Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 011623
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
925 AM MST WED JUL 1 2015

.SYNOPSIS...EXPECT SCATTERED MAINLY AFTERNOON AND EVENING
THUNDERSTORMS INTO EARLY NEXT WEEK. SLOWER MOVING STORMS WILL START
TO INCREASE HEAVY RAINFALL CONCERNS. DAYTIME TEMPERATURES WILL
REMAIN CLOSE TO SEASONAL NORMALS INTO THIS HOLIDAY WEEKEND.

&&

.DISCUSSION...DEBRIS CLOUD FROM THE PREVIOUS 18 HOURS OF CONVECTION
CONTINUES TO DIMINISH...ALLOWING GOOD HEATING TO START COOKING UP
STORMS EARLIER TODAY. THE 12Z SOUNDING ISN`T QUITE AS DRAMATIC AS
WHAT WE SAW YESTERDAY BUT STILL VERY RESPECTABLE FOR THESE PARTS.
PRECIPITABLE WATER AROUND 1.4 INCHES WITH MODIFIED MOST UNSTABLE
CAPE AROUND 1400 TO 1700 J/KG. THE FLOW IS STILL RATHER BRISK ABOUT
750 MB AS WELL...BUT THIS WILL START TO CHANGE LATER TODAY.

THE HIGH CENTER NORTH OF OUR AREA AND ORIENTATION OF THE ASSOCIATED
RIDGE AXIS HAS BEEN EXTREMELY FAVORABLE FOR THE EASTERLY FLOW AND
GREAT STORM STRUCTURE. STARTING TODAY THE LARGE SCALE PATTERN WILL
BEGIN TO REORIENT THE RIDGE FROM NEVADA THROUGH NEW MEXICO WITH OUR
FLOW GAINING AN INCREASINGLY DOMINANT SOUTHERLY COMPONENT. FOR THE
NEXT 24 HOURS THIS SHOULD SHOW ITSELF AS A SLOW WARMING TREND IN THE
MID LEVELS (ESPECIALLY EAST OF TUCSON) AND WEAKENING STORM LEVEL
FLOW. FOR TODAY THAT MEANS EARLIER ONSET OF CONVECTION BUT LESS
COVERAGE ACROSS EASTERN AREAS. THE SWEET SPOT IS SANTA CRUZ COUNTY
FOR CONVECTION AND POTENTIAL HEAVY RAINFALL. WE WILL ALSO NEED TO
WATCH FOR AN INCREASING TREND OF PUSHING OUTFLOWS FROM THE SOUTH
INSTEAD OF EAST. WE TWEAKED THE FORECAST PACKAGE BASED ON THIS.

PLEASE SEE THE PREVIOUS DISCUSSION BELOW FOR ADDITIONAL DETAILS.

&&

.AVIATION...VALID THRU 02/18Z.
DEBRIS CLOUDS SLOWLY DIMINISHING THIS MORNING BECOMING SCT EARLY
THIS AFTERNOON. ISOLD TO SCT TSRA/SHRA AFT 02/19Z. BRIEF WIND GUSTS
OF 45 KTS WILL BE POSSIBLE WITH THE STRONGEST STORMS. SURFACE WIND
WILL BE LESS THAN 12 KTS OUTSIDE OF ANY TSRA. AVIATION DISCUSSION
NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...ADEQUATE MOISTURE AND A FAVORABLE FLOW PATTERN WILL
CONTINUE TO PROVIDE A CHANCE OF MAINLY AFTERNOON AND EVENING SHOWERS
AND THUNDERSTORMS INTO THE UPCOMING HOLIDAY WEEKEND WITH HIGH
TEMPERATURES WITHIN A FEW DEGREES OF NORMAL.

