high risk
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Everything posted by high risk
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more for damaging wind, as wind profiles are strong but somewhat unidirectional. Still, there is perhaps enough low-level backing of winds closer to the sfc flow to make it so that an isolated tornado cannot be ruled out. Instability is limited (which prevents a more robust threat), but low-level lapse rates will be good. Forecasts like these intrigue me.....
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Seems like a pretty good shot that northern VA, eastern WV, western MD, and south-central PA will get a MRGL risk for severe Friday, with an outside chance of an eventual SLGT.
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The isothermal profile surprises me, as the models have shown a pretty significant low-level inversion. That could certainly up the threat of stronger overnight surface gusts. 11pm: 60 at DCA, 57 at BWI, and 55 at IAD.
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Definitely think we have some thunder potential overnight, but I haven't seen any forecast sounding with surface-based instability. So, while there will be strong winds just above the surface, it seems like the chances of them mixing down are low. I'm still more intrigued by the late afternoon/early evening time period Friday when we'll have modest but surface-based instability.
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NAM nest shows a dramatic warm frontal passage, with low 40s for DC metro at 8pm and near 60 by midnight.
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There definitely does appear to be a window of opportunity west and northwest of DC Friday afternoon. Instability is limited, but there is some cape, and lapse rates will steepen as the colder temps aloft arrive. The shear is outstanding, and there will be forcing along the arriving front.
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Thunder definitely seems to be on the table for most of the area Thursday night and for points east on Friday. Good elevated instability early Friday:
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The mageval.ncep.noaa.gov is the site for parallel versions of models. If you click on GFS, you get the parallel GFS, which is the FV3GFS. If you don't believe me, check out the 12z 'GFS' on mageval and compare it to the TT FV3GFS plots.
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go ahead and check for yourself. It's clearly listed as the 18z run on 12/4. It clearly ran, and that's the NCEP site which can plot it directly from the files on the supercomputer. There is clearly some issue with the other sites that have to download the data.
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18z FV3GFS (per mageval.ncep.noaa.gov) took a bit of a step back. 0.5" liquid line stays well south in VA, with the DC area on the northern edge.
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Ummm, Sunday looks dry and overall a pretty nice day.
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00z GFS taking a big step towards the idea of at least a close call on Tuesday
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ha! There is no way (in terms of manpower and computer resources) to do the complete set of retrospective testing and evaluation that needs to be done (much of the past 3 years were rerun with the FV3GFS and assessed as part of the validation) for both the GFS and GEFS systems concurrently.
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correct. There will be no change to the GEFS when the FV3GFS replaces the GFS in operations.
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Yes, but it will not be concurrent with the switch of the GFS to the FV3 core. The GEFS upgrade to FV3 is still over a year away.
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This event is our reminder to always toss GFS thermal profiles in cold air damming situations.
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It's worth noting that the HRRR has rain at the start and then transitioning quickly to sleet and then snow, with a heavier burst of snow around 10AM. NAM nest is similar, with an initial period of rain and sleet, followed by some heavier snow, also around 10AM.
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18z 12km NAM still has the 2m freezing line running right through the District at noon Thursday.
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The precip type is computed off of the thermodynamic profiles; the water equivalent of snow (+sleet) is from the model microphysics. That's how that can differ. And this is clearly a case when the 10:1 ratios won't come close to working.
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I really have a hard time accepting the GFS having most of the DC and Baltimore metro areas in the mid 30s tomorrow at 12z. I think we've seen plenty of winter precipitation cases in which the GFS has failed to properly model evaporative cooling and then eroded low-level cold air too quickly. While the NAMs can hold on to low-level cold air a little too long, their track record in this kind of setup is superior. I'm not calling for an OMG snow here in the I-95 corridor, but a few hours of snow and then sleet (and perhaps a longer period for the next tier of counties north and west) is still very much on the table, IMO.
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Significant ice storm near the cities? That's going to be extremely difficult to accomplish given the very warm antecedent ground/road temperatures.
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The problem is that the hi-res guidance is now in good agreement that the line clears most of the area by midday, and there is limited opportunity for the atmosphere to destabilize in advance, especially from DC and points north. Chances are better for southern MD and points further east and south, where guidance shows either more warm advection ahead of the line or a later arrival of storms allowing more heating to occur. That said, shear in the local area will be strong, so if instability ends up larger than currently progged, we could certainly have a greater threat, including TORs.
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reports of significant damage in Mt Airy. New tornado warning in southern MD.
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MD issued by SPC. Watch possible as the strengthening line to the west approaches.
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great question. The issue may not be the amount of total cape, but the distribution of it. I think in these low instability/high shear events, you can work with 500 or so, but there needs to be some instability just above the sfc. Tall, skinny cape usually doesn't get it done. That forecast sounding has lousy low-level lapse rates and likely would not get the job done, assuming it's correct. History says that these low instability/high shear events rarely work out here, but there are exceptions.
