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December 2011 General Discussion/Obs


Chicago Storm

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the models change every 6 hours. Oh, and the very end of the long range is the FIRST day of winter.

http://www.americanw...nterobs-thread/

Meh, I still say a ton of threats, sucky busts, and nice surprises will occur in the med-long range. Models have just been TOO bad. The other day the GFS had a thickness of 494 one run (sfc temps mid-teens) and the very next run it was 544 (sfc temps upper 30s) around day 14. Its ridiculous how bad it is in the long range, better off reading the farmers almanac. :thumbsup:

need a torched 15-20" season to set you straight.

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some crazy shear from 850mb down to the sfc on the western side of the lake creating that convergent boundary. LE precip has made it all the way out here.

from LOT

ONE INTERESTING FEATURE

TONIGHT IS THAT THE REGIONAL GEM DEVELOPS A WEAK MESO LOW ACROSS

THE SOUTHERN HALF OF THE LAKE...DUMPING 4+ INCHES OF SNOW ACROSS

RACINE/KENOSHA/LAKE AND EVEN MCHENRY COUNTIES TONIGHT AND INTO

TOMORROW MORNING. THE PREVIOUS RGEM RUNS SHOWED SIMILAR

OUTCOMES... BUT MORE ACROSS LAKE COUNTY INDIANA/COOK COUNTY AND

NOWHERE NEAR AS INTENSE AS THE CURRENT RUN. WILL MONITOR TO SEE IF

TRENDS LEAN IN A HIGHER DIRECTION BUT FOR NOW WILL KEEP IT IN THE

SUB HALF IN RANGE.

:stun:

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some crazy shear from 850mb down to the sfc on the western side of the lake creating that convergent boundary. LE precip has made it all the way out here.

from LOT

ONE INTERESTING FEATURE  

TONIGHT IS THAT THE REGIONAL GEM DEVELOPS A WEAK MESO LOW ACROSS  

THE SOUTHERN HALF OF THE LAKE...DUMPING 4+ INCHES OF SNOW ACROSS  

RACINE/KENOSHA/LAKE AND EVEN MCHENRY COUNTIES TONIGHT AND INTO  

TOMORROW MORNING. THE PREVIOUS RGEM RUNS SHOWED SIMILAR  

OUTCOMES... BUT MORE ACROSS LAKE COUNTY INDIANA/COOK COUNTY AND  

NOWHERE NEAR AS INTENSE AS THE CURRENT RUN. WILL MONITOR TO SEE IF  

TRENDS LEAN IN A HIGHER DIRECTION BUT FOR NOW WILL KEEP IT IN THE  

SUB HALF IN RANGE.

Setup isn't great by any means although certainly good enough for lake precip with delta T's peaking around 16-17 and inversion heights into the 5k foot range. Could at least have some minor accums especially away from the shore.  Areas near the shore may tend to stay mixed or at least warm enough to prevent much in the way of sticking but decently cool airmass so could be enough even there especially in any heavier bursts.  That possible mesolow will need to be watched...we know how those can screw up a forecast.

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Some thoughts from NIU weather....

So...if you're wondering when "the shoe will fall", the GFS says something

significant might hit us around the 15th, but that's in model la-la land

where everything is taken with a huge salt pile. Until then, however,

just weak systems coming through here, while both coasts get hit with significant

systems.

It is interesting to also note that when we have never had a snowstorm

by this time of the season, no winters have had above average snowfall

in recorded history, which goes against my forecast, of course. Will it come

true? Stay tuned...a few big snows can train wreck a lack of a snowy winter.

In summary, look for near average temperatures and much below

average rainfall and snowfall over the next 10 days.

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Setup isn't great by any means although certainly good enough for lake precip with delta T's peaking around 16-17 and inversion heights into the 5k foot range. Could at least have some minor accums especially away from the shore. Areas near the shore may tend to stay mixed or at least warm enough to prevent much in the way of sticking but decently cool airmass so could be enough even there especially in any heavier bursts. That possible mesolow will need to be watched...we know how those can screw up a forecast.

Ya would think a change to snow further inland where precip is once the BL cools later tonight.

We had a few flakes mixing in with light rain about 30 mins ago.

