[BeauDodson]

In this thread http://www.easternuswx.com/bb/index.php?sh...3851&st=100

Forecast thoughts I put out on Friday

Early thoughts on the powerful cold front

1. Greatest risk of severe confined to the better moisture region (better being relative speaking) along the immediate Gulf. Confidence medium

2. Potential for isolated severe (mainly wind event) across a large portion of the Mississippi Valley and Missouri Valley. Confidence low

3. Powerful cold front with temperaturs falling 30-40 degrees in a 24 hour periond will sweep across the Central United States. Confidence high

4. High winds of 30-40 mph with frontal system. Confidence high

5. Period of snow across Missouri, Iowa, Illinois, Wisconsin. Possible accumulating snow for portions of this region (eastward). Confidence medium

Of interest...

700 mb wind fields of nearly 100 mph over portions of IL and IN on Thursday Morning.

850 wind fields increasing dramatically across portions of the Ohio Valley on Wednesday Night into Thursday.

A dramatic increase in the 500mb wind fields on Thursday across the Ohio Valley. Winds progged to be 130-140 mph over IL, IL, and MI.

Strongest winds appear to be on the east side of the trough. So this is something that has to be considered as far as what happens with the strength of a possible low coming out of the Arkansas region. Would rather see the stronger winds on the west side.

The potential exist for a stronger low to form than is currently being shown across Arkansas-Mississippi. Low would track into the Ohio Valley and strengthen. If this is the case then the odds increase for a significant snow event across portions of the Missouri Valley and slightly eastward. There would also be a greater risk of severe thunderstorms across the southlands.

This is still a day 5-7 event. We all know what that means. :pepsi:

Couple of maps I made - not as good as J down in Memphis - but perhaps he can teach me a few tricks. :)


http://www.usawx.com/arcticblastofnovemberairpy1.gif


http://www.usawx.com/severeweatheroutlookynovember282930.gif


:snowman:

As far as the area that might see snow :) LONG way off but if we can get the secondary storm or wave to ride up the front then I think there is a decent shot at some snow - especially across portions of Missouri, Iowa, Illinois, Wisconsin, and part of Indiana. The rest of that area should see at least some change-,ver after frontal passage.

Something to watch :)

I didn't include the obvious areas that are going to get snow...back in the Plains and northward.

Rough map of the area I believe could see some frozen precip (first attempts at this map making stuff)

http://www.usawx.com/midweeksnownovember282006y.gif

[BeauDodson]

Going to update a few maps shortly...

Trend is for SPC now to expand the risk area further north for some severe

NWS Offices are starting to talk more and more about what I mentioned on Friday as a possible winter storm type event as a possible wave or low forms on the front and moves into the Ohio Valley.

Springfield mentions heavy snowfall chances. Still low/medium conf. smile.gif

But moving in the right direction


Springfield

UNFORTUNATELY OUR METEOROLOGICAL CRYSTAL BALLS BECOME INCREASINGLY
MURKY IN THE WEDNESDAY NIGHT THROUGH FRIDAY TIME FRAME WITH WIDE
VARYING SOLUTIONS AMONG THE VARIOUS MEDIUM RANGE MODELS. THE 00Z GFS
NOW SLOWS THE FRONT DOWN CONSIDERABLY AFTER IT CLEARS OUR CWA AS A
WEAK FRONTAL WAVE RIDES UP THE FRONT AS UPPER LEVEL TROUGH HANGS
BACK OVER THE PLAINS ALLOWING FOR A CONTINUATION OF PRECIPITATION
OVER THE OZARKS WEDNESDAY NIGHT INTO THURSDAY. GFS WOULD HAVE US
FIRMLY IN THE COLD AIR BY THEN WITH SOME POTENTIAL FOR ACCUMULATING
SNOWS.

