Severe Thunderstorm Warning 235, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
100 PM CDT WED AUG 28 2002

...TIMING/LOCATION OF CONVECTION WILL AGAIN BE THE CHALLENGE...

SYNOPSIS...MORNING U/A ANALYSIS CONTINUES TO SHOW A CUT OFF UPPER
LOW OVER THE INTERMOUNTAIN WEST WITH UPPER HIGH OVER NEW MEXICO.
IN BETWEEN THESE TWO FEATURES A 60-80 KNOT SUBTROPICAL JET SUPPLYING
THE CENTRAL PLAINS WITH PACIFIC MOISTURE.  LATE MORNING SURFACE
ANALYSIS REVEALED LOW PRESSURE OVER SOUTH DAKOTA WITH TROUGH
STRETCHING SOUTH THROUGH WESTERN CWA.  AGAIN LEFTOVER CONVECTIVE
BOUNDARIES ARE SCATTERED THROUGHOUT THE HIGH PLAINS IN THE WAKE OF
OVERNIGHT CONVECTION.

DISCUSSION...ISOLATED CONVECTION ALONG LEFT OVER OUTFLOW BOUNDARIES
ALREADY GETTING GOING ACROSS THE CWA AS OF 17Z.  MODIFIED MORNING
SOUNDING SHOWS THAT WE ARE ALREADY CAP FREE WITH AROUND 1000 J/KG
OF CAPE.  SHOULD CONTINUE TO SEE SOME ISOLATED CONVECTION POP HERE
AND THERE ACROSS THE CWA AND CONTINUE INTO THE EVENING AS CAPE
APPROACHES 2K THIS PM.

EVENING CONVECTION WILL PROBABLY DIMINISH AFTER SUNSET OVER THE CWA
HOWEVER LOOKS TO BE A REPEAT OF LAST NIGHT WITH AN MCS ORGANIZING
OVER THE FOOTHILLS BY LATE EVENING.  ALSO LIKE LAST NIGHT CORFIDI
VECTORS AND 700-300 THICKNESS BOTH SHOW AN EAST TO SOUTHEASTWARD
PROPAGATION INTO THE WESTERN CWA.  ETA HAS NOSE OF 30 KNOT LLJ INTO
SW NEBRASKA...ELEVATED CAPE ON THE ORDER OF 1000 J/KG...ELEVATED CINH
LESS 50 J/KG...AND PWS AROUND 1.25 INCHES SO THE THREAT IS THERE FOR
SOME LOCALLY HEAVY RAINFALL.  GIVEN THE INHERENT UNCERTAINTY
SURROUNDING MCS DEVELOPMENT/MOVEMENT AND ALSO MAGNITUDE OF CORFIDI
VECTORS NEVER DROP BELOW 10 KNOTS SO FEEL COMFORTABLE NOT
INTRODUCING LOCALLY HEAVY RAIN WORDING INTO ZFP...NOT TO SAY THAT I
WOULD BE AT ALL SURPRISED TO SEE ISOLATED 2-3 RAINFALLS.  FFG IS
HIGH AND THE BIGGEST THREAT WILL BE OVER THE SANDHILLS SO HYDRO
CONCERNS REALLY ARENT THERE.

MCS MAY LINGER INTO THE MORNING...PRIMARILY SOUTHWESTERN PORTION OF
THE CWA.  AFTER THAT CLEARING SHOULD AGAIN COMMENCE WITH MODERATE
INSTABILITY, LACK OF A CAP, AND LINGERING BOUNDARIES DURING THE
AFTERNOON ISOLATED CONVECTION WILL AGAIN BE A POSSIBILITY SO WILL
LEAVE THE 20 POPS IN FOR TOMORROW PM.

LOOKS LIKE THURSDAY NIGHT COULD BE ANOTHER NIGHT WITH THE THREAT OF
AN MCS DEVELOPING.  ETA (AND TO A LESSER EXTENT THE AVN) BOTH SHOW
ANOTHER PIECE OF ENERGY ROTATING AROUND THE PERIFERY OF THE UPPER
HIGH THURSDAY NIGHT WITH AN EVEN STRONGER LLJ (40+ KNOTS)
DEVELOPING. NOSE OF THE LLJ LOOKS TO BE FURTHER NORTH HOWEVER ETA
PAINTS PRECIP AREAWIDE.  THIS FAR OUT NOT WISE TO TRY AND GET CUTE
WITH TIMING AND LOCATION.

