Jump to content
  • Member Statistics

    17,163
    Total Members
    7,904
    Most Online
    Michael Butler
    Newest Member
    Michael Butler
    Joined

Feb 24-25, 2022 Ice/Sleet/Rain/Snow (yeah sure) Storm Thread


WinterWxLuvr
 Share

Recommended Posts

2 minutes ago, high risk said:

        This is a fair point.     None of these accumulation computations is making any attempt to determine how efficiently the ice can accrete.    They're just looking for freezing rain as the precip type at the top of the hour, and if that is found, all of the QPF from the past hour (or in some cases, 3 or 6 hours!) goes into the freezing rain bucket.    In fact, only the RAP/HRRR actually have a true tallies of freezing rain and sleet.

I feel like I've heard that before, but that bolded part is truly nuts and ends up being so misleading, especially for models that only have those 3/6 hour intervals. 

Link to comment
Share on other sites

15 minutes ago, high risk said:

        This is a fair point.     None of these accumulation computations is making any attempt to determine how efficiently the ice can accrete.    They're just looking for freezing rain as the precip type at the top of the hour, and if that is found, all of the QPF from the past hour (or in some cases, 3 or 6 hours!) goes into the freezing rain bucket.    In fact, only the RAP/HRRR actually have a true tallies of freezing rain and sleet.

Interesting info, thanks. I always take that with a HUGE grain of salt (or sleet?). So are the images that TT and others generate coming directly from model output of this, or do they use some algorithm of their own based on that? 

Link to comment
Share on other sites

9 minutes ago, NorthArlington101 said:

I feel like I've heard that before, but that bolded part is truly nuts and ends up being so misleading, especially for models that only have those 3/6 hour intervals. 

         Right!    It's most pronounced for the NAM beyond 48 hours or the GFS beyond day 5, as those models have hourly output through those times, although that assumes that the various sites are actually pulling in the hourly data.    The bottom line, though, is that it definitely inflates freezing rain and sleet totals.

  • Like 1
  • Thanks 1
Link to comment
Share on other sites

2 minutes ago, Always in Zugzwang said:

Interesting info, thanks. I always take that with a HUGE grain of salt (or sleet?). So are the images that TT and others generate coming directly from model output of this, or do they use some algorithm of their own baaed on that? 

          I don't know for sure, but I think that they're at least using the precip type information directly from the models and not computing it themselves.   Regardless, it's applying an instantaneous precip type to an accumulated precip.

  • Thanks 1
Link to comment
Share on other sites

1 minute ago, high risk said:

          I don't know for sure, but I think that they're at least using the precip type information directly from the models and not computing it themselves.   Regardless, it's applying an instantaneous precip type to an accumulated precip.

Thanks. Yeah that certainly makes those plots pretty dubious on the amounts, though perhaps the areal coverage of that ptype might be somewhat more useful. I mean really, 1.50 inches of QPF is not going to give you 1.50 inches of ice of course, to use an extreme example...and which I have actually seen in the past! 

  • Like 1
Link to comment
Share on other sites

One of the trends I'm noticing in the area of ice accretion is the NBM coming around now to a more pronounced icing scenario compared to its previous runs. NBM is no where near perfect, but it does take into consideration a lot of different guidance and uses a blend of the data to calculate final ensemble means. It also utilizes FRAM Ice accretion numbers, which is more of a true ice measurement process based on a complex algorithm developed by a myriad of meteorologists and data scientists using both a data driven and physical attribution of ice processes that create the overall environment necessary for ice to accumulate. Long story short, it is immensely more accurate a better measure for overall risk assessment and forecasts within operation settings. 

NBM likely to exhibit a bit of a warm bias given the overall setup and how it underplays the depth of the surface cold layer due to raw data inputs that can skew a mean upward. So, when the NBM is harping at ice accretion within the realm of being more impactful, one has to take notice. 

Here's the latest NBM forecast signaling the potential at these leads. It will be something to monitor, and I'll update the forum, when I can on these numbers since FRAM is only accessed through internal collaboration and NBM internal products, or a paid site like Pivotal Weather.

1167535600_NBMFRAM022300z.thumb.png.86e132fbe97f530dc393acdc219e41b7.png

This is more significant compared to the previous runs with totals approaching the 0.1" over the M/D and even getting into the outer burbs of the Balt/DC corridor. 

I know I have not been high on this event given my lack of posting (Also been crazy busy out here!), but there's a chance for a modest impact event that would certainly throw a monkey wrench on the Friday AM commute. Definitely one to keep tabs on, especially north of I-70 and the Parrs ridge front into Western HoCo and MoCo. 

  • Like 5
Link to comment
Share on other sites

Image

This is the current CIPS Analog guidance with probability of ZR exceeding 3+ hrs within the domain inside a 48hr period. This is centered at 00z Friday, so there's a pretty solid signal for some ZR over areas north of I-70 as shown just using CIPS guidance. 

Link to comment
Share on other sites

LWX posted watches for Garrett/Allegany in MD and Mineral County in WV.  Up to 0.3” ice and 1” of snow/sleet.  

Good write-up too by LWX explaining the set-up and possibilities:

Complex (but somewhat typical for this area) storm system will
affect the area Thursday into Friday. A lead shortwave will be
responsible for an initial round of precipitation Thursday,
then a stronger shortwave will force an area of low pressure to
develop along the stalled front to our south, before tracking to
our west and north Thursday night and possibly redeveloping
offshore Friday. Meanwhile, a strong Arctic high will be located
over Canada feeding cold/dry air southward which will become
dammed east of the Appalachians. The atmosphere may be cold
enough (or at least wet bulb low enough) for precipitation to
start as some snow or sleet for parts of the area. However, the
air aloft will warm with time, eventually leading to a rain or
freezing rain scenario. Surface temperatures are always tricky
during CAD, but probabilities support the greatest chance of any
icing generally north and west of I-95...but particularly
within a couple counties of the PA border where the greatest QPF
is expected Thursday night to Friday morning. In some of these
areas, especially in the Cumberland MD area, the wedge may not
break until the trailing cold front arrives later Friday
morning.

