WINTER STORM WARNING, Let the fun (or dread) begin...

Magenta denotes winter storm warnings and purple means winter weather advisory

The National Weather Service has updated the Winter Storm Watch into a Winter Storm Warning in effect from 8:00 AM Sunday to 10AM Monday. 1-3 inches of snow and sleet is expected before the changeover to freezing rain is complete.  The warning text is below with bold added for emphasis.

URGENT - WINTER WEATHER MESSAGE
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
834 PM EST SAT DEC 7 2013

MDZ004>006-009-010-VAZ039-040-042-050>053-501-502-080945-
/O.UPG.KLWX.WS.A.0008.131208T1400Z-131209T1200Z/
/O.NEW.KLWX.WS.W.0010.131208T1300Z-131209T1500Z/
FREDERICK MD-CARROLL-NORTHERN BALTIMORE-MONTGOMERY-HOWARD-MADISON-
RAPPAHANNOCK-LOUDOUN-ORANGE-CULPEPER-
PRINCE WILLIAM/MANASSAS/MANASSAS PARK-FAIRFAX-NORTHERN FAUQUIER-
SOUTHERN FAUQUIER-
INCLUDING THE CITIES OF...FREDERICK...WESTMINSTER...
GAITHERSBURG...COLUMBIA...WASHINGTON...LEESBURG...CULPEPER...
MANASSAS...MANASSAS PARK...FAIRFAX...WARRENTON
834 PM EST SAT DEC 7 2013

...WINTER STORM WARNING IN EFFECT FROM 8 AM SUNDAY TO 10 AM EST
MONDAY...

THE NATIONAL WEATHER SERVICE IN BALTIMORE MD/WASHINGTON HAS
ISSUED A WINTER STORM WARNING FOR SNOW...SLEET...AND FREEZING
RAIN...WHICH IS IN EFFECT FROM 8 AM SUNDAY TO 10 AM EST MONDAY.
THE WINTER STORM WATCH IS NO LONGER IN EFFECT.

* PRECIPITATION TYPE...SNOW AND SLEET...THEN CHANGING OVER TO
  FREEZING RAIN MID AFTERNOON AND CONTINUING THROUGH MONDAY MORNING.

* ACCUMULATIONS...1 TO 3 INCHES OF SNOW AND SLEET...FOLLOWED BY A
  QUARTER INCH OF ICE.

* TIMING...SNOW AND SLEET WILL BEGIN SUNDAY MORNING...THEN WILL
  CHANGE TO FREEZING RAIN SUNDAY AFTERNOON. FREEZING RAIN WILL
  CONTINUE SUNDAY NIGHT...EVENTUALLY CHANGING TO RAIN LATE MONDAY
  MORNING. THE GREATEST ACCUMULATION OF ICE WILL TAKE PLACE ON
  SUNDAY NIGHT.

* TEMPERATURES...UPPER 20S.

* WINDS...NORTH 5 TO 10 MPH.

* IMPACTS...HAZARDOUS TRAVEL CONDITIONS ARE PROBABLE DUE TO SLICK
  ROADS AND ICY CONDITIONS ESPECIALLY IN VALLEY LOCATIONS. DOWNED
  TREE BRANCHES AND LIMBS ALONG WITH POWER OUTAGES ARE LIKELY.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A WINTER STORM WARNING MEANS THAT A WINTER STORM SYSTEM WILL
IMPACT THE AREA WITH SIGNIFICANT AMOUNTS OF SNOW...SLEET...AND
FREEZING RAIN. TRAVEL IS LIKELY TO BE SEVERELY IMPACTED SUNDAY
AFTERNOON THROUGH MONDAY MORNING.

Why this wintry mess instead of some good old snow...

The storm setup does not favor snow, in fact, if not for our geography, we would probably just be getting rain. The mountains to the west allow for cool air to pool in a phenomenon called Cold air damming (CAD)
Why not snow?
Simply put,  the primary low will track to our west, drawing warm air on its east side north. we usually get snow when we are on the west side of the storm while the east side gets rain. We will be on the arm side of the storm. So why are we still getting wintry mix? Because of CAD
Cold Air Damming
High pressure to the north pumps cold air into the Mid Atlantic Region. This air jams up against the Appalachian mountains, creating an extension of the high pressure  along the Appalachian mountains .When a storm system arrives from the west, warm air overruns the cold, producing precip. Initially, the cold and dry air mass would cause any precipitation to evaporate, lowering the temperature of the air column through evaporative cooling, but eventually, precip will reach the ground. If the airmass is cold enough, the preip would be frozen. Below is a graphic drawn from the 00z CMC run, which demonstrates the cold air damming. The black arrows denote air flow from the arctic high to our north and the yellow lines show the isobars, which denotes a certain air pressure. Notice how a tongue of high pressure extends into the Mid Atlantic. Since the cold wedge is driven up against the mountains, precipitation over WV is in the form of rain as the warm air advects (travels) northwards with the low.