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from LOT afternoon AFD... The NAM doesn't even have this but atleast something to watch. Thing to watch in the long range is if the ridging breaks down in the Pacific and if storms can start coming in further south on the west coast. GFS hints at it in the long range

ON THURSDAY NIGHT...AS MENTIONED ABOVE...DIGGING H5 TROUGH WILL

SPAWN A WEAK SURFACE LOW WHICH WILL TRACK ACROSS NORTHERN GREAT

LAKES AND SEND AN ARCTIC FRONTAL BOUNDARY TOWARD AREA. MODELS HAVE

BEEN CONSISTENT IN SPITTING OUT A STRIPE OF VERY LIGHT QPF NEAR OR

OVER CWA IN RESPONSE TO THIS FEATURE. WITH NEGATIVE TEEN AIR AT

H85 BUILDING IN FROM THE NORTH BEHIND ARCTIC FRONT...SUSPECT WAVE

WILL RIDE ALONG LOW LEVEL BAROCLINIC ZONE. A PEEK AT GFS TIME

HEIGHT AT ORD FOR THURSDAY NIGHT PERIOD SHOWS SATURATION AND

ADEQUATE LIFT INTO -15C FAVORED SNOW GROWTH ZONE.

THEREFORE...DESPITE QPF ONLY IN THE HUNDREDTHS UP TO MAYBE A TENTH

OR SLIGHTLY MORE...WITH VERY COLD AIR MASS...SNOW WOULD BE HIGH

RATIO AND POSSIBLY RESULT IN FIRST WIDESPREAD LIGHT ACCUMULATING

SNOW OF THE SEASON FOR MANY (IF SCENARIO PANS OUT...POTENTIAL FOR

AN INCH OR TWO OF SNOW). FOR NOW...HAVE BUMPED UP POPS IN GRIDS TO

CHANCE ACROSS THE AREA GIVEN SOME UNCERTAINTY IN EXACTLY WHERE

BEST SNOW POTENTIAL WILL OCCUR. LIGHT SNOW MAY LINGER INTO EARLY

FRIDAY FOR EASTERN PORTION OF CWA BEFORE WAVE SHIFTS OFF TO THE

EAST.

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from LOT afternoon AFD... The NAM doesn't even have this but atleast something to watch. Thing to watch in the long range is if the ridging breaks down in the Pacific and if storms can start coming in further south on the west coast. GFS hints at it in the long range

ON THURSDAY NIGHT...AS MENTIONED ABOVE...DIGGING H5 TROUGH WILL

SPAWN A WEAK SURFACE LOW WHICH WILL TRACK ACROSS NORTHERN GREAT

LAKES AND SEND AN ARCTIC FRONTAL BOUNDARY TOWARD AREA. MODELS HAVE

BEEN CONSISTENT IN SPITTING OUT A STRIPE OF VERY LIGHT QPF NEAR OR

OVER CWA IN RESPONSE TO THIS FEATURE. WITH NEGATIVE TEEN AIR AT

H85 BUILDING IN FROM THE NORTH BEHIND ARCTIC FRONT...SUSPECT WAVE

WILL RIDE ALONG LOW LEVEL BAROCLINIC ZONE. A PEEK AT GFS TIME

HEIGHT AT ORD FOR THURSDAY NIGHT PERIOD SHOWS SATURATION AND

ADEQUATE LIFT INTO -15C FAVORED SNOW GROWTH ZONE.

THEREFORE...DESPITE QPF ONLY IN THE HUNDREDTHS UP TO MAYBE A TENTH

OR SLIGHTLY MORE...WITH VERY COLD AIR MASS...SNOW WOULD BE HIGH

RATIO AND POSSIBLY RESULT IN FIRST WIDESPREAD LIGHT ACCUMULATING

SNOW OF THE SEASON FOR MANY (IF SCENARIO PANS OUT...POTENTIAL FOR

AN INCH OR TWO OF SNOW). FOR NOW...HAVE BUMPED UP POPS IN GRIDS TO

CHANCE ACROSS THE AREA GIVEN SOME UNCERTAINTY IN EXACTLY WHERE

BEST SNOW POTENTIAL WILL OCCUR. LIGHT SNOW MAY LINGER INTO EARLY

FRIDAY FOR EASTERN PORTION OF CWA BEFORE WAVE SHIFTS OFF TO THE

EAST.

DVN seems to be on the same page..

THESE MODELS

INDICATE A LIGHT QPF EVENT...IN THE FORM OF SNOW BASED ON THERMAL

PROFILES...OVER THE CENTRAL TO SOUTHERN HALF OF THE FORECAST AREA.

WHILE MOISTURE WILL BE LIMITED...THE MODERATE FORCING FOR A SEVERAL

HOUR PERIOD MAY BE ENOUGH TO PRODUCE A BAND OF SNOWFALL IN THE RANGE

OF AT LEAST 1 TO 2 INCHES. WITH INCREASING CONFIDENCE...HAVE RAISED

PRECIPITATION CHANCES FROM SLIGHT...INTO THE 30 PERCENT RANGE OVER

THE FORECAST AREA.

