April 30-May 5 Plains/MW/OV Severe Weather, SPC Risk Level: Day 1-3 Slight Risk - Forecasts & OBS Options

[ChiWxWatcher]

I thought that this deserves a look.

ZCZC SPCSWOD48 ALL
ACUS48 KWNS 270839
SPC AC 270839

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0339 AM CDT FRI APR 27 2012

VALID 301200Z - 051200Z

...DISCUSSION...
MODEL CONSENSUS IS THAT SYNOPTIC PATTERN WILL GRADUALLY TRANSITION
TO A MORE PROGRESSIVE BUT LESS PREDICTABLE QUASI-ZONAL FLOW REGIME
BY MONDAY /DAY 4/. EARLY MONDAY A STATIONARY FRONT SHOULD EXTEND
FROM THE CAROLINAS WWD THROUGH WRN TX. SOME THREAT FOR SEVERE STORMS
MAY EXIST IN THE UNSTABLE WARM SECTOR FROM ERN NM INTO WRN TX...BUT
CURRENT INDICATIONS ARE THIS REGION WILL REMAIN SOUTH OF THE
STRONGER FLOW ALOFT.

WARM SECTOR WILL GRADUALLY DEVELOP NWD THROUGH THE CNTRL PLAINS DAY
5 AS OH VALLEY SFC RIDGE SHIFTS EAST AND LEE TROUGH WITH
ACCOMPANYING SLY LLJ BECOMES ESTABLISHED OVER THE PLAINS. A FEW
SEVERE STORMS COULD DEVELOP FROM WRN OK INTO KS ALONG THE DRYLINE AS
WELL AS FARTHER NORTH IN WARM ADVECTION REGIME OVER THE UPPER MS
VALLEY...BUT AT THIS TIME CAPPING CONCERNS OVER THE PLAINS LOWER
CONFIDENCE IN A HIGHER COVERAGE EVENT.

POTENTIAL FOR A GREATER COVERAGE SEVERE EVENT MAY EVOLVE BY DAY 6
OVER THE UPPER MS VALLEY REGION FROM MN...IA INTO WI WHERE MODELS
INDICATE PROGRESSIVE NRN STREAM TROUGH WILL AMPLIFY UPSTREAM FROM
RETURNING MOIST AXIS. MODEL DIFFERENCES EXIST IN AMPLITUDE AND
TIMING OF THIS FEATURE...BUT A SEVERE RISK AREA MAY NEED TO BE
INTRODUCED FOR THIS REGION IN THE NEXT EXTENDED UPDATE.

..DIAL.. 04/27/2012

This post has been edited by ChiWxWatcher: Apr 27 2012, 07:08 AM

[jdrenken]

The Euro has a derecho type look to it on 03MAY12-04MAY12

[ChiWxWatcher]

Day 5 risk issued for the Chicagoland area.

ZCZC SPCSWOD48 ALL
ACUS48 KWNS 280906
SPC AC 280906

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0406 AM CDT SAT APR 28 2012

VALID 011200Z - 061200Z

...DISCUSSION...
MODEL CONSENSUS IS THAT UPPER PATTERN WILL HAVE TRANSITIONED TO A
QUASI-ZONAL PROGRESSIVE BY TUESDAY /DAY 4/. MODIFIED CP AIR WILL
GRADUALLY RETURN NWD THROUGH THE PLAINS...MS AND OH VALLEYS BENEATH
MODERATELY STRONG FLOW ALOFT. POTENTIAL FOR A HIGHER COVERAGE OF
SEVERE STORMS MAY EVOLVE OVER ERN PORTIONS OF THE NRN PLAINS INTO
THE UPPER MS VALLEY DAY 4 DOWNSTREAM FROM AN EJECTING SHORTWAVE
TROUGH. HOWEVER...MODELS DIFFER ON AMPLITUDE AND TIMING OF THIS
FEATURE WITH THE ECMWF BEING SLOWER AND EJECTING THE IMPULSE NORTH
OF THE MORE UNSTABLE WARM SECTOR. THERE IS ALSO UNCERTAINTY
REGARDING HOW EARLY WARM ADVECTION STORMS WILL AFFECT NWD BOUNDARY
LAYER RECOVERY.

SEVERE THREAT WILL LIKELY SHIFT A LITTLE FARTHER EAST TOWARD THE
GREAT LAKES AND OH VALLEY WEDNESDAY /DAY 5/ AS ANOTHER IMPULSE MOVES
THROUGH THE TROUGH AND STORMS DEVELOP ALONG AND JUST AHEAD OF A COLD
FRONT SUPPORTED BY A MOISTENING WARM SECTOR.

..DIAL.. 04/28/2012

[WeatherMonger]

Can't remember the last time being in a Day 5 outlook. Wouldn't mind seeing a bit of a SW trend heading into it. But it might not be there in 3 days let alone 5. Can't imagine somethig would actually pan out on one of my days off, be interesting to watch unfold.