The precipitation should start out as a little snow. As the warm air  intrudes into the cold airmass at upper levels, the snow melts then refreezes forming sleet. As the warm air increasingly erodes the cold air, only a surface layer of cold air remains because warm air is less dense so it rises. Eventually, the cold air loses as a new low also forms to the east of the high pressure tongue. As a result, the cold northerly flow is cut off and replaced with warmer southerly and easterly flow.

The rate at which the cold air erodes is a major issue when forecasting. An difference of a degree or two could result in vastly different scenarios. Computer models tend not to do well with CAD events due to their low resolution. The NAM should handle the CAD better because of it's higher grid resolution.

NAM

GFS

Thanks for reading, 

Alex

Rain ending tonight, Winter Storm Watch issued...

 The cold front has passed and temperatures are dropping tonight to the upper 30s with some rain. Saturday will be cloudy in the morning with some lingering showers then clearing with highs in near 40. Saturday night will be clear with temperatures in the mid 20s and sunday will feature the weather event of the week, the appearance of old man winter.

The National Weather service has issued a Winter Storm Watch for our region spanning from just west of DC into West Virginia. Main hazards include snow and sleet during the onset on Sunday changing to freezing rain before finally changing to rain by Monday morning as warm southerly flow from the south erodes the cold air over our region.

The National Weather Service Watch text below, bold and color added for emphasis

URGENT - WINTER WEATHER MESSAGE

NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
233 PM EST FRI DEC 6 2013

DCZ001-MDZ004>007-009>011-013-014-016-VAZ039-040-042-050>057-501-
502-070345-
/O.EXB.KLWX.WS.A.0008.131208T1400Z-131209T1200Z/
DISTRICT OF COLUMBIA-FREDERICK MD-CARROLL-NORTHERN BALTIMORE-
HARFORD-MONTGOMERY-HOWARD-SOUTHERN BALTIMORE-PRINCE GEORGES-
ANNE ARUNDEL-CHARLES-MADISON-RAPPAHANNOCK-LOUDOUN-ORANGE-CULPEPER-
PRINCE WILLIAM/MANASSAS/MANASSAS PARK-FAIRFAX-
ARLINGTON/FALLS CHURCH/ALEXANDRIA-STAFFORD-SPOTSYLVANIA-
KING GEORGE-NORTHERN FAUQUIER-SOUTHERN FAUQUIER-
INCLUDING THE CITIES OF...WASHINGTON...FREDERICK...WESTMINSTER...
GAITHERSBURG...COLUMBIA...BALTIMORE...ANNAPOLIS...WALDORF...
LEESBURG...CULPEPER...MANASSAS...MANASSAS PARK...FAIRFAX...
ALEXANDRIA...FALLS CHURCH...FREDERICKSBURG...WARRENTON
233 PM EST FRI DEC 6 2013

...WINTER STORM WATCH IN EFFECT FROM SUNDAY MORNING THROUGH
MONDAY MORNING...

THE NATIONAL WEATHER SERVICE IN BALTIMORE MD/WASHINGTON HAS
ISSUED A WINTER STORM WATCH...WHICH IS IN EFFECT FROM SUNDAY
MORNING THROUGH MONDAY MORNING.

* PRECIPITATION TYPE...SNOW AND SLEET WILL CHANGE OVER TO FREEZING
  RAIN SUNDAY AFTERNOON. FREEZING RAIN IS EXPECTED TO LAST UNTIL
  LATE SUNDAY NIGHT OR MONDAY MORNING BEFORE CHANGING TO RAIN.

* ACCUMULATIONS...1 TO 2 INCHES OF SNOW AND SLEET AND A QUARTER
  INCH OR MORE OF ICE ACCUMULATION IS POSSIBLE.

* TIMING...SNOW AND SLEET ARE EXPECTED TO BEGIN SUNDAY MORNING. A
  CHANGEOVER TO FREEZING RAIN IS EXPECTED MIDDAY SUNDAY AND WILL
  CONTINUE INTO THE NIGHT BEFORE CHANGING OVER TO RAIN LATE SUNDAY
  NIGHT OR MONDAY MORNING.

