Tuesday... We're looking at that

2:31PM 2/16/2015 UPDATE 
 Nothing much has changed since last night. 6-8 inches is the final call. Snow onset is expected within the next 1-2 hours from south to north. At first the snowflakes will be very fine and have needle and plate structures due to the dry air. Reports have shown that the snow changes over to dendrites (the traditional snowflake structure) about 30 minutes after onset. The snow will stick immediately due to cold temperatures.

Snow Incoming

ORIGINAL TEXT:
Well we're within the time period in which the models have stopped jumping 50 miles a run, alternating between snow and no snow. All major models have settled for snow but still have some differences to resolve. Despite this, the NWS has gone ahead and upgraded the winter storm watch to a warning.

THE NATIONAL WEATHER SERVICE IN BALTIMORE MD/WASHINGTON HAS
ISSUED A WINTER STORM WARNING FOR SNOW...WHICH IS IN EFFECT FROM 6
PM MONDAY TO NOON EST TUESDAY. THE WINTER STORM WATCH IS NO
LONGER IN EFFECT.

* PRECIPITATION TYPE...SNOW.

* ACCUMULATIONS...4 TO 8 INCHES.

* TIMING...SNOW IS EXPECTED TO DEVELOP MONDAY EVENING AND
  CONTINUE THROUGH TUESDAY MORNING. HEAVIEST SNOW IS EXPECTED
  MONDAY NIGHT AND EARLY TUESDAY MORNING.

* WIND CHILL...5 TO 10 BELOW ZERO TONIGHT AND MONDAY MORNING.

* TEMPERATURES...SINGLE DIGITS TONIGHT. HIGHS IN THE LOWER 20S
  MONDAY. TEMPERATURES IN THE TEENS MONDAY NIGHT AND TUESDAY
  MORNING.

* WINDS...NORTHWEST 10 TO 15 MPH OVERNIGHT. WINDS BECOMING
  SOUTHEAST 5 TO 10 MPH MONDAY NIGHT INTO TUESDAY MORNING.

* IMPACTS...THE COMBINATION OF GUSTY WINDS AND COLD TEMPERATURES
  WILL CONTINUE TO MAKE DANGEROUS WIND CHILLS THAT CAN QUICKLY
  CAUSE HYPOTHERMIA AND FROST BITE THROUGH MONDAY MORNING.
  BEGINNING MONDAY EVENING...ROADS WILL BECOME SNOW COVERED AND
  SLIPPERY WITH VISIBILITIES BEING REDUCED TO ONE HALF MILE OR
  LESS AT TIMES. THE COMBINATION OF SNOW COVERED ROADS AND LOW
  VISIBILITY WILL MAKE TRAVELLING DANGEROUS.

Some points about the snow:

This map is a modified version of the NWS official forecast.

The storm is set to travel south of us, keeping us firmly in the cold sector. For once we get cold snow. No worries about mixing or melting. Temperatures will be in the mid teens while it snows. It'll be pretty fluffy powder. However, some models have been depicting a rather sharp cutoff in precipitation amounts to the north due to the extremely cold and dry air around. This may be a concern if the storm tracks any more south. We are still set for decent snow right now. Not perfect, but no one can complain about a warning criteria event.

Snowfall ratios are expected to be above the 10:1 average. Ratios will probably be more around 14:1 and may approach 20:1 at times. This will help to boost snow accumulations. Currently we're looking at 4-8 inches-more to the south and less to the north due to the cutoff.

School will probably be cancelled Tuesday. There is an outside chance at delay or cancellation Wednesday.

The next chance at snow will be Wednesday. A quick snow squall possible. Probably won't be as bad as the last one we had.

I'll keep this post updated as the storm progresses.

Thanks for reading

-Alex

Miller B Screwjob

1/26/2014 9:00PM Update:
Don't look at the radar, it's almost impossible to tell what's going on. convergence cause by the coastal low and a system to our west has promoted the growth of snow showers around the region. The focus of the convergence has just shifted into the DC metro from the west. Snow will fall tonight 1-3 inches expected. Due to cold temperatures, any moisture will freeze, possibly resulting in icy spots.

School forecast:

• Delay: 67%
• Closing: 30% (Snow totals are a bit iffy and we need to verify on the high side to get off)
• Nothing: 3% (somewhat arbitrary number but you get the point: low)

So 97% Chance of getting some part of school off.

1/26/2015 6:00PM Update:
Hope has returned. Light to moderate snow has entered MoCo. Could be the beginning to a decent bit of snow. Things are looking up again.

Be careful out there. Temperatures are now dropping quite rapidly and any liquid has frozen so slipper spots may be present. School delay/closing/opening forecast will come out at 9. Nothing is set in stone so do your hw.

1/26/2015 5:00PM Update:
The energy transfer is complete and so clipper is dead and the coastal low has started strengthening. The remnants of the clipper will help extend an area of low pressure to the west of the storm called a Norlun Trough. Precipitation and position of Norluns are almost impossible to forecast with complete accuracy. One can only blanket the general area and say you're at risk for snow, not sure how much though. The NWS has kept a broad area of 2-3 inch forecasts to reflect this. Some will get less, some may get more. In any case, precip has started to move west over the bay towards us while some precip is also approaching from the west. What happens in the next few hours will be interesting. Let's see if we can score some heavy snowfall.

Dover Delaware radar shows precip pivoting in our direction and trying to expand across the bay

Radar over the DC region shows precip movement in all directions. Quite unusual. A small bit of precip is moving towards DC from both west and east.

1/25/2015 11:15 PM Update:
This is the explanation for why we don;t have a simple 5-8 inch cold powdery clipper system, but instead a convoluted and in some ways, ironic, mess.

