I'm watching a very interesting system that may be developing for the Wednesday/Thursday time frame here in the DC area.

Most models show a phased system moving out of the Southeast, off the coast of the Carolinas and then up the coast.

The GFS run for Wednesday night shows a low pressure system rapidly intensifying off the coast

and throwing moisture back into our region.  The temperatures here are noteworthy.  The blue line is sub-freezing temperatures and we are north of that line.  This model suggests that the precipitation that falls will fall in the form of snow.

Interesting.

The total precipitation forecast from the same model through the duration of the storm for us looks like this:

It's a little tough to see but our area falls within the 0.1 - 0.5 range with a very sharp gradient towards the coast.  Using the old 10-to-1 ratio for liquid precipitation to frozen, this implies 1-5 inches of snow for our area.

More interesting.

As always, this is dependent on a lot of things but especially on storm track.  A track closer to the coast would mean more precipitation but also warmer temperatures as air is pulled from the relatively-mild Atlantic.  A track further from the coast would mean less precipitation - and a few solutions have a total miss with the storm moving off the coast too far to affect our weather.

Here's the GFS estimate for snow cover after the storm:

In this scenario, Delaware gets the bulk of the snow but you can see how close the areas of heavier snow are to this region.

The bad news in all of this is that the storm is likely to slow down and pound areas affected by Sandy (the Jersey shore especially) with winds, rain and surf.  Just what they don't need.

Let's see what the evening models hold but for now, there's a chance that some rain will start Wednesday, possibly changing to snow as nightfall approaches with better chances of snow north and west of DC but less overall precipitation the further west you go.

That's the weather forecaster in me being careful with the forecast.  The GFS above has no such hedging.  If I made a forecast entirely based on that, I would say "plan for snow Wednesday night".

We wait for the evening model run.

Possible Nor'easter MIdweek

Hope everyone did well during and after Sandy.

Models (the GFS and Euro) have been trending towards a solution that would bring a phased low pressure system out of the Gulf of Mexico northward along the coast as a Nor'easter for the Tuesday-Thursday time frame.

I'll post some model data later but the last few runs have turned away from an "off the coast" solution and now bring precipitation chances to our area.

Temperatures will be cool but not cold so precipitation type for the DC area looks to be rain at this point but stay tuned.

Here's Something You Don't See Everyday

The warning map from the Sterling NWS:

The pink color over the water is a hurricane warning.  The bright red in West Virginia?

Blizzard warning.  Wow.

6-12 inches of heavy snow possible with very strong winds.  A lot of that depends on how much cold air wraps around the system.  The atmosphere is marginal for snow but the dynamics of this storm are impressive and all of the models point to snow. 

Sandy Still Moving NE

The 11 PM update - Sandy is still tracking as expected.  Officially, the storm is still moving northeastward but has come about 15 degrees westward in the past 6 hours.  A previous heading of 050 is now 035.

This left turn should continue to a northwest heading by midday tomorrow.  Landfall still looks like Monday evening in south-central New Jersey.

No practical changes to our forecast.  Winds are picking up and rain is falling throughout the DC area.  This will continue and get more intense throughout the day tomorrow.  Gusts to 65 mph in localized areas will be possible tomorrow evening.

Stay safe!

Sandy Located 250 Miles off Cape Hatteras, Moving NE

Here is the latest advisory from the Hurricane Center:

Right now the storm is moving to the Northeast so the "capture" and turn in towards land has yet to happen.  Until it does, the location of landfall will be a bit of a guessing game with everywhere from Long Island  to Delaware still in play.

The most likely scenario is for a central-New Jersey landfall which would likely produce a very serious situation for New York City and areas along the Long Island Sound.  Because winds flow counterclockwise around a hurricane, the winds north and northeast of the center will be "piling" water up on shore.  Combine that with a full moon and high tide and you get a life-threatening storm surge situation.

Here in the DC area things are still forecast as described in the last post.  The weather for the balance of today should be tolerable.  Rain will start later this afternoon / evening and things will get breezy.  Overnight, though, the rain and wind really get going and by morning we should be seeing winds consistently around 30 mph and heavy rain.

Tomorrow starts bad and just goes downhill from there.  Winds increase throughout the day, rain continues.  By nightfall gusts to 60 mph are possible.

On Tuesday the rain hangs around but the winds start to decrease somewhat although I think breezy conditions persist until later in the week.

Expect 5-8 inches of rain, stream & creek flooding, maybe some flooding issues in the Old Town, Alexandria and Georgetown, DC areas that are prone to it.

Still watching the models to see how they track the storm.  Until that left turn happens, there's still some uncertainty.

