Finals Week and Jan 22-24 Possible Storm

Jan 19 6:30 PM Update:
The European Model shifted south with the low.  Otherwise, non of the other models have changed much. The GFS still jackpots Central MD and Northern VA. Basically nothing has changed since the last update. A major snowstorm is still likely. We're waiting for the lead time to shorten and our storm to begin its trek across the US so we can parse out where the best dynamics for snow growth and banding will occur.

This morning, Paul Kocin wrote up the extended forecast for the HPC. Him and Louis Uccellini conducted research on NE snowstorms and created the NE Snowfall Impact Scale and thus is very well regarded as an expert on snowstorms. He wrote some very nice things as well as some things to watch:

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1100 AM EST TUE JAN 19 2016

VALID 12Z FRI JAN 22 2016 - 12Z TUE JAN 26 2016

HIGHLIGHTS...

LETS CUT TO THE CHASE. THE MAIN EVENT IN THE MEDIUM RANGE IS THE
POTENTIAL FOR A SIGNIFICANT EAST COAST SNOWSTORM FROM FRIDAY
THROUGH SUNDAY/DAYS 3 TO 5.  THERE HAS BEEN AND CONTINUES TO BE
RELATIVELY GOOD AGREEMENT ESPECIALLY BETWEEN THE MODEL ENSEMBLES.
COMPARING THE OPERATIONAL RUNS TO THE ENSEMBLE MEANS DOES INDICATE
SOME DIFFERENCES THAT ARE SMALL IN THE LARGE SCALE BUT CRUCIAL TO
THE FORECAST.  ALL MODELS SUGGEST THAT MAJOR DEVELOPMENT FOR THIS
SYSTEM WILL OCCUR AS IT MOVES TO THE MID ATLANTIC COAST AND THEN
THE SYSTEM OCCLUDES...BECOMES MORE VERTICAL AND THEN CONTINUES
NORTHEASTWARD WITH THE MOVEMENT OF THE UPPER TROUGH.  WITH THAT IN
MIND...THE STORM WILL LIKELY SLOW IN ITS FORWARD MOVEMENT AS IT
MOVES OFF THE MID ATLANTIC COAST AND THEN WILL LIKELY ACCELERATE
NORTHEASTWARD OR ANOTHER TRIPLE POINT LOW MAY DEVELOP FARTHER
NORTH AND EAST. THE 00Z ECMWF SUGGESTS BOTH SCENARIOS.  IN EITHER
EVEN...THE OVERALL SPEED OF THE SYSTEM IS IMPORTANT TO AFFECT THE
AMOUNT OF SNOW IN ANY ONE AREA.  THIS WILL BE AN IMPORTANT TREND
TO FOLLOW AS THE MORNING MODEL SOLUTIONS START COMING IN.

IN ADDITION...ANY TRENDS EITHER NORTH OR SOUTH WILL IMPACT
SNOWFALL AMOUNTS ALONG THE NORTHERN EDGE OF THE HEAVIEST SNOW AS
WELL AS THE ISSUES OF MIXING/CHANGEOVER ALONG THE SOUTHERN EDGE OF
THE SYSTEM.  THERE HAVE BEEN SUBTLE NORTH/SOUTH SHIFTS WITH THIS
FORECAST BUT WILL HAVE TO BE ASSESSED WHEN THE MORNING MODELS
ARRIVE. THERE HAVEN'T BEEN LARGE CHANGES WITH THE OVERNIGHT CYCLE.

IN GENERAL...THE OPERATIONAL GFS RUNS ARE SLIGHTLY MORE
PROGRESSIVE THAN THE OPERATIONAL ECMWF RUNS. IN PARTICULAR THE 06Z
GFS TRENDED FASTER THAN PREVIOUS RUNS RESULTING IN LOWER SNOWFALL
AMOUNTS DUE TO LOWER SNOWFALL DURATION. THE 00Z UKMET IS SIMILAR
TO THE ECMWF AND TO SOME EXTENT THE GFS BUT THE 00Z CANADIAN WAS
MUCH MORE PROGESSIVE THAN ANY OTHER MODEL AS WELL AS THE CANADIAN
ENSEMBLES.  AS A RESULT...LATER IN THE FORECAST...THE NAEFS MEAN
IS FASTER THAN THE GFS MEAN DUE TO THE CONTRIBUTION OF THE
CANADIAN SOLUTIONS.   AT THIS TIME...THE HIGHEST PROBABILITIES FOR
THE HEAVIEST SNOW BETWEEN THE ISSUES WITH THE NORTHERN EDGE AND
THE SOUTHERN MIX/CHANGEOVER IS CURRENTLY SUGGESTED TO RUN FROM
NORTHERN VIRGINIA TO EASTERN PENNSYLVANIA/NEW JERSEY INTO SOUTHERN
NEW ENGLAND.

