Area Forecast Discussion
Issued by NWS Dallas/Fort Worth, TX

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000
FXUS64 KFWD 280030 AAA
AFDFWD

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE FORT WORTH TX
730 PM CDT SAT SEP 27 2014

.UPDATE...
MINOR GRID UPDATES WERE NEEDED MAINLY FOR SKY CONDITIONS BASED ON
SATELLITE TRENDS...WHICH INDICATE CLEARING SKIES ACROSS THE
NORTHERN HALF OF THE REGION. MID LEVEL CLOUDS SHOULD HOLD ON
ACROSS THE SOUTH THROUGH THE EVENING AND MOST OF THE OVERNIGHT
HOURS. OTHERWISE...SOME LIGHT ECHOES ON RADAR ARE SHOWING UP OVER
THE FAR SOUTHEAST COUNTIES BUT LITTLE IF ANY PRECIPITATION IS
EXPECTED. THESE LIGHT SHOWERS WILL COME TO AN END LATE THIS
EVENING AS THE UPPER LOW RESPONSIBLE FOR THE ACTIVITY MOVES EAST
OF THE AREA AND WEAKENS.

30

&&

.AVIATION...
/ISSUED 642 PM CDT SAT SEP 27 2014/
VFR CONDITIONS ARE EXPECTED TO PREVAIL AT THE TAF SITES THROUGH
12Z MONDAY.

A WEAKENING UPPER LEVEL LOW OVER THE HILL COUNTRY WILL CONTINUE
TO MOVE EAST THROUGH SUNDAY. ISOLATED SHOWERS SOUTH OF A COMANCHE
TO WACO TO PALESTINE LINE ARE EXPECTED TO DISSIPATE AFTER SUNSET.
THERE WILL BE SOME VFR CUMULUS WITH SCT-BKN MID AND HIGH CLOUDS.

EAST TO SOUTHEAST WINDS AT SUSTAINED SPEEDS AT LESS THAN 10 KNOTS
WILL PREVAIL THROUGH SUNDAY MORNING...WITH WINDS BECOMING
EAST-NORTHEAST DURING THE DAY SUNDAY.

58


&&



.PREV DISCUSSION... /ISSUED 350 PM CDT SAT SEP 27 2014/

EARLY AFTERNOON WATER VAPOR SATELLITE IMAGERY SHOWED AN UPPER
LEVEL LOW PRESSURE SYSTEM CENTERED OVER THE HILL COUNTRY...EAST OF
DEL RIO...MOVING SLOWLY EAST. SATELLITE IMAGERY SHOWED LARGE SCALE
FORCING FOR ASCENT ASSOCIATED WITH THIS UPPER LOW TO THE NORTH AND
EAST OF ITS CENTER OF CIRCULATION. VISIBLE SATELLITE IMAGERY HAD
BEEN SHOWING ALTOCUMULUS CLOUDS IN PLACE OVER MOST OF NORTH AND
CENTRAL TEXAS THROUGHOUT THE DAY TODAY. THIS IS CONSISTENT WITH
12Z UPPER AIR ANALYSIS OVER THE REGION WHICH SHOWED ABUNDANT MID
TO UPPER LEVEL MOISTURE BUT SOMEWHAT DRY LOWER LEVELS OF THE
ATMOSPHERE. THE BEST LOW-LEVEL MOISTURE WAS FOUND ACROSS SOUTH
TEXAS...OR GENERALLY DUE EAST OF THE UPPER LOW. WHERE DEEP
MOISTURE THROUGH THE ENTIRE ATMOSPHERE WAS INTERACTING WITH THE
LIFT OF THE UPPER LOW...WIDESPREAD RAIN SHOWERS WERE ONGOING EARLY
THIS AFTERNOON. THIS INCLUDES AREAS GENERALLY ALONG AND EAST OF A
LINE FROM AUSTIN TO SAN ANTONIO. ELSEWHERE...ONLY ISOLATED RAIN
SHOWERS WERE FOUND DUE TO WEAKER LIFT AND A RELATIVELY DRY LOW-
LEVEL ATMOSPHERE.

THROUGH SUNSET...HAVE A MENTION OF ISOLATED RAIN SHOWERS OR
THUNDERSTORMS IN THE FORECAST FOR LOCATIONS ALONG AND SOUTHWEST OF
A LINE FROM GRAHAM TO HILLSBORO TO PALESTINE. THE COVERAGE OF ANY
PRECIPITATION IS EXPECTED TO REMAIN IN THE 10 TO 20 PERCENT
RANGE DUE TO THE LIMITATIONS MENTIONED ABOVE. NO SIGNIFICANT
IMPACTS ARE EXPECTED FROM THIS PRECIPITATION...AND CLOUD TO GROUND
LIGHTING IS THE ONLY EXPECTED HAZARD AT THIS TIME.

