December 25-29th Storm Disco

[Geos]

Can't wait lol.  I'm on the sleet bandwagon now given the slight southeastward trends this evening.  Some of the models would indicate over 5" of sleet verbatim given the 3:1 ratio general rule.  Can't really see much snow falling here, or nearby with such strong WAA knifing in from the southeast aloft.  Despite some of the southeast trends of the system the intense WAA should keep the appreciable snow accumulations well northwest of this area.  A burst or two of heavy snow would be possible given the strong dynamics, but intense WAA should negate that to a few brief bursts here and there.  

 

Looking forward to some pictures of drifting sleet. 

 

SLP just south of Texarkana now.

 

 

 

Made it to freezing! 31.8° to be exact.

[cyclone77]

Looking forward to some pictures of drifting sleet. 

 

 

 

 

DVN has noted the slight southeastward shift in things with the latest update.  

 

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE QUAD CITIES IA IL

1159 PM CST SUN DEC 27 2015

.UPDATE...

ISSUED AT 1144 PM CST SUN DEC 27 2015

DURING THE FIRST PHASE OF THIS WEATHER EVENT...BE PREPARED FOR

HEAVY SLEET MONDAY MORNING FOR MOST OF EASTERN IOWA...WESTERN

ILLINOIS...AND NORTHEAST MISSOURI...AND A TRANSITION TO FREEZING

RAIN ALONG AND SOUTH OF HIGHWAY 34. ADDITIONALLY...EASTERLY WINDS

WILL INCREASE AND GUST OVER 40 MPH.

SOME OF THE TRENDS IN THE 00Z/12.28 GUIDANCE...SUCH AS THE

NAM/GFS/NMM...HAVE BEEN TO COOL THE THERMAL RIDGE ALOFT

SLIGHTLY...INITIAL FORECAST CHANGES WERE MADE TO INCREASE SLEET

CHANCES/COVERAGE AND DECREASE OVERALL POTENTIAL FOR FREEZING RAIN.

THESE GRID CHANGES HAVE BEEN REFLECTED IN THE UPDATED TEXT OF THE

CURRENT WINTER WEATHER HEADLINES...WITH A SOUTHWARD SHIFT OF THE

MAIN FREEZING RAIN ZONE AS IT LOOKS LIKE SLEET WILL BE THE

DOMINATE WINTRY PRECIPITATION TYPE.

AS SFC TEMPS WARM INTO THE MID 30S ALONG AND EAST OF THE

MISSISSIPPI RIVER DURING THE AFTN...AND TO THE SOUTH OF HIGHWAY

30...A CHANGEOVER TO A PERIOD OF PLAIN RAIN IS POSSIBLE AND MORE

LIKELY THE FURTHER SOUTH YOU GO...WHICH IS GOOD NEWS FOR AREAS

THAT RECEIVE ICE ACCUMULATION MONDAY MORNING.

[Hoosier]

Excruciatingly slow temperature drop but have made it down to 35. 

[Geos]

6z HRRR, holds sleet over Chicago through 21z.

 

Upper 20s just NW of Milwaukee.

[LansingWeather]

Wow, DTX went with a WWA for the southern half of the watch. That really surprises me, high winds, sleet accumulation to a half inch and .1-.2" of ice? They are always too conservative...

[HillsdaleMIWeather]

Wow, DTX went with a WWA for the southern half of the watch. That really surprises me, high winds, sleet accumulation to a half inch and .1-.2" of ice? They are always too conservative...

 

DTX in a nutshell. They even are underdoing the accumulations throughout the advisory.

[Hoosier]

6z NAM coming in with a lot of sleet here.  Would almost be like a poor man's GHD if it's right.

[HillsdaleMIWeather]

06Z NAM is also more icey for longer in the areas getting ice.

[Stebo]

Wow, DTX went with a WWA for the southern half of the watch. That really surprises me, high winds, sleet accumulation to a half inch and .1-.2" of ice? They are always too conservative...

Only thing I can think of is they are thinking the precip rates will be too high for accretion, beyond that I think it is a bad call by them, which would be the second major burn by them this winter.

[RCNYILWX]

6z NAM coming in with a lot of sleet here. Would almost be like a poor man's GHD if it's right.

