Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 201054
AFDHGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
454 AM CST THU NOV 20 2014

.DISCUSSION...
THE WARM AIR ADVECTION PATTERN HAS BEGUN WITH THE REGION FALLING
UNDER A PRONOUNCED SOUTHEASTERLY FETCH OVER THE NEXT FEW DAYS. MID
TO UPPER 40 INTERIOR DEW POINTS WILL INCREASE INTO THE MEAN UPPER
50S BY THE CLOSE OF THE DAY...THICKENING CLOUD COVER AND A HIGHER
CHANCE FOR SCATTERED SHOWERS. THE HIGHEST PROBABILITY OF SHOWERS
WILL BE FOCUSED ALONG THE WESTERN CORRIDOR OF THE CWA...ESPECIALLY
OVER THE SOUTHWESTERN FORECAST AREA OR THOSE COUNTIES SURROUNDING
MATAGORDA BAY. HIGHER REZ MODELING IS FOCUSING QPF IN THIS AREA AS
IT DEVELOPS A WEAK CYCLONIC CIRCULATION NEAR MATAGORDA BAY.
ISENTROPIC UPGLIDE WILL BECOME MORE EFFICIENT OVER THE NEXT 36
HOURS AS SW-S WINDS ALONG THE APPLICABLE THETA SURFACE PRODUCES
SUB 20 CONDENSATION PRESSURE DEFICITS AND FURTHER SATURATES A
DEEPER COLUMN = MORE AREAL SHOWERS. 15 TO 20 KNOT NEAR SURFACE
WINDS MAKING IT ASHORE AND CREATING FRICTIONAL SPEED CONVERGENCE
WILL SATURATE THE LOWER LAYER TO PRODUCE STREAMER-LIKE SHOWERS...
TRANSITIONING FURTHER NORTH DURING THE WARMTH OF THE DAY. AS THE
COLUMN SATURATES UP THROUGH FRIDAY...THERE IS A HIGHER CHANCE FOR
MORE WIDESPREAD AREAL SHRA COVERAGE TOMORROW. VERY MILD AND WARM
CONDITIONS WITH AN AMPED UP SOUTH WIND...60S IN THE MORNING WARMING
INTO THE LOWER TO MIDDLE 70S. QUITE THE CHANGE IN A VERY SHORT
TIME! FOR PERSPECTIVE...PLEASE REFER TO THE CLIMATE SECTION BELOW.

SATURDAY IS STILL THE TARGET DAY FOR STRONG TO SEVERE WEATHER.
ALL OF THE INGREDIENTS ARE IN PLACE FOR A POSSIBLE ACTIVE WEATHER
DAY...FROM THE HIGH SHEAR TO THE IMPRESSIVE UPPER LEVEL DIVERGENCE
CREATED BY A DEEP SHORTWAVE TROUGH PASSAGE ACROSS CENTRAL AND NE
TEXAS. THE REGION DISPLAYS TWO PEAKS IN TORNADO FREQUENCY...ONE IN
THE MONTH OF MAY AND THE OTHER IN NOVEMBER. THE NATURAL TENDENCY
TO DESIRE HIGH THERMODYNAMIC INDICES NEEDS TO BE TEMPERED DUE TO
THE SEASON...COOL SEASON SEVERE WEATHER CAN RUN ON MUCH LOWER
THERMO DRIVERS. LOW TOPPED TORNADOES CAN AND WILL OCCUR DURING
THESE COOLER MONTHS UNDER LOWER CONVECTIVE TEMPERATURES...CAPE...
L.I.`S...ETC...COLD SEASON TORNADO CLIMATOLOGY SHOWS THAT A RANGE
OF 500-1500 ML CAPE OCCURS DURING TORNADIC EVENTS WITH THE 50TH
QUARTILE FALLING AROUND 1200....EFFECTIVE SHEAR IN THE LOW TO MID
40S...SRH IN THE 100 TO 300 RANGE. ALL OF THESE VALUES FALL IN
LINE WITH THE LATEST SOUNDINGS PROGS. IF THE REGION CAN SEE SOME
SUN BEHIND A LIFTING WARM FRONT EARLY DURING THE DAY SATURDAY...THERE
WOULD BE A HIGHER POTENTIAL FOR SEVERE TO BE ACHIEVED. HIGH TOTAL
SHEAR VALUES WITH FAST MOVING STORM MOTION(S) LEANS THE PRIMARILY
THREAT TOWARDS WIND DAMAGE. LOWER WBZ HEIGHTS MAY INTRODUCE A HAIL
THREAT...AS WELL. REGARDLESS OF THE THERMO AND DYNAMIC INDICES THE
EXTREMELY HIGH PVA PERPENDICULAR TO THE FLOW OF SUCH A SHARP MID-
UPPER TROUGH SHOULD KICK OFF AT LEAST STRONG DISCRETE CELLS THAT
MAY EVOLVE INTO A MORE ORGANIZED MCS OR QCLS THAT ADVERSELY IMPACTS
THE AREA FROM AS EARLY AS NOON THROUGH AS LATE AS SATURDAY EVENING.