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DVN seems to be on the same page..

THESE MODELS

INDICATE A LIGHT QPF EVENT...IN THE FORM OF SNOW BASED ON THERMAL

PROFILES...OVER THE CENTRAL TO SOUTHERN HALF OF THE FORECAST AREA.

WHILE MOISTURE WILL BE LIMITED...THE MODERATE FORCING FOR A SEVERAL

HOUR PERIOD MAY BE ENOUGH TO PRODUCE A BAND OF SNOWFALL IN THE RANGE

OF AT LEAST 1 TO 2 INCHES. WITH INCREASING CONFIDENCE...HAVE RAISED

PRECIPITATION CHANCES FROM SLIGHT...INTO THE 30 PERCENT RANGE OVER

THE FORECAST AREA.

pretty bullish.

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No accumulation on grassy surfaces with this morning's snow, but there was some accumulation on tree branches in Wauwatosa, at least.

I was at UWM this morning: there was a little accumulation on the grass with the half dollar sized flakes coming down! Lake effect might accumulate a little tonight as N winds blow in off the land instead of the 40° lake.

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I was at UWM this morning: there was a little accumulation on the grass with the half dollar sized flakes coming down! Lake effect might accumulate a little tonight as N winds blow in off the land instead of the 40° lake.

With the air temperature likely below freezing, overnight will be our opportunity if the lake bands can head S/SW soon enough. Could be some bands forming in N Lake Michigan according to MKX and the RGEM.

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from LOT afternoon AFD... The NAM doesn't even have this but atleast something to watch. Thing to watch in the long range is if the ridging breaks down in the Pacific and if storms can start coming in further south on the west coast. GFS hints at it in the long range

ON THURSDAY NIGHT...AS MENTIONED ABOVE...DIGGING H5 TROUGH WILL

SPAWN A WEAK SURFACE LOW WHICH WILL TRACK ACROSS NORTHERN GREAT

LAKES AND SEND AN ARCTIC FRONTAL BOUNDARY TOWARD AREA. MODELS HAVE

BEEN CONSISTENT IN SPITTING OUT A STRIPE OF VERY LIGHT QPF NEAR OR

OVER CWA IN RESPONSE TO THIS FEATURE. WITH NEGATIVE TEEN AIR AT

H85 BUILDING IN FROM THE NORTH BEHIND ARCTIC FRONT...SUSPECT WAVE

WILL RIDE ALONG LOW LEVEL BAROCLINIC ZONE. A PEEK AT GFS TIME

HEIGHT AT ORD FOR THURSDAY NIGHT PERIOD SHOWS SATURATION AND

ADEQUATE LIFT INTO -15C FAVORED SNOW GROWTH ZONE.

THEREFORE...DESPITE QPF ONLY IN THE HUNDREDTHS UP TO MAYBE A TENTH

OR SLIGHTLY MORE...WITH VERY COLD AIR MASS...SNOW WOULD BE HIGH

RATIO AND POSSIBLY RESULT IN FIRST WIDESPREAD LIGHT ACCUMULATING

SNOW OF THE SEASON FOR MANY (IF SCENARIO PANS OUT...POTENTIAL FOR

AN INCH OR TWO OF SNOW). FOR NOW...HAVE BUMPED UP POPS IN GRIDS TO

CHANCE ACROSS THE AREA GIVEN SOME UNCERTAINTY IN EXACTLY WHERE

BEST SNOW POTENTIAL WILL OCCUR. LIGHT SNOW MAY LINGER INTO EARLY

FRIDAY FOR EASTERN PORTION OF CWA BEFORE WAVE SHIFTS OFF TO THE

EAST.

Sounds like a step in the right direction! :thumbsup:

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FWIW...The latest HRRR develops a nice LE band tonight and targets SE. WI and NE. IL.

Edit: The 18z RGEM is still aggressive too, mostly for NE. IL.

22z HRRR has more of a NE. IL target. It even kicks out 3-4" near ORD...That's not going to happen, but it's fun to see.

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LER has quickly turned to LES here.

Here it's slowly turning over to pure LES. 35° with a mix still. Probably a 70/30 ratio now.

100% snow at 9:30pm. Starting to stick too.

I was hearing the possibility of one main semi-organized band later tonight developing south of MKX.

Where can I see the HRRR data?

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