Pulled this sounding near your area at 15z. Big question I had at the office today/yesterday and I still have is with that magnitude of warm nose aloft and impacts on ptype. Looks like +5 or +6C on that sounding already at 15z. Then looking closer to ORD at 18z shows nearly +10C in the warm nose above 850 mb:

This is pretty similar to the 00z run w.r.t. maxT aloft. There's definitely a good subfreezing/refreezing layer down low, but with such warm temps aloft if NAM is close on thermal profile, I'd still be more concerned with freezing rain rather than sleet. Farther north and west, certainly higher sleet probabilities but even there wonder if models are overdoing sleet accums if the very warm air aloft verifies.

One of my coworkers has been doing a lot of work on ptype tools for the grids and he found from several past cases that predominant sleet typically has a lower maxT aloft, more like +1.5. Latest work has focused on accounting for positive (melting) and negative (freezing/refreezing) areas in the sounding, similar to CAPE and CIN.

[Hoosier]

Pulled this sounding near your area at 15z. Big question I had at the office today/yesterday and I still have is with that magnitude of warm nose aloft and impacts on ptype. Looks like +5 or +6C on that sounding already at 15z. Then looking closer to ORD at 18z shows nearly +10C in the warm nose above 850 mb:

This is pretty similar to the 00z run w.r.t. maxT aloft. There's definitely a good subfreezing/refreezing layer down low, but with such warm temps aloft if NAM is close on thermal profile, I'd still be more concerned with freezing rain rather than sleet. Farther north and west, certainly higher sleet probabilities but even there wonder if models are overdoing sleet accums if the very warm air aloft verifies.

One of my coworkers has been doing a lot of work on ptype tools for the grids and he found from several past cases that predominant sleet typically has a lower maxT aloft, more like +1.5. Latest work has focused on accounting for positive (melting) and negative (freezing/refreezing) areas in the sounding, similar to CAPE and CIN.

 

 

 

Thanks for chiming in.  I had just taken a quick glance at 6z NAM precip type output and nothing else.  Warm layer aloft certainly looks robust on the NAM and there's the pretty decent subfreezing layer down below as you mentioned, but maybe it won't be enough.  I guess we'll find out soon.

[OHweather]

Pulled this sounding near your area at 15z. Big question I had at the office today/yesterday and I still have is with that magnitude of warm nose aloft and impacts on ptype. Looks like +5 or +6C on that sounding already at 15z. Then looking closer to ORD at 18z shows nearly +10C in the warm nose above 850 mb:

This is pretty similar to the 00z run w.r.t. maxT aloft. There's definitely a good subfreezing/refreezing layer down low, but with such warm temps aloft if NAM is close on thermal profile, I'd still be more concerned with freezing rain rather than sleet. Farther north and west, certainly higher sleet probabilities but even there wonder if models are overdoing sleet accums if the very warm air aloft verifies.

One of my coworkers has been doing a lot of work on ptype tools for the grids and he found from several past cases that predominant sleet typically has a lower maxT aloft, more like +1.5. Latest work has focused on accounting for positive (melting) and negative (freezing/refreezing) areas in the sounding, similar to CAPE and CIN.

One question that I'm not sure on...when forming snow crystals in the clouds you typically need temps of -10C or colder; does that same rule apply when you're re-freezing rain drops? That warm layer is certainly deep and robust enough to completely melt the snowflakes. I know with a shallower warm layer that only partially melts the snowflakes it's much easier to get sleet. The cold layer is deep but the coldest temp is only around -5C briefly. I guess we'll find out soon either way.

[RCNYILWX]

Thanks for chiming in. I had just taken a quick glance at 6z NAM precip type output and nothing else. Warm layer aloft certainly looks robust on the NAM and there's the pretty decent subfreezing layer down below as you mentioned, but maybe it won't be enough. I guess we'll find out soon.

I think this is a really excellent potential case for future study based on what happens. Even if the warmer models with maxT aloft verify and it still sleets alot, this will be a pretty extreme case of still supporting sleet, probably on the higher end of what's possible without true arctic air in place in the boundary layer.

My guess is the morning forecast update will bump sleet accums up some, especially NW 1/3 of CWA and wondering if WSW will be expanded southward, unless they just go with an Ice Storm Warning.

