12/3-12/6 MW/GL snow event?

[baroclinic_instability]

The discussion from earlier, thanks to Jomo for bringing it up when he did. Looks valid here.

"Note how the weak shortwave phases with the upper low around the Aleutians, deamplifies over the Rockies, then weakly phases again with the polar branch over the Dakotas. There is a lot of variability right there, and depending on how far south the wave takes will influence the strength of the cross barrier flow across the Rockies and subsequent lee troughing and moisture/thermal transport (note the lee trough the models develop after 48 hrs). Getting back to what I said earlier though, with clippers, what generally happens is stronger upper shortwaves develop strong frontogenesis aloft. Because the frontal boundary is tilted over cold air (static stability), this results in qpf that generally ends up farther N. Here is a "model" cold front to help you visualize a typical orientation of a cold front using a vertical cross section:

If the upper level shortwave aloft is weaker, this usually results in stronger frontogenesis in the lower levels closer to the surface, which results in a farther S track. As you can see, clippers are usually quite tough to forecast and I have seen many times where the snow band is off kilter by 50-100 miles within the final 24 hours of the forecast. Small scale errors with how models simulate the development of a clipper grows FAST with time.

As others have said, I think it is a "wash" from a climo standpoint. If you feel the wave is potentially going to be more intense and or/of greater amplitude, possibly shift the track a tad north. if you feel it will be weaker and/or of less amplitude, shift the track a tad south. This of course does not take into account the placement of the baroclinic zone. if you feel that may be farther N or S, also take that into account when forecasting the track. Also, stronger waves usually support deeper frontogenesis and slightly wider snow bands, so take that into consideration as well. "

[Natester]

Nice returns over Cedar Rapids but it's not reaching the ground.

[baroclinic_instability]

NAM QPF field for the current time frame already hundreds of miles of. Just horrible.

[KokomoWX]

URGENT - WINTER WEATHER MESSAGE

NATIONAL WEATHER SERVICE INDIANAPOLIS IN

247 PM EST FRI DEC 3 2010

...WINTER WEATHER ADVISORY IN EFFECT FOR SATURDAY...

.A CLIPPER SYSTEM MOVING SOUTHEAST THROUGH THE NORTHERN PLAINS

WILL ARRIVE IN INDIANA OVERNIGHT. THIS SYSTEM WILL BRING SNOWFALL

AMOUNTS OF 2 TO OVER 4 INCHES ACROSS THE AREA BY SATURDAY

AFTERNOON.

INZ021-028>031-035>049-051>057-060>065-067>072-040400-

/O.NEW.KIND.WW.Y.0007.101204T0600Z-101205T0000Z/

CARROLL-WARREN-TIPPECANOE-CLINTON-HOWARD-FOUNTAIN-MONTGOMERY-

BOONE-TIPTON-HAMILTON-MADISON-DELAWARE-RANDOLPH-VERMILLION-PARKE-

PUTNAM-HENDRICKS-MARION-HANCOCK-HENRY-VIGO-CLAY-OWEN-MORGAN-

JOHNSON-SHELBY-RUSH-SULLIVAN-GREENE-MONROE-BROWN-BARTHOLOMEW-

DECATUR-KNOX-DAVIESS-MARTIN-LAWRENCE-JACKSON-JENNINGS-

INCLUDING THE CITIES OF...LAFAYETTE...FRANKFORT...KOKOMO...

CRAWFORDSVILLE...ANDERSON...MUNCIE...INDIANAPOLIS...TERRE HAUTE...

SHELBYVILLE...BLOOMINGTON...COLUMBUS...VINCENNES...BEDFORD...

SEYMOUR

247 PM EST FRI DEC 3 2010

...WINTER WEATHER ADVISORY IN EFFECT FROM 1 AM TO 7 PM EST

SATURDAY...