* TEMPERATURES...AROUND 30 DEGREES.

* WINDS...LIGHT NORTHERLY WINDS.

* IMPACTS...HAZARDOUS TRAVEL CONDITIONS ARE PROBABLE DUE TO SLICK
  ROADS AND ICY CONDITIONS SUNDAY AND POSSIBLY INTO MONDAY.
  INCREASED POWER OUTAGES ARE POSSIBLE.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A WINTER STORM WATCH MEANS THERE IS A POTENTIAL FOR SIGNIFICANT
SNOW...SLEET...AND ICE ACCUMULATIONS THAT MAY IMPACT TRAVEL.
CONTINUE TO MONITOR THE LATEST FORECASTS.

The mixture of sleet and snow would be more dense than normal snow and would cool down the road surface more effectively leading to more accumulations. what is worrying is the ice. at last an quarter inch is possible, which means accumulation may exceed the 1/4 inch criteria for an ice storm. this will cause major headaches for travel and may cause power outages.Remember to stay safe  and heed all NWS warnings

Thanks for reading, 

-Alex

Chances Increasing for some Wintery Precip

Current Radar

The Forecast:
Rain is still coming on Friday through early Saturday morning as the storm currently producing winter weather over the central US comes our way with .5 -1 inch of rain possible. Highs will be in the 50s on Friday ,dropping as a cold front pushed through. Saturday will be cloudy in the morning and then clearing, with highs in the low 40s as high pressure builds. 

Bristol, Oklahoma, which is near Tulsa, on the afternoon of December 5th

Saturday night we be mostly clear as temperatures drop below freezing and the next storm system approached on sunday morning, with a strong possibility of wintery mix of snow, freezing rain, and sleet that will change to rain on monday before possible ending with a little snow on Monday night.

Official NWS forecast

Sunday: Snow likely before 9am, then snow, freezing rain, and sleet likely between 9am and noon, then rain, freezing rain, and sleet after noon. High near 33. Chance of precipitation is 90%. New precipitation amounts between a half and three quarters of an inch possible.

Sunday Night: Snow, freezing rain, and sleet before 1am, then rain or freezing rain. Low around 32. Chance of precipitation is 80%.
-------------------------------------------------------------------------------------------------------------------------------------

 A new model, the NAM
Previously, I have been discussing the American GFS (Global Forecast System) model, the ECMWF (European Center for Medium Range Weather Forecasting) model, and the Canadian CMC/GEM (Global Environmental Multiscale) model. The image below is from the NAM (North American Mesoscale Model), which is a short range, higher resolution model that only forecasts weather over the lower 48. This model's increased resolution allows the rain/snow line to be pinpointed quite more accurately. Its shortfall is that it only forecasts for the US and tends to overestimate precipitation amounts. The NAM forecasts a winter storm from Saturday to Monday with a lot of freezing rain.

NAM Precipitation type at 10PM EST (03Z) on Sunday night

The 18z GFS run went nuts, giving us around a foot of snow. this is very unlikely to happen given the shallowness of the cold air mass and the storm track to the west of us.

Total precipitation (if all was liquid) forecast from the GFS

Winter storm Xaver impacting Europe
Winter storm Xaver is battering Northern Europe with heavy rain and high winds up to 160 kph (100mph). It has shut down all rail service to Scotland and killed a person in Scotland. In addition, the Glasgow train station was evacuated when debris shattered the glass roof.  Fortunately, Xaver brings a potent storm surge to an area that is well protected by levees so flooding danger is not especially high.

Source: http://www.dw.de/powerful-winter-storm-xaver-hits-scotland-germany-braces-for-its-arrival/a-17272948

Hamburg Fish Market flooded by the storm

Source: http://www.ndr.de/regional/sturm1061.html

Storm warnings for Germany. Pink indicates highest danger  and green indicates no danger

Measured wind gusts so far

Below is a video of Xaver battering the coast of Germany.

Test Post-Please disregard

This is where I will be testing out links, seeing if pictures will update automatically ect.

Saved image

Copied from site

Major Ice Storm to impact South-Central US, Will is come here?

