December Forecast Discussion

[Snowless in Carrollton]

time for the mid-south/tn folks to take over the board...... for east coasters this one is over

Hopefully it's not over for the Deep South too.

[bjohnson102184]

While I agree on the details AND geography part..............this is the second EURO solution in a row, with support from other operationals and ensembles so I believe models are beginning to zero in on a "legitimate" solution. Sure models will shift - but this is in the EURO's wheelhouse......at 144. Time will tell.

Euros wheelhouse is 7-9 days....euro ensemble 5-7 and what model supports the euro op I must have missed them?

GFS/GEFS/CMC vs euro ?

[BNAwx]

100 miles will make a huge difference is all I mean...if you are in BNA in the wheel house right now, you might be PO'd if you just got a little glop in the aftermath....

I can never get too excited until I see it falling from the sky around here. I've been under a "Heavy Snow Warning" before when an un-forecasted warm tongue of air magically rode straight up I-65 only to give me rain and back-end light snow. Seen multiple upper level lows pound areas all around me while I get a dusting to an inch. Murphy's law applies around these parts.....

[jburns]

Some people don't know their geography super well...However, it really is too early for details...

But its not to early in his career to get these type "details" correct.

[Mr Bob]

I can never get too excited until I see it falling from the sky around here. I've been under a "Heavy Snow Warning" before when an un-forecasted warm tongue of air magically rode straight up I-65 only to give me rain and back-end light snow. Seen multiple upper level lows pound areas all around me while I get a dusting to an inch. Murphy's law applies around these parts.....

The 2000s have been rife with these types of misses all over the TN Valley...I know exactly what you mean...it is always nicer to have the classic set up with the cold air in place a la Jan 2011...I never trust these events until I see it falling...

[tonysc]

Very well put. The details are only of entertainment value. However, when looking at the general pattern, keep in mind that the last four runs of the GFS have a somewhat similar scenario of a Pacific storm diving SSE in the eastern Pacific in about a week and subsequently turning eastward, picking up lots of Gulf moisture while moving into the SE ~1/1 along the southern boundary of Arctic air, which is forced down by impressive blocking to the north. So, the general idea of some sort of SE winter storm threat for around 1/1 may already have merit. Also helping: the just released 12Z GEFS concurs with this general idea with lots of Pacific/Gulf moisture moving eastward across the SE along the southern boundary of Arctic air near 1/1. Even it has ~1" of QPF falling within a day or two of 1/1 for many areas. The last four GEFS means have something similar.

Speaking of dreaming, the 12Z GFS puts down 0.87" of liquid equivalent in the form of pure snow at KATL 1/1-2! Once the snow starts early on 1/1, KATL falls to below 32 and pretty much doesn't get back above it through the end of the run (7 AM on 1/5)...96 straight subfreezing hours. Over a deep snowcover, it gets down to 12 F 1/3 AM! A second small snow falls early on 1/5 due to a 2nd/weaker Miller A! This is the winter wx dream of a lifetime for me. Who knows when this good of a dream will come along again?

Now that just warms the cockels of my heart

[Spidyr2k]

...I never trust these events until I see it falling...

Words to live by for most of us in the SE, especially in Dec. +1

[franklin NCwx]

For all the Tenn folks here is the Euro ensemble mean for next wed. It seems to be the on the western edge of the guidance. Looks to be a good hit for Nashville.

[burgertime]

For all the Tenn folks here is the Euro ensemble mean for next wed. It seems to be the on the western edge of the guidance. Looks to be a good hit for Nashville.

Not out yet on AccuPro....I think Bob has access to SV's ENS maps for the Euro? He might be able to help you out. Typically I see them around 4:30 on AccuPro.

[Wow]

Euro ENS definitely on board with a split flow pattern beginning the new year

[franklin NCwx]

Not out yet on AccuPro....I think Bob has access to SV's ENS maps for the Euro? He might be able to help you out. Typically I see them around 4:30 on AccuPro.

Do you get 6 hour intervals?

[GaWx]

Folks,

The 12Z Euro ensemble mean is quite encouraging regarding any potential SE winter storm threat for ~1/1. Why? First of all,it, like the 0Z run, gives the SE some really good moisture 12/31-1/2 with 0.75-1" of QPF for many inland areas as the system traverses the SE (same timing as GFS suite). Secondly, it is ~ 2C colder at 850 mb than the 0Z Euro ensemble mean due to a stronger Arctic high to the north. The 0C 850 line on the 0Z mean was up into S KY and S VA during much of the precip. The 12Z run has the 0C line about 200 miles further south (S TN/S NC) implying at least a close call to wintry precip. for many inland areas. Even if it isn't cold enough for snow, it would appear that there could be ZR/IP, especially if there is some wedging.

[Wow]

Folks,

The 12Z Euro ensemble mean is quite encouraging regarding any potential SE winter storm threat for ~1/1. Why? First of all,it, like the 0Z run, gives the SE some really good moisture 12/31-1/2 with 0.75-1" of QPF for many inland areas as the system traverses the SE (same timing as GFS suite). Secondly, it is ~ 2C colder at 850 mb than the 0Z Euro ensemble mean due to a stronger Arctic high to the north. The 0C 850 line on the 0Z mean was up into S KY and S VA during much of the precip. The 12Z run has the 0C line about 200 miles further south (S TN/S NC) implying at least a close call to wintry precip. for many inland areas.

Don't forget Lucy!

[burgertime]

Do you get 6 hour intervals?

Yep it comes in 6 hour intervals. By the way snowfall on the Euro has a one inch swatch across northern LA most of MS, northern AL, NW GA and all of TN with Nashville area with around 2 - 3 inches.

[GaWx]

Don't forget Lucy!

Lol, don't worry...I NEVER forget Lucy! So, I'm still taking with a grain and know it can all disappear tomorrow. However, this is the first time this season I've seen anything like this setup suggesting actual Miller A'ish winter storm potential fairly consistently in the model consensus.....and actually the first in two years since there were zero modeled threats anything like this last winter. This just tells me that if everything just happens to line up just right, we could get a winter storm around 1/1. The odds are low this far out (~12 days), but I'm merely talking potential. Also, climo does improve some as we approach Jan.

[appstate00]

Already snowing at Snowshoe, WV

http://snowshoemtnweather.com/

[valkhorn]

Interesting discussion out of MRX this afternoon.

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE MORRISTOWN TN

252 PM EST THU DEC 20 2012

.SHORT TERM (TONIGHT THROUGH FRIDAY NIGHT)...STRONG SURFACE LOW

PRESSURE SYSTEM WILL MOVE NE INTO MI TONIGHT AND ENE THROUGH THE E

GREAT LAKES ON FRIDAY. COLD FRONT BOWING THROUGH THE E TN VALLEY

WILL MOVE THROUGH THE SOUTHERN APPALACHIANS TONIGHT. PREFRONTAL

DOWNSLOPING WINDS WILL END AS WINDS SHIFT SW BEHIND THE FRONT. AREAS

OF PRECIPITATION WILL TAPER OFF BEHIND THE FRONT. WINDS WILL SHIFT

TO THE NW THIS EVENING AND REMAIN BREEZY AND BECOME STRONG OF

FRIDAY. NEAR POST FRONTAL RELATIVE HUMIDITY REMAINS SHALLOW WHILE

COLD AIR ADVECTION IS STRONG. LIGHT SHOWERS AND DRIZZLE WILL CONTINUE

IN CYCLONIC FLOW ESPECIALLY ACROSS THE NORTHERN PART OF MRX CWA.

FREEZING LEVEL FALLS HARD AFTER 21/00Z. THE LIGHT PRECIPITATION WILL

LIKELY SHIFT BRIEFLY TO FREEZING DRIZZLE AS DEPTH OF RH DOES NOT

EXTEND INTO THE SNOW GROWTH REGION. WRAP AROUND MOISTURE MOVES INTO

THE AREA AFTER 21/06Z WITH HIGHER RH EXTENDING UP INTO THE SNOW

GROWTH REGION CONTINUING INTO MID DAY FRI. THIS WILL ALLOW FOR SOME

LIGHT SNOWFALL ACROSS NE TN/SW VA. TEMPERATURES WILL FALL INTO THE

20S TONIGHT. STRONG NORTHWEST WINDS WILL KEEP WIND CHILL VALUES

BELOW FREEZING FRIDAY. A WIND ADVISORY WILL BE REQUIRED AREAWIDE

WITH AN ADDITION WARNING POSSIBLE ACROSS THE HIGHER ELEVATIONS.

LIGHT SNOW AND CLOUDS CONTINUE TO SCOUR OUT FRIDAY NIGHT WHILE

TEMPERATURES CONTINUE TO FALL TO BELOW NORMAL WITH WIND CHILLS

RANGING FROM THE SINGLE DIGITS TO THE TEENS.

.LONG TERM...(SATURDAY THROUGH THURSDAY)...AN ACTIVE EXTENDED

FORECAST. A BREAK PERIOD OF SURFACE AND UPPER RIDGING WILL PRODUCE

DRY CONDITIONS FOR SATURDAY AND SUNDAY...BUT A DEVELOPING SOUTHERN

STREAM SHORT-WAVE WILL INDUCE CYCLOGENESIS OVER THE SOUTHERN PLAINS

BY SUNDAY NIGHT AND MONDAY. THIS WAVE WILL HELP PULL A FRONT NORTH

ACROSS THE TENNESSEE VALLEY FOR MONDAY. INCREASING ISENTROPIC LIFT

AHEAD OF A FRONTAL BOUNDARY WEST OF THE AREA WILL SPREAD RAIN OVER

THE AREA. THERE IS A CHANCE THAT PRECIPITATION MAY BEGIN AS

SNOW/SLEET OR FREEZING RAIN ACROSS THE NORTHEAST SECTIONS OF THE

FORECAST AREA.

THIS BOUNDARY WILL PULL SLOWLY EAST ACROSS THE AREA TUESDAY...BUT

ANOTHER NORTHERN AND SOUTHERN STREAMS WAVES WILL PHASE OVER THE

SOUTHERN PLAINS TUESDAY. THIS SYSTEM WILL PULL NORTHEAST TOWARD THE

SOUTHERN APPALACHIANS FOR TUESDAY NIGHT AND WEDNESDAY. GFS AND ECMWF

HAVE DIFFERENT TRACKS OF THE SURFACE LOW. GFS BRINGS THE LOW OVER

EAST TENNESSEE...WHILE THE ECMWF IS SLIGHTLY FARTHER EAST. EITHER

WAY..MODELS SHOW STRONG DYNAMICS OVER THE AREA WEDNESDAY AND

WEDNESDAY NIGHT WITH NORTHWEST FLOW OROGRAPHIC LIFT FOR THURSDAY AND

FRIDAY.

DEPENDING ON LOCATION OF BEST FRONTO-GENESIS...THERE IS A POTENTIAL

OF HEAVY RAINS WEDNESDAY AND WEDNESDAY NIGHT. ALSO...DEPENDING ON

EVOLUTION/TRACK OF SURFACE LOW...PRECIPITATION MAY CHANGE OVER TO

SNOW LATE WEDNESDAY NIGHT AND CONTINUE THROUGH FRIDAY. HEAVY SNOW

ACCUMULATIONS ARE POSSIBLE OVER THE MOUNTAINS DUE TO A NORTHWEST

FLOW EVENT. CONFIDENCE IS STILL LOW...BUT WILL NEED TO MONITOR FOR

THE POTENTIAL OF HEAVY RAINS AND MOUNTAINS SNOW. THE PRECIPITATION

MAY CHANGE TO SNOW ACROSS THE VALLEYS AS WELL LATER IN THE EVENT.

[NavarreDon]

Best wording out of GSP in a while!

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...

AS OF 230 PM THURSDAY...STILL DIFFICULT TO PUT TOO MUCH STOCK INTO

ANY PART OF THE FCST FOR THE MIDDLE OF NEXT WEEK AS ALL THE MODELS

ARE STRUGGLING WITH RUN TO RUN CONTINUITY WITH THE DEVELOPMENT AND

MOVEMENT OF A POTENTIALLY POWERFUL UPPER LOW MOVING SOMEWHERE FROM

THE PLAINS TO SOMEWHERE EAST. THE FCST FOLLOWS CLOSEST TO THE HPC

DEPICTION OF WEATHER SYSTEMS AND THE OPERATIONAL GFS.

WE SHOULD START OUT DRY AT 00Z MONDAY WITH A FLAT UPPER RIDGE MOVING

OVERHEAD AND WEAK HIGH PRESSURE IN PLACE. THIS WILL QUICKLY CHANGE

AS A WEAK UPPER WAVE APPROACHES FROM THE WEST. WARM ADVECTION...LOW

LEVEL UPGLIDE...AND DPVA WILL SPREAD IN FROM THE WEST IN SPITE OF

THE WEAK APPEARANCE OF THIS WAVE. THE NET EFFECT IS THE ACTIVATION

OF A WEAK WARM FRONT THAT POKES IN FROM TN. THE FCST WAS ALTERED IN

FAVOR OF THE MOSGUIDE POP FOR SUNDAY NIGHT...WHICH SHOWS ONLY A

SLIGHT CHC OVER THE SW MTNS AND NE GEORGIA. FOR MIN TEMPS...AN

INVERSE LAPSE RATE WAS ADDED TO ACCOUNT FOR THE LOW LEVEL WARM

ADVECTION THAT SHOULD MAKE RIDGETOPS WARMER THAN VALLEYS. THE RESULT

IS LIGHT RAIN BREAKING OUT FROM SW TO NE ACROSS THE MTNS AROUND

DAYBREAK. THIS INITIAL SYSTEM WILL SPREAD ACROSS THE FCST AREA WITH

WEAK UPGLIDE AND WEAK UPPER DIVERGENCE. IT SHOULD NOT AMT TO MUCH...

BUT WARRANTS PRECIP CHANCES CLIMBING UP INTO THE CHC RANGE ACROSS

THE WHOLE AREA THROUGH CHRISTMAS EVE. THE PRECIP TYPE SHOULD BE

RAIN.

THE QUANDARY IS WHAT TO DO WITH LATE CHRISTMAS EVE AND EARLY

CHRISTMAS MORNING. THE MODELS AGREE THAT WARM ADVECTION WILL

CONTINUE OVERNIGHT AND THAT SHOULD PROBABLY ELIMINATE ANY CHANCE OF

SUB FREEZING TEMPS...THUS THE ONLY PRECIP TYPE THAT SHOULD BE

EXPECTED IS RAIN...GIVEN THE WARM TEMPS ALOFT IN FCST SOUNDINGS. AS

THE INITIAL SOURCES OF LIFT MOVE OFF TO THE EAST...THERE COULD BE A

SIZEABLE LULL IN PRECIP ACTIVITY DURING THIS TIME...IF THE GFS IS

RIGHT. HOWEVER...WITH A NOD TO THE ECMWF WHICH SHOWS A CONTINUATION

OF FORCING...THE FCST WAS KEPT IN THE CHC CATEGORY. TEMPS WILL BE

COOL DUE TO EXTENSIVE CLOUDS AND THE THREAT OF PRECIP.

MEANWHILE...THE NEXT UPPER SYSTEM WILL BE DEEPENING AS IT MOVES OUT

OVER THE PLAINS. HERE IS WHERE THE UNCERTAINTY REALLY CREEPS IN...AS

THE LATEST GFS MOVES THE UPPER LOW MUCH CLOSER...OVER THE CUMBERLAND

PLATEAU AND TN VALLEY...ON WEDNESDAY AND WEDNESDAY NIGHT. IT SHOULD

BE MENTIONED THAT THE 12Z ECMWF IS VERY SIMILAR WITH THIS STRONG AND

DYNAMIC UPPER LOW MOVING PAST JUST WEST LATE WEDNESDAY. A COLD AIR

DAMMING WEDGE WILL LIKELY SET UP IN ADVANCE OF A SURFACE LOW ON

TUESDAY NIGHT WHICH WILL LINGER INTO WEDNESDAY. THE MODELS SHOW

STRONG FORCING AND DEEP MOISTURE TUESDAY NIGHT AND WEDNESDAY.

CONFIDENCE IS NOT HIGH ENOUGH TO GO ABOVE A LIKELY POP BECAUSE OF

THE POOR CONSISTENCY. IF THE MODELS ARE RIGHT WITH THE TIMING...

ANOTHER POWERFUL COLD FRONT WOULD BLAST ACROSS THE WESTERN CAROLINAS

WEDNESDAY AFTERNOON...BUT THE LINGERING WEDGE WOULD PRECLUDE ANY

SEVERE STORMS. PRECIP CHANCES LINGER INTO WEDNESDAY EVENING AND FALL

OFF OUTSIDE THE MTNS. AS LOW PRESSURE PULLS AWAY...MUCH COLDER AIR

FUNNELS IN ACROSS THE REGION...CHANGING PRECIP TO SNOW OVER THE MTNS

AND LEADING TO A PERIOD OF NW FLOW SNOWSHOWERS ON THE TN BORDER THAT

CONTINUES THROUGH THURSDAY. TEMPS SHOULD BE MUCH COLDER...PERHAPS

TEN DEGREES BELOW NORMAL FOR A CHANGE ON THURSDAY. AGAIN...

CONFIDENCE IS NOT GREAT...BUT THIS IS SOMETHING TO KEEP AN EYE ON.

[GaStorm]

Lol, don't worry...I NEVER forget Lucy! So, I'm still taking with a grain and know it can all disappear tomorrow. However, this is the first time this season I've seen anything like this setup suggesting actual Miller A'ish winter storm potential fairly consistently in the model consensus.....and actually the first in two years since there were zero modeled threats anything like this last winter. This just tells me that if everything just happens to line up just right, we could get a winter storm around 1/1. The odds are low this far out (~12 days), but I'm merely talking potential. Also, climo does improve some as we approach Jan.

I really hope this one can happen. Does climo favor the first week of January vs. mid month on major storms? I think I remember you posting something on this before but can't remember.

[GaWx]

I really hope this one can happen. Does climo favor the first week of January vs. mid month on major storms? I think I remember you posting something on this before but can't remember.

Major ATL S/IP in JAN: 1, 2-3, 7, 7-8, 9, 9-10, 12, 18, 18-19, 22, 23, 26, 28, 29-30

Major ATL ZR in JAN: 1, 7, 7-8, 8, 9, 13-4, 17-8, 18-9, 21, 22-23, 23, 23,, 28-9, 28-30, 30, 30-31

Eyeballing these dates tell me that mid and late month may be a bit more favorable than the first week. However, early Jan. seems to be more favorable than most of Dec..

[WilkesboroDude]

Might be able to see some snow tomorrow east of the mountains...(Wilkesboro, Mount Airy, etc...)

NWS Blacksburg

A few light snow showers or flurries may make it to the Blue Ridge by sunrise as moisture is pushed east from strong winds. This may also tend to focus more snow farther south into the northwest NC ridges before the deeper moisture lifts northward and the flow veers more northwest later in the day. This should allow for a few inches in the warning area by dark Friday and 1-3 elsewhere along the far western slopes. Could see some -shsn/flurries sneak further east with heating during the afternoon but thinking most accumulations will stay west of the New River valley Friday.

[burgertime]

lol 18z is really south this run

[rduwx]

Well, more changes on the 18z gfs. Has a sfc low in the gulf at 129. Looks like cold air could be an issue though.

[WilkesboroDude]

Blacksburg

Long term /Sunday night through Thursday/...

The long range models have now significantly changed with the track of the surface low associated with this system...moving it from the Gulf Coast states northeast over the Appalachians. This results in the possibility for a winter weather event for our area middle-week if air is cold enough in the lowest layers as advertised by the GFS. A quick look at the

12z European model (ecmwf) now comes more in line with the GFS with the timing and track of this system...but is warmer in the lower levels.

With abundant cloud cover anticipated...reduced the diurnal spread in temperatures Tuesday and especially Wednesday when widespread precipitation is expected with broad area of ascent. Forecast position of parent high not ideal for classic cold air damming...however the GFS and to a lesser extent...the Canadian model are stronger with surface high in southeast Canada and thus create a stronger low level wedge and colder temperatures. If this verifies...there is a potential for accumulating winter precipitation...as snow or ice. GFS forecast soundings indicate a strong warm nose above the surface in the east. For now...forecast temperatures are warm enough for the precipitation to fall as liquid in most areas but this system will have to continue to be monitored.

[oconeexman]

I really hope this one can happen. Does climo favor the first week of January vs. mid month on major storms? I think I remember you posting something on this before but can't remember.

I'll speak for upstate SC it has been the best for major storms here in the last 30 years!

[Jon]

@ 144, 1004mb over GA/SC border, freezing line along the spine of apps...this run much more east, gonna go off coastal NC...

[beanskip]

18z may be doing what I mentioned earlier -- waiting til the last minute to blow up the ULL. Much colder than 12z run -- 0C line almost down to NC at 3z on the 26th -- it was up in Maryland on the 12z run at 3z the 26th.

[Jon]

@150, low off coast of Wilmington, NC....mountains cash in on some of that white stuff this run most likely.

[burgertime]

18z may be doing what I mentioned earlier -- waiting til the last minute to blow up the ULL. Much colder than 12z run -- 0C line almost down to NC at 3z on the 26th -- it was up in Maryland on the 12z run at 3z the 26th.

It is and sweet baby jesus NC folks are going to wish for hour 150 to come true.

[GaStorm]

Major ATL S/IP in JAN: 1, 2-3, 7, 7-8, 9, 9-10, 12, 18, 18-19, 22, 23, 26, 28, 29-30

Major ATL ZR in JAN: 1, 7, 7-8, 8, 9, 13-4, 17-8, 18-9, 21, 22-23, 23, 23,, 28-9, 28-30, 30, 30-31

Eyeballing these dates tell me that mid and late month may be a bit more favorable than the first week. However, early Jan. seems to be more favorable than most of Dec..

I can't remember the last time we had anything significant around the first of January so maybe we are overdue. Thanks for the info!