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January 20-22 “bring the mojo” winter storm threat


lilj4425
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13 minutes ago, eyewall said:

If anything the 18z GFS pushed the ZR a bit farther southeast and the main round of snow is in a much shorter period.

I think what I was looking at was onset through about Friday mid morning or so. The forecast sounding had a very slight and pesky warm nose around 750mb but it definitely does erode, as you mention, to favor snow later Friday until the end of the event. 

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GSP :D 

 

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 215 pm EST Tuesday: The pattern will get active once again
through the short-term period as a series of northern stream waves
dive southeast through the Great Lakes region Wednesday night into
Thursday and amplify a positively tilted trough from the Upper
Midwest to the central Plains. The trough will help to drive a moist
cold front into the southern Appalachians Wednesday night, which
will slip southeast of the area through Thursday. Anticipate mainly
liquid ptypes with the fropa, except at the higher peaks and
increasingly along the Tennessee border in brief, post fropa
northwest flow. Since the highest QPF over the western mountains
should be one-half inch or less, this should not be sufficient for
hydro issues to develop, even with some mountain snow melt.

It has become questionable how much of a lull will develop between
the cold fropa and redeveloping upglide over the stalling boundary.
A consensus is building that a sharpening upper jetlet may develop
along the southern Appalachians Thursday night through Friday. The
amplifying upstream trough will be potent, but now appears less
likely to cut off west of the Appalachians and more likely to get
picked up by the northern stream. The main uncertainty during the
Thursday night to Friday period is how vigorous any surface waves
become along the stalled boundary draped to our southeast. The ECM
has stronger development and pulls more moisture, and thereby QPF,
over the region Friday, while the GFS has a more muted response. The
ECMWF has trended slightly toward the GFS, but the GEFS ensembles
have plenty of snowy members still. Will use an ensemble approach to
profiles and keep mainly snow across the region, but with a snow,
sleet, and freezing rain mention for the southeast third. This will
be introduced into the HWO. Temps will be shaded below guidance as
cold air damming develops Friday from 1040 mb high pressure over New
England. The wintry precipitation will continue into the early
extended period.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 225 pm EST Tuesday: Wintry precipitation may well be ongoing
in the forecast area Friday night as surface wave development
continues along a frontal zone stalled near the coast. Profiles look
cold overall, but with any warm nose energy aloft likely affecting
locations southeast of I-85 where QPF may be better. It increasingly
appears that the best overlap of cold, snow-supporting profiles and
decent QPF will be over the northwest NC Piedmont Friday night into
Saturday morning. And, any ice accumulations will be more likely
over the southeast Piedmont. However, considerable uncertainty
exists with this system and it remains too early to feature any
Watch products. The wintry potential will be addressed in the HWO,
and first cut accumulations will likely be advertised on Wednesday
for the entire late week period.

The system should pull away to the northeast later Saturday, but
reinforcing energy digging into the eastern CONUS trough will
amplify the pattern to keep cold air over the region through the
rest of the weekend and into early next week. There is some
potential for clipper-type waves to dig into the trough and bring
scattered snow showers to the NC mountains periodically, but this
will be very hard to time. Temperatures remain below climatology
well into next week.
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Couple thoughts on the potential phasing: It seems like the 18z models diverge on whether or not the baja low gets left behind around hr 60-66.  Are we to believe the NAM/RGEM at hour 60 or the GFS/ICON?

For the 00z runs tonight, we will be at hour 54 of the divergence... have to think that close to it happening, we will get some resolution. 

FWIW, the 12z Ukmet was actually similar looking to the 18z NAM at 5h with the phasing, just not as strong, and I  think the ukmet has a dry bias as well on the n/w side of a precip shield.

 

 

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Couple thoughts on the potential phasing: It seems like the 18z models diverge on whether or not the baja low gets left behind around hr 60-66.  Are we to believe the NAM/RGEM at hour 60 or the GFS/ICON?
For the 00z runs tonight, we will be at hour 54 of the divergence... have to think that close to it happening, we will get some resolution. 
FWIW, the 12z Ukmet was actually similar looking to the 18z NAM at 5h with the phasing, just not as strong, and I  think the ukmet has a dry bias as well on the n/w side of a precip shield.
 
 
yeah, 6z tomorrow puts us in range of the 3k NAM

Sent from my SM-S115DL using Tapatalk

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