[ChiWxWatcher]

Can't remember the last time being in a Day 5 outlook. Wouldn't mind seeing a bit of a SW trend heading into it. But it might not be there in 3 days let alone 5. Can't imagine somethig would actually pan out on one of my days off, be interesting to watch unfold.

I think we were sometime last year and then it didn't materialize for some reason...but don't quote me on that. It should be interesting. There are some model differences...but the main threat, as of now, is a straight line wind damage/derecho event.

[USA Weather]

The one day when we finally get a Day 4-8 outlook is when I leave for school at 8 am and don't come back until 7 pm. But if a tornado watch gets issued, they are supposed to cancel afterschool activities. That would allow me to get home at 4 (hopefully).

[ChiWxWatcher]

What do you guys think this event will turn out to be?

[wxman1952]

I'm ready for this and hopefully a change from this cold pattern. Bring it on!

[The Snowman]

Nice to see so many Chicago (and Illinois) folk on here. I have to say, I'm pretty excited about it.
The 6z GFS portrayed a MCS-style system in southern Wisconsin around 7:00 PM CDT on the 2nd. Getting my camera ready for some good shots.

[WeatherMonger]

Quick question, most of the talk seems to be geared towards squall/derecho event mainly in the IA/WI/N. IL area. Is the areal coverage of the SPC outlook due to uncertainty of placement or are we lookig at more discrete cells further south? Hasn't been much of anything that I can find about the southern extent of their delineation. Seems like a broad area for an already narrowed down region.

[The Snowman]

FWIW

Attached image(s)

 

[jdrenken]

FWIW

For those who are guest or not familiar with this parameter...I'll ask the obvious questions...

1. Time stamp?
2. What is it exactly?

[jdrenken]

Quick question, most of the talk seems to be geared towards squall/derecho event mainly in the IA/WI/N. IL area. Is the areal coverage of the SPC outlook due to uncertainty of placement or are we lookig at more discrete cells further south? Hasn't been much of anything that I can find about the southern extent of their delineation. Seems like a broad area for an already narrowed down region.

If you look at the 6hr precipitation of the GFS, you can see that there are some cells that develop around the US-54/US-24/I-72 area.

This sounding is outside of Camp Point, IL.

[The Snowman]

For those who are guest or not familiar with this parameter...I'll ask the obvious questions...

1. Time stamp?
2. What is it exactly?

1- Hour 108-114
2- 6-hour precip.

My apologies.

[Gilbertfly]

LOT. . .

NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
317 PM CDT SAT APR 28 2012

THE PLENTIFUL MOISTURE...COUPLED WITH CURRENTLY FORECAST HIGHS IN
THE UPPER 70S AND 80S ON WEDNESDAY...ALSO RESULTS IN THE GFS
ENSEMBLES FEATURING 90% PROBABILITIES OF SB CAPE GREATER THAN 1200
J/KG. THIS IS IMPRESSIVE FOR SO FAR OUT...AND PART OF THE REASON
WHY SPC HAS INCLUDED THE ENTIRE REGION FOR 30% PROBABILITIES OF
SEVERE TSTORMS IN ITS DAY 5 OUTLOOK. IT IS FAIRLY RARE FOR OUR CWA
TO BE INCLUDED IN A DAY 5 SEVERE OUTLOOK...SO THIS PERIOD CERTAINLY
BEARS WATCHING FOR HIGHER END TSTORM ACTIVITY.

coooooool

[Gilbertfly]

12Z GFS. . . for 12Z May2nd

[The Snowman]

ECMWF has a slightly hotter warm sector in the general Midwest region.

ECMWF
http://meteorology.lyndonstate.edu/common/...50&hour=120

GFS
http://meteorology.lyndonstate.edu/common/...50&hour=120

Hour 120
850mb temps and winds

[Gilbertfly]

Also from today's 12Z GFS...a little slippery on the 2nd...this is for ORD

[Gilbertfly]

ECMWF has a slightly hotter warm sector in the general Midwest region.

yeah, i'll be watchin' the trend there over the next 2-3 runs

[Gilbertfly]

DVN. . .

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
254 PM CDT SAT APR 28 2012

TUESDAY THROUGH SATURDAY...VERY ACTIVE PATTERN WITH WARM AND HUMID
CONDITIONS TO START THE MONTH OF MAY. THE FRONT WILL BE SHIFTING
BACK AND FORTH ACROSS THE CWA DURING THIS TIME FRAME WITH NUMEROUS
OPPORTUNITIES FOR THUNDERSTORM ACTION. TUESDAY THROUGH THURSDAY WILL
HAVE MAX TEMPS AROUND 80 WITH DEWPOINTS IN THE HUMID 60S. WITH
INSTABILITY IN PLACE AND THE FRONT NEARBY SEVERE WEATHER WILL BECOME
LIKELY ANYTIME DURING THIS PERIOD.