Clear as Mud!

Good eve (or morning),

What is making this forecast a bear is the amount of warm air being pulled into the storm aloft (~5,000 ft up)  as it comes up the coast.  This is vastly different from model to model.  The NAM keeps the warm layer aloft to our east, and pounds us with snow.  Meanwhile, the European model from this morning has temps well above freezing ~ 5,000 ft up by 10 am on Thrs, and is a sucky sleet and rain fest.  Even the GFS and Canadian Models from this morning pulled this stunt at some point on Thrs, where snow changed to sleet and rain due to warm air aloft.  Man… if we stay all snow, this could end up 10 to 20″… but if it doesn’t (which was how it appeared this afternoon), then 4 to 8″, maybe 10″ before changing over.  Suspect we’ll be sorting this out into Thrs morning, cos we really don’t know for sure until the bloody thing starts to come up the coast.  Clear as mud, eh?!

A few other things.

This is looking like a three-part storm:

The first part of the storm for Weds night is really straight forward.  The initial slug of moisture coming up the coast will encounter some really cold air entrenched over the region, and there will be a period of moderate to heavy snow Weds night.  Due to the cold air, this snow will also stack up quickly, with a high snow-to-liquid ratio.  This “part” of the storm is good for 4 to 8″ of snow, perhaps even 10″.

Part two is the coastal low passing to our east, or perhaps inland Thrs morning.  This is where we could either see snow pile up or change to sleet, freezing rain, and rain.  We’ll be tracking the weather features about 5,000 ft up (850 mb) to sort this out. This is the make-or-break part of the storm… and will occur during the morning and early afternoon Thrs.

Part three is the “parent” upper-air low, the feature that helped generate the surface coastal low.  This will come thru Thrs afternoon and evening, and will likely be responsible for a bonus round of light to moderate snow or sleet. We often see this with big storms… the upper-air energy (aka “vort”) that spawned the whole bloody mess comes barreling thru after you think it’s all over, and drops another 2 to 4″of snow.

On to what is rolling in at this hour.  The Short-Range Ensemble models (SREFs) offer zero clarity… with everything to 1-2 feet of snow to snow and a whole lot of rain.  More notable is the latest NAM (00z), which is still all about a heavy snow event… keeping the warm layer aloft to our east.  So far, that’s all we have.

Well, will update u tomorrow.

Fun!

Weds/Thrs?

Happy late weekend…  I’m gonna be sans internet Monday until Noon due to a work issue, so I wanted to get this out.  Hope folks enjoyed our light snow event  Sunday… now on to more pressing matters.Models are still having all sorts of fun with a coastal low for Weds-Thrs.   It seems to be a good bet that we’ll have a low developing in the Gulf on Weds. The upper-air energy that will trigger this Gulf low will be tracking across central California Monday, so we’re not waiting for a jet streak or coastal jump or some other divine intervention.  It’s there, moving ashore.  The question is:  Will this low track up the East Coast, or slide a bit farther east out to sea?  With the jet stream buckling just enough, we may very well end up- with this low coming up the coast.  The European and Canadian Model are all-in for a snow storm for Weds and Thrs, while the GFS still keeps the low a bit offshore.  I’m starting to think we have ourselves a winner.  With the jet stream not quite as flat (west-to-east) as it has been, things seem to becoming together for a true East Coast storm.  My only question is this:  Will it track too far west and give us a wintry mix, or track up the slot and give us all-snow?

So, we’re still status quo for the mid- to late-week storm… still there, but far from a done deal.

I’ll ping y’all when we come back online mid-day Monday.

Light Snow Sunday

Quick FYI – Quick-hitting upper-air disturbance will generate light snow Sunday afternoon.  The window for snow is between 1 and 7 pm, and the best chance for accumulations (we’re talking a trace to an inch) are across central and nrn MD and srn PA.  Should the disturbance track a bit farther south, then we could see a bit more (1-3″), but that’s about the high end… and an outlier solution.  If anything changes I’ll pass it along.

Not Impressed

It’s Friday… HH should’ve started hours ago (It’s 5 pm in London, right?!), but alas… I’m here.  The weekend Wx looks to be as flat-out boring as the flat jet stream that is driving it.  The jet stream is oriented “flat”… flowing rapidly from east to west – and this gets you a bunch of fast-moving, quick-hitting disturbances for the weekend.

Saturday:  Some flurries or light snow, but this one looks less and less impressive with each model run.  If this current model trend keeps going like this, Saturday will be sunny with highs in the 70s (not really).  So, some light snow or flurries Saturday, little to no accumulation.

Sunday:  This one fizzled too.  Clouds, with perhaps some light snow or flurries.  Minor accumulations, if any.

Sunday Night into Monday morning:  Yet another disturbance comes zipping along, and this one the models actually have a more widespread (albeit still light) snow falling.  It is courtesy of one of our fabled “vorts” (upper-air spinner), and these can be pretty efficient snow producers.  I’ll keep you posted about this little bugger, cos it could pose a problem for the Monday morning commute.  Not a shut-downer, but the kind of thing that would be just enough snow to pooch the works.