Storm on Track for Landfall

Here's the latest from the National Hurricane Center:

Based on the models I've seen in the last few hours, I think their track might be a touch too far south.  The location of landfall isn't significant when you talk about whether or not we'll see any effects (we will) but it does have an impact on how extreme the effects could be.

For us, the size of the storm pretty much guarantees we will experience the expected effects:  rain and wind.  I think the weather starts deteriorating tomorrow afternoon with rain spreading in from the southeast.  The winds will be picking up too.  Expect sustained winds tomorrow night around 20-25 mph.

Monday is the most unpleasant day of the next three - especially as the day wears on.  Expect the wind to continue increasing through Monday afternoon and evening.  By Monday night we could see sustained winds around 40 mph with gusts over 50.  On the present track. the rain would fall heavily and fairly steadily throughout Monday.

By Tuesday things should start winding down but I think it stays windy until later in the week.  Rain is still possible on Tuesday - especially for the first half of the day. 

The big concerns for our area are:

1. Flooding.  We could see 5 or more inches of rain over the next three days.  Especially if the strike is south of the projections.  

2. Wind damage.  There are two factors to consider.  The first is that the winds will be quite strong for an extended period of time - maybe as much as 12 hours of tropical storm-force winds (40 mph+).  It is unusual - especially for this area - to experience a wind event like this one.  The second factor is that the ground will be extremely saturated during the period of strongest winds.  There will be tree-related damage.  Power outages are almost certain.

GFS-forecast wind gusts for Tuesday morning.  Our area is just south of the 70 mph zone indicating possible gusts in the   60-65 mph range for Monday night / Tuesday morning.

Much like winter storms - this will soon be down to small-scale forecasting.  Predicting where exactly the heaviest rain will fall and where the strongest winds will blow is very difficult.  So it makes sense to be prepared for the worst and hope we get something better.


Make no mistake, these models show a virtually unprecedented situation for this extended region over the next three days.  In a central-New Jersey strike scenario, New York City would see at least 5 feet of storm surge as winds and high-tide combine. 

Keep an eye on the conditions, use good sense, stay home on Monday if you can and treat the conditions with respect.  Be safe.

I'll post an update later today.

Track Shifts Southward

Here's the 11 AM update from the National Hurricane Center:

showing that the anticipated landfall has shifted south into southern New Jersey / Delaware  However, and I can't stress this enough:  don't focus on where the center makes landfall.  Yes, a southward shift to the track means that we in the DC area will likely experience more effects from the hurricane.  High winds and rain will definitely be a problem.  But this storm is large.  And if the extratropical transition I mentioned a few posts ago happens, the effects of the storm will be felt over a very large area.

On the coast, the big concern is from the center northward.  It is there that the winds will be strongest, and the problem with tides and surf will be the greatest.

Right now, as you can see from the graphic above, Sandy has weakened considerably due to dry air intrusion.  This dry air has disrupted the circulation and caused the cyclone to be a minimal hurricane.  Forecast models suggest that the storm will reintensify once it moves north and passes over the warm waters of the Gulf Stream.

After that, the models suggest a lot of cold air will enter the cyclone's circulation which will start that process of tropical-to-extratropical transition.

Hurricane Sandy.  You can see the exposed center of circulation and the thickest clouds to the northwest.  This is caused by dry air surging into the hurricane's circulation.

A hurricane is a complex engine requiring precise circulatory patterns of air to sustain intensity.  Storms like this become so large, they create their own environments but larger-pattern flow can affect them.

 The graphic above shows the typical Northern Hemisphere hurricane circulation pattern.  The spiral rain bands bring warm surface air into the cyclone where it spins up into thunderstorms near the center of circulation and especially in the area right around the center called the "eyewall".

Air then descends within the eye back to the surface.

As you might remember from previous posts:  ascending air creates clouds and descending air dries out the atmosphere.  This is why the eye is clear.

Above the storm is the outflow sector.  Air that ascends in the storm must flow outward to complete the cycle.  If the outflow or the inflow is blocked, the storm cannot intensify.  If strong upper-level winds cut across this circulation and disturb the outflow, the hurricane can fall apart.  Check out this dramatic example of windshear tearing a hurricane apart:

 See how the low level circulation is exposed as the thickest clouds are blown away by the shear?  Some of this is happening to Sandy right now.   Because of the shear, it wouldn't be entirely surprising to see Sandy being downgraded to a Tropical Storm later tonight.

 Unfortunately, there's plenty of time left for the storm to strengthen again before landfall.

So...where are we?

For now, expect a southern New Jersey landfall sometime on Tuesday.  We should start seeing some initial effects here as early as Saturday night with some initial rain bands.  The winds will increase throughout the period and the rain/wind maximum should happen by Monday night into Tuesday.

