Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS48 KWNS 120859
SWOD48
SPC AC 120859

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0359 AM CDT SAT JUL 12 2014

VALID 151200Z - 201200Z

...DISCUSSION...
GENERALLY WEAK FLOW AND HIGH HEIGHTS WILL PERSIST ACROSS THE WESTERN
U.S. WHILE A TROUGH DOMINATES THE EAST...AT LEAST FOR THE FIRST PART
OF THE MEDIUM-RANGE PERIOD.

...DAY 4...
UNUSUALLY LARGE DIFFERENCES APPEAR AT THE START OF THIS FORECAST
PERIOD BETWEEN DETERMINISTIC VERSIONS OF THE GFS AND EURO WITH THE
GFS INDICATING 1) FASTER EASTWARD PROGRESSION OF THE STRONG COLD
FRONT OFF THE EASTERN SEABOARD...AND 2) FASTER DE-AMPLIFICATION OF
THE LARGE-SCALE TROUGH IN THE EAST. THE EURO ENSEMBLE MEAN APPEARS
SIMILAR TO THE DETERMINISTIC GFS WITH RESPECT TO SURFACE LOW
LOCATION IN CENTRAL QUEBEC BUT THE TRAILING COLD FRONT REMAINS
NEAR/ALONG THE EAST COAST THROUGH MIDDLE OF DAY 4.
MEANWHILE...DETERMINISTIC UKMET IS A COMPROMISE AND SUGGESTS A
SURFACE LOW IN SOUTHERN QUEBEC WITH A TRAILING COLD FRONT ALONG THE
EASTERN SEABOARD AT 00 UTC 16 JULY/TUESDAY EVENING. A MAJORITY OF
GUIDANCE DOES SUGGEST AT LEAST SOME SEVERE WEATHER POTENTIAL
CONTINUING AS THE FRONT MOVES TO THE EAST COAST ON DAY 4/TUESDAY.
HOWEVER...GIVEN THE SPREAD IN SOLUTIONS AT SUCH A RELATIVELY SHORT
FORECAST RANGE...THE PRUDENT APPROACH IS TO FORECAST PREDICTABILITY
TOO LOW AT THIS TIME.

...DAYS 4 THROUGH 6....
SOMEWHAT BETTER MODEL CONSISTENCY IS EVIDENT FROM THE FRONT
RANGE/HIGH PLAINS INTO THE SOUTHERN PLAINS WHERE MOST GUIDANCE
INDICATES A REGIME SUPPORTIVE OF UPSCALE MCS EVOLUTION. GIVEN THE
POTENTIAL FOR LOW-LEVEL UPSLOPE FLOW BENEATH NORTHWEST FLOW
ALOFT...DIURNALLY AND OROGRAPHICALLY FORCED CONVECTION MAY GROW
UPSCALE AND SPREAD EAST AND SOUTHEAST AMIDST NORTHWEST STEERING FLOW
AND SUSTAINED ASCENT ALONG FRONTAL ZONE FORECAST TO STALL OVER THE
REGION. SINCE WIDESPREAD/SIGNIFICANT SEVERE WEATHER IN THIS TYPE OF
REGIME IS SO DEPENDENT ON MESOSCALE FACTORS SUCH AS FRONTAL/OUTFLOW
BOUNDARY LOCATION/PLACEMENT AND LOW-LEVEL JET
INTENSITY...PREDICTABILITY AT THIS STAGE REMAINS TOO LOW TO
HIGHLIGHT A GREATER PROBABILITY RISK AREA.

..CARBIN.. 07/12/2014


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