TO PUT THIS SYSTEM IN CONTEXT...THE POTENTIAL SNOWFALL
DISTRIBUTION HAS SIMILARITIES TO SEVERAL MAJOR EAST COAST STORMS
IN RECENT PAST INCLUDING THE 5-6 FEBRUARY 2010 SNOWSTORM/THE
JANUARY 1996 BLIZZARD OF 1996 AND THE PRESIDENTS DAY OF FEBRUARY
2003. JANUARY 1996 IS LIKELY TO BE MORE WIDESPREAD/HEAVY BUT ONLY
TIME WILL TELL. THE MECHANISMS COMING TOGETHER FOR A MAJOR
SNOWFALL ARE TEXTBOOK.

IN THE WEST...PRECIPITATION SHOULD WANE ALONG THE COAST DAY 3 INTO
DAY 4...WITH THE NEXT MAJOR PRECIPITATION EVENT EXPECTED ACROSS
THE PACIFIC NORTHWEST BY NEXT MONDAY OR TUESDAY...WITH SEVERAL
INCHES OF LIQUID EQUIVALENT EXPECTED.

CONFIDENCE...

THIS IS A HIGH CONFIDENCE EVENT THIS FAR OUT IN ADVANCE BUT THAT
ALSO SUGGEST THAT SMALL CHANGES CAN HAVE SIGNIFICANT CHANGES TO
IMPACT. THERE IS STILL 3 TO 4 DAYS FROM THE EVENT AND MANY MODEL
SOLUTIONS TO COME.  THERE HAS BEEN EXCELLENT CONTINUITY RELATIVE
TO AVERAGE AND PERHAPS SIMILAR TO WHAT WAS OBSERVED WITH THE
FORECASTS PRIOR TO 5-6 FEBRUARY 2003...WHICH WAS FORECAST AS MUCH
AS 8 DAYS IN ADVANCE.  OTHER STORMS HAVE BEEN MUCH LESS
PREDICTABLE.  THIS MAY BE ONE CASE WITH A HIGH DEGREE OF
PREDICTABILITY BUT WE SHALL SEE.

KOCIN

Jan 19 2016 10:00AM Update
The shortwave that becomes our storm is coming ashore in the pacific northwest. We are rounding curve into the home stretch. Models still have not wavered from bringing heavy snow to the region. If anything, the 00z Euro upped the ante once again, bringing widespread totals of over 3 feet west of DC. The GFS and the Canadian have more "realistic" snow totals, between 20 and 30 inches.

The Weather Prediction Center (WPC) places the rapidly deepening low east of the Delmarva Peninsula on Saturday morning. This is a near ideal track for heavy snow; it would be perfect if the storm was just another 20-50 miles east, then we would be deep in the deform band behind the storm as opposed to flirting with the dryslot. As with any strong coastal low, we will have to watch for the rain/snow line, especially those who are below the fall line. A track farther east would also keep cold entrenched in the region, preventing a changeover to sleet or rain which would lower snow totals.

Our local NWS office is also on-board with a major snowstorm.

.LONG TERM /FRIDAY THROUGH MONDAY/...
THE THREAT FOR A SIGNIFICANT WINTER STORM CONTINUES FOR THE MID-
ATLANTIC REGION FRIDAY-SATURDAY NIGHT.

MODEL GUIDANCE IS IN AGREEMENT THAT AN INTENSIFYING SFC LOW WILL BE
IN THE VICINITY OF CAPE HATTERAS SATURDAY MORNING. THE DETERMINISTIC
GFS AND EURO ARE IN AGREEMENT PLACING THE SFC LOW JUST NORTH OF
THE CAPE...HOWEVER THE EURO IS ABOUT 6 HRS SLOWER. EITHER WAY...A
SIGNIFICANT WINTER STORM IS PROGGED TO REACH THE MID- ATLANTIC
WITH SNOW SPREADING NORTHWARD FRIDAY. AT THIS TIME...MODEL
GUIDANCE HAS TEMPERATURES ABOVE FREEZING IN VICINITY OF I-95 AND
EAST. THIS WOULD CAUSE LOWER SNOWFALL RATIOS AND THEREFORE LESSER
AMTS. THIS MAY LEAD TO A RAIN-SNOW LINE AS WELL. THESE DETAILS
WILL TAKE TIME TO IRON OUT AS WE ARE STILL 4 DAYS AWAY. CONFIDENCE
IS HIGHER FOR ACCUMULATING SNOWFALL ALONG AND WEST OF THE BLUE
RIDGE THROUGH SATURDAY NIGHT.

