January 5-6 Thing II: STORM MODE

[high risk]

1 minute ago, psuhoffman said:

Wrt NAM, I often toss is, it’s way to jumpy and prone to wild tangents. But it does sometimes pick up on a mid level warm push that can lead to a north shift on this type of setup and it’s not often this locked in and when it is sometimes it’s onto something. But not always. 

         The NAM tends to do funky things with placement of coastal lows and such, but once it has the synoptics nailed, there is no better model for identifying warm layers in warm advection events and dry slots.     The question, though, is whether it has nailed the synoptic details for this system.    It's probably slightly early to think with confidence that it has, but it shouldn't be immediately tossed onto the garbage heap.    The 3km version, though, is FAR superior to the 12 km.

[Maestrobjwa]

1 minute ago, Solution Man said:

Icon(I know it’s the Icon), it’s coming in hot, meaning heavy snow 

Oooh nice wraparound too 

[nj2va]

I don’t think RGEM is budging from favoring CVA (near EZF) with the heaviest rates.

ETA:  Looks like its cutting totals to the north (M/D) and upping totals in the south (RIC).

[clskinsfan]

Yeah. ICON way better. Ticked north just a touch. baby steps. 

[yoda]

18z ICON, FWIW, is all snow DC metro 

[Terpeast]

According to LWX WSW, it looks like they are banking on a warm nose up to and along i-66 and maybe a bit north of that. Still calling for 5-9” locally up to 12”

[clskinsfan]

[Weather Will]

WB 18Z ICON precip shield did tick north, compared to 12Z.

[weathercoins]

18z ICON has some really nice stuff in DC at 39 hours.  Still south of others but a tad more north than it’s been I think

[TSSN+]

Models keep swinging. Icon north, Nam little north, rgem south. 
 

 

[notvirga!]

Icon nearly doubled the snow output for Baltimore county. 

[Interstate]

9 minutes ago, yoda said:

URGENT - WINTER WEATHER MESSAGE
National Weather Service Baltimore MD/Washington DC
354 PM EST Sat Jan 4 2025

MDZ003>006-008-011-505>508-050500-
/O.CON.KLWX.WS.A.0002.250106T0300Z-250107T0600Z/
Washington-Frederick MD-Carroll-Northern Baltimore-Cecil-Southern
Baltimore-Northwest Howard-Central and Southeast Howard-Northwest
Harford-Southeast Harford-
354 PM EST Sat Jan 4 2025

...WINTER STORM WATCH REMAINS IN EFFECT FROM SUNDAY EVENING THROUGH
LATE MONDAY NIGHT...

* WHAT...Heavy snow possible. Total snow and sleet accumulations of
  5 inches or greater and ice accumulations up to one tenth of an
  inch possible. A localized band with up to 10 inches of snow is
  possible if heavy banding sets up this far north.

* WHERE...Portions of central, north central, northeast, and
  northern Maryland.

* WHEN...From Sunday evening through late Monday night.

* IMPACTS...Travel could be very difficult. The hazardous conditions
  could impact the Monday morning and evening commutes.

Yep LWX is still weary of the southern track to  make the call to a WSW for the Northern tier of counties in MD.

[jayyy]

ICON came in more in line with the NAM RAP HRRR GFS for sure. Not a huge bump north, but certainly noticeable for central MD

[nj2va]

Crazy how solutions are still diverging.   RGEM heads south.  A really great run for EZF.

[LeesburgWx]

You would think this is 2002 with these model swings. Crazy they are wavering so much being so close in now

[konksw]

Feels to me that if things are generally bookending a specific area the spot in the middle is the best bet. 

[MN Transplant]

4 minutes ago, nj2va said:

Crazy how solutions are still diverging.   RGEM heads south.  A really great run for EZF.

 

Is it that they are diverging, or are the NAM/GFS just on an island with the north solution? 

[Ellinwood]

Final forecast as I will be too busy to work on it tomorrow. Shifted everything a bit south overall, especially east of the Appalachians. Still not buying huge snow totals on the south side given the mixing issues.

[wawarriors4]

6 minutes ago, nj2va said:

Crazy how solutions are still diverging.   RGEM heads south.  A really great run for EZF.

It is a good run for EZF. The Nam for EZF with its hole was comical. I really do like the 5-8”+ with some ice on top as a forecast around FXBG from NWS LWX.

[stormtracker]

2 minutes ago, Solution Man said:

Heart of the batting order coming up, where’s @stormtracker?

Here.  Had to do a dinner run.  Grilling later.  But Loading up the GFS and ready.   Just kinda wild how the model spray is still going on this close to the event.  The NAM warm layer is kinda frustrating me a bit.  Not sold on it and it's still outside the useful range, but NAM does sniff these thermal issues out rather well sometimes.

[das]

26 minutes ago, StormyClearweather said:

NWS Blend

Looks solid. Although, the max in MoCo being mid-County vs. Parrs Ridge rarely verifies. 1 in 10 times, maybe. The upglide on any low level flow with any easterly component is real. 

