Area Forecast Discussion
Issued by NWS Amarillo, TX

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FXUS64 KAMA 040221
AFDAMA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE AMARILLO TX
921 PM CDT THU SEP 3 2015

.UPDATE...A SHORTWAVE TROUGH IS RIDING OVER THE RIDGE CENTERED OVER
OKLAHOMA THIS EVENING WHICH HAS AIDED IN THE FORMATION OF SOME
SHOWERS AND THUNDERSTORMS OVER FAR EASTERN NEW MEXICO AND COLORADO. A
FEW SHOWERS MAY SNEAK ACROSS THE BORDER THIS EVENING INTO THE FAR
WESTERN PANHANDLES...SO HAVE ADDED A MENTION OF ISOLATED SHOWERS AND
THUNDERSTORMS UNTIL ABOUT MIDNIGHT. OTHERWISE...MINOR UPDATES WERE
MADE TO THE GRIDS TO ACCOUNT MINOR DIFFERENCES IN THE MOISTURE NEAR
THE SURFACE OVER THE WESTERN COUNTIES. THE REST OF THE FORECAST
REMAINS ON TRACK.

BIEDA

&&

.AVIATION...06Z TAFS...SOUTH TO SOUTHEASTERLY WINDS BTWN 10 TO 20 KTS
WILL CONTINUE OVERNIGHT INCREASING TO 15 TO 25 KTS AFT 04/14Z. A WEAK
TROUGH PASSING OVER THE PANHANDLE REGION WITH ANOTHER EXPECTED TO
FOLLOW WILL BRING CLOUDS AOA 10K FT AGL...BUT LITTLE TO NO CHANCE OF
THUNDERSTORM FORMATION IS EXPECTED OVER TAF SITES. VFR CONDITIONS
WILL PREVAIL THROUGH THE TAF PERIOD.

BIEDA

&&

.PREV DISCUSSION... /ISSUED 605 PM CDT THU SEP 3 2015/

DISCUSSION... WATER VAPOR IMAGERY LOOPING BACK TO LAST EVENING
SHOWED A MARKED INCREASE IN MID-HIGH LEVEL MOISTURE STREAMING
NORTHWARD INTO NEW MEXICO FROM TROPICAL STORM KEVIN IN THE EASTERN
PACIFIC. THESE TRENDS ARE EVIDENT IN THE EL PASO SOUNDINGS AND
SATELLITE DERIVED PRECIPITABLE WATER VALUES ACROSS MUCH OF NEW
MEXICO. TRACKING THE PLACEMENT OF THIS MONSOON MOISTURE PLUME WILL BE
KEY IN DETERMINING PRECIPITATION CHANCES OVER THE NEXT COUPLE OF
DAYS.

A COUPLE OF SUBTLE WAVES IN THE SOUTHWEST FLOW ALOFT MAY HAVE MINOR
INFLUENCE ON POSITION OF THE SURFACE TROUGH BUT FOR THE MOST PART NO
SIGNIFICANT MOVEMENT OR DEEPENING IS EXPECTED. THIS STEADY-STATE
FEATURE WILL GENERALLY BE POSITIONED FROM WESTERN KANSAS THROUGH FAR
SOUTHEAST COLORADO INTO NORTHEAST NEW MEXICO THROUGH THE EVENING AND
THEN MAY REPOSITION SLIGHTLY FURTHER WEST BY LATE TOMORROW.
CONVERGENCE NEAR THIS SURFACE TROUGH BENEATH MOIST MID LEVELS SHOULD
RESULT IN AT LEAST ISOLATED DIURNALLY DRIVEN CONVECTION ESPECIALLY
NEAR HIGHER TERRAIN IN NORTHEAST NEW MEXICO. FOR ANY OF THE
CONVECTION THAT MAKES IT INTO THE FORECAST AREA...IMPACTS SHOULD BE
MINIMAL GIVEN TYPICAL THERMODYNAMIC PROFILES SEEN IN THIS PATTERN
WITH WEAK MID LEVEL LAPSE RATES ATOP A FAIRLY SIZABLE SURFACE MIXED
LAYER YIELDING WEAK INSTABILITY. GUSTY WINDS AND MODERATE TO POSSIBLY
HEAVY DOWNPOURS ARE LIKELY WITH THE MOST INTENSE THUNDERSTORMS.

3-6 KM THETA-E SHOWS THE MOISTURE PLUME WELL. MODELS ARE IN GENERAL
AGREEMENT ON HOW THIS WILL EVOLVE AND SHOW THIS PLUME SHIFTING
EASTWARD SUNDAY AS UPPER RIDGE DEAMPLIFIES SLIGHTLY. THIS MAY
REFOCUS PRECIPITATION CHANCES FURTHER EAST ALTHOUGH PROBABILITIES
SHOULD BE SLIGHTLY LOWER THAN PREVIOUS DAYS FURTHER WEST INTO NEW
MEXICO WHICH WAS AT LEAST PARTIALLY DRIVEN BY TERRAIN INDUCED
CIRCULATIONS. AT THE VERY LEAST SOME FAIRLY EXTENSIVE MID UPPER
CLOUDS MAY ACCOMPANY THIS EASTWARD SHIFT OF THE MOIST PLUME AND HAVE
INCREASED CLOUD COVER DURING THIS PERIOD.

BETTER PRECIPITATION CHANCES ARRIVE NEXT WEEK AS DISTURBANCES
TRAVERSE THE NORTHERN EDGE OF THE RIDGE WHICH CONTINUES TO SLOWLY
DEAMPLIFY AND RETROGRADE. A BLENDED APPROACH TO EXTENDED FORECAST
WAS ACCEPTED ALTHOUGH DIFFERENCES IN DETERMINISTIC GUIDANCE AND
ENSEMBLE SPREAD ARE STILL QUITE LARGE...ESPECIALLY FROM MID WEEK INTO
LATE WEEK. CONFIDENCE ON ANY ONE PERIOD HAVING HIGHER PRECIPITATION
PROBABILITIES THAN ANOTHER IS LOW BUT HAVE THE HIGHEST PROBABILITIES
ON TUESDAY SINCE MEDIUM RANGE GUIDANCE ARE SOMEWHAT IN AGREEMENT ON
TIMING OF ONE OF THESE SHORTWAVES THEN. THEREAFTER CONFIDENCE IS
VERY LOW. ECMWF DEPICTS A SECOND SHORTWAVE TRAVERSING THE CENTRAL
PLAINS INTO THE MIDDLE MISSISSIPPI VALLEY BY MID WEEK. THIS FEATURE
IS ABSENT FROM THE GFS WHICH REMAINS MORE CONSOLIDATED WITH THE
SHORTWAVE TROUGH ACROSS THE GREAT LAKES REGION AND MORE ELONGATED
WITH UPPER RIDGING ACROSS THE SOUTHERN PLAINS. REGARDLESS OF WHICH
MODEL IS MORE ACCURATE...THE PATTERN SUPPORTS RETAINING AT LEAST LOW
PROBABILITIES OF PRECIPITATION.

BRB

&&

.AMA WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
OK...NONE.

&&

$$

98/15



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