April 18-20th Plains/MW/GL/OV Severe Weather, SPC Risk Level: Moderate - Forecasts & OBS Options

[Chicago Storm]

Possible...

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0355 AM CDT THU APR 14 2011

VALID 171200Z - 221200Z

THE MEDIUM RANGE MODELS BEGIN THE DAY 4 TO 8 PERIOD WITH ZONAL FLOW
ACROSS THE CONUS ON SUNDAY AND SUNDAY NIGHT/DAY 4. ON MONDAY/DAY
5...AN UPPER-LEVEL TROUGH DEVELOPS IN THE SWRN STATES WITH THIS
FEATURE MOVING INTO THE ROCKIES MONDAY NIGHT. THE MODELS ARE NOW IN
VERY GOOD AGREEMENT...MOVING THE SYSTEM INTO THE HIGH PLAINS ON
TUESDAY WITH MOISTURE RETURN TAKING PLACE ACROSS THE SRN PLAINS DUE
TO A WELL-DEVELOPED LOW-LEVEL JET. STRONG THUNDERSTORM DEVELOPMENT
WILL BE POSSIBLE FROM TUESDAY AFTERNOON/DAY 6 THROUGH TUESDAY NIGHT
ON THE WRN AND NRN EDGE OF THE MOIST AXIS FROM THE SRN PLAINS AND
OZARKS NEWD ACROSS THE MID-MS AND OH VALLEYS. ON WEDNESDAY/DAY
7...THE ECMWF AND GFS DIVERGE SHARPLY WITH THE GFS MOVING A COMPACT
SYSTEM ACROSS THE CNTRL ROCKIES AND THE ECMWF DEVELOPING A BROAD
UPPER-LEVEL TROUGH IN THE WRN STATES. DO TO THESE LARGE
DIFFERENCES...CONFIDENCE IS VERY LOW LATE IN THE DAY 4 TO 8 PERIOD.
AT THIS POINT...TUESDAY AND TUESDAY NIGHT HAVE THE GREATEST
POTENTIAL FOR SEVERE WEATHER BUT WILL NOT OUTLOOK AN AREA DUE TO
UNCERTAINTIES OF MAGNITUDE AND TIMING CONCERNING THE UPPER-LEVEL
SYSTEM.

..BROYLES.. 04/14/2011

[SEMIweather]

Possible...

More than possible...

[WeatherMonger]

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0359 AM CDT FRI APR 15 2011

VALID 181200Z - 231200Z

...DISCUSSION...
PER 00Z ECMWF/GEFS GUIDANCE...AN INITIALLY ZONAL WEST-EAST UPPER
FLOW REGIME TO BEGIN THE PERIOD WILL QUICKLY AMPLIFY TO A DEGREE
WITH SHORTWAVE FEATURES EMBEDDED WITHIN LOW AMPLITUDE
WEST-SOUTHWESTERLY FLOW ALOFT THROUGH MID/LATE WEEK. THAT SAID...A
MODEST PREDICTABILITY REGIME EXISTS /ESPECIALLY BY DAY 6-8/ OWING TO
THE LOW AMPLITUDE NATURE OF THE UPPER PATTERN.

ON DAY 4/MONDAY...AS A SHORTWAVE TROUGH POTENTIALLY SPREADS EASTWARD
OVER THE NORTHERN ROCKIES AND MOISTURE BEGINS TO RETURN ACROSS THE
SOUTH-CENTRAL CONUS...CURRENT THINKING IS THAT ELEVATED
TSTMS...PERHAPS SOME SEVERE WITH HAIL...WILL INCREASE MONDAY
NIGHT/EARLY TUESDAY ACROSS PORTIONS OF THE MIDWEST AND MIDDLE/UPPER
MS VALLEY.