Next Week:  The jet stream will begin to buckle just a little – with a ridge (north-ward shift) forming over the western U.S., which will allow a bit more of a trof (a southward dip in the jet stream) to form over the eastern U.S.  At the same time, things in the north Atlantic start to slow down enough that we could get an East Coast storm during the latter half of the week.  It’s something we’re watching, and the target days appear to be Weds into Thrs.  As you’ve all seen with the hype over the now-defunct weekend blizzard, it’s foolish to say much more.  I’m a bit fearful folks are gonna grab the latest run of the European Model (the “Burning Bush” as I now affectionately call it) – which has an East Coast snowstorm next week – and try and make some noise with it.  This storm will probably come and go a half-dozen times in the models between now and next week.  Given that the “trigger” for this storm is a piece of energy currently sitting over the Bering Sea off the southwest coast of Alaska, well… let’s just see where this thing goes for a few days before projecting its path up the East Coast.  Just sayin’.  :)

Have a great weekend, everyone, and I’ll keep you posted if anything worth posting posts.

E

New Years Storm? Depends…

This image is a compilation of the GFS (top left) and its ensembles forecast valid for Thursday, Jan 2, at 1 pm (EST).  The approximate rain/snow line is highlighted in solid magenta, while precipitation over the preceding 6 hours is given in hundreds of inches (i.e. 25 = 0.25" liquid, which would equate to 2 to 3" of snow).  Some of the ensemble runs are slower, with the storm not yet fully developed, while others have a full-fledged winter storm about to unfold.  This image is courtesy of the PSU EWall.

This image is a compilation of the GFS (top left) and its ensembles forecast valid for Thursday, Jan 2, at 1 pm (EST). The approximate rain/snow line is highlighted in solid magenta, while precipitation over the preceding 6 hours is given in hundreds of inches (i.e. 25 = 0.25″ liquid, which would equate to 2 to 3″ of snow). Some of the ensemble runs are slower, with the storm not yet fully developed, while others have a full-fledged winter storm about to unfold. This image is courtesy of the PSU EWall.

 

The models have been targeting the first few days of the New Year for a potential winter storm along the East Coast.  But there is also utter chaos in the models, with everything from a major snowstorm to ice to rain to nothing.  To illustrate this, I grabbed the GFS ensemble forecast chart – courtesy of the PSU EWall – valid for Thursday, January 2, at 1 pm, EST (see above).  This is just one model and its tweaks and reruns, and does not account for what other models are saying for the same time.  I annotated the image to make it a bit easier to interpret.

 

 

 

 

 

Pcp Type – What a Mess!

As we get closer to the weekend storm, determining the type and duration of the precipitation type is turning into quite a challenge.  The latest GFS Ensembles (tweaks and reruns of the GFS) show a great deal of uncertainty regarding where the freezing line aloft (850mb/~5,000 ft) will set up.  Any temperature above freezing aloft would be too warm for snow (sleet or ice), while subfreezing temperatures aloft would increase chances for snow.  Basically, if you’re above 0°C/32°F aloft, you can forget snow.  So knowing where this demarcation will be is critical to determining pcp type.

The rather messy “Spaghetti” plot below shows the individual runs of the ensemble’s temperature placement as a solid line, with the critical “0” line (0°C/32°F) above the ground in the cluster of lines right over MD.  This very important rain/snow indicator could end up anywhere from northern Virginia to the PA line based just on the GFS and its Ensembles alone!  This does not even begin to account for what other models are saying… and highlights how difficult the p-type will be with this storm.

This image depicts the GFS ensemble "spaghetti" plot for the 850mb (~5,000 ft) temperature.  Each line represents one run of the GFS Ensembles from 12z, 12/12/2013.  The critical 0°C (32°F) contour is depicted by the group of lines labeled with a "0" over the central Mid-Atlantic.  Image is courtesy of the Penn State University.

The top image depicts the GFS ensemble “spaghetti” plot for the 850mb (~5,000 ft) temperature. Each line represents one run of the GFS Ensembles from 12z, 12/12/2013. The critical 0°C (32°F) contour is depicted by the group of lines labeled with a “0” over the central Mid-Atlantic. The bottom image is the consensus of all the ensembles, which shows the critical freezing line running east-west between Baltimore and Washington, D.C.  Image is courtesy of the Penn State University

Chilly Jerry Carney Monday…

Coldest air of the season will blast in this Saturday.  Monday morning will feature winter-like temperatures, with the latest forecast guidance indicating morning lows in the teens.  Ooof!

Monday morning temperatures from the Friday evening run of the NAM; values in the teens!  Image courtesy of the PSU Ewall.

Monday morning temperatures from the Friday evening run of the NAM; values in the teens! Image courtesy of the PSU Ewall.

Baltimore Snow Climatology

I did a little digging, and came up with some surprising numbers inre to snow and the Mid-Atlantic.  Actually, the Subject Line shouldn’t be “Feast or Famine“, but rather “Lots of Famine, with a rare Feast“.  here are the details.