[RCNYILWX]

One question that I'm not sure on...when forming snow crystals in the clouds you typically need temps of -10C or colder; does that same rule apply when you're re-freezing rain drops? That warm layer is certainly deep and robust enough to completely melt the snowflakes. I know with a shallower warm layer that only partially melts the snowflakes it's much easier to get sleet. The cold layer is deep but the coldest temp is only around -5C briefly. I guess we'll find out soon either way.

The work I alluded to one of my coworkers is doing to incorporate into ptype forecasting may shed some light on that. He's tweaking the current probability of weather type tool many NWS offices use (at least in central region) to incorporate the Bourgouin method of p-type forecasting available in BUFKIT. Whether refreeze occurs depends on the integrated negative energy in the sounding, so my take is obviously the deeper and colder the refreeze layer the better to get sleet as dominant ptype to overcome the positive energy, because a robust and deep warm layer not only melts the ice crystals, it warms the rain drops.

Here's a link to a pdf of the Bourgouin paper: https://www.google.com/url?sa=t&source=web&rct=j&url=http://employees.oneonta.edu/blechmjb/JBpages/M361/BUFKITlabs/Bourgouin/Bourgouin2000.pdf&q=bourgoin%20precipitation%20type&ved=0ahUKEwic4qCElP7JAhXIbSYKHcPoCLgQFggeMAE&usg=AFQjCNEWk22bda6NBOLz7x6z6GclutiUhw&sig2=HqLA9H_POeX-gBZ945topg

[Hoosier]

I think this is a really excellent potential case for future study based on what happens. Even if the warmer models with maxT aloft verify and it still sleets alot, this will be a pretty extreme case of still supporting sleet, probably on the higher end of what's possible without true arctic air in place in the boundary layer.

My guess is the morning forecast update will bump sleet accums up some, especially NW 1/3 of CWA and wondering if WSW will be expanded southward, unless they just go with an Ice Storm Warning.

 

 

RAP and HRRR have really been signaling Lake and Porter counties for potentially significant ice accums. 

[RCNYILWX]

RAP and HRRR have really been signaling Lake and Porter counties for potentially significant ice accums.

We actually were about to include Lake and Kankakee in the WSW in the afternoon issuance but decided last minute to put them in the Freezing Rain Advisory.

[Hoosier]

We actually were about to include Lake and Kankakee in the WSW in the afternoon issuance but decided last minute to put them in the Freezing Rain Advisory.

 

 

Tricky call.  They shouldn't have a problem at least getting advisory amounts unless sleet somehow dominates.

[OHweather]

The work I alluded to one of my coworkers is doing to incorporate into ptype forecasting may shed some light on that. He's tweaking the current probability of weather type tool many NWS offices use (at least in central region) to incorporate the Bourgouin method of p-type forecasting available in BUFKIT. Whether refreeze occurs depends on the integrated negative energy in the sounding, so my take is obviously the deeper and colder the refreeze layer the better to get sleet as dominant ptype to overcome the positive energy, because a robust and deep warm layer not only melts the ice crystals, it warms the rain drops.

Here's a link to a pdf of the Bourgouin paper: https://www.google.com/url?sa=t&source=web&rct=j&url=http://employees.oneonta.edu/blechmjb/JBpages/M361/BUFKITlabs/Bourgouin/Bourgouin2000.pdf&q=bourgoin%20precipitation%20type&ved=0ahUKEwic4qCElP7JAhXIbSYKHcPoCLgQFggeMAE&usg=AFQjCNEWk22bda6NBOLz7x6z6GclutiUhw&sig2=HqLA9H_POeX-gBZ945topg

Interesting, thank you! It looks like the positive area is a bit larger than the negative on the two NAM soundings...so it will be interesting to see if ZR or IP dominates should those temp profiles be close to accurate. I'd personally lean ZR.

[RCNYILWX]

Tricky call. They shouldn't have a problem at least getting advisory amounts unless sleet somehow dominates.

Starting to get the lower dewpoints in from the east. Constant feed of drier air due to the prolonged easterly flow makes this one really tricky. Slow northward movement of the SLP and the huge high to the north. I think icing potential is fairly limited on the Chicago shore, but could see pingers for a decent duration.