BY DAY 5/TUESDAY...THE AFOREMENTIONED SHORTWAVE TROUGH IS EXPECTED
TO CROSS THE NORTHERN PLAINS/UPPER MIDWEST. SEVERE TSTMS SEEM
PROBABLE TUESDAY AFTERNOON/NIGHT ACROSS PORTIONS OF THIS
MIDWEST/MISSISSIPPI VALLEY TO UPPER GREAT LAKES REGION...ESPECIALLY
INCLUDING PORTIONS OF MO/IL. HOWEVER...MODEST NUMERICAL GUIDANCE
VARIABILITY REGARDING THE UPPER MIDWEST SHORTWAVE TROUGH...COUPLED
WITH SOME CONCERN FOR A STRONG ELEVATED MIXED LAYER/CAP ACROSS THE
WARM SECTOR GIVEN THE PROGGED POSITION OF THE UPPER
TROUGH...PRECLUDES THE AREAL DELINEATION OF A 30 PERCENT SEVERE RISK
AREA AT THE CURRENT DAY 5 JUNCTURE.

BY DAY 6/WEDNESDAY...THE COLD FRONT SHOULD STALL IN A GENERAL
NORTHEAST-SOUTHWEST ORIENTATION FROM THE OH VALLEY TO THE SOUTHERN
PLAINS. AN ISOLATED SEVERE THREAT MAY EXIST ALONG THIS FRONTAL
ZONE...WITH A SEVERE THREAT ALSO POSSIBLE ACROSS PORTIONS OF
OK/NORTH TX NEAR A POSSIBLE SURFACE LOW/FRONT/DRYLINE TRIPLE POINT.
BUT AGAIN...SPECIFIC PREDICTABILITY IS QUITE LIMITED BY THIS
JUNCTURE AMID LOW AMPLITUDE SOUTHWESTERLY/CYCLONIC UPPER FLOW.

..GUYER.. 04/15/2011

[WolfSpider]

The main radar I use might be down for that time.

The NWS Chicago/Romeoville WSR-88D KLOT radar is in the initial stages of a catastrophic failure of the gearing in the radar pedestal. A five person team from the WSR-88D Radar Operations Center (ROC) will perform a rebuilding of the gears in the pedestal. This is a significant failure, and the reconstruction of the pedestal gears will require that the radar be out of service for 7 to 10 days. The condition was identified when other routine maintenance was being performed.
Because the problem was discovered early, it is believed that the radar pedestal still has some operational service time left. In order to utilize and maximize this remaining service time, the radar will only be operated sparingly until the reconstruction begins. Operation of the system will be curtailed during quiet weather, and the radar placed into service when widespread or significant rain is within the coverage area.
The radar will then be down through at least late next week while the reconstruction of the pedestal is being completed.

[wsushox1]

We'll see.

[SEMIweather]

It's still several days out, but I don't think this timeframe is looking as good for my area as it did a day or two ago.

On Monday, there is going to be a lot of instability present in Oklahoma, but very poor wind shear, and a strong cap. We're going to need a trigger to break that cap, and as of right now, I don't see one...but if we do end up breaking the cap Monday, then I could see some pulse severe storms affecting Oklahoma.

Tuesday looks more like a squall line setup for Oklahoma.

The good news is it looks like we are entering an active period, with another system affecting the Southern Plains late next week.

[CentralIllinois]

it looks like it could be a interesting time frame coming up

[SKYWARN1]

IMO i do not see anything that just screams outbreak or anything but I am sure some severe weather will be possible with this system. I wish us here in Ohio could get into the action it's been rather uneventful in this neck of the woods so far, but its still early.

[SEMIweather]

it looks like it could be a interesting time frame coming up

I think this is more of an Illinois event to be honest, hope you see something good.

[SEMIweather]

The 00z NAM backs up what the GFS has been showing for Oklahoma on Monday; a high CAPE/low shear environment with a strong cap. Ick.

[SEMIweather]

00z GFS leads me again to believe that nothing is going to happen here on Monday. Doubt the SPC even throws in a See Text down here; I just see no signs of anything being able to initiate.

