Severe weather? October 28-30

[CrazyC83]

It doesn't have SPC backing yet, but the GFS is showing something quite ominous in the days leading up to Halloween. Temperatures should be well above normal, and shear off the charts. Instability should be the main limiting factors, but it is still early.

Most likely it would be the 28th in the Plains down to Texas, 29th in the Midwest, Great Lakes and Mississippi Valley down to the Gulf Coast, and 30th in the Northeast and Mid-Atlantic if still strong enough.

[srainhoutx]

One issue may well be the return of moisture from the GOM. Guidance is struggling with the setup even as close as Day 3. I will add that if we do see a fairly stout Cold Front diving into the Plains as some of the guidance has suggested, it could get interesting for severe weather followers.

[CrazyC83]

One issue may well be the return of moisture from the GOM. Guidance is struggling with the setup even as close as Day 3. I will add that if we do see a fairly stout Cold Front diving into the Plains as some of the guidance has suggested, it could get interesting for severe weather followers.

It's an extremely difficult setup.

Positive factors for severe weather:
*Climatology. Such systems have a long history of major severe weather/tornado outbreaks in mid to late fall.
*Wind shear. Models suggest that mid and upper-level shear will be off the charts, so any supercell should be rotating, suggesting tornadoes are the main threat.
*Moisture return. Dewpoints in the 60s could reach as far north as the southern Great Lakes on October 29.
*Strength of the low. GFS takes the low down to 977mb over Lake Superior on October 29.

Negative factors for severe weather:
*Position of the low. Early models suggest that the low could either be over the lower Great Lakes (which would just scream major outbreak) or as far north as Hudson Bay, which would be VERY hard for Gulf air to reach. Anywhere beyond Lake Superior/northern Ontario would be out of reach for Gulf air.
*Instability. That makes it a very tricky forecast, since CAPE would be quite low over much of the region making initiation more difficult. Daytime heating would be crucial, but any such development could be bad.

[WindRunner]

One of the biggest issues here (and as of Friday, one of the biggest inconsistencies as well) is that this trough digging is a direct result of downstream development and amplification from Lupit's extratropical transition, partially aided and most definitely complicated by the ET of Neki, occuring not long after Lupit's. I remember looking at the Euro - typically one of the more reliable and certainly one of the more consistent models, historically - and seeing remarkable inconsistency with this event. Looking at the 12z run this past Thursday showed a weak frontal wave developing over the FL peninsula in this time frame and sliding up the east coast, with a moderate bit of strengthening associated with its progression. By the next run (00z Fri), the frontal low was shown as developing a couple hundred miles south of the central Gulf coast - though this was the same frontal system and energy portrayed in the previous run, just a different location several hundred miles farther west. Yet again, the next run (12z Fri) showed the same low on the same front developing just west of Houston - a shocking trend that was a complete flip-flop of the pattern, from a trof in the Midwest and ridge off the Pacific coast to a trof in the Intermountain West and a huge ridge over the East. Because of that, I'm waiting until at least tomorrow before looking at any models for that event, as the ET of Lupit should be nearing completion and the run-to-run variation should be down significantly (if it hasn't become stable already).

But yes, although I haven't looked at the smaller scale details of this event, we definitely appear to be in store for a respectable second-season outbreak as that system progresses eastward.

[CrazyC83]

ZCZC SPCSWOD48 ALL
ACUS48 KWNS 260829
SPC AC 260829

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0329 AM CDT MON OCT 26 2009

VALID 291200Z - 031200Z

...DISCUSSION...

LATEST MEDIUM RANGE MODELS ARE IN GENERAL AGREEMENT REGARDING THE
SPEED/MOVEMENT OF UPPER LOW EJECTING FROM THE CNTRL/SRN ROCKIES NEWD
INTO THE GREAT LAKES/OH VALLEY REGION DURING THE DAY4-5 TIME FRAME.
BOTH THE GFS AND ECMWF SUGGEST STRONG MID LEVEL FLOW WILL TRANSLATE
THROUGH THE BASE OF THE TROUGH INTO THE MS VALLEY WHERE DEEPENING OF
THIS LOW PRESSURE SYSTEM WILL BE NOTED THROUGH A DEEP LAYER. WITH
MOISTURE/INSTABILITY EXPECTED TO RETURN ACROSS THE SCNTRL
U.S...THUNDERSTORMS SHOULD READILY DEVELOP ALONG ADVANCING COLD
FRONT ACROSS OK/TX DAY4...THEN SHIFT EWD INTO THE MS VALLEY DAY5
WHERE FRONTAL INTENSIFICATION IS EXPECTED. IF SUFFICIENT
INSTABILITY CAN RETURN TO IL/IND ORGANIZED SEVERE THUNDERSTORMS WILL
LIKELY OCCUR AS INTENSE HEIGHT FALLS/FORCING WILL BE NOTED ACROSS
THIS REGION.

..DARROW.. 10/26/2009

CLICK TO GET WUUS48 PTSD48 PRODUCT

[CrazyC83]

Downtown Shreveport was hit for the second time in 2009...

Seems to be picking up now.

[CrazyC83]

Upgrade to moderate risk at 0100Z?

MESOSCALE DISCUSSION 2162
NWS STORM PREDICTION CENTER NORMAN OK
0705 PM CDT THU OCT 29 2009

AREAS AFFECTED...SRN AND CNTRL AR

CONCERNING...TORNADO WATCH 783...

VALID 300005Z - 300100Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 783 CONTINUES.