[yoda]

Well written afternoon AFD from LWX (408 pm) about the event and the uncertainty 

SHORT TERM /SUNDAY EVENING THROUGH MONDAY NIGHT/...
Tomorrow evening, attention turns to a system approaching from the
west. A closed upper low and associated surface low will track
eastward from the Central Plains toward the Mid-Mississippi Valley
during the day tomorrow, through the Ohio Valley tomorrow night into
Monday, and then overhead Monday night.

Warm advection aloft well in advance of the low will start to
overrun very cold air in place at low-levels tomorrow evening.
Precipitation will break out in association with that warm advection
driven ascent, and then gradually spread northeastward over the
course of the night. Onset times of precipitation are expected to be
around 6-9 PM in the Alleghenies, central Shenandoah Valley, and
central Virginia, 9PM-midnight in the northern Shenandoah Valley,
DC/Baltimore Metros, and southern Maryland, and after midnight in
far northeast Maryland. Precipitation will be all snow at onset, and
should pick up in intensity fairly quickly. The strongest push of
warm advection/frontogenetic forcing is expected to move through
during the second half of the night, leading to the heaviest
precipitation rates. Snowfall rates may reach 1-2 inches per hour
for a time late Sunday night where the heaviest bands set up. This
time period with heavier precipitation rates will linger a bit into
Monday morning, with precipitation becoming lighter late Monday
morning through Monday afternoon as the strength of the low-level
warm advection weakens a bit. The system`s upper level low will move
overhead Monday night, potentially leading to a secondary burst of
briefly moderate to locally heavy snow. Precipitation will than wind
down during the late evening/overnight hours.

At this juncture, there is a bimodal distribution in model guidance
with respect to the track of the system and resultant precipitation
amounts/types. The GFS/NAM, and the CAMs that are driven by GFS/NAM
lateral boundary conditions (HRRR/FV3/3km NAM/WRF-ARW/WRF-NSSL) are
further north with QPF axis, and would bring significant, warning
level amounts of precipitation to the entire forecast area.
Individual members within that camp differ with respect to how far
north a warm nose aloft would make it. The HRRR and NAM-Nest
illustrate that spread with respect to the handling of the warm
nose. The 12 and 18z HRRR keep nearly all of the CWA snow for the
entire event, while the NAM-Nest works the warm nose northward to
roughly I-66/US-50. In the example of the NAM-Nest, locations north
of I-66/US-50 would get warning level snowfall (likely in excess of
6 inches), while locations further south would get a few inches of
snow, and then sleet and freezing rain on top of that (resulting in
warning level impacts). In the HRRR scenario, the entirety of the
forecast area would receive warning level snow, with some locations
even closing in on a foot of snow.

The other half of the bimodal distribution is global models from
international modeling suites (the Euro, Canadian, UKMET, and ICON).
These models have the QPF max suppressed further to the south,
placing it across central Virginia to southern Maryland. In this
scenario, locations north of I-66/US-50, and especially north of I-
70 would receive reduced amounts of precipitation, resulting in
advisory level snowfall, while locations further south across
central VA to southern Maryland would receive warning level snowfall
(potentially even closing in on a foot of snow), along with some
minimal mixing with sleet or freezing rain.

Since all of the above scenarios provide warning level impacts
(whether it be from all snow or a mix of snow and sleet/freezing
rain) from the I-66/US-50 corridor southward, confidence was high
enough to upgrade the Winter Storm Watch to a Winter Storm Warning.
Further north (across northern Maryland and portions of the WV
Panhandle), the Winter Storm Watch was left in place to account for
uncertainty in QPF amounts, since snow in those locations could be
either advisory level (2-5"), or warning level (5+") depending on
which solution verifies. This area will continue to evaluated, with
decisions on advisory versus warning likely being made overnight
after 00z guidance is available.

 

[yoda]

And LWX DOES mention the ICON btw

[Newman]

Only looking 36hrs out into the Ohio Valley, we're talking QPF differences of 1-2" in some locations between the HRRR (long-range, I know), the NAM, and the RGEM. The NAM and RGEM being drastically different arises from their depiction of the mid-level vort sliding through, of which the NAM is much more potent and neutrally tilted to allow for a healthy PVA regime, the RGEM is simply flatter and less robust. Looking at H5 trends between the two, it seems they are converging closer together without an all-out "fold" of one model to the other. I suppose we'll see, the Sterling NWS AFD is excellent if you haven't checked it out. Also to note... there are some timing differences to make note of, but not *that* large between these models to expect such huge differences

[TSSN+]

5 minutes ago, Newman said:

Only looking 36hrs out into the Ohio Valley, we're talking QPF differences of 1-2" in some locations between the HRRR (long-range, I know), the NAM, and the RGEM. The NAM and RGEM being drastically different arises from their depiction of the mid-level vort sliding through, of which the NAM is much more potent and neutrally tilted to allow for a healthy PVA regime, the RGEM is simply flatter and less robust. Looking at H5 trends between the two, it seems they are converging closer together without an all-out "fold" of one model to the other. I suppose we'll see, the Sterling NWS AFD is excellent if you haven't checked it out. Also to note... there are some timing differences to make note of, but not *that* large between these models to expect such huge differences

Literally 12-24hrs away from starting there that’s wild. 

