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12/20-12/21 Moderate/Intense Clipper Event?


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850's at ORD are -4C at 12Z. The event is over by then. There will be no mixing during the main event. Freezing drizzle or snow grains after the snow is done due to drying above 800mb is possible, but a bonafide mixing scenario is not going to happen. Using 1000-500mb thicknesses in this situation is tricky, as mid-level thicknesses are pretty high due to WAA aloft, but never get that close to... or over 0C.

That's what I said the other day...do not use the 540 line for this event (never should rely on that anyway). It's going to be misleading given the deep layer of sufficiently cold but not very cold temps in the column.

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AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE QUAD CITIES IA IL

1019 AM CST MON DEC 20 2010

UPDATE

..MAJOR REVISIONS TO THE OVERALL FCST

12Z UA DATA COMBINED WITH RADAR/SFC OBS SHOW THE SNOW BREAKING OUT

MUCH SOONER THAN EXPECTED. COMBINATION OF RUC TRENDS AND INCOMING

WRF INDICATE THE 290K CONDENSATION PRESSURE DEFICITS AND 290K

OMEGA DEPICT REASONABLY WELL WHAT IS CURRENTLY GOING. WAA

STRENGTHENS THE OMEGA BY LATE MORNING AND INTO THE AFTERNOON. THE

STRONGEST FORCING IS CURRENTLY ROUGHLY ON A KALO TO KEWANEE LINE

AND WILL SLOWLY SHIFT TO THE NORTH/EAST.

THUS HAVE EXPANDED THE CURRENTLY HEADLINES AND HAVE MADE THEM

EFFECTIVE IMMEDIATELY. IT APPEARS THAT 2 TO NEARLY 4 INCHES MAY

OCCUR BY SUNSET WITH ANOTHER INCH OR TWO POSSIBLE OVERNIGHT. FCST

SOUNDINGS IN THE SOUTH GET TO AROUND FREEZING SO A RASN MIX IS

POSSIBLE IN THE SOUTHERN THIRD OR SO OF THE CWFA.

One of the "surprises" I was potentially talking about. These things always have a few. Interested to see how much this area eventually sees with current trends.

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the snow ended here about 1/2 hour ago well before the radar showed the echoes moving NE away from me(radar finally showing no echoes over ne NOW)

The thein f snow s set up EXCACTLY where it was during the first "super clipper" a few weeks ago

yep, incredibly similar placement, will be interesting to see if Champaign out does Chicago again. Band really streaking south but hardly moving east.

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heavy banding def setting up futher south than thought. Wonder how long it takes LOT to adjust things for their SW area.

this is sort of comical..(not blaming NWS for tough forecast)

my orginal forecast at 4am was flurries in the morning a chance of snow in the afternoon and into tonight befire changing to ZR- up to an inch..

now they just updated and said 1-2 inches possible today with snow,,,,but now the snow looks over

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this is sort of comical..(not blaming NWS for tough forecast)

my orginal forecast at 4am was flurries in the morning a chance of snow in the afternoon and into tonight befire changing to ZR- up to an inch..

now they just updated and said 1-2 inches possible today with snow,,,,but now the snow looks over

Is that the discussion or was that a pt/click forecast? The NWS system is not made too well for rapid updating in the grids though either way...sometimes when they try and quickly update based off current trends things like this happen.

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Is that the discussion or was that a pt/click forecast? The NWS system is not made too well for rapid updating in the grids though either way...sometimes when they try and quickly update based off current trends things like this happen.

so to sum up the forecast people heard today was scattered flurries in the morning, then a 50% chance of light snow in the afternoon and evening up to one inch...

what happened (unless trends change) 1 to 1.5 inches(est. just north of here) inch or so before noon or 2pm in not so light snow at times,,, then its over..

discussion early this am

SHORT TERM...TODAY THROUGH WEDNESDAY...

PRECIPITATION CURRENTLY OVER IOWA EXPECTED TO ENHANCE AND EXPAND

SOUTHEAST INTO NORTHERN AND EASTERN ILLINOIS TODAY...AS LIFT

INCREASES ALONG THE BAROCLINIC ZONE. QUITE A BIT OF DRY AIR AT THE

LOWER LEVELS NEEDS TO SATURATE...SO WILL CONTINUE WITH THE 40

PERCENT POPS FOR THIS AFTERNOON ACROSS THE NORTH AND NORTHEAST...

WITH MAINLY FLURRIES ELSEWHERE. HEAVIEST SNOW AXIS CONTINUES TO

REMAIN TO OUR NORTH...BUT MAY STILL SEE A HALF INCH OR SO ACROSS

THE NORTHEAST EDGE OF THE CWA THROUGH THIS EVENING.