THE TORNADO AND WIND DAMAGE THREAT WILL LIKELY CONTINUE ACROSS WW
784 THROUGH WATCH EXPIRATION. THE AREA WILL CONTINUE TO BE MONITORED
FOR THE POSSIBILITY OF NEW WW ISSUANCE LATER THIS EVENING TO REPLACE
THE CURRENT WATCH.

A CLUSTER OF TORNADO SUPERCELLS IS CURRENTLY ONGOING IN SRN AR AND
NW LA ALONG THE AXIS OF THE LOW-LEVEL JET AND ON THE NWRN EDGE OF
MODERATE INSTABILITY. THE LOW-LEVEL JET IS CREATING VERY STRONG
LOW-LEVEL SHEAR PROFILES. THE LATEST WSR-88D VWP FROM THE SHREVEPORT
LA VICINITY SHOWS AN IMPRESSIVE HODOGRAPH WITH ABOUT 40 KT OF 0-1 KM
SHEAR. THIS COMBINED WITH 50 TO 60 KT OF 0-6 KM SHEAR AND THE
MODERATE INSTABILITY SHOULD BE FAVORABLE FOR TORNADO SUPERCELLS. AN
ISOLATED STRONG TORNADO WILL BE POSSIBLE WITH THE MOST INTENSE AND
PERSISTENT ROTATING STORMS EARLY THIS EVENING. WITH 50 KT OF FLOW
JUST ABOVE THE SFC...THE STORMS SHOULD ALSO BE EFFICIENT WIND DAMAGE
PRODUCERS.

..BROYLES.. 10/30/2009


ATTN...WFO...JAN...LZK...SHV...TSA...

LAT...LON 33199208 33389308 33759314 34009375 34369394 34389425
34199421 34199442 34909444 35049418 34999376 35229329
35119301 35099265 34879247 35059213 34979174 34689165
34309178 34129143 34109164 34159171 34069192 33349196
33199208

[IvanSurvivor]

Is there a severe weather potential for the Florida Panhandle over the next couple days?

[CrazyC83]

Is there a severe weather potential for the Florida Panhandle over the next couple days?

Maybe tomorrow night/Saturday morning, but instability should be lower tomorrow.

[CrazyC83]

0537 PM TORNADO MAGNOLIA 33.27N 93.24W
10/29/2009 COLUMBIA AR EMERGENCY MNGR

TREE DOWNED ON NURSING HOME...MOBILE HOME PARK SUSTAINED
DAMAGE WITH A PERSON TRAPPED...IN NE PART OF CITY

[IvanSurvivor]

Is there a severe weather potential for the Florida Panhandle over the next couple days?

Maybe tomorrow night/Saturday morning, but instability should be lower tomorrow.

Thanks

[CrazyC83]

http://www.ktbs.com/pages/live-coverage-chat/

Coverage from Shreveport

[CrazyC83]

Never seen these words before:

FLASH FLOOD STATEMENT
NATIONAL WEATHER SERVICE SHREVEPORT LA
720 PM CDT THU OCT 29 2009

LAC015-017-031-TXC419-300215-
/O.CON.KSHV.FF.W.0103.000000T0000Z-091030T0215Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
CADDO LA-BOSSIER LA-DE SOTO LA-SHELBY TX-
720 PM CDT THU OCT 29 2009

...FLOOD EMERGENCY IN SHREVEPORT AND BOSSIER CITY...

...A FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 915 PM CDT FOR
SHELBY COUNTY...AND DE SOTO...BOSSIER AND CADDO PARISHES...

AT 720 PM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS CONTINUED TO
DETECT THUNDERSTORMS PRODUCING FLASH FLOODING OVER THE WARNED AREA.

THE SHREVEPORT FIRE DEPARTMENT IS RESPONDING TO NUMEROUS FLOODED ROADS
ACROSS THE CITY OF SHREVEPORT. NUMEROUS CARS HAVE STALLED IN HIGH
WATER...WITH HIGH WATER RESCUES IN PROGRESS CITYWIDE. PORTIONS OF
INTERSTATE 20 IN SHREVEPORT ARE UNDERWATER...AND MAY BE CLOSED THIS
EVENING SHOULD THIS ADDITIONAL HEAVY RAINFALL CONTINUE.

LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO STONEWALL...
SHREVEPORT...RED CHUTE...GREENWOOD...EASTWOOD AND BOSSIER CITY

PRECAUTIONARY/PREPAREDNESS ACTIONS...

ADDITIONAL RAINFALL AMOUNTS OF TWO TO FOUR INCHES ARE POSSIBLE IN THE
WARNED AREA...ESPECIALLY IN SHREVEPORT AND BOSSIER CITY...THROUGH 915 PM.

BE ESPECIALLY CAUTIOUS AT NIGHT WHEN IT IS HARDER TO RECOGNIZE THE
DANGERS OF FLOODING. IF FLASH FLOODING IS OBSERVED ACT QUICKLY. MOVE
UP TO HIGHER GROUND TO ESCAPE FLOOD WATERS. DO NOT STAY IN AREAS
SUBJECT TO FLOODING WHEN WATER BEGINS RISING.

DO NOT UNDERESTIMATE THE POWER OF FLOOD WATERS. ONLY A FEW INCHES OF
RAPIDLY FLOWING WATER CAN QUICKLY CARRY AWAY YOUR VEHICLE.

A TORNADO WATCH REMAINS IN EFFECT UNTIL 900 PM CDT THURSDAY EVENING
FOR SOUTHWESTERN ARKANSAS AND NORTHWESTERN LOUISIANA AND NORTHEASTERN
TEXAS.