PLEASE PAY ATTENTION TO FORECASTS FOR UPDATES THIS WEEK ABOUT THIS
WINTER STORM.

SUNDAY AND MONDAY: HIGH PRESSURE WILL BUILD INTO THE AREA BEHIND THE
DEPARTING LOW SUNDAY. SEASONABLY CHILLY CONDITIONS ARE EXPECTED. A
WEAK COLD FRONT MAY MOVE THROUGH THE AREA MONDAY...BUT THERE WILL BE
LITTLE MOISTURE ASSOCIATED WITH IT.

&&

Jan 18 2016 9:00PM Update
The stakes have risen. Computer models have continued to hold on to the idea Mid-Atlantic snowstorm.  If anything, agreement has increased for a major snowstorm. 

Here's the current idea of storm progression:
Friday: Front-end Thump
Precipitation begins Friday morning as snow, becoming heavy into afternoon and night. The low will pass through the Southeast during this period and being to transfer to the developing coastal storm offshore. This is part of the storm we have the highest confidence in.
Saturday Morning: Wind-driven Precipitation
A coastal low will bomb out east of the Delmarva peninsula. Winds will increase, with sustained winds in the 20-30 mph range, possibly gusting up to 60 mph. Due to the close track and strength of the storm, mixing with rain or sleet is possible during the height of the storm, especially in the eastern areas. We also may be stuck in a dry slot, between the deformation band to the west and the low to the east. There is little confidence in the forecast at this time period. There are still many details to be worked out since they depend on exactly where the coastal low sets up; check back later.
Saturday Evening: Winding down
As the storm pulls away to the NNE, precip will change back over to snow. Another few inches would be possible with the passage of the deformation band before winding down. It is unknown exactly when the precipitation will shut off. I'm guessing sometime in the early evening.

As I mentioned before, the digital snowstorm has looked better and better with each model run. Both the GEFS and EPS Ensemble mean snowfalls for this storm has increased to around a foot and the operational runs of both these Ensembles have given us totals approaching 2 feet. The upper level and mid level low tracks are ideal for this area. Remarkably the GFS and the Euro have nearly identical solutions in this aspect. Where they differ is the surface low placement and precipitation distribution. Warm air intrusion at the mid levels is an issue on the GFS. Mixing is definitely possible so snow forecasts will vary. The important thing is the increased agreement on a major snowstorm. Whether we get something historic, as depicted in some of the model runs, remains to be seen.

EPS Ensemble Mean (51 member mean)-Classic snowstorm look

Original Text
As we head into late Janurary, things have been bleak over the past new weeks. A pattern that was supposed to increase snow chances lead to two cutters, a coastal storm @38 degrees F and a two dustings, one from an arctic front and another from a coastal storm that got shunted south, resulting in under half an inch of snow. I also told some of you that winter would be over in 2-3 weeks. In retrospect that was probably not a good idea as most models have no clue what's going to happen in the next week let alone a month in the future. But anyways, Let's forget about what's going to happen in February and just look at next 7 days.

Chance #0
An arctic front will crash through tonight, dropping temperatures into the low 20s and will bring an outside chance of a snow shower. Chances are the snow we saw today will be all. However, the cold airmass that comes will set us up for the rest of the week.

Chance #1
The next chance of snow will be Wednesday. This will be a clipper type disturbance (storm is giving it too much). It will act like most clippers, dying when it hits the Appalachians. Some non-accumulating flurries look likely at the moment. The bigger story is that the energy from this clipper help set the stage for the next storm as it heads off to sea.

Chance #2
A strong shortwave will hit the West coast in 3 days. As it tracks eastward, cold high pressure drops out of Canada, reinforcing a cold air wedge ahead of the storm. At the upper level, energy associated with the previous clipper will drop south, forcing the shortwave south. The storm is expected to track across the SE before turning the corner and heading up the coast, where current models have it bombing out during the January 22nd to 24th time frame, 6 days out. The operational models vary from a major snowstorm to a major rainstorm. However, operational models are prone to being wildly different from actual outcomes (being very wrong) this far out. Thus, to account for variations in initial conditions, we look at ensemble runs of the models. They are basically 20-50 low resolution runs with random variations in initial conditions. We look at the means of these results. A larger spread would mean lower confidence. What we want is the ensemble mean to show a tightly clustered low track as well as a high mean snowfall. We really can't ask for anything more. All 3 major global ensemble means (GEM/CMC, ECMWF, and GFS) give us more than 6 inches of snow. There are a multitude of possible outcomes with this storm. It looks likely that we can at least expect accumulating snow of some sort. How much will depend on how the atmosphere evolves over the next week. Updates will come as more information is gleamed about the situation.