&&

.PREV DISCUSSION...WV IMAGERY THIS MORNING SHOWS WRN AZ/NRN BAJA CA
IMPINGED BETWEEN HIGH PRESSURE CENTERED OVER THE GREAT BASIN AND LOW
PRESSURE CENTERED NEAR 25N/123W. THIS SETUP HAS CREATED A SE/NW
ORIENTED JET WHICH IS FUNNELING DEEPER MOISTURE INTO THE AREA FROM
BOTH THE GULF OF MEXICO AND FROM THE GULF OF CALIFORNIA. IN
FACT...THE GFS/NAM LAYER PWAT IS SHOWING VALUES CLOSE TO 2 INCHES
NEARING THE WRN AZ/MEXICO BORDER LATER ON THIS MORNING.

IR IMAGERY SHOWS SOME RESIDUAL CLOUD COVER IN THE WAKE OF EARLIER
CONVECTION. THIS SHOULD HELP TO MODERATE TEMPERATURES A DEGREE OR
TWO TODAY...WITH THE EXCEPTION OF THE WHITE MOUNTAINS WHERE VERY
LITTLE CONVECTION OCCURRED TODAY. LAST SEVERAL RUNS OF HI-RES MODELS
INCLUDING THE HRRR/RUC ARE CURRENTLY SHOWING CONVECTION BEGINNING TO
REDEVELOP NEAR THE AZ/MEXICO BORDER AROUND 01/19Z AND GRADUALLY
FILLING IN TOWARD THE NORTH AND WEST THROUGH THE AFTERNOON HOURS.
LATEST RUNS OF THE NAM/RUC MODELS INDICATE THE PRESENCE OF 1000-2000
J OF CAPE AT THE SAME TIME WITH FAIRLY LITTLE CIN...SO IT SHOULD NOT
TAKE MUCH FOR STORMS TO GET GOING TODAY ONCE DAYTIME HEATING BEGINS.

STORM MOTION IS EXPECTED TO BE SLIGHTLY MORE TOWARD THE NORTHWEST
TODAY AS COMPARED TO TUESDAY...WITH HAIL AND DAMAGING WINDS THE MAIN
THREAT. STEERING FLOW WILL BE SLIGHTLY WEAKER...SO WILL NEED TO BE
MORE AWARE OF LOCALIZED FLASH FLOODING TODAY...ESPECIALLY FOR AREAS
WHICH RECEIVED THE HEAVIEST RAINFALL OVER THE LAST 24 HOURS.

FRIDAY THROUGH THE WEEKEND WILL SEE THE REORIENTATION OF THE RIDGE
AXIS FROM CHIHUAHUA THROUGH EASTERN BORDER AREAS AND THEN INTO
UTAH...CREATING A LONG SOUTHERLY FETCH INSTEAD OF EASTERLY. THESE
PATTERNS TEND TO EMPHASIZE HEAVIER RAINFALL AS WELL AS MORE
WIDESPREAD CONVECTIVE ORGANIZATION IMMEDIATELY UPSTREAM IN SONORA.
AS SUCH...IT SEEMS THAT DAILY CHANCES FOR SHOWERS AND THUNDERSTORMS
WILL CONTINUE FOR THE NEXT SEVERAL DAYS...AND ONLY SLIGHT
MODIFICATIONS HAVE BEEN MADE TO THE POP GRIDS AT THIS TIME. LOCATION
OF THE HEAVIEST RAINFALL/BEST CHANCES FOR CONVECTION WILL BE HIGHLY
DEPENDENT ON THE CONDITIONS WHICH OCCURRED DURING THE PREVIOUS 12 TO
24 HOURS...SO IT IS LIKELY THAT MINOR TWEAKS WILL OCCUR WITH EACH
FORECAST PACKAGE.

LOOKING A LITTLE FURTHER AHEAD...IT SEEMS WE MAY HAVE A SLIGHT
DOWNTURN IN THUNDERSTORM ACTIVITY AND A REDUCTION IN DAYTIME
TEMPERATURES BY THE MIDDLE OF NEXT WEEK...AS MORE SWLY FLOW IMPACTS
THE AREA. STAY TUNED.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

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MEYER/LADER


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