THE NATIONAL WEATHER SERVICE IN INDIANAPOLIS HAS ISSUED A WINTER

WEATHER ADVISORY FOR SNOW...WHICH IS IN EFFECT

FROM 1 AM TO 7 PM EST SATURDAY.

* ROADS MAY BECOME SLIPPERY DUE TO SNOW AND THUS MAKE TRAVEL DIFFICULT.

* ACCUMULATIONS OF 2 TO AROUND 4 INCHES CAN BE EXPECTED.

* THE SNOWFALL IS EXPECTED TO BEGIN IN THE NORTHWEST AFTER 1 AM AND

SPREAD EAST ACROSS THE AREA. THE HEAVIEST SNOWFALL RATES ARE

LIKELY TO OCCUR BETWEEN 5 AM AND NOON.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A WINTER WEATHER ADVISORY FOR SNOW MEANS THAT PERIODS OF SNOW

WILL CAUSE PRIMARILY TRAVEL DIFFICULTIES. BE PREPARED FOR SNOW

COVERED ROADS AND LIMITED VISIBILITIES...AND USE CAUTION WHILE

DRIVING.

[Moneyman]

18z NAM is a bit farther north and a tad wetter. Looks like Chicago gets in on the main band.

[Moneyman]

NAM is still off though. 12 Hour QPF has northern MN receiving nothing, looking at the radar, it looks like moderate snow falling over there.

[Hoosier]

NAM is still off though. 12 Hour QPF has northern MN receiving nothing, looking at the radar, it looks like moderate snow falling over there.

Make sure to check obs to verify if it's actually reaching the ground.

[baroclinic_instability]

Make sure to check obs to verify if it's actually reaching the ground.

Yah, good point. NAM is still fail though. Twin Cities already snowing good, NAM would have it dry. That band is shifted way N and East.

[The_Global_Warmer]

The discussion from earlier, thanks to Jomo for bringing it up when he did. Looks valid here.

"Note how the weak shortwave phases with the upper low around the Aleutians, deamplifies over the Rockies, then weakly phases again with the polar branch over the Dakotas. There is a lot of variability right there, and depending on how far south the wave takes will influence the strength of the cross barrier flow across the Rockies and subsequent lee troughing and moisture/thermal transport (note the lee trough the models develop after 48 hrs). Getting back to what I said earlier though, with clippers, what generally happens is stronger upper shortwaves develop strong frontogenesis aloft. Because the frontal boundary is tilted over cold air (static stability), this results in qpf that generally ends up farther N. Here is a "model" cold front to help you visualize a typical orientation of a cold front using a vertical cross section:

If the upper level shortwave aloft is weaker, this usually results in stronger frontogenesis in the lower levels closer to the surface, which results in a farther S track. As you can see, clippers are usually quite tough to forecast and I have seen many times where the snow band is off kilter by 50-100 miles within the final 24 hours of the forecast. Small scale errors with how models simulate the development of a clipper grows FAST with time.

As others have said, I think it is a "wash" from a climo standpoint. If you feel the wave is potentially going to be more intense and or/of greater amplitude, possibly shift the track a tad north. if you feel it will be weaker and/or of less amplitude, shift the track a tad south. This of course does not take into account the placement of the baroclinic zone. if you feel that may be farther N or S, also take that into account when forecasting the track. Also, stronger waves usually support deeper frontogenesis and slightly wider snow bands, so take that into consideration as well. "

Question.

As the system sheers out will the snow band shift back south if the UL's are weaker? Or will this change everything going forward the next couple of days? I have no rooting interest just curious how much this current evolution has on the final outcome. Also if the Main Precip being generated at a higher level, will this have an effect on the dry air underneath? Would it take longer for lower levels to saturate or does the stronger forcing overcome it even easier or does it become a wash?

Thanks in Advance.

[Natester]

[baroclinic_instability]

Question.