The Forecast:

The rest of the workweek will feature springlike warmth, with temps in the upper 60's on Thursday and near 60 on Friday. Unfortunately, springlike sun is not in the forecast. A storm system currently dropping snow in the central US will bring us rain and drizzle. This will clear out by Saturday, leaving us with cooler temperatures in the low 40s. this will be followed by another storm, which has the potential to bring us a wintery mix transitioning to rain from sunday into the beginning of the next workweek. These storms will bring heavy snow and crippling ice to the south central US. Following it will be near record cold temperatures from an arctic high.

A map of all US weather hazards as of 12/4/2013

Dark Purple stands for Ice storm warning, which means forecasts of over 1/4 inch of freezing rain expected.

Magenta stands for Winter storm warning, which between 4 inches (10 cm) to 7 inches (18 cm) or more of snow or usually 3 inches (7.6 cm) or more of snow with a large accumulation of ice is forecast.

Blue is Winter Storm Watch ,which means that winter storm conditions are possible

Blue-purple stands for Winter Weather Advisory, which means minor impacts from winter weather is expected.

7 Day Forecast Total Snow Accumulation

7 Day Forecast Total Ice (Freezing Rain) Accumulation

Up to a foot of snow is expected and over an inch of ice in some places. An inch of ice will certainly cripple travel and cause major power outages due to tree damage and even just the ice weighing down transmission lines themselves

What the Models say....

Snowfall amounts through Wednesday... Quite a lot of it... Probably not going to verify though.

Snowfall on Monday only. Notice the very tight gradient. DC is right on the rain/snow line. The dark blue line stands for the freezing line. This is the classic example where a few degrees can be the difference between heavy rain and heavy snow. 

GFS forecast precipitation amounts through Monday this is more likely to verify than the snow amounts. What does not fall as winter precipitation will fall as rain.

Forecast Low temperatures from the GFS model for Wednesday at 7AM. This model forecasts temperatures in the teens to low 20s for the area instead of single digits as the ECMWF (European Model) had forecasted yesterday.

GFS model animation

Model forecasts can vary model to model and run to run. wide variations signal a complicated and low-confidence forecast.  For example, the CMC (Canadian Model) shows a weaker and more southerly storm that gives us snow while the GFS Model shows a stronger storm that gives us rain in the same time-frame.

GFS

CMC

So which one is right? most likely neither. As mentioned before, a lot can range in the next few days and more often than not, the actual outcome is a blend of these model solutions.

Elsewhere
A storm system, dubbed Xaver by the Berlin Institute of Meteorology, is forecast to bring high winds and heavy rain to Northern Europe.

Thanks for reading and may the odds for snow be ever in our favor, 

-Alex

My patch of Arizona

Planted with Hens and Chicks, Opuntia cactus, and an Agave

The Siberian Express

The ForecastIt has been quite warm this week in the Mid-Atlantic with highs approaching the low 50's compared to the previous weeks when the temperatures struggled to reach 40. The National Weather Service calls for highs in the 50s for the remainder of the week accompanied by rain.
While we bask in the relative warmth for the rest of the week, the setup increasingly favors a cold, cold, December. As we speak, a winter storm is dropping down from Canada. However, this storm will only give us rain. It will be followed by a storm that is poised to be a major winter storm in the cnetral US. this will also be rain maybe with a little sleet on the onset. After the next bout of rain coming in near the end of the week, temperatures will plummet. The forecast high for Tuesday, December 10th is only 35 degrees.

Winter storms approaching the East Coast

The GFS model portrays a wet and cold pattern for the Mid Atlantic area with a few chances for snow. However, due to the uncertain nature of long range forecasts, the details will not be finalized until the storm is approaching the immediate area. The rain/snow line in this area is notoriously difficult to predict and the difference in temperature of a few degrees can differentiate between a major winter storm and a cold rain.

Total modeled precipitation through December 11th gives 2.5 to 3 inches of liquid equivalent precipitation for our area.

Cross Polar Flow

Cross polar flow is typically when weather pattern allows cold air from siberia to directly travel across the arctic and enter North america. This often results in bone chilling temperatures. Below is a diagram showing modeled anomalies in the 500mb height, which represents the elevation abouve sea level of a certain pressure reading. Lower heights means lower temperatures.

The European model forecasts temperatures at 7AM on Wednesday next week to be in the low teens to single digits. This cold blast will arrive on Tuesday after the second storm.

Winter is kicking into full swing and hopefully we can score a decent snowstorm or two out of this cold snap. The bananas won't like it much though... single digit temperatures cannot be good for a plant that is essentially a column of water...

A final note: If there are any errors or things that you do not understand in these posts, please do not hesitate to ask me for clarification.

Thanks for reading!

 -Alex