WILL HAVE TO KEEP AN EYE ON THE LIFT ASSOCIATED WITH THE UPPER LOW
AS IT HAS BEEN SLOWER TO MOVE EAST THIS AFTERNOON THAN PREVIOUSLY
EXPECTED. HOWEVER...CURRENT THINKING IS THAT AFTER SUNSET THE LOSS
OF HEATING WILL ONLY CAUSE RAIN CHANCES TO DIMINISH. MAY HAVE TO
EXTEND SOME LOW CHANCE OF RAIN SHOWERS OVER THE FAR SOUTHEASTERN
CWA THIS EVENING IF MID-LEVEL SHOWERS HANG ON CLOSE TO THE UPPER
LOW AFTER SUNSET. THE UPPER LOW AND ITS ASSOCIATED FORCING ARE
EXPECTED TO MOVE EAST OF THE CWA BY SUNRISE SUNDAY MORNING.

SUNDAY THROUGH TUESDAY...THE UPPER LOW TO OUR SOUTH IS MOVING EAST
AT LEAST IN PART BECAUSE OF THE INFLUENCE OF A STRONG UPPER TROUGH
CURRENTLY OVER THE WESTERN CONUS COAST EARLY THIS AFTERNOON. THIS
FEATURE...WHILE STRONG AND IMPRESSIVE LOOKING ON WATER VAPOR RIGHT
NOW...IS NOT EXPECTED TO CONTINUE EAST OVER THE PLAINS EARLY THIS
WEEK. EVEN THOUGH THIS TROUGH IS STRONG...IT IS ACTUALLY SOMEWHAT
SMALL WHEN COMPARED TO THE VERY LARGE UPPER LEVEL RIDGE IN PLACE
OVER THE EASTERN TWO THIRDS OF THE CONUS PER 12Z UPPER AIR
ANALYSIS. THE WEST COAST TROUGH WILL BE STRONG ENOUGH TO NUDGE THE
UPPER LEVEL RIDGE...AND THE SMALL UPPER LOWS TRAPPED UNDER THE
UPPER RIDGE...TO THE EAST EARLY NEXT WEEK. HOWEVER FOR NORTH TEXAS
THIS WILL ONLY SERVE TO AMPLIFY A SHORTWAVE RIDGE OVER THE
CWA...LEADING TO MOSTLY CLEAR SKIES AND ABOVE NORMAL TEMPERATURES
THROUGH THE MIDDLE OF THE UPCOMING WEEK. LEFT THE FORECAST DRY
WITH HIGHS IN THE LOW 90S EACH DAY DURING THIS PERIOD.

THE WEST COAST UPPER TROUGH IS EXPECTED TO CONTINUE SLOWLY EAST
WHILE SLOWLY WEAKENING AND TRANSITIONING INTO A CLOSED CIRCULATION
MONDAY NIGHT. THE INTERACTION OF THE UPPER TROUGH WITH THE LARGE
UPPER RIDGE TO ITS EAST WILL HELP TO PUSH AND BREAK DOWN THE UPPER
RIDGE...MAKING ROOM FOR THE NEXT STRONG UPPER TROUGH WHICH IS
EXPECTED TO PUSH SOUTHEAST OVER THE NORTHWESTERN CONUS STARTING
TUESDAY. THIS NEXT SYSTEM...WHICH CURRENTLY RESIDES OVER THE BAY
OF ALASKA...WILL MOVE SOUTHEAST TOWARDS THE PLAINS WEDNESDAY
AFTERNOON AND EVENING. MODELS INDICATE THAT THIS WILL RESULT IN
SOME STRONG LEE SIDE CYCLOGENESIS OVER THE SOUTHERN PLAINS AS
EARLY AS WEDNESDAY AFTERNOON...WHICH MAY BE ENOUGH TO BRING SOME
THUNDERSTORMS OVER THE FAR WESTERN CWA DURING THE PEAK HEATING
HOURS OF THE DAY ON WEDNESDAY.

