Funnel Cloud in Arizona, April 26, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
930 AM MST THU APR 26 2007

.SYNOPSIS...A WEAK WEATHER DISTURBANCE WILL MOVE ACROSS NORTHERN
ARIZONA TODAY AND TONIGHT BRINGING SOME CLOUDINESS AND A SLIGHT
CHANCE FOR LIGHT SHOWERS AND THUNDERSTORMS ALONG AND NORTHEAST OF
THE MOGOLLON RIM. OTHERWISE...WARM AFTERNOON TEMPERATURES AND
GENERALLY DRY CONDITIONS CAN BE ANTICIPATED INTO SATURDAY.

&&

.DISCUSSION...NORTHERN ARIZONA REMAINS AHEAD OF AN APPROACHING LOW
PRESSURE SYSTEM THIS MORNING. LOWER-TO-MID LEVEL MOISTURE LOOKS TO
CONTINUE INCREASING THROUGH THE DAY...AND WE MAY SEE SOME ISOLATED
SHOWERS BY THIS AFTERNOON AND EVENING. OTHERWISE...MOST LOCATIONS
WILL STILL EXPERIENCE MAX TEMPS A FEW DEGREES ABOVE DAILY NORMS THIS
AFTERNOON UNDER INCREASING CLOUDINESS. REMAINDER OF FORECAST IS IN
LINE WITH CURRENT THINKING WITH NO SIGNIFICANT UPDATES BEFORE
AFTERNOON PACKAGE.

KD

.PREV DISCUSSION FROM 315 AM...A WEAK UPPER LEVEL STORM SYSTEM WILL
SETTLE ACROSS THE SOUTHWEST STATES TODAY. SOME MID LEVEL COOLING
WITH DEEP ADIABATIC LAPSE RATES WILL HELP CREATE SOME MID-LEVEL
SATURATION AND RESULT IN WIDELY SCATTERED HIGH BASED SHOWERS AND
THUNDERSTORMS THIS AFTERNOON. THERE COULD ALSO BE SOME STRONG GUSTY
LOCALIZED WINDS ASSOCIATED WITH THESE HIGH BASED SHOWERS. A FAIRLY
STRONG WESTERN U.S. 500 MB HIGH PRESSURE RIDGE IS FORECAST TO BECOME
WELL ESTABLISHED ACROSS THE WESTERN STATES FRIDAY INTO SUNDAY WITH
5820 TO 5850 HEIGHTS OVER ARIZONA. WE ARE EXPECTING DAYTIME HIGH
TEMPS TO RUN ALMOST 10 DEGREES ABOVE NORMAL BY SATURDAY.

THE LOW PRESSURE TROUGH THAT SETTLE OVER ARIZONA TODAY IS FORECAST
TO CLOSE OFF OVER MEXICO AND THEN COME BACK NORTHWARD ON SUNDAY WITH
SOME MID-LEVEL SUBTROPICAL MOISTURE. THE UNCERTAINTY IN THE FORECAST
WILL BE HOW MUCH LOW LEVEL MOISTURE WILL COME NORTHWARD WITH THIS
SYSTEM. FOR NOW WE DECIDED TO PAINT SOME 20 TO 30 PERCENT CHANCE OF
PRECIP. ACROSS NORTHERN ARIZONA MAINLY FROM THE MOGOLLON RIM SOUTH.
ANOTHER WEATHER DISTURBANCE IN THE WESTERLIES IS FORECAST BY THE GFS
TO COME THROUGH ON TUESDAY THUS PICKING UP SOME OF THE REMNANT
MOISTURE FROM THE SYSTEM THAT CAME THROUGH ON SUNDAY...FOR THIS
REASON WE CONTINUED THE LOW CHCS OF PRECIP THROUGH TUESDAY.

THE LONG WAVE TROUGH THAT HAS BEEN ENTRENCHED OVER THE WESTERN
STATES FOR A GOOD PART OF APRIL...WILL GET ANOTHER SHOT OF ENERGY
AND COLD AIR FROM THE NORTH PACIFIC MONDAY INTO TUESDAY. THIS SYSTEM
WILL BE MUCH COLDER AND DEEPER WITH 500 MB HEIGHTS AS LOW AS 5450
MB. THIS SYSTEM IS FORECAST BY THE GFS TO HAVE A STRONG COLD FRONT
ASSOCIATED WITH IT AS WELL AS VERY STRONG WINDS ALONG AND AHEAD OF
THE FRONT. THE GFS AND THE ECMWF ARE IN FAIRLY GOOD AGREEMENT WITH
THIS SYSTEM LATE NEXT WEEK. MODEL CONSISTENCY HAS NOT BEEN WELL
ESTABLISHED SINCE THIS DEEP SYSTEM HAS APPEARED IN THE LAST MODEL
RUN OR TWO. FOR NOW WE WILL INDICATE SOME LOW CHCS OF
PRECIP...CLOUDS...COOLING DAYTIME HIGHS AND STRONG GUSTY WINDS
DURING THE THURSDAY AND FRIDAY TIME PERIODS.

&&

.AVIATION...FOR THE 18Z PACKAGE...CLOUD COVER WILL CONTINUE TO
INCREASE TODAY...WITH CLOUD BASES LOWERING TO AROUND 15 KFT MSL.
THERE IS A SLIGHT CHANCE OF HIGH-BASED SHOWERS OR THUNDERSTORMS FROM
18Z UNTIL 02Z...BUT THE PROBABILITY IS TOO LOW TO INCLUDE IN TAFS.
AVIATION DISCUSSION NOT UPDATED FOR AMENDMENTS.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...NONE.

&&