What makes this storm so unusual and the reason for the hype surrounding it is the unusual path it is expected to take.  I can't remember nor can I find an example of a storm that "hooked" to the west and made a direct-hit landfall on this part of the country.  There have been plenty of "drive by" storms (Irene comes to mind) but this left turn to a due west heading may well be unprecedented.

It's not unusual to have this kind of flow pattern in the fall and winter.  Sometimes big winter storms get caught up in this type of flow and hover in an area for a couple of days.  In fact, with winter storms, we snow lovers hope for that type of situation.

But for a hurricane to be in the right place at the right time to be caught in that kind of flow?  Unprecedented.

And for a hurricane to be absorbed into another system instead of torn apart by it?  Well, I can only think of the Perfect Storm example.

While the entire region will be affected in some way, the coastal areas north of the center could experience conditions that haven't really been seen there before.

And in DC, we could see winds on Monday night and Tuesday sustained in the 40-60 mph range with higher gusts.  If the storm track is further south, look for that to shift to Sunday night / Monday.

Sandy Update: 11 PM

Latest update from the Hurricane Center continues the same forecast rationale but shows the turn in towards land happens a bit faster and, thus, landfall is further south - in central NJ.  That's not so great for us here in DC as it likely means more rain and wind probably starting on Sunday and lasting until Tuesday.

Sandy Threat: 5 PM Update

Here's the latest Hurricane Center update:

Not much change in the forecast rationale.  This update carries the storm through landfall in New Jersey.  The storm will be quite large (in areal extent) by landfall so the center isn't really a focus - this storm will effect the region from the Carolinas to the upper Northeast especially along the coast.

There are still some crucial details to sort out - and that should happen in the next couple of days.  Temperatures around here on Monday and Tuesday will struggle to get out of the 40's with wind and occasional heavy rain.  Snow is possible in the mountains.

All we can do is watch the models and see if anything changes but at this point, there's pretty good indications for a serious weather event in the Mid-Atlantic and Northeast early next week.

Sandy Trouble for the Mid-Atlantic / Northeast?

Hi everyone!  I guess we're starting a bit early this year.

For the record:  I expect this winter to be significantly snowier than last winter - so, if that ends up being the case, there will be lots to blog about.

First, though, there's Sandy.

In 1991, right around this time in fact, an intense low pressure system developed off the coast of Canada and moved southward because of a large blocking high pressure system.  The storm became so large and organized that it actually absorbed a hurricane (Grace) and became a hurricane itself.  The Perfect Storm, as it would be known, eventually impacted the Mid-Atlantic and Northeast - largely through huge surf and the resulting coastal damage.  If the storm had actually made landfall, it would have been much much worse.

Satellite image of The Perfect Storm on the morning of November 1, 1991.  The hurricane has already formed in the center of the circulation although NOAA elected to leave it unnamed to prevent confusion.

While this is not the same situation, we have another case where a large system (in this case, a strong cold front moving across the country) could significantly affect the track of a hurricane (in this case, Sandy).  And this time, it looks like the effects on the east coast could be more direct - especially if certain model solutions verify.

Weather forecasts are fraught with conditional language.  "Could", "if", "might", "chance" are the vernacular of most meteorologists and the reason - as I've often mentioned - is that the atmosphere is a hugely complex system where any small change in a particular parameter could change everything about a forecast.


That said, it seems likely Sandy will continue to move north or north-northeastward for the next 36 hours or so before curving somewhat more to the northeast.  At that point, several factors will combine and how they combine is really important.

Most models now forecast Sandy's northeastward motion to accelerate on Saturday and Sunday.  If the timing of the incoming cold front is just right, sometime on Sunday the accompanying trough may "capture" Sandy and that's where the problems really begin.

A couple of days ago, this "capturing" looked unlikely to happen.  Now the timing and system locations look more and more like it will happen.  In fact, only one model right now suggests that the storm will pass harmlessly out to sea - i.e. that the trough will miss the capture and Sandy will become what is referred to as a Fish Storm.  And actually, looking at the latest model runs, I think that one has jumped on board as well.

The official National Hurricane Center forecast (at 11 AM 10/25) shows the capture taking place on Sunday and the storm turning in towards land by Monday with potential landfall on Tuesday as an extratropical storm or hybrid.

At the same time, colder ocean surface temperatures and interaction with the trough will probably cause Sandy to begin transition to an extratropical cyclone.  In technical terms, Sandy will be changing from a warm-core low (tropical system) to a cold-core low (extratropical).  In practical terms, the winds at the center of circulation will begin to weaken but the wind field itself would spread out significantly from the center meaning that places well inland could have tropical storm-force winds.