00Z ECMWF/00Z NOGAPS/18Z DGEX ARE EVEN MORE GLOOM AND DOOM THAN THE
GFS WITH AN EVEN STRONGER TROUGH POSSIBLY CLOSING OFF OVER THE
SOUTHERN HIGH PLAINS WITH A STRONGER FRONTAL WAVE AND EVEN BETTER
SHOT OF ACCUMULATING AND POTENTIALLY HEAVY snowfALL IN OUR
NEIGHBORHOOD. THANKFULLY THE CANADIAN MODEL IS MUCH MORE PROGRESSIVE
WITH THE SYSTEM AND DOESNT DEVELOP A SECONDARY WAVE. THE 00Z GFS
ENSEMBLES SHOWED A VERY LARGE DEGREE OF VARIANCE WHICH DOES NOT LEND
ANY OVERWHELMING SUPPORT TO THE OPERATIONAL 00Z RUN OF THE GFS OR
ANY OF THE OTHER 00Z MODELS FOR THAT MATTER. GIVEN THE VERY LOW
CONFIDENCE WAS NOT OVERLY INCLINED TO START SHOUTING BIG STORM FROM
THE ROOF TOPS AND CERTAINLY COULDN'T JUSTIFY 60-70% POPS LIKE THE
MEX GUIDANCE HAS...HOWEVER GIVEN THE PREPONDERANCE OF THE EVIDENCE
FROM THE ECMWF/GFS/NOGAPS/DGEX IT WAS ALSO HARD TO JUSTIFY
MAINTAINING A DRY FORECAST. AFTER EXTENSIVE COLLABORATION WITH
NEIGHBORS THE CONSENSUS WAS TO LINGER PRECIP THROUGH WEDNESDAY NIGHT
AND TO INTRODUCE CHANCES POPS THURSDAY INTO THURSDAY EVENING WITH
MENTION OF WINTERY PRECIPITATION IN THE GRIDS. THE MOST CERTAIN PART
OF THE FORECAST FOR THE WEDNESDAY NIGHT THROUGH FRIDAY TIME FRAME IS
THAT IT WILL CHANGE OVER THE NEXT COUPLE DAYS...SO STAY TUNED.

THANKS FOR THE COLLABORATION THIS MORNING NEIGHBORS.






PAH now talking about the potential second low and snow


THE REAL
WRINKLE IN THE FORECAST FOR THE LOCAL AREA OCCURS WHEN A CHANNELED
VORT ROTATING ALONG THE WESTERN LIMB OF THE CLOSED LOW IS SHUNTED
INTO THE DESERT SOUTHWEST...THEN NEWD TO TX/OK ON THURSDAY.

THROUGH 00Z WEDNESDAY/TUESDAY EVENING/...THE UKMET/ECWMF AND GFS
GUIDANCE SHARE SIMILAR HEIGHT FIELDS WITH THE LARGE SCALE
TROUGH...BUT DIFFER IN THE FOCUS OF THE CORE OF THE UPPER LOW. THE
GFS AND ECMWF LEAN TOWARD A 50H LOW OVER WRN ND...WHILE THE
UKMET SHOWS A DIFFUSE AREA OF LOW PRESSURE OVER ID AND MT. THE KEY
TO THE POTENTIAL FOR A WINTRY MIX OF PRECIPITATION FOR THE WFO PAH
FORECAST AREA WILL LIE IN THE EXISTENCE AND TRACK OF ANY SHORTWAVE
THAT DEVELOPS ALONG THE WESTERN LIMB OF THE CLOSED LOW OVER
OR/WA/NV AFTER 00Z WEDNESDAY. WHERE THIS FEATURE GOES...SO GOES
THE ORIENTATION AND SPEED OF THE FULL LATITUDE TROUGH OVER THE
MIDWEST.

ESSENTIALLY...THE SLOWER THE MOVEMENT OF THE MAJOR TROUGH THROUGH
THE WFO PAH FORECAST AREA...THE GREATER MOISTURE AND COLD AIR
INTRUSION WILL BE IN PLACE FOR THE DEVELOPMENT OF MIXED
PRECIPITATION ON THURSDAY AND THURSDAY NIGHT. THE LAST TWO
GFS/ECMWF MODEL CYCLE RUNS ARE HINTING AT THE DEVELOPMENT OF A
SECONDARY CLOSED LOW NEAR THE FOUR CORNERS REGION OF THE DESERT SW
BY LATE WEDNESDAY AFTERNOON. SHOULD THIS MODEL FORECAST TREND CONTINUE
TO HOLD TRUE...THE ENTIRE EWD MOVEMENT OF THE FULL LATITUDE TROUGH
WILL BE SLOWED DOWN.