As the system sheers out will the snow band shift back south if the UL's are weaker? Or will this change everything going forward the next couple of days? I have no rooting interest just curious how much this current evolution has on the final outcome. Also if the Main Precip being generated at a higher level, will this have an effect on the dry air underneath? Would it take longer for lower levels to saturate or does the stronger forcing overcome it even easier or does it become a wash?

Thanks in Advance.

That is a good question. In some storms, especially on the heels of a strong storm, easterly low level flow can kill off high based qpf. In this case the strength of the mesoscale forcings are significantly stronger than typical synoptic forcings and it really had no issues at all saturating the low levels. Loop the chanhassen radar over the twin cities. Watch how quickly it saturates.

http://rap.ucar.edu/...e=-1&duration=3

[BowMeHunter]

<stebo> who honestly draws a track a straight line <stebo>

[hawkeye_wx]

Nate, it is not looking good for Cedar Rapids. We had to put our hope in the wetter GFS, but the 12z GFS had at least an inch here by evening and it appears we may not even see a flurry from the initial band. Maybe we can still get an inch from the deformation zone late tonight.

Any thoughts, OceanSt?

[OceanStWx]

Nate, it is not looking good for Cedar Rapids. We had to put our hope in the wetter GFS, but the 12z GFS had at least an inch here by evening and it appears we may not even see a flurry from the initial band. Maybe we can still get an inch from the deformation zone late tonight.

Any thoughts, OceanSt?

I'm not too concerned yet. Just taking it's time to saturate, in essence delaying the start time. Still look on track for advisory snows, considering it is really the first of the year.

[mnchaser]

That is a good question. In some storms, especially on the heels of a strong storm, easterly low level flow can kill off high based qpf. In this case the strength of the mesoscale forcings are significantly stronger than typical synoptic forcings and it really had no issues at all saturating the low levels. Loop the chanhassen radar over the twin cities. Watch how quickly it saturates.

http://rap.ucar.edu/...e=-1&duration=3

It may be saturating fast now, But radar was showing showing precip here around 8:00 AM even with 25-30 dbz bands..It didn't really start snowing until about 10 AM...Just my input.

[baroclinic_instability]

It may be saturating fast now, But radar was showing showing precip here around 8:00 AM even with 25-30 dbz bands..It didn't really start snowing until about 10 AM...Just my input.

That is pretty fast for a winter storm. I have forecasted many events where it never saturated. Saturating dry low level east flow in 2 hours is quite an accomplishment, especially when the dominant forcing is 10000 feet in the air.

[prinsburg_wx]

It may be saturating fast now, But radar was showing showing precip here around 8:00 AM even with 25-30 dbz bands..It didn't really start snowing until about 10 AM...Just my input.

yeah it took about an hour and a half here as well before it started snowing even though radar was showing otherwise

[baroclinic_instability]

yeah it took about an hour and a half here as well before it started snowing even though radar was showing otherwise

Be careful with RADAR since the elevation scans are tilted w/height. Just because you see reflectivities doesn't mean snow/or qpf at the surface.

[weatherbo]

IWX had a very underwhelming AFD concerning anything past tonight. This is a bit surprising considering they expanded the LE watches and have moderate/heavy snow accums over much of N Indiana, and this being the first big lake event. This is rare for them.

[mnchaser]

That is pretty fast for a winter storm. I have forecasted many events where it never saturated. Saturating dry low level east flow in 2 hours is quite an accomplishment, especially when the dominant forcing is 10000 feet in the air.

Totally agree, I remember many busts of storms due to never fully saturating, hasn't happened in a few years though..Southern MN seems to be back on track for some decent winters compared to the early 2000s...But my statement was more so directed towards areas further south and east..with the models showing a slight weakening trend that way...I would assume they would have more trouble with virga?

[baroclinic_instability]

This storm is spectacular in so many ways. Check out the jet folds aloft associated with the divergent jet stream circulation aloft. Usually doesn't look this impressive.

[Indystorm]

Surprise. Surprise. IWX has now added Elkhart county to the LES watch for Sat. night through Monday with up to 8" plus in my area and a foot to foot and a half westward. Prolonged period with good fetch. Should be quite the event if it pans out as now expected.