MOST MODELS NOW SHOWING THE DOUBLE-BARREL STRUCTURE OF THE

INCOMING STORM SYSTEM TONIGHT...WITH THE NORTHERN LOW THE MORE

DOMINANT AS AN UPPER CLOSED LOW IS NEARBY. UNFORTUNATELY THERE IS

STILL NOT MUCH AGREEMENT AS TO THE STRENGTH OF THIS LOW...BUT THEY

AGREE THE PRECIPITATION THREAT SHOULD TAPER FROM SOUTH TO NORTH

OVERNIGHT. FORECAST SOUNDINGS SHOW NO ICE CRYSTALS LEFT AFTER

MIDNIGHT...SO SHOULD SEE MORE OF A DRIZZLE OR FREEZING DRIZZLE

SITUATION BY LATE IN THE NIGHT

10:30 am discussion

DISCUSSION

ISSUED 1035 AM CST MON DEC 20 2010

SNOW HAS SHIFTED INTO THE FORECAST AREA QUITE A BIT FASTER THAN

EARLIER THOUGHT. BASED ON THE RADAR TRENDS...IT APPEARS THE SNOW

BAND OUT TO OUR WEST WAS SHIFTING MORE NORTHEAST AND SETTING UP

ACRS OUR FAR NORTH AND NORTHEAST...NORTH OF INTERSTATE 74. HAVE

INCREASED THE POPS FOR THIS MRNG AND AFTN IN THOSE AREAS BASED ON

CURRENT TRENDS WITH RADAR AND SATELLITE DATA. WITH A FASTER TIMING

ON THE ONSET OF THE PRECIP INTO OUR AREA TODAY...WOULD THINK THE

SNOW SHOULD SHIFT JUST OFF TO OUR EAST AND NORTH AT A FASTER PACE

AS WELL AND WILL ADJUST THE POPS FOR TONIGHT BASED ON THE LATEST

FORECAST SOUNDINGS...WHICH SUGGEST MOST OF OUR AREA WILL LOSE THE

ICE CRYSTALS...INDICATING THE POTENTIAL FOR DRIZZLE OR FREEZING

DRIZZLE. THAT THREAT SHOULD CONTINUE INTO TUE MRNG. MAY NEED A

HEADLINE ACRS OUR NE TO ADDRESS THE THREAT FOR SOME LIGHT ICING

OVERNIGHT...BUT WILL ADDRESS THAT IN THE AFTN PACKAGE. UPDATE

SHOULD BE OUT SHORTLY.

SMITH

3:30 Zone

INCLUDING THE CITIES OF...PEORIA

338 AM CST MON DEC 20 2010

TODAY...CLOUDY. SCATTERED FLURRIES IN THE MORNING

THEN A

50 PERCENT CHANCE OF SNOW IN THE AFTERNOON. HIGHS IN THE LOWER

30S. SOUTHEAST WINDS 10 TO 15 MPH WITH GUSTS TO AROUND 25 MPH.

TONIGHT...SNOW LIKELY IN THE EVENING

THEN A CHANCE OF FREEZING

RAIN OR SNOW AFTER MIDNIGHT. SNOW ACCUMULATION UP TO 1 INCH. NOT

AS COLD. NEAR STEADY TEMPERATURE AROUND 30. SOUTHEAST WINDS 10 TO

15 MPH. CHANCE OF PRECIPITATION 70 PERCENT.

8 AM UPDATE

INCLUDING THE CITIES OF...PEORIA

804 AM CST MON DEC 20 2010

TODAY

CLOUDY WITH A 50 PERCENT CHANCE OF SNOW. HIGHS IN THE

LOWER 30S. SOUTHEAST WINDS 10 TO 15 MPH. GUSTS UP TO 25 MPH IN

THE AFTERNOON.

TONIGHT...SNOW LIKELY IN THE EVENING

THEN A CHANCE OF FREEZING

RAIN...SNOW AND AREAS OF FREEZING DRIZZLE AFTER MIDNIGHT. SNOW

ACCUMULATION UP TO 1 INCH. NOT AS COLD. NEAR STEADY TEMPERATURE

AROUND 30. SOUTHEAST WINDS 10 TO 15 MPH. CHANCE OF PRECIPITATION

70 PERCENT.

TUESDAY

11 AM UPDATE

INCLUDING THE CITIES OF...PEORIA

1056 AM CST MON DEC 20 2010

REST OF TODAY

OCCASIONAL SNOW. NEW SNOW ACCUMULATION AROUND

1 INCH. HIGHS IN THE LOWER 30S. SOUTHEAST WINDS 10 TO 15 MPH.

GUSTS UP TO 25 MPH IN THE AFTERNOON. CHANCE OF PRECIPITATION

90 PERCENT.

TONIGHT

CLOUDY. CHANCE OF SNOW OR PATCHY FREEZING DRIZZLE IN

THE EVENING...THEN PATCHY FREEZING DRIZZLE AFTER MIDNIGHT. NOT AS

COLD. NEAR STEADY TEMPERATURE AROUND 30. SOUTHEAST WINDS 10 TO

15 MPH. CHANCE OF PRECIPITATION 40 PERCENT.

1 PM UPDATE SNOW STOPPED JUST BWFORE ISSUED

INCLUDING THE CITIES OF...PEORIA

1255 PM CST MON DEC 20 2010

REST OF TODAY

SNOW. SNOW ACCUMULATION OF 1 TO 2 INCHES. NEAR

STEADY TEMPERATURE IN THE LOWER 30S. SOUTHEAST WINDS 10 TO 15 MPH

WITH GUSTS TO AROUND 25 MPH. CHANCE OF PRECIPITATION 90 PERCENT.

TONIGHT

CLOUDY. CHANCE OF SNOW OR PATCHY FREEZING DRIZZLE IN

THE EVENING...THEN PATCHY FREEZING DRIZZLE AFTER MIDNIGHT. NOT AS

COLD. NEAR STEADY TEMPERATURE AROUND 30. SOUTHEAST WINDS 10 TO

15 MPH. CHANCE OF PRECIPITATION 40 PERCENT.

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