[SchaumburgStormer]

Down to 31. Radar returns crawling north. Like others have said, this is going to be tricky. I imagine we see a lot of surprises both in amount and p type.

[RCNYILWX]

Interesting, thank you! It looks like the positive area is a bit larger than the negative on the two NAM soundings...so it will be interesting to see if ZR or IP dominates should those temp profiles be close to accurate. I'd personally lean ZR.

You're welcome! I think it's pretty fascinating stuff and is a more in depth physical explanation of how the warm layers and refreezing layers play a role on determining ptype vs strictly looking at the maxT aloft and coldest T in the freezing layer which is more arbitrary. Starting to get UP reports in central IL at PNT and BMI, so we'll see how things trend. Will be interesting to look at aircraft soundings too.

[Kaner88]

08z HRRR coming in pretty cold compared to previous runs. Surface temperatures in the upper 20s for northern Illinois by 16z.

[Hoosier]

Starting to get the lower dewpoints in from the east. Constant feed of drier air due to the prolonged easterly flow makes this one really tricky. Slow northward movement of the SLP and the huge high to the north. I think icing potential is fairly limited on the Chicago shore, but could see pingers for a decent duration.

 

 

I've noticed that dewpoint rises sometimes lag behind models a bit in these types of setups.  As is, models don't really have dews getting above freezing here until late afternoon or even later. 

[HillsdaleMIWeather]

RGEM has over .5 of ice in my area from the new 06Z Run

 

[Kaner88]

RGEM has over .5 of ice in my area from the new 06Z Run

 

That's the old 06z run, new 06z accumulation maps not out yet.

[SchaumburgStormer]

.SHORT TERM...

401 AM CST

THROUGH TUESDAY...

A MAJOR WIND AND ICE EVENT FOR A GOOD PORTION OF THE AREA...ALONG

WITH SOME OTHER ACCOMPANYING IMPACTS...IS BEGINNING TO UNFOLD INTO

THE REGION EARLY THIS MORNING. NO CHANGES PLANNED TO THE SPATIAL

EXTENT OF THE CURRENT MYRIAD OF HEADLINES...AS THEY COVER THIS

DYNAMIC SYSTEM WELL...WITH JUST SOME MINOR SHIFTS TO TIMING TO

COVER PRIME THREAT TIMES. WE ARE AT THE STAGE NOW OF INCORPORATING

OBSERVATIONAL TRENDS INTO THE GOING FORECAST WITH HOPEFULLY

ADJUSTMENTS MORE SO THAN MAJOR SHIFTS...AND THUS FAR THAT IS THE

CASE. HOWEVER BEING IN A TRANSITIONAL PRECIPITATION EVENT WHERE

SPECIFIC SURFACE AND ALOFT TEMPERATURES PLAY CRITICAL ROLES MAKES

THIS PARTICULARLY CHALLENGING.

THE MOST NOTEWORTHY CHANGES/OBSERVATIONS IN SUMMARY ARE THE OVERALL

FORECAST PRECIPITATION AMOUNTS HAVE BEEN INCREASED AREAWIDE LATE

MORNING THROUGH THE AFTERNOON AS IT IS MORE APPARENT CONVECTIVE

ELEMENTS AND SLANTWISE INSTABILITY WILL IMPINGE INTO THE AREA. THE

OVERLAP AREA OF THESE HEAVIER INTENSITY/AMOUNTS AND THE STILL COLD

ENOUGH FOR FREEZING RAIN APPEARS TO BE ALONG/NORTH OF INTERSTATE

80 AND ALONG AND WEST OF ILLINOIS 47...SO HAVE BUMPED UP FORECAST

ICE ACCUMULATIONS IN THESE AREAS AND PLACED HEAVY WORDING IN THE

FORECAST. HAVE ALSO ADDED ISOLATED/SCATTERED THUNDER...ALTHOUGH

THAT SHOULD BE MAINLY AFTER THE PEAK ICING TIME.