[daddylonglegs]

Nothing happening around here yet. Shovel is still buried in the garage.

[janetjanet998]

MLI now has light snow in that narrow but intense band, even a few fine flakes falling here on the SE edge of that band

[janetjanet998]

DVN

HORT TERM...TONIGHT AND SATURDAY

FORECAST FOCUS ON THE FIRST SHOVELING EVENT OF THE SEASON.

WILL STAY THE COURSE WITH HEADLINES WITH TOTAL ACCUMULATIONS

EXPECTED TO RANGE FROM OVER 5 INCHES IN NORTHEAST IA/NORTHWEST IL

TO LESS THAN AN INCH IN OUR SOUTHWEST CWA. ACTUALLY NO ACCUMULATIONS

FORECAST IN NORTHEAST MO. INTENSE WARM ADVECTION ORIENTED NW-SE

SHOULD MOVE ACROSS THE CWA FROM LATE THIS AFTERNOON INTO EARLY

TONIGHT WITH MODERATE TO LOCALLY HEAVY SNOWS. FORECAST SOUNDINGS

INDICATE DECENT OMEGA IN THE DENDRITIC GROWTH ZONE. THERE IS THE

POSSIBILITY OF ISOLATED AMOUNTS OF OVER 6 INCHES IN THE MOST INTENSE

BAND IF IT GOES CONVECTIVE. WILL NEED TO MONITOR FOR AN UPGRADE TO A

WARNING. THEN THE BAND SHOULD MOVE OFF TO THE EAST OR DIMINISH...

FOLLOWED BY THE DEFORMATION ZONE LATER TONIGHT INTO SATURDAY MORNING.

THE FN 2D FRONTOGENESIS DEPICTS QUITE WELL THE BANDS OF STRONG

FORCING.

THE SNOW SHOULD WIND DOWN OR END FROM WEST TO EAST ON SATURDAY. THE

ADVISORY EXPIRES 6 PM SATURDAY BUT THIS CAN BE CANCELLED SOONER ON

SATURDAY. THIS SYSTEM WILL HAVE A SHARP ACCUMULATION GRADIENT SO ANY

DEVIATION FROM THE EXPECTED TRACK OF THE SYSTEM WOULD OBVIOUSLY

CHANGE AMOUNTS DRAMATICALLY.

[turtlehurricane]

Light snow being observed as far east as Decorah and Monticello, IA. No snow yet along the Mississippi in Prairie Du Chien or Dubuque, but cloud bases are lowering. Radar indicates snow should start in far SW WI shortly.

[BowMeHunter]

IWX had a very underwhelming AFD concerning anything past tonight. This is a bit surprising considering they expanded the LE watches and have moderate/heavy snow accums over much of N Indiana, and this being the first big lake event. This is rare for them.

I thought it was good AFD.

[Hoosier]

Surprise. Surprise. IWX has now added Elkhart county to the LES watch for Sat. night through Monday with up to 8" plus in my area and a foot to foot and a half westward. Prolonged period with good fetch. Should be quite the event if it pans out as now expected.

Dang, I might have to pull the trigger on a chase. Have largely been ignoring the lake aspect but this sounds like it could be good.

[weatherbo]

Surprise. Surprise. IWX has now added Elkhart county to the LES watch for Sat. night through Monday with up to 8" plus in my area and a foot to foot and a half westward. Prolonged period with good fetch. Should be quite the event if it pans out as now expected.

Watch stops 5 miles north of me, but I'd expect an advisory here if things go as planned which is usually the case down this way. Still though, I have "snow, heavy at times with moderate accums" in my forecast. should be an exciting weekend around here. I have noticed in the past with the nice nnw bands, I usually get amoounts close to what Goshen receives.

[weatherbo]

I thought it was good AFD.

Oh, they revised it because they left out the longterm completely at first.