowing snow and perhaps some sporadic power outages.

START TIME: Daybreak Tuesday over the Lower and Mid-Hudson Valley, Capital District between 9AM and Noon with areas north of the CD between Noon and 3 PM

END TIME:  When its finished...seriously very Late Thursday night.


I'll have more on the storm this evening as well as maps including a snowfall forecast, too.

Sep 19, 2014

Last Night's Chill

Last night the temperature dropped to 33 degrees at my house.  For northern Herkimer and northern Warren counties and all of Hamilton County the growing season has come to an end, as temperatures last night, across these locations, dropped into the upper 20s to near freezing.

The weather this weekend will feature more seasonable to even above normal temperatures by a few degrees before another cool snap heads in for the first part of next week.

Aug 5, 2014

Tropical systems to threaten Hawaii..while Bertha threatens North Atlantic shipping lanes

Trop. Storm Julio
Tropical cyclone activity in the Pacific Ocean continues at above normal levels with the 10th named system, Tropical Storm Julio  located about 1145 miles to the SW of the Southern Tip of the Baja Peninsula. Julio is forecast to move toward the WNW over the next 5 days and slowly intensify to hurricane strength. Winds are currently near 60 mph this early Tuesday morning and are forecast to increase to near 85 mph by Friday morning then weaken to near 75 mph by Sunday morning.


NHC forecast track for Julio
Currently sea surface temperatures are very warm along the forecast path of Julio which has the storm located to the ENE of the Big Island of Hawaii by Sunday morning.

Major Pacific Hurricane Iselle
 Of greater concern for the Hawaiian Islands is MAJOR Hurricane Iselle. Early this morning Iselle was located about 1055 miles to the ESE of Hilo, Hawaii, moving toward the West at 9 mph. Iselle is a Category 3 hurricane (it was a CAT 4 storm yesterday) with maximum winds of 125 mph. Iselle is expected to weaken very slowly over the next 24 hours with a slight turn toward the WNW. It is possible that tropical weather watches may be required for (parts of) the Hawaiian Islands later today or tonight; for sure ALL interests in the Hawaiian Islands are advised to monitor the progress of Iselle. The forecast track for Iselle is fairly straightforward with the system expected to affect the Hawaiian Island during Thursday through Friday. The uncertainty is in how strong will it be when it does impact the Islands' weather.
Forecast track of Iselle

For now the potential for Iselle to be a strong tropical storm (with winds of 55-73mph) when it affects Hawaii is estimated to be about 70%; there is about a 20% chance that it could be a weaker tropical storm and a bout a 10% chance that it could still be a minimal hurricane.


Over in the Atlantic the second named tropical cyclone of the season continues to churn toward the north-northeast and out to sea away from the U.S. mainland  at a speed of near 22 mph. It is also weakening as increasing wind shear aloft continue to push the strongest convection toward the northeast, away from the lower-level circulation. Loop of Tropical Storm Bertha . The forecast track of Bertha calls for acceleration and continued weakening over the next 36 hours. After this time Bertha is expected to become a post-tropical or extratropical cyclone that will rapidly accelerate toward the east or east-northeast and perhaps affect Western Europe (Iberian Peninsula) and/or  the British Isles by Sunday.
Forecast track for Bertha

Aug 1, 2014

Tropical Storm Bertha forms to the east-southeast of Barbados

IR satellite picture of Trop. Storm Bertha

 An area of convection as flared up to the north and northeast of the low pressure circulation over the Atlantic Ocean located to the ESE of the Lesser Antilles. The organization of the system now warrants classification of the disturbance as a tropical storm - in this case  Tropical Storm Bertha. The NHC is now issuing advisories on this system
The storm is moving toward the WNW at 20 mph with maximum winds of near 40 mph. Environmental conditions currently around the storm's circulation and along its forecast path only favor marginal intensification.
Latest position/strength of TS BERTHA

"Spaghetti" model plots
The "spaghetti plots are tightly clustered on WNW track and the official NHC track is pretty much in agreement. Due to the expect WNW track at a rather brisk forward speed Watches and Warnings have been posted for parts of the Lesser Antilles and also across some islands in the Greater Antilles chain.
Official NHC forecast track for Bertha





















Tropical Warnings/Watches currently in effect
A TROPICAL STORM WARNING is in effect for:
* Barbados * St. Lucia  * Dominica 
A TROPICAL STORM WATCH is in effect for:
* Puerto Rico * Vieques  * Culebra * U.S. Virgin Islands
* St. Vincent and The Grenadines

Jul 31, 2014

Potpourri Weather Post

Don't be surprised by today's storms


KENX radar
There could be a few thunderstorms today and they might be locally strong or marginally severe. Main threats for today: hail 1/2" to perhaps 1" in diameter, winds gusting 40-50mph, heavy rain and of course DANGEROUS cloud to ground lightning. One small line of storms is moving out of Eastern NY State (with a warning out for Washington and Saratoga counties in NY) to Bennington county in VT. More scattered cells are "popping" up farther to the west.  




31 July 12z Albany, NY Rawindsonde 
The reason for only a marginal threat 
of severe weather for today is that  CAPE (potential instability) is small, wind shear is moderate and lapse rates are weak as indicated by the morning "sounding" from Albany NY (which I modified for the expected maximum temperature and dew point for today [at the surface]). 