Tuesday to me looks like a squall line threat down here, although I can already tell it's possible that, like with every other system that came through here over the last two months, the convection could fire just to the east. I definitely think there will be a fairly big wind damage threat here on Tuesday though, with more discrete storms possible further to the northeast closer to the low where surface winds are backed somewhat.

[Chicago Storm]

If current trends continue i'll be chasing in IL/MO on Tuesday.

[WolfSpider]

This image from Skilling's blog shows were the severe weather might be.

[The Snowman]

The main radar I use might be down for that time.

For something like this the NWS has to turn it on for the night/day.

[The Snowman]

It's nice not to have any severe storms on Sunday night.

[Illinois blizzar...]

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0400 AM CDT SAT APR 16 2011

VALID 191200Z - 241200Z

...DISCUSSION...
PER 00Z ECMWF/GEFS/UKMET GUIDANCE...A RELATIVELY LOW AMPLITUDE/FAST
MOVING BELT OF WEST-SOUTHWESTERLY MID-UPPER FLOW WILL PREVAIL
THROUGH THE MIDDLE/LATE PART OF THE UPCOMING WEEK. OWING TO THE LOW
AMPLITUDE NATURE OF THE UPPER PATTERN...A MODEST PREDICTABILITY
REGIME EXISTS ESPECIALLY BY DAYS 6-8.

FOR DAY 4/TUESDAY...ALTHOUGH A MODEST DEGREE OF LARGE SCALE
VARIABILITY STILL EXISTS AMONGST AVAILABLE NUMERICAL GUIDANCE...A
SHORTWAVE TROUGH IS EXPECTED TO CROSS THE MO VALLEY/UPPER MIDWEST ON
TUESDAY. AHEAD OF AN ADVANCING SURFACE LOW/COLD FRONT...IT SEEMS
LIKELY THAT A RELATIVELY MOIST AIRMASS /LOWER TO PERHAPS MIDDLE 60S
F SURFACE DEWPOINTS/ WILL BE IN PLACE ACROSS THE REGION. AFTER THE
POSSIBILITY OF SOME EARLY MORNING HAIL...SEVERE TSTMS ARE PROBABLE
TUESDAY AFTERNOON/NIGHT ESPECIALLY ACROSS PORTIONS OF THE
MIDWEST/OZARKS AND MIDDLE MISSISSIPPI/LOWER OH VALLEYS...PERHAPS
CENTERED ACROSS PORTIONS OF IL/MO. GIVEN AMPLE LOW LEVEL
MOISTURE/VERTICAL SHEAR...WELL-ORGANIZED SEVERE STORMS INCLUDING
SUPERCELLS/BOWS SEEM LIKELY TUESDAY AFTERNOON/NIGHT...WITH ALL
SEVERE HAZARDS POSSIBLE INCLUDING TORNADOES.

INTO DAY 5/WEDNESDAY...THE COLD FRONT SHOULD STALL IN A GENERAL
NORTHEAST-SOUTHWEST ORIENTATION FROM THE OH VALLEY TO THE SOUTHERN
PLAINS. AN ISOLATED SEVERE THREAT MAY EXIST ALONG THIS FRONTAL
ZONE...WITH AT LEAST A CONDITIONAL-TYPE SEVERE THREAT ALSO POSSIBLE
ACROSS PORTIONS OF OK/NORTH TX NEAR A POSSIBLE SURFACE
LOW/FRONT/DRYLINE TRIPLE POINT. BUT GIVEN CURRENT EXPECTATIONS FOR
MODEST LARGE SCALE FORCING...A SEVERE RISK AREA IS NOT CURRENTLY
WARRANTED.