AS THE SAME TIME...MANUAL ANALYSIS OF THE 925/850 MB TEMPERATURE
FIELDS SHOW THE DEVELOPMENT OF A SHARP ZONE OF THERMAL ADVECTION
THROUGH ERN MT/WY...WRN ND/SD/NWRN NE...IN ADVANCE OF THE UPPER
AIR TROUGH CURRENTLY MOVING ONSHORE. HOW THE COLD AIR INTERACTS
WITH THE DEVELOPING CLOSED LOW IN THE NWRN U.S. WILL LIKELY
DETERMINE THE S/EWD EXTENT AND TRANSPORT OF LOW LEVEL SUB-
FREEZING AIR INTO THE NRN PLAINS THROUGH MONDAY. THE
SPATIAL/TEMPORAL EFFECTS OF THIS ARCTIC AIR WITH THE UPPER TROUGH
WILL EVENTUALLY DETERMINE THE SCOPE AND INTENSITY OF ANY MIXED
PRECIPITATION THAT FALLS IN THE WFO PAH FORECAST AREA ON THURSDAY.

FOR THIS PACKAGE...ADJUSTED GRID/TABULAR/TEXT FORECAST TO SUGGEST
A CHANCE EVENT FOR MIXED PRECIPITATION THURSDAY. THE GREATEST
CHANCE OF SNOW OR SLEET OVER SRN IL AND SERN MO AT THIS TIME.

[brettjrob]

From this morning's OUN AFD:

Quote

GROWING CONCERN FOR POST-FRONTAL PRECIP OF THE FROZEN OR FREEZING
VARIETIES IS DUE TO THE SLOWER AND SHARPER DEPICTION OF THE UPPER
TROF ON THE 18Z DGEX AND THE SIMILAR 00Z ECMWF. EVEN THE FASTER
GFS SHOWS A SHARPER TROF AXIS MOVING ACROSS ON THU. GFS AND DGEX
INDICATE VERY IMPRESSIVE FRONTOGENETIC FORCING N OF THE SFC
FRONTAL ZONE BEGINNING WED AND CONTINUING INTO THU AHEAD OF THE
UPPER TROF. WITH TEMPS FALLING WED AND WED NIGHT BEHIND FRONT...
WHICH WE HAVE DEPICTED IN OUR HOURLY T GRIDS... THERE EASILY
SHOULD BE ENOUGH BOUNDARY-LAYER COLD AIR BY LATE WED NIGHT TO
PRODUCE A RISK OF -FZRA/FZDZ/PL IN THE REGION OF ISENTROPIC LIFT N
OF THE SHALLOW FRONTAL SURFACE. PL/SN MORE LIKELY TO PREVAIL
FARTHER NW WHERE COLD AIR WILL BE DEEPER. DGEX DROPS WIDESPREAD
0.5-2 INCH WATER EQUIVALENT ACROSS OUR CWA WED NIGHT INTO THU...
WHICH WOULD BECOME A MAJOR WINTER STORM IF SFC TEMPS FALL BELOW
FREEZING. DGEX QPF SEEMS A BIT MUCH... AND EVEN IF IT VERIFIES IT
WILL BE LIQUID AT LEAST AT THE ONSET.

DESPITE EXPECTED WARM GROUND TEMPS... GRADUAL MODIFICATION OF THE
COLD AIR... AND RELATIVELY LOW CONFIDENCE IN THE OVERALL SCENARIO
WED-THU... WE HAVE ENOUGH CONCERN THAT WE MOST LIKELY WILL ISSUE
A WINTER STORM POTENTIAL OUTLOOK LATER THIS MORNING. EXAMINATION
OF THE 06Z GFS AND DGEX WILL HAVE A LOT OF INFLUENCE ON THE
OVERALL TONE OF THAT PRODUCT. 24

[BeauDodson]

SUNDAY UPDATE


Updated thoughts and maps :)

No big changes in my thoughts from Friday.

A few added comments and updated maps - (thanks J for giving me some tips on my first attempt at real maps)


1. Greatest risk of severe confined to the better moisture region (better being relative speaking) along the immediate Gulf. Confidence medium

2. Potential for isolated severe (mainly wind event) across a large portion of the Mississippi Valley and Missouri Valley. Confidence medium for isolated severe

3. Powerful cold front with temperatures falling 30-40 degrees in a 24 hour period will sweep across the Central United States. Confidence high

4. High winds of 30-40 mph with frontal system. Confidence high

5. Period of snow across portions of the Plains, Missouri Valley, and Ohio Valley. Confidence increasing for light snow across much of this region and potentially heavier snow on the southern and eastern portion of the outlook.