I was looking at the NAO data (North Atlantic Oscillation) and snowfall for BWI, and it showed what we already know: a negative phase of the NAO (a blocking high) is almost always required for snowy winters.  Not exclusively, but it’s a pretty strong driver.  What was more interesting is the shift in snow climatology for these parts, which is likely a function of the warmer climate regime we find ourselves in.  I went and grabbed the snowfall data for Baltimore (BWI), which goes back to 1950.  Now, I know there are people out there who will claim there’s some sort of conspiracy in the data, and I’ll admit snowfall is notoriously difficult to measure.  However, this only applies IF it’s snowing; I mean, if there’s no snow to measure, you can’t possibly screw that up.  The data is straight from the NWS… and valid for BWI.  Areas north and west of I-95 in the Piedmont typically get more snow, while areas south and east get less.  BWI is a happy medium ground for this region.

So, here it is… the moment that you’ve been waiting for. (if you’re still reading (and I can’t blame you if you threw in the towel))

Since 1950 (63 years), 10 of the 15 least snowy winters have occurred since 1990.  And 1988-89 makes the list but not the “since 1990” cutoff.  Here they are, rated in order…

BWI Snow Departure Winter Year Dud Rank
1.2 -16.8 1972-73 1
1.8 -16.2 2011-12 2
2.3 -15.7 2001-02 3
3.2 -14.8 1997-98 4
4.0 -14 1958-59 5
4.1 -13.9 1991-92 6
4.6 -13.4 1980-81 7
6.2 -11.8 1950-51 8
8.0 -10 2012-13 9
8.2 -9.8 1994-95 10
8.3 -9.7 1988-89 11
8.5 -9.5 2007-08 12
8.7 -9.3 2000-01 13
9.1 -8.9 2008-09 14
9.4 -8.6 1990-91 15

The departure from average is based on a normal of 18″.  My childhood being in the 70’s and 80’s (TMI, really), you can see how I grew thinking that snow was just a given.  Ha!!

On the flip side, 4 of the 15 most snowy, most awesomest winter have occurred since 1990.  (and don’t dare disagree with “awesomest”or you’ll be immediately removed from this list!).  But here’s the kicker.  The top 3 have all been since 1995.  here’s that list:

BWI Snow Departure Year Booyah Rank
77.0 59 2009-10 1
62.5 44.5 1995-96 2
58.1 40.1 2002-03 3
51.8 33.8 1963-64 4
46.5 28.5 1960-61 5
43.4 25.4 1966-67 6
43.0 25 1957-58 7
42.5 24.5 1978-79 8
35.6 17.6 1982-83 9
35.2 17.2 1961-62 10
35.2 17.2 1986-87 11
34.3 16.3 1977-78 12
34.1 16.1 1959-60 13
32.8 14.8 1965-66 14
26.1 8.1 1999-00 15

Winter #15, 1999-2000, most of this snow fell in one storm… the very January 2000 storm that was the birth of this list.

Anyhow, it appears that we have settled into a regime where the odds of getting hosed during winter have gone up, but so have the odds of the occasional blockbuster.  I can only hope we’re due.

Hard Freeze for Central MD

Our first hard freeze – even for typically warmer urban locales – looks like a good bet for Monday morning.  The NAM sfc temperature forecast for 7 am, Monday Nov 4 (below) depicts freezing temperatures almost all the way to the still warm Bay.

Temperature forecast from the NAM for Monday, Nov 4, at 7 am, EST.  A hard freeze is expected, which would end the growing season for most of the region.

Temperature forecast from the NAM for Monday, Nov 4, at 7 am, EST. A hard freeze is expected, which would end the growing season for most of the region.

Positive NAO

If you want to see what a “positive” NAO (North Atlantic Oscillation) looks like, see below.  The chart shows pressure departures aloft  (500mb/~15,000 ft up) from late Weds night (10/30) over the northern Atlantic.  Blues are areas where pressure is lower than normal (stronger lows/storm centers), while oranges are areas where the pressure is higher than normal (stronger highs).  The contours basically show you the alignment of the jet stream.  The tighter these lines are together, the faster the winds… and the wind flows parallel to these lines.  The low spinning counter clockwise and the high spinning clockwise act to pull the jet stream “tight”, and the net result is 60- to 70-degree weather in late autumn.  The bar chart at the bottom shows the phase and intensity.

Anyhow, these phases tend to last 4 to 6 weeks, and then it resets…  sometimes to the same phase, other times it flips.

500mb departures from normal for 00z, October 31 (8 pm EDT on October 30, 2013).  The bottom of the chart shows the daily evolution of the NAO since July.  This is a classic "positive" NAO... the "North Atlantic Shop Vac", which acts to suck the cold air out of North America.  This setup typically yields, warm, wet weather over the central and eastern U.S.

500mb departures from normal for 00z, October 31 (8 pm EDT on October 30, 2013). The bottom of the chart shows the daily evolution of the NAO since July. This is a classic “positive” NAO… the “North Atlantic Shop Vac”, which acts to suck the cold air out of North America. This setup typically yields, warm, wet weather over the central and eastern U.S.