FOR DAYS 6/7 THURSDAY/FRIDAY...AVAILABLE 00Z BASED GUIDANCE IS
GENERALLY INDICATIVE OF ANOTHER SHORTWAVE TROUGH CROSSING THE
WESTERN/CENTRAL STATES. GIVEN THE ARRIVAL OF LARGE SCALE FORCING FOR
ASCENT...IT IS PLAUSIBLE THAT A SEVERE TSTM THREAT WILL BE FOCUSED
ESPECIALLY ON THE WEST EDGE OF THE MOIST AXIS POTENTIALLY INCLUDING
PORTIONS OF THE SOUTHERN PLAINS/LOWER MO VALLEY TO MIDDLE MS VALLEY
THURSDAY INTO FRIDAY.

..GUYER.. 04/16/2011

This post has been edited by Illinois blizzard: Apr 16 2011, 08:41 AM

[jdrenken]

If current trends continue i'll be chasing in IL/MO on Tuesday.

Even closer than your last 2-day chase!

[jdrenken]

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
632 AM CDT SAT APR 16 2011

.DISCUSSION...
/350 AM CDT SAT APR 16 2011/

LOW LEVEL MOISTURE TRANSPORT WILL INCREASE MONDAY NIGHT INTO
TUESDAY UNDER STEEP MID-LEVEL LAPSE RATES COMING IN FROM THE WEST
ON STRONG ZONAL FLOW. DO NOT EXPECT MUCH MORE THAN ISOLATED
THUNDERSTORMS ON MONDAY AS FORECAST SOUNDINGS ARE SHOWING A
SUBSTANTIAL WARM LAYER BETWEEN 800-600MB. AS WE GO INTO MONDAY
NIGHT THROUGH TUESDAY NIGHT...THUNDERSTORM CHANCES WILL INCREASE
AS LARGE SCALE ASCENT INCREASES AHEAD OF A RATHER STRONG MID LEVEL
SHORTWAVE TROUGH. SET-UP WITH THE CONFLUENT TROUGH AND NORTHEAST-
SOUTHWEST ORIENTED COLD FRONT IS SIMILAR TO WHAT WE HAVE SEEN ON
TWO OCCASIONS EARLIER THIS MONTH...HOWEVER FORECAST MLCAPES FROM
BOTH THE GFS/ECMWF ARE ON THE ORDER OF 2000 J/KG. GIVEN THESE
VALUES...DECENT ASCENT AND 40-50KT DEEP LAYER SHEAR IT SEEMS THAT
WE ARE SETTING UP FOR ANOTHER ROUND OF SEVERE WEATHER DURING THIS
PERIOD. THIS SYSTEM MOVES QUICKLY EAST WHICH WILL LIKELY PROVIDE
DRY DAYS WEDNESDAY AND THURSDAY...BUT GFS/ECMWF DO SHOW ANOTHER
STORM SYSTEM WHICH WILL LIKELY GIVE US ANOTHER ROUND OF
THUNDERSTORMS LATE IN THE WEEK.

BRITT

[jdrenken]

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
651 AM CDT SAT APR 16 2011

.DISCUSSION...
ISSUED 328 AM CDT SAT APR 16 2011

LONG TERM...SUNDAY THROUGH WEDNESDAY...

TUES/TUES NIGHT STILL LOOK LIKE THE BEST SHOT AS ANOTHER
AGGRESSIVE SYSTEM MAKES ITS WAY OUT OF THE CENTRAL PLAINS INTO THE
MIDWEST. MODELS MAY BE A LITTLE OVERBLOWN WITH THE SFC SYSTEM AS
IT MOVES ACROSS THE FA WITH A WIDE OPEN WAVE ALOFT AND SUCH A DEEP WRAPPED
UP SYSTEM AT THE SFC...HOWEVER...MODELS ARE HINTING AT A BIT OF A
NEG TILT AS THE TROF MOVES INTO THE FA AND WILL HAVE TO BE WATCHED
CAREFULLY. FOR NOW...NO PROBLEMS WITH GOING LIKELY ON DAY 4.

HJS

[jdrenken]

LSX is already issuing a HWO brief for Tuesday. Who has hijacked the office?