Of interest...

There is still not a strong signal that a major outbreak of severe weather will occur along the Gulf Coast. Marginal conditions...strong wind fields though. Would expect mainly a wind/hail event with an isolated tornado not out of the question - especially in Southeast Texas and Louisiana. Potential exists for a second round of storms if the second storm system can get cranking - Thursday onward.

Second strong vort max seems more and more likely - swinging in from the Southwest and moving into the MO and OHIO VALLEYS on Thursday and Friday. This still to me looks like it could be a stronger than forecast storm. Models on Friday were not picking up on this potential but they are now. As I mentioned on Friday it appears that this could bring a round of snow/frozen precip to a large section of the Middle United States. Some accumulation of snow is possible. 500 mb vort map is showing this nicely on the 12z gfs run.

300mb wind fields show a second jet moving down through the Rockies on Thursday...strong max is on the east side of the trough and pulling away from the Ohio Valley at that time.

500 mb wind fields show that second max moving across this region on Friday Morning.

Precip Water Values of 1-1.5" extend all the way into Indiana and Northern Illinois with this system. Locally heavy rainfall will be possible and the 5 day rainfall totals indicates that nicely.

http://www.hpc.ncep....medr/95ewbg.gif


GFS brings a nice tongue of dew points into Iowa and Wisconsin on Wednesday Night. This in front of rapidly falling temps and points. Sharp cold front - still very impressive - moving across the Missouri Valley at that time. Slowing down as a possible wave/low moves up from the southwest shortly after that time.

CAPE values not extremely impressive, but it is November, across the southlands. CAPE values do range from 300-500 from Iowa back to the Gulf Coast. A higher spike of CAPE - 1000+ extends into Central Texas on Wednesday Night.

Thicknesses drop RAPIDLY behind the arctic front. This sets the stage for frozen precipitation as a second wave/low moves from Texas/Oklahoma into the Ohio Valley on Thursday/Friday. Depending on the strength of this system areas from Oklahoma to Indiana and Kentucky could see accumulating snow. This is still a wild-card/low confidence forecast. I am glad to see more model support for it now.

Living in this region one becomes accustomed to winter storms not panning out. Exciting is increasing though :) at the potential.
850 wind fields increasing dramatically across portions of the Ohio Valley on Wednesday Night into Thursday.

If this storm system can lay down a snow cover from Oklahoma to Illinois/Indiana/Kentucky then temperature forecasts will have to be lowered substantially on Friday Night into Saturday. Obviously :)


UPDATED MAPS

http://www.usawx.com/secondcallmapnovember26th2006y.gif
Expanded isolated severe a bit further north

http://www.usawx.com/secondcallmapwinterstorm2006nov26thy.jpg
Expanded snow area to the west/southwest and added higher probability region.

Other maps that were mentioned above

http://www.usawx.com/avnfff_500_wind_120.gif


http://www.usawx.com/updatedavn_114_500.gif


http://www.usawx.com/updateddewpointmapavn_sfc_td_66.gif


http://www.usawx.com/updatedavn_1000-850_120.gif


Those on my Sunday Morning Thoughts :) and maps


The thoughts above are dealing with the Central United States and do not include the ongoing/deceloping winter storm across the Northern Plains/Rockies.

[Rib]

Sorry Buckeye...

Attached File(s)

•  bigdogb.jpg (8K)
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[dfuzz]

Big question Beau is where the second wave forms and rides up the front. I don't think we are going to get a handle on this for another couple of days but someone in the Midwest or Ohio Valley is going to get some snow out of this.

[madscientist]

Hopefully we can get that second low to form. :thumbsup:

[BeauDodson]

dfuzz, on Nov 26 2006, 11:09 AM, said:

Big question Beau is where the second wave forms and rides up the front. I don't think we are going to get a handle on this for another couple of days but someone in the Midwest or Ohio Valley is going to get some snow out of this.

Agree. Winter storms are extremely fickle in this region. I don't get excited until I see it snowing outside my window :P

Its a wild card system - but something to finally watch!

[BeauDodson]

rob_22, on Nov 26 2006, 11:07 AM, said:

Sorry Buckeye...