ALSO CONTINUED AN ADJUSTMENT OF A BIT SLOWER TEMPERATURE RECOVERY

IN THE IMMEDIATE LOW-LEVELS RESULTING IN LONGER SLEET DURATION

ALONG AND NORTH OF I-88...WITH THAT POTENTIALLY THE DOMINANT

PRECIPITATION TYPE MOST OF THE MORNING IN THAT REGION. HAVE UPPED

SLEET ACCUMULATION TO AROUND AN INCH THOUGH HIGHER TOTALS

CERTAINLY POSSIBLE DEPENDING ON RATE. WHILE IMPACTS DURING THE

MORNING MAY BE LESS IF THIS MAINLY SLEET/INTERMITTENT SNOW

MATERIALIZES...THE ICING POTENTIAL IN THE AFTERNOON WITH STRONG

WINDS STILL LOOKS ON TRACK.

A VERY POTENT SYSTEM IN ALMOST EVERY DEFINITION IS CENTERED OVER

THE ARKLATEX EARLY THIS MORNING...WHICH WILL HAVE A TRACK RECORD

WHEN IT IS FINISHED LATE TONIGHT WITH AFFECTING ALMOST EVERY

CENTRAL CONUS STATE WITH SOME FORM OF IMPACTING WEATHER. A 70

DEGREE TEMPERATURE DIFFERENCE FROM NORTHWEST IOWA TO NORTHERN

MISSISSIPPI EARLY THIS MORNING HIGHLIGHTS THE BAROCLINICITY THAT

THE WARM AND MOIST ADVECTION IS OVERRIDING INTO OUR AREA.

PRECIPITATION WITH THE LEADING EDGE OF THIS IN THE SOUTHERN CWA

HAS BEEN A LIGHT MIXED BAG THUS FAR. NEAR DAYBREAK INTENSITY LOOKS

TO UPTICK IN RESPONSE TO INCREASING DIFFLUENCE AND LOWER TO MID-

LEVEL F-GEN. THIS WILL CAUSE A PRONOUNCED WET-BULBING COOLING

EFFECT AS INHERENT DRY AIR BECOMES SATURATED WITHIN THE LOW-LEVEL

NORTHEAST FLOW. EARLY MORNING AMDAR DATA NEAR CHICAGO INDICATE A

WARM NOSE AROUND 2C ALOFT AND A LOW-LEVEL COLD NOSE AROUND -5C...

BOTH OF WHICH THE RAP SEEMS TO BE INITIALIZING WELL WITH OVER ITS

PAST FEW RUNS...LENDING SOME CONFIDENCE OF FINE TUNING THE

FORECAST TOWARD IT THIS MORNING. THE VERTICAL PROFILES AND

EXPECTED UPTICK IN PRECIP INTENSITY SHOULD CAUSE THE MAIN TYPE AT

FIRST TO BE ICE PELLETS OR EVEN SOME LIGHT SNOW /WHICH HAS BEEN

REPORTED/. BEING WITHIN THE LOW-LEVEL CONVEYOR BELT OF THIS MATURE

SYSTEM THIS MORNING...WITH 45 KT NORTHEAST 925MB FLOW PER

PROFILERS...THIS SEEMS TO SUPPORT THE TREND FOR P-TYPE TO WANT TO

REMAIN AS SLEET WITH OCCASIONAL SNOW IN FAR NORTHERN PARTS OF THE

CWA INTO LATE MORNING WITH MINOR ACCUMULATIONS. MORE IMPORTANTLY

FOR IMPACTS IT ALSO KEEPS THE FREEZING RAIN CORRIDOR IN PLACE TO

THE SOUTH OF THIS...THROUGH THE MORNING AND EVEN POTENTIALLY EARLY

AFTERNOON. TO HELP VISUALIZE...THIS IS ROUGHLY 30 MILES OR SO

NORTH OR SOUTH OF INTERSTATE 80.

THE AREAS IN THE SHADOW OF THE LAKE...INCLUDING CENTRAL AREAS OF

THE CHICAGO METRO...STILL LOOK LIKE THEY COULD STRUGGLE TO SEE

TEMPERATURES DROP MUCH DUE TO THE STRONG ADVECTION FROM THE

LAKE...SO ICING IS A LITTLE LESS OF A THREAT FOR THESE IMMEDIATE

NEARSHORE LOCATIONS...INCLUDING DOWNTOWN. HOWEVER WIND SPEEDS WILL

BE THE MAXIMUM...GUSTING TO IMPRESSIVE MAGNITUDES TO 50 TO 60 MPH

THIS AFTERNOON AND EARLY EVENING.