Some of the factors that will have an effect on this system:

1. There will be an interesting play between air temperatures
and precipitation with the initial round Thursday due to wet
bulb processes, which may ultimately determine the
strength/breadth of the CAD.

2. There will be very dry air at the surface, so precipitation
could have a hard time progressing northward Thursday.

3. While not a common solution in models, there is some
potential for a more prolonged period of sleet near the PA
border which could reduce freezing rain accumulations.

4. For much of the area, temperatures will be marginal for the
event, and the preceding days have been very warm. Any areas
where freezing rain is light or brief may not have as much of an
impact as it would otherwise.

5. Uncertainties about if and how much temperatures drop
Thursday evening and rise thereafter, as well as QPF during the
second wave, which will largely be focused north of the area.

In the end, issued a Winter Storm Watch due to the potential of
more than a quarter inch of ice for Allegany, Garrett
(especially eastern), and Mineral Counties. This is based on a
combination of NBM probabilities, QPF forecasts, and CAD
climatology. Interesting enough, if western Garrett stays warm
and sees mostly rain, we may have to monitor localized minor
hydro issues. It`s also possible places like Catoctin Mountain
could near a quarter inch of ice, but confidence/areal coverage
is expected to be much lower in these areas. We will evaluate
the need for advisories/warnings later today.
Link to comment
Share on other sites

I would say that it is going to rain, but now it appears that it’ll barely do that in the DC area.
We might be the worst city in the east in terms of getting bad weather. Our location is wretched

9a738fd26833275f48fa3cfabebb5cbf.jpg
Link to comment
Share on other sites

23 minutes ago, Weather Will said:

WB 6z EURO has backed off amounts even along the MD/PA border.  Everyone above freezing by 9am Friday.

DFD9DB85-8ED2-467C-85C1-96DDC3E824EF.png

708E7B13-163D-4AA0-946C-A499638E5D6E.png

Good. Honestly who wants bad icing? If we stay below 32 the entire event; that would have my attention. But the idea we get a warm nose way up into PA would generally mean any ice accumulation would eventually commence with its melting processes. 

Link to comment
Share on other sites

We’ve acknowledged we’re losing some marginal snow events (which is why our mean is falling) due to climate change. But I think that extends even more drastically to ice events. They are all marginal by nature, happening along a narrow scope of conditions where the boundary layer is just cold enough despite warmth above. And the boundary layer is the most affected by warning and especially warning due to increased UHI effects which extend well beyond metro areas now in a lesser but still real way. 
 

I’m not saying ice storms are impossible now but I think they are a lot harder to come by here than 20 years ago. I’ve seen a few setups Ute last 5 years that I thought synoptically should support icing that ended up 35 degree rain. 

  • Like 5
Link to comment
Share on other sites

1 hour ago, psuhoffman said:

We’ve acknowledged we’re losing some marginal snow events (which is why our mean is falling) due to climate change. But I think that extends even more drastically to ice events. They are all marginal by nature, happening along a narrow scope of conditions where the boundary layer is just cold enough despite warmth above. And the boundary layer is the most affected by warning and especially warning due to increased UHI effects which extend well beyond metro areas now in a lesser but still real way. 
 

I’m not saying ice storms are impossible now but I think they are a lot harder to come by here than 20 years ago. I’ve seen a few setups Ute last 5 years that I thought synoptically should support icing that ended up 35 degree rain. 

For sure..I think we need a pretty wild set up to get a significant ice storm particularly E of the blue ridge at this point, along PA line maybe being the exception

Link to comment
Share on other sites

9 minutes ago, Weather Will said:

WB 12Z 3K NAM:  this starts in the far west/southwest suburbs in the am and moves N and NE during the afternoon tomorrow.  Marginal temps low to mid 30s for most areas but everyone goes well above freezing after 9 am Friday.

97BC0FCF-7AF7-42A9-892A-FE9FD2989D26.png

C5F5A320-5C21-4298-8B75-610E722DE385.png

In my experience, one can divide the modeled freezing rain by 5 or 10, and it might verify.  I would love to be wrong and wake up to a legit ice storm.

Link to comment
Share on other sites

2 hours ago, psuhoffman said:

We’ve acknowledged we’re losing some marginal snow events (which is why our mean is falling) due to climate change. But I think that extends even more drastically to ice events. They are all marginal by nature, happening along a narrow scope of conditions where the boundary layer is just cold enough despite warmth above. And the boundary layer is the most affected by warning and especially warning due to increased UHI effects which extend well beyond metro areas now in a lesser but still real way. 
 

I’m not saying ice storms are impossible now but I think they are a lot harder to come by here than 20 years ago. I’ve seen a few setups Ute last 5 years that I thought synoptically should support icing that ended up 35 degree rain. 

yeah i honestly can't remember the last real ice storm I experienced.  there might've been one in NYC while I lived there - but as you say, climate change + the UHI makes them a real rarity (especially the UHI in Manhattan)

Link to comment
Share on other sites

Surface temps around the metro area tomorrow evening, and the precip totals won't be huge, but there is a pretty clear signal for a period of sleet or freezing rain for a lot of us.    Even if sfc temps warm up above freezing, there is a still a cold layer immediately above in pretty much all guidance for at least a few hours.

  • Like 4
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...