[wxmvpete]

11 minutes ago, yoda said:

Well written afternoon AFD from LWX (408 pm) about the event and the uncertainty 

SHORT TERM /SUNDAY EVENING THROUGH MONDAY NIGHT/...
Tomorrow evening, attention turns to a system approaching from the
west. A closed upper low and associated surface low will track
eastward from the Central Plains toward the Mid-Mississippi Valley
during the day tomorrow, through the Ohio Valley tomorrow night into
Monday, and then overhead Monday night.

Warm advection aloft well in advance of the low will start to
overrun very cold air in place at low-levels tomorrow evening.
Precipitation will break out in association with that warm advection
driven ascent, and then gradually spread northeastward over the
course of the night. Onset times of precipitation are expected to be
around 6-9 PM in the Alleghenies, central Shenandoah Valley, and
central Virginia, 9PM-midnight in the northern Shenandoah Valley,
DC/Baltimore Metros, and southern Maryland, and after midnight in
far northeast Maryland. Precipitation will be all snow at onset, and
should pick up in intensity fairly quickly. The strongest push of
warm advection/frontogenetic forcing is expected to move through
during the second half of the night, leading to the heaviest
precipitation rates. Snowfall rates may reach 1-2 inches per hour
for a time late Sunday night where the heaviest bands set up. This
time period with heavier precipitation rates will linger a bit into
Monday morning, with precipitation becoming lighter late Monday
morning through Monday afternoon as the strength of the low-level
warm advection weakens a bit. The system`s upper level low will move
overhead Monday night, potentially leading to a secondary burst of
briefly moderate to locally heavy snow. Precipitation will than wind
down during the late evening/overnight hours.

At this juncture, there is a bimodal distribution in model guidance
with respect to the track of the system and resultant precipitation
amounts/types. The GFS/NAM, and the CAMs that are driven by GFS/NAM
lateral boundary conditions (HRRR/FV3/3km NAM/WRF-ARW/WRF-NSSL) are
further north with QPF axis, and would bring significant, warning
level amounts of precipitation to the entire forecast area.
Individual members within that camp differ with respect to how far
north a warm nose aloft would make it. The HRRR and NAM-Nest
illustrate that spread with respect to the handling of the warm
nose. The 12 and 18z HRRR keep nearly all of the CWA snow for the
entire event, while the NAM-Nest works the warm nose northward to
roughly I-66/US-50. In the example of the NAM-Nest, locations north
of I-66/US-50 would get warning level snowfall (likely in excess of
6 inches), while locations further south would get a few inches of
snow, and then sleet and freezing rain on top of that (resulting in
warning level impacts). In the HRRR scenario, the entirety of the
forecast area would receive warning level snow, with some locations
even closing in on a foot of snow.

The other half of the bimodal distribution is global models from
international modeling suites (the Euro, Canadian, UKMET, and ICON).
These models have the QPF max suppressed further to the south,
placing it across central Virginia to southern Maryland. In this
scenario, locations north of I-66/US-50, and especially north of I-
70 would receive reduced amounts of precipitation, resulting in
advisory level snowfall, while locations further south across
central VA to southern Maryland would receive warning level snowfall
(potentially even closing in on a foot of snow), along with some
minimal mixing with sleet or freezing rain.

Since all of the above scenarios provide warning level impacts
(whether it be from all snow or a mix of snow and sleet/freezing
rain) from the I-66/US-50 corridor southward, confidence was high
enough to upgrade the Winter Storm Watch to a Winter Storm Warning.
Further north (across northern Maryland and portions of the WV
Panhandle), the Winter Storm Watch was left in place to account for
uncertainty in QPF amounts, since snow in those locations could be
either advisory level (2-5"), or warning level (5+") depending on
which solution verifies. This area will continue to evaluated, with
decisions on advisory versus warning likely being made overnight
after 00z guidance is available.

 

That's an excellent breakdown of why they felt more confident on warnings for southern/central zones and maintaining watches for the northern zones. Well done, LWX!

[clskinsfan]

2 minutes ago, wxmvpete said:

That's an excellent breakdown of why they felt more confident on warnings for southern/central zones and maintaining watches for the northern zones. Well done, LWX!

Whoever wrote it is very good at hitting on the science, for us weenies that want it, while making it easily readable for the general public. Excellent write up. 

[Wetbulbs88]

20 minutes ago, Ellinwood said:

Final forecast as I will be too busy to work on it tomorrow. Shifted everything a bit south overall, especially east of the Appalachians. Still not buying huge snow totals on the south side given the mixing issues.

This seems far too north and wide given recent guidance. I don't think any model shows more than 4" above M-D Line. 

Points for being independent-minded. Hope this pans out!

[SnowenOutThere]

GFS is out and running. No real change through hour 18 besides maybe a bit more confluence and a tinny bit stronger low

 

[LP08]

Heights a little lower out front through 24.