WINDS QUICKLY BECOME NORTHWEST IN THE TROUGH`S WAKE SUNDAY...DRY
AND STABLE UNDER NW FLOW TO BEGIN THANKSGIVING WEEK. THE SURFACE
COLD FRONT WILL PASS ACROSS THE REGION EARLY MONDAY MORNING...A
COOLER AND DRY AIR MASS EARLY IN THE WORK WEEK WILL KEEP MORNINGS
IN THE 40S WITH AFTERNOONS WARMING INTO THE AVERAGE LOW TO MID
60S. THANKSGIVING DAY IS FORECAST TO BE PLEASANT...MOSTLY SUNNY
WITH AFTERNOON TEMPERATURES IN THE AVERAGE UPPER 60S. 31

&&

.AVIATION...
MAINLY VFR CONDITIONS ACROSS THE REGION THIS MORNING WITH CIGS
GENERALLY BETWEEN 4000-7000K FT, BUT 2800-4000 ACROSS WRN AREAS.
MODELS INSIST ON SOME RAPID LLVL MOISTURE RETURN TODAY W/ SOME
AREAS TRANSITIONING TO MVFR AS SCT AREAS OF -RA DEVELOP. NOT REAL
CONFIDENT REGARDING EITHER SINCE RIGS IN THE GULF NOT DISPLAYING
MUCH DIFFERENCE THAN WHAT WE SEE INLAND ATTM. SO WILL GENERALLY
KEEP MORE OPTIMISTIC TAFS IN PLACE FOR THE SHORT TERM AND SEE HOW
THINGS PLAY OUT. WILL ADVERTISE GRADUALLY LOWER CIGS TONIGHT...
PROBABLY INTO MVFR TERRITORY...BUT AGAIN MORE OPTIMISTIC THAN
SOME OF THE IFR SUGGESTIONS POSED BY SOME OF THE MODELS. 47

&&

.MARINE...

SE WINDS INCREASE LATER TODAY AND SHOULD SUPPORT CAUTION CRITERIA
OFFSHORE LATER THIS AFTN AND ADVISORY CRITERIA TONIGHT. ADVSY
CONDITIONS WILL THEN PERSIST INTO SATURDAY IN ADVANCE OF AN
APPROACHING STRONG STORM SYSTEM. BY THEN...SEAS SHOULD BE 5-8 FEET
WITH SE/S WINDS OF 17-23 KNOTS AND A LONG FETCH. STRONG TO SEVERE
THUNDERSTORMS MAY BE POSSIBLE OVER THE COASTAL WATERS SATURDAY
AFTERNOON AND NIGHT AS THE STORM SYSTEM PASSES THROUGH. MODERATE SW
FLOW CAN BE EXPECTED IN ITS WAKE SAT NIGHT & SUNDAY. NEXT FRONT
PENCILED IN TO PUSH OFF THE COAST LATE SUNDAY NIGHT. 47

&&

CLIMATE...
HOUSTON RECORDED A RECORD LOW OF 30 DEGREES THIS MORNING. THE
HIGH TEMPERATURE THIS AFTERNOON WAS 69 DEGREES. THE HIGH IS
SIGNIFICANT BECAUSE HIGH TEMPERATURES HAVE NOT EXCEEDED 58
DEGREES SINCE NOV 11TH. THE LAST TIME HOUSTON RECORDED 7
CONSECUTIVE DAYS WITH HIGH TEMPS AT OR BELOW 58 DEGREES DURING THE
MONTH OF NOVEMBER WAS BACK IN 1907. THE TEMPERATURE WAS BELOW 58
DEGREES BETWEEN 11/11/1901 AND 11/18/1907. THAT WAS ALSO THE LAST
TIME (UNTIL THIS YEAR) THAT HOUSTON SUFFERED A DAILY AVERAGE
TEMPERATURE DEPARTURE GREATER THAN 10 DEGREES PER DAY FOR EIGHT
CONSECUTIVE DAYS.

                    1907                    2014

          DATE  TEMP  DEP              DATE  TEMP  DEP

          NOV 11  45  -18              NOV 12  51  -13
          NOV 12  40  -24              NOV 13  41  -22
          NOV 13  42  -22              NOV 14  41  -22
          NOV 14  43  -20              NOV 15  48  -14
          NOV 15  51  -12              NOV 16  50  -12
          NOV 16  45  -17              NOV 17  44  -18
          NOV 17  50  -12              NOV 18  44  -18
          NOV 18  50  -12              NOV 19  50  -11

LASTLY...SEVERE WEATHER IN NOVEMBER DOES OCCUR. SOME OF THE MORE
NOTORIOUS TORNADO OUTBREAKS THAT HAVE AFFECTED SE TX OCCURRED
DURING NOVEMBER. HERE ARE A FEW REMINDERS...

DATE         EF SCALE        LOCATION

NOV 8  2011    EF-1          HOUSTON AND TEXAS CITY

NOV 17 2003    EF-2          24 TORNADOES - 72 INJURIES

NOV 6  2000    EF-1          CONROE AND SHEPHERD

NOV 16 1993    EF-1          DOWNTOWN HOUSTON - 26 MINOR INJ

NOV 21 1992    EF-4          KATY...HOUSTON...CHANNELVIEW
                             LAST EF-4 TO AFFECT SE TX

NOV 15 1987    EF-2          4 TORNADOES
                             CALDWELL AND NORMANGEE
                             5 KILLED AND 35 INJURED

43

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      69  60  73  62  72 /  30  50  50  40  70
HOUSTON (IAH)              70  62  74  62  73 /  30  30  30  30  80
GALVESTON (GLS)            69  65  71  66  72 /  30  30  30  20  90

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION FROM NOON CST TODAY THROUGH
     THIS AFTERNOON FOR THE FOLLOWING ZONES: WATERS FROM
     FREEPORT TO THE MATAGORDA SHIP CHANNEL 20 NM TO 60 NM...
     WATERS FROM HIGH ISLAND TO FREEPORT 20 TO 60 NM.

&&

$$

DISCUSSION...31/47



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