MUCH LIKE THURSDAY OVERNIGHT CONVECTION COULD LINGER INTO THE MORNING
FRIDAY.  INSTABILITY FORECAST TO BUILD WITH LITTLE IF ANY CAP BY
AFTERNOON SO SOME ISOLATED AFTERNOON CONVECTION IS CERTAINLY NOT
OUT OF THE QUESTION.  GOING FORECAST ALREADY HAS 30 POP FOR THE
AFTERNOON...WILL GO AHEAD AND REMOVE THE TIMING AND LEAVE THE POPS
AS THEY ARE FOR FRIDAY.

UPPER FLOW TURNS MORE WESTERLY AND LLJ FURTHER EAST SO NOT TOO
LIKELY THAT WE WILL SEE ANOTHER NIGHT OF NOCTURNAL CONVECTION FRIDAY
NIGHT.  GOING FORECAST HAS FRIDAY NIGHT DRY...ANY AFTERNOON
CONVECTION THAT DOES FORM DURING THE DAY COULD LINGER INTO FRIDAY
NIGHT BUT MY CONFIDENCE IN REDEVELOPMENT DURING THE AFTERNOON
REALLY ISNT HIGH ENOUGH TO INTRODUCE EVENING POPS FRIDAY NIGHT.
PLUS THE FORECAST IS PRETTY WELL FILLED WITH TSRA CHANCES AS IT IS SO
TO AVOID FLIP FLOPPING FRIDAY NIGHT CAN STAY DRY FOR NOW.

HEIGHTS BUILD ON SATURDAY WITH H8 TEMPS WARMING TO 30+ IN THE WEST
LOOKS LIKE IT COULD BE A FAIRLY HOT DAY SATURDAY.  WILL GO AHEAD
AND GIVE TEMPS A PUSH INTO THE LOW TO MID 90S.  AS FAR AS CONVECTION
GOES...BOTH THE ETA AND AVN ARE IN AGREEMENT ON LEE CYCLOGENESIS
DURING THE DAY SATURDAY WITH MODERATE INSTABILITY/WEAK CINH AND
SUBTROPICAL JET IN THE NEIGHBORHOOD LOW CHANCE POPS ARE CERTAINLY
JUSTIFIED.

EXTENDED...ECMWF AND GLOBAL CONTINUE TO HAVE THEIR DIFFERENCES INTO
NEXT WEEK AS THE CLOSED LOW OVER THE INTERMOUNTAIN WEST IS FORECAST
TO OPEN UP TO MORE OF AN OPEN WAVE.  TRANSITIONS FULL CIRCLE TO A
RATHER STRONG L/W RIDGE IN THE WEST...WHILE GLOBAL MUCH FLATTER WITH
RIDGING IN WEST AND TRANSITIONS TO MORE OF A ZONAL FLOW.  CONFIDENCE
IS NOT ALL THAT GREAT WITH EITHER OF THE SOLUTIONS AS MODELS ARE
NOTORIOUS FOR TRYING TO OPEN UP AND WEAKEN UPPER LOWS TO QUICKLY...SO
IF ANYTHING TO SLOWER MORE GRADUAL PATTERN CHANGE OFFERED BY THE
GLOBAL IS THE MOST REASONABLE.

WITH LOW CONFIDENCE IN ALL OF THE MODELS REALLY DONT FEEL CONFIDENT
ENOUGH TO MAKE ANY SIGNIFICANT CHANGES IN THE OUTER PERIODS. GLOBAL
AND ECMWF ARE BOTH ADVERTISING A FROPA ON SUNDAY...AND THIS HAS
BEEN CONSISTENT OVER THE PAST COUPLE OF DAYS SO WILL GO AHEAD AND
BREAK DOWN AND INTRODUCE SLIGHT CHANCE POPS SUNDAY.  BEYOND THAT
WILL LEAVE THE EXTENDED DRY AS THERE REALLY ARE NO STRONG
INDICATIONS OF PRECIP MON-WED.

.LBF...NONE.

IZZI/AWJ