CHAP/RI computations for 31 July 2014 for Eastern NY State
Using the data I then "ran" the Convective Hazard Assessment Program or CHAP (also know as Ricks' Index or RI)  to gauge the probability of severe weather. An RI value of < 110 implies NO SEVERE thunderstorms while a value of 160 implies SEVERE thunderstorms are likely. The RI can also be useful in predicting potential hail size, maximum wind from the storms, radar VIL [storms that reach or exceed this value of the VIL could be severe] and rainfall. Today's RI = 116 so hail size could be around 1/2 or so, winds could gust to 40-45 mph. The Probability of Precipitation (PoP) for today is 40% with the Probability of Severe storms (PoSVR) is only 7%. Rainfall of around 8/10 ( 0.80") is possible in storms with MAXIMUM potential rainfall of 2". Storms will tend to move quickly towards the ENE at 30-35 mph, so I would think that the threat for any flash flooding from today's storms is LOW.

Atlantic Tropical Disturbance to the southeast of the Leeward Islands

From the National Hurricane Center
TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT THU JUL 31 2014

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

1. A Hurricane Hunter aircraft has recently begun investigating the
low pressure system located about 550 miles east of the southern
Windward Islands.  Preliminary reports from the aircraft indicate
that this system is producing winds to near gale force.  However,
satellite images indicate that the associated showers and
thunderstorms have diminished significantly since this morning.
Therefore the low currently does not meet the criteria to designate
it as a tropical cyclone.  Showers and thunderstorms could
redevelop later today or tonight, which could result in tropical
cyclone formation.  Interests in the Lesser Antilles should continue
to monitor the progress of this disturbance as it moves
west-northwestward at 15 to 20 mph, and watches or warnings may be
required for some of these islands later today or tonight.
* Formation chance through 48 hours...high...70 percent.
* Formation chance through 5 days...high...70 percent.

Forecaster Pasch

Visible Satellite picture of tropical disturbance 93L

Model forecast tracks for tropical disturbance 93L


Jul 20, 2014

Derecho expected for the Northern Plains and Western Great Lakes

This upcoming week will feature some significant and widespread heat and humidity from the east facing slopes of the Rockies to the East Coast. The weather setup for this week  features a sprawling high pressure area surface and aloft , acting like a heat pump, extending from the Southwest States to the Great Lakes.

The image to the left is the 500 hPa level (approximately 18,000 feet above the surface of the earth) from Sunday morning 20 July 2014  8AM EDT. An upper air chart such as this is called a constant pressure chart; on the chart the pressure is 500 hPa but the 500 hPa pressure is "located" at a different "height" above ground.) Think of upper-air maps as a topographic map of the atmosphere. The solid black lines are the actual heights of the 500 hPa and also can serve or approximate the the direction of the the winds aloft at near 18,000 feet. The distance between these contours can also approximate the wind speed -in general the closer the distance between any two contours, the stronger the winds and the greater the distance between the contours then the lighter the winds. The center of the "heat" producing high is located over southwest New Mexico with an elongated axis of higher heights extending to western South Dakota. From the Pac Northwest States to northern Wisconsin, a flow of air bringing some Pacific moisture prevails along with embedded disturbances that will cause ascent or lift.

The combination of all of these above features is expected to cause a significant severe weather outbreak across the Northern Plains to Wisconsin during Monday into Tuesday morning (July 21-22). Here is the severe weather outlook from SPC for Monday 21 July. The severe weather will initially start over the the border region of North and South Dakota with Montana as scattered but intense supercells during Monday afternoon, capable of producing severe hazards of damaging winds, large hail and a few tornadoes. These supercells are then expected to merge into a strong progressive derecho over the eastern parts of the Dakotas and then move rapidly east across and towards Minnesota to Wisconsin by late Monday night into Tuesday morning.

This derecho is expected to cause extremely strong winds of hurricane force (75 mph) or more in places along its path. The remnants of this system may also  redevelop and perhaps affect our area during Tuesday night, though probably not as intense. Often times these derecho are "episodic" in nature, that is they tend to develop on consecutive days and may even form over the same geographic region or move across the same region as the predecessor derecho did. Progressive derechos during the summer tend to form and become quite intense during extreme heat and or heat waves. The pattern for the development of these derechos is often referred to as "ridge-rollers and the ring-of-fire"

Jun 28, 2014

Potential for Tropical system off the Southeast US Coast

An area of disturbed weather off the the Southeast U.S. coast has been designated (disturbance) 91L by the National Hurricane Center. While not a true warm core system - yet - it will develop a warm core over time. Pic 1 is the location of the low and the convection associated with it.
Pic 1
  
 As you can see the the area of lowest atmospheric pressure is removed from the area of strongest convection. This is a satellite signature of unfavorable wind shear aloft which leads to a very disorganized system.





 
Pic 2

The model tracks for this nascent system are displayed in (Pic 2). There is a lot of "scatter" (basically in two clusters):  one group/cluster tracking the system toward the SW, while the other is on a track toward the SE. So a forecast S-SE motion is forecast. likely.





Since the motion is toward the south -  and south moving tropical systems tend not develop much or only very gradually (in the northern hemisphere) - only a slight or low probability (Pic 3) for development of this system is expected over the next 48 hours. 

Pic 3

If the system should intensify and attain sustained wind speeds of 40 mph or more then it will be "christened" with the name Arthur.