I didn't really go beyond a certain time-frame ;) - obviously the snow wouldn't just end at point x ;)

[madscientist]

ShadowAngel, on Nov 26 2006, 11:13 AM, said:

Agree. Winter storms are extremely fickle in this region. I don't get excited until I see it snowing outside my window :P

Its a wild card system - but something to finally watch!

That's the Midwest for you. If I had a penny for every snow that busted in my lifetime, I might have the equivalent of a quarter. But hopefully, our dreams will come true. And with the arctic air behind it, that could bring temps down into the single digits, or even below zero.

[blizzard00]

nice maps

[BeauDodson]

blizzard00, on Nov 26 2006, 11:25 AM, said:

nice maps

JKT in Memphis has been helping me :) He seems to be the new map expert.

[Michsnowfreak]

WIth cold air pouring in, Id like to lay some snow down to get snowcover going, so even if I can just get some snow I'll be happy, but I'm not gonna lie, I want that baby to line up perfectly for me!!!

[AlaninKY]

ShadowAngel, on Nov 26 2006, 12:13 PM, said:

Agree. Winter storms are extremely fickle in this region. I don't get excited until I see it snowing outside my window :P

Its a wild card system - but something to finally watch!

It's a real long shot to think Paducah/Louisville Lower Ohio Valley Region has a shot at any snow till later toward end of December. Flurries seem to be the best to hope for this week and I wouldn't count on that. Granted JB is talking about system maybe ending as snow and ice, but I doubt much more than flurries at end of event at best.
Hate to throw cold water on our snow chances this week in lower Ohio Valley.
I just recall seeing these type of arctic shots before under somewhat similar situations in early December is why I have little faith of snow action in lower Ohio Valley.
Let's hope I'm wrong and that a nice snow event will happen! :snowman:

[Ytterbium.]

I think the snow threat should trend east with time.

[tornadotony]

Ytterbium., on Nov 26 2006, 11:51 AM, said:

I think the snow threat should trend east with time.

:weenie:

[BeauDodson]

NCEP

MODEL TRENDS...

DEEP CYCLONE MOVING EAST ACROSS PACIFIC NORTHWEST ON TUESDAY...
AFTER 48 HOURS...THE NAM HAS TRENDED SOUTHWARD WITH THE SYSTEM
OVER ITS PAST DAY OF RUNS...INCLUDING THE SHORTWAVE ROUNDING ITS
EASTERN PERIPHERY WHICH TAKES OVER AS THE MAIN SYSTEM THEREAFTER.
THIS SHIFTS THE NAM SURFACE LOW SOUTHWARD AS WELL. THE
ECMWF...OVER ITS PAST COUPLE DAYS OF RUNS...HAS TRENDED SOUTHWARD
WITH ITS UPPER CENTER STARTING MON NIGHT.

SYSTEM ATTEMPTING TO CLOSE OFF IN GREAT BASIN LATE WEDNESDAY...
THE NAM HAS TRENDED LESS BROAD WITH THE MAIN UPPER TROUGH AND
TAKES THE FORMER UPPER CENTER MORE SOUTHEASTWARD THAN SEEN ON ITS
00Z RUN...THOUGH IT IS IN LINE WITH ITS 06Z RUN. THE ECMWF HAS
ALSO TRENDED TOWARDS A MORE CLOSED SYSTEM IN THE GREAT BASIN OVER
ITS PAST COUPLE DAYS OF RUNS...WITH AN EVEN DEEPER CENTER THAN THE
NAM AT 500 HPA.

SYSTEM ATTEMPTING TO CLOSE OFF IN GREAT BASIN LATE WEDNESDAY...
MOST OF THE GUIDANCE NEARLY CLOSES OFF A CYCLONE NEAR SOUTHERN
UTAH EARLY WED MORNING.

ROTH

[LocoAko]

ShadowAngel, on Nov 26 2006, 12:29 PM, said:

JKT in Memphis has been helping me :) He seems to be the new map expert.

Powerpoint?

[Logan11]

Gotta love the temperature spread on either side of this front. It is going to be a lot of fun from KY right up to NY watching this unfold.

LocoAko, on Nov 26 2006, 01:14 PM, said:

Powerpoint?

[Thunderhead Hawkins]

Huntsvillle mentions some snow/freezing rain in their forecast for North Alabama Thursday night into friday and Memphis has the same for north mississippi.