Before Two days Ago...
All we knew was that a clipper was coming after the wet coastal storm on Saturday. I wrote it off as trending north and a non-event. We all wished that it would dig south. Lo and behold, it did. We were happy.

Two days Ago...
We were set for a decent event. The GFS and the NAM agreed on dropping 5+ inches of powder over the DC area and although the Euro gave less precip, it had the same general idea too. New England wasn't going to get anything. Temps weren't an issue as the clipper (primary low) would zip to our south and northerly winds on the backside would draw in cold air. The models were relatively consistent with their solutions. It could stop digging now. But it didn't.

Last Night...
The Canadian short term model, the RGEM, dug the storm way south, but the low was so strong, that southerly flow ahead of the storm ruined our temps. It also killed off the primary low before it got east of us, this leaving no northerly flow to cool us until the coastal low got going, which by then, was too late. This was worrying. The other models also decided that a coastal low was the way the storm would do. This coastal low would have a western extension, bringing us snow. We were now depending on a dying clipper and a moody unpredictable "teenage" coastal low to bring snow.
What was worse was that the Euro came in with a screwjob too. A different one. When the primary low died to the west of us, the precip shield would also die just to the west too. Then energy would transfer to the coastal. which would bomb out and clobber the NE. The moral of the story is be careful what you wish for. We wanted south and it went south. Too far south...

However...
Fortunately the GFS has held fast to it's idea of snowbands off the coastal low. Hope we can cash in on this storm. The short term models seem to like it too. And the Euro like overamping storms and making the too strong. Just keeping it optimistic here.


1/25/2015 9:55PM Update:
The last model run before the storm (00z model suite) has started. The NAM came out first. not the most reliable model. But still worth a look due to its higher resolution. Until you see that it comes out worse. 1-3 inches for most of us, not including melting. Also screws over NYC. I guess that's a plus. Or an indicator that something is wrong.

The NAM gives counties just NW of us 3-6 but gives us 1-3 and NYC around 10-15 inches of snow.

NYC snow forecast: 2-3 feet of snow.

1/25/2015 8:40PM Update:
 Percentages for closing tomorrow lowered to 45%, chance of early release raised to 12.5% and chance of nothing raised to 40% on the account that the primary low is weakening too rapidly, temperatures are too warm, and the coastal low will travel too far to the east to give us much.

Snow forecast language altered to reflect long duration. Totals will not be reached it coastal low skips to the east.

Original Text:
Well, here we go again. Another complicated setup in which we may get a decent snow... or get screwed over. It is almost painful to watch the models spit out feet of snow in the Northeast while we get only a few inches at best. Hurts even more to see a near perfect clipper system for us 2 days ago turn into a monster snowstorm for someone else which in turn screws us over. Just another winter in the Mid-Atlantic region I guess. We get a dying clipper and they get a historic blizzard. 
Take, for example, the forecast for New York City.

• Snow with widespread blowing snow. The snow could be heavy at times. Some thunder is also possible. Low around 21. Wind chill values between 5 and 10. Windy, with a north wind 22 to 32 mph, with gusts as high as 46 mph. Chance of precipitation is 100%. New snow accumulation of 11 to 17 inches possible.
• Tuesday Snow with widespread blowing snow. The snow could be heavy at times. Some thunder is also possible. High near 24. Wind chill values between zero and 5. Windy, with a north wind 34 to 37 mph, with gusts as high as 49 mph. Chance of precipitation is 100%. New snow accumulation of 10 to 14 inches possible.

This is less than a half day's drive away. What have we done wrong?


Ok. Rant over. We actually have a chance at some decent snow despite the fact that half the models say no and the rest say meh. This will be a drawn out event. However, everything will start out as rain. It's a race between cold temperatures and the dying low. If our temps don't drop fast enough, our precip will all be rain and little to no snow. Currently, models depict changeovers in the early morning. After that, we get light precip for a day or so as the primary low dies and a new one forms to the east of us. That low will be what gives the NE a blizzard.

Snowday forecast for MCPS:
Chances of

• Delay-2.5%
• Early Release-2.5%   12.5%
  
• Closing-65%   45%
• Nada-30%  40%

My snow forecast for Montgomery County

• Upcounty 
•  3-6 inches of snow  by Tuesday night
•  Changeover to snow between 3AM and 5AM Monday morning
• Downcounty
•   2-4 inches of snow by Tuesday night
•  Changeover to snow between 5AM and 7AM Monday morning

Maybe calling this a screwjob was too harsh. Compare to the NWS Sterling forecast. Pretty similar.

I guess the NWS has finally learned it's lesson on the urban heat island. The went out of their way to make sure DC is forecasted to get less than the surrounding region.

January 25-27 Possible Storm

I have been hearing many people talking about a snowstorm on Monday but not a mention of Friday's storm. Apparently people don't care about weekend snow. Anyways, here's what I think of the Monday time frame- too far out to tell for sure, but not looking so hot at the moment.

The best case scenario is a Miller B system, where a parent low weakens and redevelops a secondary low off the coast. The secondary low rapidly strengthens, bringing precip to the region. Typically, the reformation takes place too late because the parent low approaches too far to the north. In order for us to cash in on a Miller B, the parent low needs to be quite strong in order to "dig" far enough south for the storm to reorganize before it gets to us.

Models have been trending away from a snowy scenario towards a weaker, more northerly low.

4 successive GFS runs showing the storm at the same time period (7AM Monday). 00Z is the oldest and therefore the farthest south. 18Z is the most recent and the farthest north, illustrating the northward trend.

That being said, many things can change. After all, we are still very far away from the actual event. It took 6 runs to get from a storm that was so far south that it gave us nothing to a storm that is too far north. It can easy swing back. Fluctuations will probably diminish after the Friday-Saturday storm so we will wait until then to see. Don't let your hopes run too wild.

Thanks for reading, Alex