WENT AHEAD AND MENTIONED A SLIGHT CHANCE OF THUNDERSTORMS ACROSS
THE FAR WESTERN CWA WEDNESDAY AFTERNOON AS THE ECMWF/CANADIAN/GFS
ALL SHOWED SOME CONVECTIVE ACTIVITY NEAR A DRYLINE LOCATED FROM
NEAR WICHITA FALLS TO ABILENE AT THAT TIME. CONFIDENCE IN THIS
PANNING OUT IS SOMEWHAT LOW AT THIS TIME AS THE POSITION OF THE
DRYLINE COULD BE MUCH FARTHER WEST...AND FORCING FOR ASCENT ALONG
THE DRYLINE MAY NOT BE ENOUGH TO OVERCOME A MID-LEVEL CAPPING
INVERSION WITH THE UPPER LEVEL DYNAMICS FORECAST TO BE OFF TO THE
NORTHWEST AT THAT TIME. REGARDLESS...COULD NOT IGNORE THE
CONSISTENCY OF 12Z GUIDANCE AND THE PRESENCE OF THE DRYLINE WITH
AROUND 2000 J/KG OF CAPE FORECAST WEDNESDAY AFTERNOON. IF STORMS
DO DEVELOP...THEY MAY BE ORGANIZED WITH MODELS ALSO ADVERTISING
35-40 KTS OF DEEP LAYER SHEAR OVER THE SAME AREA. A SUPERCELL
STORM MODE WOULD BE FAVORED...BUT A LOT CAN CHANGE BETWEEN NOW AND
WEDNESDAY AFTERNOON...SO FOR NOW THIS IS A SCENARIO WE WILL WATCH
CLOSELY AS PROBABILITIES ARE TOO LOW TO HIGHLIGHT ANY SPECIFIC
ASSOCIATED HAZARDS AT THIS TIME.

WEDNESDAY NIGHT INTO THURSDAY...12Z GUIDANCE WAS ON AVERAGE 6-12
HOURS FASTER WITH THE COLD FRONT THAN MODELS WERE YESTERDAY.
BECAUSE THIS STORM SYSTEM REMAINS THOUSANDS OF MILES AWAY AND
SEVERAL DAYS OUT...THE TIMING OF THE FRONT WILL LIKELY CONTINUE TO
CHANGE IN MODEL FORECASTS UNTIL WE GET TO MONDAY OR TUESDAY...OR
SIMPLY CLOSER TO THE EVENT. WENT AHEAD AND SPED UP THE TIMING OF
POPS IN THE FORECAST TO LOOSELY MATCH THE INCREASE OF SPEED OF THE
FRONT FROM 12Z GUIDANCE. CONTINUED TO LINGER POPS LATER THAN
WHAT MODELS INDICATE IS NECESSARY TO ACCOUNT FOR UNCERTAINTY IN
THE TIMING OF THE FRONT. REGARDLESS...MODELS NOW INDICATE THAT THE
BEST CHANCE OF RAIN ACROSS THE CWA IS GOING TO BE DURING THE DAY
ON THURSDAY AS OPPOSED TO THURSDAY AFTERNOON OR EVENING.

THE COVERAGE OF SHOWERS AND THUNDERSTORMS AND THE INTENSITY OF
PRECIPITATION ASSOCIATED WITH THIS PRECIPITATION...IS STILL
EXPECTED TO BE CLOSELY TIED TO THE UPPER LEVEL DYNAMICS ASSOCIATED
WITH THE BAY OF ALASKA UPPER LOW. THE GFS AND ECMWF CONTINUE TO
KEEP THE BEST DYNAMIC LIFT TO THE NORTH OF THE CWA WHICH GENERALLY
FAVORS A LOWER COVERAGE OF STORMS AND LOWER RAINFALL AMOUNTS ON
AVERAGE. THE CANADIAN IS ADVERTISING A MORE SOUTHERN SOLUTION
WHICH WOULD FAVOR MORE MUCH NEEDED RAINFALL FOR THE REGION. AT
THIS TIME THE GFS AND THE ECMWF SEEM TO REPRESENT THE MOST
CONSISTENT SOLUTION...SO LEFT POPS LOW...IN THE 20-30 PERCENT
RANGE EXPECTING A SCATTERED COVERAGE OF STORMS ALONG THE FRONT AT
THIS TIME.

FRIDAY AND SATURDAY LOOK SIGNIFICANTLY DRIER AND ABOUT 10 DEGREES
COOLER THAN OUR START TO THE WEEK. RAIN CHANCES LOOK TO BE NEAR
ZERO BEHIND OUR LATE WEEK STORM SYSTEM WITH TEMPERATURES TOPPING
OUT IN THE LOWER TO MID 80S.

CAVANAUGH



&&


.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX  69  91  68  91  69 /   0   0   0   0   5
WACO, TX              64  91  64  92  66 /   5   0   0   0   5
PARIS, TX             64  86  64  87  64 /   0   0   0   0   5
DENTON, TX            63  90  62  91  64 /   0   0   0   0   5
MCKINNEY, TX          64  90  62  90  63 /   0   0   0   0   5
DALLAS, TX            69  91  69  91  70 /   0   0   0   0   5
TERRELL, TX           67  92  66  91  67 /   0   0   0   0   5
CORSICANA, TX         66  91  66  91  67 /   0   0   0   0   5
TEMPLE, TX            65  91  65  91  66 /   5   0   0   0   5
MINERAL WELLS, TX     63  89  64  90  64 /   0   0   0   0   5

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$




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