GaWx

I see the 1/2” of ZR on WB Euro. However, I recently posted that the WB Euro algos for ZR vs IP appear to be off in that it has too much ZR at the expense of IP. In S Franklin Cty in case you didn’t see this, the 925s never get above -3C and the 850s never rise above +2C. That imo would mean little ZR RDU/Franklin Cty and 1.5-2” more IP than what’s on the Euro output.

GEPS (2/22-3):

This next SW is mildly interesting on the 12Z Euro as at face value it is a close call for a light wintry event here and nearby (coastal SE) with the low going across S FL in combo with lingering Arctic air to the N: EPS has a decent Miller A storm signal:

The WB Euro algos for ZR vs IP appear to me to be too tilted to ZR and too little for IP. Note that the GFS and CMC on WB both tend to have more IP than Euro. Looking at the 12Z Euro qpf/850s, it has for RDU ~10 times as much qpf as ZR vs IP. But that’s despite highest 850’s staying near +1C and warmest 925s being -3C! I believe that if the algos were corrected that nearly all of the ZR at RDU is really IP. Thus the Euro’s sleet map showing 0.2” should imo be ~2.2” of sleet to go along with the 4.1” of Kuch snow meaning 6.3” of snow/IP with almost no ZR at RDU.

12Z Euro

YW. Total UK RDU qpf 1.5”. Of this ~0.1” is snow, ~0.1” is sleet, ~1.1” is ZR (ouch), and 0.2” is rain.

Based on 850s, RDU gets ~1” of snow in the first few hours. But then it changes to a short period of sleet followed by a long period of ZR with even a short period of rain at the very end (33F).

I’m checking this link’s worst icestorms for the E Piedmont and am looking for wx maps to see: http://americanlifelinesalliance.com/pdf/IceStormSummaries.pdf Per this link, 2/13-15/1960 was worst icestorm in 33 years in much of NC. Here is a link to the 2/12-14/60 wx maps, suggesting a Miller A: https://library.oarcloud.noaa.gov/swm.docs.lib/1960/19600212.pdf https://library.oarcloud.noaa.gov/swm.docs.lib/1960/19600213.pdf https://library.oarcloud.noaa.gov/swm.docs.lib/1960/19600214.pdf Per this snow map from Webb, it also was a big snow producer for much of NC, with 3.7-5” in RDU area:

Yep. 850s are +2 or lower for 3/4 of the qpf keeping ZR much lower than GFS; total qpf ~0.95” CMC, similar to gfs but much less than 1.65” of icon

With 850s at +4 for the majority of the qpf on the 12Z GFS, mainly ZR at RDU would agree with the past….if those 850s were to verify.

12Z GFS:

From what I experienced in ATL and SAV (and confirmed by what I’ve studied), the conversion of ZR to accrual on branches/bushes approached 50% under ideal accrual conditions (winds not too strong, rain not too heavy, temps not right at 32, etc).

I think that’s conservative at this point per model consensus, which suggests at least ~twice that much accretion is quite possible. But a long ways to go.

That (12Z Icon) could mean ~0.7” of ice accretion on trees in RDU, a huge problem that would be similar to 2002. It takes only 0.5” of accretion for widespread power outages:

12Z Icon for RDU suggests ~0.1” qpf of snow, ~0.2” qpf of sleet, and ~1.35” of ZR. Temps get to as low as 27F at end of ZR.

The preliminary AO for today per CPC is -5.26, well predicted. This would compare to the alltime record -AO for Feb, -5.29 (2/5/1978).

I’ve found based on analysis of 850s for SE winter storms going back many decades that +1 to +2 850s tend to be sweet spot for sleet and +3 to +5+ tends to be sweet spot for ZR.

That’s the point. 2002 was Miller B/quite different. Miller A (upcoming storm) typically not as associated with major ice. But model consensus still shows a lot of ZR. Maybe that will change.

For comparison, here are the sfc maps for Dec of 2002 Miller B major icestorm for NC:

The 18Z Euro AI is similarly quite suppressed to the 12Z.

18Z GFS:

It did very well for the early Jan 2018 historic coastal SE winter storm. I remember it clearly as I was following it extra closely for obvious reasons. It was the first global to move the offshore low NNE instead of NE, which resulted in much higher qpf on the coast and that verified. So, this was at least an exception.

18Z Icon 120 850 0C line further SE than 12Z Icon 126 in NC/NW SC/N GA (toward the 12Z Euro AI):

12Z Euro AI way colder/further SE 850 0C line than other models (hour 126, which is as of 18Z on Feb 19th): Fayetteville to Gainesville: 12Z Euro op: N of RDU to TN 12Z GFS: S VA to TN 12Z CMC: S VA to TN 12Z Icon: S VA to TN

0Z GEFS (see below) and other models remain insistent on a rare sub -5 AO tomorrow. Today’s preliminary is already down to -4.8. There have been only 12 such periods since 1950 (average of once every 6 years). In Feb, itself, there’s only been 4 periods of sub -5 (one every 15 Febs on average): -2/10-11/2021 (only La Niña Feb instance): major GSO icestorm 2 days later -2/6-7, 14/2010 (El Nino): 2 SE US winter storms (2/5, 2/12-13) -2/5-6/1978 (El Nino): several SE light snows 2/2-9 -2/13-16/1969 (El Nino): major winter storm 2/15-17 Charlotte to Asheville to GSP Today’s 0Z GEFS based AO forecast: