Feb. 8-12 Model Discussion Part III

[DaculaWeather]

Low is down to 1002mb

[DaculaWeather]

FFC

ALL OF THIS SUPPORTS THE LOWER QPF VALUES WITH

PRECIPITATION CONFINED MAINLY TO THE 00Z TO 12Z THURSDAY PERIOD.

WITH SOME UNCERTAINTY REMAINING ON SNOWFALL TOTALS I WILL HOLD OFF

ONE MORE PERIOD ON ISSUING A WINTER WEATHER ADVISORY...BUT I WILL

ENHANCE THE SPECIAL WEATHER STATEMENT WITH THIS ISSUANCE. IF THE QPF

FORECAST DOES NOT DECREASE...A WINTER WEATHER ADVISORY WILL BE NEEDED

FOR THE WEDNESDAY NIGHT/THURSDAY MORNING PERIOD ACROSS NORTH GEORGIA.

[CaryWx]

RAH is just really conservative with snow fall forecast. I think it is because they got burned back in Jan 08 when they had the area under WSW and calling for 6-12", but boundry layer issues kept it as rain most of the day and only a about an inch of fell across the area. Since then, you are hard-pressed to see them call for any accumulation outside of 12 hours before the event.

Yes, but you don't at least have a potential advisory in those 'border' counties to Morehead's CWA. Unless they are overdoing it with the watches. Likewise for the Wakefield boys.

Coordination anyone?

[Brick Tamland]

RAH is just really conservative with snow fall forecast. I think it is because they got burned back in Jan 08 when they had the area under WSW and calling for 6-12", but boundry layer issues kept it as rain most of the day and only a about an inch of fell across the area. Since then, you are hard-pressed to see them call for any accumulation outside of 12 hours before the event.

Yet, they were very bullish with the last system four days ahead of time. Of course it turned out to be nothing here.

[NCStateMMY]

Yes, but you don't at least have a potential advisory in those 'border' counties to Morehead's CWA. Unless they are overdoing it with the watches. Likewise for the Wakefield boys.

Coordination anyone?

HAZARDOUS WEATHER OUTLOOK...UPDATED

NATIONAL WEATHER SERVICE RALEIGH NC

328 PM EST TUE FEB 8 2011

NCZ011-027-028-042-043-077-078-085-086-088-089-091200-

HALIFAX-NASH-EDGECOMBE-JOHNSTON-WILSON-HARNETT-WAYNE-SCOTLAND-HOKE-

CUMBERLAND-SAMPSON-

328 PM EST TUE FEB 8 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL NORTH CAROLINA.

.DAY ONE...THIS AFTERNOON AND TONIGHT.

HAZARDOUS WEATHER IS NOT EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY.

A PERIOD OF SNOWFALL IS POSSIBLE WEDNESDAY NIGHT INTO THURSDAY

MORNING IN AREAS ALONG AND EAST OF INTERSTATE 95... AS LOW

PRESSURE TRACKS OFF THE CAROLINA COAST. AT THIS TIME... THERE IS A

GOOD CHANCE OF MEASURABLE SNOW IN THIS AREA... AND TOTALS UP TO AN

INCH ARE POSSIBLE. A WINTER WEATHER ADVISORY MAY BE NEEDED FOR

THIS AREA... AND PEOPLE ARE ADVISED TO KEEP A CLOSE EYE ON THE

LATESTS FORECASTS AND CONDITIONS FOR WEDNESDAY NIGHT AND THURSDAY

MORNING.

$$

GIH

Looks like they are cosidering at least a WWA

[WeatherNC]

Yes, but you don't at least have a potential advisory in those 'border' counties to Morehead's CWA. Unless they are overdoing it with the watches. Likewise for the Wakefield boys.

Coordination anyone?

They do coordinate, and RAH mentioned they may have to entertain a WWA for the Counties along and east of 95 in there CWA in future packages. Not sure what the criteria is for you guys under a warning, here it is "1/4" ICE AND/OR 3" SNOW/SLEET IN 12 HOURS" and as the HPC often does when issuing there 4,8, and 12" SN prob maps, it is based heavily on the SREF to see if the prob supports that the criteria will be met.

[polarexpress00]

FFC

ALL OF THIS SUPPORTS THE LOWER QPF VALUES WITH

PRECIPITATION CONFINED MAINLY TO THE 00Z TO 12Z THURSDAY PERIOD.

WITH SOME UNCERTAINTY REMAINING ON SNOWFALL TOTALS I WILL HOLD OFF

ONE MORE PERIOD ON ISSUING A WINTER WEATHER ADVISORY...BUT I WILL

ENHANCE THE SPECIAL WEATHER STATEMENT WITH THIS ISSUANCE. IF THE QPF

FORECAST DOES NOT DECREASE...A WINTER WEATHER ADVISORY WILL BE NEEDED

FOR THE WEDNESDAY NIGHT/THURSDAY MORNING PERIOD ACROSS NORTH GEORGIA.

Hey Cheez looks like they did exactly what we said they would do.

[griteater]

RAH is just really conservative with snow fall forecast. I think it is because they got burned back in Jan 08 when they had the area under WSW and calling for 6-12", but boundry layer issues kept it as rain most of the day and only a about an inch of fell across the area. Since then, you are hard-pressed to see them call for any accumulation outside of 12 hours before the event.

Do you recall the specific date in Jan '08? Just curious what the setup was for them calling for large amounts

[NCStateMMY]

Do you recall the specific date in Jan '08? Just curious what the setup was for them calling for large amounts

It was the weekend of January 18-20. I remember b/c my grandfather was in the hospital and I was worried about if they could get him from Nash General to Wake Med to the Heart Center if the conditions got bad. We had had a trace event a couple of days earlier on the 17th and the TV mets were calling it a precursor to the bigger event that was suppossed to be on the 19th. It stayed rain in Rocky Mount most of the day until after sunset when it changed to snow and dusted lightly.

[superjames1992]

Do you recall the specific date in Jan '08? Just curious what the setup was for them calling for large amounts

I think this is the one they are referring to.

http://www4.ncsu.edu/~nwsfo/storage/cases/20080119/

[CaryWx]

WeatherNC, thanks for the clarification.

[NCStateMMY]

I think this is the one they are referring to.

http://www4.ncsu.edu...cases/20080119/

That is the one.

[jburns]

WINTER STORM WATCH FOR NC TRIAD.

A WINTER STORM WATCH HAS BEEN ISSUED FOR THE TRIAD. PERSONS IN THE TRIAD CAN GO TO THE ROOFTOPS OF THEIR TALLEST BUILDINGS, LOOK DIRECTLY EAST AND WATCH A WINTER STORM. THIS DEVELOPING SITUATION IS MUCH DIFFERENT THAN 2 WEEKS AGO WHEN THEY HAD TO LOOK SOUTH TO WATCH A STORM, AND A MONTH AGO WHEN THEY HAD TO LOOK NORTH.

[WeatherNC]

I think this is the one they are referring to.

http://www4.ncsu.edu/~nwsfo/storage/cases/20080119/

yep, and it was not 6-12", more like 3-5" heaviest along the 95 corridor, here was there thinking

Warning Decision Process

WFO RAH winter weather philosophy includes a targeted lead time for Winter Storm Watches of 24 hours and for Winter Storm Warnings of 12 to 18 hours. These lead times can be increased if confidence is unusually high, if sociological factors require it (such as a holiday weekend or first storm of the season) and if collaboration among adjacent offices necessitates it.

The Watch/Warning/Advisory decision making during this event was very difficult. Generally, forecasters knew that the arctic cold air arriving from the west with the northern stream trough would be chasing the moisture associated with the southern stream upper trough and distant surface low. This was a classic case of relatively limited precipitation in the cold air over the western Piedmont, with a lack of cold air (at least initially) where moisture was more plentiful over the Coastal Plain. Model thicknesses and forecast soundings indicated a transition from rain to snow from northwest to southeast during the day Saturday, as cooling in the lowest 5 thousand feet pushed the thermal profile to slightly sub-freezing isothermal.

One weak winter storm was already threatening central North Carolina on Tuesday January 15 when forecasters recognized the upcoming weather pattern would potentially lead to southern stream short waves that could produce cyclogenesis across the Gulf of Mexico and East Coast during the weekend and early the next week. On Wednesday, forecasters monitored the system and it appeared that the track of the surface low and moisture would remain largely southeast of the area.

Forecasters on Thursday recognized that this storm would fit the “Miller A” pattern of limited freezing precipitation (freezing rain and sleet) and a narrow transition zone. Forecasters accepted a GFS/ECMWF solution that brought system closer to the coast but kept the center offshore. Model guidance was inconsistent and portrayed a variety of solutions. Details regarding the potential phasing of the southern stream trough with the northern stream were a significant unknown and forecasters kept the forecast conservative. Snow was first introduced to the weekend forecast for the RAH CWA in the 400 PM ZFP issuance on Thursday with a rain/snow mix in the north an northwest portion of the CWA in the morning and then with the rain mixing with snow eastward during the day Saturday. The 18Z HPC snow accumulation guidance included a potential for 4 to 6 inches of snow accumulation across parts of the RAH CWA.

During the midnight shift on Friday morning, the event was close enough to warrant the issuance of a Winter Storm Watch for the northern Piedmont and Coastal Plain region for the potential of 2 to 4 inches of snow. Snow accumulation guidance from HPC issued at around 07Z agreed with the potential for up to 4 inches of snow from the NC mountains to the Piedmont largely because of concern over an intense 150 to 170 knot jet at 250 mb. The Heavy Snow Discussion from HPC issued at 451 AM on Friday morning noted the continued inconsistency and the southeastward trend in the NWP guidance. In addition, the HPC Model Diagnostic Discussion issued Friday morning noted the importance of the potential phasing of the northern and southern jets.

Forecasters during the day shift on Friday were impressed with the intense dynamics observed with the system (note the impressive upper trough south of Texas in the water vapor imagery at 1815Z.) This short wave trough over the Mexico was still digging south during the midday hours and convection was ongoing across the Gulf of Mexico. This in part led forecasters to believe that the developing storm system had the potential to intensify more than the NWP guidance was suggesting; resulting in stronger cyclogenesis and greater amounts of precipitation (closer to the NAM solution.) Colder air was expected to be edging into the area during the day from the northwest and the low levels were expected to be cooled by diabatic processes (evaporation and melting.) As noted by HPC in the 412 PM Heavy Snow Discussion, the 12Z Friday model guidance was coming into better agreement (the NAM was still an outlier) with a slower and more amplified solution. Interestingly, the HPC Heavy Snow Discussion mentioned that snow accumulations would be limited because of above freezing surface temperatures. After collaborating with neighboring offices, WFO RAH issued a Winter Storm Warning for portions of the northern Piedmont and northern Coastal Plain with a Winter Weather Advisory for the remainder of the RAH CWA. Snow accumulations were expected to be greatest in the Interstate 95 corridor when amounts were forecasted to range between 3 and 5 inches.

During the evening shift on Friday, forecasters noted some potential points where the predicted accumulations could be overdone. Snow to liquid equivalent ratios were expected to be 8:1 or even 6:1 because of the relatively warm atmosphere. In addition, the above freezing temperatures at and just above the surface were expected to initially melt the snow and a portion of the falling snow would go toward cool the near ground temperature and the ground itself. During the midnight shift on Saturday morning, forecaster confidence at RAH was low and decreasing despite the fact that the event was about to begin. The diminished confidence stemmed from several factors, including an evolving depiction of QPF values across central NC with each model run and the fact that the 00Z models were having great difficulty in forecasting the observed weather just 6 hours after model initialization time. The 00Z Saturday GFS/NAM were too slow and too far south with the precipitation across the Carolinas (note the difference between the 3 hour NAM20 QPF ending at 12Z and the 1 hour RTMA observed precipitation analysis over SC and NC which already showed up to 0.10 inches in 1 hour.) Forecasters realized that the primary lifting mechanisms will be divergence aloft from a strong upper level jet and mid level frontogenesis, but the various ways these fields were progged by the models was disconcerting. In addition, observed temperatures and dew points were still in the upper 30s to lower 40s during the predawn hours.

With the poor model performance in handling the short term and uncertainty in the QPF, forecasters decided to leave the Warnings and Advisories as they were. The midnight shift did note that this would be a borderline Warning event and that there was potential for Warning criteria snow in the southern Coastal Plain. The ZFP issued at 407 AM on Saturday morning generally included 1-2 inches in the advisory area with 2-3 inches in the Warning area with potentially higher amounts.

Forecasters on Saturday morning were troubled with mixed signals when analyzing the observed and guidance data. The 12Z proximity soundings came in on average 3 to 6 m higher with 1000-850 and 850-700 mb thicknesses than progged by the models. In addition, the NAM and GFS BUFR soundings were too cool in the lowest 5,000 feet relative to the observed 06Z and 12Z KGSO soundings as well as too cool over RDU relative to AMDAR aircraft soundings between 11 and 13z. Colder and drier air was believed to be on its way with the observed soundings displaying an increasingly backing wind profile in the lower layers. Dew points over southwestern VA and northwestern NC were dropping into the teens which meant the potential for further near surface cooling via evaporation.

The subsidence on the back side of the short wave that produced the initial round of precipitation across central NC was noted during the late morning hours in the drying shown on satellite imagery and a large lull in the precipitation across the western Carolinas. This break in the precipitation allowed surface temperatures to climb into the lower 40s before the onset of the second round of precipitation.

The Advisory was allowed to stand across the Triad because of the models poor performance with precipitation amounts upstream, indications that the cold air is showing signs of infiltrating the Triad and snow ratios will accordingly increase closer to 9:1 or 10:1, and forcing for ascent was expected to continue into the late afternoon hours.

Across the Warning and the remainder of the Advisory areas, the forecast rationale and resultant snowfall amounts were generally unchanged from the previous package. It was noted that the accumulations would likely be on the lower end of the Advisory/Warning range. Uncertainty in the location of an expected sweet spot where the arrival of the colder air will co-exist with the higher QPF made it difficult for forecasters to trim back the Warning. In fact, the locations in which the forecasters contemplated downgrading the Warning (the northwestern tier of counties – Person, Orange, Alamance, and Chatham) were the locations that received the most snow. Finally, the forecasters realized that most of the accumulation will occur on grassy surfaces, cars, and rooftops given the above freezing near surface temperatures and already wet ground.

Forecasters during the afternoon Saturday were relieved to see the second area of precipitation develop and spread across central NC. The precipitation had already developed or changed to snow in the Triad area around 200 PM and the changeover was moving into the western portions of the Triangle area by 300 PM. Snow accumulations on the order of a coating to a third of an inch were already reported in the Triad area by 300 PM. With conditions rapidly changing over to snow, forecasters were still hesitant on pulling the warning despite the fact they realized it may be a long shot. While it was not clear at the time the warning decision was made (1-3 PM), the fact that the surface temperature was failing to fall below 33 degrees in the RAH CWA during the afternoon and early evening hours was a chief reason Warning criteria snow accumulations were never realized. The Winter Weather Advisory was dropped across the Triad area at 752 PM and the remainder of the Advisories and Warnings were updated. All of the Advisories and Warnings were cancelled at 1158 PM.

[Brick Tamland]

Great, another storm with snow to the west, snow to the south, and snow to the east of the Triangle.

[chapelhill]

Those birds are juncos and yes, they are in a feeding frenzy, happens every snow.

Feeding frenzy behavior applies to squirrels too. Here comes your

[Lowpressure]

Great, another storm with snow to the west, snow to the south, and snow to the east of the Triangle.

Dude, just move and spare us all the babble- really.

[Tacoma]

From the NWS GSP for the mtns. of wnc.LOW PRESSURE IS EXPECTED TO DEVELOP AND TRACK EAST ALONG THE GULF

COAST WEDNESDAY NIGHT BEFORE MOVING OVER THE WESTERN ATLANTIC ON

THURSDAY. TEMPERATURES ARE FORECAST TO REMAIN SUFFICIENTLY COLD

FOR PRECIPITATION TO FALL AS SNOW. THERE REMAINS THE POTENTIAL FOR

ONE TO TWO OF INCHES OF SNOW TO ACCUMULATE IN THE MOUNTAINS...WITH

THE GREATEST AMOUNTS GENERALLY AT HIGHER ELEVATIONS. THE GREATEST

SNOWFALL RATES MAY OCCUR BEFORE SUNRISE THURSDAY...POSSIBLY

CREATING POOR MORNING ROAD CONDITIONS.

[griteater]

Panovich is going with 1-2 inches for CLT and surrounding areas

[jburns]

Dude, just move and spare us all the babble- really.

He should know by now that it is nearly impossible to get snow in Raleigh when the legislature is in session. Serious hot air island.

[griteater]

From the NWS GSP for the mtns. of wnc.LOW PRESSURE IS EXPECTED TO DEVELOP AND TRACK EAST ALONG THE GULF

COAST WEDNESDAY NIGHT BEFORE MOVING OVER THE WESTERN ATLANTIC ON

THURSDAY. TEMPERATURES ARE FORECAST TO REMAIN SUFFICIENTLY COLD

FOR PRECIPITATION TO FALL AS SNOW. THERE REMAINS THE POTENTIAL FOR

ONE TO TWO OF INCHES OF SNOW TO ACCUMULATE IN THE MOUNTAINS...WITH

THE GREATEST AMOUNTS GENERALLY AT HIGHER ELEVATIONS. THE GREATEST

SNOWFALL RATES MAY OCCUR BEFORE SUNRISE THURSDAY...POSSIBLY

CREATING POOR MORNING ROAD CONDITIONS.

Gotta say fritschy, I recall you stating several days ago that you thought we would have plenty of cold air with this storm, and that it would just come down to whether or not we had enough moisture - good call....on the other hand, DT said that the pattern in no way supported a suppressed storm track and that he thought it would cut inland - fail

[GaStorm]

For those that think the NWS is conservative check out David Chandley's forecast. Lol.

“I am expecting a trace to a dusting of snow for most of the metro area, with accumulating snow in the northern suburbs into the north Georgia mountains,” Chandley said.

http://www.wsbtv.com/news/26789175/detail.html

[bingcrosbyb]

Guys time to nowcast. Let's put some of the longer range coarser models aside. Courtesy of the Birmingham NWS. Confirms my suspicions when looking at the current SPC upper level maps.......

FARTHER TO THE EAST IS A BIT MORE UP IN THE AIR...SO TO SPEAK. ALL

MODELS STILL SUGGEST THAT MOISTURE LEVELS WILL BE DIMINISHING AS

THE SYSTEM MOVES EASTWARD ALONG THE GULF COAST. I AM NOT AS

CONFIDENT THAT IT WILL (BE DIMINISHING). IN FACT...LOOKING AT THE

CONDITIONS AND OBSERVATIONS IN THE TEXAS AND OKLAHOMA PANHANDLES

THIS AFTERNOON...I`M STARTING TO WONDER IF THIS THING MAY ACTUALLY

BE STRONGER THAN MODELS ARE FORECASTING WHEN IT ARRIVES HERE. I

MEAN...THERE`S A 60 DEGREE SPREAD ACROSS JUST A 200 MILE AREA IN

WEST TEXAS...WITH WINDS BLOWING 30 KNOTS VIRTUALLY DIRECTLY TOWARD

EACH OTHER. THAT`S A LOT OF FRONTOGENESIS AND BAROCLINICITY. I CAN

ONLY IMAGINE A SURFACE LOW REALLY GETTING CRANKED UP BEYOND WHAT

THE MODELS ARE CURRENTLY FORECASTING. TRANSLATE THAT

DOWNSTREAM...AND THERE IS STILL THE POSSIBILITY THAT WE COULD HAVE

A MUCH LARGER 2+ INCHES SNOW AREA THAN THE MODELS SUGGEST. SO --

ASIDE FROM THE ADDITION OF THE AFOREMENTIONED COUNTIES WILL NOT

MAKE ANY OTHER CHANGES TO THE WINTER STORM WATCH AREA EVEN THOUGH

IT MAY SEEM TO CONFLICT A LITTLE WITH OUR CURRENT SNOW AMOUNT

FORECAST.

[packfan98]

Is anyone else having trouble getting the 12z GFS ensemble members off of Raleighwx's website? I got them off of the Penn State site but they are hard to read and it doesn't show the snow totals.

http://raleighwx.ame...rs/12zf048.html

[burgertime]

Every run seems to keep the s/w just a tad stronger and the energy in the lakes a tad weaker.

[Tacoma]

we were so close in the southeast of having a nice snowstorm, just to see it maybe get wasted even though I will take a inch or two better than nothing. I'm sticking with the maybe for now, who knows storms have trended stronger at the last minute. Yes cold air will be plentiful during the storm. seems like we always are looking for the cold and now we're looking for the moisture, you know if it were warm to be rain we would probably get a couple of inches which would be maybe 15-20 of snow. GO FIGURE!

[strongwxnc]

GSP AFD for the foothils

NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC

332 PM EST TUE FEB 8 2011

.

DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY.

LOW PRESSURE IS EXPECTED TO DEVELOP AND TRACK EAST ALONG THE GULF

COAST WEDNESDAY NIGHT BEFORE MOVING OVER THE WESTERN ATLANTIC ON

THURSDAY. TEMPERATURES ARE FORECAST TO REMAIN SUFFICIENTLY COLD FOR

PRECIPITATION TO FALL AS SNOW. THERE REMAINS THE POTENTIAL FOR UP

TO AN INCH OF SNOW TO ACCUMULATE IN THE FOOTHILLS AND PIEDMONT.

THE GREATEST SNOWFALL RATES MAY OCCUR BEFORE SUNRISE

THURSDAY...POSSIBLY CREATING POOR MORNING ROAD CONDITIONS.

From the NWS GSP for the mtns. of wnc.LOW PRESSURE IS EXPECTED TO DEVELOP AND TRACK EAST ALONG THE GULF

COAST WEDNESDAY NIGHT BEFORE MOVING OVER THE WESTERN ATLANTIC ON

THURSDAY. TEMPERATURES ARE FORECAST TO REMAIN SUFFICIENTLY COLD

FOR PRECIPITATION TO FALL AS SNOW. THERE REMAINS THE POTENTIAL FOR

ONE TO TWO OF INCHES OF SNOW TO ACCUMULATE IN THE MOUNTAINS...WITH

THE GREATEST AMOUNTS GENERALLY AT HIGHER ELEVATIONS. THE GREATEST

SNOWFALL RATES MAY OCCUR BEFORE SUNRISE THURSDAY...POSSIBLY

CREATING POOR MORNING ROAD CONDITIONS.

[Rankin5150]

Thanks to everyone for the updates today! I have a question. Does anyone remember the Jan 1988 storm? If I am not mistaken, the Jan 1988 (or 1987?) system was progged to drop 1-2" of snow in Charlotte area, all the way up to start time of the event and then we ended up with 12". I AM NOT SAYING that this exttreme would happen by no stretch, but I wonder if that system had the same look as this one? I think Foothills or someone (cannot remember) did a case study on this storm. TIA for any input!

[burgertime]

Well no shock here the 18z is holding serve it looks like with a big cup of fail.

[downeastnc]

Thanks to everyone for the updates today! I have a question. Does anyone remember the Jan 1988 storm? If I am not mistaken, the Jan 1988 (or 1987?) system was progged to drop 1-2" of snow in Charlotte area, all the way up to start time of the event and then we ended up with 12". I AM NOT SAYING that this exttreme would happen by no stretch, but I wonder if that system had the same look as this one? I think Foothills or someone (cannot remember) did a case study on this storm. TIA for any input!

Yeah with modeling the way it is now surprises like that are gonna be harder to come by. Dec 1989 was like that here called for a chance of flurries and got a blizzard instead lol.

Feel pretty good that I am gonna see snow, MHX seems bullish but the QPF average for around here on most models is .30-.50" and if that is right then 2-4" seems a good bet.