We could be looking at practically every weather effect you can think of from a storm like this.  There would be big problems with surf, coastal beach erosion and wind damage at the coast - especially at and north of the center landfall location.  Winds of 70-80 miles per hour at the coast would be common - even in places like New York City and especially in Long Island and points to the north.  Rainfall amounts will vary by location and I'm not sure at this point how much we'll see here but areas in the northeast will likely receive many inches of rain and elevated areas - especially in Pennsylvania and New York - could see a lot of heavy, wet snow.  Tropical storm-force winds could affect the entire region which means a lot of tree damage.

Here is one of the latest model runs showing the storm position on Halloween just off of New York City:

If this verifies, this would be a historic storm - the type that gets named afterwards (and I don't mean something like "Sandy"). 

In some models, the storm actually does a loop before heading out to sea.  During this loop is when we in the DC area stand the best chance of receiving precipitation although I think that we would see winds and clouds before then.

The time frame for effects here looks to be starting on Sunday and lasting into Tuesday night with wind and clouds initially, some rain during the curve into the coast and then, depending on what it does next, some lingering effects.

There is a lot of uncertainty as to the particulars of who-sees-what.  Right now, what seems least likely is that Sandy will go harmlessly out to sea (unfortunately).  Readers in the northeast and along the coast should consider making preparations soon and we'll watch this for the next couple of days to see what its going to do.

Snow is fun and big storms in the winter are fun but there's nothing fun about this one.  This could be really bad - especially north of the DC area along the coast.  Let's hope something changes in the next 48 hours to take Sandy out to sea.

More to come.

South south south.

As you probably know by now given the forecast trends, the storm track has continued to shift south bringing less and less snow and less cold air to our region.

What looked like a bullseye 3 days ago has become another disappointment in this unusual winter.

I expect to see some snow later this afternoon and evening but certainly no important accumulations.

Guess we would have been better off asking the first model what was going to happen rather than depending on the GFS.

With the further-south track also comes less cold air so any precipitation will likely start as rain and change to snow.

The Return

Both of me, and possibly of SNOW!

I've been conspicuously absent from this blog since, well, August when Irene came along and flooded everything.  Actually, it was Lee that flooded everything but Irene didn't help.

In any case, there hasn't been much to blog about this winter - certainly no one wants to read a blog about the 1/2 inch of snow that's likely to fall on any given day.

But this weekend looks like the first (last?) real chance at a real snowstorm.  If it happens, and the models hold, it looks like we might be in the bullseye for this one which makes it fun, too.  At least it gives me something to write about.

Let's start where we always do:  the models.

Sorry.

The GFS at 57 hours (10 PM Saturday night) shows a pretty good storm organizing in the southeast US.  Note the blue line indicating the freezing point for this particular part of the atmosphere.  We want to be north of that line and at this hour, we're right on it.  That's a good thing.

Also a good thing?  That high pressure area in the Great Lakes that will be moving east and bringing cold air to our area which should make for fewer precipitation issues (snow vs. rain vs. sleet).

By 66 hours, the storm is really getting wound up.  It's phasing (or phased) with northern stream energy from the jet stream and is beginning the turn up the coast.  Notice that we're in the freezing zone by this point.  It's too early to tell how the precipitation will start, but if these model forecasts hold, the major portion of it should be snow.

At 75 hours, early afternoon on Sunday, the main event should be in full swing around here.  This shows moderate to heavy precipitation in our area and that we're well to the north of the freezing line.  The potential for significant accumulating snow exists.  But the storm track means everything and we're still more than 3 days from this model time.

At 78 hours, late afternoon Sunday, we're still in the thick of it.  The storm looks to slide off the coast, right along the freezing line so this likely means not much for our Northeast neighbors but a possible bullseye for us.

By Sunday night the storm is moving away, precipitation ends from west to east and our storm is done. 

Of course, the question is "how much?"

For now, I think the concentration should be on whether the models hold for another day.  If these runs don't change much and the other models fall into line, this looks like the real deal.  The ECMWF has been flip-flopping between a more southerly track and a more northerly track.  The southern solution means less precipitation for us so this all bears watching.

For now - the probability exists, I'd say better than 50%, for a significant snowstorm with 3+ inch accumulations starting late Saturday night and ending Sunday night. The possibility for more exists of course but this is the highest probability range for now.

Just for fun:  the GFS "clown" map:

which shows us just outside of the 4-6 inch range or so.  These aren't all that accurate this far out except to show the path and pattern of the snowfall.

Stay tuned.