THE INGREDIENTS FOR THE WINDS TODAY AND INTO EARLY EVENING CONTINUE

TO JUST BE TRULY STRIKING. PRESSURE FALLS OF AROUND 15MB ARE

FORECAST BETWEEN 10AM AND 3PM OVER MUCH OF THE CWA THIS AFTERNOON.

HAVE CONTINUED WITH FORECAST HIGH END WIND GUSTS AND CORRELATED

DUAL IMPACT WITH ANY ICED LINES AND LIMBS. WIDESPREAD POWER

OUTAGES STILL LOOK POTENTIALLY REALIZED WHERE THE HEAVIER ICE

ACCUMULATIONS OCCUR.

AS THE STACKED SYSTEM CENTER AND ASSOCIATED DEEP TROPOSPHERIC FOLD

MOVES TOWARD THE AREA MID-AFTERNOON...THE WARM MOIST CONVEYOR

BELT NOSE PUSHES INTO THE AREA WITH SOME HEAVY PRECIPITATION AGAIN

LIKELY. ELEVATED INSTABILITY VALUES SUPPORT THUNDER INCLUSION. THE

LOW WILL PASS OVER WITH WINDS THEN EASING. FORCING LOOKS ENOUGH

STILL TO WARRANT SCATTERED RAIN SHOWERS ACROSS THE AREA AND

POSSIBLY EVEN SOME DRIZZLE. THE CHANCE FOR SOME OF THIS TO BE SNOW

SHOWERS INCREASES OVERNIGHT...ALTHOUGH THE INTENSITY SHOULD BE

LIGHT ENOUGH WITH MARGINAL SURFACE TEMPERATURES TO NOT REALLY HAVE

ANY ACCUMULATION. SOME OF THESE SHOWERS MAY LINGER INTO TUESDAY

MORNING...WITH WRAPAROUND COLD ADVECTION KEEPING TEMPERATURES

FROM RISING ANY AND HIGHS IN THE 30S.

[snowstormcanuck]

From DTX:

 

INITIALLY DRY THERMAL PROFILES MAY YIELD A FEW SNOWFLAKES DURING
INITIAL SATURATION, BUT NOTHING WORTH AN EXPLICIT MENTION IN THE
FORECAST. INSTEAD, THE DOMINANT PRECIP TYPES ARE FORECAST TO BE
SLEET AND FREEZING RAIN AS STRONG SOUTHERLY FLOW ALOFT SPREADS OVER
COLD HIGH PRESSURE THAT WILL REMAIN FIRMLY IN PLACE. EVEN IN THE
DETROIT METRO AREA, THE WARM NOSE IS MODELED TO BE QUITE ELEVATED
/CENTERED AT 750MB/ TO WELL INTO THIS AFTERNOON, YIELDING HIGH
CONFIDENCE IN SLEET AS THE DOMINANT PTYPE TO START. A TRANSITION TO
FREEZING RAIN AND THEN RAIN WILL EVOLVE DURING THE EVENING AS STRONG
MOISTURE ADVECTION FORCES SURFACE DEWPOINTS ABOVE FREEZING. A
SIMILAR EVOLUTION IS EXPECTED FOR ALL LOCATIONS. ONE ITEM OF NOTE IS
POTENTIAL FOR EASTERLY FLOW ACROSS LAKE ERIE/ST CLAIR COULD CUT INTO
WINTRY PRECIP POTENTIAL IN WAYNE/MONROE COUNTY. THIS IS ACCOUNTED
FOR IN THE FORECAST WITH WSW WORDING SUGGESTING LESSER AMOUNTS
TOWARD THE LAKESHORE.

 

I've never heard them mentioning Lk Erie/St. Clair influencing the thermals of Detroit proper compared to "inland" areas. Just viscerally it wouldn't seem to ring true, but I guess if water temps are very warm it's possible?

[HillsdaleMIWeather]

Precipitation is rapidly approaching, seems to be doing well at staying sleet and freezing rain right now.

[Chambana]

Howling winds, heavy rainfall and 32 degrees this is a first. It's a darn good thing the temps are on the rise throughout the day, or you would be dealing with a nightmare scenario. Everyone up north be safe during the ice storm.

[weathergy]

Almost looks like a middle finger sideways, lol

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